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Alkylation Of Benzene With Long Chain Olefins Using Ionic Liquid As Catalyst

Posted on:2006-06-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:C Z QiaoFull Text:PDF
GTID:1101360155461583Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Linear alkylbenzenes (LAB), as an important intermediate in the detergent industry, are usually mixtures of C1014 alkyl benzenes obtained by alkylation of benzene with C1014 mixed paraffin and olefins in the presence of HF or AICI3 catalyst. Because of the corrosivity and potential environmental hazards associated with HF or AICI3, as well as difficulties in catalyst recycling, a great deal of effort has been made in searching for alternative environmentally benign catalysts. However, the common solid catalysts such as H-ZSM-5, H-ZSM-12, HY and lays still retain certain drawbacks, such as low conversion and selectivity, deactivation and high ratio of benzene to olefin, etc.The synthesis of LAB using chloroaluminate ionic liquids as a direct replacement for solid AICI3 promises significant improvement in the reaction selectivity, combined with ease of product separation and elimination of catalyst leaching. The characteristics of benzene alkylation with 1 -dodecene catalyzed by chloroaluminate acidic ionic liquids can be summarized as follows:(i) Higher alkylation activity for low temperature that allows quantitativealkenes conversions at adequate feed rates under satisfactory mixing. In otherwords, inter-phase mass transfer in a larger range of operation conditionscontrols the apparent reaction rate.(ii) Higher selectivity for the desirable 2-phenyl LAB than traditionalcatalysts.(iii) Sufficient density difference between immiscible ionic liquid and reaction mixture means ease of liquid/liquid separation and little of catalyst leaching. Fast continuous separation of ionic liquid catalyst from reaction mixture thus recycling to the reaction zone is needed.(iv) Due to the moisture-sensitivity of chloroaluminate acidic ionic liquid, sustainable alkylation's activity with long catalyst life using feed containing trace water exists an unsettled problem. New method must be developed to alter this situation.(v) N, N' -Dialkylimidazolium chloroaluminate ionic liquids proved to beone of the best catalyst candidates, and their Lewis acidities can be adjusted toobtain the best performances. These can easily be prepared on an industrial scale,are liquid at the reaction temperature, and are very poorly miscible with theproducts, are corrosive liquids in the presence of protons. When exposed tomoisture, these chloroaluminate salts produce hydrochloric acid, similarly toaluminium chloride. Though this can be avoided by the addition of some protonscavenger such as costly alkylaluminium derivatives in laboratory investigation,there is not a practical solution for industrial application yet.In this work, chloroaluminate ionic liquid [BMIMJfAlCU] was synthesized andcharacterized. Toluene was chosen as solvent for [BMIMJC1 synthesis so as tomaintain the reaction temperature. Acetonitrile and acetic ether recrystallization wasdemonstrated to be the best purification method. Element analysis and IR detectionconfirmed the composite and structure of the synthesized [BMIMjCl. Acetonitrilewas used as an IR spectroscopic probe to compare the relative Lewis acidic strengthsof ILs with different AICI3 proportions.Then, reaction network information for alkylation of benzene with 1 -dodecene was investigated using the [BMIM][A1C14] ionic liquid. The experimental results show that the rearrangement of alkyl chain is not prohibited within 0-5 °C comparedwith AICI3 catalysis. The predominance of rearranged products indicates that the alkyl carbonium ion formed. Besides, the isomerization of products was not detected in the temperature range of 0-75 °C. It is believed that the reaction proceeds by way of carbonium ions mechanism. The formation of different isomers from 2- to 6-LAB can be regarded as parallel reactions.Moreover, the batch reaction performances were investigated using orthogonal experimental method. It shows that the most important factor that governed the conversion of olefin and selectivity of LAB is reaction temperature. Moreover, the effects of molar ratio of AICI3 in ionic liquid to 1-dodecene and that of benzene to 1-dodecene on its conversion and selectivity are obviously in different degrees. The reaction temperature, molar ratio of benzene to 1-dodecene and the amounts of catalyst compared with the traditional reaction technologies are decreased. Further, the experimental results demonstrate that the ionic liquid catalyst had higher activity at 25.0 °C even if the molar ratio of AICI3 in ionic liquid to 1-dodecene and that of benzene to 1-dodecene are 0.07 and 8.Specially, in allusion to the physics and chemistry characteristics of benzene alkylation with 1-dodecene catalyzed by acidic [BMIM][AlCLt] ionic liquid, a revised continuous flow reactor equipped with a special bell type of settling-separating-discharging device is proposed. In this way the in situ separation of product mixtures from ionic liquid was realized and the stability of ionic liquid catalyst for the alkylation reaction was tested. A considerably longer running time of catalyst and higher efficiency were attained.Besides, immobilization of [BMIM][AlCLt] ionic liquid on mesoporous silica by different processes was carried out also. The catalytic properties of the immobilized catalyst for benzene alkylation with 1-dodecene were studied and compared with the same type of common IL. The reaction selectivity of the immobilized [BMIM][A1CL?] ionic liquid catalysts from one-step or two-step preparation method was found to be almost similar, but obviously different from the supported AICI3. A significantenhancement in the selectivity of 2-isomer (from 37.4% to 52.5%) has been observed over the immobilized IL catalysts, although a much lower activity than that of [BMIM][A1C14] IL itself.Specially, a continuous mixing-reacting-separating-recycling experimental setup has been designed and constructed. A static mixing reactor was used to realize the needed fast mixing and chemical reaction. The continuous fast separation of ionic liquid from reaction mixture carried out in a combined liquid-liquid settling phase separator. The mixing and separation performances of this system along with the operable region of synchronously accomplishing have been investigated. Results of running tests show that the continuous efficient fast mixing and separation between ionic liquid catalyst and reaction mixture can be synchronously accomplished within some flow ratio ranges of the recycling reaction mixture and the ionic liquid catalyst injected. The moisture-sensitive ionic liquid catalyst can be effectively maintained and recycled in the system. Alkylation tests demonstrate that the setup can be successfully used to synthesize LAB continuously with relatively higher 2-phenyl LAB selectivity.Furthermore, starting with the chemistry mechanism of deactivation, metal Al was adopted to compensate the loss of [BMIMjfAlCU] catalyst owing to both benzene and trace water. A tube packed with metal Al thread was inserted between the static mixer reactor and the continuous liquid-liquid settling phase separator. ICP-AES detection results of Al content in the reactants phase from Al compensation to the reaction system tests demonstrate that metal Al may be an important choice to improve the reusability of moisture-sensitive ionic liquid [BMIMJfAlCU] as catalyst.Lastly, continuous reaction tests for benzene alklylation with olefins in industrial material have been carried out. Results show that refined industrial olefins material can meet with the requests of continuous alkylation reaction. Owing to the dilution of massive alkanes in the industrial olefin material, the reaction rate is relatively lower than that of by using reagent materials thus resulting the lower...
Keywords/Search Tags:benzene, 1-dodecene, long chain olefins, alkylation, ionic liquid, recycling, in-situ compensation of Al, industrial olefin material
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