酯交换制生物柴油的CaO固体碱催化剂

CaO as a Solid Base Catalyst for Transesterification of Soybean Oil

用不同的前驱物合成了三种CaO催化剂,并以X射线衍射(XRD)、扫描电子显微镜(SEM)、程序升温脱附(TPD)等方法加以表征.这些CaO被用作大豆油(SBO)经酯交换制取脂肪酸甲酯(FAME),即生物柴油的催化剂,由方解石制备的氧化钙(Cal(N))表现了最好的SBO酯交换活性.检测发现CaO的酯交换活性与它们的碱性强度密切相关,当暴露于CO2气氛下,显著降低了CaO的酯交换催化活性(Raman光谱测试显示当置CaO于常温空气中,其表面形成的CaCO3和Ca(OH)2将阻止CaO继续参与SBO的酯交换反应).CO2的毒化颇受制于CaO前驱体种类,Cal(N)比来自文石的CaO(即Ara(N))有更好的抗CO2毒化能力;这些受损的CaO催化活性可部分复原.提出了CaO催化剂受CO2毒化及其再生的机理,同时讨论了SBO酯交换活性相到底是CaO固体表面,拟或溶解了的CaO的问题.

Three different calcium oxide catalysts were synthesized from different precursors and characterized by Xray diffraction （XRD）, scanning electron microscopy （SEM）, and temperature-programmed desorption （TPD）. They were used as catalysts in the transesterification of soybean oil （SBO） for the production of fatty acid methyl esters （FAME）, namely biodiesel. Calcium oxide from calcite （Cal（N）） showed the highest activity towards the transesterification of SBO. The transesterification activity of CaO was found to be highly related to the basicity of the catalysts. The catalytic activity of CaO greatly decreased when CaO was exposed to CO2. （Raman spectroscopic studies demonstrated that the formation of CaCO3 and Ca（OH）2 on the surface of CaO when CaO was exposed to room air prevented CaO from participating in the transesterification of SBO）. The degree of poisoning was highly dependent on the type of precursors with Cal（N） more resistant to CO2 poisoning than CaO from aragonite （Ara（N））. Deactivated CaO catalysts could be partially regenerated. A mechanism was proposed to explain the poisoning and regenerating processes. Furthermore, whether the solid phase of CaO or dissolved CaO was the active species in the transesterification of SBO was also investigated.