Biodiesel Production and Purification with a Hydrophobic Sintered Glass Filter

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Wu, Jiafu
Biodiesel , Hydrophobic coatings , Water and oil separation , Octadecyl trichlorosilane
Octadecyltrichlorosilane (OTS) has been chemically grafted onto sintered glass filters to render them hydrophobic. These hydrophobic filters were subsequently employed for the purification of biodiesel. Various properties of the OTS-coated sintered glass filters were evaluated, such as the water contact angle, water sliding angle, solvent flux, and the breakthrough pressure. These characterizations revealed that the highest breakthrough pressure was achieved when the OTS had been applied onto the filters by means of a toluene coating solution with an OTS concentration of 1.9 vol %. The biodiesel employed in this investigation was synthesized from methanol and cooking oil via a base-catalyzed transesterification reaction. Glycerol and fatty acid salts were obtained as side products via this transesterification reaction. The excess unreacted methanol was first removed by rotary evaporation, and hydrochloric acid (HCl) was then mixed with the biodiesel to neutralize the fatty acid salt and to coarsen the glycerol droplets. After sedimentation, water was added into the biodiesel to enable the formation of a water/glycerol phase and to reduce the glycerol concentration in the biodiesel. Optimization experiments revealed that the addition of water to the biodiesel at a concentration of 1.00 wt % provided the optimum effect, with no significant reduction of the glycerol content being achieved at higher water concentrations. The water/glycerol phase was removed by the OTS-coated sintered glass filter under a vacuum of 30 mbar. A relatively constant flux of 34.1± 0.6 L/m2 h was achieved during the course of the separation process. Karl Fisher titrations revealed that the water concentration in the biodiesel permeate primarily remained constant as the separation progressed. However, the filter did not offer reproducible results when the separation experiments were repeated during different times of the year, possibly due to differences in the humidity. The hydrophobic filters introduced here may be candidates for the separation of oil/water mixtures.
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