Biodiesel production from tannery fleshings: Feedstock pretreatment and process modeling

Abstract

During raw hide processing, tanning industries generate large quantities of wastes containing a considerable amount of fat which can be converted into biodiesel. A typical representative of such wastes is fleshings – which however, usually contains a significant amount of free fatty acids, proteins and other impurities. Pretreatment was suggested as a means of processing this acidic feedstock, thereby enabling the reduction of the free fatty acid content under the limit value of 0.5% w/w when the alkali catalyst is then appropriate for transesterification. The feedstock pretreatment process involved the refining melting of fresh pigskin fleshings with subsequent extraction using a methanol or methanol solution with an equimolar amount of alkali i.e. tetramethylammonium hydroxide, isopropylamine and cyclohexylamine. A mathematical model of the pretreatment process was proposed, verified and used in further simulation calculations – which confirmed that deacidification employing methanolic alkali solutions is more efficient than pretreatment with pure methanol; in addition, the free fatty acids can be removed to the demanded level in just one step (fat initial acid value=20mgKOH/g, mass ratio of methanol to oil=1.5). The fat pretreated by the suggested procedure was used for alkali catalyzed transesterification. The prepared biodiesel met most of the EN 14214 requirements with respect to the limitations caused by the used fleshings fatty acid profile.