Atalysts, normally robust acids for example hydrochloric acid, phosphoric acid, or sulfuric acid, are far more favorable when the starting raw materials are rubber seed oils, waste cooking oils, and tobacco oils, which have a higher FFA content because they inhibit the soap formation in the course of the reaction. The level of sulfuric acid catalyst varied from 0.three to 2 . These percentages are determined by the oil volume employed for the reaction of acid esterification, and the level of catalyst impacts the method yield [52]. On the other hand, the water content material of raw supplies impacts the activity of acid catalysts. In the event the water concentration is five wt. , the reaction is entirely stopped. Mainly, Br sted acid and Lewis acid, as homogeneous acid catalysts, were utilised for the transesterification process (Figure 2).Catalysts 2021, 11,reaction. The level of sulfuric acid catalyst varied from 0.3 to two . These percentages are according to the oil volume employed for the reaction of acid esterification, plus the level of catalyst impacts the method yield [52]. On the other hand, the water content material of raw materials impacts the activity of acid catalysts. If the water concentration is 5 wt. , the reaction is of 24 completely stopped. Mostly, Br sted acid and Lewis acid, as homogeneous6acid catalysts, had been applied for the transesterification process (Figure 2).Phosphoric acid Liquid Br sted acids Sulfuric acid Hydrochloric acid Homogeneous acid catalysts BF3 TiCl4 Liquid Lewis acids HFCl4 2THF Sc(OTf)3 OthersFigure 2. Classification of homogeneous acid catalysts for biodiesel production.Figure 2. Classification of homogeneous acid catalysts for biodiesel production. Br sted AcidBr sted Acid acid catalysts are regularly utilized for direct esterification [53]. In Br sted Br stedacid, the sulfuric acid (H2 SO4are often used forof option in business. In[53]. In Br sted Br sted acid catalysts ) seems to become the catalyst direct esterification industrial processes, H2 SO4 is usedSO4a catalystto be the catalyst of decision in sector. In industrial acid, the sulfuric acid (H2 as ) appears for Bevantolol Biological Activity organic synthesis. Br sted acids, like sulfonic acid and sulfuric acids, are typically utilised to catalyze the transesterification reaction processes, H2SO4 is utilized as a catalyst for organic synthesis. Br sted acids, like sulfonic as a way to supply a higher biodiesel yield [51]. By utilizing this sort of homogeneous acid acid and sulfuric acids, production was 90 inside 15 minthe transesterification reaction in are generally utilised to catalyze below harsh conditions, such catalysts, the biodiesel order to supply a higher biodieselpressure and 1.7 wt. H2 SO4 . Side reactions, such as cataas a 240 C temperature, 70 bar yield [51]. By utilizing this sort of homogeneous acid lysts, the biodiesel production was 90 withinsuch harsh conditions [54]. Hydrochloric as a dehydration of alcohol, were also observed below 15 min beneath harsh circumstances, such 240 (HCl), polyphosphoricpressure and 1.7sulfonicH2SO4and mixtures of these catalysts acid temperature, 70 bar acid, soluble aryl wt. acids . Side reactions, which include dehydrawere also employed as homogeneous acid catalysts for the transesterification Hydrochloric tion of alcohol, were also observed beneath such harsh circumstances [54]. course of action. Even acid if esterification was an extremely old reaction, new homogeneous acid catalysts had been required, which targeted the following targets. Initially, equimolar amounts of alcohol and FFA have been used to perform the reaction, rather of an SS-208 Biological Activity excess of one particular or both.