Preparation And Application Of Magnesium/Silicon Adsorption Materials In The Biodiesel Purification Process

Magnesium silicate gel is successfully synthetized from sodium silicate andmagnesium chloride by non-hydrothermal method on the basis of laboratory’spreliminary work. The magnesium hexasilicate/PES membrane adsorbent is preparedby using DMAC as solvent, PES polymer as matrices material and magnesiumhexasilicate as functional sites. The structures of magnesium hexasilicate, magnesiumsilicate gel and magnesium hexasilicate/PES membrane are characterized byanalytical methods of scanning electron microscopy analysis, fourier transforminfrared spectroscopy analysis, hermogravimetry and differential scanning calorimetryanalysis and X-ray powder diffraction analysis. Their adsorption behavior for freefatty acids from biodiesel and the decoloration performance of magnesiumhexasilicate are investigated. The effects of contact time, adsorbent dosage andtemperature on the adsorption and decoloration performance are studied.The physical characterization results show that the thermal stability ofmagnesium hexasilicate and magnesium silicate gel is good. They are amorphousstates of poor crystalline nature. For magnesium hexasilicate/PES membrane,magnesium hexasilicate is equably dispersed in PES polymer.The stability of biodiesel is studied. Results show that the biodiesel stability is alittle poor and the acid value increases with the extension of time. After130days, theacid value reaches8.87mg KOH/g, which is seriously beyond the standard value.Adsorption of different adsorbents for free fatty acids from biological is investigated.Results show that the maximum adsorption capacity of magnesium silicate is largerthan activated carbon and silica. And the maximum adsorption capacities ofmagnesium hexasilicate, hydrothermal2:1magnesium silicate gel andnone-hydrothermal4.5:1magnesium silicate gel are larger. They are359mg/g,367 mg/g and426mg/g.The adsorption results show that the maximum adsorption capacity ofmagnesium hexasilicate is360mg/g under the following optimum conditions:calcination temperature450℃, calcination time4h, contact time5h, magnesiumhexasilicate mass0.50g, temperature25℃. And the static adsorption processesfollow Langmuir isotherm equation. The maximum adsorption capacity of magnesiumsilicate gel is470mg/g under the following optimum conditions: contact time4h,magnesium silicate gel mass0.50g, temperature25℃. And the static adsorptionprocesses follow Freundlich isotherm equation. The maximum adsorption capacity ofmagnesium hexasilicate in the magnesium hexasilicate/PES membrane is305mg/gunder the following optimum conditions: calcination temperature450℃, calcinationtime4h, contact time4h, magnesium hexasilicate/PES membrane0.50g,temperature25℃. Though the maximum adsorption capacity is lower, the vacuumfiltration step is removed. So the process is greatly simplified and the cost is reduced.Magnesium hexasilicate is also used to decolor the deep color biodiesel. Resultsshow that the optimal conditions are: calcination temperature450℃, calcinationtime4h, contact time70min, magnesium hexasilicate mass0.50g, temperature25℃.The decoloring efficiency can reach7.5%, and the unpleasant smell of the biodieselcan be almost eliminated after decoloration.The above results show that magnesium hexasilicate, magnesium silicate gel andmagnesium hexasilicate/PES membrane have perfect adsorption behavior for freefatty acids from biodiesel. They have certain effect on reducing acid value anddecoloring biodiesel.