Study On The Preparation Of Functionalized Ionic Liquids And Their Application In Catalytic Reaction

Ionic liquids,a kind of environmentally friendly solvent and catalyst,are composed of organic cations and organic/inorganic anions.Compared with traditional solvent,ionic liquids have attracted significant attention of scholars from various fields because of their low saturated vapor pressure,strong dissolving ability,excellent thermostability,and good reusability.Moreover,the anions and cations of ionic liquids can be modified by introducing the acid functional groups onto the surface of ionic liquids and the functionalized acidic ionic liquids were obtained.Functionalized acidic ionic liquids perform excellent catalytic activity in the organic reaction,which can replace the corrosive liquid acids used in many reactions,such as transesterification,esterification,condensation reaction,hydrolysis reaction,and Friedel alkylation reaction.Therefore,six kinds of sulfonic acid functionalized ionic liquids have been synthesized and characterized by FT-IR,1H NMR and 13C NMR,four of them basing on quaternary ammonium were synthesized for the first time and relative less expensive.Physical property data such as density and viscosity were measured for binary mixtures of ionic liquids with water and methanol at the different temperatures.Then,the synthesized ionic liquids were used as catalyst in the synthesis of biodiesel and polyoxymethylene dimethyl ethers(DMMn).Furthermore,quantum chemistry calculations were performed to explore the microstructure of some ionic liquids,the interations of ionic liquids with small molecule solvent and reveal the mechanism of reaction catalyzed by ionic liquids.The main contents are as follows:(1)Six acid-functionalized ionic liquids were synthesized and listed as follows:[Ps-N-Ch(Me)2][p-TSA],[Ps-N-Ch(Me)2][HSO4],[Ps-N-Bz(Me)2][p-TSA],[Ps-N-Bz(Me)2][HSO4],[Ps-mim][p-TSA]and[Ps-mim][HSO4].The first four lists were reported for the first time.The structure of them were characterized by FT-IR,1H NMR and 13C NMR,which indicate that the synthesis method is feasible with high purity of ionic liquids.Furthermore,the thermostability of ionic liquids was characterized by the thermogravimetric analysis(TGA),the results exhibit that ionic liquids have high thermostability and their thermal decomposition temperature is higher than 300 ?.(2)Density and viscosity data were measured for binary mixtures of six ionic liquids with water and methanol in the temperature range of 303.15 to 328.15 K at atmospheric pressure.The densities of the pure ILs and its mixtures with water and methanol were successfully described by a quadratic and empirical equation,respectively.The viscosities of the pure IL and its mixtures with water and methanol were well correlated using the Vogel-Fulcher-Tammann equation.The physical properties of pure IL such as the thermal expansion coefficient,molecular volume,standard entropy,and lattice energy were calculated by the empirical and semi-empirical equations based on the density data of pure IL.The densities of each binary mixtures are always between the values for the pure components,which decrease slightly in a linear way with the increase of temperature and increase rapidly with the mass fraction of IL.The viscosities of the two binary mixtures decrease greatly when solvent was added into the IL and temperature was increased.(3)The transesterification of palm oil and methanol catalyzed by Bronsted acidic ionic liquids were investigated.Among all the tested ionic liquids,[Ps-N-Ch(Me)2][p-TSA]exhibits the highest catalytic activity and was chosen as catalyst for further research.A study on optimizing the reaction conditions was performed by orthogonal experiment based on the single factor experiment.The maximum biodiesel yield reaches 98.4%under the optimal reaction conditions at a methanol/oil molar ratio of 24:1,a catalyst dosage of 3.0 wt%,a reaction temperature of 120 ?,a reaction time of 150 min and a stirring speed of 400 rpm.The reusability experiment exhibits that the catalyst can be reused five times with negligible loss of the activity.In addition,the transesterification process can be well described by the pseudo first-order kinetic model and the activation energy is 122.93 kJ/mol.The refined biodiesel meets the biodiesel standard GB/T 20828-2007 and ASTM D6751-07,which can be used as fuel in diesel engines.