METHOD FOR PRODUCING ALPHA-HYDROXY CARBOXYLIC ESTERS IN THE GAS PHASE

Abstract

The present invention relates to a process for preparing alpha-hydroxycarboxylic esters from the alcoholysis of alpha-hydroxycarboxam ides in the gas phase, characterized in that the conversion is effected in the presence of water.

Claims

1. A process for preparing alpha-hydroxycarboxylic esters, the process comprising: performing an alcoholysis reaction of an alpha-hydroxycarboxamide and an alcohol in a gas phase in the presence of a heterogeneous catalyst, wherein a molar ratio of the alcohol to the alpha-hydroxycarboxamide is 2-25 mol/mol, and wherein the alcoholoysis reaction is performed in the presence of 0.01-10 mol/mol of water relative to the alpha-hydoxycarboxamide.

2. The process according to claim 1, wherein the catalyst is a zirconium dioxide catalyst.

3. The process according to claim 1, wherein the alcoholysis reaction is performed at a reaction temperature of 150-300 C.

4. The process according to claim 1, further comprising treating the alpha-hydroxycarboxamide, the alcohol, or both with a cationic ion exchanger prior to the performing of the alcoholoysis reaction in the gas phase.

5. The process according to claim 1, wherein the alpha-hydroxycarboxamide is hydroxyisobutyramide and the alcohol used is methanol.

6. The process according to claim 1, wherein ammonia is formed and the process further comprises feeding the ammonia into a hydrogen cyanide preparation process or an ammoxidation process.

Description

Comparative Examples 1-4

[0049] A solution of 20% by weight of HIBA in methanol is fed by means of an HPLC pump (Knauer) with a flow rate of 1 g/min into an evaporator consisting of a stainless steel capillary tube of length 1 m wound around a 500 W heating cylinder. The gas mixture that arises is passed into a fixed bed reactor of length 33 cm and internal diameter 1 cm. The catalyst charge consists of 100 g of yttrium-doped zirconium dioxide (dopant concentration 8.3% by weight). The corresponding WHSV based on HIBA is 0.2 h.sup.1. The results in terms of conversion and selectivity of the experiments conducted at four different reactor temperatures, each at a reaction pressure of 400 mbar, are listed in Tab. 1.

TABLE-US-00001 TAB.1 Conversion and selectivity at various temperatures without water Reaction HIBA Comparative temperature/ conversion/ Selectivity/% Example C. % Acetone MMA HIBAc AMPN MHIB 1 220 80 1 0 1 8 90 2 240 86 3 1 2 12 82 3 260 91 5 2 4 18 71 4 280 94 10 4 2 23 54 HIBAc = hydroxyisobutyric acid MMA = methyl methacrylate

[0050] When the reaction temperature is increased by 60 C., the conversion of HIBA increases from 80% to 94%. At the same time, the selectivity for the desired MHIB target product decreases from 90% to 54%, and the selectivity for, for example, the unwanted AMPN by-product rises from 8% to 23%. Without the addition or presence of water (according to the Mitsubishi Gas Chem. patent publication EP 2415750), no optimization point is found that reduces by-production of AMPN, reduces acetone elimination from hydroxyisobutyramide and achieves selectivities >93%.

EXAMPLES 1-9

[0051] Examples 1-9 were conducted in the same apparatus as Comparative Examples 1-4. However, 1% by weight of water was added to the feed at the expense of methanol. The reaction temperature was 220 C. The results in terms of HIBA conversion and MHIB selectivity for zirconium dioxide catalysts doped with various oxides are shown in Tab. 2.

TABLE-US-00002 TAB. 2 Various zirconium dioxide catalysts with 1% water Doping/ Pore Surface HIBA MHIB % volume/ area/ conversion/ selectivity Example by wt. Dopant cm.sup.3/g m.sup.2/g % % 1 18.83 CeO.sub.2 0.27 101 97.7 96.5 2 0.43 K.sub.2O 0.35 86.5 96.7 96.5 3 9.7 La.sub.2O.sub.3 0.29 106 96.4 95.9 4 8.8 La.sub.2O.sub.3 0.28 100 96.6 94.7 5 4.5 Y.sub.2O.sub.3 0.28 114 96.9 93.7 6 0.3 103 96 92.2 7 12.6 P.sub.2O.sub.5 0.17 140 96.2 91.6 8 7.3 ZnO 96.3 91.6 9 8.3 Y.sub.2O.sub.3 0.26 115 97.9 91.1

[0052] What are noticeable are the distinctly elevated conversions and selectivities compared to Comparative Examples 1-4 without water in the feed. Particularly good values are exhibited by the Ce, K and La-doped catalysts.

