Preparation And Industrial Pilot Plant Experimental Study Of Catalyst For Nitrous Oxide Direct Decomposition

Based on a project funded by Kailuan?Group?Limited Liability Company,the work in this paper aim to develop a catalyst to abate nitrous oxide produced in the adipic acid plant by direct decomposition method.This work included two parts of investigation.One was to develop a suitable catalyst in laboratory scale.And the another was to produce industrial catalyst and build a pilot test for measuring activity of the catalyst to decompose N₂O emitted from the adipic acid plant.In the first part of the experimental work,a series of composite oxide catalysts were prepared for N₂O decomposition by impregnation method in the laboratory.The activity of the catalysts was evaluated in a micro-fixed bed reactor.The catalysts were characterized by means of XRD?BET?H₂-TPR etc.A series of CoCuCeFe/?-Al₂O₃ catalysts and CoCuNiZn/?-Al₂O₃catalysts were designed by orthogonal test method and prepared by impregnation method.Experimental results indicated that all the catalysts exhibited spinel structures under calcinated at 550°C for 4 hours.The specific surface area of the catalyst decreased with the increasing metal oxide loading.The copper oxide in the catalyst could reduce the reduction peak temperature and significantly increase the catalyst's activity.The optimum condition was that the loading of Co,Cu,and Zn were 9%,16%,and 3%,respectively.The N₂O decomposition could reach to 100%when the reaction temperature was 528°C.By mechanical mixing of a certain proportion of H?molecular sieves in?-Al₂O₃,the obvious plugging phenomenon was not found in the present study which might show that H?molecular sieves could enhance the reaction activity of CoCuZn catalyst.As for the second part of study,about two hundreds kilograms of industrial catalyst were produced and examined their reaction activity for N₂O decomposition in a pilot plant.Given the cost of industrial catalyst preparation,we selected P-DF-03 type pseudo-boehmite as carrier precursor and the industrial grade material such as cobalt nitrate,copper nitrate and cerium nitrate as active component precursors to make up five grass shaped catalyst by extrusion molding.First of all,the influences of the HNO₃ concentration,sesbania powder dosage,and liquid/powder ratio on the physical properties and reaction activity of the catalyst were investigated by the method of single factor experiment.It showed that the mechanical strength of the catalyst increased firstly and then decreased with increasing HNO₃ concentration and liquid/powder ratio.Excessive sesbania powder would decrease the mechanical strength of the catalyst pellet.Industrial catalyst production included the exploration the molding conditions of the catalyst fabrication based on above laboratory results.The active component precursors of the catalyst were cobalt nitrate,copper nitrate and cerium nitrate with industrial grade material.Given the cost of industrial catalyst preparation,we selected P-DF-03 type pseudo-boehmite as carrier precursor.First of all,the influences of the HNO₃ concentration,sesbania powder dosage,and liquid/powder ratio on the physical properties and reaction activity of the catalyst were investigated by the method of single factor experiment.It showed that the mechanical strength of the catalyst increased firstly and then decreased with increasing HNO₃ concentration and liquid/powder ratio.Excessive sesbania powder would decrease the mechanical strength of the catalyst pellet.The content of liquid and sesbania powder had not significant effect on the activity of the catalyst.On the basis of above findings,the effects of the HNO₃ concentration,sesbania powder content,and liquid content on the physical properties and reaction activity of the catalyst were further investigated by the orthogonal experimental method.The optimum preparation conditions were 0.6%,3%and 0.35 mL/g for nitrate concentration,sesbania powder content and the ratio of liquid to pseudo-boehmite,respectively.The performance of nitrous oxide decomposition in reactor including space velocity,initial N₂O concentration,and raw material gas inlet temperature was also assessed.In the first experiment,a total 92 kg of CoCuCe/?-Al₂O₃ catalyst was randomly packed in a ID560*H720 reactor.Nitrous mixed gas came from an adipic acid plant exhaust gas.The maximum N₂O conversion could be 93.3%when the space velocity was2500 h^-1,inlet temperature was 550°C,and inlet N₂O concentration was10%in the raw material gas,respectively.At this moment,the temperature of reactor outlet was 647.2°C.During the second step,the maximum conversion rate could get up to 99.27%after another 43 kg of catalyst was refill in the reactor.The temperature of reactor outlet was694.5°C,space velocity was 2288 h^-1,inlet temperature was 520°C,and N₂O concentration was 11.71%in inlet raw material gas at this point.This temperature of the reactor outlet met the requirements of cooperative enterprises that is the reaction temperature of outlet within 700°C when the N₂O conversion rate reach to 99%.