Study On The Selective Hydrogenation Of 2-Methyl-3-butene-2-ol

The selective hydrogenation of methylbutynol to methylbutenol is a typical industrial intermediate reaction for synthesis of vitamin E and pesticides pyrethroids,where Lindlar catalyst with high reactivity,selectivity and ease to prepare has been widely applied commercially for decades.Beginning from selection of catalyst carriers,conditions to prepare catalyst was investigated to give high reactivity and selectivity.Eggshell catalyst structre was easily obtained by CaCO3 carrier due to its compact and poreless structure,which eliminate internal diffusion and improve reactivity and selectivity.A higher selectivity was obsevered in catalyst with lower coating rate and Pd/Pb ratio despite a decrese in reaction rate.The paticle size of a lower coating rate catalyst showed no direct influence on reaction,while narrow distribution of catalyst partical size favors reaction stability and controllability evidently.Therefore,CaCO3 carrier with narrow particle size distribution,coating rate of 5%,Pd/Pb ratio of 5-6.5 and sodium formate as reducing agent are considered as optimal conditions for catalyst preparation.Results of single-factor experiments showed that reaction selectivity improved while rate declined under conditions of lower temperature,lower hydrogen pressure and less catalyst input.Higher rate of agitation benefited the decrease of external diffusion so as to increase reaction rate,while higher quinoline input seldomly influenced reaction rate.Moisture content of raw materials affected reaction rate through phase transformation,and industial grade methylbutynol-water azeotrope,30%water contained,can effectively improve reaction selectivity.Temperature of 313.15 K,1200 r/min of agitation,hydrogen pressure of 0.5 MPa,0.5%mass of raw material input of catalyst dosage and 30%mass of catalyst input of quinoline dosage were considered as optimal conditions,in which methylbutynol,30%water contained,was fully converted in 75min and selectivity of 97.8%was gained.Composition of reaction system was given via GC-MS,and five side-products were obsevered.Apart from overhydrogention side-product amylene alcohol,others were all dimers:2,2-dimethyl-5-(2-methylprop-l-en-1-yl)-tetrahydrofuran,2,7-dimethyloct-3-ene-2,7-diol,2,5,5-trimethylhepta-3,6-dien-2-ol,and 2,7-dimethyloct-4-ene-2,7-diol.Hence,reaction network was proposed recorrdingly.