Valorization of rice husk silica waste:Organo-amine functionalized castor oil templated mesoporous silicas for biofuels synthesis

Abstract

Rice husk is a rich source of waste silica which has potential for application in the preparation of porous materials for use as catalyst supports or sorbents. Here we report on the synthesis of rice husk silica (RHS) and mesoporous templated rice husk silica (MT-RHS) using sodium silicate, obtained from rice husk ash, and castor oil as a pore directing agent. The resulting silicas were functionalized with 3-aminopropyltriethoxysilane (APTS) or 3-diethylaminopropyltrimethoxysilane (DEPA), and their catalytic activity evaluated in the transesterification of model C4–C12 triglycerides (TAG) to their corresponding fatty acid methyl esters, of relevance to biodiesel synthesis. Castor oil templating enhances the surface area of rice husk silica, and introduces uniform 4 nm mesopores, albeit as a disordered pore network. Post-synthetic grafting of silica by APTS or DEPA resulted in base site loadings of 0.5 and 0.8 mmolg−1 respectively on RHS and MT-RHS. Turnover frequencies of amine-functionalized MT-RHS were 45–65% greater than those of their amine-functionalized RHS counterparts for tributyrin transesterification. Switching from a primary (APTS) to tertiary (DEPA) amine increased activity three-fold, delivering 80% tributyrin conversion to methyl butyrate in 6 h. DEPA-MT-RHS was effective for the transesterification of C8 and C12 triglycerides, with methyl caproate and methyl laurate selectivities of 93% and 71% respectively in 24 h.

Publication DOI: https://doi.org/10.1016/j.micromeso.2019.109868
Divisions: College of Engineering & Physical Sciences > Energy and Bioproducts Research Institute (EBRI)
College of Engineering & Physical Sciences
Additional Information: © 2019, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/ Funding: Leverhulme Royal Society African Award and Mkwawa University College of Education (MUCE).
Uncontrolled Keywords: Biodiesel,Catalysis,Organic-inorganic hybrids,Rice husk silica,Sol-gel synthesis,Solid base,Templated silica,Chemistry(all),Materials Science(all),Condensed Matter Physics,Mechanics of Materials
Publication ISSN: 1387-1811
Full Text Link:
Related URLs: https://linking ... 387181119307255 (Publisher URL)
http://www.scop ... tnerID=8YFLogxK (Scopus URL)
PURE Output Type: Article
Published Date: 2020-03-01
Published Online Date: 2019-11-05
Accepted Date: 2019-11-02
Authors: Elimbinzi, Elianaso
Nyandoro, Stephen S.
Mubofu, Egid B.
Manayil, Jinesh C. (ORCID Profile 0000-0002-9864-3332)
Lee, Adam F.
Wilson, Karen

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