The Research On Metalloporphyrins Catalyzed O₂ Oxidation Of Cellulose To Produce Formic Acid And Glycolic Acid

Due to the declining coal and oil reserves but sharply increasing oil prices, and more concerns about environment issues, scientists have been focusing on cellulose whose use and conversation is considered an effective way to develop the sustainable energy and green chemicals. However, the utilization of most cellulosic resources is very low currently. Therefore, how to increase the conversion of cellulose in order to obtain high value-added and special performance fine chemical products has become the research focus.This paper explained the author's recent works on these topics, with focus on metalloporphyrin-catalyzed O2 oxidation of microcrystalline cellulose in NaOH solution to produce tiny molecule compounds such as formic acid and glycolic acid. The influence factors on reaction were investigated and preliminary mechanism of oxidative degradation of microcrystalline cellulose by metalloporphyrin was also discussed.The details are summarized as follows:1. The qualitative and quantitative analysis of oxidation products of microcrystalline cellulose were studied by GC-MS,HPLC-MS and HPLC methods. The main products in this reaction system are formic acid and glycolic acid, and other products such as gluconic acid, lactic acid, acetic acid and acetylpropionic acid also have been found. A quantitative HPLC method for the oxidation products of microcrystalline cellulose were established with high accuracy and good reproducibility.2. Several water-soluble and insoluble metalloporphyrin catalysts were prepared. The author also investigated catalytic performance on the O2 oxidation of microcrystalline cellulose in order to produce formic acid and glycolic acid. The result showed that TSPPFeCl has the best catalytic effects.3. After examining various reaction time and temperature, types and amount of catalyst, pressure of oxygen, amount and types of alkali, the author has found the optimized conditions for this transformation:under 5 mL 0.5 mol/L NaOH solution, 0.5 g of microcrystalline cellulose and 1 mg TSPPFeCl, with the temperature (150℃) and pressure of oxygen (2 MPa) reacted for 6 h, obtained the total yield of 98.20%. The yields of formic acid and glycolic acid were 20.06% and 49.36%, respectively. 4. In order to understand the mechanisms of this transformation in alkaline environment, the author compared diverse changes of configuration on the cellulosic surface under different condition and various degrading effects of intermediates with or without metalloporphyrin, analyzed the potential intermediate, and discussed the reaction process in this thesis. After that, in addition of available degradation mechanisms of cellulose and previous experiments, a preliminary mechanism was proposed. The SEM results showed that microcrystalline cellulose processed a stripping reaction under NaOH conditions and macromolecular crystal structure would be destructed. Through hydroxyl radical capture experiments by using DMSO and methylene blue, hydroxyl radicals were found in the reaction system and proved that there is radical process in the O2 oxidation catalyzed by metalloporphyrin. The systemic research of cellulose intermediate found that the addition of metalloporphyrin lead to an easier oxidation of glucose acid, lactic acid, acetic acid and levulinic acid into formic acid and glycolic acid. It also found that oxalic acid is extremely unstable in this system, and easier convert to formic acid.