Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
1998-03-05
2001-06-05
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...
C554S191000, C554S195000, C568S903000, C568S913000, C560S265000
Reexamination Certificate
active
06242620
ABSTRACT:
BACKGROUND OF THE INVENTION
Fatty alcohols, i.e., predominantly linear, monohydric primary alcohols containing at least 8 carbon atoms, are important raw materials for the production of a number of products, for example, emulsifiers or surfactants. Fatty alcohols can be manufactured by catalytic high-pressure hydrogenation of fatty acid esters, preferably methyl esters. Typically, distilled methyl esters are passed in liquid form, together with a large excess of hydrogen, over fixedly arranged copper-containing mixed oxide catalysts, such as copper/zinc catalysts for example, at temperatures above 200° C. and under pressures of around 250 to 300 bar. Fatty acid esters are used instead of fatty acids in order to protect the catalysts against attack by the free carboxyl groups. The process is described in detail in U.S. Pat. No. 5,180,858, the entire contents of which are incorporated herein by reference.
Carboxylic acid esters suitable for conversion to the corresponding alcohols via catalytic hydrogenation must contain little or no sulfur-containing compounds or metallic soaps such as sodium, potassium, and calcium in order not to poison the hydrogenation catalyst. Carboxylic acid esters, particularly fatty acid methyl esters used in the production of alcohols such as fatty alcohols prepared from the corresponding carboxylic acid and an alcohol using a sulfur-containing catalyst such as para-toluene sulfonic acid and subsequently treated with a base such as KOH to remove harmful and unwanted contaminants are particularly susceptible to sulfur- and soap contamination. In order to be able to use these esters for hydrogenation to the corresponding alcohols, the ester would have to at least be washed with water or, more typically, distilled to bring the amount of sulfur-containing compounds and soaps to acceptable levels.
SUMMARY OF THE INVENTION
In its broadest aspect, the invention relates to a process for removing sulfur and soap contaminants from carboxylic acid esters. This process comprises contacting a carboxylic acid ester with an aqueous base such as aqueous potassium or sodium hydroxide at a temperature of from about 225° F. to about 280° F. Any water present is then removed and the dried crude ester is contacted with an absorbent such as silica gel or hydro-silica gel. The absorbent is then removed and the resulting purified ester contains little or no detectable sulfur and/or soap contamination.
Another aspect of the present invention relates to a process for making carboxylic acid esters containing little or no detectable sulfur and/or soap contamination. This process is particularly useful in instances where there are sulfur-containing contaminants present in the ester such as when a sulfur-containing catalyst is used in a direct esterification reaction. For example, when a carboxylic acid such as a fatty acid and a low molecular weight alcohol such as C
1-4
alkanol are reacted in the presence of a sulfur-containing acid catalyst such as para-toluene sulfonic acid, the crude ester thus formed may contain sulfur contaminants. After the reaction has been completed, the crude ester is heated in the presence of an aqueous base such as aqueous sodium or potassium hydroxide to a temperature of from about 225° F. to about 280° F. Any water present is then removed and the dried crude ester is then slurried with an absorbent such as silica gel or hydro-silica gel. The absorbent is then removed.
Yet another aspect of the invention relates to a method of making alcohols using carboxylic acid esters prepared as described above. The method comprises contacting a carboxylic acid ester with hydrogen at a temperature of from about 200 to about 250° C. and under a pressure of from about 200 to about 250 bar in the presence of a catalyst-effective amount of a hydrogenation catalyst such as a copper-zinc catalyst as described in detail in U.S. Pat. No. 5,180,858.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Not Applicable.
DETAILED DESCRIPTION OF THE INVENTION
For purposes of this invention, the term carboxylic acid includes mono- and dicarboxylic acids. The term soap refers to metallic salts of fatty acids having from 6 to 36 carbon atoms such as the sodium, potassium, and calcium salts.
According to one aspect of the present invention, sulfur and soap contaminants can be removed from a carboxylic acid ester by contacting the ester with an aqueous base such as aqueous sodium or potassium hydroxide at a temperature of from about 225° F. to about 280° F. Any water present is removed simultaneously and the dried crude ester is then contacted with an absorbent such as silica gel or hydro-silica gel. The absorbent is then removed and the resulting ester contains little or no detectable sulfur and/or soap contamination. The amount of soap in an ester is reflected in the metal content which can be determined by atomic absorption spectroscopy. The type of soap contamination in an ester will depend upon the nature of the base used to treat the crude ester in the first step of the process according to the invention. Therefore, for example, if KOH is used, potassium soaps will be the contaminant in the purified ester and the amount of soap will be reflected by the amount of potassium. If NaOH is used, sodium soaps will be the contaminant and the amount of soap will be reflected by the amount of sodium.
The first step of the process comprises contacting a carboxylic acid ester with an aqueous base at a temperature of from about 225° F. to about 280° F. Any carboxylic acid ester can be used in the process according to the invention. Any ester made by reacting a saturated or unsaturated aliphatic carboxylic acid, a saturated or unsaturated aliphatic dicarboxylic acid, an aromatic carboxylic acid or an aromatic dicarboxylic acid with a saturated or unsaturated aliphatic alcohol or aromatic alcohol can be used. The process is most useful in the preparation of alkyl esters of saturated and unsaturated carboxylic acids having from 6 to 36 carbon atoms and mixtures of such saturated and unsaturated carboxylic acids. While the alkyl portion of the ester can be any alkyl group having from 1 to 22 carbon atoms, the preferred alkyl groups are those having from 1 to 4 carbon atoms. Thus, the preferred esters are methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, and tert-butyl esters of saturated and unsaturated carboxylic acids having from 6 to 36 carbon atoms. The process is particularly applicable to methyl esters of fatty acids such as methyl oleate, methyl isostearate or the dimethyl ester of C
36
dimer acid which are subsequently converted to the corresponding fatty alcohols by catalytic hydrogenation since these esters must contain a minimum of sulfur-containing compounds and soaps which, if present, are highly likely to poison the hydrogenation catalyst.
The base present in the aqueous base solution can be any alkali metal hydroxide or alkaline earth metal hydroxide such as KOH, NaOH, Ca(OH)
2
, and the like. Preferred bases are NaOH and KOH with the most preferred being KOH. The most preferred aqueous base is 45% aqueous KOH. The amount of the base can be in the range of from about 0.05% to about 0.25% of active or dry base based on the weight of ester.
The aqueous base is mixed with the ester beginning at ambient temperature and the mixture is heated to a temperature of from about 225° F. to about 280° F. with the preferred range being from 225° F. to about 235° F. The time that the mixture remains in the temperature range of from about 225° F. to about 280° F. is not critical as long as the mixture achieves a temperature of at least 225° F. During the heat-up period, most of any water present is removed via distillation. The pressure above the mixture can be decreased, if desired, to facilitate the water removal. The dried ester is cooled to a temperature of less than about 200° F. and then contacted with an absorbent such as silica gel or hydro-silica gel. Typically, the hot, dried ester is stirred together with the absorbent. The absorbent can remain in contact with the ester f
Blewett C. William
Elsasser A. Fred
White Charles M.
Carr Deborah D.
Drach John E.
Henkel Corporation
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