Читать книгу Biodiesel Technology and Applications - Группа авторов - Страница 18

Chemical homogenous catalysts include combination of base and acid catalysts. NaOH, KOH, and methoxides are the base catalysts while HCl and H₂SO₄ are the acid catalysts [39]. Acid catalysts are mostly used to overcome the problem of FFAs in the reaction system but the rate of trans esterification by acid catalyst is slower than alkaline or base catalysts [8]. Chemical catalytic processes either alkaline or acid catalysis both have several disadvantages. Alkaline catalysis provides high conversion of triacyl glycerol into the alkyl esters in a very short time but it has many drawbacks. Alkaline catalysis is very prone to FFA concentration (>2.5%) in the reaction system because high FFA concentration results in saponification reaction producing soaps and leads to loss in enzymatic activity and makes difficult to separate transesterification by-product, i.e., glycerol from bio-diesel. Hence, biodiesel yield decreases. Moreover, it needs high energy requirement [40]. To counter FFA problem, acid catalysts are used, e.g., sulfuric acid but it also causes some technical problems regarding separation and purification of glycerol. Moreover, acid catalysis is a slow process compared to alkaline process. Reactors, pipelines, and other equipment are badly affected by acid catalysts because of their corrosive nature that can increase the cost of biodiesel production [41].