Patent Application
20100093932
The present invention is directed to a process for the continuous hydrogenation of carbon-carbon double bonds in an unsaturated polymer to produce a hydrogenated polymer, said unsaturated polymer being based on a conjugated to diolefin and at least one other copolymerizable monomer, in the presence of a solvent and a catalyst, preferably a homogeneous catalyst.
Chemical reactions can be conducted in batch mode, continuous mode or semi batch mode operations. Hydrogenation of diene based polymers using a catalyst is usually realized by a semi batch process up until now.
U.S. Pat. No. 5,561,197 and U.S. Pat. No. 5,258,467 teach the production of hydrogenated polymers using organo-metallic catalysts in a semi batch mode.
Yet, most often, continuous processes are more advantageous in terms of operation, maintenance, production and cost. In general, the most common types of reactors used in a continuous process are continuous stirred tank reactors and tubular reactors. For heterogeneous hydrogenation reaction systems (where the catalyst used is in solid phase while the unsaturated polymer is in liquid phase), fluidized bed reactors, bubble columns and slurry reactors are typically used. For example, a fixed bed heterogeneous hydrogenation catalyst is used to hydrogenate low molecular weight polydienes which may contain functional groups such as hydroxyls (U.S. Pat. No. 5,378,767).
Sometimes, depending on the throughput of the process, more than one reactor is used; U.S. Pat. No. 6,080,372 discusses such an application where a three phase slurry hydrogenation of glucose is conducted in a series of continuous stirred tank reactors and bubble columns.
Static mixer reactors are receiving attention because of their low energy requirement. U.S. Pat. No. 6,593,436 discloses how a static mixing plug flow reactor is used for manufacture of silicone copolymers. It also discloses the various general factors such as 1) rate of flow of the liquid mixture; 2) length of mixer element; 3) relative miscibility of reactants and 4) intensity of shear impacted by the static mixer element design and configuration that are considered in choosing a particular internal geometry of the static mixer reactor especially for processing high viscous polymers. They developed a process where at least two or more static mixers in series or parallel are used to produce the silicone copolymer. The advantage with this kind of alignment of reactors is that very high viscous copolymers can be produced at lower shear forces and lower energy inputs. Also, the process they studied consists of single phase reactants.
U.S. Pat. No. 4,629,767 discusses a process for hydrogenation of diene polymers with a heterogeneous catalyst. They used an up-flow fixed bed reactor in their invention. The disadvantage with this type of reactor is that the heat transfer will not be efficient as some hot spots can occur in the fixed bed and also the pressure drop occurring in this type of reactor is very high compared to a static mixer reactor.
U.S. Pat. No. 6,037,445 reveals a continuous process for functionalizing polymers where a liquid comprising the polymer and the gas having the functionalizing agent are introduced continuously at a dispersing zone and the dispersion zone being a static mixer of type Sulzer SMX® or SMXL® from Koch engineering or Kenics® helical mixers from Chemineer Inc. Their invention gives the details of the continuous process especially for carbonylation or manufacture of ester functionalized ethylene-butene-1 polymers.
U.S. Pat. No. 7,057,064 involves a continuous process for enantioselective catalytic hydrogenation of beta-ketoesters, where a static mixer with several in-line mixers is used to enhance the mass transfer (absorption) of hydrogen into the solution. The process proposed by them is used to target non-polymer hydrogenation at very low mean residence time (in the order of 15 to 30 minutes).
In all the above documents, the static mixers are predominantly used for either creating high mass transfer (as they create high interfacial area) or as dispersers where uniform bubble size is needed. Also, in the above cited inventions, static mixers are rarely used as an one pass reactor operated with high mean residence times.
It was an objective of the present invention to provide a process for the hydrogenation of carbon-carbon double bonds in unsaturated polymers, wherein a high degree of hydrogenation can be achieved in a continuous process, with to the benefit of low costs for both equipment and energy.
This objective is solved by a process for the continuous hydrogenation of carbon-carbon double bonds in an unsaturated polymer based on a conjugated diolefin and at least one other copolymerizable monomer to produce a hydrogenated polymer, in the presence of a solvent and a catalyst, wherein said unsaturated polymer, said catalyst and hydrogen are passed through a reactor equipped with static internal elements.
