Development of heterogeneous catalysts prepared from biopolymers: Methoxylation of terpenes.

The methoxylation of terpenes (α-pinene, β-pinene and limonene) was carried out in a batch reactor over poly(vinyl alcohol) and chitosan cross-linked with sulfosuccinic acid (PVA-CH-SO₃H) at 60 C.  Catalysts with different amount of sulfonic acid groups were prepared. These catalysts were characterised by FTIR-ATR and TGA. It was observed that the characteristic bands of the sulphonic groups are present in the catalyst. The methoxylation of β-pinene was carried out using PVA-CH-SO₃H catalysts. The catalytic activity increases with the number of sulphonic groups in the PVA-CH matrix up to a maximum value obtained with the PVA-CH-SO₃H/1.5 catalyst (8.79x10^-4 mol/h.g_cat). This behaviour may be explained by the increase in the number of active sites present in the polymer matrix. However, with the PVA-CH-SO₃H/2.0 catalyst, a decrease in catalytic activity (7.23x10^-4 mol/h.g_cat) is observed, which may be associated with impediments to the mobility of β-pinene within the PVA-CH matrix. It was found that, when beta-pinene was used as the substrate, the catalytic activity was much higher than for the other substrates (alpha-pinene and limonene). Alpha-pinene is less reactive than beta-pinene but more reactive than limonene. The catalytic activity increases as fowling: 1.23x10^-4 mol/h.g_cat (limonene) < 2.85x10^-4 mol/h.g_cat (a-pinene) < 8.79x10^-4 mol/h.g_cat (b-pinene). The selectivity towards terpenic hydrocarbons and terpenic ethers in the presence of the PVA-CH-SO₃H catalyst was also studied. It was found that the selectivity towards terpenic ethers (S_ether) decreases as the terpene conversion increases (S_ether=61.3% to PVA-CH-SO₃H/0.5; S_ether=59.4% to PVA-CH-SO₃H/1.0; S_ether=58.2% to PVA-CH-SO₃H/1.5; and S_ether=57.8% to PVA-CH-SO₃H/2.0 catalyst). A study was also carried out on the effect of catalyst mass on the methoxylation of beta-pinene. It was observed that the conversion of beta-pinene increases with increasing catalyst mass.