The Process And Kinetics Research On Dehydration Of Glycols Assisted With Additives In Near-Critical Water

Recently,Near-critical water(NCW)has been gradually developed based on the arisen green chemistry and used as a new medium and an excellent solvent.The prominent properties of NCW is its high ionization constant and low dielectric constant as compared as the normal water,so that NCW has the characteristics of own acid-base catalytic function and the ability of dissolving organic and inorganic compounds.Those excellent properties make NCW used as catalyst in organic reaction as well as reactant and solvent.NCW is usually used as the reactant,medium and solvent in organic synthesis reaction because of its outstanding characters.Its catalytic performance allows certain acid/base-catalyzed reaction to be happened without additional of acid/base catalysts and avoids the neutralization of salt.The performances of excellent transfer and green environmental etc.of NCW have made its potential applied in organic reactions,waste recycling and other fields.Generally,the organic synthesis reaction would be initiated with the additives assisted.At present,the research of NCW is mainly focused on the use of NCW as the reaction medium and the effects of experimental parameters on the reaction,while the additional of some additives and the promotion effect of additives on the reaction in NCW are seldom considered.Introducing some additives to NCW system according to specific reaction type for purpose and researching the effect of additives on organic reaction are very meaning.In the processing,disclose the mechanism of reaction with additives and find out the optimal experimental condition by exploring the function principle relationship between characteristics of NCW,additives,reactant,and products and.In order to improve the application of NCW in organic synthesis reaction and make use of NCW for better economic results.Base on above ideas,three typical glycols,which are 2,3-butanediol,1,4-butanediol and diethylene glycol,are selected and studied the dehydration of them with additional of different additives in NCW.The work mainly includes the effect of reaction parameters(such as temperature,pressure,time reactant/water(r/w)ratio and additives/reactant(a/r)ratio)and the effect of additives on the dehydration of glycols; the possible by-products identification;the possible dehydration mechanisms of glycols;the kinetics of reaction based on the first order;the mechanism simulation of cyclo-dehydration of diethylene glycol based on the quantum research method.The details are given as follows:1.The rearrangement study of 2,3-butanediol in NCWThe rearrangement of 2,3-butanediol(BDL)after introducing CO₂ as the additives in NCW has been investigated for the first time by utilizing the high-pressure reactor designed by ourselves.Detecting the conversion of BDL and the yield of methyl ethyl ketone(MEK)at the temperature range of 250～340℃with different initial pressure of CO₂ in different time.In order to affirm the stimulative contribution of CO₂,the value of pH was calculated after introducing CO₂ in NCW.The reaction kinetics was fitted based on the first-order reaction.The activity energy(Ea)was calculated based on the experimental data.And the results demonstrated that the values of two Ea weren't differential each other,which were 46.07 kJ/mol and 42.77kJ/mol without or with introducing CO₂,respectively.2.The dehydration study of 1,4-butanediol in NCWThe dehydration of 1,4-butanediol(BD)in NCW with additional of different additives,which are Fe₂(SO₄)₃,ZnSO₄ and NaHSO₄ have been investigated.The effects of different additives on the yield of target product tetrahydrofuran(THF)and the conversion of BD at the temperature range of 260～340℃,time of 60～180min and with r/w of 1:10～1:50 were studied.Ea was calculated based on the experimental data and the first-order reaction.The results showed Fe₂(SO₄)₃ had the prominent effect on the cyclo-dehydration of BD and the Ea was 37.23kJ/mol.The dehydration mechanism of 1,4-butanediol was proposed based on above results.3.The dehydration study of diethylene glycol in NCWThe dehydration of diethylene glycol(DEG)was studied at the temperature of 250～360℃and time of 60～240min after introducing different additives.The reaction kinetics was fitted based on the first-order reaction and the activity energy(Ea)was calculated base on the experimental data with different additives.The dehydration of DEG was researched by orthogonal array design(OAD)and the optimum cyclo-dehydration condition was reaction temperature of 360℃,time of 60min,r/w ratio of 1:50,a/r ratio of 1:10 and with Fe₂(SO₄)₃ as the additive.Based on the above results,the dehydration mechanism of DEG was proposed.4.The quantum simulation cyclo-dehydration of diethylene glycol The cyclo-dehydration of DEG was researched by the quantum simulation and the different reaction channels were proposed.The geometries of all species(reactant, intermediates,transition state,products)were optimized and the vibration frequencies were calculated by DFT/B3LYP.The relativities of all species were verified by calculating IRC and the optimum pathway was suggested.The results suggested that the optimal pathway by simulating was coincided with the reaction mechanism presented from the result of experiment.