Process for producing low VOC coalescing aids

Abstract

A process comprising reacting a mono- or di-carboxylic acid and/or acid anhydride with a glycol ether in the presence of phosphoric acid to produce a glycol ether ester product having low color and low VOC content.

Claims

1. A process for the preparation of a glycol ether ester, the process comprising contacting in a reaction zone a mono- or di-carboxylic acid and/or acid anhydride with a glycol ether of the following formula: ##STR00004## wherein R.sub.1 is a C.sub.1-C.sub.8 alkyl group, phenyl, or benzyl, R.sub.2 is H, methyl or ethyl, and n=1 or 4, in the presence of a catalytic amount of phosphoric acid under reaction conditions sufficient to produce a reaction product mixture comprising a glycol ether ester product and water, wherein the water is at least partially vaporized in the reaction zone and is passed to a separation zone where the water is substantially removed from the process, wherein the process is operated under conditions of temperature and pressure such that essentially no glycol ether leaves the separation zone, other than as a component of an azeotrope, wherein the temperature at the top of the separation zone is at most the boiling point of the azeotrope, and wherein the azeotrope is formed by water and the glycol ether.

2. The process of claim 1 wherein the maximum temperature in the separation zone is less than the boiling point of the pure glycol ether.

3. The process of claim 1 further comprising a neutralization/extraction step wherein the reaction product mixture is contacted with an alkaline material to produce a neutralized product mixture comprising an organic phase and an aqueous phase, the neutralized product mixture comprising a glycol ether ester product and at least one salt, and wherein the contacting is conducted under conditions sufficient to extract the at least one salt into the aqueous phase.

4. The process of claim 3 further comprising allowing phase separation, then recovering the neutralized product.

5. The process of claim 4 further comprising heating the neutralized product at subatmospheric pressure to remove water and low boiling organics to produce a purified product.

6. The process of claim 5 further comprising filtering the purified product to produce a final product comprising the glycol ether ester product.

7. The process of claim 1 wherein the molar ratio of glycol ether to carbonyl moiety of carboxylic acid or anhydride is from 1.05 to 1.25 over the course of the reaction.

8. The process of claim 1 wherein the purified and/or final product has a color of less than 25 APHA.

9. The process of claim 1 wherein the VOC content of the purified and/or final product is less than 1 weight percent as determined by EPA Method 24.

10. The process of claim 1 wherein the product has a boiling point above 250 C. at 760 mmHg, measured as defined in the 2004/42/EC Solvents Directive for Decorative Paints.

11. The process of claim 1 wherein the glycol ether comprises DPnB and the ester comprises DPnB adipate.

12. The process of claim 1 wherein the separation zone comprises a distillation column and the distillation column is operated using a process control scheme that includes controlling the temperature at the top of the column.

13. The process of claim 1 wherein the glycol ether is dipropylene glycol n-butyl ether (DPnB), and the carboxylic acid is adipic acid, the process further comprising: (a) contacting the reaction product mixture with NaOH, and optionally an extraction aid, preferably isopropanol, to produce a neutralized product mixture comprising an organic phase and an aqueous phase, the neutralized product mixture comprising DPnB adipate product and at least one salt, and wherein the contacting is conducted under conditions sufficient to extract the at least one salt into the aqueous phase, (b) allowing the organic phase and the aqueous phase to separate, then recovering the organic phase, (c) purifying the organic phase by removing residual water, DPnB and organics having a lower boiling point than the glycol ether ester product under vacuum using heating, optionally with inert gas stripping, (d) optionally, filtering residual solids from the product.

Description

SPECIFIC EMBODIMENTS OF THE INVENTION

(1) The following example is given to illustrate the invention and should not be construed as limiting its scope. All pressures are absolute, not gauge, unless otherwise indicated.

