Study On Selective Regulation Of Fischer-Tropsch Synthesis And Olefin Metathesis

Fischer-Tropsch Synthesis（FTS）is an important process for catalytic conversion of synthesis gas（CO+H₂）into clean energy and high value-added chemicals.There are many Fischer-Tropsch synthesis products.Following the ASF（Anderson-Schulz-Flory）distribution,how to break the ASF distribution and achieve the targeted regulation of the products is one of the most challenging topics in the field of synthesis gas conversion.In the ASF distribution,the selectivity of the ethylene-butene product is often slightly lower than the predicted value.The root cause is that the ethylene-butene species generated on the surface of the active site may be adsorbed again on the active site,and hydrogenation or chain growth may occur.As a result,overall selectivity is reduced.It can be seen that by regulating the reaction of olefin species in the catalyst,selective regulation is expected.In this paper,a Fischer-Tropsch synthesis-olefin metathesis bifunctional catalyst is designed.Syngas produces olefins at Fischer-Tropsch synthesis active sites,and olefins are processed again with olefin metathesis active sites.Achieve selective regulation.The effects of factors such as reaction conditions,loading of disproportionate active species,and molecular sieve support on the selectivity of functional catalysts were systematically studied.The main research contents are as follows:（1）Co₂C is used as a Fischer-Tropsch synthesis component,and W/USY is an olefin metathesis component to form a functional catalyst.The effects of a series of parameters such as mixing method,reaction hydrogen-carbon ratio,and mass ratio of two components on the functional catalyst product were systematically studied,and a model reaction test of olefin metathesis components was conducted to explore the mechanism.The study found that the olefin selectivity of the Co₂C component alone is as high as 88%.After coupling with the W/USY component,olefins are greatly reduced,producing a large amount of isoparaffins,of which the selectivity of isobutane is as high as 52%.The selectivity of isoparaffins reaches 70%.Although mechanical mixing will increase methane selectivity,closer contact will increase isomerization selectivity.The optimal hydrogen-carbon ratio of the catalyst is 1:1;the optimal loading of W in the W/USY component is 10%;the optimal ratio of the two is Co₂C:W/USY=1:5.The model reaction test found that the CO in the syngas greatly promotes the formation of isomerized products,and the mechanism needs further study.（2）The effect of the acid properties of USY on functional catalyst products was systematically investigated.Mainly explored two aspects:one is to use different concentrations of citric acid to carry out different degrees of acid etching on the metathesis catalyst carrier USY,and systematically studied the influence of a series of parameters such as acid concentration,acid strength,acid type on functional catalyst products,The study found that within a certain range,as the acid concentration increased,the acid density of the catalyst was reduced,so that the metathesis effect was weakened,the selectivity of isobutane was gradually reduced,and the distribution of reaction products was gradually toward C₅₊The deviation makes the C₅₊isoparaffin increase.And further explore the correlation between different concentrations of citric acid etching modified USY and the selectivity of reaction products.The second is to study the effect of the change of different Na content in the carrier USY on the change of acid properties and then on the functional catalyst product.The system characterizes and tests the functional catalyst through a series of parameters such as acid concentration,acid strength,and acid type.The study found that different Na content catalysts have different acid distributions,and there are different degrees of difference in acid strength and acid amount.These differences will change the environment of olefin metathesis and affect the effect of olefin metathesis.The higher Na content will cause the acid strength of the catalyst to be significantly reduced,and the acid density of the catalyst will also be reduced,resulting in a reduction in the metathesis effect of olefins,resulting in a reduction in the selectivity of the single component isobutane in the product C₅₊direction offset.