Catalytic Dehydration Of Methanol To Dimethyl Ether

Petroleum is on the advance,realizing the diversification of energy and exploiting low-cost oil substitutes and clean energy alternatives has been a priority of the agenda.Our country is rich in coal resources,converting coal to alternative fuel to petrol and diesel is accordant with the situation of our country,which can safeguard energy security and stabilize sustainable development.As environment-friendly and the versatility characteristic,dimethyl ether has become a hot subject in the area of chemical engineering and energy.The comparative advantages of DME are as follows:high cetane number,higher calorific value evenly matched with LPG,only C-O and C-H bond,gives no residuary solutionin in combustion process,lower NOx emission as well as CO and near zero smoke amounts.The most popular technique of methanol dehydration to DME is mature with high degree of automation,facility operation,no special requirements to the equipment,be apt to install large scale,higher purity,virtually no waste emissions and corrosion.However the future development trend is one-step way,currently,solid acid catalyst for methanol dehydration requires high reaction temperature,unable to match the optimal temperature of methanol synthesis on copper-based catalysts.So enhancing their ability to adapt to lower temperature is of great significance.Catalyst ?-Al2O3 is selected as the research object,which is often used in producing DME from methanol,various precipitation agents were used for preparation of catalyst precursor,a systematic research has been made to study the activity and stability in methanol dehydration reaction in order to find out the best one.Then template agent P-123 was introduced,a three-factor uniform experiment design was utilized on purpose to determine the optimal conditions.Further,two distinct forms of Zr02 were introduced into the mixture including the monoclinic phase and amorphous phase,its purpose is to reverse acidic property of Al2O3.The catalysts were characterized by NH3-TPD,XRD,N2 adsorption and TEM technology,and evaluated in the process of methanol dehydration.The experimental results came to the following conclusions:1.The catalyst ?-Al2O3 prepared by urea exhibits excellent catalytic activity for methanol dehydration.The one prepared using Na2C03 as precipitant displayed lowest activity as its surface is covered by residential Na+not completely removed.2.The use of template and pore-forming agent greatly improved catalytic activity as well as surface area,pore volume and pore size.The uniform experiment result showed that the main effect factors follow the order temperature>urea>P-123,and the optimizing conditions are shown as follows:n(P-123):n(Al3?)=0.0173,n(urea):n(Al3+)=35,calcination temperature of 700?.3.The introduction of monoclinic phase of Zr02 reduced catalyst activity,the surface acid strength enhanced,but the amounts of acid sites reduced,while the amorphous phase of Zr02 showed higher activity,the amounts of acid sites increased,but weak strength reduced,the moderate acidic sites can also be found.The specific surface areas of the former one is smaller and pore diameter increased,however the latter is quite the opposite.4.The weak acidic site of catalyst has an effect on catalyst performance,the activity showed a significant dependence on enhanced weak acid strength and amounts of weak acidic sites of the alumina.The performance of catalyst with proper proportion between weak and moderate acidic sites is not sensitive to temperature.Strong acidic sites are more susceptible to competitive promoting side reactions and generating unsaturated hydrocarbons,which are coke precursors.5.Catalyst with multi-pore distribution is beneficial to methanol dehydration.6.Catalyst with wide dispersion diffraction peaks and poor level of crystallinity performed well in dehydration,?-Al2O3 was inferior to AlOOH.There is a competitive reaction between multiple planes,a individual ?-Al2O3(400)plane is beneficial to dehydration.