Manufacture of neopentyl glycol (III)

Abstract: Neopentyl glycol is made from isobutyraldehyde and paraformaldehyde; the aldol reaction product is directly mixed with a lower alcohol for hydrogenolysis.

Description: This invention relates to the manufacture of neopentyl glycol (NPG) from isobutyraldehyde and paraformaldehyde, and is restricted to the use of certain specified steps and conditions in the hydrogenation of the product of the reaction of paraformaldehyde and isobutyraldehyde (IBAL). It is known to react paraformaldehyde with isobutyraldehyde, see e.g., U.S. Serial No. 691,927 (issued as U.S. Patent No. 5,144,088) and U.S. Serial No. 716,177. Obtained is a product comprising, in the case of Serial No. 691,927, hydroxypivaldehyde (HPA), and in Serial No. 716,177, 3-hydroxy-2,2-dimethylpropylhydroxypivalate. The products are hydrogenated to make NPG. The two applications describe different catalyst systems for the aldol reaction; the hydrogenation step is distinguished primarily by the fact that the feed material for it, i.e. the reaction product of the aldol step, after dissolution in a suitable alcohol, may be fed directly to the hydrogenation step. This is due to the use of paraformaldehyde as the formaldehyde reactant, which greatly reduces the presence of water and avoids other complications. The present application is an improvement of both inventions, and in the manufacture of NPG generally, in that the present application recognizes the unique composition of the aldol reaction product made using paraformaldehyde and optimizes the hydrogenation process for it, i.e. for any aldol process utilizing paraformaldehyde. In the present invention, the aldol reaction is not limited to the use of the catalysts described in the above applications, but embraces any reaction of IBAL and paraformaldehyde. While the present application is limited to the hydrogenation and/or hydrogenolysis of substantially water-free reaction products of IBAL and paraformaldehyde, certain prior art may be considered relevant wherein HPA or another product obtained from the reaction of IBAL and aqueous formaldehyde is converted to NPG through hydrogenation; such references include those employing copper chromite hydrogenation catalysts, for example. References which employ copper chromite and other hydrogenation catalysts with the conventional aqueous formaldehyde system may be exemplified by U.S. Patent No. 4,855,515, which recites the historical development of the reaction and emphasizes the use of a particular catalyst in the hydrogenation step. U.S. Patent No. 3,808,280 discloses the use of triethylamine as a catalyst for the (aqueous) formaldehyde/isobutyraldehyde reaction. Each of the above references employs formaldehyde in the form of aqueous formaldehyde. Paraformaldehyde is used by Snam S.p.A. in UK Patent No. 1,017,618 to react with IBAL in the presence of a tertiary amine to produce a reaction product containing apparently predominantly HPA which may be hydrogenated to NPG. However, the instant invention teaches the addition of a suitable alcohol solvent prior to hydrogenation which produces a high purity NPG product by simple distillation, obviating the need for additional expensive purification steps. While zur Hausen et al, U.S. Patent No. 4,250,337 may use the aldol reaction product directly in their hydrogenation step, they also teach the use of small amounts of water, in contrast to the process of the present invention, which advantageously uses an alcohol in the hydrogenolysis step. As a result, our invention achieves high NPG purities together with high yields unlike the aforementioned patent which can only achieve equivalent purities at uneconomical yields. Other prior art processes which emphasize the hydrogenation step include U.S. Patent Nos. 4,094,914 to Rottig et al and 4,933,473 to Ninomiya et al. Ninomiya et al especially recognize the formation of the HPA dimer in the aldol reaction product. While Rottig et al use alcohols in a vapor phase hydrogenation, they do not employ paraformaldehyde in the aldol step as applicants do nor do they recognize or demonstrate