**Distillation of Natural Fatty Acids and Their Chemical Derivatives**

Steven C. Cermak, Roque L. Evangelista and James A. Kenar *National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture USA* 

#### **1. Introduction**

Well over 1,000 different fatty acids are known which are natural components of fats, oils (triacylglycerols), and other related compounds (Gunstone & Norris, 1983). These fatty acids can have different alkyl chain lengths (typically ten or more carbon atoms), 0-6 carbon-carbon double bonds posessing *cis*- or *trans*-geometry, and can contain a variety of functional groups along the alkyl chain (Gunstone et al., 2007b). Of these, there are approximately 20-25 fatty acids that occur widely in nature, are produced from commodity oils and fats, and find


Table 1. Fatty acid composition of selected fats and oils (Evangelista & Cermak, 2007; Knapp, 1993, O'Brien, 2004; Stauffer, 1996)

Distillation of Natural Fatty Acids and Their Chemical Derivatives 111

The fatty acid composition of fats and oils varies widely depending on the source (Table 1). Coconut and palm kernel oils contain high amounts of medium chain saturated fatty acids like lauric and myristic acids (Table 2). Palm, tallow and lard oils are high in longer saturated fatty acids (palmitic and stearic acids) and monounsaturated oleic acid. Canola, and sunflower oils are high in oleic acid while soybean oil has more linoleic acid. Rapeseed

The first step in fatty acid production (Fig. 1) is the splitting or hydrolysis of the triglyceride molecules of fats and oils in the presence of water to yield glycerine (10% yield) and a

Triglyceride Water Fatty Acids Glycerine

This can be done batch-wise using the Twitchell process (Ackelsberg, 1958; Twitchell, 1898) or continuously at high pressure and temperature like the Colgate-Emery process (Barnebey & Brown, 1948). Typically, the crude fatty acids obtained by the Colgate-Emery process are considerably lighter in color in comparison to those obtained by the Twitchell process. The degree of triglyceride hydrolysis is important as residual mono-, di-, triglycerides and free glycerol in the fatty acid prior to distillation will result in more distillation pot residue (Potts, 1956). The fatty acids from the fat splitting process are relatively dark in color and contain various impurities. The fatty acids are subsequently purified or separated into

Purification of fatty acids by distillation has been practiced for well over a hundred years and is still the most common and most efficient means of producing high purity fatty acids. Distillation removes both the low and high boiling impurities as well as odor substances. Distillation of fatty acids may be either batch or continous process, at atmospheric pressure or under reduced pressure. It may be simple distillation involving purification of mixed fatty acids or fractional distillation consisting of both purification and separation of fatty acids according to chain length (Gervajio, 2005; Muckerheide, 1952; Potts & White, 1953). Because of the inherent sensitivity of fatty acids toward heat, the distillation methods employed should be conducted at as low a temperature as practically and economically feasible while maintaining the shortest residence time of the fatty acid in the distillation unit. Today's, modern distillation units rely upon high vacuum, effective heating, short contact times, effective mass transfer

Fig. 1. Splitting or hydrolysis of fat or oil triglycerides to fatty acids and glycerine

RCOOH R'COOH R"COOH

+

CH2OH

CHOH

CH2OH

and crambe are good sources of long chain fatty acids like erucic acid.

mixture of fatty acids (96% yield), (Gunstone et al., 2007a).

+ 3 H2O

fractions by distillation and fractionation.

**2. Distillation methods used in fatty acid industry** 

between vapor and condensate, and steam economy (Lausberg et al., 2008).

CH2OCR

O

O

O

CHOCR'

CH2OCR"

major use for food and nutrition applications with the remainder being used by the oleochemical industry to produce soaps, detergents, personal care products, lubricants, paints, and more recently, biodiesel. Approximately 17 commodity fats and oils are obtained from various domesticated plants and animals. The largest vegetable oil sources are the oilseed crops (soybean, rapeseed, sunflower, and cottonseed) grown in relatively temperate climates. Another major oil source are oil-bearing trees (palm, coconut, and olive) grown in tropical or warm climates (O'Brien et al., 2000). The triglyceride-containing oils are extracted from oilseeds by mechanical pressing or by using solvent extraction (*n*-hexane). Seeds containing high oil contents are usually mechanically extracted first to reduce the oil content in the seed by 60% before solvent extraction. Animal fats are obtained by rendering inedible animal byproducts like fat trim, meat, viscera, bone, and blood, generated by slaughter houses and meat processing industry and mortalities on farms (Dijkstra & Segers, 2007; Hamilton et al., 2006). World fat and oil production in 1998 was 101 million tons, of which 14.2% (14.3 million tons) was used as basic oleochemicals (Hill, 2000). In 2009, the global production of fats and oils increased to 137.5 million tons with 21.2% (29.3 million tons) used for non-food industrial purposes (Gunstone, 2011). This growth was driven by the high petroleum prices as well as the growing demand for natural or renewable products (de Guzman, 2009).


