The Research On Hydrolysis Of Cellulose With Chlorine Functionalized Carbon-based Solid Acid

Cellulose is widely distributed and largely reserved in nature. The hydrolysate after cellulose hydrolysis can be converted into fuels and chemicals, which is regarded as a better way for cellulose efficient utilization and environmental friendliness. Although these homogeneous reactions such as liquid acid-and enzyme-driven reactions act as highly effective methods for cellulose hydrolysis in the industry, there are some shortcomings, e.g. separation of catalyst with products and environmental pollution. In order to overcome the problems that the homogeneous catalyst brought into the reactions, carbon-based solid acid (CSA) is introduced into homogeneous catalysis, which have been widely used in biodiesel synthesis and cellulose hydrolysis. However, compared with the reactions in biodiesel production, the efficiency of cellulose hydrolysis is unsatisfactory, mainly because the interaction between CSA and cellulose is not strong enough. Although phenolic OH bonded to CSA has the ability to adsorb cellulose, the adsorption effect is not satisfactory for breaking the hydrogen bonds in cellulose. Therefore, we attempt to introduce chlorine atoms with strong electronegativity on CSA, which will cooperate with hydroxy to break the hydrogen bonds in cellulose, exposing glycosidic bonds. As a result, the catalytic sites on catalysts and glycosidic bonds are located close enough in space to permit the hydrolysis of cellulose.1. In the paper, the effect of four inorganic salts on cellulose hydrolysis is studied preliminarily. The result shows that the halides and nitrates can promote the cellulose hydrolysis. However, the differences in the promotion effect between halides and nitrates indicate that the promotion of chloride to the cellulose hydrolysis is not only connected with ion exchanging but also due to the fact that chlorine could disrupt the cellulose crystalline structure, releasing the glycosidic bonds parcelled in hydrogen bonds network, so that the sulfonic groups contact with glycosidic bonds to start the hydrolysis process. Finally, we determine to introduce chlorine atom on CSA.2. The functional carbon-based solid acid 1-CCSA was successfully prepared by sulfonation of carbonized polyvinyl chloride(PVC) and the effect of carbonization temperature and time on the performance of catalyst was investigated. The characterization results show that 1-CCSA is an amorphous carbon composed of aromatic carbon sheets bearing active sites such as -SO3H,-OH,-COOH groups, especially covalent chlorine which is benefit to promote the catalytic performance. The polymerization degree of catalyst increases with the increase of carbonization temperature and time and the sites at the edges of aromatic carbon sheets, which can be replaced by oxidation and reduction, decrease, resulting in the decrease of the density of oxygen-containing functional groups on 1-CCSA. As for the catalytic performance of 1-CCSA, the reducing sugar yield decreases with the increase of carbonization temperature and time, which is consistent with the density of oxygen-containing functional groups and the adsorbability of catalyst. However, there are some differences in the changing degree, indicating that the performance of catalyst is controlled not by some one factor, but by the overall structure of catalyst.3. The functional carbon-based solid acids 2-CCSA and 3-CCSA were prepared by sulfonation of carbonized PVC and cellulose, PVC and PE, respectively and also the effect of PVC proportion on the structure and performance of catalyst was investigated. The TG-DTG results show that no matter co-pyrolysis of PVC and cellulose or PVC and PE, the interaction between the two occurred, and the actual yield of carbon precursor is higher than the theoretical yield, showing that the mixture is in favor of the formation of carbon precursor. However, the difference is that PVC promotes the pyrolysis of cellulose but suppresses that of PE. The former is due to the HCI released from PVC acting as a catalyst to accelerate the decomposition of cellulose, and the latter is because of the chansfer of chlorine radical from PVC to PE. The characterization results show that these two catalysts are amorphous carbons and the polymerization degree increases with the increase of PVC proportion. The remarkable differences between these two catalysts and traditional CSA are that the covalent chlorine is introduced onto CSA, which increases the interaction between catalyst and cellulose. The density of-SO3H on these catalysts increases with the increase of PVC proportion, which shows that the adding of PVC is not only introducing a new functional group on the catalyst but also effecting the structure of catalyst, which is benefit to supporting-SO3H. The adsorbability of these catalysts is remarkably higher than CSA derived from cellulose and increases with the increase of PVC, indicating that the adsorbability of catalyst is not only associated with covalent chlorine but also the sulfonic acid groups. In the same conditions, the catalytic performance of these catalysts is higher than traditional CSA and 1-CCSA, and also increases with the increase of PVC. It is consistent with the adsorbability of catalyst but the degree of change is different, indicating that the performance of catalyst is controlled not by adsorbability, but by the overall structure of catalyst.In this paper, three functional CSAs were synthesised from PVC, cellulose and PE. Compared with the traditional CSA, these catalysts hydrolyze cellulose efficiently. At the same time, the mixture of PVC and cellulose or PE controls the structure of catalyst optionally, which will lay a foundation for the design of other new catalyst.