Polyethylene glycol stearate is widely used in pharmaceuticals and cosmetic industries. The current work describes the synthesis and optimization of polyethylene glycol stearate by esterification of polyethylene glycol 600 and stearic acid using Fermase CALBex 10000, a commercial immobilized lipase B in a solvent-free system. The impact of various parameters that include temperature, reaction time, biocatalyst loading, agitation, acid to alcohol molar ratio, and amount of molecular sieves was optimized to achieve maximum conversion. The highest conversion of 86.98% was obtained in 6 h under the following optimized conditions: temperature 70°C, biocatalyst loading 0.5%, acid to alcohol molar ratio 1:4, speed of agitation 300 rpm, and molecular sieves 5% (w/w). The final condensate product was analyzed through Fourier transform infrared spectroscopy to confirm the functional group and also by 1H nuclear magnetic resonance spectroscopy. The immobilized catalyst can be reused up to four cycles, exhibiting more than 60% of its initial activity.
BACKGROUND: The current work describes the application of ultrasound and its improving effect on the synthesis of polyethylene glycol (PEG) stearate using Fermase (Fermase CALB™10,000 Candida antarctica Lipase B) as a biocatalyst via esterification of PEG600 and stearic acid. The influence of various parameters like molar ratio, temperature, speed of agitation, enzyme loading, effect of addition of molecular sieves and other factors associated with ultrasound, i.e. duty cycle and power, has been studied and optimized.RESULT: A total of 84.34% of PEG stearate was obtained at ultrasound frequency of 22 kHz with 50 W power, 60 ∘ C temperature, stirring speed 200 rpm, mole ratio of PEG600-stearic acid 1:1, 3% (w/w) molecular sieves, immobilized enzyme loading 0.5% (w/w) and duty cycle 50%. The enzyme showed reusability up to the fifth cycle. The reaction is conducted in a solvent free system which is an additional benefit. CONCLUSION: A maximum conversion of 84.34% was obtained in 3 h of reaction time in the presence of ultrasound as compared to 6 h in the absence of ultrasound denoting the intensified effect of ultrasound on the synthesis.
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