Now biodiesel is commonly produced by using basic catalysts,
such as sodium or potassium hydroxides, since these catalysts give
high yield in short reaction times. However, in the case of oils with
high contents of free fatty acids (FFAs), such as microalgal oils,
alkaline catalysis presents some problems due to the formation of
soaps, which decreases the biodiesel yield and increases the purification
costs. Acid catalysts transform both FFAs and acylglycerols
into methyl esters (5). However, the reaction velocity of transesterification
with an acid-catalyst is much slower than with an
alkaline one and more methanol is required (6). In addition, acid
catalysts are highly corrosive and so are seldom used on an industrial
scale.
Lipases also catalyse the transformation of both FFAs and acylglycerols
to methyl esters, but at lower temperatures than in
alkaline and acid catalysis (3040C). Moreover, the purification of
biodiesel is easier, cheaper and entails a lower consumption of
water, because neither alkalis nor acids need to be separated, only
the excess of alcohol and the glycerol. This glycerol is also easily
recuperated at a high degree of purity (without mixing with alkalis
or acids), and it can be used in nobler applications. On the other
hand, if the lipase is immobilized, the separation of the reaction
mixture and the catalyst is straightforward. Many works on the
enzymatic production of biodiesel have studied the effect of
methanol on the stability of the lipase, because when methanol
exceeds the solubility limit in the reaction mixture the lipase is
irreversibly deactivated. To address this problem several alternatives
have been put forward, such as the addition of methanol by
steps (7), the immobilization of lipase (8) and the utilization of
solvents, such as tert-butanol (9).
Now biodiesel is commonly produced by using basic catalysts,such as sodium or potassium hydroxides, since these catalysts givehigh yield in short reaction times. However, in the case of oils withhigh contents of free fatty acids (FFAs), such as microalgal oils,alkaline catalysis presents some problems due to the formation ofsoaps, which decreases the biodiesel yield and increases the purificationcosts. Acid catalysts transform both FFAs and acylglycerolsinto methyl esters (5). However, the reaction velocity of transesterificationwith an acid-catalyst is much slower than with analkaline one and more methanol is required (6). In addition, acidcatalysts are highly corrosive and so are seldom used on an industrialscale.Lipases also catalyse the transformation of both FFAs and acylglycerolsto methyl esters, but at lower temperatures than inalkaline and acid catalysis (3040C). Moreover, the purification ofbiodiesel is easier, cheaper and entails a lower consumption ofwater, because neither alkalis nor acids need to be separated, onlythe excess of alcohol and the glycerol. This glycerol is also easilyrecuperated at a high degree of purity (without mixing with alkalisor acids), and it can be used in nobler applications. On the otherhand, if the lipase is immobilized, the separation of the reactionmixture and the catalyst is straightforward. Many works on theenzymatic production of biodiesel have studied the effect ofเมทานอลในเสถียรภาพของเอนไซม์ไลเปส เพราะเมื่อเมทานอลเกินละลายในส่วนผสมของปฏิกิริยาที่มีเอนไซม์ไลเปสสะท้อนที่ปิดใช้งาน เพื่อแก้ไขปัญหานี้หลายตัวเลือกได้ย้ายไปข้างหน้า เช่นเมทานอลโดยการเพิ่มขั้นตอนที่ (7) ตรึงโปเอนไซม์ไลเปส (8) และการใช้ประโยชน์ของหรือสารทำละลาย เช่น tert-บิวทานอ (9)
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