Patent Application
20140018574
The present invention relates to a process for preparing acrylic acid by a thermolysis of poly-3-hydroxypropionate catalyzed by at least one molecular organic active compound having at least one tertiary nitrogen atom which has a covalent bond to three different carbon atoms in the molecular organic active compound.
Acrylic acid is an important monomer which, owing to its marked tendency to free-radical polymerization, finds use as such, in the form of its alkyl esters and/or in the form of its alkali metal salts especially for preparation of polymers obtainable by free-radically initiated polymerization.
Depending on the individual acrylic monomers used for formation of the respective polymer, it can be used, for example, as an adhesive or as a superabsorbent for water or aqueous solutions. The latter are polymers in which at least a portion of the polymerized acrylic acid is in a form neutralized with alkali metal bases, for example NaOH (cf., for example, DE 102004004496 A1 and DE 102011076931 A1). These polymers generally have a marked absorption tendency for aqueous liquids (cf., for example, US 2010/0041549 and “Modern Superabsorbent Polymer Technology”, Buchholz/Graham, Wiley VCH, New York, 1998).
The field of use thereof is especially in the sector of hygiene articles, for example diapers, and particularly high demands are therefore made on the purity of acrylic acid used for the preparation thereof.
A disadvantage of acrylic acid is, however, that the capacity thereof for free-radical polymerization is so marked that it frequently sets in not just when it is triggered in an intentional manner by means of suitable free-radical initiators. In other words, acrylic acid, especially in the condensed phase, has a non-negligible tendency to unwanted free-radical polymerization (for example initiated by ever-present thermal energy and/or electromagnetic radiation), and this can take a comparatively violent and uncontrolled course due to the exothermicity thereof.
In the course of storage and/or transport of acrylic acid, it is therefore necessary for safety reasons to counteract such unwanted free-radical polymerization by addition of polymerization inhibitors to the acrylic acid. Such an addition, however, is disadvantageous in that it impairs any later intentionally initiated free-radical polymerization.
A further disadvantage of acrylic acid is due to the fact that, present in the liquid phase, it unavoidably ages with time as a result of Michael addition onto itself and onto the addition products which form.
While acrylic acid thus has an excellent “reaction form”, its “storage form (depot form)/transport form” is not entirely satisfactory.
A significantly more advantageous depot form/transport form in this respect of acrylic acid is poly-3-hydroxypropionate.
In this document, this is understood to mean macromolecular compounds having at least one structural section of the general formula I
where n is an integer ≧6.
The structural section of the general formula I is the polycondensate (the polyester) of 3-hydroxypropionic acid (=the hydrate of acrylic acid) with itself.
Poly-3-hydroxypropionates, in contrast to acrylic acid, are essentially not subject to any aging process under standard conditions (=25° C. and a pressure of 1.0133·105 Pa (=standard pressure)). More particularly, poly-3-hydroxypropionate, which is typically in the solid state of matter under standard conditions, can be both stored and transported without any problem.
The prior art discloses that structural sections of the general formula (I) present in a poly-3-hydroxypropionate can be split by the sole action of elevated temperatures (of an elevated temperature) as required to give acrylic acid (the dehydrate of 3-hydroxypropionic acid) (cf., for example, U.S. Pat. No. 2,568,636 A, U.S. Pat. No. 2,361,036 A and EP 577206 A2).
The acrylic acid can be converted from the gas phase which comprises acrylic acid and is obtained in the thermal splitting (in the “thermolysis”) to the liquid phase in a manner known per se by absorptive and/or condensative measures. In general, this liquid phase may already be the acrylic acid suitable for further uses, for example free-radical polymerizations. Especially when the acrylic acid thus obtained can be supplied without intermediate storage to the further use thereof in the context of, for example, a free-radically initiated polymerization, it will be possible to undertake the aforementioned conversion of the acrylic acid to the liquid phase advantageously without additional use of polymerization inhibitors (which impair a free-radically initiated polymerization).
A further disadvantage of acrylic acid obtained as described by thermolysis of poly-3-hydroxypropionate (or originating from such a thermolysis) is that it does not have the fingerprint of low molecular weight aldehydes present therein as impurities which is a typical result in the case of preparation processes of acrylic acid by heterogeneously catalyzed partial oxidations of C3 precursor compounds of acrylic acid (e.g. propylene, propane, acrolein, glycerol, propionic acid, propanol etc.) (cf., for example, DE 102011076931 A1).
Such aldehydes, even in amounts of 1 to 10 ppm by weight, based on the weight of the mass of acrylic acid, are found to be extremely disruptive in the case of use of the acrylic acid and/or of the conjugated (Brønsted) base for preparation of polymers by free-radically initiated polymerization, optionally in a mixture with other mono- and/or polyunsaturated (for example mono- and/or polyethylenically unsaturated) compounds (for example, they can undesirably retard the free-radically initiated polymerization or impair the preparation of polymer with particularly high molecular weight (as is desirable especially in the superabsorbance sector) owing to their “regulating action”).
It is also known from the prior art that the temperatures required for appropriate splitting rates in the case of thermolysis of poly-3-hydroxypropionate to acrylic acid can be considerably reduced by the addition of suitable splitting catalysts to the poly-3-hydroxypropionate to be split (or to a splitting mixture comprising the latter).
As potential splitting catalysts of this kind, WO 2011/100608 A1 considers a comparatively wide variety of chemical substance classes (which in a formal sense also comprise organic amines), but these do not show any unifying structural feature essential for advantageous usability as such a splitting catalyst.
By way of example, the splitting catalysts used in WO 2011/100608 A1 are merely nonvolatile salts such as Na2CO3, FeSO4.7H2O and Ca(OH)2.
Use of salts as splitting catalysts, however, is disadvantageous in that they necessarily remain in the splitting residues due to the nonvolatility thereof.
WO 2011/100608 proposes, in this regard, completely decomposing the organic constituents of the splitting residues by corresponding thermal action to leave salts present, in order to be able to reuse the remaining salts as splitting catalysts, but the reusability of such remaining salt residues as splitting catalysts is generally impaired as a result of carbon deposits, for example, present therein and due to chemical change which has occurred (e.g. Na2CO3→Na2O). However, disposal of salt residues is generally costly.
U.S. Pat. No. 2,361,036 considers, as catalysts for a thermolysis of poly-3-hydroxypropionate, those substances which are also considered as catalysts for preparation of poly-3-hydroxypropionate by ring-opening polymerization of β-propiolactone. In this case, a wide variety of potentially suitable substances is likewise listed, and this also comprises various nitrogen-comprising organic compounds, for example the potentially carcinogenic N,N-dimethylaniline, but these likewise do not show any unifying structural feature essential for advantageous usability as such a splitting catalyst.
Mentioned by way of example in U.S. Pat. No. 2,361,036 are merely thermolyses of poly-3-hydroxypropionate in which sodium carbonate is used as the splitting catalyst, which is associated with the disadvantages already described.
It was therefore an object of the present invention to provide a process, improved over the prior art processes, for preparation of acrylic acid by a thermolysis of poly-3-hydroxypropionate catalyzed by at least one active compound.
Accordingly, a process is provided for preparing acrylic acid by a thermolysis of poly-3-hydroxypropionate catalyzed by at least one molecular (i.e. non-salt, nonionic) organic active compound having at least one tertiary nitrogen atom which has a covalent bond to three different carbon atoms (to not more and not less than these three and not to any other atom type either), wherein the at least one molecular organic active compound
Processes for preparing poly-3-hydroxypropionate as usable for the process according to the invention (suitable for the process according to the invention) are known in the prior art (more particularly in all the prior art detailed hereinafter in the present document).
For example, poly-3-hydroxypropionate (suitable for (all) the process(es) according to the invention) can be obtained by dehydrating polycondensation of 3-hydroxypropionic acid (cf., for example, Chinese Journal of Synthetic Chemistry, Vol. 15 (2007), No. 4, pages 452-453). Typical relative weight-average molecular weights MW (i.e. based on the weight of atomic hydrogen) of poly-3-hydroxypropionate obtainable in this way may, for example, be 1000 to 20 000 (but also less or more).
