| Biodiesel is a clean and renewable energy.The clean and efficient production of biodiesel is the key to commercial applications of biodiesel.The method of enzymatic biodiesel production is clean and environment friendly.For the enzymatic production of biodiesel,it needs to resolve the problems of the inhibition of enzyme activity by the reactant methanol and the byproduct glycerol,slow reaction rate and enzyme's adaptability to waste oil.Both the drip-feeding of methanol and the immediate removal of glycerol can decrease inhibition to the enzyme,but also overcome the limit of reaction equilibrium and promote the reaction.The construction of the device and system which combined enzymatic synthesis of biodiesel,the drip-feeding of methanol and the immediate removal of glycerol and the optimization of operational conditions were conductive to promoting industrial application of enzymatic method.Firstly,the synthesis of biodiesel catalyzed by Novozym435 immobilized lipase was operated and studied based on the shaking table test method.The influences of the dropping speed of methanol,water content,reaction stages and reaction temperature on the yield of biodiesel were examined.Furthermore,the fixed bed reactor and the system which combined enzymatic synthesis of biodiesel,the drip-feeding of methanol and the immediate removal of glycerol were developed and studied.In the fixed bed reactor,the Novozym435 immobilized lipase was used as catalyst,soybean oil as raw material,the influence of dropping speed of methanol,the circulation speed of the materials,temperature,alcohol oil ratio,immediate removal of glycerol on the yield of biodiesel were investigated.The highest biodiesel yield of 98.75%was obtained when the dropping speed of methanol is 2.66×10-4 g methanol/(g oil·min),the circulation speed of the materials is 6.45 g oil/min,temperature is 60?,alcohol oil ratio is 6:1,reaction time is 560 min.The reused times of the immobilized lipase is more than 26 times.The adaptability and tolerability of the immobilized lipase to waste oil and the impact of the acid value of raw material on the enzymatic efficiency were studied.The mixture of soybean oil and oleic acid,waste oil with the acid value 124 mg KOH/g oil were used as reactant respectively.The result shows that the Novozym435 immobilized lipase can catalyze the transesterification of glycerides and the esterification of fatty acids.Glycerides in raw material has little impact on the esterification of fatty acids,but the presence of fatty acids would strongly affect the transesterification of glycerides.When the content of fatty acid in raw material is 50%,the reaction rate reduced 1/2.The process of biodiesel production which combined the pre-esterification of waste oil with glycerol and the enzymatic transesterification was constructed.The pre-esterification of waste oil with glycerol was used to reduce the acid value,by which the acid value of waste oil could dropped to 2.65 mg KOH/g oil from 124 mg KOH/g oil.The glycerides in waste oil was converted to biodiesel by enzymatic transesterification in the fixed-bed reactor,and the biodiesel yield can reach 98.78%when reaction time was 1185 min.The byproduct glycerol which was generated from the transesterification process can be reused in pre-esterification of waste oil.When Novozym435 immobilized lipase was used to catalyze waste oil for biodiesel production,it had shorter life-time because of the complex composition and high impurity content of waste oil.After six-time recycling,enzyme's catalytic efficiency decreased,biodiesel yield decreased to 95.4%,and after eight-time recycling,the biodiesel yield is only 65.67%. |
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