Schwarzer and Gutsche (2005) described a process for preparing citrostadienol — free phytosterols. The patented invention relates to a process for the production of phytosterols by alkali-catalyzed transesterification of DD, neutralization of the catalyst and removal of the unreacted alcohol. The phytosterols are crystallized in hydrocarbon by lowering the temperature, optionally after the addition of an adequate quantity of aqueous methanol, and are then removed and purified by filtration, washing and drying. The resulting products have a citrostadienol content of less than 0.5%.

Pan et al. (2005) described a method to separate phytosterol and synthesize vitamin E succinate (VES) from rapeseed oil deodorizer distillate (RSDD). The RSDD was esterified with methanol in the presence of sulfuric acid and further cooled to room temperature. After storage at -3°C for 12 h, the esterified RSDD was centrifuged and the precipitate was separated as raw sterols (wet cake). The filtrate was used as the raw material to synthesize VES. The content and total recovery of phytosterol was above 85% and 80%, respectively, after the first crystallization and 95% and 45%, respectively, after the second crystallization.

Isolation of tocopherol succinates from sterol-removed, succinated DD mixture by crystallization was investigated by Lin et al. (2007). Membrane technology was also evaluated for its effectiveness to separate tocopherol succinates from mixtures containing sterols and tocopherols. Crystallization was conducted at low temperature with different solvents, including hexane, petroleum ether and a mixture of acetone and methanol (4:1, v/v). The crystallization results showed that recovery of tocopherol succinates from the cake fraction was poor with all solvents tested, with less than 10% of original tocopherol succinates in the raw material being crystallized under conditions employed. Among the solvents tested, hexane was better for the recovery of non-a-tocopherol succinates in the cake fraction. Furthermore, a high property of FFA was co-crystallized along with tocopherol succinates for all solvents used, leading to tocopherol succinates contents in the cake fractions lower than that in the raw material. Two nanofiltration membranes (DS-7 and AP01) were also examined using hexane or petroleum ether as a solvent. The recovery of tocopherol succinates was over 60%. However, their concentration was increased only by 6%. A combined process was then evaluated which include crystallization before succinylation, succinylation, first-stage membrane separation and second-stage membrane separation. The final tocopherols concentration derived from this combined process was as much as that of the original DD.

De Areal Rothes and Verhe (2005) developed a process where acid esterification was applied to corn oil deodorizer distillate (CoDD) in order to increase the ratio of free/esterified sterols that influenced the yield of crystallization. The sterol fraction was further isolated from the FAME by dry fractionation (crystallization). However, more research is required in order to obtain high-purity compounds.