Patent Application
20200262778
The present invention relates to a process for the production of allyl alcohol and to a process for converting the allyl alcohol produced into acrylic acid.
Acrylic acid is a chemical for which the worldwide demand is high, about 5 Mt/a (million ton per annum) in 2008 and potentially rising to about 9 Mt/a by 2025. A known route for the production of acrylic acid comprises the oxidation of propene into acrolein (propenal) and then oxidation of the acrolein into acrylic acid. See for example “On the partial oxidation of propane and propene on mixed metal oxide catalysts” by M. M. Bettahar et al. in Applied Catalysis A: General, 145, 1996, p. 1-48. The overall reaction stoichiometry for this route is as follows:
CH2=CHCH3+1.5O2→CH2=CHCOOH+H2O.
A disadvantage of the above-mentioned route for the production of acrylic acid is that two oxygen atoms have to be introduced into the propene by the use of an oxygen containing gas at high temperature (about 350° C.) and with release of a large amount of heat (about 600 kJ/mol). A further disadvantage is that propene has to be used which may be derived from propane. Both propene and propane are currently only readily available from fossil feedstocks and are therefore not renewable.
WO 2011/063363 discloses the conversion of malonate semialdehyde to 3-hydroxypropionic acid (3-HPA) and the subsequent conversion of the 3-HPA to acrylic acid.
WO 2001/16346 describes a process for producing 3-HPA from glycerol by fermentation. The 3-HPA may then be converted into acrylic acid.
EP 2495233 describes a process in which acrylic acid may be derived from biomass-derived lactic acid.
Cristina Della Pina et al., Green Chemistry, 2011, 13(7), 1624 discloses a synthesis of acrylic acid from 3-HPA and several routes to produce 3-HPA, with starting materials including 1,3-propanediol and glycerol.
Zhang, ACS Catalysis, 6(1), 143-150; 2016 discloses a method of oxidizing allyl alcohol to acrylic acid.
In addition to acrylic acid, monoethylene glycol is also a chemical for which the worldwide demand is high, about 20 Mt/a (million ton per annum) in 2008. Monoethylene glycol may be advantageously produced from sugar sources, such as sucrose, glucose, xylose or fructose and the corresponding polysaccharides, cellulose, hemicellulose, starch and inulin. A disadvantage of this route is that in addition to monoethylene glycol, a significant amount of monopropylene glycol is also formed. It may even be the case that two to three times more monopropylene glycol is formed than monoethylene glycol. See for example “Hydrogenolysis Goes Bio: From Carbohydrates and Sugar Alcohols to Platform Chemicals” by Agnieszka M. Ruppert et al. in Angew. Chem. Int. Ed., 2012, 51, p. 2564-2601.
In contrast to acrylic acid and monoethylene glycol, the worldwide demand for monopropylene glycol is not high, about 1.5 Mt/a (million ton per annum) in 2008 and projected to rise only to about 3 Mt/a by 2025. Currently, it is estimated that the worldwide demand for monoethylene glycol is ten times higher than that for monopropylene glycol. Because of this lower demand for monopropylene glycol, processes for converting sugar sources into monoethylene glycol may not be commercialized, unless the selectivity to monoethylene glycol would be drastically increased. Such selectivity increase is difficult to achieve. Consequently, there is currently a need in the art to valorize the monopropylene glycol that is automatically formed when transforming sugar sources into monoethylene glycol. A desired valorization could be an application wherein the monopropylene glycol is converted into a chemical for which the worldwide demand is high.
The above-mentioned monopropylene glycol is just one example of a C3-oxygenate. C3-oxygenates contain 3 carbon atoms and 1 or more oxygen atoms. There are C3-oxygenates other than monopropylene glycol, which may contain 1, 2 or 3 oxygen atoms and which may also be formed as undesired by-products in certain production processes such as biomass conversion processes. Such biomass conversion processes may include the aqueous phase reforming of sugars, as disclosed by N. Li et al. in Journal of Catalysis, 2010, 270, p. 48-59. Examples of such other C3-oxygenates include: 1-propanol, 2-propanol, propanal, acetone, monohydroxyacetone, 2-hydroxypropanal, dihydroxyacetone and 2,3-dihydroxypropanal.
Accordingly, it would be advantageous to valorize C3-oxygenates in general, including for example monopropylene glycol, which may be formed as undesired by-products in certain production processes such as biomass conversion processes.
