Study On Heterogeneous Hydrolysis And Synthesis Of Glycosyl Surfactant By Carbon Based Catalysts

Glycosyl surfactant is composed with carbohydrate and aliphatic chain as hydrophilic and hydrophobic polar group, respectively. According to its wide material sources, efficient biodegradability, non toxic and excellent surface ability, glycosyl surfactant is believed to be ideal substitute for petroleum- based surfactant. Currently, the existing glycosyl surfactants are synthesized by esterification or transesterification using edible sugars as raw materials, such as glucose, sucrose, starch and sorbitol. In the other hand, toxic organic solvent, cosolvent or phase transfer catalysts are applied for purpose of promoting the reaction between incompatible two phases, which overlook the strained food supplies in China and violate the principle of green chemistry.An environmental benign process is proposed in this research for the preparation of novel glycosyl surfactant: cellooligosaccharide esters. Regarding the !Green Chemistry" as guidelines, the heterogeneous synthesized process was conducted under green solvent, carbonbased solid acid catalyst, microwave assistance, carbon- based solid base catalyst and ultrasonic emulsification, with lignocellulosic biomass as raw material. The mechanism of heterogeneous process was also discussed in this research.The wood powders from shrub willow were used as lignocellulosic raw material with partial size small than 0.7 mm. The shrub willow powders were pretreated in five mass of sulfolane under 1704 for 1.5h with the maximum lignin conversion of 89.8%. The sulfolane could be reused more than 7 times after dehydration by 0.2% NaOH, with lignin conversion still more than 80%. The composition and properties of raw materials during the pretreatment were characterized by GC-MS, SEM, XRD, FT- IR, TG-MS and other modern instrumental analysis methods. The mechanism of pretreatment process was proposed here, which believed that the pretreatment of shrub willow in sulfolane was a collaborative process of nucleophilic attack by negative oxygen ions and free radical actions from lignin thermal degradation. Owing to the efficient dissolved ability of aromatic material in sulfolane, lignin was peeled and degraded from heterogeneous interface between lignocellulose and sulfolane. Unwanted degradation of carbohydrate during the pretreatment process was attributed to the electrophilic attack of-1, 4- glycoside bond, !-1, 3- glycoside bond and hydrogen bond in holocellulose by proton from water and organic acids under reaction conditions. A small amount of sugar derives were detected according to 13.9% loss of hemicelluloses and 3.8% loss of cellulose.The carbon- based solid acid catalysts(SCC, SCH, SCL and SCR) were prepared by carbonization at 500 4 for 5 h and sulfonation at 110- 120 4 for 5 h under nitrogen atmosphere, using microcrystalline cellulose, xylan, alkali lignin and residues from pretreatment process, respectively. According to the characterization of structure and properties of by EA, TG, SEM, XRD, RS, FT- IR, BET, NH3-TPD and other modern instrumental analysis methods, the prepared carbon- based solid acid catalysts were believed to be amorphous carbon with fused polycyclic hydrocarbon unit, which loaded with SO3 H, OH and COOH as active groups. The BET surface area of SCC, SCH, SCL and SCR were 2.10 m2/gm1.86 m2/gm1.95 m2/g and1.91 m2/g, and the toal acid density were 2.11mmol/gm1.87 mmol/gm2.20 mmol/g and 2.09 mmol/g, respectively. 0.2 g of microcrystalline cellulose, 0.15 g of prepared catalyst and 3 mL deionized water were mixed and reacted at 1204 for 1 h under microwave assistant, the conversion of microcrystalline cellulose were 83.1%, 78.8%, 83.4% and 81.9% respectively corresponded to different catalysts. Duo to its dispersion action of electron cloud, the fused polycyclic hydrocarbon unit showed positive effect on catalytic activity, hydrothermal stability and reuse ability.The hydrolysis process of holocellulose from pretreatment process was conducted at 1204 for 1 h under 150 w of microwave irradiation, with 0.2 g of holocellulose, 0.15 g of SCR and 3 m L deionized water. As shown in ionic chromatograph analysis results, the dosage of monose, cellobiose, other cellooligosaccharides, and sugar derives were 26.8%, 55.2%, 17% and 1%, respectively. In spite of its small specific surface area, low acid density and acid strength, SCR showed well performance on catalytic hydrolysis of holocelluose, which is more efficient than other solid acid catalysts and a little more than H2SO4. The Na+ exchange experiment, EA, BET, NH3-TPD, IC and other analysis methods were applied for characterization of catalysts and hydrolysate. SCR showed more efficient performance on catalytic selectivity and reuse ability than H2SO4 as a result of the fused polycyclic hydrocarbon unit in the structure of SCR, which is in favor of dispersion of electron cloud. In comparison to traditional heat process, microwave irradiation resulted in higher hydrolysis yield of holocellulose and less degradation of monose, which could be ascribed to its synchronous and uniform heating efficiency.The orthogonal test table L9(34) was adopted in investigation of impact factors of carbon carrier, and average pore size was proved to be more important than mass ratio of K2CO3 and carbon, calcination temperature and time. The optimum conditions for preparation of carbon carrier were as follows: average pore size of 2.87 nm, mass ratio of K2CO3 and carbon of 0.5, calcination temperature of 4504 and calcination time of 2 h. The catalytic performance of K2O/C was detected by the transesterification between sucrose and methyl oleate. The highest yield of sucrose esters was 86.4% under ultrasonic emulsified condition with mole ration of methyl oleate and sucrose 2: 1, ultrasonic irradiation 15 min, tansesterification at 1254 for 2 h. K2O/C showed efficient performance after 4 times reused. The structure and properties of K2O/C was characterized by BET, XRD, FT- IR, TLC and other modern instrumental analysis methods. Higher specific surface area and average pore size were believed to be more efficient for catalytic performance. The absorbed air in the pore of carbon carrier could be removed under vaccum, which is in favor of loading and dispersion of K2CO3 solution into interior of carbon carrier under vacuum impregnated condition. The K2O/C with higher base strength and density could be obtained due to the formation of homodisperse active site of K2O-C during high temperature activated process, in which K2CO3 reacted with activated OH and formed CO2 and H2 O.Methyl oleate and cellooligosaccharides with mole ratio of 2: 1 were emulsified under ultrasonic irradiation with 20 kHz frequency and 150 W power. The highest yield of cellooligosaccharide oleate esters of 85.6% could be obtained under the condition as follows: 5% dosage of K2O/C was added after remove of bulk of water from emulsified system under vacuum, the reactants were reacted at 1254 for 2 h with remove of water and methanol from system. The properties of cellooligosaccharide oleate esters were characterized by FT- IR, 1H NMR, 13 C NMR, TLC and other modern instrumental analysis methods. The prepared cellooligosaccharide oleate esters showed well surface activity with degree of esterification of 19.8%, HLB value of 9.89, surface tension of 32.1 mN/ m, CMC of 0.152 g/L, emulsified power of 28.1%, and well stability performance in harder water. The immiscible two phase of cellooligosaccharide solution and methyl oleate could form uniform and stable emulsified system by the cavitation of ultrasound, which remarkably enhanced the collision probability between sugar molecular and oil molecular. The negative oxygen ions attacked carbonyl carbon in methyl oleate molecular, which was formed by deprotonation of active OH in cellooligosaccharide molecular. The cellooligosaccharide oleate esters were prepared by the nucleophilic substitution actions with the methanol as by- product which was removed from reaction system and promoted the reaction conduct toward positive direction.