Table 2. Nomenclature of selected fatty acids and their respective melting and boiling points. aGunstone et al., 2007b. bKnothe & Dunn, 2009. cBudde, 1968. dFarris, 1979. eEthyl ester. f Double bonds in the all *cis*- geometry.

major use for food and nutrition applications with the remainder being used by the oleochemical industry to produce soaps, detergents, personal care products, lubricants, paints, and more recently, biodiesel. Approximately 17 commodity fats and oils are obtained from various domesticated plants and animals. The largest vegetable oil sources are the oilseed crops (soybean, rapeseed, sunflower, and cottonseed) grown in relatively temperate climates. Another major oil source are oil-bearing trees (palm, coconut, and olive) grown in tropical or warm climates (O'Brien et al., 2000). The triglyceride-containing oils are extracted from oilseeds by mechanical pressing or by using solvent extraction (*n*-hexane). Seeds containing high oil contents are usually mechanically extracted first to reduce the oil content in the seed by 60% before solvent extraction. Animal fats are obtained by rendering inedible animal byproducts like fat trim, meat, viscera, bone, and blood, generated by slaughter houses and meat processing industry and mortalities on farms (Dijkstra & Segers, 2007; Hamilton et al., 2006). World fat and oil production in 1998 was 101 million tons, of which 14.2% (14.3 million tons) was used as basic oleochemicals (Hill, 2000). In 2009, the global production of fats and oils increased to 137.5 million tons with 21.2% (29.3 million tons) used for non-food industrial purposes (Gunstone, 2011). This growth was driven by the high petroleum prices as well as

(°C)

Ester

Boiling Pointc (°C/(10 mm Hg)

Acid Methyl

Ester

the growing demand for natural or renewable products (de Guzman, 2009).

Symbol Systematic Name Trivial Name Melting Pointa,b

Saturated fatty acids Acid Methyl

Unsaturated fatty acidsf

ester. f

10:0 decanoic capric 31.0 -13.5 150 108 12:0 dodecanoic lauric 44.8 4.3 173 133 14:0 tetradecanoic myristic 54.4 18.1 193 161 16:0 hexadecanoic palmitic 62.9 28.5 212 184 18:0 octadecanoic stearic 70.1 37.7 227 205 20:0 eicosanoic arachidic 76.1 46.4 248d 223d 22:0 docosanoic behenic 80.0 53.2 263 240 24:0 tetracosanoic lignoceric 84.2 58.6 --- 198(0.2)e

16:1 9-hexadecenoic palmitoleic 0.5 -34.1 180(1)a 182 18:1 9-octadecenoic oleic 16.3 -20.2 223 201 18:2 9,12-octadecadienoic linoleic -6.5 -43.1 224 200 18:3 9,12,15-octadecatrienoic linolenic -12.8 -52.4 225 202 20:1 9-eicosenoic gadoleic 23.0 --- 170(0.1)a 154(0.1)e 20:4 5,8,11,14-eicosatetraenoic arachidonic -49.5 --- 163(1)a 194(0.7)a 22:1 13-docosenoic erucic 33.5 -3.5 255 242

Table 2. Nomenclature of selected fatty acids and their respective melting and boiling points. aGunstone et al., 2007b. bKnothe & Dunn, 2009. cBudde, 1968. dFarris, 1979. eEthyl

Double bonds in the all *cis*- geometry.

The fatty acid composition of fats and oils varies widely depending on the source (Table 1). Coconut and palm kernel oils contain high amounts of medium chain saturated fatty acids like lauric and myristic acids (Table 2). Palm, tallow and lard oils are high in longer saturated fatty acids (palmitic and stearic acids) and monounsaturated oleic acid. Canola, and sunflower oils are high in oleic acid while soybean oil has more linoleic acid. Rapeseed and crambe are good sources of long chain fatty acids like erucic acid.

The first step in fatty acid production (Fig. 1) is the splitting or hydrolysis of the triglyceride molecules of fats and oils in the presence of water to yield glycerine (10% yield) and a mixture of fatty acids (96% yield), (Gunstone et al., 2007a).

Fig. 1. Splitting or hydrolysis of fat or oil triglycerides to fatty acids and glycerine

This can be done batch-wise using the Twitchell process (Ackelsberg, 1958; Twitchell, 1898) or continuously at high pressure and temperature like the Colgate-Emery process (Barnebey & Brown, 1948). Typically, the crude fatty acids obtained by the Colgate-Emery process are considerably lighter in color in comparison to those obtained by the Twitchell process. The degree of triglyceride hydrolysis is important as residual mono-, di-, triglycerides and free glycerol in the fatty acid prior to distillation will result in more distillation pot residue (Potts, 1956). The fatty acids from the fat splitting process are relatively dark in color and contain various impurities. The fatty acids are subsequently purified or separated into fractions by distillation and fractionation.