The corresponding polydispersity Q (the ratio of weight-average relative molecular weight MW to number-average relative molecular weight Mn (Q=MW/Mn)) is generally at values of ≦2.5, frequently at values of ≦2. It is also possible to obtain polydispersities Q of ≦1.5.
U.S. Pat. No. 2,568,636, U.S. Pat. No. 2,361,036 and U.S. Pat. No. 3,002,017 A disclose preparing the polyester of 3-hydroxypropionic acid (one which is suitable for the process according to the invention) proceeding from β-propiolactone by ring-opening polymerization. Corresponding ring-opening polymerizations are also disclosed by WO 2011/163309 A2 and EP 688806 B1. According to the latter, the relative weight-average molecular weight MW of poly-3-hydroxypropionate (suitable for all the processes according to the invention) obtainable in this way may, for example, be 5000 to 2 000 000, or 20 000 to 500 000, or 30 000 to 400 000. Relative weight-average molecular weights Mw above 100 000 are considered typical for the use of poly-3-hydroxypropionate contemplated in EP 688806 B1. The corresponding polydispersities Q are generally likewise at values of ≦2.5.
The thesis “Multi-Site Catalysis—Novel Strategies to Biodegradable Polyesters from Epoxides/CO and Macrocyclic Complexes as Enzyme Models” by Markus Allmendinger, University of Ulm (2003), discloses that, by carbonylating reaction of ethylene oxide dissolved in an aprotic solvent with carbon monoxide at elevated pressure, elevated temperature and in the presence of a catalyst system comprising at least one cobalt source, a product mixture comprising poly-3-hydroxypropionate is obtainable directly (i.e. without forming propiolactone (oxetan-2-one) as an intramolecular cyclic ester of β-hydroxypropionic acid (=3-hydroxypropionic acid) as an intermediate), from which the poly-3-hydroxypropionate can be removed by precipitation (for example by lowering the temperature and/or adding a precipitation liquid) and then employing one or more mechanical separating operations, for example filtration and/or centrifugation.
J. Am. Chem. Soc. 2002, 124, pages 5646-5647, DE 10137046 A1, WO 03/011941 A2 and J. Org. Chem. 2001, 66, pages 5424-5426 confirm these facts.
Typical relative weight-average molecular weights MW of poly-3-hydroxypropionates (suitable for all the processes according to the invention) obtainable in the course of the aforementioned carbonylations of ethylene oxide may, for example, be 1000 to 20 000 or to 15 000, in many cases 2000 to 12 000, and frequently 3000 to 10 000 or 4000 to 10 000. In principle, however, higher and lower relative weight-average molecular weights MW are also obtainable by this procedure. The corresponding polydispersity Q is generally at values of ≦2.5, frequently at values of 2. In many cases, Q is 1.5 to 1.8. However, it is also possible to establish polydispersities Q below 1.5 or below 1.4 (cf. DE 10137046 A1).
In the prior art preparation processes described to date, essentially a poly-3-hydroxypropionate homopolymer (homopolyester) is obtained.
In other words, an individual macromolecule of the respective poly-3-hydroxypropionate consists essentially exclusively of a structural section of the general formula (I) and forms a polyester of the general structure II
where n≧6 and a, b are a head group (a) bordering the polyester and an end group (b) bordering the polyester.
The nature of the respective head group/end group depends on the preparation process used in each case and on the preparation conditions employed in each case.
For example,
a may be
and
b may be
Alternatively,
a may be
and
b may be
Normally, the relative molecular weight of a head group/end group is ≦150, usually ≦120 and generally ≦100.
According to the details so far, n in polyesters of the general structure II (and hence also in structural sections of the general formula I relevant in accordance with the invention) may, for example, be ≧6 and ≦30 000, or ≧8 and ≦25 000, or ≧10 and ≦20 000, or ≧15 and ≦15 000, or ≧20 and ≦10 000, or ≧25 and ≦8000, or ≧30 and ≦5000, or ≧40 and ≦2500, or ≧50 and ≦1500, or ≧60 and ≦1000, or ≧60 and ≦750, or ≧60 and ≦500, or ≧60 and ≦300, or ≧60 and ≦175, or ≧60 and ≦150, or ≧60 and ≦125, or ≧60 and ≦100.
In principle, however, a poly-3-hydroxypropionate copolymer is also useful for the process according to the invention (for all the processes according to the invention) (copolyester). Such a copolymer comprises, as well as structural sections of the general formula (I), also different structural sections. For example, such poly-3-hydroxypropionate copolymers are possible by the process for ring-opening polymerization of cyclic esters and/or cyclic ethers described in EP 688806 B1 when the molar proportion of β-propiolactone in the mixture of cyclic esters and cyclic ethers to be polymerized is only ≧80 mol %, or only 85 mol %, or only ≧90 mol %, or only ≧95 mol %, or only ≧98 mol %, or only ≧99 mol %. Useful cyclic esters other than 3-propiolactone include, for example, β-butyrolactone, pivalactone, δ-valerolactone and ε-caprolactone. Useful cyclic ethers other than β-propiolactone include, for example, ethylene oxide, propylene oxide and butylene oxide.
According to the teaching of WO 2011/100608 A1, poly-3-hydroxypropionate (suitable for all the processes according to the invention), however, can also be prepared either as a homopolymer or as a copolymer by a biotechnological route in genetically modified biological organisms (for example from sugars or from alternative “renewable” carbon sources to these). Useful biological organisms of this kind include, for example, bacteria, algae, yeasts, fungi or plants.
The relative weight-average molecular weight of biotechnologically produced poly-3-hydroxypropionate may be up to 100 000, or up to 200 000 or more.
The aforementioned relative weight-average molecular weight is normally ≧1000 or ≧5000.
The proportion by weight of structural sections of the general formula (I) in such “biotechnologically” obtainable poly-3-hydroxypropionate may, for example, be ≧40% by weight, or ≧50% by weight, or ≧60% by weight, or ≧70% by weight, or ≧80% by weight, or ≧90% by weight, or ≧95% by weight, or ≧97% by weight, or ≧98% by weight, or ≧99% by weight.
For the purpose of the inventive catalyzed thermolysis thereof, a biotechnologically produced poly-3-hydroxypropionate may either remain in the biological organism that produces it (in the total amount of the biological organisms that produce it=total amount of bioorganisms=in the “biomass”) or be extracted therefrom beforehand (cf. WO 2011/100608 A1).
If the poly-3-hydroxypropionate remains in the biomass during the inventive catalyzed thermolysis thereof, it is appropriate in application terms to substantially dry the biomass prior to the onset of thermolysis of the poly-3-hydroxypropionate (advantageously in application terms, a process for vacuum drying and/or for freeze-drying is employed in this regard). In principle, such drying of the biomass, however, may also be effected only in the course of the temperature increase required for the thermolysis (before the temperature at which the splitting sets in has been attained; this applies in a completely corresponding manner and generally for any poly-3-hydroxypropionate which is obtained in moist form in the course of preparation thereof and is to be split in accordance with the invention).
If the biomass comprises, for example, bacteria, it may be necessary to deactivate (to pasteurize or to sterilize) them prior to the relevant thermolysis (with respect to its biological characteristics). This can be accomplished, for example, by heating under pressure and with the optional use of steam, i.e. by “autoclaving” or “sterilizing”. It will be appreciated that the deactivation can also be accomplished with dry heat (“hot air sterilization”). Alternatively, the deactivation can also be undertaken by irradiating or by chemical methods.
If a catalyzed thermolysis (catalyzed in accordance with the invention) of biotechnologically produced poly-3-hydroxypropionate is undertaken still in the presence of the biomass, it is advantageous, prior to the thermolysis, to destroy the cell walls of those cells (for example the cell walls of the bacteria) in which it has been synthesized and/or in which it has been stored. Such destruction can be effected, for example, mechanically by the action of appropriate forces. For example, the biomass can be homogenized in a mixer with rotating blades (for example an Ultraturrax). Alternatively, the biological organisms (especially in the case of microorganisms) can also be triturated in a simple manner (for example in a mortar with sand or Al2O3, or with a pestle, or in a glass bead mill). In the case of action of sound waves (for example ultrasound), the cells are destroyed by constant collision (cavitation forces). A particularly preferred mechanical method for destruction of cell walls is the nitrogen decompression method. This involves enriching nitrogen in the cells at elevated gas pressures in accordance with Henry's law. A subsequent instantaneous pressure release can subsequently bring about the bursting of the cell walls.
