Solid Base Catalysts Derived From The Industrial Magnesium Slag For Biodiesel Synthesis

Fast diminishing supply of fossil fuels and rapidly increasing negative environmental consequences have spurred more researchers to search for new, clean and environmental-friendly energy resources. Biodiesel, as an alternative diesel renewable fuel, has attracted a growing number of countries’attentions. Recently, the industrial biodiesel manufacturing process is a homogenous process which is corrosive to equipment, difficult to separate and easy to form by-products and waste water. But, heterogeneous catalysis can solve these problems. Especially, due to high catalytic activity, easy separation, regeneration and environmental-friendly advantage, solid base catalyst arouses more researchers’interests.The magnesium slag is an industrial solid waste generated in the production process of magnesium. The magnesium slag, including the elements calcium, magnesium, silicon, sodium, chlorine and oxygen and so on, is a kind of basic slag. In order to change the waste into the valuable, reach the energy conservation and emission reduction and realize circular economy, the solid base catalysts were prepared from the magnesium slag in this paper. The prepared conditions were studied and the catalysts were characterized with thermogravimetry and differential thermal analysis (TG-DTA), powder X-ray diffraction (XRD), temperature-programmed desorption of CO2 (CO2-TPD), nitrogen adsorption-desorption and fourier transformed infrared (FT-IR) spectroscopy. Their catalytic activity was evaluated with the transesterification of rapeseed oil and cottonseed oil with methanol and the optional reaction conditions were optimized. The contents and conclusions are organized as follows:1. The influence of the calcium compounds on the activity of CaO/MS catalyst derived from magnesium slag was studied and Ca(OH)2 was selected as the unique calcium sources. After calcined at 600 ℃, the catalyst with 27% CaO was labeled as CaO-H/MS.2. Using CaO-H/MS catalyst, the transesterification of rapeseed oil with methanol was studied by the method of single facor. The biodiesel yield can excess 90% in 4 h under the optional reaction conditions of 60℃,8:1 molar ratio of methanol to oil and 3% catalyst loading3. Using CaO-H/MS catalyst, the factors influenced on the transesterification of cottonseed oil with methanol was investigated by the method of orthogonal experiment. The order of these factors were catalyst amount> methanol/oil molar ratio> reaction time> reaction temperature. The biodiesel yield can excess 90% in 5 h under the optional reaction conditions of 65℃,8:1 molar ratio of methanol to oil and 3% catalyst loading.4. Na2SiO3/MS catalyst was prepared by impregnation method. There exist strong effects between magnesium slag and Na2SiO3 by the analysis of XRD and CO2-TPD, which makes Na2SiO3 better dispersed on magnesium slag and crystal structure and basic amount of the catalyst more changed than that of magnesium slag and Na2SiO3.5. The catalyst exhibits better water resistance, and washing with NaOH solution has good effective for the regeneration of the catalyst.6. Na2SiO3/MS catalyst was used in the transesterification of rapeseed oil with methanol. The experimental design in this work was a 5-level-4-factor central composite design (CCD). And within certain limits, reaction temperature and reaction time have less effect on the transesterification. With the increase of reaction temperature and reaction time, the yield of biodiesel rises firstly, and then the trend is reversed when reaction temperature and reaction time exceed a certain values. For the influences of the alcohol/oil molar ratio and catalyst content on the yield of biodiesel are similar trend to the influences of reaction temperature and reaction time.