Preparation Of 1,4-Cyclohexanediol By Catalytic Hydrogenation Of Ruthenium-Based Catalyst

In recent years,the polyester industry has gradually come out of the downturn.With the increase in the price of raw material PTA?pure terephthalic acid?,the production capacity of the polyester market broke out,the old equipment resumed production,and the new unit was put into production.At the same time,with the increasingly strict enforcement of environmental protection,some polyester enterprises have reduced production or stopped production,and the polyester industry has gradually achieved an optimized industrial layout.An important raw material for preparing polyester,1,4-cyclohexanedimethanol,is mainly prepared by stepwise hydrogenation of dimethyl terephthalate.However,the preparation process has problems such as harsh reaction conditions,environmental pollution,and difficulty in recovery of the catalyst.Therefore,ruthenium-based catalysts for the stepwise preparation of 1,4-cyclohexanedimethanol for dimethyl terephthalate were prepared.Firstly,a series of Ru-Re/AC bimetallic catalysts and Ru/AC,Re/AC mono metal catalysts were prepared using the modified activated carbon as a support for the first hydrogenation reaction of dimethyl terephthalate.Experiments were conducted to investigate the effects of different factors on the catalytic performance of the catalyst.It was found that the catalytic performance of Ru4.17Re0.83/AC catalyst is optimal.After reacting for 3 hours at50?under a hydrogen pressure of 3 MPa,the conversion of the reactant was 97.91%,and the selectivity of dimethyl 1,4-cyclohexanedicarboxylate was also 99.88%.In order to further explore the relationship between catalyst structure and performance,the catalysts were characterized by XRD,XPS,H₂-TPR and TEM.It was found that the catalyst has excellent catalytic performance when the Re species content of the Ru-Re/AC bimetallic catalyst is low.When the Re species content is too high,the catalytic performance is rapidly lowered.This is because there is an interaction between the two metals.When a small amount of Re is added,the metal Ru can effectively promote the reduction of ReO_x,and the catalyst contains Re⁰,which is favorable for the hydrogenation reaction;When an excessive amount of Re is added,the interaction between the metals is too strong,which affects the distribution of the surface species of the catalyst and further affects the performance of the catalyst.Next,a series of Re/AC catalysts were prepared for the second hydrogenation reaction.The effects of different carrier treatment methods,second component and other factors on the performance of the catalyst were investigated.It was found that the Re₅/AC catalyst using activated carbon treated with hydrogen and nitric acid as a carrier has the strongest performance.It was reacted at 220?,10 MPa for 10 hours,the reactant conversion rate was 98.85%,and the target product selectivity was 66.37%.Further,the catalyst was subjected to a series of characterizations such as H₂-TPR,XRD,XPS,TEM,and the like.Analytical studies have found that there is an interaction between the carrier and the active component,and the magnitude of its effect varies with the amount of loading.When the Re load is low,the interaction is large.As the Re load increases,the interaction decreases slightly and then increases slightly.At low loading,the catalyst has a low reduction temperature,and it contains the most Re⁰ species,and a large number of defect sites on the surface of the activated carbon,which contribute to the improvement of its catalytic performance.