GB2068942A

GB2068942A - Continuous Process for Catalytic Decolorization of Esters

Info

Publication number: GB2068942A
Application number: GB8100119A
Authority: GB
Original assignee: Engelhard Minerals and Chemicals Corp
Current assignee: Engelhard Minerals and Chemicals Corp
Priority date: 1980-01-24
Filing date: 1981-01-05
Publication date: 1981-08-19
Also published as: AU6563280A; IT8147612A0; DE3102160A1; JPS56110650A; FR2474487A1

Abstract

Dicarboxylic acid esters, derived from alcohols with 7 to 10 carbon atoms, e.g. phthalate esters can be decolorized by a continuous process involving treatment with hydrogen in the presence of a catalyst comprising palladium on a carrier at a temperature from 100 to 175 DEG C and at a pressure from 5 to 35.5 bars (60 to 500 psig), preferably 14.8 to 28.6 bars (200 to 400 psig).

Description

SPECIFICATION Continuous Process for Catalytic Decolorization of Esters This invention relates to a continuous process for decolorizing esters, in particular esters used as plasticizers for resins. The process is particularly useful for removing undesirable color from phthalate esters which are useful as plasticizers for polyvinyl chloride resins and which may be operated in a continuous rather than batchwise manner. In accordance with this invention, esters of phthalic acid are decolorized by treatment with hydrogen under very mild hydrogenation conditions in the presence of a catalyst comprising palladium on a carrier, e.g., carbon or alumina.

The treatment of various organic acids and esters for the removal of color therefrom by hydrogenation is known in the prior art. British Patent 1,336,776 relates to a process for producing colorless esters of mono- or polycarboxylic anhydrides or acids and alcohols having up to 20 carbon atoms by carrying out the esterification reaction employing a strong acid, such as sulfuric acid as catalyst at atmospheric pressure in the presence of hydrogen and a hydrogenation catalyst, such as palladium, or platinum on a carrier. U.S. Patent 3,839,481 removes the azulene color from a mixture of methylnaphthalenes by hydrogenation with a catalyst which may comprise palladium on alumina at 250C to 1 500C under a hydrogen pressure of 3 to 10 bars. U.S.Patent 3,646,238 treats raw detergent alkylate with a hydrogen-containing gas in the presence of a catalyst which may comprise palladium on alumina at a temperature in the range of 10 to 930C and at a pressure in the range of from about 1.3 bars to about 4.6 bars to improve the color and odor characteristics of the alkyl benzene sulfonates prepared from the alkylate. U.S. Patent 3,359,250 relates to a process for decolorizing dipentane polymers by treating with hydrogen at a temperature in the range of 500C to 1 250C at atmospheric pressure in the presence of a noble metal catalyst, such as platinum or palladium on carbon or alumina.

Most plasticizers are products of simple esterification reactions between a dicarboxylic acid or anhydride and one or more aliphatic alcohols in the presence of an esterification catalyst, such as sulfuric acid or p-toluene sulfonic acid. The catalyst is removed from the product in a washing step. The purity standards of commercial plasticizers are currently very high; phthalate esters for use as plasticizers must be substantially colorless and odorless. Phthalate esters, particularly di-2-ethylhexyl phthalate, di-isooctyl phthalate (DOP), di-isononyl phthalate, and di-isodecyl phthalate (DIDP), are industrially important as plasticizers for polyvinyl chloride (PVC) resins. The phthalic esters constitute the principal category of plasticizers for polyvinyl chloride resins because they satisfy the broadest range of processing and performance requirements at the lowest cost.

The purity of the plasticizer depends on the quality of the alcohol used in the esterification process. Excessive product colorization occurs fairly frequently in the manufacture of plasticizer esters; the severity of the problem will depend very often on the nature of the starting materials and the process conditions.

Manufacturers of the plasticizer esters exercise careful control over the feedstock and process conditions. In the event that the color of the product is off-specification, the esters are sometimes treated with various decolorizing agents, such as carbon and clay, or with bleaching agents, such as borohydride and ozone. Frequently none of these expedients is effective in producing a product that meets color specifications. There is, therefore, a need for phthalic ester plasticizer decolorization treatment as provided by the process of the present invention. The present invention provides a process for the decolorization of esters by mild catalytic hydrogenation without loss of the ester product.