In a preferred embodiment the unsaturated polymer, the catalyst and hydrogen are passed through a reactor equipped with static internal elements, having an open blade geometry.
It has been found that static internal elements have a strong impact on the reactor's capability of creating eddies and vortices of sufficient intensity within the working fluids comprising diene polymers which are highly viscous and ensure a good performance of hydrogenation.
The internal elements preferably have an open blade geometry.
The hydrogenation reaction is highly exothermic, especially at the very beginning of reaction, and accordingly, temperature control is of very high importance, especially when highly efficient catalysts are used, especially organo-metallic catalysts, preferably rhodium, ruthenium, osmium or iridium metal complex catalysts.
The polymers which are hydrogenated according to the present continuous process are polymers which contain carbon-carbon double bonds and which are based on a conjugated diolefin and at least one other copolymerizable monomer.
The conjugated diolefin is preferably one or more substances selected from butadiene, isoprene, piperylene and 2,3-dimethylbutadiene, more preferably butadiene and/or isoprene, and most preferably butadiene.
At least one other copolymerizable monomer is preferably one or more substances selected from acrylonitrile, propyl acrylate, butyl acrylate, propyl methacrylate, methacrylonitrile, butyl methacrylate and styrene, and most preferably acrylonitrile and styrene.
Further examples of suitable monomers are esters of ethylenically unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid with generally C1-C12 alkanols, such as methanol, ethanol, n-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, tert.-butanol, n-hexanol, 2-ethylhexanol, or C5-C10 cycloalkanols, such as cyclopentanol or cyclohexanol, and of these preferably the esters of acrylic and/or methacrylic acid, examples being methyl methacrylate, n-butyl methacrylate, ter-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate and tert butyl acrylate.
The hydrogenation of the polymer is undertaken in solution. Preferred solvents for the polymer and the hydrogenation process include benzene, toluene, xylene, monochlorobenzene and tetrahydrofuran, with monochlorobenzene and tetrahyrodofuran being more preferred and monochlorobenzene being most preferred. The concentration of the unsaturated polymer in the solvent may be from about 1 to about 40 wt.-%, preferably from about 2 to about 20 wt.-%.
The hydrogenation is undertaken in the presence of a homogeneous or heterogeneous catalyst, which preferably is an organo-metallic catalyst, most preferred a rhodium, ruthenium, titanium, osmium, palladium, platinum, cobalt, nickel or iridium either as metal or preferably in the form of metal compounds (cf., for example, U.S. Pat. No. 3,700,637, DE-A-25 39 132, EP-A-0 134 023, DE-A-35 41 689, DE-A-35 40 918, EP-A-0 298 386, DE-A-35 29 252, DE-A-34 33 392, U.S. Pat. No. 4,464,515 and U.S. Pat. No. 4,503,196).
Preferred metals for the heterogeneous catalyst are one or more metals selected from platinum, palladium, nickel, copper, rhodium and ruthenium. The heterogeneous catalyst can be preferably supported on carbon, silica, calcium carbonate or barium sulphate.
Preferably, the catalyst is a homogeneous catalyst.
Specially suited are osmium catalysts having the formula
OsQX(CO)(L)(PR3)2
in which Q may be one of hydrogen and a phenylvinyl group, X may be one of halogen, tetrahydroborate and alkyl- or aryl-carboxylate, L may be one of an oxygen molecule, benzonitrile or no ligand, and R may be one of cyclohexyl, isopropyl, secondary butyl and tertiary butyl said tertiary butyl being present only when one R is methyl, with the proviso that when Q is phenylvinyl X is halogen and L is no ligand and when X is alkyl- or aryl-carboxylate Q is hydrogen and L is no ligand, said halogen being selected from chlorine and bromine. Preferably, Q is hydrogen, X is selected from chlorine, tetrahydroborate and acetate, L is an oxygen molecule or no ligand and R is cyclohexyl or isopropyl. Additional alkyl- or aryl-carboxylates include chloroacetate and benzoate.
