硅胶自环己烷中吸附环己酮和苯甲酸

Adsorption of Cyclohexanone and Benzoic Acid from Cyclohexane onto Silica Gel

硅胶表面有自由羟基和缔合羟基,在吸附气体和蒸气时自由羟基起主要作用.Elder等,Rochester等,Mills等研究了硅胶自溶液中的吸附作用,认为硅胶表面羟基在溶液吸附中起主要作用,但对自由羟基和缔合羟基各自的作用尚无明确的看法. 本工作用经不同温度处理的亲水硅胶(表面总羟基浓度不同)和甲基化硅胶(只含有缔合羟基或不同表面浓度的自由羟基的硅胶)为吸附剂,测定了自环己烷中吸附环己酮和苯甲酸的等温线,以及几种硅胶样品的红外光谱图,探讨了表面自由羟基和缔合羟基在溶液吸附中的作用.

The adsorption isotherms of cyclohexanone and benzoic acid from cyclohexane onto silica gels,heated at various temperature(200,400,500,600 and 700℃)or treated with(CH)SiCl have been determined at 35℃.Some of above-mentioned silica gels were studied by IR.After the surface of silica gels were treated with(CH)SiCl,the free hydroxyl group disappeared,but the associated hydroxyl group did not change,then the adsorption of cyclohexanone and benzoic acid decreased slightly.This fact shows that the associated hydroxyl groups are not important in the adsorption from solutions.On the surface of silica gel,only the free hydroxyl groups reacted with(CH)SiCl and the amount of adsorption changed correspondingly with the degree of trimethylsilylation.Furthermore,the adsorption from solutions did not take place at all on the silica surface whose free OH had been removed entirely.Those facts indicate that the free hydroxyl groups play the role of adsorption centres.The fact that the amount of the monomolecular adsorption shows a maximum on the surface of silica gel heated at 400℃,suggests that the concentration of the free hydroxyl group may have a maximum at this temperature.