Biodiesel production with enhanced alkanol recovery
Processes for making biodiesel are improved by fast, vapor fractionating a crude biodiesel containing alkyl ester, lower alkanol and a catalytically effective amount of base catalyst to obtain a lower alkanol fraction having a low content of water without undue loss of alkyl ester despite the presence of active catalyst.
1 . A process for recovering lower alkanol from a crude biodiesel containing alkyl esters of fatty acids, lower alkanol, and a catalytically effective amount of base catalyst, comprising subjecting the crude biodiesel that contains less than about 0.5 mass percent water to fast, vapor fractionation conditions to provide a lower boiling fraction containing lower alkanol.
2 . The process of claim 2 wherein the lower alkanol is at least one of methanol, ethanol and isopropanol.
3 . The process of claim 1 wherein the lower alkanol is methanol and the vapor fractionation conditions comprise a maximum temperature of less than about 120° C.
4 . The process of claim 3 wherein the vapor fractionation is effected by falling film evaporation.
5 . The process of claim 1 wherein the vapor fractionation is effected by falling film evaporation.
6 . A process for making biodiesel comprising:
a. contacting a glyceride-containing feed and lower alkanol under transesterification conditions comprising the presence of a base catalyst, wherein the molar ratio of lower alkanol to glyceride is at least about 3.15:1 to provide a crude biodiesel containing alkyl esters of fatty acids, glycerin, lower alkanol, base catalyst, and less than about 0.1 mass percent water, said contacting being for a time sufficient to convert at least about 90 mass percent of the glycerides in the glyceride-containing feed;
b. separating by phase separation said crude biodiesel to provide a heavier glycerin-containing layer and a lighter alkyl ester-containing layer, wherein a portion of the water and a portion of the base catalyst are contained in each of the heavier and lighter layer;
c. subjecting the lighter layer while it contains a catalytically effective amount of base catalyst to vapor fractionation conditions to provide a lower boiling fraction containing lower alkanol and a higher boiling fraction containing alkyl esters and base catalyst;
d. recycling at least a portion of the lower boiling fraction to step (a) as a portion of the lower alkanol; and
e. contacting the higher boiling fraction with an aqueous acid solution in an amount sufficient to at least neutralize the base catalyst.
7 . The process of claim 6 wherein step (a) comprises using at least two sequential reaction zones with an intermediate phase separation to remove a heavier, glycerin-containing layer.
8 . The process of claim 7 wherein the lower boiling fraction of step (c) is recycled per step (d) without separation of water.
9 . The process of claim 8 wherein the lower alkanol is methanol.
10 . The process of claim 9 wherein the vapor fractionation is effected by falling film evaporation.
11 . An apparatus for conducting the process of claim 9 .
12 . The apparatus of claim 11 in which a falling film evaporator is used to effect step (c).
13 . The apparatus of claim 12 in which the falling film evaporator has tubes of an average diameter of between about 2 and 10 centimeters and a length of at least one meter.
14 . A process for making biodiesel comprising:
a. contacting a glyceride-containing feed and lower alkanol under transesterification conditions comprising the presence of a base catalyst, wherein the molar ratio of lower alkanol to glyceride is at least about 3.15:1 to provide an intermediate containing alkyl esters of fatty acids, glycerin, lower alkanol, base catalyst, and less than about 0.1 mass percent water, said contacting being for a time sufficient to convert at least about 90 mass percent of the glycerides in the glyceride-containing feed;
b. separating by phase separation said intermediate to provide a heavier glycerin-containing layer and an intermediate lighter alkyl ester-containing layer, wherein a portion of the water and a portion of the base catalyst are contained in each of the heavier and lighter layer; and
c. contacting the intermediate and lower alkanol wherein the molar ratio of alkanol to glyceride in the intermediate is at least about 3.15:1 under transesterification conditions comprising the presence of a base catalyst for a time sufficient to convert at least 98 mass percent of the glycerides in the glyceride-containing feed and provide a crude biodiesel product.
15 . The process of claim 14 wherein the crude biodiesel product is subjected, while it contains a catalytically effective amount of base catalyst, to vapor fractionation conditions to provide a lower boiling fraction containing lower alkanol and a higher boiling fraction containing alkyl esters and base catalyst.
16 . The process of claim 14 wherein the crude biodiesel product is substantially single phase.
17 . The process of claim 14 wherein step (c) is conducted in a plug flow reactor.
18 . The process of claim 14 wherein the lower alkanol is methanol.