A Study On Conversion Of Coal And Biomass To Chemicals By Selective Oxidation

As the depeting of petroleum resource, coal and biomass becoming the potential substitute of petroleum, thus the study on the conversion of coal and biomass into chemicals that required by human beings is significant. This study focuses on the selective oxidation of coal and biomass into high-valued chemicals in hot water. The main content and results are as follows:1. The oxidation reaction of lignite in the hot water using oxygen was studied. The effect of parameters on the yield of benzene polycarboxylic acids (BPCAs) were investigated, and the process and mechanism of the oxidation were deeply studied. The results showed that the oxidation temperature, alkali/coal mass ratio, oxidation time and initial oxygen pressure are the primary factors that affect the BPCAs yield. The BPCAs are derived from the oxidative breakage of the aromatic clusters in the lignite.2. The primary problem of the production of BPCAs from coals is the large amount of alkali consumed in the process. The method to decrease the consumed alkali was investigated in this section. It was found that with the oxidation temperature increased, the consumed alkali in the process was decreased dramatically; meanwhile, the oxidation time was shortened obviously. For example, the conventional method to oxidize lignite requires a temperature of240℃and an alkali/coal mass ratio of3/1; however, when the oxidation temperature was increased to300℃, merely an alkali/coal mass ratio of0.8/1was required. Besides, the reaction time of30min was shortened to1min. This new method dramatically improves the economic and production efficiency of the BPCAs from coals. A higher oxidative temperature demands lower salting out effect to avoid deep oxidation of the intermediates.3. The utilization of lignite is a world problem due to its low colification and high water content. With respect to the method studied in our work, however, the yield of BPCAs is low with lignite as the substrate because of its low content of aromatic clusters. But the content of aliphatic structures is relatively rich in lignite, there may be lots of small-molecular fatty acids in the products accompanied with BPCAs. The results show that20-40wt%of small-molecular fatty acids including oxalic acid, formic aicd and acetic acid was obtained in addition to ca.20wt%of BPCAs. These small-molecular fatty acids are derived from the opening of aromatic rings and the oxidation of aliphatic structures.4. For the purpose of avoiding alkali used in the oxiation process of lignite, lots of catalytic system was screened to produce BPCAs and small molecular fatty acids from coals using oxygen. The results show that when using sodium metavanadate dissolving in water as the catalytic system, the lignite can be converted to BPCAs and small-molecular fatty acids with high selectivity. The V-O species are critical for the catalytic oxidation of lignites. This method shows an effective way to utilize the low-colification coals such as lignite.5. The catalytic system for oxidation using sodium metavanadate in water was applied into the oxidation of biomass-based carbohydrates. The results show that this catalytic system has an excellent performance for conversion of carbohydrates into formic acid. A65%yield was obtained from cellulose and64%yield was obtained from hemicellulose. The products in the liquid phase only included formic acid, and which can be separated by extraction method. The recoved catalytic system can be reused for many times without any substantial decrease in the selectivity of formic acid.6. The lignin and lignocellulose including wheat straw and corncob were were chosen as the substrate to be oxidized in the aquous solutions of sodium metavanadate. The results show that yield of formic acid exceed50%can be obtained in addition to small amount of acetic acid with wheat straw and corncob as the substrates.