HPW/MCM-41 catalyzed isomerization and dimerization of pure pinene and crude turpentine

• α-Pinene, β-pinene and crude turpentine give similar product distribution in isomerization/dimerization.
• Dimerization involves a quick isomerization and the dimers are formed from isomeric compounds.
• Crude turpentine can be used to produce chemicals that are generally formed from pure pinenes, suggesting an efficient and cheap way for turpentine utilization.
• HPW/MCM-41 is more active than bulk HPW and HPW/Al-MCM-41.

Turpentine is biomass derived from metabolites of plants and often utilized via isomerization or dimerization of pure pinene that are separated from crude turpentine. This work is aimed to demonstrate the possibility of using crude turpentine to replace pure pinene in the acid catalyzed reactions. Firstly, H3PW12O40 (HPW) was loaded on MCM-41 using wet impregnation to enhance the dispersion of acid sites. Characterizations show that HPW is well dispersed and the acid concentration depends on the HPW amount. Then the isomerization and dimerization of α-pinene, β-pinene and crude turpentine were investigated in detail. Regardless the kind of reactant used, the product distribution is very similar in each type of reaction. Controlled experiment shows the dimerization involves a quick isomerization and thus the dimers are formed from the isomeric compounds. Moreover, components besides pinene, like oxygen-containing compounds, in crude turpentine also take part in the reactions. The reaction network is proposed based on experiment and theoretical computation. HPW/MCM-41 shows higher activity than bulk HPW, and 80% HPW/MCM-41 is the best, which leads to equal conversion (or yield) in the isomerization (or dimerization) for all the three reactants. This work shows that crude turpentine can be used to produce chemicals that are formed from pure pinene.

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