A new mechanism for pore enlargement in mesoporous materials and its application on biodiesel production.

In the conventional method of synthesis by using cyclohexylamine (CA) as template produces in the pore range of 0–3 nm. To enlarge the pore size which is suitable for biodiesel synthesis, the modified synthesis method is adopted by using CA as a template. In this novel method, pore size is enlarged to 7 nm. Cyclohexylamine was applied as a template for AlPO4 and AlSiO4 molecular sieves synthesis. In AlSiO4 synthesis, tetraethyl orthosilicate hydrolyzed to produce ethyl carbocation which is used for ethylation of CA in the presence of aluminum chloride. This ethylated CA size is large enough to produce a large pore size (7 nm). In AlPO4 two types of pore are produced with a pore size of 3 and 7 nm. The 3 nm are created by CA and 7 nm by the binding of CA with phosphoric acid. The synthesized materials are analyzed by physicochemical characterization. AlPO4 has a neutral framework, but the synthesized AlPO4 has acidity which is evidence for the CA binding with phosphoric acid. The synthesis of a promising catalyst (AlPO4-7 and AlSiO4-7) with an enlarged pore that can be effectively applied for the production of biodiesel from waste cooking oil (WCO) at room temperature. The acidity of the synthesized AlPO4 and AlSiO4 are 0.168 and 0.548 mmol/g. These catalysts are active at room temperature due to higher acidity. So the reaction takes place faster and it will reduce the reaction time. It is observed that AlSiO4 produces 90% biodiesel and AlPO4 produces 72% biodiesel with a shorter reaction time. This result reveals that 7 nm pores are suitable for biodiesel production. The diethyl ether selectivity of AlPO4 and AlSiO4 is 24% and 4%, respectively. This is due to the 3 nm pore size created by CA in AlPO4 and it favors diethyl ether synthesis. [ABSTRACT FROM AUTHOR]