Studies On Direct Of CH₄ And CO₂ To Acetic Acid By Two-step Reaction Sequence

The conversion and utilization of CH4 and CO2 is one of the most significant subjects for study in the field of catalysis. It has important implications for resources, energy and environment that are essential to human survival. The chemical utilization of CO2 on a large scale entails an abundant supply of hydrogen. Unfortunately, in most cases (under the oxygen-free condition) it is a high energy-consuming and a thermodynamically disadvantageous process to synthesize directly high value-added chemicals from CH4. Therefore, it is of great necessity to find a route to convert CH4 and CO2 in an oxygen- and hydrogen-free way with a low consumption of energy.The oxygen-free homologation of CH4 through the two-step reaction provides the field of chemistry and technology with the prospect that the division of one reaction into two may circumvent the limitations of the reaction thermodynamics. But is this method fit for general application? Can it be taken as an elementary technique in chemistry and technology? This dissertation attempts to find the answers to these questions with research efforts made into the direct synthesis of acetic acid from CH4-CO2 by the two-step reaction sequence.As an important organic chemical raw material, acetic acid is widely used in food industry, printing and dyeing industry and pharmaceutical industry and ranks first among the organic acids in terms of the industrial output. The important of acetic acid is to organic chemistry like that sulfuric acid to inorganic industry.In its earliest stage of development, acetic acid was produced through fermentation. Later methods include the carbonylation of methanol, the liquid oxidation of butane, light oil and acetaldehyde. The carbonylation of methanol is the major method being in current use, through which 55 % of acetic acid on the international market and 98 % on the American market is produced. However, the catalyst system involved in the method istoxic, highly corrosive and expensive.The current commercial technology to produce acetic acid from CH4 is a process of indirect conversion, taking the three individual steps of transferring CH4 to syngas, syngas to methanol and methanol to acetic acid, each of which uses a separate catalyst and reactor. Because of the thermodynamic limitations, the reaction of CH4 to syngas must be carried out under the harsh condition of high temperature, which consumes plenty of energy and necessitates sophisticated technological equipment. As a result, the cost of this process makes up more than 60 % of the total cost involved in the production of acetic acid. Therefore, to renovate the synthesis of acetic acid is of great significance to improve the economic performance of the conversion of CH4.Based on a summary of the development of Cl chemistry at home and abroad and author's working experience in the study of CO2 hydrogenation, this dissertation proposes the method of direct synthesis of acetic acid from CH4 and CO2 through a two-step reaction sequence in a mild condition, makes a preliminary study of the performance of several kinds of Cu-Co, Pd, Rh, Ru-Co catalysts by making use of a micro-reactor apparatus designed by the author, characterizes the concerned catalysts by means of TPR, TPSR, XRD, TG-DTA, TEM, SEM&EDS and "in situ" FT1R etc, relates their characteristics to their reactivity, and comes to the following conclusions:(1) The direct synthesis of acetic acid from CH4 and CO2 in a mild condition can be effected by first producing surface carbon species (CHX) through the interaction of CH4 and a catalyst and then making the surface carbon species react with CO2 or CO2/H2. The thermodynamic barrier of total reaction can be consequently overcome. This method does not involve the processes of transferring CH4 to syngas, syngas to methanol and methanol to acetic acid, which simplifies the technological process and is applicable under mild conditions.(2) The direct synthesis of acetic acid from CH4 and CO2 by a two-step reaction has non-catalytic nature. Besides the performance of a cat...