Study On Furfural Clean Production From Corncob Via "One Step Method"

In the past60years, furfural industry in China has developed into the largest all over the world. However, development of furfural production in China has long been blocked by problems of high pollutants and high energy consumption. It was indicated that there about20t wastewater (COD>18000mg/L) generated and more than25t water steam was consumed to obtained1t furfural. In the recent years, the reuse of furfural wastewater by converting it into steam has been applied by most of the furfural plants in China. However, due to the fouling problem, the actual wastewater treatment efficiency could never reach the design index. Today, furfural plants have fallen into a hobble due to increasingly acute regulation and competition.General situation of furfural production and the research on hydrolysis of lignocellulose and furfural production were summarized firstly. Then, mass and energy balance in furfural production was analyzed and, factors such as furfural yield, furfural concentration in product vapor (or formation rate)、thermal efficiency of boiler and heat exchanger which affect the balance of the system was discussed in detail. It was indicated that any unilateral increasing could never satisfied the need of the running of the furfural production system and systemative method must be applied to promote the under-developed furfural production situation.Since the reuse of wastewater that was rich in acetic acid is an essential part of furfural production and a prerequisite of this research, the origin and output of acetic acid was analyzed at first. Then, furfural degradation kinetics in "acid steam" media was studied so as to confirm the feasibility of wastewater reuse. Then, a calculation that based on this furfural degradation kinetics indicated that there about4.5%of furfural potential yield (about10%of total furfural loss) decomposed in "acid steam" phase. Obviously, it could be inferred that most of the furfural loss was caused by its composed (or polymerized) in the liquid phase. Therefore, promotion in separating furfural from the liquid phase was the crucial step to reduce furfural loss.Aimed at lowering the reaction temperature and increasing furfural formation rate, Lewis acid FeCl3AICl3were applied in catalyzing the dehydration of xylose into furfural. Kinetics of furfural degradation and kinetics of xylose dehydration in Lewis acid media were studied. Additionally, calculated maximum furfural yields were obtained from a three factor model and the dehydration reaction mechanism of xylose was obtained consequently. Furfural selectivity and kinetics parameters indicated that the furfural yield exceeded70%when it was catalyzed by FeCl3or AlCl3and, the dehydration reaction rate of furfural was more than10times higher than that catalyzed by H2SO4. Consequently, FeCl3and "acid steam" co-catalyzed furfural production from corncob was mainly studied in chapter4. A SEM analyse indicated that the microscopic cellulose structure of hydrolyze residue was broken much more severe as FeCl3added and used as catalyst. Then, the micro channels in the particle open and the mass transfer efficiency, the diffuse efficiency in the liquid reaction increased. It was deduced that the mass transfer and the surface renewal could be promoted by reducing the porosity of particle materials layer and increasing pressure drop once the particle material was broken to the ground. In addition, s series contrast experiments indicated that AICl3was more effective for promoting furfural yield.Aimed at promoting the furfural separation from liquid phase and reducing its loss, both of enhancing methods on distillation separation and steam stripping were studied. Experiment results indicated that the enhancing effect of cation on the separation of furfural was depending on its ionic strength, high ionic strength causing high separation efficiency. Additionally, impact effects of one-valence cations on furfural separation from liquid phase could be fitted by Furter equation, but the effect of bivalent and trivalent cations only could be fitted by an amendatory Furter equation due to the complex affect mechanism. In order to save salt resource and production cost, concentrated seawater which rich in metal ions was used as salting out agents. Similar separation efficiencies were obtained when concentrated seawater and simulate seawater was used as salting out agent respectively. But it was also indicate that the furfural separation efficiency in the former was a litter higher due to the effect of Ca2+and Mg2+that contained in concentrated seawater.Fouling problems which severely hampered the evaporation and reuse of wastewater was studied. Firstly, the formation mechanism of fouling in heat exchange tubes was inferred and simulation experiments on the formation and eliminating f fouling for the evaporation of wastewater were conducted. The results indicated that there was almost no fouling formed when the wastewater was neutralized to alkalescence by adding NaOH or Na2CO3. Then, the formation mechanism of fouling could be inferred as following:Acetic acid catalyzed polymerization of dissolving lignin and residual furfural in the wastewater at high temperature. The polymeric substances thus forming and remaining in the heat exchange tubes. Consequently, fouling formed as polymeric substances was hydrothermal carbonized which catalyzed by acetic acid. Although fouling could be eliminated by adding sodium carbonate, few furfural manufactures would apply this method due to the high cost. Therefore, a flocculation method which aimed at removing large particles of dissolving lignin and floatable lignocellulose materials was applied. Simulation experiments results indicated that fouling also could be restrained as a certain cationic polyacrylamide flocculants was used. Therefore, pretreatment of furfural wastewater by flocculation was promising not only because of its simple and low cost, but also almost all of the acetic acid was remained.The last Chapter was the application, optimization, summary and perspective of all the previous fundamental research. There were three steps of research in this chapter. Firstly, xylose degradation kinetics in FeCl3catalyzed and NaCl salting out media was studied. The results indicated that furfural yield could only be promoted dramatically by salting out effect of NaCl. Secondly, furfural production from corncob catalyzed by FeCl3in chloride salting out media was studied, and the concentration range of catalyst and salting out agent, range of reaction temperature were obtained. Thirdly, in order to obtain maximum furfural yield, RSM method was used in optimizing all of the reaction parameters. The element of reaction temperature, FeCl3concentration, acetic acid concentration and concentrated ratio of seawater (or concentration of chlorine salts) optimizes combination was obtained. Furthermore, a maximum furfural yield model was obtained. Finally, an optimal furfural clean production process was establishede as almost all the pollutants could be avoided. Furthermore, the results indicated that the material cost could be reduced38%, and more than80%of the potential furfural yield could be obtained by this process.