Study On The Measurement Of H/C Ratio In Porous Coked Catalyst

Fluid catalytic cracking(FCC)process is one of the most important secondary processing technologies in petroleum refineries.It utilizes the continuous circulation of the porous microspheres zeolite catalyst in the reactor and regenerator to achieve the continuous catalytic cracking of heavy feedstock.In the operation of FCC units,it is often necessary to regularly measure the characteristics of the coke deposited on the deactivated catalyst(coked catalyst)after reaction for monitoring and adjusting the operating status of the unit.Among them,the H/C mass ratio is one of the most commonly measured parameters,which is often used to evaluate the stripping efficiency of coked catalyst.In the industry,the measurement of the H/C mass ratio in porous coked catalyst is generally calculated by analyzing the flue gas composition.The content of carbon in the coke can be determined by measuring the content of CO and CO2 in the flue gas.By analyzing the content of O2 in the flue gas,the content of Hydrogen in the coke can be further obtained.However,in actual industrial operation,due to operating fluctuations,sampling errors,instrument operation and other reasons,the measured flue gas compositions are not often accurate,resulting in large deviation of the calculated H/C mass ratio.Sometimes,it is even higher than the H/C mass ratio of the feedstock.Previous methods of acid-soluble & elemental analysis and TG-mass spectrometry have been used to measure the H/C mass ratio.These methods have some shortcomings.For example,the analysis process is too cumbersome or the equipment is too expensive.The purpose of this study is to design a new measurement method of H/C mass ratio in porous coked catalyst coke.It is expected that it has the advantages of accurate measurement,low cost and simple operation.In this study,two kinds of porous coked catalysts,FCC and MTO,were first investigated by thermogravimetric analysis.It was found that there was a certain amount of adsorped water and bound water in porous catalysts by measuring the weight loss in coked catalyst in nitrogen flow at high temperature.The water quality can sometimes be as high as 1% of the total mass of the catalyst.The presence of this part of water is the main reason leading to the large errors in traditional elemental analysis.Therefore,the measurement of H/C mass ratio in the porous coked catalyst must be carried out after tit is dried to remove the water in it,and then take measures to measure the masses of H2 O and CO2 accurately in the flue gas.Furthermore,the effects of dehydration temperature and time were investigated by thermogravimetric analysis.The optimum operating temperature and time with rapid dehydration and without thermal cracking of coke were thus determined for the coked catalyst.Based on the above understanding,this study proposes an H/C mass ratio measurement method for porous coked catalyst based on dehydratration and post-absorption weighing,and designs and builds a set of H/C mass ratio measuring instruments according to the method.The measuring instruments mainly have three major systems,including the gas purification system,the sample combustion system and the flue gas absorption system.The gas purification system is mainly used to remove the impurity gas which affects the measurement of H2 O and CO2 in the inert gas and the oxidizing gas.The sample combustion system is used for the combustion of the coke.The contact of CO in the flue gas with CuO can convert all CO into CO2.The gas absorption system is mainly used for the absorption of H2 O and CO2 gas and the removal of impurity gases.In the measurement process,the porous coked catalyst first dehydrate,and then burns the coke by the oxidizing gas,and finally uses high-precision balance to measure the mass increase of H2 O and CO2 absorption container to calculate the masses of hydrogen and carbon in coke and the H/C mass ratio.In order to improve the accuracy of mass measurement of H2 O and CO2,the designs of each system were all optimized.The accuracy of the method was first proved by the measurement of polypropylene(a standard material with an H/C molecular ratio of 2)using the designed instrument.In the measurement process,the measurement of the catalyst with different coke contents,i.e.3g for MTO and 13 g for FCC,was carried out,respectively.The results showed that the reproducibility of the method was better.The error analysis of H/C ratio and coke quantity showed that the method has higher accuracy,the error can be controlled within 5%.Compared with the traditional method of H/C mass ratio,the mass of the catalyst sample used in this method is g-level,while the mass of the traditional elemental analysis method is mg level,which can effectively reduce the sampling and instrument operating errors,and improve the measurement accuracy.In addition,the total cost of the instrument below the 50,000 Yuan,much lower than the thermogravimetric-mass spectrometry method.This method is not only suitable for the measurement of FCC catalyst,but also for the measurement of hydrogen and carbon contents and H/C mass ratio of porous catalysts used in other industrial processes.