In accordance with the present invention there is provided a continuous process for decolorizing an ester of dicarboxlyic acid or anhydride and an alcohol containing 7 to 10 carbon atoms per molecule of alcohol. The process comprises contacting the ester with hydrogen at a temperature in the range of about 1000C to 1 7SaC, preferably 1 400C to 1 500C, and at a hydrogen pressure in the range of about 5 to 35.5 bar (60 to 500 psig) in the presence of a catalyst which comprises palladium supported on a carrrier. In accordance with one aspect of the invention, the carrier may be carbon, or preferably, alumina. The hydrogen to ester mole ratio may range from 0.1 to 10; preferably the hydrogen to ester mole ratio is within the range of about 0.5 to about 1.5.The liquid hourly space velocity of the ester is preferably in the range of about one to four liquid volumes of ester per volume of catalyst per hour.

In accordance with another aspect of the invention, the dicarboxylic acid or anhydride is phthalic acid or its anhydride.

In accordance with a preferred embodiment of the invention, a phthalic acid ester requiring color improvement is heated to an elevated temperature and charged in a continuous process to a reactor containing catalyst, preferably in the form of a fixed bed, and comprising palladium, on an alumina support. In the reactor, the ester, in admixture with hydrogen at a hydrogen pressure in the range of about 14.8 to 28.6 bars (about 200 to 400 psig) is contacted with the catalyst at a temperature between 1000C to 1 750C and a rate within the range of about one to four liquid volumes of ester per volume of catalystgper hour (v/hr/v). Hydrogen and treated ester are withdrawn from the reactor, and unreacted hydrogen is separated from the treated ester at substantially the reactor pressure and recycled to the reactor.Treated ester is withdrawn from the separator, residual hydrogen is removed from the treated ester, and the decolorized ester product is ready for use as a plasticizer in resins.

The process of the invention is illustrated diagrammatically in the accompanying figure showing a preferred embodiment thereof.

With reference to the figure, an ester is introduced through a supply line 1 to a pump 2 where its pressure is raised to the desired reaction pressure. The reaction pressure is selected to maintain a hydrogen partial pressure in the reactor of at least 5 bar. The total reactor presssure may be in the range of 5 to 35.5 bar (60 to 500 psig), preferably 14.8 to 28.6 bar (200 to 400 psig). The ester is passed through a heater 3 where it is heated to an elevated temperature which is high enough to provide the desired reaction temperature within the range of 1000C to 1 500C in a reactor 4, into which the heated ester is introduced. Reactor 4 contains a catalyst comprising palladium on a suitable carrier, such as carbon or alumina pellets.A suitable heating fluid, e.g., steam, from a supply line 6 is introduced through a valve 7 to a heater 3 as required and as determined by a temperature controller 8 to supply heat for heating the ester charge material. Hydrogen for the reaction is introduced from a suitable source of supply of relatively high purity hydrogen through supply line 9 and control valves 11 and 12. Fresh hydrogen is supplied to the reactor 4 as required and at a rate determined by the combined action of a pressure controller 1 3 and a rate-of-flow controller 14. It is desirable to maintain a reasonably high concentration of hydrogen at the catalyst surface in order to maintain a reasonable reaction rate. The reactants are most likely presented to the active sites of the wetted catalyst from the liquid phase.As hydrogen pressure increases, the solubility of the hydrogen in the ester also increases, thus providing more hydrogen at the catalytic active sites. In any event, hydrogen transport has to proceed from the bulk gas phase to the liquid phase to the catalyst surface, and the rate of such transport is increased by an increase in hydrogen partial pressure. Operating at a minimum pressure of about 5, preferably 14.8, bars provides a sufficient hydrogen partial pressure to attain a satisfactory rate of reaction while avoiding the necessity of requiring such large volumetric flow rates of hydrogen gas as tj require an uneconomically large reaction vessel and associated equipment.The hydrogen pressure, however, should not be so high as to cause a significant amount of ring hydrogenation, which is favored by higher pressres. This factor and practical engineering and economic considerations warrant an upperlimit on the pressure of about 35.5, preferably 28.6 bars.

The ester undergoing decolorization treatment, preheated to the desired temperature, is mixed with hydrogen, suitably in a mole ratio of 1 mole of hydrogen for each mole of ester, and the ester and hydrogen mixture contacted with a bed of granular catalytic material. The ester and hydrogen mixture pass through the reactor wherein a mild catalytic hydrogenation reaction takes place effecting decolorization of the ester. The reactor may be operated in trickle flow such that the liquid ester trickles downwardly over the catalyst in the reactor or the reactor may be operated in a flooded condition with the mixture of ester and hydrogen passing either downwardly or upwardly through the catalyst bed. In some cases, excellent decolorization has been obtained by flowing the reactants upwardly through the catalyst mass.

Treated ester is withdrawn, together with unreacted hydrogen, from the reactor 4 through a flow line 1 5 and passed to a cooler 1 6 where it is cooled to a temperature below 1000C, preferably about 500 C, by cooling water supplied to a product cooler 16 through a flow line 17. The cooled product and unreacted hydrogen are passed to a high pressure separator 1 8 maintained at reactor pressure by control valve 19 responsive to pressure controller 20. Unreacted hydrogen separated from the treated ester is recycled to the reactor through a flow line 21 by means of a recycle compressor 22.

