Biodiesel production by pervaporation-assisted esterification and pre-esterification using graphene oxide/chitosan composite membranes

- A series of GO/CS composite membrane was successfully synthesized and characterized.
- The integrated PV ehances conversion by removing water preferentially.
- Temperature, wt% of embedded GO, catalyst and alcohol/acid ratio strongly influence the conversions.
- The ratio of water production and removal rates is important in evaluating the membranes.

In this study, a series of novel graphene oxide/chitosan (GO/CS) composite membranes was successfully synthesized and fully characterized. The performance of GO/CS composite membrane was then evaluated by integrating with the esterification of acetic acid with ethanol or the pre-esterification of palmitic acid with methanol, both essential in biodiesel production. Typically, esterification and pre-esterification are reversible reactions, which are limited by chemical equilibrium, resulting in a low product yield. In our study, reaction and separation were conducted in two separated steps or in a single one by means of a catalytic membrane. The preferential removal of water through the membrane in a PV-assisted process enhanced the conversion. The results show clearly that temperature, wt% of embedded GO within a polymeric CS-based membrane, and initial ratio of alcohol/acid are important parameters to enhance conversion because it acts on the kinetics of both pervaporation and esterification/pre-esterification. The enhanced catalytic membrane of the PV-assisted pre-esterification can only be observed when a proper amount of Amberlyst-15 catalyst is used. Additionally, the results of PV-assisted esterification/pre-esterification show that the ratio of water removal (by membrane) and water production (by esterification) rates play a significant role in evaluating the catalytic membrane. Under specific conditions, the conversions of PV-assisted esterification and pre-esterification by the catalytic membrane could be higher than those without PV-assisted up to 8% and 20%, respectively. This process could offer a key technology for biodiesel production in the future.

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