WO 2014/108415 and WO 2014/108417 describe processes of converting monopropylene glycol to acrylic acid.
WO 2014/108418 describes a process of converting glycerin to acrylic acid. The latter two documents propose the combination of dehydration and oxidation routes, proceeding via the intermediates acrolein or propanal.
Surprisingly, it is found that the above-mentioned C3-oxygenates can be valorized by means of a dehydration process to produce allyl alcohol which may then be converted into acrylic acid. Advantageously, in such way, the C3-oxygenate may be converted via allyl alcohol into acrylic acid, a chemical for which the worldwide demand is high. Further, advantageously, in such way, allyl alcohol and subsequently acrylic acid may be produced from a renewable feedstock since the starting C3-oxygenates may originate from biomass conversion processes. Further advantages of the present invention appear from the detailed description below.
Accordingly, the present invention relates to a process for producing allyl alcohol, the process comprising:
dehydrating a C3-oxygenate comprising 1,2- or 1,3-propanediol;
wherein the dehydration is performed in the presence of a basic catalyst.
The process of the invention may further comprise the step of converting the dehydrated C3-oxygenate comprising allyl alcohol into acrylic acid.
The present invention further relates to a process of producing acrylic acid, the process comprising:
dehydrating a C3-oxygenate comprising 1,2- or 1,3-propanediol in the presence of a basic catalyst to form allyl alcohol; and oxidizing the allyl alcohol to acrylic acid.
One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
The present inventors have surprisingly found that use of a basic catalyst in the dehydration of a C3-oxygenate comprising 1,2- or 1,3-propane diol results in good yields of intermediates, especially allyl alcohol, which may then be converted into acrylic acid. While other intermediates may be formed in addition to allyl alcohol, such as propanal or 1-propanol, it is believed that in the presence of a basic catalyst, rapid isomerisation of allyl alcohol to propanal is suppressed.
The dehydrated C3-oxygenate, notably allyl alcohol, together with other intermediates such as propanal or 1-propanol, is preferably subsequently converted by oxidation into acrylic acid. Suppression of isomerisation is helpful in reducing by-products in the conversion.
The overall process, including the optional conversion to acrylic acid, is illustrated in the following general reaction scheme wherein the starting material for the last step of the process is a C3-allyl alcohol:
In the process of the invention, the starting material is a C3-oxygenate. Within the present specification, a C3-oxygenate means a compound which contains 3 carbon atoms and 2 oxygen atoms. The other atoms in such a C3-oxygenate are hydrogen atoms.
Thus the C3-oxygenates containing 2 oxygen atoms which may suitably be used in the present invention are monopropylene glycol (1,2-propanediol) and 1,3-propanediol.
Surprisingly, with the process of the present invention the above-mentioned disadvantages are avoided, while at the same time, advantageously, by means of the present invention C3-oxygenates, such as monopropylene glycol which may be formed as undesired by-products in certain production processes such as biomass conversion processes, may be valorized by transforming them into allyl alcohol which is then available for further conversion into a chemical for which the worldwide demand is indeed high, namely acrylic acid. Thus, in the process according to the invention, the C3-oxygenate preferably comprises a fraction obtained as a by-product in a biomass conversion process for production of monoethylene glycol. The biomass may typically comprise a sugar source.
The basic catalyst used in the process of the present invention preferably comprises an element with an electronegativity of less than 2.0, more preferably less than 1.5 and most preferably less than 1.0 (values based on Allred-Rochow scale).
Advantageously, the catalyst may comprise an element selected from Group 1 and/or Group 2 of the Periodic Table, with Na, K, Rb, Cs, Mg, Ca, Sr and Ba being preferred, especially K.
The basic catalyst may comprise a metal oxide or metal hydroxide. Preferably the metal oxide MOx, or the corresponding metal oxide where the catalyst is a metal hydroxide, has an electronegativity EN(MOx) of less than 2.5, less than 2.2, less than 2.0, less than 1.8, less than 1.6 or less than 1.4 (based on Allred-Rochow electronegativity of M EN(M) and O EN(O) and equation (1) below:
EN(MOx)=(EN(M)0.5+x EN(O)0.5)/(1/EN(M)0.5+x/EN(O)0.5) (1)
A preferred catalyst is KOH.