Example 1: Manufacture of DPnB Adipate

(2) A 10-gallon, 316 stainless steel reactor, rated for 750 psig (5.27 Mpa), equipped with a variable speed agitator/impeller, a nitrogen sparger, a cartridge filter, and a multiple use pipeline header is used. The reactor body is jacketed and the reactor head is traced to provide means for heating and cooling with SYLTHERM 800 brand heat transfer fluid, which is available from The Dow Chemical Company. The reactor is connected to a 5-foot4-inch stainless steel, jacketed column packed with 5 feet of Goodloe brand structured packing. The column is equipped with an overhead 316 stainless steel, 2-pass heat exchanger with a total surface area of 25 square feet as a condenser, which is connected to a receiving vessel and to a vacuum system. The head of the reactor is operated at reduced temperature relative to the reactor jacket to minimize degradation reactions. For the reaction, the reactor head tracing and the column jacket are operated at the same temperature of 95 C. This is selected to minimize the loss of reactants in the overheads. The reactor and peripheral equipment are operated with a process control unit.

(3) The reaction step is performed as follows: The initial materials are well mixed at 120 rpm using the built in agitator/impeller. The initial pressure in the reactor is 550 mmHg (73 kPa). The reactor is heated by heating oil up to 190 C. in 2.5 hrs, and is maintained at that temperature for 6 hours. After two hours of heating and reaching 177 C., the pressure is reduced to 60 mmHg (8 kPa) for the next two hours of operation. During the pressure decrease, special attention is paid to the column overhead temperature, which is maintained at or below the boiling point of the DPnB/water azeotrope. This ensures that the DPnB concentration in the vapor does not exceed the DPnB concentration of the water/DPnB azeotrope. Vapor from the column is condensed at 5 C. in the overhead condenser. Part of the condensed material is returned in the column as reflux. The progress and rate of the esterification reaction between DPnB and adipic acid is monitored by the amount of recovered distillate and by the rate that column overhead distillate is produced. At the end of the reaction step, when the recovered overhead distillate mass approaches the expected target and the distillate flow rate approaches zero, the reactor pressure is increased to 760 mmHg (101 kPa) and the reactor content is cooled to 80 C. By analysis, the reactor contains 91.64% wt DPnB adipate, 6.71% wt DPnB, 2.90% wt monoester of DPnB and adipic acid and 0.014% wt of water (the analysis is performed only for organic components and water, using gas chromatography (GC) and Karl Fischer titration, respectively). The GC analysis is performed using a Hewlett-Packard 6890 Gas Chromatograph equipped with flame ionization and thermal conductivity detectors, and a Hewlett-Packard 7673 auto-injector with a 100-sample tray. The instrument is linked to a Hewlett-Packard ChemStation comprising an IBM computer with HP62070AA software. The DPnB, the adipic acid, and the DPnB Adipate are analyzed in a 30 m0.32 mm ID1.5 film Restek RTX200 capillary column using a constant helium column pressure of 15 psig (205 kPa). The dipropylene glycol n-butyl ether adipate monoester is analyzed in a 30 m0.25 mm ID0.25 film Zebron ZB-1 capillary column using a constant helium flow of 1.1 mL/minute. The injector and detector temperatures are set at 300 C. and the oven temperature is programmed from 100 C. to 290 C.

(4) At this point, 0.386 kg sodium hydroxide is added to the mixture in the reactor, based upon titration and the expected neutralization requirement, as a 50% solution (0.772 kg). The materials are mixed at 60 rpm using the built in agitator/impeller. Calculation of the amount of NaOH needed for the neutralization of the catalyst advantageously is accomplished using the formula:
NaOH.sub.m=(0.125R.sub.mMAD.sub.x)+(0.8164H.sub.3PO.sub.4.sub.m)

(5) where NaOH.sub.m=Mass of sodium hydroxide (kg) R.sub.m=Current reaction mass (kg) MAD.sub.x=Monoadipate mass fraction H.sub.3P.sub.4.sub.m=Mass of phosphoric acid loaded 100% basis (kg)

(6) Analysis of the neutralized reaction mixture by GC shows 0.21-0.43% remaining unneutralized monoester.

(7) A mixture of 3.677 kg water and 0.28 kg isopropanol (IPA) is added to the reactor to extract most of the salt. IPA is added at 1/100th of the expected reaction mass remaining after completion of the reaction. The materials are mixed at 60 rpm using the built in agitator/impeller.

