Study On Preparation And Several Key Technologies About Industry Application Of Ru-based Catalyst For Ammonia Synthesis

The ruthenium catalyst supported on active carbon has the properties of high activity at low temperature and low pressure,high cost,methanation,poor mechanism.Meanwhile,in the future of its industrial application,the following several key problems should be solved:the mechanical strength of Ru catalyst,cost of Ru catalyst.This paper studied on the preparation of Ru/AC catalyst which based on the precursor of RuCl3,and several key technologies of its industry application were also studied,the main research results are obtained as following:1.Investigated the prepare process of the Ru/AC catalyst supported on the coconut carbon support.The carbon support was treated with nitric acid,which could introduce amounts of surface oxygen-containing groups such as carboxyl,phenol,and lactone,and improved the dispersion and catalytic activity of Ru catalyst.The dispersion of prepared Ru catalyst with impregnation-precipitation method is higher,and the Ru particle size is in the range of 2-3 um.At the reaction conditions of 10 MPa,10000 h-1,H2/N2=3 the activity of Ru catalyst at 400 and 375 °C is 23.1%,20.4%respectively.2.The influence of preparing process to the mechanical strength of Ru/AC catalyst was studied,and the effects of ball-milling,graphitization,oxidation,and nitric acid treatments to the mechanical strength of the ruthenium catalyst were also investigated.The test results indicated that ball-milling treatment could enhance the abrasion strength of carbon support greatly.The best ball-milling conditions are:the ratio of medium-size to small-size ball is 10/70,ball-milling time is 120 min,and ball-milling velocity is 140 r/min.The regular-shaped carbon after thermal treatment,oxidation,nitric acid modification,its compressive strength and crush strength is 101 N/cm,658.1 N/cm2 respectively.The granular coconut active carbon after graphitization,the abrasion ratio is 0.71%,and the bulk crushing is 2.56%at 2 MPa,meanwhile,the abrasion ratio and bulk crushing ratio of prepared Ru catalyst at 1 MPa is 0.28%and 0.31%,respectively,which meet the mechanical strength requirement of industry catalyst.3.Investigated the effects of various pretreatments on the regular activated carbon and granular coconut carbon,and studied the influence of treatments with hydrogen and the nitric acid to the performance of regular activated carbon and prepared Ru catalyst.Meanwhile,the purity,surface texture,surface oxygen-containing groups of regular activated carbon and granular coconut activated carbon were also studied after pretreatment.After hydrogen and nitric acid treatments,the elements such as P,S could removed partly from regular activated carbon,and the pore structure,surface appearance could be further improved,then the dispersion of prepared Ru catalyst has a great improvement,and the reaction rate of Ru catalyst reaches 101.2 mmolg-1h-1 at the reaction conditions of 400 ?,10 MPa,10000 h"1.While after thermal treatment,the activated carbon is partly graphitic,and the surface impurities are basically removed,but the surface area decreases obviously.However,after gas oxidation and nitric acid treatments,the pore structure recovered and surface oxygen groups increased significantly,and the reaction rates of Ru catalyst supported on regular activated carbon at 375,400 ? is 68.64 and 113.33 mmolg-1h-1,respectively,after heat-resisting for 16 h at 475 ?,the Ru catalyst could also keep good catalytic activity.And the activity of Ru catalyst supported on granular activated carbon at 375,400 ? is 18.5%and 22.4%,respectively,the correspond reaction rates is 92.9 and 108.9 mmolg-lh-1,respectively.4.To reduce the using cost of Ru catalyst,the iron catalyst coupled with Ru catalyst,and studied the reaction conditions on performance of iron catalyst coupled with Ru catalyst in series(denoted as Fe-Ru catalyst)for ammonia synthesis,meanwhile,compared the effect of catalysts in series and mixed loading in reactor.At low temperature(375-425 ?),low pressure(10-15 MPa),low space velocity(5000-18000 h-1),the outlet ammonia concentration of ruthenium catalyst is 33.4-37.6%higher than that of iron catalyst,and the outlet ammonia concentration of Fe-Ru catalyst is 45.6-63.5%higher than that of single-iron catalyst.While at the same reaction pressure and space velocity,the outlet ammonia concentration of Fe-Ru catalyst is higher than that of iron catalyst.Meanwhile,the process of loading reactors were joined in series was more suitable to Ru catalyst,and the process of iron catalyst coupled with Ru catalyst was in favor of cost reduction for Ru catalyst.