利用甲酸與碳搭載銠金屬及乙醇水混合液系統高效催化木質素液化解聚反應

Abstract

我們開發出利用甲酸與碳搭載銠金屬觸媒 (Rh/C) 催化高效率液化木質素的系統。使用最適化後的混合溶劑溶劑環境 (乙醇/水 = 3/1, v/v)，可以在溫和條件 (250 oC, 3 h) 進行分解後，經由四氫呋喃 (THF) 溶劑萃取可得到89.3 wt% 的生質油 (bio-oil)；而酚類單體產率為2.89 wt%，其中烷基癒創木酚類 (alkyl guaiacols) 占單體產物的主要部分。甲酸與Rh/C在此系統中扮演的角色亦在本研究中進行詳細的討論，甲酸可以經由熱分解作為液相氫源使用，也發現同時具備酸催化的特性，可促進木質素結構中醚鍵的水解反應 (hydrolysis reaction)，進行初步液化分解。使用Rh/C 觸媒可促進烯基愈創木酚類 (alkenyl guaiacol) 轉換為烷基癒創木酚類(即氫化反應, hydrogenation)。此外，藉由本研究開發出的系統，可有效降低生質油的分子量 (Mn.= 467 g mol-1)，同時降低O/C比值 (0.61 to 0.26)，表示本系統具有增進木質素高值化的潛力。

We present an efficient liquefaction of alkali lignin in an ethanol-water mixed solvent system with the presence of formic acid and carbon-supported rhodium (i.e. Rh/C) catalyst. At an optimized reaction condition of 250 oC and 3 h, the result showed the maximum yield of 89.3 wt% of bio-oil. For monomers of bio-oil, the total yield of monomeric products was as high as 2.89 wt%, in which alkyl guaiacols accounts for the main proportion. We found that formic acid was not only used as a liquid-phase hydrogen source, but also could serve as an organic acid that catalyzes hydrolysis reaction of C-O-C ether bonds presenting in lignin during lignin liquefaction. The role of Rh/C is demonstrated for improving the conversion of alkenyl to alkyl guaiacols (i.e. hydrogenation reaction) during lignin liquefaction. In addition, smaller fragments (Mn.= 467 g mol-1) as well as lower O/C ratio (0.61 to 0.26) indicate that our system has a potential for upgrading the generated bio-oil.