ester hydrogenolysis. German Patent No. 1,014,089 discloses a process for producing neopentyl glycol from IBAL and aqueous formaldehyde. A tertiary amine catalyst is not used in this process. The present invention provides a method of making neopentyl glycol comprising the steps of: a) reacting paraformaldehyde with isobutyraldehyde via an aldol reaction in the presence of a tertiary amine catalyst of the formula R 1 R 2 R 3 N, wherein R 1 , R 2 and R 3 are independently selected from alkyl groups having from 1 to 15 carbon atoms and aryl groups and R 1 and R 2 may form a substituted or unsubstituted cyclic group having from 5 to 15 carbon atoms, b) hydrogenating the reaction product comprising hydroxypivaldehyde obtained in step (a) in the liquid phase in the presence of a hydrogenation catalyst and in the presence of an alcohol of the formula RR'CHOH, wherein R and R' are independently selected from hydrogen and alkyl Groups having from 1 to 5 carbon atoms, and c) recovering the neopentyl glycol obtained in step (b), with the proviso that no metal oxide catalyst is used in the aldol reaction of step (a). The obtained NPG, which may be recovered by simple distillation, has a purity of at least 99%. Preferably, the alcohol is recovered prior to recovering the neopentyl glycol and is recycled. It is preferred that the hydrogenation reaction is conducted at a temperature of from 100°C to 200°C. It is preferred that the hydrogenation reaction is conducted at a pressure of from 3.45·10 3 kPa to 20.69·10 3 kPa (500 psi to 3000 psi). Preferably, the reaction of isobutyraldehyde with paraformaldehyde employs a molar ratio of paraformaldehyde to isobutyraldehyde of from 0.5:1 to 2:1, more preferably from 1:1 to 1.12:1. We prefer to use a hydrogenolysis feed containing 40% to 90% alcohol; the preferred alcohol is methanol. Our invention will be described in detail in connection with the examples to follow. In the discussion below, it is important to keep in mind the basics of the reactions discussed. First is the aldol reaction: Product (1), which is the major product, is HPA. Product (2) corresponds to 3-hydroxy-2,2-dimethylpropylhydroxypivalate, which will be referred to herein as "HNHP", which stands for hydroxyneopentylhydroxypivalate. HNHP is generally a minor product made by the Tishchenko reaction of HPA. In the presence of an appropriate catalyst, pressure, heat and hydrogen, the reaction product including both HPA and HNHP is hydrogenated to form NPG: The conventional aqueous processes for making NPG by the above route have the disadvantages of significant wastewater quantities, a significant incidence of ester and acid impurities not readily separable from NPG and which must be saponified and neutralized, creating another waste stream, an extraneous extraction step on the waste stream to increase efficiency, and a relatively expensive purification step. By using the process of our invention using paraformaldehyde, rather than the prior art formaldehyde process, the just-recited disadvantages are obviated. Our process not only avoids these disadvantages but also conducts the hydrogenation step with much greater efficiency. The purity of the NPG product obtained by simple distillation following the teachings of this invention is higher than that obtained by prior art. The process taught by the instant invention is much more environmentally friendly than prior art aqueous processes. The volume of wastewater discharged by our process is approximately 80% less than seen in conventional aqueous processes. Additionally, it has been demonstrated, as will be described herein, that the generation of HPA using paraformaldehyde followed by catalytic hydrogenation in an alcoholic solvent can be performed under conditions of hydrogenolysis so that ester impurities are reduced to their corresponding alcohols. A NPG product can be obtained from the reduced effluents at >99.5% purity by simple distillation in yields at least comparable to the conventional NPG process using aqueous formaldehyde. The high NPG purity of the hydrogenated aldol effluent makes it feasible to eliminate