| Biodiesel has the ad vantages of reproduction, easy biodegradation , low combustion emissions of pollutants than diesel petrochemical, and it is the ideal fuel oil substitutes.So it has been paid much attention recently.Room temperature ionic liquid is liquid materials totally formed by ions under the room temperature or nearby (-30-50℃). It is also called ionic liquid or room temperature molten salts. In recent years, ionic liquid is received more and more research efford due to their application as an eviroment-friendly solvent in organic synthesis.Ionic liquids have different types, like substituted N-alkyl-N'-alkylimidazolium, N-alkylpyridinium, tetraalkylammonium, tetraalkylphosphonium cation and so on, among which the ionic liquid that composed of the organic N-alkyl-N'-alkylimidazolium as the cation have attracted specied interest, and the N-methylimidazolium ionic liquid also received much research attention. Nevertheless, there are only a few reports for acidic ionic liquid for application in synthesis of biodiesel. For this reason, acidic ionic liquid was synthesized based on N-alkylimidazole. And it was applied in production of biodiesel.This paper divides into four parts:1. Study on preparation of acidic ionic liquidsFive ionic liquids (ILs), namely, 1-alkyl-3-methylimidazolium hydrosulfate ([CnMImM]HSO4; alkyl includes ethyl,butyl, hexyl and octyl) , were synthesized and characterized by 1HNMR and FT-IR spectra. The physical proper-ties including solubility, density, viscosity, thermostability, conductivity, pKa were measured and reported for the first time. And it was researched how physical properties are affected by changes in alkyl chain length. The results showed that the alkyl chain length had the most dramatic effect on the properties. The density of [CnMIm]HSO4 decreased with increasing length of alkyl in imidazole; Their viscosities are interrelated with length of alkyl in imidazole, and the viscosity of [C4MIm]HSO4 was the lowest , which viscosity number is 16.359×10-3Pa·s; Because of effect of hydrogen bond and Van Der Waals forces, the pKa of [C6MIm]HSO4 was the least, which pKa is 0.695; The limiting molar conductivity of [CnMIm]HSO4 was more than that of KCl, and the limiting molar conductivity of [C4MIm]HSO4 was the lowest and its limiting molar conductivity was 570.93 S·cm2·mol-1; Their solubility depends on the polarity of the solvents, and they were easy to dissolve in higher polarity solvents; They were stable at temperatures lower than 240℃and behave as Newtonian fluids. Quantitative temperature-dependences of density and viscosity have been obtained. 2. Study on determination of acidic ionic liquids by HPLCA method was developed to assay the purity and then determination of 1-hexyl-3-methylimidazolium bromide ([C6MIm]Br) and 1-hexyl-3-methylimidazolium hydrosulfate ([C6MIm]HSO4) with high performance liquid chromatography (HPLC). The [HMIm]Br and [C6MIm]HSO4 were separated successfully on the the EclipsexDB-C8 column (4.6mm×150mm, 5.0μm) with a mobile phase of methanol and water (92:8, V:V) at 0.50 mL·min-1. The UV detector wavelength was 209nm. The retention time of [C6MIm]Br and [C6MIm]HSO4 was 2.302min and 2.701 min. The detector limits of [C6MIm]Br and [C6MIm]HSO4 were 0.080mg·L-1 and 0.070mg·L-1. The proposed methods showed good linearity for determination of [C6MIm]Br and [C6MIm]HSO4 in a concention range of 1.00-35.00mg·L-1.The relative standard deviation (RSD) of [C6MIm]Br and [C6MIm]HSO4 was 0.99% and 1.89%. The recovery of [C6MIm]Br and [C6MIm]HSO4 was 99.7-101.88% and 97.3%- 104.20% (n=3) .The method was sensitive, accurate and suitable for analysis and determination of [C6MIm]Br and [C6MIm]HSO4.3. Study on application of acidic ionic liquids in esterification and transesterificationBecause traditional acidic catalysts have shortcomings of serious side reaction,difficult recycle, polluting the environment, corrosing equipment and so on, the five kinds of green Bronsted acid catalyst function of ionic liquids were synthesized in the research, and, application of five acidic ionic liquids with a hydrogen sulfate acid group in esterification utilizing oleic acid and methanol was explored and their catalytic mechanism was disscussed. The experimental results were showed 1-hexyl-3-methyl-Imidulium hydrogen sulphate ([C6MIm]HSO4) was the best catalyst of acidic ionic liquid in esterification. Under optimal esterification conditions: n(methanol): n(oleic acid)=2.5:l,ω(oleic acid):ω([C6MIm]HS04)=1: 0.08, temperature 90℃and time 16h, mass fraction of methyl oleate could reach more than 91%. The ionic liquids were stable and could be reused. Methyl oleate was separated from raw material easily; even if ionic liquid was reused beyond 6 times, the conversion of esterification was not decreased.In order to looking for high-activity catalysts in transesterification, five acidic ionic liquids of N-methylimidazolium hydrogen sulfates (shortened title CnMImHSO4, n = 0,2,4,6,8) have been synthesized. Their performs used as catalyst for the transesterification of rapeseed oil with menthanol were investigated using monofactorial experiments and orthogonal analysis experiments. The obtained results shew high catalytic acitivity for [C6MIm]HSO4 in the transesterification. According to the results of orthogonal analysis, the optimum experimental condition were reaction time of 18 h, oil to methanol ratio of 1 : 15 (n : n), and catalyst to oil ratio of 0.06 : 1(ω:ω). The yield of products was beyond 93 %. [C6MIm]HSO4 is stable and effective even after 5 cycles (with yields above 90%). Furthermore, the catalyst is eco-friendly, which indicats wide-applications in the future.4. Study on immobilization of acidic ionic liquidsBecause of the large viscosity of ionic liquid , in the process of recovery it was easy to create greater losses. To overcome these shortcomings, 1-allyl-3-hexylimidazolium hydrosulfate ([AHM]HSO4) with a high catalytic activity in esterification and transesterification has been synthesized and characterized using 1HNMR and FT-IR spectroscopy. [AHIM]HSO4 was immobilized successfully withγ-mercaptopropymethyldimethoxylsilane by silica (SMPMDMS). The catalytic performance of the immobilized ionic liquid (Imm IL) for esterification with different carboxylic acids and alcohols were studied and compared to concentrated sulfuric acid (H2SO4) and ionic liquid (IL) under the same conditions. Results indicated that although less catalytic activity (≈82%) than H2SO4 (≈92%) and IL(≈88%), Imm IL had higher catalytic selectivity(≥98%) and be easier to separate and more environment friendly. In addition, Imm IL possessed good repetition of operational performance which could be reused 10 times without much loss in activities. Possible catalytic mechanism of Imm IL was also discussed in this paper.
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