Lignin derivatives formation in catalysed thermal decomposition of elephant grass lignocellulose

Abstract

Decomposition of elephant grass (Panicum maxima) lignocellulose was carried out with Pd and Ni/Pt-doped alumina as catalysts; chromic oxide was also used in some cases. For systems that contained no chromic oxide, formation of gaseous and volatile liquid products was highest for Ni/Pt, intermediate for Pd/λ- and least for Pd/λ-alumina. Non-volatile (tar) liquid product formation, on the other hand, was highest for Pd/λ-, intermediate for Pd/λ- and least for Ni/Pt-alumina. In these systems, product formation in detectable and measurable amounts was first observed at 140oC. For systems that contained chromic oxide, product formation was first observed at 60oC. The order of reactivity of the catalysts was Ni/Pt- > Pd/λ- > Pd/λ- alumina for the gaseous and Pd/λ- > Pd/λ- > Ni/Pt-alumina for the volatile liquid products in the range of 100 140oC. For the non-volatile (tar) liquid products, the order was Pd/λ- > Pd/λ- > Ni/Pt-alumina in the range of 60 - 80oC and Pd/λ- > Ni/Pt- > Pd/λ- alumina at 100 120oC. Generally, gaseous and volatile liquid products increased with increase in temperature. Also, all the three product types were formed in significantly higher concentrations in systems without chromic oxide than those with it. Mass spectral analysis of the tar product of two Ni/Pt-alumina samples run at 180oC and 200oC without chromic oxide gave several products amongwhich 4-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-3, 5-dimethylbenzaldehyde, 3-isobutyl-4-hydroxy-5-methoxybenzaldehyde, 3-methoxycinnamic acid, and ethanone- 1(4hydroxy-3-methoxyphenyl) were identified. Nigerian Journal of Chemical Research Vol. 7 2002: 14-24