three processing steps: caustic treatment, a distillation or evaporation step such as wiped-film evaporation, and IBAL extraction (see U.S. Patent No. 4,935,555 to Elias et al). We have produced a NPG product in purities greater than 99.5% using this simplified processing scheme. Finally, we have demonstrated to our great surprise that high NPG purities can be achieved at hydrogenation pressures as low as 3.45·10 3 kPa (500 psi) H 2 . The present invention includes as an initial step the method of making HPA, and particularly its dimer, 2-[1,1-dimethyl-2-hydroxymethyl]-5,5-dimethyl-4-hydroxy-1,3-dioxane, and subsequently NPG, by reacting IBAL with paraformaldehyde in the presence of a tertiary amine catalyst to obtain HPA and HPA dimer. The HPA and its dimer are hydrogenated by the process disclosed herein to obtain NPG. Whether or not the HPA or its dimer is isolated and/or purified, they are conveniently hydrogenated in the form of a methanol (or other alcohol as described elsewhere herein) solution, and in the presence of a copper chromite catalyst, for example, to obtain the desired neopentyl glycol. The HPA dimer hydrogenates as readily as HPA itself. As is known in the art, if the amine chosen has a boiling point lower than the boiling point (reflux temperature) of IBAL, pressure may be necessary. Our invention provides a process in which only minimal water is present and is therefore relatively easier to perform since it greatly reduces the separation requirements and disposal of wastewater; the process is also considerably more efficient than prior art processes, since the HPA product can be used directly, i.e. without an arduous separation or purification process, for the hydrogenation step to NPG. The process is also more efficient in that fewer by-products are made, a high yield is obtained at a faster rate, and indeed one need not be concerned with the complications of by-products. Paraformaldehyde is easier and safer to store under properly controlled conditions than aqueous formaldehyde, as well as resulting in lower emissions. We may use various tertiary amines. Specifically, we may use as catalysts any tertiary amines of the general formula R 1 R 2 R 3 N where R 1 , R 2 , and R 3 are independently selected from alkyl groups having from 1 to 15 carbon atoms and aryl groups, and R 1 and R 2 may form a substituted or unsubstituted cyclic group having from 5 to 15 carbon atoms. Following are several examples of the invention: Example 1 (A) 80 g of IBAL, 37.2 g of paraformaldehyde, and 5.6 g of triethylamine were charged with stirring into a 250 ml 3-neck roundbottom flask equipped with a reflux condenser, and stirbar. The apparatus was lowered into a heated oil bath (80°C) and moderate IBAL reflux was observed within minutes. After 6 hours, the reaction was terminated, cooled to 60°C, then diluted in 400 g of methanol. The reaction effluent was charged to an autoclave together with 4.0 g of CuCr 2 O 4 and hydrogenated for 1.5 hours at 150°C and 6.89·10 3 kPa (1000 psi) H 2 . (B) The aldol reaction followed by batch hydrogenation was repeated as described above except that 95.5 g of aqueous formaldehyde (37 wt.%) was used rather than paraformaldehyde. The batch hydrogenation was performed after diluting the reaction mixture in 400 g methanol using 4.0 g of CuCr 2 O 4 . The results from the two experiments are compared and summarized in Table I. The results clearly demonstrate the differences in purity and yield of the conventional aqueous process and our paraformaldehyde process. Experiment Formaldehyde Type % Aldol/CH 3 OH (A) paraformaldehyde 20 (B) aqueous 20 GC Analysis of Hydrogenated Effluent % Isobutyl Alcohol 5.43 10.40 % Triethylamine 5.68 6.44 % Neopentyl Glycol 84.08 67.12 % Hydroxyneopentylhydroxypivalate 3.28 4.82 % Neopentyl Glycol Purity 98.39 96.35 % Neopentyl Glycol Yield 97.54 85.35 Example 2 HNHP hydrogenolysis compared to methylisobutyrate hydrogenolysis: The following solutions were prepared: (A) NPG 47.6 wt.% HNHP 2.4 wt.% triethylamine 2.3 wt.% methanol 47.6 wt.% (B) methylisobutyrate 5 wt.% methanol 95 wt.