12-磷钨酸插层MgAl水滑石的合成、表征及催化酯化原油脱酸性能

采用离子交换法合成了不同Mg/Al物质的量比的12-磷钨酸(H_3PW_(12)O_(40),HPW)插层水滑石(LDHs),采用XRD、FT-IR、Raman、ICP-AES、TG-DSC等分析手段表征其物化性质,Hammett指示剂-正丁胺滴定法测定其酸强度和酸量分布。进一步将其用于原油催化酯化脱酸反应,并与NO_3型LDHs对比,探讨酯化活性与催化剂性质之间的关系。结果表明,催化剂的活性主要受酸性和比表面积的影响。HPW插层LDHs的酯化活性明显优于NO3型LDHs,归因于增强的酸性和增大的比表面积。对于弱酸性的NO_3型LDHs,酯化活性与比表面积呈正向关系,Mg/Al物质的量比为4时,具有最大的比表面积和脱酸活性。而对于较强酸性的HPW插层LDHs,酯化活性主要受到酸量的影响,Mg/Al物质的量比为2的催化剂具有最高的酸量和脱酸活性。

Synthesis and characterization of 12-tungstophosphoric acid intercalated MgAl layered double hydroxides and their application as esterification catalysts for deacidification of crude oil

12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) intercalated layered double hydroxides (LDHs) with various Mg/Al molar ratios were synthesized by an ion-exchange method. The samples were characterized by XRD, FT-IR, Raman, ICP-AES and TG-DSC. The acid strength and amount of acidic sites of catalysts were measured by Hammett indicator and n-butylamine titration technique. Furthermore, HPW intercalated LDHs were used as esterification catalysts for deacidification of crude oil and compared with their nitrate LDHs precursors. The relationship between the catalytic activity and the property of HPW intercalated LDHs was investigated. It is found that the catalytic activity of LDHs mainly depends on the acidity and the specific surface area. HPW intercalated LDHs exhibit a much higher catalytic activity than nitrate LDHs owing to the increased acidity and specific surface area. Due to the poorer acidity, the activity of nitrate LDHs is proportional to their specific surface area. The nitrate LDH with Mg/Al molar ratio of 4 exhibits the highest specific surface area and deacidification ratio. However, for highly acidic HPW intercalated LDHs, the amount of acidic sites dominates the catalytic activity and the HPW intercalated LDH with Mg/Al molar ratio of 2 has the highest acidity and esterification activity.