(8) The agitator/impeller is slowed to 15 rpm, the phases are allowed to separate, and 5.53 kg of the aqueous-salt layer is drained from the reactor, of which the last 0.08 kg is brown in color. The first aqueous 5.45 kg is colorless. 1.02 kg of reaction mixture trapped in process lines is finally drained and is also colorless.

(9) The reactor pressure is reduced to 25 mmHg absolute (3 kPa) and the reactor is heated up to 170 C., and nitrogen is then introduced to strip any remaining traces of unreacted DPnB. The reactor effluent is condensed in the overhead condenser and accumulated without refluxing in the column. The reactor pressure is raised to 760 mmHg and its temperature is lowered to 25 C. The reactor is drained and the drained material has a sample composition by GC of 104% wt DPnB adipate, 0.05% wt DPnB and 0.17% wt water. The >100% value for DPnB adipate falls within the 5% error for the analysis of this compound when it is present as the main component.

(10) The reactor content is filtered using the cartridge filter to remove the salt and the filtered material is analyzed by GC. The filtered sample composition is 98% wt DPnB adipate, 1.2% wt DPnB and 0.25% wt water. The material color is 10.3 APHA and the VOC % is 0.5.

Comparative Experiment 2: Manufacture of DPnB AdipateNeutralization after Stripping (not an Embodiment of the Invention)

(11) The following materials are charged to the reactor system of Example 1, in kg: 7.5 adipic acid, 22.9 DOWANOL DPnB brand glycol ether (available from The Dow Chemical Company), 0.473 85% phosphoric acid (aq.) and 0.25 deionized water. The mixture has approximately the same composition as the starting mixture of Example 1, and has a 2.25 molar ratio of DOWANOL DPnB to adipic acid and 8% mol of phosphoric acid based upon adipic acid. The mixture is heated to 190 C. The reactor pressure is decreased from 800 mmHg to 120 mmHg (107 kPa to 16 kPa) during the heating period. The reactor is kept at these conditions for 6 hrs. The esterification reaction progress manifests itself by the production of water. The vapor from the reactor is condensed in the column condenser at 5 C. Part of the condensed material is returned in the column as the reflux flow. The overhead temperature of the column varies in the range of 65-80 C., which is 10-25 C. higher than the temperature of DPnB/water azeotrope at this pressure. A sample of reactor content taken at the end of this period indicates that material in the reactor contains 91% wt DPnB adipate, 13% wt DPnB and 3% wt monoester. All adipic acid is consumed by the reaction. The color of a 3.3 kg sample is 27 APHA, which exceeds the color target maximum of 25 APHA. The reactor pressure is gradually decreased to 10 mmHg (1.3 kPa) in order to remove the remaining DPnB from the reactor. The overhead temperature of the column gradually increases to 122 C., which is significantly higher than the boiling point of the DPNB/water azeotrope and is more consistent with the boiling point of pure DPnB at this pressure.

(12) A sample of reactor content is taken after 3 hrs at these conditions. The composition of the sample is 99.5% of DPnB adipate, 0.4% wt of DPnB and 3.6% wt of monoester. The sample has a dark brown color, significantly exceeding 100 APHA. As in Example 1, the material is cooled to 80 C., and is treated with 0.29 kg of sodium hydroxide and 12 kg of water. The quantity of sodium hydroxide is consistent with the remaining amount of phosphoric acid present after the large 3.3 kg sample is removed with a 2 mole ratio of sodium hydroxide to phosphoric acid. A sample is taken after neutralization. The composition of the sample is 97.9% of DPnB adipate, 0.5% wt of DPnB and 3.5% wt of monoester. These steps did not significantly improve the color of the material, which is significantly higher than 100 APHA.

(13) These two examples illustrate the importance of the procedures described in the invention. The material in the reactor is heated to the same temperature (190 C.); nevertheless, in Example 1 the final product has very little color, while in the Comparative Experiment 2 the final product has a dark brown color. In Ex. 1, the process involves neutralizing before stripping, while C.E. 2 does not.