Preparation And Study Of Dimethoxymethane To Methyl Methoxyacetate And Polymethoxy Dimethyl Ether By High Performance Solid Acid Catalysts

Methyl methoxyacetate?MMAc?is an important intermediate for the synthesis of ethylene glycol from syngas route.In this study,an easily-operated method was first developed to pretreat the sulfonic acid resin-based catalysts by using different solvents from dimethoxymethane?DMM?to MMAc.SAresin-sulfolane-393K,which referred to the sulfonic acid resin modified by sulfolane at 393 K for 6 h,exhibited an excellent activity and stability for 50 h with about 100%?99.66%?DMM conversion and 100%?99.96%?MMAc selectivity under 363 K and 5.0 MPa.The influence of different solvents?such as n-hexane,toluene,acetone,methanol,dimethyl sulfoxide,and sulfolane?treatment and the effect of sulfolane-treatment temperatures were studied.The higher dipole moment value of solvents and treatment in sulfolane at lower?353 K?or at higher?413 K?temperature resulted in lower carbonylation efficiency.After modification by sulfolane,the residual H₂O was significantly reduced and the CO adsorption capacity was obviously enhanced.The nitrogen adsorption-desorption results exhibited the larger average pore diameter and pore volume along with the smaller BET surface area.FT-IR spectrum proved that sulfolane indeed entered the pores and changed the surface structure of SAresin.The effect of consecutive reaction temperature variations from 333 to 433 K of SAresin-393K and SAresin-sulfolane-393K was carried out under the same condition and both resin catalysts compared the similar changing trends but SAresin-sulfolane-393K exhibited much higher?11.72%?MMAc selectivity.The outstanding activity and stability of SAresin-sulfolane-393K were corresponded to its very low H₂O content,excellent CO adsorption capability and relatively large pore diameters and pore volumes.The industrial production of MMAc is achieved via the DMM carbonylation.The effect of different kinds of industrial raw materials as well as reaction temperature,CO pressure,CO/DMM ratio,reaction time,drying temperature,water content and recycle times of catalyst were systematically investigated using a slurry phase reactor.A highly efficient sulfonic acid resin was used without the help of any solvent and the DMM conversion reached nearly 100%,with 50.66%MMAc selectivity at 393 K and 6.0 MPa CO for 6 h,with a CO/DMM ratio of only 1.97/1.After removing water from DMM,the MMAc selectivity got as high as 68.83%under the same reaction conditions.Besides,this resin catalyst could be reused nineteen times in a slurry phase reactor.In particular,this resin was used as a heterogeneous catalyst for MMAc synthesis,and continuously performed in a fixed bed reactor for 300 h without obvious loss of activity,exhibiting the excellent stability for DMM carbonylation.The mixtures were successfully separated by reasonable design and control of the distillation process and 99.18%purity of MMAc could be obtained.This highly active and reusable sulfonic acid resin catalyst as well as this direct one-step carbonylation to produce an MMAc process exhibited excellent foreground in industrial application.The Bronsted acid site in 8-MR or 12-MR of HMOR was selectively poisoned in order to clarify the influence of different acid sites for DMM carbonylation to MMAc.The 8-MR of HMOR was poisoned by using different concentrations of NaNO₃ solution.Besides,the 12-MR of HMOR was poisoned by pyridine possessing the similar diameter?0.585 nm?as 12-MR channel?0.67 nm×0.70 nm?.The MMAc selectivity?77.65%?of HMOR-NaNO₃,which was poisoned in 8-MR sites,displayed nearly 2.5 times more than that?31.47%?of the untreated HMOR.However,HMOR-Py adsorbing pyridine in 12-MR sites exhibited almost no carbonylation activity?0.55%?.These phenomena evidently proved that DMM carbonylation hardly occurred in 8-MR acid sites while DMM disproportionation was readily conducted.Bronsted acid sites in 12-MR of HMOR were the only active sites for DMM carbonylation to MMAc.Polymethoxy dimethylether(DMM_3-7)has wide applications as a diesel additive to increase the hexadecane value of diesel fuel and to improve the fuel utilization efficiency.For the synthesis of DMM_3-7 from DMM and trioxymethylene?TOX?,this work systematically studied the effects of different conditional parameters on the conversions and products selectivity with the sulfolane-treated sulfonic acid as the catalyst and the reaction routes were proposed according to the results of products analysis by GC-MS.It was observed that trace amounts?ppm level?of H₂O left in the reaction system significantly influenced the reactants conversions and products selectivity.With raising H₂O content,more white precipitation paraformaldehyde?PF?was gradually produced,while methanol was substantially generated to lower the selectivity of DMM_3-7.The sulfolane-treated method was first proposed and sulfolane solvent was acted as dehydration and pore-forming reagent,that resulted in the absorbed H₂O in the surface/pores of NKC-9 sulfolane obvious decrease from 2154 to 198 ppm.Meanwhile,13X molecular sieve was applied to significantly reduce H₂O content of DMM from 710 to 54 ppm.When the reaction was proceeded at 313 K and 1.0 MPa for 2 h with a DMM/TOX mass ratio of 2/1,the conversions of DMM and TOX and the selectivity to DMM_3-7 were obviously promoted to 52.91%,93.34%,and 61.58%from43.59%,88.41%,and 45.27%,respectively.Comparing to literatures reports,the mass selectivity to DMM_3-7 was higher than 60%that make it promising for industrial applications.