Basic Research On Screening And Preparation Of Catalysts For Nonoxidative Conversion Of Methane To Alkanes And Olefins

Nonoxidative conversion of methane to ethylene,aromatics and hydrogen has made significant progress in recent years.The successful development of the highly efficient Fe（?）SiO₂ catalyst has attracted wide attention.Igneous mineral with high-temperature-resistance is widely distributed on earth.The formation of igneous mineral is similar to the preparation of Fe（?）SiO₂.Iron,titanium and other active metal elements in igneous mineral are possible to be active sites of catalyst.In this paper,the catalyst used for nonoxidative conversion of methane was screened in igneous,then prepared through solid phase sintering.Catalytic effect of basalt and feldspar on nonoxidative conversion of methane to C₂ hydrocarbons was studied.Feldspar catalysts modified by Pb²⁺ and Fe³⁺ were prepared by the method of ball-milling and solid phase sintering.The active site of feldspar was confirmed.The main results were as follows:（1）Both of granite,basalt,andesite and rhyolite have a certain catalytic effect on nonoxidative conversion of methane.Under the same reaction conditions,the catalytic effect of basalt is the best.Under the conditions of reaction temperature（950 ℃）,GHS V（4 L/h）,and the basalt dosage（2 g）,the conversion of methane was 11.3%,and the selectivity of C₂ hydrocarbons was 16.96%.Feldspar has stable catalytic activity.In contrast,quartz has no catalytic activity and biotite is rapidly deactivated within three hours.（2）Nonxidative conversion of methane to C₂ hydrocarbons and coke by basalt is classified to catalytic pyrolysis of methane.Gas space velocity and reaction temperature have important influence on the catalytic activity of basalt.At the same temperature,when the GHSV increased,the selectivity of ethane increased,however,the selectivity of acetylene reduced.At the condition of methane GHSV 4 L·h-1,when the temperature reached up to 1025 ℃.the conversion of methane increased to 5.12%.（3）Through high-temperature calcination the impurities of quartz and calcite in the natural feldspar can effectively eliminate.As a result,the structure of albite changed to labradorite.Under the conditions of reaction temperature（950 ℃）,GHSV（4 L/h）,and the labradorite dosage（2 g,50-100 mesh）,the conversion of methane was 6.95%and the yield of C₂ hydrocarbons was 5.31%.Increasing reaction temperature,reducing gas space velocity and decreasing the feldspar particle size are all conducive to the conversion of methane and the formation of C₂ hydrocarbons.The selectivities of ethane,ethylene and acetylene are significantly affected by the reaction temperature and the methane GHSV.（4）Pb²⁺ successfully enters into the alkali（or alkaline earth metal）sites,however,partial Fe³⁺ enter into the tetrahedral sites of feldspar through doping modification.The catalytic activity of feldspar is mainly determined by alkali（alkaline earth metal）sites.Pb²⁺ doping can effectively improve the catalytic activity of feldspar.Under the conditions of reaction temperature（800 ℃）,GHSV（0.5 L/h）,and the catalyst dosage（0.25 g,300 mesh）,when the Pb content increased from 0%to 5%,the conversion of methane increased from 3.32%to 8.19%while the yield of C₂ hydrocarbons increased from 3.31%to 8.11%.Feldspar has significant effect on activation of methane,nevertheless,has little effect on the selectivity of ethane,ethylene and acetylene.