Treated ester product from the separator 18 is passed through a line 23, provided with a control valve 24 responsive to a liquid level controller 26, to a desorber 27 maintained at near-atmospheric pressure where hydrogen dissolved in the product at the reaction pressure existing in the high pressure separator 1 8 is released from the treated ester product. Hydrogen separated from the treated product in the desorber 27 is passed through a flow line 28 to a flare. The decolorized ester product is withdrawn from the desorber through product line 29 and pumped by a pump 30 to product storage facilities, not illustrated.

The effectiveness of the process of this invention for decolorizing certain esters will be evident from a consideration of the following examples.

Examples A number of test runs were made with phthalic esters commonly used as plasticizers for polyvinyl chloride In the following examples, various catalysts comprising palladium on alumina carriers of varied forms and surface areas were tested for their effectivensss in decolorizing the phthalic esters.

The standard reaction conditions and catalyst pretreatment conditions are as follows: Catalyst load: 40 ml, exponentially loaded Temperature: 1 500C Pressure: 14.8 bars (200 psig) of H2 Hydrogen flow: 1 50 ml Hdminute Esterfeed rate: 40-160 ml/hour The catalysts were prereduced according to the following sequence: Temperature: 1 500C Pressure: 28.6 bars (400 psig) of H2 Hydrogen flow: 1 50 ml H2/minute Time 4 hours The color index of the ester feed and decolorized products was determined in accordance with ASTM Method D-1209-69 (Reapproved 1974), Standard Test Method for Color of Clear Liquids (Platinum-Cobalt Scale).A Varian Cary 1 7 spectrophotometer, provided with a 100 mm light path ceil was used at the fixed wavelength of 455 mm. The reproducibility of the color number determination is +2 units. The spectrophotometer cell was carefully cleaned before each color determination was made and the accuracy of the measurements obtained was periodically determined by rechecking the calibration curve with the standard platinum-cobalt color solutions.

Whenever the.presence of suspended solid particles in the reaction substrate was suspected, filtration through a fine fritted glass filter was carried out in order to avoid erroneous results due to light scattering. The same procedure was applied to all reaction substrate and products, prior to their color determinations.

Example 1 Di-isodecyl phthalate (DIDP) having an ASTM Color Number of 32.5 was charged continuously to a trickle bed reactor where it was contacted with hydogen in the presence of a catalyst comprising 0.5% palladium on 8-14 mesh alumina (Al203) having a B.E.T. surface area of 300 m2/g, (Catalyst 1) under the standard reaction conditions set forth above.

Catalyst 1 Feed Elapsed Sample Volume (mI) Time (hr) Color No.

1 260 6.5 9.0 2 80 2.0 5.0 3 100 2.5 3.5 4 50 1.25 2.0 5 90 2.25 3.5 6 120 3.0 0 7 240 6.0 0 Totals 940 23.5 Example 2 Di-isodecyl phthalate (DIDP) having an ASTM Color Number of 113.5 was treated under the same reaction conditions and with the same catalyst charge as in Example 1 with the following results: Catalyst 1 Feed Elapsed Sample Volume (mI) Time (hr) Color No.

1 120 3.0 16.0 2 260 6.5 16.0 3 110 2.75 16.0 4 120 3.0 16.0 Totals 610 15.25 Example 3 Di-isooctyl phthalate (DOP) having an ASTM Color Number of 104.0 was treated under the same standard reaction conditions and with the same catalyst (Catalyst 1) as in Example 1. In this thirty six hour run, 720 ml of DOP were charged to the reactor at a feed rate of 20 ml/hour. The color numbers of various samples of treated DOP ranged from 21.5 to 23.5.

Examples 4--8 In the following examples, a series of runs were made on di-isodecyl phthalate (DIDP) having an ASTM Color Number of 45 using palladium on alumina catalysts comprising various forms of alumina supports and various metal loadings.

Example 4 36.8 g of 0.5% Pd on 3.175 mm alumina pellets, having a B.E.T. surface area of 8O7190.r2/g, (Catalyst 2) was charged to the trickle bed reactor of Example 1. The DIDP was treated with hydrogen under the conditions of Example 1 with the following results: Catalyst 2 Feed Elapsed Sample Volume (mlJ Time (hr) Color No 1 80 2 Discarded 2 240 6 1.5 3 120 3 3.5 4 160 1 7.0 Totals 600 12 Example 5 29.4 g of 0.5% (Pd on 1/8" alumina spheres having a B.E.T. surface area of 335 m2)g, (Catalyst 3) was charged to the reactor of Example 3 and the DIDP treated as in Example 4 with the following results: Catalyst 3 Feed Elapsed Sample Volume /m/) Time (her) Color No.

