Supported Tungstophosphoric Acid and Modified of SBA-15 as Solid Acids for THF Polymerization
|Course||Physical and chemical|
|Keywords||HPW laoding catalysts Al-SBA-15 Solid acid Tetrahydrofuran polymerization reaction|
As a versatile intermediate in synthetic spandex, polyurethane and polyether ester elastomers, PolyTHF (PTMEG) is widely applied in the textile, automotive, military equipment, medical equipment and other fields. PTMEG is prepared by cationic ring-opening polymerization from tetrahydrofuran. Among of polymerization process, the preparation of catalysts is the most important step. With the increasing of environmental pressure, THF polymerization traditional homogeneous catalysts are eliminated for equipment corrosion and serious waste pollution issues.To develop environment friendly solid acid catalyst has become the present research hotspot.Heteropolyacid is an effective, stable and environmentally benign catalysts that shows the nicer catalytic capability in Polymerization, alkylation, isomerization and other chemical reactions in recent years. But heteropolyacid is easy to be dissolved, it is hard to be recycling and reuse. The supported heteropolyacid can solve these problems.In addition, as a new type of high specific silicon-based mesoporous materials, Al-SBA-15 has almost the same pore size, uniform porous, adjustable acidic and also has irreplaceable advantage in solid acid catalysis. Particularly the larger pore volume and pore size is sutiable for macromolecular polymerization.Based on the above discussion, this paper covers two parts, the first part is that HPW/A12O3 and HPW/SBA-15 catalysts were prepared by impregnation method and the influence of catalytic performances of different carrier on the products yields and number average molecular weight were investigated; the second part is Al-SBA-15 catalysts were prepared with different ratio of silicon and aluminium and applied in THF polymerization. According to the comparison of texture properties and THF polymerization evaluation results between Al-SBA-15 and Al-MCM-41, we tried to explore the influence of texture to polymer molecular number.1. The interactions between heteropoly acid and carrier surface decided the structure form of the heteropoly acid, catalyst acidity and the discretion of the catalytic activity. Al2O3 is both sexes oxides supports, its surface alkaline bits interacting with the active component HPW strongly led to HPW Keggin structural damage. Only in high loading, the catalyst had better catalytic activity. SBA-15 surface has weak acidity silicon hydroxyl and corresponding weaker interaction with HPW. At lower loadings, HPW highly well dispersed in SBA-15 with its complete Keggin structure forms, It was found that the PTMEG yield was 57%, and the number average molecular weight was around 3000 when the loading of HPW was 30%. Through investigating the influence of HPW/MCM-41 and HPW/SBA-15 catalysts in THF polymerization, we found number average molecular weight of the PTMEG was decided by the pore size of the catalyst when HPW laoding was lower. Large pore size led to high number average molecular weight of the PTMEG obtainded. For higher HPW laoding catalysts, the factors of affecting polymer molecular number was relatively complex. The conversion of PTMEG was decided by effectively acid active centers of the catalyst.2. The obtained Al-SBA-15 samples with different ration of were well-ordered and had the similar porous texture with mesoporous molecular. Both Bransted and Lewis acid sites were observed from Py-IR, also the catalysts had weak and strong acid center. With the improvement of aluminum content, the acid amount of the catalyst increase gradually, the yield of PTMEG also gradually improve, but the molecular weight polymer remain in 1800 or so unchanged. The texture properties and THF polymerization evaluation results between Al-SBA-15 and Al-MCM-41 were contrasted and we found:conversion of THF was linear proportional of acidic centers of the catalyst, the more centers, the higher THF conversion. the number average molecular weight of the polymer was only decided by pore size, not other facters.