The basic catalyst component may be present in pure form, or may be supported on a carrier. Suitable carriers include C, SiO2, Al2O3, ZrO2, TiO2, and other oxides and mixtures, or part of a compound (e.g. as mixed oxide).
A catalyst comprising K/ZrO2, especially KOH/ZrO2, is particularly preferred. More preferably, the KOH loading on the carrier may be greater than or equal to 0.5, 1, 3, 5 wt % and less than or equal to 30, 20, 15, 10, and preferably is from 5 to 15 wt %.
In the process of the invention, the C3-oxygenates are preferably diluted in water. Thus the use of an aqueous monopropylene glycol and aqueous 1,3-propanediol feed is advantageous, or water may be supplied separately to the reaction along with the C3-oxygenate feed. The C3-oxygenate feed may comprise a fraction, preferably an aqueous fraction, from a biomass conversion process.
Preferably the monopropylene glycol or 1,3-propanediol is diluted in water at a concentration of greater than 10, 20, 30, 40 or up to 50% v/v and at a concentration of less than 100, 90, 80, 70, 60 or 50% v/v.
The dehydration step is preferably carried out a temperature of from 325° C. to 450° C., more preferably from 350° C. to 420° C., and most preferably from 380° C. to 410° C.
The dehydration step may take place in a dehydration reactor and the reaction products therefrom may subsequently be fed to a separation unit, e.g. a distillation column, for extraction.
Allyl alcohol produced in the dehydration step may be extracted as a top stream along with water and any other oxygenates such as propanal and propanol. Preferably, allyl alcohol and water are extracted together, for example as a middle fraction. Having respective boiling points of 97° C. and 100° C., and potentially forming an azeotropic mixture, it is both economically and technically advantageous to recover allyl alcohol and water together rather than separating allyl alcohol from water prior to undertaking any oxidation to produce acrylic acid.
1-propanol which may also be formed during dehydration has a boiling point of 98° C. and may also be extracted from the distillation column together with the allyl alcohol/water mixture. Thus a combined feed of allyl alcohol, water and 1-propanol derived from the dehydration process, such as obtained as a middle fraction therefrom, may be introduced into an oxidation reactor.
Other dehydration products having lower boiling points than the “close boilers” of allyl alcohol, water and 1-propanol, such as propanal (boiling point of 48° C.), may be separated by distillation as a top fraction.
Any unconverted glycol is preferably recycled. For example, unconverted glycol may be removed, along with the least volatile (or heavy) components such as 2-ethyl-4-methyl-1,3-dioxolane, the ketal product of MPG and propanal, as a bottom fraction from the distillation column and then recycled to the dehydration reactor.
By not isolating the allyl alcohol from its close boilers, the distillation resistance of the dehydration “effluent” may be drastically reduced. Distillation resistance provides a useful means for determining whether the work up of a product mixture by distillation is economically viable and the concept thereof is discussed in J. P-Lange, ChemSusChem 2017, 10, 245-252.
Distillation resistance Ωprod is based on the mass ratio of each component i over the target product fi/fprod and on the temperature gap ΔTi [° C.] between their atmospheric boiling point and that of the next heavier component as per equation (2) below. Non-condensable products and the bottom stream are omitted from this calculation as these products do not need to undergo evaporation+condensation.
Ωprod[1/° C.]=100*Σ(fi/fprod)/ΔTi (2)
It may be seen that the product of the dehydration step includes three close-boilers, namely allyl alcohol (97° C.), 1-propanol (98° C.) and water (100° C.). Their small ΔTi makes distillative separation challenging, as confirmed by Ωprod˜130 (Table 1).
By recovering these close boiler components as a mixture so that they may be fed unseparated to the oxidation step, then the distillation resistance falls to 9.4 (Table 2).
It will be understood that a significant factor in the quantum of distillation resistance when allyl alcohol is separated derives from the need to evaporate 6 t of water per t of allyl alcohol (based on 50% MPG in water). Further efficiencies in the process may be obtained by either reducing the water dilution of the feed or by reaching higher yield per pass (assumed here at 30 mol %) or both.
Allyl alcohol produced by dehydration as per the above process may then be fed, preferably together with the water, with air or oxygen into an oxidation reactor to be converted to acrylic acid.
The oxidation step may be carried out at a temperature of from 250° C. to 450° C., preferably from 300° C. to 400° C., more preferably from 310° C. to 380° C., and most preferably from 315° C. to 360° C.
