Diacylglycerols are widely used in a variety of applications such as additives for improving plasticity of oils and fats, as well as edible oils in the food industry, and as a base material for the production of cosmetics and drugs. Generally, the preparation of such diacylglycerols involves an esterification reaction of glycerol with its corresponding fatty acid, an alcohol interchange reaction of glycerol with oil or fat, or the like, with the use of an alkali catalyst, or an enzyme such as a lipase, or the like. However, the use of an enzyme catalyst is preferable from the viewpoints of the yield and purity of the diacylglycerols synthesised and energy savings.
Japanese Patent Application No. 71495/1989 describes a lipase-catalysed reaction process that includes the reaction of a fatty acid or the like with glycerol in the presence of a 1,3-position selective lipase while removing water formed by the reaction outside the system to obtain a diacylglycerol at high yield and purity. The drawback of this process is that it is not able to investigate production conditions at an industrial level.
Japanese Patent Application No. 330289/1992 describes a process in which glycerol is added in an equimolar amount or more to a fatty acid to react. The reaction is stopped when the concentration of a diacylglycerol has been enhanced, insoluble glycerol is separated, and the reaction is further conducted while dehydrating, thereby synthesising diacylglycerol at a high esterification reaction rate by improving dehydration efficiency. This process involves technical difficulties such as necessity of stopping the reaction at the time the concentration of the diglyceride reaches a peak.
Japanese Patent Application No. 234391/1998 describes a process in which a mixture of a fatty acid or the like and glycerol or the like is reacted in a flow tube type reactor filled with a lipase while controlling the superficial velocity of the mixture in the reactor to at least 0.05 cm/s. This technique is easy to operate and can improve the reaction rate to some extent, but is insufficient in the purity of the resulting diglyceride and the industrial scale-up technique.
U.S. Pat. No. 6,361,980 describes a process for preparing diacylglycerol, which comprises of an enzyme-packed tower that includes an immobilised lipase preparation, carrying out an esterification reaction between: (1) an acyl group donor selected from the group consisting of a fatty acid, a lower alcohol ester thereof, and a mixture thereof; and (2) an acyl group acceptor selected from the group consisting of glycerol, a monoacylglycerol, and a mixture thereof; to obtain a reaction fluid from said enzyme-packed tower; reducing the water content or lower alcohol content in said reaction fluid; and subsequent to said reducing, recirculating the reaction fluid to said enzyme-packed tower, wherein a residence time of said reaction fluid in said enzyme-packed tower is 120 seconds or less; to obtain a diacylglycerol, wherein said reducing comprises dehydrating or de-alcoholising said reaction fluid is by feeding said reaction fluid though a spray nozzle, in a dehydration process. However, this process is costly as it requires the use of expensive purified fatty acids as raw material.
In view of the above, it would be advantageous to provide a process for producing a high-purity diacylglycerol at a high yield in a short period of time at an industrial level.