% A batch hydrogenation was performed on each solution using 1.4 wt.% CuCr 2 O 4 at 150°C for 1 hour at 6.89·10 3 kPa (1000 psi) H 2 . Ester hydrogenolysis was monitored. The results follow in Table II. These results are surprising in that the ester impurities indigenous to the process in this invention are more easily hydrogenolyzed than a typical ester such as methylisobutyrate; they are also surprising in that we are able to hydrogenate easily at relatively low pressures and temperatures. This allows the recovery of high purity NPG product by simple distillation. Ester % Hydrogenolysis HNHP 65.7 % Methylisobutyrate 1.4 % Example 3 Effect of stoichiometry on aldol condensation efficiencies: A batch reaction was performed at moderate IBAL reflux temperatures. Reactions were terminated 0.25 hours after IBAL reflux ceased. Reaction charge consisted of 0.050 equivalent of TEA relative to starting IBAL concentration and paraformaldehyde was varied as designated. Results are shown in Table III. RUN # Condition %Conversion (IBAL) %Selectivity HPA HNHP 1 stoichiometric paraformaldehyde 85-90% 85-90% 1-5% 2 6% excess paraformaldehyde 93% 91% 2.3% 3 12% excess paraformaldehyde >99% 87-90% 3-6% Example 4 Isobutyraldehyde (2000.0 g, 27.74 mol), paraformaldehyde (929.3 g, 29.40 mol), and triethylamine (140.3 g, 1.39 mol) were charged with stirring into a 5 ℓ roundbottom flask fitted with a reflux condenser. The apparatus was lowered into a water bath (50°C). The bath was heated to a temperature of 80°C over a period of 1.5 hours. The reaction was terminated (6 hours) and the clear, faintly yellowish aldol effluent was diluted in methanol to make a 50 wt.% aldol in methanol solution. The hydrogenation was performed by passing the methanolic aldol effluent upward through a fixed-bed of CuCr 2 O 4 at 160°C, 0.5 LHSV, and 6.89·10 3 kPa (1000 psi) H 2 at >5:1 mole ratio H 2 :HPA. The results are as shown: Components Hydrogenated Solution (GC area %) Neopentyl Glycol Purity CH 3 OH 35.340 IBA 1.697 IBacid 0.000 TEA 3.723 HPA 0.000 NPG 58.577 99.67% esters 0.194 HNHP 0.424 IBA = isobutyl alcohol IBacid = isobutyric acid TEA = triethylamine HPA = hydroxypivaldehyde NPG = neopentyl glycol esters = e.g., neopentyl glycol monoformate, neopentyl glycol monoisobutyrate HNHP = hydroxyneopentylhydroxypivalate Example 5 Hydrogenation was performed by passing a methanolic aldol effluent (prepared as described in Example 4) upward through a fixed-bed of barium promoted CuCr 2 O 4 at 160°C, 6.89·10 3 kPa (1000 psi) H 2 at >5:1 mole ratio H 2 :HPA, and 0.5 LHSV. Results follow: Components Hydrogenated Solution (GC area %) Neopentyl Glycol Purity CH 3 OH 31.894 IBA 2.149 IBacid 0.004 TEA 3.378 HPA 0.007 NPG 61.574 99.55% esters 0.277 HNHP 0.455 IBA = isobutyl alcohol IBacid = isobutyric acid TEA = triethylamine HPA = hydroxypivaldehyde NPG = neopentyl glycol esters = e.g., neopentyl glycol monoformate, neopentyl glycol monoisobutyrate HNHP = hydroxyneopentylhydroxypivalate Example 6 Hydrogenation was performed by passing a methanolic aldol effluent (prepared as described in Example 4) downward through a fixed-bed of barium promoted CuCr 2 O 4 at 160°C, (3.45·10 3 kPa (500 psi) H 2 at >5:1 mole ratio H 2 :HPA, and 1.0 LHSV. Results follow: Components Hydrogenated Solution (GC area %) Neopentyl Glycol Purity CH 3 OH 33.400 IBA 2.043 IBacid 0.040 TEA 3.600 HPA 0.000 NPG 59.232 99.36% esters 0.382 HNHP 1.249 IBA = isobutyl alcohol IBacid = isobutyric acid TEA = triethylamine HPA = hydroxypivaldehyde NPG = neopentyl glycol esters = e.g., neopentyl glycol monoformate, neopentyl glycol monoisobutyrate HNHP = hydroxyneopentylhydroxypivalate Example 7 Isobutyraldehyde (300.0 g, 4.16 mol), paraformaldehyde (131.51 g, 4.16 mol), and triethylamine (21.0 g, 0.21 mol) were charged with stirring into a 1 ℓ roundbottom flask fitted with a reflux condenser and equipped with an overhead stirrer. The charge was heated until a moderate isobutyraldehyde reflux was achieved. The slurry-phase reaction mixture became clear and homogeneous within 1.5 hours. The reaction was terminated when isobutyraldehyde reflux ceased. The clear, faintly yellowish aldol effluent was diluted in methanol to make a 30 wt.