Preparation Of High Molecular Solid Acid And Its Application In Biodiesel Synthesis

With the rapid development of global economy, oil consumption is steadily increasing while the reserve is decreasing. As a result, the worldwide oil resource is falling into exhaustion day by day. Meanwhile, exhaust gas produced by burning fossil fuels aggravate environmental pollution. In this background, the development of renewable and clean energies has attracted wide spread concern around the world. Biodiesel is a good alternative or additive to conventional diesel fuels because of the advantages of renewability, biodegradability, lower pollution emissions, nontoxicity,better lubricity and high flash point, as compared with the fossil diesel fues.Currently, biodiesel, consisting of FAMEs, is mainly prepared from refined edible oils through esterification of free fatty acids or transesterification of triglyceride with short chain alcohols in the presence of homogeneous strong acid or base as catalysts, respectively. Nevertheless, the refined edible oils for biodiesel production are not favored as the raw feedstock for the high cost and competition with food, particularly for populous China. Moreover, homogeneous catalysts for biodiesel preparation have disadvantages of equipment corrosion, tedious processes of purifying products, excessive waste water, environmental pollution, and catalysts without recycle rate. However, polymeric solid acid have many advantages, such as less corrosiveness, reusability, non-saponification problem, easy modification, high activity and so on, also has broad prospects in the field of biodiesel industry. Thence, three sorts of functionalized mesoporous polymeric solid acid were prepared successfully and were studied for producing biodiesel from low-cost non-edible oils with the high free fatty acids(FFAs), and following tasks are mainly to carry out:(1) The imidazole functionalized mesoporous polymers(PDVB-VI) was hydrothermally synthesized by copolymerization of DVB and VI. The ionic liquid with different anions([CF3SO3], [HSO4], [Cl], [PW12O40]) functionalized mesoporous polymeric solid acid catalysts(PDVB-[C3VI][X]) were prepared by quaternary ammoniation of PDVB-VI with 1,3-propanesultone, followed by ion exchanging with CF3SO3 H, H2SO4, HCl or H3PW12O40, respectively. These catalysts were well characterized with FT-IR, elemental analysis, nitrogen adsorptiondesorptiona and SEM technologies, which were further used for the production of biodiesel via acid-catalyzed esterification of oleic acid. The results showed that the catalytic performance of these ionic liquid with different anions functionalized mesoporous polymeric solid acid decreased in the following order: PDVB-[C3VI] [CF3SO3] >PDVB-[C3VI][HSO4] >PDVB-[C3VI][Cl] >PDVB-[C3VI][PW12O40], and the conversion of oleic acid reaching to 96.5%, 78.6%, 58.8%, 36.3%, respectively, were obtained in the presence of 4 wt. % catalyst dosage with 30 : 1 of molar ratio of methanol to acid at 130 oC for 4 h. The results also showed that the activity of PDVB-[C3VI][CF3SO3] is higher than the others. Therefore, the reaction conditions were evaluated with an orthogonal experiment using PDVB-[C3VI][CF3 SO3] as the catalyst. Under the optimal reaction conditions of 4 wt. % catalyst dosage with 30 : 1 of molar ratio of methanol to acid at 130 oC for 4 h, the conversion of oleic acid could reach to 96.5% using PDVB-[C3VI][CF3SO3] as the catalyst.(2) In order to improve the activity of the catalyst, the mesoporous polymeric solid acid functionalized with both the sulfonic group and the ionic liquids group(PDVB-SO3H-[C3VI][HSO4]) was synthesized from sulfonation of the ionic liquid functionalized mesoporous polymeric solid acid PDVB-[C3VI][HSO4] by chlorosulfonic acid. The catalyst(PDVB-SO3H-[C3VI][HSO4]) was well characterized with XPS, FT-IR, elemental analysis, nitrogen adsorption-desorptiona, TEM, SEM and TGA technologies. It was demonstrated that the both sulfonic and ionic liquid groups have been successfully incorporated on the surface of the mesoporous polymers and the catalyst(PDVB-SO3H-[C3VI][HSO4]) possessed abundance of mesoporosity, large surface area(281.00 m2/g) and a high acidity of 2.58 mmol H+ g-1. The catalytic performance of the catalyst was investigated by esterification of FFAs in Euphorbia lathyris L. crude oil(aicd value: 24.42 mg KOH/g) with methanol. Therefore, the reaction conditions were valued with an orthogonal experiment using PDVB-SO3H-[C3VI][HSO4] as the catalyst. Under the optimal reaction conditions(molar ratio of methanol to oil 50:1, catalyst loading 6 wt.%, reaction time 3 h, reaction temperature 65 oC), the conversion of free fatty acids could reach to 96.4% using PDVB-SO3H-[C3VI][HSO4] as catalyst. Interestingly, it shows excellent catalytic performance for the one-step transformation of Jatropha curcas L. oil with high acid value(15.9 mg KOH/g) to biodiesel FAMEs via simultaneous esterification of FFAs and transesterification of triglycerides with methanol. Under the optimal reaction conditions(molar ratio of methanol to oil 50:1, catalyst loading 6 wt.%, reaction time 8 h, reaction temperature 160 oC), the FAMEs content of 95.4% was obtained.(3) A novel multi-sulfonic acid functionalized mesoporous polymeric solid acid catalyst was prepared by grafting multi-sulfonic acid group onto ethylenediamine functionalized mesoporous polyer, which was prepared via anchoring ethylenediamine onto mesoporous polydivinylbenzene(PDVB) by covalent bonds. The catalyst(PDVB-SO3H-CH2-En-SO3H) was well characterized with XPS, FT-IR, elemental analysis, nitrogen adsorption-desorptiona, TEM, SEM and TGA technologies. It was demonstrated that the sulfonic groups were successfully incorporated onto mesoporous polydivinylbenzene and the catalyst(PDVB-SO3H-CH2-En-SO3H) possessed abundance of mesoporosity, large surface area(369.00 m2/g) and high acidity of 1.98 mmol H+ g-1. The reaction conditions were valued with an orthogonal experiment using PDVB-SO3H-CH2-En-SO3 H as catalyst. Under the optimal reaction conditions(molar ratio of methanol to oil 30:1, catalyst loading 4 wt.%, reaction time 4 h, reaction temperature 100 oC), the conversion of oleic acid could reach to 98.1 %. Furthermore, under the same reaction condition, the conversion of palmitic acid, lauric acid, tetradecanoic acid, and stearic acid were 92.5%, 90.3%, 89.0% and 92.5%, respectively. It should be noted that the catalyst can be applied for the esterification of different carbon chain fatty acids with methanol.