(4)In the synthesis of polyoxymethylene dimethyl ethers,the effect of different raw material were first discussed,the results display that the synthesis of DMMn from trioxymethylene and methylal is an appropriate reaction scheme under the same catalyst based on the highest conversion of trioxymethylene,selectivity and yield of DMM3-8.Among all the tested ionic liquids sythsized in second chaper,[Ps-N-Ch(Me)2][HSO4]displays the best catalytic performance,and its catalytic performance was systematically explored by the single factor experiment.From the results,the optimal reaction conditions obtained were as follows:the stirring speed of 400 rpm,molar ratio of methylal to trioxymethylene of 3:1,reaction temperature of 120 ?,the amount of catalyst of 4.0 wt%,and reaction time of 3 hr.The conversion of trioxymethylene reaches 85.08%,and the selectivity and yield of DMM3-8 are 58.63%and 49.88%,respectively.The catalyst was reused for six times,and the catalytic activity was not changed obviously.(5)A system theoretical study for the geometrical structures and electronic properties of[Ps-mim][p-TSA]and[Ps-N-Ch(Me)2][HSO4]sythsized in second chaper were carried out based on the density functional theory.Their interaction between cation and anion were also studied at B3LYP/6-311++G(d,p)level.It is found that:1)In the[Ps-mim][p-TSA]ion pair,twelve most stable configurations were obtained,all of which have multiple hydrogen bonds.When the hydrogen atom in cation and oxygen atom in anion are the formation of hydrogen-bond O-H…O,the geometrical structure is low energy and high stability.Natural bond orbital analyses indicate that the orbital interaction from the anion to cation occurs mainly through the LPO??*O-H and LPO??*C-H interactions,which is relative to C-H…O and O-H…O hydrogen bonds.2)In the[Ps-N-Ch(Me)2][HSO4]ion pair,ten most stable configurations were obtained,all of them have multiple hydrogen bonds.When the hydrogen atom in cation and oxygen atom in anion are the formation of hydrogen-bond O-H…O,the geometrical structure is low energy and high stability.Natural bond orbital analyses exhibit that the charge transfer from anion to cation occurs mainly through the LPO??*O-H and LPO??*C-H interactions,which is associated with C-H…O and O-H…O hydrogen bonds.Furthermore,the calculated results reveal that there are strong electrostatic interactions between anion and cation in addition to the existence of hydrogen bonds.The high interaction energies of the two ionic liquids studied here indicate that they have higher melting point,viscosity and good thermal stability,which is consistent with the experimental data.(6)In order to better understand the property of the binary system of methanol and[Ps-N-Ch(Me)2][HSO4]ionic liquid,the interactions of methanol molecule with anion[HSO4]-,cation[Ps-N-Ch(Me)2]+,and ion pair[Ps-N-Ch(Me)2][HSO4]were investigated in detail by density functional theory calculation.The vibration frequency and NBO analyzes were performed.The calculation results show that the hydrogen bonds are widely distributed in these systems,which play a significant role in the stability and miscibility of methanol with[Ps-N-Ch(Me)2][HSO4]ionic liquid.The interaction of methanol molecule with anion[HSO4]-mainly involves the charge transfer from the lone pair of electrons on the oxygen atom in anion to H-O bond on the anti bond orbital of methanol molecule,while the charge transfer from methanol to cation[Ps-N-Ch(Me)2]+ is mainly through the lone pair of electrons on the oxygen atom in methanol molecule to C-H or H-O bond on the anti bond orbital of cation.When the interaction type is LPO45??*O38-H40,the most stable configuration was obtained.In addition,the introduction of methanol in ionic liquid has significant influence on the hydrogen bond interaction between anion and cation,which further effects the physical and chemical properties of ionic liquid such as density and viscosity,the most significant change is the sharp decline in the viscosity of ionic liquid.(7)By performing density functional theory calculations,the detailed reaction mechanism for the synthesis of polyoxymethylene dimethyl ethers via condensation reaction of trioxymethylene and methylal were studied in the absence and presence of catalyst[Ps-N-Ch(Me)2][HSO4]ionic liquid.In the absence of catalyst,the condensation reaction of methylal with formaldehyde from the decomposition of trioxymethylene takes place with an activation energy of positive and reverse reactions of 65.42 and 73.56 kcal/mol,respectively.While in the catalyzed condensation reaction,the H40 atom of ionic liquid attacks the 048 atom of methylal molecule,which makes the 048-C47 bond of methylal be broken and the generation of carbocation C47+.Then it improves the electrophilic ability of carbocation C47+ and reduces the reaction barrier.The results indicates that the reaction takes place more easily.Both of the activation energy of positive and reverse reaction are reduced to 13.31 and 21.45 kcal/mol,respectively.In our study,the microscopic mechanism of the synthesis of polyoxymethylene dimethyl ethers catalyzed by[Ps-N-Ch(Me)2][HSO4]ionic liquid was proposed,and the microscopic nature of ionic liquid in the catalytic reaction was revealed.