subject: The Direct Method of the Application of Natural Gas in Chemical Industry [print this page] The Direct Method of the Application of Natural Gas in Chemical Industry
According to transformation ways, the chemical application of natural gas can be divided into two categories: direct method and indirect method. Direct method is to obtain products like ethane, carbinol and arene through direct-reaction oxidization of natural gas. At present, there are three different lines in direct method. They are the direct productions of carbinol and formaldehyde made of natural gas, ethene through coupled oxidation of natural gas, and arene made of natural gas under the oxygen-deprived condition.
(1) The direct production of carbinol and formaldehyde by natural gas
The technology of producing carbinol through synthesis gas made of natural gas has many shortages, such as high capital investment, complex engineering design and high production cost. Therefore, the ways to produce carbinol by natural gas through one-step synthesis have been being explored at home and abroad, and some achievements characterized by homogeneous oxidation and heterogeneous catalysis oxidation have been obtained. Better effectiveness can be gained through homogeneous oxidation, through which the transformation ration of methane can reach 4% to 15%, and the selectivity can reach 60% to 90%. UOP Company now is developing a new technology to make use of methane to directly produce carbinol at low temperatures and low pressures. This new technology is to transform methane into carbinol by using metal catalyst to activate a kind of perhydrol synthesized at the beginning. Compared to the production by indirect method, the estimated investment can be reduced 58%, energy consumption 60%, and carbon dioxide emission 33%.
(2) The production of ethene through coupled oxidation of natural gas
With the improvement of global chemical market, the study on the production of ethene by coupled oxidation of methane has been more and more valued. At present, more than 40 laboratories in the world have been studying on more than 2000 kinds of catalysts to create new technologies. However, the reaction of the production of ethene by coupled oxidation of methane can lead to the integration of surface-initiated gas-phase radical and gas-solid reaction. Because of the existence of gaseous oxygen, it is difficult to control free radicals. During the process of producing ethene, the transformation ration is relatively low (lower than 25%), and the separation of products is also hard. Therefore, although it has been regarded as the best technology line to produce low carbon olefin directly by methane, it still has many disadvantages, which cannot meet the technological and economic demands of industrialization. It is still the hot issue to search another catalyst system with hot activity, high selectivity and long time stability.
(3) The production of arene by natural gas
There are two ways to produce arene through direct catalysis and transformation of methane, namely, production under aerobic condition and production under oxygen-deprived condition. It has been proved that the reaction caused by the production process under aerobic condition is difficult to control and the transformation ratio of methane as well as the selectivity and productivity of arene are low. Compared to the production under aerobic condition, the production process under oxygen-deprived condition is more productive. The study on the non-oxidative aromatization of methane has already attracted people's attention. It is said that the non-oxidative aromatization of methane catalyzed by Mo/HZSM-5 has broken a new path for the direct application of methane.