Nonmechanical destruction processes are preferably employed in the case of cell walls which cannot be broken mechanically in a simple manner (for example in the case of yeast cells). Repeated freezing and thawing destroys the cell walls as a result of shear forces. Chemical (for example with toluene) and/or enzymatic lysis can destroy the cell membrane or cell wall. In addition, treatment with hypotonic buffer solutions can bring about the lysis of cells.
As a basic requirement, an active substance for use as a splitting catalyst in accordance with the invention should have maximum mass-specific catalytic action. In other words, a minimum use amount of the active substance should be sufficient to display the desired catalytic action.
In-house studies by the applicant have shown that this is the case for amines as molecular organic active compounds when the compound is a tertiary amine in the inventive sense. This means a molecular organic active compound which has at least one tertiary nitrogen atom which has a covalent bond to three different carbon atoms of the molecular organic active compound, without any oxygen atom bonded to any of these carbon atoms via a covalent double bond.
One reason for this is probably that primary and secondary amines can react with ester groups, as present in poly-3-hydroxypropionate to be split in accordance with the invention, to give amides. However, the nitrogen atom present in the amide group thereof is covalently bonded to a carbon atom which has a covalent double bond to an oxygen atom. The electron-attracting effect thereof, however, is prohibitive for usability as an efficient molecular organic active compound in the context of the present application.
For the purposes of maximum mass-specific catalytic splitting action, a molecular organic active compound to be used as a splitting catalyst in accordance with the invention, advantageously in accordance with the invention, has more than one tertiary nitrogen atom having a covalent bond to each of three different carbon atoms of the molecular organic active compound, with the proviso that none of these carbon atoms simultaneously has a covalent double bond to an oxygen atom. Favorably in accordance with the invention, any molecular organic active compound to be used as a splitting catalyst comprises at least two or at least three tertiary nitrogen atoms of this kind.
Most preferably, the relevant molecular organic active compound comprises only nitrogen atoms which are tertiary nitrogen atoms of the type detailed above.
The restriction to hydrogen, carbon, nitrogen and oxygen as possible atomic constituents of a molecular organic active compound suitable as a splitting catalyst in accordance with the invention ensures that this can optionally be fully combusted with residues remaining in the context of the relevant thermolysis, without any risk of formation of particularly problematic combustion gases.
Furthermore, the above restriction also limits, in a natural manner, side reactions which are unwanted in the context of the relevant thermolysis, and simultaneously promotes economically advantageous availability of the molecular organic active compound.
Advantageously in accordance with the invention, an inventive molecular organic active compound suitable as a splitting catalyst does not have any oxygen atom to which a hydrogen atom is covalently bonded. In this way, possible unwanted esterification of acrylic acid formed in the course of the thermolysis is counteracted.
The exclusion of radicals of an aromatic or of a substituted aromatic hydrocarbon ensures that molecular organic active compounds to be used as splitting catalysts in accordance with the invention are toxicologically comparatively safe compared to active compounds such as N,N-dimethylaniline, for example. This is particularly with a view to further use of the acrylic acid obtained in the course of an inventive thermolysis for preparation of polymers which find use in the hygiene sector.
The term “aromatic hydrocarbon” shall comprise both monocyclic aromatic hydrocarbons (e.g. benzene) and polycyclic aromatic hydrocarbons (which have at least two aromatic ring systems bonded to one another (e.g. naphthalene or biphenyl)). Substituted aromatic hydrocarbons derive from aromatic hydrocarbons by replacement of at least one hydrogen atom by a substituent (=an atom other than hydrogen or an (atom) group (=group of atoms chemically bonded to one another) other than a hydrogen atom) (examples of such substituted aromatic hydrocarbons are, for example, phenyl chloride (a hydrogen atom in the benzene is replaced by a chlorine atom) or toluene (a hydrogen atom in the benzene is replaced by the methyl group)).
The term “radical” expresses the fact that, in contrast to the aromatic hydrocarbon or to the substituted aromatic hydrocarbon, there is an unoccupied (free) covalent single bond therein, which may be localized either on an aromatic ring or on a substituent (e.g. —C6H5=phenyl radical or —CH2—C6H5=benzyl radical, or C6H5—(C═O)—=benzoyl radical).
More preferably in accordance with the invention, the at least one molecular organic active compound does not have any aromatic ring system at all, i.e. no heteroaromatic ring either (the latter comprising at least one atom other than carbon in the aromatic ring).
The lower boiling point limit of the molecular organic active compounds suitable as a splitting catalyst in accordance with the invention (this boiling point at standard pressure is ≧150° C., better ≧160° C. or ≧170° C., advantageously ≧180° C., preferably ≧185° C., more preferably ≧190° C. and most preferably ≧195° C.) ensures that the inventive molecular organic active compounds, in the course of the thermolysis of poly-3-hydroxypropionate that they catalyze, need not normally necessarily be discharged from the splitting mixture with the acrylic acid formed in the splitting, but may generally remain in the splitting mixture (the latter can be promoted by a rectification column which is positioned atop a splitting reactor and is operated in reflux). By gradually adding fresh poly-3-hydroxypropionate to be split to the splitting mixture, it is possible in this case to make multiple (repeated) use of the action of one and the same splitting catalyst addition.
The upper boiling point limit of the molecular organic active compound suitable as a splitting catalyst in accordance with the invention (this boiling point at standard pressure is ≦350° C., preferably ≦345° C., better ≦340° C., advantageously ≦335° C., particularly advantageously ≦330° C. or ≦325° C., very particularly advantageously ≦320° C. or ≦315° C., even better ≦310° C. and at best ≦300° C., or ≦290° C., or ≦280° C., or ≦270° C., or ≦260° C., or ≦250° C. and ≦240° C., or ≦230° C., or ≦220° C.) opens up the possibility, after the catalyzed thermal splitting (catalyzed thermolysis) has ended, of removing the at least one molecular organic active compound used as a splitting catalyst in accordance with the invention subsequently from residues which generally remain in the relevant thermolysis (for example from remaining biomass), for example by distillative and/or rectificative means, optionally under reduced pressure, and thus obtaining it as a product of value for a process according to the invention in reutilizable form.
The melting point of molecular organic active compounds to be used as splitting catalysts in accordance with the invention, which is at comparatively low temperatures compared to the boiling point and is required in accordance with the invention (this melting point at standard pressure is ≦70° C., advantageously ≦60° C., particularly advantageously ≦50° C., better ≦40° C., preferably ≦30° C., more preferably ≦20° C. or ≦10° C., even more preferably ≦0° C. or ≦−10° C., and at best ≦−15° C.) is advantageous in that it ensures that the molecular active compound to be used in accordance with the invention as a splitting catalyst normally melts at a lower temperature than the poly-3-hydroxypropionate to be split itself and as a result can optionally function as a solvent or as a dispersant with respect to the poly-3-hydroxypropionate to be split. In the extreme case, the thermal splitting catalyzed in accordance with the invention (the thermolysis catalyzed in accordance with the invention) of the poly-3-hydroxypropionate can thus be effected from the solution thereof, or from the suspension thereof, or from the emulsion thereof, in the splitting catalyst. By employing a mixture of various molecular organic active compounds suitable as splitting catalysts in accordance with the invention, it is possible to bring about a melting point depression which is advantageous in the present context.