Examples of suitable osmium catalysts include OsHCl(CO)[P(cyclohexyl)3]2, OsHCl(CO)[P(isopropyl)3]2, OsHCl(O2)(CO)[P(cyclohexyl)3]2, OsHCl(O2)(CO)[P(isopropyl)3]2, Os(CH═CH—C6H5)Cl(CO)[P(cyclohexyl)3]2, Os(CH═CH—C6H5)Cl(CO)[P(isopropyl)3]2, OsH(BH4)(CO)[P(cyclohexyl)3]2, OsH(BH4)(CO)[P(isopropyl)3]2, OsH(CH3COO)(CO)[P(cyclohexyl)3]2, OsH(CH3COO)(CO)[P(isopropyl)3]2, OsHCl(CO)(C6H5CN) [P(cyclohexyl)3]2, and OsHCl(CO)(C6H5CN) [P(isopropyl)3]2. Preferred catalysts are OsHCl (CO) [P(cyclohexyl)3]2, OsHCl(CO)[P(isopropyl)3]2, OsHCl(O2)(CO)[P(cyclohexyl)3]2 and OsHCl (O2)(CO)P(isopropyl)3]2.
The quantity of the osmium catalyst required for the hydrogenation process is from about 0.01 to about 1.0 wt.-% based on the polymer and preferably from about 0.02 to about 0.2 wt.-% based on the polymer.
The selective hydrogenation also can be achieved, for example, in the presence of a rhodium- or ruthenium-containing catalyst. It is possible to use, for example, a catalyst of the general formula
(R1mB)lMXn,
where M is ruthenium or rhodium, R1 are identical or different and are each a C1-C8-alkyl group, a C4-C8-cycloalkyl group, a C6-C15-aryl group or a C7-C15-aralkyl group. B is phosphorus, arsenic, sulphur or a sulphoxide group S═O, X is hydrogen or an anion, preferably halogen and particularly preferably chlorine or bromine, l is 2, 3 or 4, m is 2 or 3 and n is 1, 2 or 3, preferably 1 or 3. Preferred catalysts are tris(triphenylphosphine)rhodium(I) chloride, tris(triphenylphosphine)rhodium(III) trichloride and tris(dimethyl sulphoxide)rhodium(III) trichloride and also tetrakis(triphenylphosphine)rhodium hydride of the formula (C6H5)3P)4RhH and the corresponding compounds in which the triphenylphosphine has been completely or partly replaced by tricyclohexylphosphine. The catalyst can be utilized in small amounts. An amount in the range 0.01-1% by weight, preferably in the range 0.03-0.5% by weight and particularly preferably in the range 0.1-0.3% by weight, based on the weight of the polymer, is suitable.
In one embodiment of the present invention the catalyst can be used with a co-catalyst. Preferably this co-catalyst is a ligand of formula RmB, where R, m and B are as defined above, and m is preferably 3. Preferably B is phosphorus, and the R groups can be the same or different. The R group of the catalyst may be a triaryl, trialkyl, tricycloalkyl, diaryl monoalkyl, dialkyl monoaryl, diaryl monocycloalkyl, dialkyl monocycloalkyl, dicycloalkyl monoaryl or dicycloalkyl monoaryl. Examples of suitable co-catalyst ligands are given in U.S. Pat. No. 4,631,315, the disclosure of which is incorporated by reference. The preferred co-catalyst ligand is triphenylphosphine. The co-catalyst ligand is preferably used in an amount in the range 0 to 5000%, more preferably 500 to 3000% by weight, based on the weight of catalyst. Preferably also the weight ratio of the co-catalyst to the rhodium-containing catalyst compound is in the range 0 to 50, to more preferably in the range 5 to 30.
The catalyst may be introduced into one or more different chambers of the multistage reactor.
The hydrogenation is carried out at a temperature in the range of from 100° C. to 260° C., preferably in the range of from 100° C. to 180° C. and a hydrogen pressure in the range of from 0.1 to about 50 MPa, preferably in the range of from 0.7 MPa to 50 MPa and more preferably in the range of from 3.5 to 10.5 MPa. Preferably, the temperature at the inlet of the reactor equipped with static internal elements is in the range of from 100 to 180° C. and the hydrogen pressure is from 2 MPa to 15 MPa.
