Abstract
A new approach has been demonstrated for the synthesis of solid ammonium sulphate attached to silica rice husk ash. The 3-(aminopropyl)triethoxysilane was immobilized onto silica at room temperature to functionalize the silica with ammine end groups (–NH2). The amine group was sulphated with sulphuric acid to produce a novel micro-rod-like shaped acidic catalyst (as seen with TEM) designated RHNH3SO4H (RH = rice husk). The TGA analysis shows that the catalyst is stable at temperatures below 200°C. The acidity measurement of the catalyst indicates that it has Brønsted acid sites. Cellulose extracted from waste of rice husk and cellulose extracted from office paper were hydrolysed to glucose in 6 h, and the glucose was hydrolysed afterwards to other products within 13 h. The catalyst is reusable many times without a significant loss of catalytic activity.
Highlights
Until recently, most ionic catalysts were synthesised and used for different purposes in liquid solutions
The amine group (–NH2) in the RHAPrNH2 was sulphated with sulphuric acid via a simple procedure at room temperature to produce a novel microstructure acidic catalyst RHNH3SO4H
The combined analyses show that sulphur and nitrogen are exhibited in RHNH3SO4H, while only nitrogen is found in RHAPrNH2
Summary
Most ionic catalysts were synthesised and used for different purposes in liquid solutions. We have recently reported the synthesis of a new type of ionic catalysts in solid state form with less environmental concerns. Those catalysts are recyclable and can be used for the same purposes as where the ionic liquids catalysts are used [1]. After its burning approximately 20% ash content comprises over 95% of amorphous silica which has very fine particle size, very high purity, high surface area, and high porosity. These properties would give rice husk utilization a very economically attractive perspective [2, 3]. A more direct and simple method was introduced by us to immobilize APTES onto silica to give a –CH2–NH2 functionality on the silica surface [7, 8]
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