1 84 2.1 Discarded 2 76 1.9 Discarded 3 80 2 3.5 4 132 3.3 1.5 5 1 60 1 Discarded 6 160 1 9.0 Totals 692 11.3 Example 6 24.0 g of 0.5% Pd on 2.2 mm alumina extrudate having B.E.T. surface area of 250 m2/g, (Catalyst 4) was charged to the reactor of Example 4 and the DIDP treted as in Example 4 with the following results: Catalyst 4 Feed Elapsed Sample Volume (mi) Time (her) Color No.

1 80 2 Discarded 2 80 2 5.0 3 80 2 2.5 4 120 3 2.5 5 1 60 1 Discarded 6 160 1 6.0 Totals 680 11.0 Example 7 37.9 g of 0.3% Pd on 3.1 75 mm pellets, having a B.E.T surface area of 80-100 m2/g (Catalyst 5) was charged to the reactor of Example 4 and the DIDP treated as in Example 4 with the following results: Catalyst 5 Feed Elapsed Sample Volume (m/) Time (her) Color No.

1 80 2 Discarded 2 100 2.5 5.0 3 60 1.5 2.5 4 120 3 5.0 5 1 60 1 Discarded 6 160 1 10.5 Totals 680 11.0 Example 8 26.0 g of 0.3% Pd on 8.5 mm alumina spheres having a B.E.T. surface area of 85 m2/g (Catalyst 6) was charged to the reactor of Example 4 and the DIDP treated as in Example 4 with the following results: Catalyst 6 Feed Elapsed Sample Volume (mlJ Time (her) Color No.

1 80 2 Discarded 2 80 2 2.5 3 100 2.5 3.5 4 100 2.5 5.0 5 160 1 - 6 160 1 7.0 Totals 680 11.0 While the invention has been described in detail with respect to a specific preferred embodiment thereof, it will be appreciated that numerous alterations may be made thereto which will fall within the scope and spirit of the invention. For example, any suitable flow rate of reactants may be employed. A flow rate of liquid reactants of at least about one liquid volume of ester per hour per volume of catalyst provides an acceptable rate of reaction. Flow rates substantially in excess of about four liquid volumes of ester per hour per volume of catalyst may provide insufficient residence time of the reactants in contact with the catalyst. Generally, at temperatures much below 1000C the reaction rate is unacceptably slow, and at temperatures substantially in excess of about 1 750C less successful decolorization is attained, probably because of undesirable side reactions. Excellent results in terms of reaction rate and degree of decolorization are obtained at 1 500C, as illustrated in the examples set forth above. Accordingly, operation at about 1 500C or within about 200C of this temperature, i.e., about 1 400C to 1 600C, is preferred.

Claims

1. A continuous process for decolorizing an ester of an alcohol, having 7 to 10 carbon atoms and a dicarboxylic acid which comprises contacting the ester with hydrogen at a temperature from 100 to 1 750C and a hydrogen pressure from 5 to 35.5 bar (60 to 500 psig) in the presence of a catalyst comprising palladium on a solid carrier.

2. A process as claimed in Claim 1 wherein the ester is a phthalate.

3. A process as claimed in Claim 2 wherein the ester is di-isooctyl phthalate.

4. A process as claimed in Claim 2 wherein the ester is di-isononyl phthalate.

5. A process as claimed in Claim 2 wherein the ester is di-isodecyl phthalate.

6. A process as claimed in any preceding Claim wherein the hydrogen and ester are present in a mole ratio from 0.1 :1 to 10:1.

7. A process as claimed in Claim 6 wherein the mole ratio is about 1:1.

8. A process as claimed in any preceding Claim wherein the catalyst carrier is carbon or alumina.

9. A process as claimed in any preceding Claim wherein the carrier is in the form of pellets.

10. A process as claimed in any preceding Claim wherein the catalyst comprises a fixed bed.

11. A process as claimed in any preceding Claim wherein the hydrogen pressure is from 14.8 to

28.6 bar (200 to 400 psig).

12. A process as claimed in any preceding Claim wherein the liquid hourly space velocity of said ester is from 1 to 4 volumes of ester per volume of catalyst per hour.

1 3. A process as claimed in any preceding Claim wherein the average time of contact between the catalyst and ester is from 1 5 minutes to one hour.

14. A process as claimed in any preceding Claim wherein the temperature is from 1 400C to 1600C.

1 5. A process as claimed in Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 8.

1 6. Esters when decolorized by a process as claimed in any of the preceding Claims.