Moreover, a comparatively low melting point of a molecular organic active compound suitable as a splitting catalyst in accordance with the invention generally causes a comparatively low dynamic viscosity of the melt thereof, not only under the conditions of the thermolysis but also under customary conditions prior to the thermolysis. The latter is significant especially when the poly-3-hydroxypropionate to be split thermolytically itself has a comparatively high melting point (for example >200° C., or >250° C.). In these cases, the thermolysis of the poly-3-hydroxypropionate catalyzed in accordance with the invention can also be effected from the solid substance thereof. If the poly-3-hydroxypropionate in such a case can be sprayed homogeneously, for example, with a comparatively volatile splitting catalyst prior to the thermolysis, this is normally beneficial for a subsequently comparatively homogeneous profile of the thermolysis. Alternatively, solid poly-3-hydroxypropionate, for splitting purposes, can be impregnated in a comparatively simple manner with a volatile splitting catalyst, or be suspended therein.
In addition, a volatile splitting catalyst can also be applied in a simple manner to solid poly-3-hydroxypropionate to be split by stripping the splitting catalyst out of the liquid substance thereof with a carrier gas, and subsequently passing the carrier gas laden with the splitting catalyst through the solid poly-3-hydroxypropionate to be split in order to strip off the splitting catalyst on the surface therefrom again.
The above relationships are fully correspondingly also advantageous especially when the thermolysis of the poly-3-hydroxypropionate is undertaken, for example, from solid biomass.
Good wetting of solid poly-3-hydroxypropionate and a comparatively high flashpoint are further advantages normally possessed by molecular organic active compounds to be used as splitting catalysts in accordance with the invention.
It is generally a characteristic feature of molecular organic active compounds which are suitable as splitting catalysts in accordance with the invention and can advantageously combine the profile of properties detailed that the molar mass M thereof is ≧100 g/mol and ≦300 g/mol, advantageously ≧120 g/mol and ≦280 g/mol, preferably ≧140 g/mol and ≦260 g/mol, and more preferably ≧150 g/mol and ≦250 g/mol.
Inventive molecular organic active compounds particularly suitable as splitting catalysts for the process according to the invention (for all the thermolysis processes detailed in the present document, and on all poly-3-hydroxypropionates which are thermolytically splittable to give acrylic acid and are detailed in the present document) are, as an illustrative list, pentamethyldiethylenetriamine (M=173.30 g/mol; b.p.=199° C.; m.p.<−20° C.; purchasable as Lupragen® N301 from BASF SE), N,N,N′N-tetramethyl-1,6-hexanediamine (M=172.31 g/mol; b.p.=212° C., m.p.=−46° C.; purchasable as Lupragen® N500 from BASF SE), bis(2-dimethylaminoethyl)ether (M=160.3 g/mol; b.p.=189° C., m.p.=60° C.; purchasable as Lupragen® N205 from BASF SE), 2,2′-dimorpholinodiethyl ether (M=244.33 g/mol, b.p.=309° C.; m.p.=−28° C.; purchasable as Lupragen® N106 from BASF SE), N,N′-diethylethanolamine (M=117.19 g/mol; b.p.=161° C.; m.p.=−70° C.), N,N-dimethylcyclohexylamine (M=127.23 g/mol; b.p.=159° C.; m.p.=−60° C.; purchasable as Lupragen® N100 from BASF SE), N-methylimidazole (M=82.12 g/mol; b.p.=198° C.; m.p.=−2° C.; purchasable as Lupragen® NMI from BASF SE) and 1,2-dimethylimidazole (M=96.13 g/mol; b.p.=204° C.; m.p.=38° C.).
Among the molecular organic active compounds listed above by way of example as splitting catalysts particularly suitable in accordance with the invention, pentamethyldiethylenetriamine is once again preferred (especially for all the thermolysis processes detailed in the present document, and on all poly-3-hydroxypropionates which are thermolytically splittable to give acrylic acid and are detailed in the present document), since it combines the properties of a splitting catalyst favorable in accordance with the invention in a particularly favorable manner.
Based on the weight of the mass of the (a) poly-3-hydroxypropionate to be split to give acrylic acid in accordance with the invention, the weight of the mass of the at least one inventive catalytically active molecular active compound in the process according to the invention is generally 0.01 to 15% by weight, or 0.05 to 10% by weight, often 0.1 to 5% by weight, preferably 0.5 to 4% by weight, or 1.5 to 3.5% by weight.
Naturally, the use amount of splitting catalyst (of the at least one catalytically active molecular organic active compound) in the process according to the invention may also be above the values mentioned above. This is especially the case when the splitting catalyst simultaneously also functions as a solvent or as a dispersant for the poly-3-hydroxypropionate to be split. Particularly in these cases, the use amounts of splitting catalyst on a basis corresponding to that above may easily be up to 50% by weight, or up to 100% by weight, or up to 150% by weight, or up to 200% by weight, or up to 250% by weight, or up to 300% by weight, or up to 500% by weight or more.
The above is also easily the case when the process according to the invention for thermolysis of poly-3-hydroxypropionate is performed on poly-3-hydroxypropionate still present in biomass, which for this purpose, advantageously for application purposes, may be slurried in the at least one molecular organic active compound for use as a splitting catalyst in accordance with the invention.
According to the melting point and solubility of the poly-3-hydroxypropionate, the process according to the invention for catalyzed thermal splitting thereof (for catalyzed thermolysis thereof) can be effected with formation of acrylic acid from the solid substance thereof, or from the melt thereof, or from the solution thereof in a solvent (for example an organic liquid), or from the suspension thereof in a (for example organic) liquid (in a dispersant) or from the emulsion thereof in a (for example organic) liquid (in a dispersant), or from the biomass thereof which comprises the poly-3-hydroxypropionate and may optionally be slurried in a (for example organic) liquid (in a slurrying agent).
The boiling point (based on standard pressure) of such a solvent, dispersant or slurrying agent is, advantageously in application terms, well (for example at least 20° C., better at least 40° C., even better at least 50° C. or at least 60° C., preferably at least 80° C. and more preferably at least 100° C.) above the boiling temperature of acrylic acid on a corresponding basis (=141° C.).
Useful such (for example organic) solvents, or dispersants, or slurrying agents, include, for example, ionic liquids, oligomeric (particularly di- to hexameric) Michael adducts (addition products) of acrylic acid onto itself and onto the addition products which form (as typically arise in the course of conventional preparation of acrylic acid (especially, for example, as bottom products in the case of retifications of acrylic acids or as residues in the case of storage of acrylic acid)), or molecular organic liquids such as dimethyl sulfoxide, N-methyl-2-pyrrolidone, dialkylformamide, relatively long-chain paraffinic hydrocarbons, relatively long-chain alkanols, γ-butyrolactone, ethylene carbonate, diphenyl ether, diglyme (=diethylene glycol dimethyl ether), triglyme (=triethylene glycol dimethyl ether), tetraglyme (=tetraethylene glycol dimethyl ether), biphenyl, tricresyl phosphate, dimethyl phthalate and/or diethyl phthalate, among which preference is given in accordance with the invention to the nonaromatic liquids.
The proportion by weight of the poly-3-hydroxypropionate in such a splitting mixture also comprising solvent, or dispersant, or slurrying agent, may, based on the weight of the total mass of the splitting mixture, be less than 95% by weight, or less than 90% by weight, or less than 80% by weight, or less than 70% by weight, or less than 60% by weight, or less than 50% by weight, or less than 40% by weight, or less than 30% by weight, or less than 20% by weight, or less than 10% by weight. In general, this proportion by weight is, however, ≧5% by weight.
The proportion by weight of the poly-3-hydroxypropionate in dry biomass may have corresponding values. In favorable cases, however, it is at values of ≧95% by weight (cf., for example, WO 2011/100608).
Irrespective of whether the poly-3-hydroxypropionate is present in the splitting mixture in the form of the melt thereof, or dissolved in a solvent, or dispersed in a dispersant as a suspension or as an emulsion (i.e. suspended or emulsified), or in slurried form as a constituent of biomass in a slurrying agent, the at least one molecular organic active compound added as a splitting catalyst is preferably present dissolved in the splitting mixture (in the melt, in the solvent, in the dispersant, or in the slurrying agent).
In general, presence of solvent, or dispersant, or slurrying agent, however, reduces the splitting rate under otherwise identical conditions.
The position of the melting point (based on standard pressure) of poly-3-hydroxypropionate depends especially on the relative weight-average molecular weight and the polydispersity Q thereof.