Acrylic acid may be suitably recovered from the oxidation reactor effluent, preferably extracted by means of absorption or reactive condensation.
When compared to other acrylic acid production routes using renewable feedstocks, the present process has a relatively high route efficiency.
In the present process, acrylic acid can be made from C3-oxygenates obtained from a renewable feedstock. That is, the present process provides a commercially useful means for obtaining acrylic acid other than from propene that would normally originate from a non-renewable, fossil feedstock. While acrylic acid could also be made from propene produced from a renewable feedstock, for example using propene produced from a sugar source (which is a renewable feedstock), after which the propene is oxidized into acrylic acid using conventional technologies as already discussed above, such an alternative route is less viable in terms of mass efficiency, carbon efficiency and/or fossil CO2 intensity (or fossil CO2 footprint).
Advantageously, the allyl alcohol feed comprises a fraction extracted from the dehydration process as hereinbefore described, which fraction may also comprise water and optionally 1-propanol.
The oxidation process itself results in a product mixture comprising close boilers, similar to the dehydration process. In the oxidation process, the close boilers comprise residual allyl alcohol and water (97° C. and 100° C. respectively), and also acrylic acid and propanoic acid (both 141° C.). The product mixture may be separated in a distillation column and acrylic acid extracted therefrom.
In order to reduce distillation resistance and thereby improve efficiency of the oxidation process, close boilers are preferably extracted together rather than undergo separation. Thus, unreacted allyl alcohol and water may be extracted together for subsequent recycling to the dehydration reactor. The product mixture from the oxidation reaction may further include acetic acid and this is also preferably extracted with the water/allyl alcohol for recycling to the dehydration reactor.
The distillation resistance is further reduced by extracting crude acrylic acid (that is acrylic acid together with propanoic acid) from the distillation column. If desired, the crude acrylic acid may subsequently be purified by isolating from any propanoic acid, for example, by known crystallisation methods.
As may be understood from Tables 3 and 4 below, the distillation resistance of the oxidation effluent is effectively reduced by about 50% when allyl alcohol and water are not extracted individually, but extracted together. Since dehydration of C3-oxygenates preferably takes place in an aqueous environment, it is efficient to recycle the allyl alcohol/water together from the oxidation effluent back into the dehydration process.
Aqueous monopropylene glycol (50% in water) was dehydrated in the presence of a catalyst.
The catalyst was made from commercial monoclinic ZrO2 (BET of 84 m2/g) obtained from Gimex Technische keramiek b.v. and KOH grains obtained from Sigma Aldrich. The catalysts with different weight percentages (0.1-10 wt %) of KOH were made by impregnation method. The required amount of KOH granules were diluted in approximately 20 mL of water and stirred by magnetic stirrer at a frequency of 450-500 rpm.
After dissolving, the required amount of ZrO2 is added and stirring continued for 4-6 hours with the same stirring speed as mentioned above. For every catalyst solution, after 2 hours stirring, the temperature was raise to 100° C. to ease water evaporation. The resulting wet paste was dried in a vacuum oven overnight at 100° C. The catalysts were designated as, for example, 10KZrO2 in which the numeral indicates the weight percentage of KOH on ZrO2.
The catalytic tests were performed on a laboratory scale by using fixed-bed down flow quartz reactor (400 mm long, 4 mm id. and 6 mm od,) suspended in an electrical furnace. The catalyst with a particle size between 0.425-0.6 mm, mixed with silica beads of similar amount and size, is placed in the reactor, sandwiched between quartz wool. The liquid feed, monopropylene glycol (MPG, obtained from Sigma Aldrich) with required flow rates were pumped into the preheater maintained at 225° C. (above the boiling point of MPG, 188° C.), along with the carrier gas, preferably Ar or N2, with a certain flow rate, before sending onto the catalyst bed.
The products were condensed using a cold trap placed at the bottom of the reactor and cooled to 10° C. Uncondensed vapours and the gases are sent into the gas chromatograph that is connected online. The liquid products of the reaction were quantified using high pressure liquid chromatography and the gaseous products were quantified by gas chromatography. All possible products were calibrated before being quantified.
Results showed production of allyl alcohol with a 47% yield and a conversion of 78%.
Allyl alcohol was oxidised to acrylic acid using a MoWVOx mixed oxide catalyst. A general reaction scheme is provided below.
