Ionic Liquids Enhanced Isobutane/butene Alkylation Catalyzed By Sulfuric Acid

Alkylate oil,the alkylation product of isobutane with butene,which mainly contains isooctane,is an ideal and clean component for gasoline due to its high octane number,low vapor pressure,free from aromatic hydrocarbons,sulfur and olefin.Currently,most industrial manufacturers use sulfuric acid as the catalyst for isobutane/butene alkylation.However,the sulfuric acid catalyzed process has problems of huge consumption of acid,considerable energy requirement in waste acid treatment,etc.In order to solve these problems,the inhibition of side reactions and improvement of the product distribution of the sulfuric acid catalyzed process need to be developed.Alkylation of isobutane and butene catalyzed by sulfric aicd is a kind of liquid/liquid reaction,the low solubility of isobutane in sulfric acid will limit mass transfer occur between the two phases,thus the polymerization,cracking and other side reactions will leading to formation of acid soluble oil and inactivation of the catalyst.In this thesis,ionic liquids with surfactant activity were added to reaction system to build emulsion systems to improve mixing state of acid and alkanes,to enhance mass transfer,to improve product distribution,and to decrease the acid consumption.The main research contents and results are as follows:In this research,a series of quaternary ammonium and phosphonium ionic liquid with surfactivity were choosen as additives,and the physicochemical properties including Hammett acidity,interfacial tension of the ionic liquid/sulfric acid system,and the isobutane dispertion as well as solubility in the mixing system were tested.It was found that with the increase of ionic liquid concentration,the acidity of the system showed a decreasing trend,but the acidity was still in the appropriate acidity range for C4 alkylation.The existence of quaternary ammonium surface-active ionic liquid increased hydrocarbon solubility in the catalytic system,which could enhance the hydrogen transfer from isobutane to C8⁺,thus improving distribution of the products.The NMR and FT-IR characterization of ionic liquid/H2SO4 showed that with the increase of ionic liquid concentration,the hydrogen-bond interaction between the anions of ionic liquids and H₂SO₄ increased and the[HSO₄（H₂SO₄）_n]^-cluster was obtained in this system,which could stabilize the system acidity.The ionic liquid/sulfuric acid systems were used to catalyze the alkylation of isobutane/butene,and the catalytic performance of quaternary ammonium and phosphonium ionic liquid were compared.Ammonium ionic liquid showed much better activity to improve product distribution.With the addtition of one opmital ammonium ionic liquid,weight percentage of C8 in the product was 87.5%,and research octane number（RON）of the alkylate could reach up to 97.8.The lifetime of the ionic liquid/H₂SO₄ system was 130 times compared with 51 times for the system with no additive,leading to decrease of acid consumption by 60%.Determination of the chemical oxygen demand of the deactivated catalytic systems after reusing reactions indicated that extension of the lifetime of the surfactant/H₂SO₄ system was due to the inhibition of the formation of acid soluble oil.Due to the excellent chemical stability and designability of Gemini ionic liquids.A series of dicationic ionic liquids with different length of spacer group were synthesized.Their chemical structures were characterized by nuclear magnetic,ESI-MS,element analysis,and the results agreed with the theoretical values.Surface active performance tests showed that with the decrease of length of the link group,the critical micelle concentration decreased.Alkylation evaluation experiment data also show that dicationic ionic liquids with the shorter link group will achieve better alkylation results.To achieve the same effect of product distribution improvement,the addition of dicationic liquid is only 1/5 of the concentration of single chain ionic liquid.Under the optimal dication ionic liquid concentration（2.5 mmol/L）,weight percentage of C8 in the product was 89.7%,and RON of the alkylate could reach 97.7.