▁mix ▁of ▁mon o - alk yl ▁est ers ▁of ▁long ▁chain ▁fat ty ▁ac ids . ▁The ▁most ▁common ▁form ▁uses ▁m eth an ol ▁( convert ed ▁to ▁sod ium ▁m eth ox ide ) ▁to ▁produce ▁m eth yl ▁est ers ▁( comm only ▁referred ▁to ▁as ▁F at ty ▁Ac id ▁M eth yl ▁E ster ▁– ▁FA ME ) ▁as ▁it ▁is ▁the ▁che apest ▁alco hol ▁available , ▁though ▁eth an ol ▁can ▁be ▁used ▁to ▁produce ▁an ▁eth yl ▁est er ▁( comm only ▁referred ▁to ▁as ▁F at ty ▁Ac id ▁Eth yl ▁E ster ▁– ▁FA EE ) ▁b iod ies el ▁and ▁higher ▁alco h ols ▁such ▁as ▁is op rop an ol ▁and ▁but an ol ▁have ▁also ▁been ▁used . ▁Using ▁alco h ols ▁of ▁higher ▁mole cular ▁weights ▁impro ves ▁the ▁cold ▁flow ▁properties ▁of ▁the ▁resulting ▁est er , ▁at ▁the ▁cost ▁of ▁a ▁less ▁efficient ▁trans ester ification ▁reaction . ▁A ▁li pid ▁trans ester ification ▁production ▁process ▁is ▁used ▁to ▁convert ▁the ▁base ▁oil ▁to ▁the ▁desired ▁est ers . ▁Any ▁free ▁fat ty ▁ac ids ▁( FF As ) ▁in ▁the ▁base ▁oil ▁are ▁either ▁converted ▁to ▁soap ▁and ▁removed ▁from ▁the ▁process , ▁or ▁they ▁are ▁est er ified ▁( y ield ing ▁more ▁b iod ies el ) ▁using ▁an ▁acid ic ▁catal yst . ▁After ▁this ▁processing , ▁unlike ▁straight ▁veget able ▁oil , ▁b iod ies el ▁has ▁comb ust ion ▁properties