磷钨酸铯催化工业蔗渣木质素制备酚类化学品

Production of phenols from catalytic conversion of industrial bagasse lignin over cesium-exchanged phosphotungstic acid catalyst

通过催化降解的方法,可以有效将木质素转为高附加值的单酚类化学品。文章首先以酸析法从蔗渣碱法造纸黑液中回收工业蔗渣木质素(IBL),接着采用Cs_(2.5)H_(0.5)PW_(12)O_(40)为催化剂,在250℃乙醇-水体系中反应180 min催化IBL降解,可得到4-乙基苯酚(8.1%),4-乙烯基苯酚(1.3%),3-甲基-4-乙基苯酚(1.9%),4-异丙基-苯酚(3.5%)和2,6-二甲氧基苯酚(7.8%)5种主要酚类化合物。以主要产物4-乙基苯酚收率为指标,考察了催化剂取代度、比表面积和孔结构、反应温度、反应时间等条件对催化效率的影响。结果表明,通过多孔炭负载可以有效提高磷钨酸铯的催化效率,以比表面积、孔体积和孔径分别为0.340 cm^3/g,5.888 nm和341.783 m^2的活性炭负载型磷钨酸铯(Cs_(2.5)H_(0.5)PW_(12)O_(40)/C2)为催化剂,在350℃乙醇-水(v/v=9/1)体系中反应120 min催化IBL降解,4-乙基苯酚的收率最高可达12.36%。

In the present study, industrial bagasse lignin（IBL） was extracted from bagasse soda pulping black liquor by acid precipitation, then production of phenols from IBL over a variety of cesium-exchanged phosphotungstic acid（CsxH（3-x）PW（12）O（40）,x=0~3） catalyst in a hot compressed water– ethanol mixed solvent is examined. It was found that Cs（2.5）H（0.5）PW（12）O（40） is highly suitable for depolymerization of IBL to phenolic monomers in high yields at 250 ℃ for 180 min. The chemical structure and contents of liquefaction products were studied in detail, by using the methods of GCMS and GC, the small molecular products mainly consist of five phenols,i.e. 4-ethyl phenol（8.1%）,4-Vinyl phenol（1.3%）, 3-methyl-4-ethyl phenol（1.9%）, 4-isopropyl-phenol（3.5%） and 2,6-dimethoxy-phenol（7.8%）.The optimal conditions for IBL conversion, including substitution degree of cesium, surface area and pore structure of catalyst, reaction temperature and time, was optimized. The porous carbon supported catalyst gives the higher 4-ethyl phenol yield, while the volume of pore、size of pore and surface area of porous carbon supported Cs（2.5）H（0.5）PW（12）O（40）/C2 catalysts are 0.340 cm^3/g, 5.888 nm and 341.783 m^2 respectively,the highest porous yield was 12.36%obtained from 350 ℃ for 120 min in ethanol-water（v/v=9/1）mixed solvent. A longer reaction time leads to the formation of polymers due to the re-polymerization reactions. Therefore, the yield of 4-ethyl phenol decreases with the increase of the reaction time after 120 min.