Synthesis Of Branched-chain Heavy Alkylbenzene Over Immobilized AlCl₃ Catalyst

Heavy alkylbenzne sulfonate(HABS) is an important surfactants with favorable interfacial properties and have been widely applied in enhanced oil recovery(EOR) in China.In industry,the raw material to synthesis alkylbenzene sulfonate surfactant for EOR is the byproducts formed in the alkylation reaction of benzene with C_10-13⁼ olefins.However,the cheap price of this raw material can not gloss over its disadvantages such as complex and indeterminate composition.In addition,its production mostly uses HF as the catalyst,which is a source of pollution and equipment corrosion.Thus,many efforts have been concentrated on solid acid catalysts because of its environmentally friendly manufacture.In this paper,branched-chain heavy alkylbenzene was synthesized over immobilized AlCl₃ catalyst via alkylation reaction of xylene with industrial mixed heavy olefins(C_14-18⁼). The effects of support types,preparation conditions of catalyst and reaction conditions of alkylation on the phyco-chemical properties and catalytic performance of the immobilized AlCl₃ catalyst were investigated.Branched-chain heavy alkylbenzene was synthesized over the higher-performance catalyst in the optimum conditions and 2L modle enlarge experiment was completed.The main results are as follows:(1) The support types influence the chloride loadings and acid distrbution in the catalyst. Three supports of SLO₂,SiO₂-Al₂O₃ and Al₂O₃ were USed to prepare catalyst.The results of Py-FT1R and Hammett titration indicated that Bronsted acid sites and Lewis acid sites existed in the three catalysts,and Lewis acid sites is the main.The acid strength of AlCl₃/Al₂O₃ is stronger than that of AlCl₃/SiO₂,but the acid amount of AlCl₃/Al₂O₃ is less than that of AlCl₃/SiO₂.The larger acid amount and temperate acid strength of AlCl₃/SiO₂ are responsible to its excellent catalytic performance in xylene alkylation with heavy olefins to form branched-chain heavy alkylbenzene.(2) Preparation temperature of AlCl₃/SiO₂ catalyst greatly affected the loading and surface structure of chloride.Both AlCl₃ contents and the ratio Cl^-/Al decrease with preparation temperature increased,however,the ratio Cl^-/Al remained basically unchanged at the same grafted temperature.The structure of chloride grafted on SiO₂ was investigated by ²⁷Al MAS-NMR.It was found that the 6-coordination Al specie dominates on the surface of catalyst prepared at low immobilization temperature of 200℃.With the increase of immobilization temperature,the amount of Al species increases.Three Al species of 6-coordination,5-coordination and 4-coordination were detected in the catalyst made at 500℃.(3) The effect of AlCl₃/SiO₂ catalyst on the selectivity of alkylbenzene isomer,the cracking and disproportionation of xylene was studied.Compared with the pure AlCl₃ catalyst;the effect of the reaction temperature,time and the composition of raw materials on immobilized AlCl₃/SiO₂ catalyst stability was also studied.The results showed that the cracking and disproportionation of xylene over AlCl₃/SiO₂ catalyst was far less than the level of AlCl₃ catalyst,but the selectivity of alkylbenzene was better than AlCl₃ catalyst,and had a very good selectivity of 2,3-LAB,which can improve the biological degradation of the surfactant. Alkylation reaction conditions of xylene obviously influence the lifetime of catalyst.Under optimal reaction conditions:reation temperature 80℃,reaction time 1 h,catalyst dosage 1g, aromatics/olefins molar ratio 10:1,the reuse times of catalyst was 11 with olefins conversion of 100%.