In the case of values of the weight-average relative molecular weight MW of poly-3-hydroxypropionate in the range from 1000 to 20 000, the corresponding melting point based on standard pressure (at customary polydispersities) is normally at values of ≦150° C., usually ≦100° C.
Even in the case of values for MW of up to 100 000, or up to 150 000, the melting point of the poly-3-hydroxypropionate based on standard pressure (at customary polydispersities) is still at values of 200° C.
In these aforementioned cases, the thermolysis process according to the invention is therefore generally advantageously executed from the melt of the poly-3-hydroxypropionate. It is advantageous in this case that the at least one molecular organic active compound or melt thereof to be added (additionally used) as a splitting catalyst in accordance with the invention dissolves completely in the melt in the catalytically active amount thereof to be added which is required in each case, or mixes completely and homogeneously with the melt of the poly-3-hydroxypropionate to be thermally split.
Otherwise, the process according to the invention for catalyzed thermolysis of poly-3-hydroxypropionate can be performed (executed) as described in the known prior art splitting processes (for example the prior art acknowledged in the present document).
In other words, splitting temperatures typically to be employed (temperatures at which the thermolysis is performed, possessed by the poly-3-hydroxypropionate or melt, solution, suspension, emulsion thereof, the biomass comprising it or the slurries of the biomass comprising it in the course of thermolysis) may vary within the range from 50 to 400° C., or within the range from 75° C. to 350° C., or within the range from 100 to 300° C. Advantageously in accordance with the invention, the splitting temperatures employed (the thermolysis temperatures, the temperatures at which the thermolysis is performed) will be 150 to 220° C. and more preferably 160 to 200° C.
Equally, the working pressure during the inventive thermolysis of the poly-3-hydroxypropionate (in the gas atmosphere) may be either at standard pressure (=1.0133·105 Pa) or above or below standard pressure. In other words, the working pressure may, for example, be 102 to 107 Pa, or 103 to 106 Pa, or 2·103 to 5·105 Pa, or 5·103 to 3·105 Pa.
If the working pressure is below standard pressure (for example at pressures down to 102 Pa or less), the acrylic acid formed in the splitting follows the pressure gradient present and is withdrawn continuously from the liquid splitting mixture in this manner.
If the working pressure is at or above standard pressure (for example at pressures up to 107 Pa or more), the acrylic acid formed in the splitting, appropriately in application terms, can be continuously stripped out of the splitting mixture, for example in liquid form (which may, for example, also be the exclusive melt of poly-3-hydroxypropionate (P3HP)), with the aid of a stripping gas (for example molecular nitrogen, noble gas, carbon dioxide, air, lean air (preferred; molecular oxygen-depleted air (generally <6% by vol. of O2))).
The measure of stripping can also advantageously be partly employed in the context of splitting under reduced pressure.
It will be appreciated that the acrylic acid formed in the course of splitting can also be distilled out of the splitting mixture, for example in liquid form, in a conventional manner following the corresponding temperature gradient.
If, for example, the gas stream which comprises the acrylic acid formed in the splitting and is flowing away from the splitting mixture, for example in liquid form, is conducted in countercurrent to descending reflux liquid through a rectification column on top of a splitting reactor, the acrylic acid can be removed in elevated purity from the liquid splitting mixture (this is advantageous, for example, when the poly-3-hydroxypropionate to be split thermolytically in accordance with the invention is not a homopolymer but a copolymer). Additional subsequent employment of any thermal separation processes can result in purification of the acrylic acid to any desired purity.
All such splitting operations on poly-3-hydroxypropionate by the action of elevated temperatures are summarized in this document by the term “thermolysis” or “pyrolysis” of poly-3-hydroxypropionate.
The process according to the invention for catalyzed thermolysis of poly-3-hydroxypropionate is applicable, inter alia, to all poly-3-hydroxypropionates detailed in this document, even if they do not have a vinylic head group and/or a vinylic end group (a vinylic head group and end group shall be understood to mean, respectively, a head group and end group which have at least one ethylenically unsaturated double bond between two carbon atoms).
It should also be emphasized that poly-3-hydroxypropionate which is prepared by carbonylation of ethylene oxide dissolved in an aprotic solvent with CO in the presence of a cobalt-comprising catalyst system at elevated pressure and elevated temperature, as described in the processes of the prior art acknowledged in this document, is subjected prior to the inventive catalyzed thermolysis thereof to a decobaltization by, for example, washing with an aqueous solution, preferably with a Brønsted-acidic aqueous solution (the reference basis for the property “Brønsted acid” in this document is 25° C. and standard pressure, and water as the co-reactant for the Brønsted acid; in other words, the addition of a Brønsted acid to water (at 25° C. and standard pressure) gives an aqueous solution which, under the conditions mentioned, has a lower pH than pure water; such aqueous solutions are what is meant by the expression “Brønsted-acidic aqueous solution”), and/or by precipitation from the product mixture comprising it with an aqueous solution, preferably with a Brønsted-acidic aqueous solution. Advantageously, the washing and/or precipitation is effective in the presence of one or more oxidizing agents for Co in oxidation states <+2. Appropriately in application terms, the precipitation and/or washing is therefore effected, for example, under air. The reason for this measure is that the applicant has found that presence of cobalt impairs the inventive catalyzed thermolysis.
Additional use of at least one inventive organic molecular active compound as a splitting catalyst in the inventive thermolysis not only enables performance of the thermolysis at relatively low temperatures, but also ensures, under given thermolysis conditions, normally especially also an elevated space-time yield of acrylic acid (the at least one molecular organic active compound, under given conditions, generally improves both the splitting rate and the selectivity of target product formation (of acrylic acid formation)).
In order to optionally counteract any unwanted free-radical polymerization of acrylic acid formed in the inventive thermolysis, appropriate polymerization inhibitors can additionally be added to the poly-3-hydroxypropionate to be split thermolytically, or to the melt thereof, or to the solution thereof in a solvent, or to the emulsion thereof in a dispersant, or to the suspension thereof in a dispersant, or to the biomass comprising the poly-3-hydroxypropionate, or to the slurry of the biomass comprising the poly-3-hydroxypropionate in a slurrying agent.
Useful polymerization inhibitors of this kind in principle include all of those which are recommended in the prior art for the purpose of inhibiting free-radical polymerization of acrylic acid in the liquid phase. Useful polymerization inhibitors of this kind include alkylphenols, such as ortho-, meta- or para-cresol (methylphenol), 2-tert-butyl-4-methylphenol, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol and 2-methyl-4-tert-butylphenol, hydroxyphenols such as hydroquinone, catechol, resorcinol, 2-methylhydroquinone and 2,5-di-tert-butylhydroquinone, aminophenols, for example para-aminophenol, nitrosophenols, for example para-nitrosophenol, alkoxyphenols such as 2-methoxyphenol, 2-ethoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether) and mono- or di-tert-butyl-4-methoxyphenol, tocopherols, for example α-tocopherol, N-oxyls such as 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl, 2,2,6,6-tetramethylpiperidine N-oxyl, 4,4′,4″-tris(2,2,6,6-tetramethylpiperidine N-oxyl) phosphite or 3-oxo-2,2,5,5-tetramethyl-pyrrolidine N-oxyl, aromatic amines or phenylenediamines, for example N,N-diphenylamine, N-nitrosodiphenylamine and N,N′-dialkyl-para-phenylenediamine, where the alkyl radicals may be the same or different and each independently consist of 1 to 4 carbon atoms and may be straight-chain or branched, hydroxylamines, for example N,N-diethylhydroxylamine, phosphorus compounds, for example triphenylphosphine, triphenyl phosphite, hypophosphorous acid or triethyl phosphite, sulfur compounds, for example diphenyl sulfide or phenothiazine, and all aforementioned inhibitors optionally in combination with metal salts, for example the chlorides, dithiocarbonates, sulfates, salicylates or acetates of copper, manganese, cerium, nickel and/or chromium.
