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

ABSTRACT

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.

Graphical Abstract

KEYWORDS:

• Aluminosilicate
• aluminophosphate
• mesoporous
• cyclohexylamine
• waste cooking oil and biodiesel

Nomenclature

Table

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Krishnaveni M

Krishnaveni M is currently a Ph.D student in the Department of chemistry, Manonmaniam Sundaranar University, Tirunelveli. Her research interests focus on biodiesel and green catalysis. She has participated and presented more than 10 papers in national and international conferences and also published 3 research articles. She has received best poster award and best innovation award in 2019 science exhibition.

Chellapandian Kannan

Chellapandian Kannan is currently working as a professor and Head in the Department of chemistry, Research Director in Manonmaniam Sundaranar University, Tirunelveli. He has more than 20 years of experience in teaching and research. His area of specialization is nanoporous solid acid synthesis, green catalysis and environmental science. He has published more than 80 research articles in reputed journals. 11 Ph.Ds are awarded. 2 patents are granted and one book was published.