PREPARATION AND PROPERTIES OF LINOLEATE ESTERS OF SUCROSE E. G . B O B A L E K , A . P . D E M E N D O Z A , A . G . C A U S A , W . J. C O L L I N G S , A N D G E O R G E K A P O Case Institute of Technology, Cleveland 6, Ohio
A pilot plant process i s described for production of sucrose esters by catalytic transesterification between the methyl esters of fatty acids and sucrose in dimethylformamide solvent. The process can be controlled to accomplish degrees of esterification from 1 to about 7, based upon the hydroxyl equivalents per mole of sucrose. Superior drying oil qualities develop at degrees of esterification exceeding 4, if the iodine value of the fatty acids exceeds about 140 and all unreacted methyl esters are removed by solvent extraction or adsorption on silica gel. In further chemical modification of these purified esters to produce more complex vehicles for paints and printing inks, either the hydroxyl or the olefinic reactive functions can be utilized. Examples are given where these products are converted to emulsions, urethane polymers, and styrenated oils.
WRING
the past several years, considerable work has been
D done and some has been published (5, 8,74, 76, 77, 24) regarding synthesis of sucrose oils through transesterification of sucrose and methyl esters of vegetable oil fatty acid mixtures which contain substantial quantities of octadecadienoic acids. Most of this work has been done on a laboratory bench i n batches of 0.5 liter or less. These studies showed that the process was feasible in principle, even though the control was difficult. The products obtained from successful synthesis were examined as drying oil vehicles for paints, inks, and other purposes. Rather low grade fatty acid mixtures which gave poor performance in natural or synthetic triglyceride drying oil showed superior performance in sucrose esters. Because the costs of both sucrose and fatty acids are low, these sucrose esters promised to be attractive products if the manufacture could be scaled up in an economical process. Further development of sucrose oils depends to a large extent upon success in controlling the manufacturing process on a larger scale. For several years, the possibility of doing so was in considerable doubt. Many earlier attempts to scale up flask batches to pilot plant Lvere unsuccessful because of poor control of several critical variables. This paper reports some procedures which have been successful in pilot plant production of esters having a degree of esterification between 2 and 7. Procedures have been reported (4, 8, 77, 24) for making monoesters. I t is difficult to prepare a product which is nearly all octaester. However, esterification degree between 6 and 7 can be handled nicely. The iodine value and type of fatty acids used can be varied over a considerable range to get oils having variable drying properties. The reaction rate of ester synthesis is not affected significantly by \,arying the composition of fatty acids. Sucrose oils show drying properties equivalent or superior to those of alkali-refined natural linseed oil at degrees of esterification of 4 \vhen the fatty acids have an iodine value of a t least 140. The original color of these oils is about 8 on the Gardner color scale commonly used in the paint and varnish industry ( 9 ) . The color of the final oil depends largely on the original color of the fatty acids used and the care that is taken with the
process. The character of the products and test methods for their characterization have been reviewed by Chiang ( 5 ) and reported in part by Bobalek, Walsh, Chiang, and Hall (3,9 ) . None of these earlier workers, however. reported on the pilot plant scale process. Hence, this paper considers the process of ester synthesis in some detail and presents ne\\ data to illustrate the use of sucrose oils as intermediates for more complicated polymers, particularly st)-renated oils and urethane oils. The more ordinary usages as drying oils have been reported by Chiang (5) and Hall ( 9 ) . Pilot Plant Equipment
The reactor, A (Figure l ) , consists of a 10-gallon electrically heated Type 316 stainless steel kettle with two ring heaters (600 watts) on the bottom and three bands of curved strip heaters mounted horizontally around the walls (1600, 2600, and 3600 watts). A temperature controller activates all the heaters, and three manual switches are installed on the side bands, alloiving zones to be heated separately. The reactor
a-
J
section
A
Section B
Figure 1. VOL. 2
Flowsheet NO.
1
M A R C H 1963
9
Figure 2.
also has a steam coil 1.4 sq. feet in surface area, which enters the bottom of the reactor loops twice midway between agitator and wall and comes out of the side. This coil can hold 140p.s.i.g. steam. The same coil is used for cooling. after switchover from process steam to water. The rectification column consists of a 3-inch, Type 316. stainless steel pipe, with a 4-inch jacket. The pipe is packed to a 5-foot height with '/Z-inch chemical-ceramic, Berl-type saddles. The rectification column is equipped with a cold finger condenser fitted a t the top, having about 0.4 sq. foot of area. The water-cooled condenser has an area of about 4 sq. feet. T h e agitator is a six-bladed, turbine impeller of 5-inch diameter. Three d/d-inch baffles are mounted vertically on the inner walls about 120' apart to promote agitation efficiency. The agitator is driven by a n infinitely variable, hydraulic drive with a 3 to 1 belt ratio (which provides up to 600 r.p.m. a t the shaft). A fine-mesh foam breaker is installed a t the liquid level on the agitator shaft. The decanter for the condenser effluent has an upper and lower section, the upper serving as a vent bottle for operation a t atmospheric pressure, or as a trap for vacuum operation. The lower section is arranged so that solvent can overflow continuously back to the reactor when it is filled to the drain level. Piping is arranged so that either the upper or lower layer of these immiscible fluids may be returned to the reactor or withdrawn. Inert gas is introduced from a cylinder through a rotameter on the side of the reactor. Thermocouples to activate a controller are located on the bottom heaters. Additional control and on-off switches are associated with the side heaters. Distillation units ( B and C, Figure 1) are used for D M F and methanol distillation, respectively. Actually, the same unit, A , is used for all three operations; but the rectification column is not used during all distillations. The cold finger condenser area provides the additional reflux efficiency required to reflux all dimethylformamide in the esterification stage of the process with minimum retention of methanol. The product (D,Figure 1) is extracted or purified with a Scheibel column (Figure 2) which has 10 interface stages (20, 27). Laboratory experiments have shown that the lower the temperature, the better is the efficiency. The cooling system (Figure 2) consists of a pair of heat exchangers that cool the materials (methanol and the product) to about 8' C. before they leave the storage tanks. During the extraction, the temperature of the materials in the column can rise to 27' C. The column is also equipped with a variable drive agitator and with storage tanks for the extract and raffinate. The operation is controlled automatically. 10
l&EC P R O D U C T RESEARCH A N D DEVELOPMENT
Scheibel column
Pretreatment of Reagents
All the materials must be dried to contain less than 0.1% water. Very small amounts of water retard the reaction and promote decomposition of the solvent, the sugar, and the product. Although there was less than 0,027G \