The present invention relates especially to the hydrogenation of nitrile rubber.
The term nitrile rubber, also referred to as “NBR” for short, refers to rubbers which are copolymers or terpolymers of at least one α,β-unsaturated nitrile, at least one conjugated diene and, if desired, one or more further copolymerizable monomers.
The conjugated diene can be of any nature. Preference is given to using (C4-C6) conjugated dienes. Particular preference is given to 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, piperylene or mixtures thereof. Very particular preference is given to 1,3-butadiene and isoprene or mixtures thereof. Special preference is given to 1,3-butadiene.
As α,β-unsaturated nitrile, it is possible to use any known α,β-unsaturated nitrile, preferably a (C3-C5) α,β-unsaturated nitrile such as acrylonitrile, methacrylonitrile, ethacrylonitrile or mixtures thereof. Particular preference is given to acrylonitrile.
A particularly preferred nitrile rubber is thus a copolymer of acrylonitrile and 1,3-butadiene.
Apart from the conjugated diene and the α,β-unsaturated nitrile, it is possible to use one or more further copolymerizable monomers known to those skilled in the art, e.g. α,β-unsaturated monocarboxylic or dicarboxylic acids, their esters or amides. As α,β-unsaturated monocarboxylic or dicarboxylic acids, preference is given to fumaric acid, maleic acid, acrylic acid and methacrylic acid. As esters of α,β-unsaturated carboxylic acids, preference is given to using their alkyl esters and alkoxyalkyl esters. Particularly preferred alkyl esters of α,β-unsaturated carboxylic acids are methyl acrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and octyl acrylate. Particularly preferred alkoxyalkyl esters of α,β-unsaturated carboxylic acids are methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate and methoxyethyl (meth)acrylate. It is also possible to use mixtures of alkyl esters, e.g. those mentioned above, with alkoxyalkyl esters, e.g. in the form of those mentioned above.
The proportions of conjugated diene and α,β-unsaturated nitrile in the NBR polymers to be used can vary within wide ranges. The proportion of or of the sum of the conjugated dienes is usually in the range from 40 to 90% by weight, preferably in the range from 55 to 75% by weight, based on the total polymer. The proportion of or of the sum of the α,β-unsaturated nitriles is usually from 10 to 60% by weight, preferably from 25 to 45% by weight, based on the total polymer. The proportions of the monomers in each case add up to 100% by weight. The additional monomers can be present in amounts of from 0 to 40% by weight, preferably from 0.1 to 40% by weight, particularly preferably from 1 to 30% by weight, based on the total polymer. In this case, corresponding proportions of the conjugated diene or dienes and/or of the α,β-unsaturated nitrile or nitriles are replaced by the proportions of the additional monomers, with the proportions of all monomers in each case adding up to 100% by weight.
The preparation of nitrile rubbers by polymerization of the abovementioned monomers is adequately known to those skilled in the art and is comprehensively described in the polymer literature.
Nitrile rubbers which can be used for the purposes of the invention are also commercially available, e.g. as products from the product range of the trade names Perbunan® and Krynac® from Lanxess Deutschland GmbH.
The nitrile rubbers used for the hydrogenation have a Mooney viscosity (ML 1+4 to at 100° C.) in the range from 30 to 70, preferably from 30 to 50. This corresponds to a weight average molecular weight Mw in the range 200 000-500 000, preferably in the range 200 000-400 000. The nitrile rubbers used also have a polydispersity PDI=Mw/Mn, where Mw is the weight average molecular weight and Mn is the number average molecular weight, in the range 2.0-6.0 and preferably in the range 2.0-4.0.
Hydrogenated nitrile rubber, also referred to as “HNBR” for short, is produced by hydrogenation of nitrite rubber. Accordingly, the C═C double bonds of the copolymerized diene units have been completely or partly hydrogenated in HNBR. The degree of hydrogenation of the copolymerized diene units is usually in the range from 50 to 100%.
