有机硫化物使Pd/树脂催化剂中毒的规律与机理

Effect of Organic Sulfur Compounds on Isoprene-Hydrogenation Reactivity over Pd/Resin and Its Poisoning Mechanism

在流体并流向上气液固三相固定床反应器中考察了同系有机硫化物对Pd 树脂催化剂上异戊二烯选择加氢活性的影响 ,并对中毒失活的催化剂进行了XPS和红外光谱研究 .结果表明 ,在低温 ( 60℃ )和液相加氢条件下 ,硫醇和二硫醚同系物使Pd 树脂催化剂活性中毒的规律是 ,随着硫化物分子量的增大 ,其毒性减弱 .在w(S) =8× 10 - 6 的条件下 ,有机硫化物使催化剂上异戊二烯加氢活性失活的程度为 :二甲基二硫醚≈乙硫醇 二甲基硫醚 >噻吩 .乙硫醇和二甲基二硫醚使Pd 树脂催化剂中毒的机理是 ,它们分别在催化剂上发生S H和S S键断裂 ,并与Pd形成带烷基基团的S Pd吸附络合物 。

Organic sulfur compounds are the important poisons for noble metal hydrogenation catalysts. Some researchers considered that the poisoning effects of the sulfur compounds are independent of the kind of them. The poisoning effects of several kinds of normal alkyl sulfur compounds on the isoprene hydrogenation over Pd catalyst supported on sulfonated resin were investigated in a fixed-bed reactor with gas-liquid-solid concurrent up-flow under the conditions of LHSV=36 h -1, p=1.0 MPa and θ=60 ℃. The reaction feed is the ideal model mixture made of isoprene,organic sulfur compound and n-hexane, and its composition is w(S)=8.0×10 -6, w(isoprene)=0.6%, w(n-hexane)=99.4%. The poisoning effects of alkyl sulfur compounds on the reactivity of isoprene hydrogenation over supported Pd catalyst are more and more serious with the decrease of the molecular mass of alkyl thiols and dialkyl disulfides. Among the mercaptans, the toxicity order is ethanethiol>n-butanethiol>n-octanethiol. The different kinds of alkyl sulfur compounds have different effects on the activity of the catalyst. When the sulfur amount is w(S)=8×10 -6 in the feed, dimethyl disulfide is the strongest poison, and coming next in poisonous effect is ethanethiol, dimethyl sulfide and thiophene. The Pd/resin catalyst samples poisoned by ethanethiol and dimethyl disulfide were studied by means of XPS and IR. The adsorption state of alkyl sulfur compounds is R-S-Pd on the catalyst surface, rather than the state of S element. The poisoning mechanism of alkyl sulfur compounds over Pd/resin catalyst was discussed also.