對二甲苯(p-Xylene)為對苯二甲酸(Terephthalic Acid)之原料，而對苯二甲酸主要用途為聚對苯二甲酸二乙酯(PET)之合成。由於PET 結構中含苯環，微生物無法分解其結構，若能將p-Xylene 中之苯環完全氫化，再將其甲基氧化為羧基，以此化合物與乙二醇進行聚合即可得結構同PET但不含苯環之生物可分解聚合物。為達成此目的， p-Xylene 氫化反應速率之提升即成為一重要課題。
在氫化反應過程中，由於氫氣在有機溶劑中之溶解度不高，氣液間
會存在著相當大之界面質傳阻力，此外在液體內部的擴散阻力與溶解度也會對反應速率造成限制。本研究在一連續式固定床反應器中進行
p-Xylene 液相氫化反應，主要以Ru/C、Ru/Al2O3及Ru-Rh/C 三種觸媒進行實驗，並於系統中加入高壓二氧化碳以形成CO2-Expanded Liquid，觀察高壓二氧化碳的存在對p-Xylene 氫化之影響。
研究發現以Ru/C 及Ru/Al2O3為觸媒時，在系統中加入二氧化碳後觸
媒皆有反應性衰退之現象，推測反應中產生少量的一氧化碳，造成觸媒的毒化。為了進一步了解觸媒衰退原因，我們分別以氧氣和二氧化碳混合氣體與丙烷代替純二氧化碳進料進行實驗，研究中發現觸媒依然有衰退現象。推測因為在加入二氧化碳反應後，產生碳氫化合物如甲烷等副產物，吸附於金屬觸媒活性位置上，造成觸媒反應性衰退，而在Ru-Rh/C的研究上，並無發現轉化率隨時間下降之現象，而是在加入二氧化碳後，III轉化率下降但不隨時間而改變。推測因為氣液間質傳阻力過大，在加入二氧化碳後，液體膨脹，反而減少了單位體積中氫氣的含量，為了進一步的了解加入高壓二氧化碳對p-Xylene 氫化之影響，我們在未來可以將反應系統改為單一相操作或Slurry Reactor 操作，來改善因為氣液質傳阻力過大而無法看出CO2-Expanded Liquid 效應之缺點。

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