Ionic Liquid-functionalized Biochar Sulfonic Acid As A Biomimetic Catalyst For Hydrolysis Of Lignocellulose

Widespread use of distributed and inexpensive lignocelluloses instead of petroleum resources to produce some important fine products, it has become one of the research hotspots in the resource and energy academe. As composition and structure of the lignocelluloses are complex, it’s the key of how efficient catalytic conversion of lignocelluloses for the food and fine chemicals to meet the the needs of development of human society. Biomass char sulfonic acid catalyst in catalytic hydrolysis of lignocelluloses,it has advantages of separation the product easily, operation the reation conveniently and the catalyst for cheap, but the catalytic activity of catalyst is slow and poor repeatability. In this paper, for efficient transformation of lignocelluloses, from the point of catalytic chemistry, environmental protection and reducing the production cost, a series of biomimetic catalysts have been designed and used to hydrolysis of lignocellulose. The main research results are achieved as follows:1. The ionic liquid of 1-(trimethoxy propyl silane)-3-methyl imidazolium chloride was grafted on biochar sulfonic acid to obtain the biomimetic catalyst BCSA-IL-Cl. The catalyst under microwave radiation can effectively multiphase catalytic cellulose hydrolysis. We studied the effects on the cellulose hydrolysis of condition including the way of heating, the reaction time, temperature, microwave power and the reaction medium. Under optimized conditions(Water medium, Microwave power 350 W, reaction temperature 90 oC, reaction time 120 min), the proposed catalyst was found to show a effective catalytic activity for the microwave-assisted hydrolysis of cellulose, the yield of RSs can reach 33.40%, and turnover number can reach 3.22, the catalytic activity is more than doubled higher than catalyst BCSA. Also this catalyst has an excellent repeatability. According to the result of 31 P MAS NMR characterization, TG-DTA characterization and adsorption ability of the catalyst to β-1,4 glycosidic bonds. We found that due to the ionic liquids connected by flexible chain on biomass char sulfonic acid, and the synergistic reaction between-SO3 H and Cl- anion of ionic liquids on the catalyst. The synergistic reaction not only enhance the-SO3 H groups of thermal stability, also enhance the acid catalyst. At the same time, the Cl- is easy to produce electrostatic effect with β-1,4 glycosidic bonds of cellulose, which can increase the affinity of catalyst on the cellulose molecules. Owing to the chloridion, the catalyst has the function of cellulose binding district which is similar to cellulose enzyme. The strongly acidic-SO3 H groups can effectively break the net of hydrogen bond which is similar to the catalyticdomain district. Based on the experimental results, a the mechanism of the biomimetic catalyst catalyze hydrolysis of cellulose was proposed.2. In order to further enhance the biomass carbon acid(BCSA) catalytic activity for hydrolysis of cellulose, we prepared a new efficiently biomimetic catalyst(BCSA-IL-Zn) by chlorozincate ionic liquid was immobilized on BCSA. The catalyst BCSA-IL-Zn catalyzed hydrolysis of cellulose under optimized conditions in water medium, the yield of RSs can reach 58.70%, and turnover number can reach 5.91. As the interaction force between ZnCl2 and-SO3 H become stronger, so the acid strength of the catalyst BCSA-IL-Zn increased and have better the thermal stability of-SO3 H. High density Cl- on the catalyst can promote adsorpt β-1,4 glycosidic bonds, which lead to reduce the activation energy of hydrolysis of cellulose.3. For the sake of direct conversion of lignocellulose, an efficiently Biomimetic Catalyst(BCSA-IL-Cu) which also have delignification(BDL) function had been prepared by chlorocuprate ionic liquid functionalized biochar sulfonic acid. The catalyst BCSA-IL-Cu directly catalyzed hydrolysis of lignocellulose under optimized conditions(microwave power 750 W, reaction temperature 110 oC, reaction time 120min) in water medium, the yield of RSs can reach 22.50%, the yield of HMF is 1.50%. Also we had studied the the mechanism of catalytic hydrolysis of lignocellulose. BCSA-IL-Cu bearing-IL-Cu and-SO3 H groups shows not only a biomimetic delignification(BDL) function, but also a functionality mimicking the cellulose binding domain(CBD) and catalysis domain(CD) of cellulose.4. A series containing F atoms biomimetic catalysts(BCSA-IL-F1-3s) was obtained by anion exchange. These catalysts can effective catalytic hydrolysis and conversion of cellulose under microwave radiation into reducing sugar and HMF. Under the optimized conditions(microwave power 350 W, reaction temperature 80 oC, reaction time 3 h), the turnover number of catalyst BCSA-IL-F1-3s catalyzed hydrolysis cellulose are 4.34-4.89, especially, the yield of HMF can reach up 27.94%. As the functional groups of IL-F1-3s existence on catalyst, the catalyst acidity become more stronger, the adsorption capacity of the cellulose molecule with catalyst have been improve, and the activation energy for the hydrolysis of cellulose reducing. The synergistic effect between IL-F1-3s and-SO3 H, which effectively promoting the hydrolysis of cellulose and the conversion of reducing sugars into HMF.5. In order to convert lignocellulose into HMF, we designed another new efficiently biomimetic catalyst(BCSA-PI-2005) which was prepared by the polyimide to modified biochar sulfonic acid. This catalyst show excellent catalytic activity and selectivity under microwave irradiation on hydrolysis of cellulose. In the pure water medium, under mild conditions, the yield of RSs and HMF can reach 25.60% and 23.10% respectively, the selectivity of HMF up to 47.43%. The results show that the polyimide on the catalyst make the catalyst have a excellent adsorption of capacity of β-1,4 glycosidic bonds, which promotes hydrolysis of cellulose. On the other hand, polyimide is a weakly basic, which can catalyze the isomerization of sugar to HMF.