Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
2000-07-15
2002-03-12
Carr, Deborah D. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
C562S830000, C562S830000
Reexamination Certificate
active
06355817
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the catalyzed production of esters primarily from alcohols and carboxylic acids or anhydrides. More particularly, the present invention is directed to an improved process for preparing plasticizer esters for polyvinylchloride (PVC) such as phthalates, adipates and trimellitates in the presence of a titanium, zirconium, or tin-based organometallic catalyst. The current invention is also useful for preparing polyol esters.
BACKGROUND OF THE INVENTION
Esters are most commonly prepared by the reaction of a carboxylic acid and an alcohol accompanied by the elimination of water. Esters may also be formed by reaction of an alcohol with various other reactants including acid anhydrides, acid chlorides, amides, nitrites, ethers, aldehydes, and ketones.
The reaction conditions under which esterification is effected can be varied considerably. The reaction proceeds very slowly at room temperature, but quite rapidly at elevated temperatures. About 99% of the limiting reagent, e.g., acids, anhydrides, or polyols, can be converted to an ester within a few hours. Limiting reagents are typically reagents which are not present in stoichiometric excess, e.g., limiting reagents used to make plasticizers include diacids and phthalic anhydride and those used to make polyol esters are polyols.
Because the esterification of an alcohol and an organic acid or anhydride is a reversible reaction, the esterification reaction normally does not go to completion. However, conversions of over 99% can be achieved by removing at least one of the esterification products, typically water, by distillation. A variety of distillation techniques are known in the art to remove the produced water from the reaction zone. One method of water removal includes carrying out the reaction in a liquid medium which may form an azeotrope having a boiling point that is lower than that of either component of the reaction. If the resulting ester has a boiling point well above 100° C. at atmospheric pressure, then the reaction temperature can be adjusted such that no liquid medium capable of forming an azeotrope is required. Additionally, an entrainer may be used to aid in the distillation of the water from the reaction mixture. Inert materials such as benzene, toluene, or xylene may be used as an entrainer in the production of phthalate esters. In addition, the reactant having the lower boiling point has also been employed as the entrainer. In this latter case, the reactant used as the entrainer is charged into the reaction mixture in excess over the stoichiometric quantities required for the reaction. Esterification processes, including those employing water removal, may be conducted in a batch or continuous mode of operation. Various esterification processes are disclosed in Volume 9 of the
Kirk-Othmer Encyclopedia of Chemical Technology
, Fourth Edition (1994), pp. 762-768, the entirety of which is hereby incorporated by reference.
The batch esterification procedure includes charging all of the reactants into the reactor at the beginning of the reaction cycle. In catalytic esterification processes, the catalyst is typically added to the reaction mixture at the beginning of the reaction cycle after reaching a target temperature. The reaction mixture is then heated and reaction begins. The temperature of the reaction mixture rises until the boiling point of the reaction mixture is achieved, at which point the entrainer, if used, and water by-product boil out of the reaction mixture. Typically, the overhead vapors are condensed, the water separated from the entrainer, and the entrainer recycled to the reactor vessel. The reaction temperature, and, therefore, the rate of reaction, is partially determined by the boiling point of the reaction mixture. When the reactant with the lower boiling point is also used as the entrainer, its concentration is gradually reduced as the reaction proceeds. Thus the reaction temperature, and, therefore, the rate constant for the reaction, increases as the reaction proceeds.
One conventional process for forming plasticizer esters is disclosed in Great Britain Patent Specification No. 1,426,057 (Imperial Chemical Industries Limited), wherein plasticizer esters are prepared from phthalic anhydride and a C
4
to C
14
alkanol or mixture of such alkanols. For example, a mixture of phthalic anhydride and one or more of these alkanols may be heated gradually up to 180° to 260° C. in the presence of a titanium catalyst (e.g., titanium isopropoxide). When the temperature reaches 180° to 260° C., the esterification is substantially complete although the residual acidity is about 0.3 to 0.05 mg KOH/gram. Aqueous sodium carbonate solution is then slowly added to the ester product to provide 1 to 12 times the stoichiometric amount of alkali. When the temperature has fallen to 150° to 200° C. water or a dilute aqueous alkali solution is admitted and the excess alkanol is removed. By this treatment, the titanium catalyst is converted to titanium oxide and precipitated, and, thereafter, may be filtered off with excess sodium carbonate and the residual acidity is reduced to less than 0.05 mg KOH/gram.
Conventional esterification processes may be accomplished in two reaction steps. The first reaction step generally occurs in the absence of an esterification catalyst, while the second reaction step may include the use of an esterification catalyst. In U.S. Pat. No. 5,349,075 to van den Berg et al. a two step esterification process with a first uncatalyzed esterification reaction step conducted at a temperature of at least 200° C., followed by a catalyzed second esterification reaction step at a temperature below 100° C. is proposed. The process employs a solid acid catalyst in the second reaction step.
U.S. Pat. No. 4,795,824 to Kippax et al. proposes a two-step esterification process for the production of dialkyl maleate by reaction of maleic anhydride with an alkyl alcohol. In the first step, maleic anhydride is reacted with an alkyl alcohol to form a monoester in the absence of a catalyst. The second esterification reaction step reacts the monoester with alkyl alcohol in the presence of an esterification catalyst to form the di-ester.
In the Russian language journal Khim. Prom-st., Ser.: Proizvod. Pererab. Plastmass Sint. Smol (1981), (8), pages 19-21, di (2-ethylhexyl) phthalate production was reportedly investigated at temperature ranges from 170°-190° C., catalyst concentrations from 0 to 2.5% of the weight of phthalic anhydride, excess alcohol from 10 to 100%, and a vacuum in the range of 350-500 mm Hg (54.7-34.7 kPa). The reference concludes that the catalyst activity is almost two times higher when added at 180° C. as compared to 165° C. The reference proposes that it is best to conduct the esterification reaction in two stages to a depth of conversion of 60-70% without catalyst and then to add esterification catalyst (tetrabutoxytitanium) after the reaction conversion is 60-70%.
In the commercial production of plasticizer esters, e.g., phthalates, adipates, and trimellitates, conversions of greater than 99% are desired. For polyol esters, e.g., esters made from aliphatic acids and trimethyolpropane (i.e., the limiting reagent), the commercially desirable conversions are at greater than 98%. Typical product applications require conversions of about 98.5% of the original number of hydroxyl groups in the poly alcohol.
Most esterification processes are capable of converting about 99% of the limiting reagent, such as acids, anhydrides or polyols, to an ester within a few hours; however, after about 90% of the limiting reagent is converted, the rate of reaction tends to slow down substantially. It may take half as long again to convert the remaining 4-5% of limiting reagent as it took to convert the initial 95% thereof Since the chemical industry is continuously seeking to increase the rate of reaction, as well as the quality of the resultant esters, it would be quite desirable to develop a process which increases the overall rate of reaction, especially du
Jones Larry O.
Lo Pei-Yi
Woods David G.
Carr Deborah D.
Collins Douglas J.
ExxonMobil Chemical Patents Inc.
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