過渡金屬催化劑／雙氧水系統及鈦矽固體催化劑／雙氧水系統處理有機硫化物以超音波協助氧化效率之探討

The Efficiency of Aromatic Sulfur Compounds under Ultrasound Assisted Oxidation in Polyoxometalate/H[feaf]O[feaf] and Titanium Silicates/H[feaf]O[feaf] Systems

柴油引擎燃燒產生的氮氧化物及懸浮固體物質，是空氣污染的主要來源。歐洲及台灣已於2005年規定柴油中硫含量需低於50 ppm，而美國也於2006年規定硫含量需低於15 ppm；現今之加氫脫硫法並無法有效的解決這個問題。超音波協助氧化脫硫方式，可在常溫、常壓下，有效率的去除柴油中的有機硫，該技術結合：超音波學、介面活性催化作用及氧化劑催化氧化反應等三項技術。以氧化劑催化反應而言，現今以過渡金屬催化劑/雙氧水系統及鈦矽固體催化劑/雙氧水系統為較先進之技術。以過渡金屬催化劑/雙氧水系統而言，試驗數據顯示以鎢為主之過渡金屬催化劑，其氧化速率大於以鋇為主之過渡金屬催化劑；此外，他們的酸化合物之氧化速率亦大於其塩化合物；在此系統中，不同的有機硫化物在超音波協助之氧化速率為46DMDBT > 4MDBT >DBT > 2MBT > BT；因此，DBT及其家族在過渡金屬催化劑/雙氧水系統中之氧化速率大於BT及其家族。然而，以鈦矽固體催化劑/雙氧水系統而言，試驗數據顯示DBT在以Ti-beta為催化劑時，並無明顯之氧化反應，但BT及其家族卻於10分鐘的反應時間內，氧化效率達到99%。因此，在超音波協助氧化脫硫系統中，可設計一雙催化劑系統，利用其相異之催化效益，提昇整體氧化脫硫之反應機制，建構適當之控制與操作條件，以達到完全去除柴油中有機硫之目的。

Diesel-powered vehicles contribute to urban air pollution in the form of NOx and particulate matter emissions. New environmental regulations call for less then 50 ppm sulfur in diesel in Europe and Taiwan by 2005, and 15 ppm in the US by 2006. However, current technologies are not sufficient to solve this problem. Ultrasound-assisted oxidative desulfurization (UAOD) process operating at ambient temperature and atmospheric pressure provides the selective removal of sulfur compounds from hydrocarbons by a combination process of oxidative catalysis, phase transfer catalysis and sonication. Currently, Polyoxometalate/H2O2 and Titanium Silicates/H2O2 Systems are most advance and newly developed technologies in oxidation reaction. In polyoxometalate/H2O2 system, this research illustrated that phosphotungstic compounds were better catalyst precursors compared to molybdenum counterparts. The acid form of phosphotungstic anion performed slightly higher in oxidation activity compared to its sodium salt. Moreover, experiment results indicated that the oxidation reaction under sonication followed pseudo first order condition. The oxidation reactivity of these sulfur compounds was found in a decreasing order of 46DMDBT ＞ 4MDBT ＞ DBT ＞ 2MBT ＞ BT under UAOD conditions. Thus, it illustrated that DBT and its families performed higher oxidative efficiency than BT and its families in this system. However, in titanium silicates/H2O2 systems, experiment results indicated that DBT was almost inactive for oxidation under UAOD process by using Ti-beta as catalyst, where BT and its families reached highest conversion percentage of sulfide to sulfone in 10minutes. Therefore, UAOD process under polyoxometalate/H2O2 system could remove most of organic sulfur compounds. The refectory compounds after this system, mostly BT and its families, could be fully removed by titanium silicates/H2O2 systems. This information is essential to design a dual catalysts system in UAOD process to reach ultralow sulfur diesel (＜15 ppm) or zero sulfur contain diesel.