% aldol in methanol solution. The hydrogenation was performed by passing the methanolic aldol effluent upward through a fixed-bed of barium promoted CuCr 2 O 4 at 130°C, 1.6 LHSV, and 14.89·10 3 kPa (2160 psi) H 2 (>5:1 mole ratio H 2 :HPA). Results follow: Components Hydrogenated Solution (GC area %) Neopentyl Glycol Purity CH 3 OH 59.877 IBA 2.440 IBacid 0.036 TEA 2.359 HPA 0.000 NPG 34.442 99.26% esters 0.255 HNHP 0.557 IBA = isobutyl alcohol IBacid = isobutyric acid TEA = triethylamine HPA = hydroxypivaldehyde NPG = neopentyl glycol esters = e.g., neopentyl glycol monoformate, neopentyl glycol monoisobutyrate HNHP = hydroxyneopentylhydroxypivalate Example 8 Isobutyraldehyde (100.0 g, 1.39 mol), paraformaldehyde (49.1 g, 1.55 mol), and triethylamine (7.39 g, 0.069 mol) were charged with stirring into a 250 ml roundbottom flask fitted with a reflux condenser and equipped with a stirbar. The charge was heated until a moderate isobutyraldehyde reflux was achieved. The slurry-phase reaction mixture became clear and homogeneous within 1.25 hours and was continued until isobutyraldehyde reflux ceased. The faintly yellowish reaction mixture was diluted in methanol to make a 10 wt.% aldol in methanol solution. The reduction was performed in a 2 ℓ autoclave reactor using 5.0 wt.% CuCr 2 O 4 at 20.69·10 3 kPa (3000 psi) H 2 for 1 hour at 70°C followed by 1 hour at 130°C. Chromatographic analyses follow: Components Hydrogenated Solution (GC area %) Neopentyl Glycol Purity CH 3 OH 84.986 IBA 0.018 IBacid 0.012 TEA 0.305 HPA 0.000 NPG 14.583 99.82% esters 0.026 HNHP 0.050 IBA = isobutyl alcohol IBacid = isobutyric acid TEA = triethylamine HPA = hydroxypivaldehyde NPG = neopentyl glycol esters = e.g., neopentyl glycol monoformate, neopentyl glycol monoisobutyrate HNHP = hydroxyneopentylhydroxypivalate

Claims: A method of making neopentyl glycol comprising the steps of: a) reacting paraformaldehyde with isobutyraldehyde via an aldol reaction in the presence of a tertiary amine catalyst of the formula R 1 R 2 R 3 N, wherein R 1 , R 2 and R 3 are independently selected from alkyl groups having from 1 to 15 carbon atoms and aryl groups and R 1 and R 2 may form a substituted or unsubstituted cyclic group having from 5 to 15 carbon atoms, b) hydrogenating the reaction product comprising hydroxypivaldehyde obtained in step (a) in the liquid phase in the presence of a hydrogenation catalyst and in the presence of an alcohol of the formula RR'CHOH, wherein R and R' are independently selected from hydrogen and alkyl groups having from 1 to 5 carbon atoms, and c) recovering the neopentyl glycol obtained in step (b), with the proviso that no metal oxide catalyst is used in the aldol reaction of step (a). The method of claim 1 wherein the alcohol comprises methanol. The method of claim 1 wherein the alcohol is recovered prior to recovering the neopentyl glycol and is recycled. The method of claim 1 wherein the hydrogenation catalyst comprises copper chromite. The method of claim 1 wherein the hydrogenation reaction is conducted at a temperature of from 100°C to 200°C. The method of claim 1 wherein the hydrogenation reaction is conducted at a pressure of from 3.45·10 3 kPa to 20.69·10 3 kPa (500 psi to 3000 psi). The method of claim 1 wherein the alcohol is present during the hydrogenation reaction is an amount of from 40% to 90% of the mixture of the aldol reaction product and the alcohol. The method of claim 1 wherein the reaction of isobutyraldehyde with paraformaldehyde employs a molar ratio of paraformaldehyde to isobutyraldehyde of from 0.5:1 to 2:1. The method of claim 8 wherein the molar ratio of paraformaldehyde to isobutyraldehyde is from 1:1 to 1.12:1. The method of claim 1 wherein the neopentyl glycol is recovered by simple distillation.

Inventors: CULLO LEONARD A, ELIAS CAROLE L, PUGACH JOSEPH, SALEK JEFFREY S, CULLO, LEONARD A., ELIAS, CAROLE L., PUGACH, JOSEPH, SALEK, JEFFREY S.
Applicants: ARISTECH CHEMICAL CORP, ARISTECH CHEMICAL CORPORATION
Application year: 1992
Main classification: C07C31
IPC codes: C07C45, C07C31, C07C29