Molecular Design And Performance Evaluation Of Chelating Rhodium-Based Catalysts For Methanol Carbonylation

As an organic chemical product,acetic acid plays an important role in industry,food and medicine.China is a large coal resource country,and methanol is abundant as the downstream product of the coal industry chain.The methanol carbonylation process is the mainstream process of acetic acid production in China,the active catalyst center is[Rh(CO)2I2]-in this reaction process.Rh catalyst is easy to form dimer[Rh2(CO)2I4]2-,which causes the catalyst to decompose and precipitate,and the valence state will be changed and then deactivated.Therefore,a large amount of water is added in case of catalyst deactivation in the industry,but at the same time,the separation cost and the energy consumption are improved in the later stage of production.The catalyst active center[Rh(CO)2I2]-monomer is easily polymerized to form RhI in the process of methanol carbonylation to acetic acid,which causes the decomposing of the Rh catalyst,resulting in the deactivation of the catalyst.According to the previous research results for the mechanism of deactivation[Rh(CO)2I2]-catalyst,used a metal ligand and an organic ligand to form chelating Rh complex catalysts with the active component Rh.Firstly,the mechanism of the catalytic reaction was obtained by theoretical calculation using a density functional method,and the internal relationship between the basic catalyst configuration and its performance was studied at the molecular level;Then,that calculated result determined the appropriate catalyst configuration,guided the laboratory synthesized of the target catalyst,combined with XPS,IR,GC-MS and other analytical means to analyze and characterize the synthetic catalyst;Finally,established the product analysis method,the catalytic reaction system conditions were optimized to obtain a high-performance Rh catalyst preparation technique.The specific research results are as follows:(1)By introducing a second metal ligand RuCl3 hydrate,the Rh(?)-Ru(?)bimetallic catalyst configuration was designed at the molecular level,and Rh(?)-Ru(?)bimetallic catalyst with asymmetric stereo chelate structure can be formed between Rh and Ru through Cl connection.The Rh(?)-Ru(?)bimetallic catalyst with the catalyst as the catalytic active center participated in the catalytic reaction.The calculated results showed that the distance between Rh and Ru was 0.3585 nm,and the intermetallic interaction and steric hindrance effect of RuCI3 made Rh(?)-Ru(?)bimetallic catalyst more stable,the reaction energy barrier of the CH3I oxidation addition which the rate-determining step was obviously reduced,the carbonylation rate was increased,and the synthesized catalyst was subjected to a carbonylation reaction.The Rh(?)-Ru(?)bimetallic catalyst had the best catalytic activity at 190?,3.5 MPa,H2O content of 6 wt%and acetic acid content of 54 wt%,with no by-products and acetic acid yield of 96.32%.No precipitate appeared in the product.The stability of the Rh-based catalyst was obviously improved,the amount of water in the system was lowered,the rate of carbonylation was increased,and the catalytic performance of the catalyst was superior.(2)The strong electron donating ability of the N,O-containing organic ligand enhances the electron-rich nature of the metal central atom Rh,and the steric hindrance caused by the ligand prevents the Rh(?)from forming a dimer resulting in subsequent deactivation.The configuration optimization and catalytic mechanism of the coordination of Rh with the organic ligand 2,2'-bipyridyl-3,3,'dicarboxylic acid ligand were calculated,the result suggested that Rh and ligand N,O coordination formed a seven-membered ring complex catalyst,which catalyzed the reaction of methanol carbonylation.The over all change of the catalyst configuration was small,and the energy barriers were reduced,which was favorable for the methanol carbonylation reaction;At 200?,3.5 MPa,H2O content of 6 wt%,acetic acid content of 54 wt%,CH3I content of 12 wt%,acetic acid yield was 96.37%,which no by-products such as dimethyl ether,methyl acetate,and no precipitation appeared,the amount of water in the system was reduced.With guranteed the catalytic activity,the catalyst participates in the reaction as a whole,and the stability of the catalyst was improved obviously.