[0053] Even the small catalytic co-feed of water, under otherwise similar or identical reaction conditions, effectively suppresses the elimination of acetone and drastically reduces the production of the unwanted AMNP by-product. Thus, the product selectivity is significantly enhanced.

Comparative Examples 5-9

[0054] Comparative Example 1 was repeated, except at a reaction pressure of 1013 mbar and, as shown in Tab. 3, at different ratios of methanol/water to HIBA. The results for Comparative Example 9 are shown in Tab. 4.

TABLE-US-00003 TAB. 3 Different feed compositions Molar ratios/mol/mol HIBA Comparative MeOH/ MeOH / H.sub.2O/ (MeOH + H.sub.2O)/ conversion/ Selectivity/% Example (MeOH + H.sub.2O) HIBA HIBA HIBA % MHIB Acetone HIBAc MAA 5 0.00 0.00 13.00 13.00 54.40 0.00 0.29 94.27 5.34 6 0.07 0.99 12.38 13.38 57.11 11.73 0.51 80.37 4.89 7 0.15 1.98 11.30 13.28 58.16 22.92 0.51 67.30 4.48 8 0.27 3.37 9.09 12.47 56.44 33.98 0.56 59.95 3.88 MAA = methacrylic acid As expected, no MHIB is formed in the absence of methanol. Below a molar ratio of methanol to HIBA of 4, no significant amounts of MHIB form even in the presence of water.

Examples 10-12 and Comparative Example 9

[0055] Comparative Example 5 was repeated with the feed compositions shown in Tab. 4.

TABLE-US-00004 TAB. 4 Different feed compositions with and without water Example/ Molar ratios/mol/mol HIBA Comp. MeOH/ MeOH / H.sub.2O/ (MeOH + H.sub.2O)/ conversion/ Selectivity/% Example (MeOH + H.sub.2O) HIBA HIBA HIBA % MHIB Acetone AMPN HIBAc MMA MAA 10 0.38 5.12 8.23 13.35 85.84 87.27 0.64 0.00 7.89 0.00 0.65 11 0.57 7.65 5.74 13.39 88.73 94.72 0.47 0.00 3.15 0.00 0.50 12 0.75 10.18 3.34 13.52 92.76 96.45 0.43 0.00 0.80 0.87 1.14 9 1.00 11.65 0.00 11.65 73.36 92.29 1.56 3.08 2.27 0.36 As shown in Tab. 4, reasonable HIBA conversions are not achieved until a molar ratio of methanol to HIBA of 5. On the other hand, the selectivities are significantly higher in the presence of water, even in the case of high molar ratios of methanol to HIBA.

Examples 14-19

[0056] Examples 14-19 were conducted analogously to Example 1, except that the overall feed was subjected to a preliminary purification by means of ion exchangers prior to feeding into the plant. For this purpose, the HIBA, MeOH and water components were mixed in the desired molar compositions and fed continuously to a cationic ion exchanger (Lewatit K2341). The loading was adjusted to 43.3 g of feed solution per h and g of ion exchanger. The treatment was conducted until the pH at the outlet of the ion exchanger column was 40.1. The feed solution thus treated was then fed into the evaporator. The resulting values are shown in Tab. 5.

TABLE-US-00005 TAB. 5 Treatment with ion exchanger Molar HIBA MHIB MeOH:HIBA HIBA % MeOH % Water % conversion MHIB selectivity Example ratio by wt. by wt. by wt. % yield % % 14 4 42.9 53.3 3.8 90.0 87.5 97.2 15 6 33.9 63.2 3.0 92.7 91.0 98.2 16 8 28.0 69.6 2.4 94.2 92.3 98.0 17 12 20.8 77.4 1.8 96.2 93.6 97.3 18 15 17.4 81.1 1.5 96.9 95.2 98.2 19 20 13.7 85.1 1.2 97.7 95.8 98.1 Much higher selectivities in terms of MHIB are achieved than without pretreatment with ion exchanger (Tab. 4).