Hydrogenated nitrite rubber is a specialty rubber which has very good heat resistance, excellent resistance to ozone and chemicals and also excellent oil resistance.
The above mentioned physical and chemical properties of HNBR are associated with very good mechanical properties, in particular, a high abrasion resistance. For this reason, HNBR has found wide use in a variety of applications. HNBR is used, for example, for seals, hoses, belts and clamping elements in the automobile sector, and also for stators, oil well seals and valve seals in the field of oil extraction and also for numerous parts in the aircraft industry, the electronics industry, mechanical engineering and shipbuilding.
Commercially available HNBR grades usually have a Mooney viscosity (ML 1+4 at 100° C.) in the range from 35 to 105, which corresponds to a weight average molecular weight Mw (method of determination: gel permeation chromatography (GPC) against polystyrene equivalents) in the range from about 100 000 to 500 000. The polydispersity index PDI (PDI=MW/Mn, where Mw is the weight average molecular weight and Mn is the number average molecular weight), which gives information about the width of the molecular weight distribution, measured here is in the range of 2.5 to 4.5. The residual double bond content is usually in the range from 1 to 18%.
The degree of hydrogenation depends on the polymer concentration, the amount to of catalyst used, the gas and liquid flow rates and process conditions. The desired hydrogenation degree is from about 80 to about 99.5%, preferably from about 90 to about 99%.
The hydrogenation degree can be determined by using Fourier Transform Infrared (FTIR) or Proton Nuclear Magnetic Resonance (NMR) techniques. According to the present invention, the disposition of the static mixer reactor can be vertical, horizontal or at any angle, or in coil shape, preferably vertical. The ratio of the length and the diameter could be from 1 up to any reasonable ratio; however, depending on the scale, usually it is preferably from 10 to 100.
It is required that the reactor be equipped with a heating and cooling system, preferably to be equipped with a jacket for heating and/or cooling fluids, the jacket having preferably two or more chambers which can be operated independently from each other. However, it is most preferably for the purpose of reducing cost and increasing productivity to locate the reactors in parallel as pipe heat exchangers which can significantly facilitate the design of the heating/cooling system. Similarly in such a way, the shell could be divided in zones to facilitate the temperature control.
The static internal element's structure could be of various forms which could provide efficient lateral mixing and minimize the backflow and shortcut. In the present invention, a reactor is used which is equipped with static internal elements typically having an open blade geometry. Such blade structures can be some commercially available elements such as Sulzer SMX® or SMXL® or SMXL-R®, or SMF® or SMV® of Koch Engineering or Kenics® KMX of Chemineer Inc., or Kenics® helical elements. These elements have a geometry that can enhance radial mixing and reduce axial dispersion. The number of the elements equipped could be 2 to 100, preferably 6-36, and most preferably 6-24. The elements could be solid or hollow so that heating/cooling medium can flow through to facilitate the temperature control. Preferably, when the reactor diameter is less than 0.1 m, solid elements are used and when the reactor diameter is larger than 0.5 m, hollow elements are used. The advantage of using hollow elements is that each local temperature can be accurately controlled.
According to the present invention, the static mixer reactor can be equipped with or without a pre-mixer before the static mixer reactor.
In a preferred embodiment, a pre-mixer is used and the unsaturated polymer, the solvent and hydrogen are passed via a pre-mixer before sending to the reactor equipped with static internal elements.