It is also possible to use different mixtures of the polymerization inhibitors mentioned. The polymerization inhibitors used are preferably phenothiazine and/or hydroquinone monomethyl ether. In addition, the aforementioned polymerization inhibitors can be supported by a molecular oxygen-comprising gas (for example air or nitrogen-diluted air (advantageously lean air=air depleted of molecular oxygen, the molecular oxygen content of which is typically <6% by volume)). Appropriately in application terms, the explosion limits of gaseous mixtures comprising acrylic acid and oxygen are noted (cf., for example, WO 2004/007405 A1). For example, the above support can be effected by stripping the acrylic acid formed in the splitting continuously out of the splitting mixture with the aid of a molecular oxygen-comprising stripping gas (such a stripping operation can be effected at reduced pressure, standard pressure, or else at working pressures above standard pressure).
According to the polymerization inhibitor (or mixture of polymerization inhibitors) used, the use amount thereof, based on the content of poly-3-hydroxypropionate in the splitting mixture, will be 10 to 1000 ppm by weight, frequently 50 to 500 ppm by weight and in many cases 150 to 350 ppm by weight.
Apart from the above-described possible additional use of a molecular oxygen-comprising stripping gas and optional promotion of polymerization inhibitors by a molecular oxygen-comprising gas, the inventive catalyzed thermolysis, appropriately in application terms, is executed with substantial exclusion of molecular oxygen, in order to prevent unwanted oxidation (especially unwanted full combustion) of organic components present in the thermolysis.
It should also be emphasized that the process according to the invention can be performed continuously or batchwise.
The acrylic acid can be converted from the acrylic acid-comprising gas phase obtained in the thermolysis of poly-3-hydroxypropionate catalyzed in accordance with the invention to the liquid phase in a manner known per se, by absorptive and/or condensative measures. In general, this liquid phase may already be the acrylic acid which is obtainable in accordance with the invention and is suitable for further uses (for example free-radical polymerizations) (especially when the acrylic acid thus obtained is not stored intermediately prior to the further use thereof in a free-radically initiated polymerization, the aforementioned conversion to the liquid phase will advantageously be undertaken without additional use of polymerization inhibitors which impair any (later) free-radically initiated polymerization).
With application of one or more thermal separation processes (such thermal separation processes may especially be rectification, extraction, desorption, distillation, stripping, absorption, azeotropic rectification and/or crystallization) to the acrylic acid-comprising liquid phase, the acrylic acid from the liquid phase can also be purified to any purity as required (for example analogously as described in documents DE 10243625 A1, DE 10332758 A1, DE 102007004960 A1 and DE 102012204436 A1, and the prior art cited in these documents).
A suitable preferred thermal separation process is the process of crystallization. Within the crystallizative separation processes, the process of suspension crystallization is preferentially employable for the aforementioned purpose (for example analogously as described in DE 102007043759 A1, DE 102008042008 A1 and DE 102008042010 A1, and the prior art cited in these documents).
The removal of the suspension crystals from the crystal suspension is, appropriately in application terms, undertaken in a wash melt wash column (cf. WO 01/77056 A1; the wash liquid used is the melt of acrylic acid crystals already purified correspondingly), preferably in a hydraulic wash melt wash column (analogously as described, for example, in WO 01/77056 A1, WO 02/09839 A1, WO 03/041832 A1, WO 2006/111565 A2, WO 2010/094637 A1 and WO 2011/045356 A1, and the prior art cited in these documents).
Incidentally, the inventive splitting of the poly-3-hydroxypropionate can be performed on the industrial scale either batchwise or continuously.
Appropriately in application terms, a continuous process regime may be configured as follows. The splitting reactor used is the bottom space of a separating column comprising separating internals (useful separating internals include, for example, mass transfer trays such as dual-flow trays; in principle, the separating column may also be empty, i.e. not have any separating internals). The liquid splitting mixture (which may be a melt, a solution, a suspension, a slurry or an emulsion) is supplied in the lower third of the separating column (in principle, the supply may also be effected directly into the bottom space; such a supply may in principle also be effected “in solid form”).
Below the feed point (advantageously from the bottom space), by means of a pump, a liquid stream (which may optionally also be a suspension or slurry) is withdrawn continuously and recycled by means of an indirect heat exchanger back into the separating column below the feed point of the splitting mixture. In the course of flow through the indirect heat exchanger, the thermal energy required for the thermolysis is supplied. Advantageously in application terms, the indirect heat exchanger is a forced circulation flash heat transferer.
At the top or via a side draw, the acrylic acid can be conducted out of the separating column. If the separating column has separating internals, condensate formation is brought about in the top region of the separating column and a portion of the condensate formed is conducted in the separating column descending as reflux liquid in countercurrent to the acrylic acid ascending in the separating column (for example conducted by a stripping gas and/or following the pressure gradient in the case of reduced top pressure). As an outlet for the highest-boiling secondary components, a portion of the bottoms liquid is discharged continuously and sent to the disposal (for example incineration) thereof.
If the inventive thermolysis is performed from the solid substance of the poly-3-hydroxypropionate or from the solid biomass comprising it (preferably dry biomass), it is appropriate in application terms to perform the process according to the invention in a heated rotary tube oven, through which a stripping gas advantageously flows, the latter discharging the acrylic acid formed. It is possible in this case to work either batchwise or continuously. In continuous operation, the material to be thermolyzed in accordance with the invention and the stripping gas are appropriately conducted through the rotary tube oven in countercurrent.
What is advantageous about acrylic acid which has been prepared by the inventive procedure (or originates from an inventive preparation) and has been converted, for example by absorptive and/or condensative measures, from the gas phase obtained in the thermolysis of the poly-3-hydroxypropionate to the condensed (preferably liquid) phase is that it does not have the fingerprint of low molecular weight aldehydes present therein as impurities which is typical of acrylic acid prepared by heterogeneously catalyzed partial oxidations of C3 precursor compounds (e.g. propylene, propane, acrolein, glycerol, propionic acid, propanol, etc.) (cf., for example, DE 102011076931 A1).
These impurities are found to be extremely disruptive in the case of use of the acrylic acid and/or of the conjugate (Brønsted) base thereof for preparation of polymers by free-radically initiated polymerization, optionally in a mixture with other mono- or polyunsaturated (for example ethylenically) compounds, even in very small amounts (1 to 10 ppm by weight based on the weight of the mass of acrylic acid) (for example, they can undesirably retard the free-radically initiated polymerization or hinder or impair the preparation of polymer with particularly high molecular weight as a result of their “regulating action”).
Accordingly, particularly advantageous processes for inventive preparation of acrylic acid are those followed by a process for free-radical polymerization in which the acrylic acid prepared, as such and/or in the form of its conjugate base (what is meant here is the conjugate Brønsted base, the acrylate anion), optionally in a mixture with other mono- and/or polyunsaturated compounds, is polymerized to polymer with free-radical initiation.
This is especially true when the process for free-radical polymerization is a process for producing a water-“superabsorbent” polymer, as used, for example, in hygiene articles such as diapers (cf. DE 102011076931 A1 and the prior art cited in the same document).
Accordingly, the present invention comprises especially the following inventive embodiments:
(Starting materials and analysis methods detailed and specified for the first time in each case for description of examples and comparative examples in the following experiments were used in a corresponding manner at the corresponding point in subsequent experiments, unless explicitly stated otherwise; all precipitations and washes of poly-3-hydroxypropionate prepared by carbonylation of ethylene oxide in the presence of a cobalt-comprising catalyst system were conducted under air)
A) Preparation of poly-3-hydroxypropionate
The carbonylating conversion was effected in an autoclave A stirrable with a paddle stirrer (the paddle stirrer was moved by means of magnetic coupling), the reaction space of which was optionally heatable or coolable from the outside. All surfaces in contact with the reaction space were manufactured from Hastelloy HC4. The reaction space of the autoclave had a circular cylindrical geometry. The height of the circular cylinder was 335 mm. The internal diameter of the circular cylinder was 107 mm. The shell of the reaction space had a wall thickness of 19 mm (Hastelloy HC4). The top of the autoclave was equipped with a gas inlet/gas outlet valve V which opened into the reaction space. The temperature in the reaction space was determined with the aid of a thermocouple. The reaction temperature was regulated under electronic control. The internal pressure in the reaction space was monitored continuously with an appropriate sensor.
