Study On Surface Hydroxylation Of Support And Performance Of The Immobilized AlCl₃ Catalyst

Linear alkylation benzene (LAB) is the primary raw material for biodegradable detergent. Nowadays, it is mostly produced industrially through the alkylation reaction of benzene with long chain olefins using HF as catalyst, which is the source of equipment corrosion and environment pollution. This thesis focuses on the synthesis of immobilized AlCl₃ via a two-step vapor method using mesoporous SiO₂ and γ-Ak₂O₃ as support and study of the surface hydroxylation of the support using hydrochlorid acid. In addition, we also investigates the activity, stability and 2-LAB selectivity of (SiO₂)-O-AlCl₂ and (Al₂O₃)-O-AlCl₂ catalyst in the alkylation reaction of benzene with mixed long chain olefins (C⁼₁₀-C⁼₁₃). Based on these experiments, the main results are as follows:(1) The stability and 2-LAB selectivity of (SiO₂)-O-AlCl₂ catalyst are remarkably increased by SiO₂ treatment with hydrochloric acid. The (SiO₂)-O-AlCl₂ catalyst exhibited the stability of 17 recycles and the selectivity of 2-LAB reaches 51% when olefins are reacted completely. The stability is much better than 11 recycles of the catalyst AlCl₃ immobilized on untreated SiO₂ under the same conditions. The optimum concentration of HCl is 3 M and the treatment period is 48 hours for surface hydroxylation of SiO₂. In addition, the immobilization temperature of AlCl₃ on the SiO₂ support pretreated by hydrochloric solution influences the lifetime of (SiO₂)-O-AlCl₂ catalyst. When the immobilization temperature reaches 200 ℃, the catalyst shows the better stability.(2) The difference of the activity and stability was also investigated in the same loadings of [-AlCl₂] (0.52 g) over (SiO₂)-O-AlCl₂ and (Al₂O₃)-O-AlCl₂ catalysts. The results showed that (SiO₂)-O-AlCl₂ catalyst exhibited the better stability than that of (Al₂O₃)-O-AlCl₂ catalyst. The recycle times of (SiO₂)-O-AlCl₂ are 7, while the recycle times of (Al₂O₃)-O-AlCl₂ are only 3. This means that the catalytic performance of active center over (SiO₂)-O-AlCl₂ catalyst is much better than that over (Al₂O₃-O-AlCl₂ catalyst. Immobilized AlCl₃ catalyst prepared by acid-treated SiO₂ support is the most appropriate catalyst from the point of catalytic performance and economy.