The pre-mixer is preferably a cylinder tank equipped with an agitator having superior mixing performance. The cylinder tank could be disposed vertically or horizontally. The volume of the pre-mixer is preferably between 1% and 100% of the volume of the reactor, depending on the scale of the reactor. For example, when the volume in the scale is larger than 100 L the volume ratio of the pre-mixer and the reactor is preferably less than 20%, and further preferably less than 10%. The ratio of the length and the diameter is preferably from 0.5 to 3.0, more preferably from 0.5 to 1.0 when the pre-mixer is disposed vertically and from 1.0-3.0 when the pre-mixer is horizontally disposed. The pre-mixer can have one or multi-agitators, depending on the volume of the pre-mixer and also the way of the pre-mixer disposition (vertical or horizontal). Preferably, the agitator(s) in the pre-mixer is a high-shear type of agitator, such as a pitched blade agitator or turbines when the pre-mixer is disposed vertically, and turbines or deformed discs when the pre-mixer is horizontally disposed. A deformed disc here is such a disc impeller which is formed by scissor-cutting 12 or 16 lines evenly from the edge toward the center of the disc and the length of the lines is ⅓ to ⅖ of the diameter of the disc and by then twisting each such formed petal by a 30-60 degree in opposite directions for the adjacent petals. The ratio of the agitator diameter and the inner diameter of the pre-mixer is preferably ⅓- 19/20, depending on the viscosity and the disposition of the pre-mixer. Preferably, for example, when the viscosity is less than 200 cp (0.2 Pas) and the pre-mixer is vertically disposed, the diameter ratio is from ⅓ to ⅔, and when the viscosity is less than 200 cp (0.2 Pas) and the pre-mixer is horizontally disposed, the diameter ratio is larger than ⅔.
The catalyst can be added to both the pre-mixer and/or to the reactor equipped with static internal elements. It is possible to add the catalyst to the reactor equipped with static internal elements at one or more different sections along the length thereof.
The reactor of this invention is preferably operated in such a way that the unsaturated polymer solution, the catalyst and hydrogen are pumped vertically from bottom to top of the reactor equipped with static internal elements.
Hydrogen can be introduced into the reaction system from the pre-mixer or the static mixer reactor via a gas sparger, in order to ensure uniform distribution thereof, or from both the pre-mixer and the static mixer reactor.
In another embodiment of the invention, the reactor equipped with static internal elements and the pre-mixer is operated in a loop mode.
The product mixture obtained in the reactor is preferably cooled in a heat exchanger and the product mixture cooled from the heat exchanger is preferably sent to a gas/liquid separator.
The invention is described in the following by way of drawings and of examples.
The drawing in
a further configuration being shown in
a still further configuration in
a Kenics®-KMX element preferably used in the reactor in
a preferred embodiment of the reactor equipped with static internal elements in
Since the hydrogenation reaction is highly exothermic, for higher concentrations of polymer solution, it is very difficult to control the reaction temperature along the length of the static mixer reactor. The configuration shown in
The static internal elements in the reactor are arranged such that each element would be at a 90° angle with its neighboring element. The aspect ratio (length to diameter ratio of the static internal element) is preferably from 0.5 to 3, further preferably from 0.5 to 1.5.
The detail of the structure is shown in
The length and diameter of the reactor equipped with static internal elements is designed and configured such that the reactants have sufficient residence time to to achieve maximum hydrogenation degree. Typical dimensions of the reactor according to the invention are shown in
The reactor 1 has a steam jacket with an interior diameter of Dj of 6.35 cm, while the reactor itself has an interior diameter DR of 3.81 cm. The jacket is made of steel 40 S, while the reactor itself is made of steel 80 SS. The length of the reactor zone LR equipped with the static internal elements is 93.76 cm, while the total length of the reactor L is 123.19 cm.
The reactants are pumped into a preheater, while the mixture is heated before it enters the reactor 1 equipped with static internal elements. At the entrance of the reactor 1 equipped with static internal elements, a gas sparger is used to distribute the hydrogen 4 uniformly. The catalyst solution 5 is pumped from the catalyst bomb simultaneously with the reactants from the preheater.
The following examples illustrate the scope of the invention but are not intended to limit the same.
A reactor 1 equipped with 24 mixing elements having open blade internal structure and the geometry indicated in
The hydrogenation degree obtained in the continuous reactor after steady state for different mean residence time is shown in TABLE II.
The process described under Example 1 was repeated, except the catalyst concentration being 130 μM and with different hydrogen flow rate, hydrogenation of the unsaturated polymer and the operating conditions mentioned in Table III. In this case the concentration of the unsaturated polymer is twice that of the polymer used in Example 1 and hence the liquid hold up was less.
The degree of hydrogenation obtained in the continuous process after steady state with the conditions mentioned in TABLE III is shown in TABLE IV.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08161098.2 | Jul 2008 | EP | regional |