The reaction space of the autoclave was at first inertized with argon (contents in the Ar: ≧99.999% by vol. of Ar, ≦2 ppm by vol. of O2, ≦3 ppm by vol. of H2O and ≦0.5 ppm by vol. of total amount of hydrocarbons).
Subsequently, the autoclave A at a controlled temperature of 10° C. was charged under argon with 16.0 g of dicobalt octacarbonyl (Co2(CO)8; supplier: Sigma-Aldrich; specification: 1-10% hexane, ≧90% Co, catalog number: 60811), 8.7 g of 3-hydroxypyridine (supplier: Sigma-Aldrich; specification: 99% content, catalog number: H57009) and 1001.2 g of diglyme (supplier: Sigma-Aldrich; specification: 99% content, catalog number: M1402), and the autoclave was subsequently closed. The temperature of the two solids was 25° C. and the temperature of the diglyme was 10° C. Then, while maintaining the internal temperature of 10° C., carbon monoxide was injected into the autoclave through the valve V until the pressure in the reaction space was 1.5·106 Pa (carbon monoxide from BASF SE, specification: 99.2% CO). Subsequently, the temperature in the reaction space was increased to 28° C. in order to verify the integrity of the autoclave A (over a period of 50 min). Then the atmosphere in the reaction space was decompressed to an internal pressure of 106 Pa by opening the valve V. The temperature of 28° C. in the interior was maintained.
Subsequently, while maintaining the internal temperature of 28° C., 97.8 g of ethylene oxide (1.5 g/min) were pumped through the valve V into the reaction space (supplier: BASF SE; specification: 99.9% purity). Thereafter, carbon monoxide was again injected into the autoclave until the pressure in the reaction space reached 6·106 Pa (while maintaining the internal temperature of 28° C.).
Then, while stirring (700 rpm), the temperature in the reaction space of autoclave A was increased in an essentially linear manner to 75° C. within 45 min. This temperature was maintained while stirring for 8 h. The pressure in the reaction space fell to 3·106 Pa within this period. Then the heating of autoclave A was switched off. Within 6 h, the temperature in the stirred reaction space cooled down in an essentially exponential manner to 25° C. (after 66 min the internal temperature had fallen to 60° C., after 165 min to 40° C. and after 255 min to 30° C.). The corresponding pressure in the reaction space was 2.8·106 Pa. Then autoclave A was decompressed to standard pressure and the reaction space was purged with argon (106 Pa) three times in succession.
In the reaction space were 1106.3 g of a dark red/brown solution as product mixture A.
Product mixture A was left to stand in a closed glass flask in a cooling space at a temperature of 7° C. for 12 h. The poly-3-hydroxypropionate which precipitated out was filtered off and the filtercake was washed with 300 g of methanol at a temperature of 25° C. The washed filtercake was dried for 10 h (10 hPa, 25° C.). The 41.4 g of poly-3-hydroxypropionate thus removed from product mixture A (first fraction) still comprised, based on the weight of the mass thereof, 1.6% by weight of cobalt (the starting weight content of Co in product mixture A, based on the weight of the maximum possible amount of poly-3-hydroxypropionate formed, was 2.97% by weight). The weight-average relative molecular weight was MW=7220.
The filtrate obtained in the removal of the poly-3-hydroxypropionate by filtration was analyzed by gas chromatography. It comprised (reported as area percent of the total area of the GC peaks) 0.9% ethylene oxide, 92.7% diglyme, 1.0% of the β-propiolactone by-product and 0.6% of the succinic anhydride by-product.
The material was combined with the methanol which had been sucked through in the course of washing of the poly-3-hydroxypropionate which had been filtered off (first fraction). The mixture thus obtained was left to stand in a cooling space at a temperature of 7° C. for 12 h. The poly-3-hydroxypropionate which precipitated out was filtered off again and the resulting filtercake was washed with 300 g of methanol at a temperature of 25° C. (as always, the methanol was sucked through the filtercake). The washed filtercake was dried again at 10 hPa and 25° C. for 10 h.
The mass of the poly-3-hydroxypropionate separated in this way from product mixture A as the second fraction was 88.0 g. Based on the weight of the mass thereof, it still comprised 1.6% by weight of cobalt. The weight-average relative molecular weight MW thereof was 5640.
The filtrate obtained in the removal of the second fraction of poly-3-hydroxypropionate by filtration was combined with the methanol sucked through in the course of washing of the second fraction of poly-3-hydroxypropionate. The mixture thus obtained was left to stand in a cooling space at a temperature of 7° C. for 12 h. The poly-3-hydroxypropionate obtained was filtered off again (third fraction) and the resulting filtercake was washed with 300 g of methanol at a temperature of 25° C. The washed filtercake was dried again at 10 hPa and 25° C. for 10 h.
The mass of the poly-3-hydroxypropionate removed in this way as the third fraction from product mixture A was 5.8 g. Based on the weight of the mass thereof, it still comprised 1.8% by weight of cobalt. The weight-average relative molecular weight MW thereof was 5240.
The filtrate obtained in the removal of the third fraction of poly-3-hydroxypropionate by filtration was combined with the methanol sucked through in the course of washing of the third fraction of poly-3-hydroxypropionate. The resulting mixture was left to stand in a cooling space at a temperature of 7° C. for 12 h. The poly-3-hydroxypropionate which precipitated out was filtered off again (fourth fraction) and the resulting filtercake was washed with 300 g of methanol at a temperature of 25° C. The washed filtercake was dried again at 10 hPa and 25° C. for 10 h.
The mass of the poly-3-hydroxypropionate thus removed from product mixture A as the third fraction was 5.3 g. Based on the weight of the mass thereof, it comprised 2.7% by weight of cobalt. The weight-average relative molecular weight MW thereof was 4230.
The elevated cobalt content of the third fraction is attributed to the fact that cobalt which was previously still dissolved now apparently also precipitates as a separate cobalt salt in the resulting solvent mixture.
A total of 140.2 g of poly-3-hydroxypropionate are removed from product mixture A. This is 87.6% of the theoretically possible maximum yield.
The cobalt contents were determined by inductively coupled plasma optical ion emission spectroscopy (ICP-OES).
The instrument used was a varian 720-ES ICP-OES spectrometer. The wavelength of the spectral line of Co used for analysis was 237.86 nm.
For sample preparation, 0.1 g of the sample to be analyzed in each case was converted to ash with a mixture of concentrated sulfuric acid, concentrated nitric acid and concentrated perchloric acid (as strongly oxidizing acids) in a quartz test tube (using temperatures of up to 320° C., the acids were quantitatively fumed off). The remaining residue was taken up in concentrated hydrochloric acid and dissolved with heating and addition of water. The resulting solution was subsequently analyzed.
The molecular weights were determined by size exclusion chromatography (SEC/GPC). The elution curve was converted to the actual distribution curve with the aid of polymethyl methacrylate (PMMA) calibration curves. The calibration was effected with narrow-distribution PMMA standards, the relative molecular weights of which were within the range from M=800 to M=1 820 000. The values outside this elution range were extrapolated.
This experiment “A)1.” was repeated several times, and mixing of various fractions removed gave a poly-3-hydroxypropionate which, based on the weight of its mass, still comprised 2% by weight of Co.
An 80 g sample of this poly-3-hydroxypropionate was washed with 658 g of a 12.5% by weight solution of acetic acid in water (the temperature of the acetic acid solution was 25° C.; it was sucked through the P3HP).
It was subsequently washed with 200 g of water (temperature=25° C.) and then with 200 g of methanol (temperature=25° C.), and the remaining solids were dried at 10 hPa and 25° C. for 10 h.
The cobalt content of the poly-3-hydroxypropionate thus obtained was 0.2% by weight.
The weight-average molecular weight prior to the wash was MW=5930, and after the wash MW=5810.