The catalyst was prepared as described in the literature [1]. Ammonium heptamolybdate (99%), and ammonium metatungstate (99%) were purchased from Alfa Aesar. Ammonium monovanadate was purchased from Merck. Typically, 2.6 g of ammonium monovanadate, 14.7 g of ammonium heptamolybdate and 2.7 g of ammonium metatungstate were dissolved in deionised water and then evaporated to dryness. This mixture was then calcined at 275° C. for 4 h and 325° C. for 4 h in air and N2 respectively. Then the powder sample was crushed and sieved to make a particle size between 0.425-0.6 mm. The obtained catalyst is designated as MoWVOx. BET surface area is 12.5 m2/g based on XRD analysis.
The catalytic tests were performed on a laboratory scale by using a fixed-bed down flow quartz reactor (400 mm long, 4 mm id. and 6 mm od,) suspended in an electrical furnace. The catalyst was mixed with silica beads of similar amount and size, and placed in the reactor, sandwiched between quartz wool.
The liquid feed, aqueous solutions of allyl alcohol (AA, Sigma Aldrich), propionaldehyde (PAL, Sigma Aldrich), 1-propanol (POL, Merck) and monopropylene glycol (MPG, Sigma Aldrich) with required flow rates were pumped into the preheater maintained at 150° C. (in case of AA, PAL, POL) and 225° C. (for MPG) along with the carrier gas, preferably Ar or N2, with a certain flow rate.
Pure oxygen is used as the oxidant and is connected to the feed stream after the stream is vaporised in the preheater and then the combination feed is allowed on to the catalyst bed. In a typical run, the reaction feed molar ratio of allyl alcohol:H2O:argon:O2 was 1:7.5:18.8:2.1.
The products were condensed using a cold trap placed at the bottom of the reactor and cooled to 5-10° C. Uncondensed vapours and the gases are sent into the gas chromatograph that is connected online. The liquid products of the reaction were quantified using high pressure liquid chromatography and the gaseous products were quantified by gas chromatography. All possible products were calibrated before being quantified.
The MoWVOx mixed oxide catalyst was tested for the oxidation of aqueous solution of allyl alcohol (30 vol %) at various reaction conditions, such as temperature and contact times.
Each reaction comprised two runs of 6-8 hours, each using a fresh catalyst: one from 340° C. to 280° C. and the other from 340° C. to 400° C. and back to 340° C.
Various process parameters were altered to determine their effect and to assist in optimising process conditions. The results are discussed in relation to the Figures, as follows:
Referring to
The results shown in
Referring to
The results shown in
Referring to
Accordingly, it will be appreciated that a balance of the reaction temperature and catalyst loading is required to optimise production of desired compounds, whilst avoiding increasing the formation of undesirable compounds.
Referring to
Referring to
By using optimised reaction conditions, the production of acrolein, proprionic acid, acetic acid, CO2 and various ‘unknown’ other compounds is kept low. It is particularly beneficial to limit the production of such ‘unknown’ (often heavy) products, as they can lead to deactivation of the catalyst.
Referring to
It can be seen from
Further comparisons are provided in Table 1 below, illustrating the effectiveness in terms of yield of using a highly basic catalyst, and the further benefits achieved when the dehydration step is carried out with such a highly basic catalyst in conjunction with using aqueous monopropylene glycol.
As can be seen from Table 1 above, the present inventors have been able to produce far higher yields of allyl alcohol from monopropylene glycol than in the prior art (references [1] to [4]). In this regard, the present inventors have been able successfully to shift the selectivity to allyl alcohol rather than other products, for example propanal.
In particular, use of a preferred KOH/ZrO2 catalyst gives higher yields of allyl alcohol (11 mol %) compared to what is known in literature, and when diluted with water further improved yields (47 mol %) may be achieved.
It is believed that the presence of a highly basic catalyst, such as K catalyst, and water suppresses (i) transfer hydrogenation and (ii) formation of oligomers leading to the benefits hereinbefore described.
As shown in
Referring to
In the process scheme of
The dehydration step (2) is preferably performed at a moderate conversion per pass, so as to limit the formation of heavy by-products. Such by-products are preferably removed before the oxidation step.
The acrylic acid (7) is recovered preferably without condensing the water (6), for example using absorption or reactive condensation.
Referring to
In the process scheme of
| Number | Date | Country | Kind |
|---|---|---|---|
| 16190861.1 | Sep 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/060108 | 4/27/2017 | WO | 00 |