Analysis of the melting characteristics (this was effected by the method of dynamic differential calorimetry (DSC) on a Q2000 differential calorimeter from TA (Thermal Analysis) Instruments; the amount of sample was 8.2 mg each time and the heating/cooling rate was 20 K/min) gave a melting range of 65.7° C. to 79° C. for the P3HP prior to the wash, and of 65.4° C. to 71.6° C. after the wash.
The elemental analysis of the P3HP (which was effected on the basis of the full combustion of the respective sample with subsequent gas chromatography analysis of the combustion products using a CHN analyzer from Elementar Analysensysteme GmbH of the vario EL cube type, and using an O analyzer from EuroVektor of the EA type) gave (figures in % by weight):
After the wash, the corresponding elemental analysis gave:
Structure and end group analysis by means of MALDI-MS and GPC-MS (as described below) gave the following assignments for the washed P3HP:
Quantitative determinations of the above structures were effected by the 1H NMR method as described below.
The result was that the analyzed sample consisted to an extent of 99% of structure 1. Protons of the vinyl group in structure 2 were visible by their 1H NMR signal. As were the protons of the ethylene glycol end groups. 1H NMR signals of aromatic protons of structure 3 were undetectable.
To determine the end groups present and the structure of the solids removed, these were analyzed both by mass spectrometry with matrix-assisted laser desorption/ionization (MALDI-MS) and by gel permeation chromatography-mass spectrometry (GPC-MS).
For the MALDI-MS analysis, the sample to be analyzed was first dissolved completely in aqueous acetonitrile (50% by volume of water, 50% by volume of acetonitrile) and then applied to a MALDI steel target with 2,5-dihydroxybenzoic acid and sodium trifluoroacetate as matrix substances (both likewise dissolved in aqueous acetonitrile), and the solvent was removed. A nitrogen laser (pulse time 3 ns, wavelength=337 nm) was used to vaporize and ionize the analyte from the steel target in a mixture with the matrix.
The GPC-MS analysis proceeded from an extract of the sample to be analyzed in tetrahydrofuran (THF) (the sample did not dissolve fully in THF), the dissolved constituents of which were separated by means of GPC prior to the MS analysis thereof. The ionization was effected by means of electrospray ionization (ESI).
Quantitative determinations of the above structures were effected by means of 1H NMR spectroscopy on a Bruker DPX 400/1 FT-NMR spectrometer at a 1H carrier frequency of 400 MHZ.
The sample concentration was 5 mg of poly-3-hydroxypropionate dissolved in 1 ml of CDCl3. The width of the excitation pulse was 8012.82 Hz. The sample temperature in the course of recording of the spectra was always 26.8° C. For excitation, a sequence of 30° pulses was used. 32 individual recordings in each case were accumulated to give the resulting spectrum.
1 ml of boron trifluoride etherate (=catalyst; BF3×(CH3—CH2—O—CH2—CH3)2; supplier: Fluka; specification: purum, catalog number: 15719) was dissolved in 300 ml of methylene chloride (=solvent; supplier: BASF SE; specification: purity 98-100%) which had been stored over molecular sieve (3 Å) as a desiccant (n a glass 3-neck flask with capacity 750 ml, magnetic stirring was effected, the internal temperature was 20° C.).
A silicone oil bath was used to bring the solution to boiling (at standard pressure). Subsequently, 24.9 g of β-propiolactone (supplier: Alfa Aesar; specification: 97%, catalog number: B23197, LOT 10140573) were continuously added dropwise to the solution boiling under reflux within 20 min while stirring.
After addition had ended, the reaction mixture was kept under reflux for another 8 h while stirring. During the progressing reaction, the solution changed color from colorless through yellow to orange.
Thereafter, the solvent was removed by distillation while stirring under reduced pressure and at an oil bath temperature of 65° C. within 30 min.
There remained 27.2 g of an orange oil which was cooled to 25° C. and solidified in the manner of a wax at this temperature. To remove the catalyst system, 400 ml of methanol (25° C.) were added, the temperature of the mixture was warmed to 50° C. and the mixture was stirred at this temperature for 1 h and 50 min until the solids had dissolved completely. Then the solution was cooled again to 25° C., and a colorless solid precipitated out.
This was filtered off and the filtercake was washed twice in succession with 10 ml of methanol each time (the temperature of the methanol was 25° C.; the methanol was sucked through the filtercake) and then dried at 25° C. and 10 hPa for 8 h. There remained 12.4 g of a colorless powder. The weight-average relative molecular weight MW thereof was 3000, with a polydispersity Q of 1.4.
The corresponding 1H and 13C NMR spectra and the ATR-FT-IR spectrum corresponded to poly-3-hydroxypropionate having a purity of >95% by weight.
The 1H and 13C NMR spectra were recorded on a Bruker DRX 500 FT-NMR spectrometer on solutions of poly-3-hydroxypropionate in CDCl3. The magnetic field strength corresponded to a 1H carrier frequency of 500 MHz.
The ATR infrared spectra were recorded with a Bruker Vertex 70 spectrometer with ATR (“attenuated total reflection”) and the method of FT-IR spectroscopy. The solid poly-3-hydroxypropionate was analyzed. For this purpose, the samples were additionally dried at 60° C. and 10 hPa for 12 h and then finely pulverized to enable optimal contact with the ATR crystal (in which total reflection proceeded).
B) Thermolytic Splittings of poly-3-hydroxypropionate Prepared in Experiments “A)1. to A)3.”
This experiment simulates an inventive thermolysis from dried bacterial biomass, the bacteria of which have formed poly-3-hydroxypropionate and the cell walls of which have been destroyed, in order to improve access of the splitting catalyst to the poly-3-hydroxypropionate.
The procedure was essentially as in experiment “B)1.a)”. Instead of using only 3 g of poly-3-hydroxypropionate from experiment “A)3.”, however, 3 g of a mixture of 2.4 g of the poly-3-hydroxypropionate from experiment “A)3.” (P3HP) and 0.6 g of dry biomass (mass ratio of “dry biomass: P3HP=1:4”, as is typical according to WO 2011/100608 A1 for P3HP prepared by biotechnological means from glucose in appropriately modified bacteria) were prepared and finely mixed by trituration in a mortar (the biomass comprised autoclaved (15 min at 121° C. and 2. 105 Pa of steam) and freeze-dried bacteria of the E. coli strain JM 109 type). The resulting mixture was used in its entirety as the sample to be split. The remaining procedure was at first as in experiment “B)1.a)”. An internal temperature of approx. 175° C. was established within 10 min, in the course of which the flask contents did not liquefy. Within 30 min, no distillate was obtained in the product flask, and therefore 90.0 mg of pentamethylethylenetriamine were added to the splitting flask. After a further 15 min, again no distillate was obtained, and so the bath temperature was increased. 15 min after attainment of an internal temperature of 185° C., the first distillate was finally collected and, after a total of 120 min at this temperature, the splitting was ended since no further distillate distilled over. Distillate droplets remaining in the distillation system were vaporized by heating with a hot air gun, liquefied in the Liebig condenser and collected in the distillate flask. The amount of condensate present in the product flask was 2.01 g.
The condensate comprised 97.1% by weight of acrylic acid, 2.1% by weight of diacrylic acid (Michael adduct) and 0.5% by weight of higher Michael adducts of acrylic acid onto itself.
Aldehydes were undetectable in the condensate. The condensate did not comprise any pentamethylethylenetriamine. The condensate likewise did not comprise any detectable amounts of constituents that can be traced back to the biomass. In the splitting flask remained 800 mg (26.7% by weight based on the total amount of biomass and poly-3-hydroxypropionate weighed in) of a light brown, tacky residue. If the 600 mg starting weight of biomass is deducted from the calculation, 8.3% by weight based on P3HP therein was still present in the splitting flask).
U.S. Provisional Patent Application No. 61/671,823, filed Jul. 16, 2012, is incorporated into the present application by literature reference. With regard to the abovementioned teachings, numerous changes and deviations from the present invention are possible. It can therefore be assumed that the invention, within the scope of the appended claims, can be performed differently than the way described specifically herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 212 424.1 | Jul 2012 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| 61671823 | Jul 2012 | US |
