Research progress on catalysts for organic sulfur hydrolysis: Review of activity and stability

The removal of organic sulfur through catalytic hydrolysis is a significant area of research in the field of desulfurization.This review provides an overview of recent advancements in catalytic hydrolysis technology of organic sulfur,including the activity,stability,and atmosphere effects of hydrolysis catalysts.The emphasis is on strategies for enhancing hydrolysis activity and anti-oxygen poisoning property of catalysts.Surface modification,metal doping and nitrogen doping have been found to improve the activity of catalysts.Alkaline components modification is the most commonly used method,the formation of oxygen vacancies through metal doping and creation of nitrogen basic sites through nitrogen doping also contribute to the hydrolysis of organic sulfur.The strategies for anti-oxygen poisoning are discussed in a systematic manner.The structural regulation of catalysts is beneficial for the desorption and diffusion of hydrogen sulfide(H_(2)S),thereby effectively inhibiting its oxidation.Nitrogen doping and the addition of electronic promoters such as transition metals can protect active sites and decrease the number of active oxygen species.These methods have been proven to enhance the anti-poisoning performance of catalysts.Additionally,this article summarizes how different atmospheres affect the activity of hydrolysis catalysts.The objective of this review is to pave the way for the development of efficient,stable and widely used catalysts for organic sulfur hydrolysis.

Role of iron-based catalysts in reducing NO_(x) emissions from coal combustion

Nitrogen oxide(NO_(x))pollutants emitted from coal combustion are attracting growing public concern.While the traditional technologies of reducing NO_(x) were mainly focused on terminal treatment,and the research on source treatment is limited.This paper proposes a new coal combustion strategy that significantly reduces NO_(x) emissions during coal combustion.This strategy has two important advantages in reducing NO_(x) emissions.First,by introducing iron-based catalyst at the source,which will catalyze the conversion of coke nitrogen to volatile nitrogen during the pyrolysis process,thereby greatly reducing the coke nitrogen content.The second is de-NO_(x) process by a redox reaction between NO_(x) and reducing agents(coke,HCN,NH_(3),etc.)that occurred during coke combustion.Compared to direct combustion of coal,coke prepared by adding iron-based catalyst has 46.1% reduction in NO_(x) emissions.To determine the effect of iron-based additives on de-NO_(x) performance,demineralized coal(de-coal)was prepared to eliminate the effect of iron-based minerals in coal ash.The effects of iron compounds,additive dosages,and combustion temperatures on de-NO_(x) efficiency are systematically studied.The results revealed that the NO_(x) emission of the coke generated by pyrolysis of de-coal loaded with 3%(mass)Fe_(2)O_(3) decreases to 27.3% at combustion temperature of 900℃.Two main reasons for lower NO_(x) emissions were deduced:(1)During the catalytic coal pyrolysis stage,the nitrogen content in the coke decreases with the release of volatile nitrogen.(2)Part of the NO_(x) emitted during the coke combustion was converted into N_(2) for the catalytic effect of the Fe-based catalysts.It is of great practical value and scientific significance to the comprehensive treatment and the clean utilization process of coal.

A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study

The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog,which would seriously affect the quality of atmospheric environment.Therefore,the decrease of NOx is of great importance for improving the efficient utilization of coal.The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation.Firstly,in the process of pyrolysis:the occurrence state and transformation of nitrogen were concluded.The influence of temperature,atmosphere,heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized;Secondly,during the process of combustion:the influence of temperature,ambient oxygen concentration,physical structure of coal char,catalyst on heterogeneous oxidation of char(N)were summarized;The effects of char surface properties,catalyst and ambient atmosphere on heterogeneous reduction of NOx were also concluded.Based on the quantum chemical calculation,the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail.Current studies focus more on the generation of HCN and NH3,but in order to reduce the pollution of NOx from the source,it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrolysis,as well as clarify the path of the generation of N2.Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.

红土镍矿与硫酸钠共热解动力学及其机理分析

采用热重-质谱联用技术,结合XRD分析,考察了红土镍矿与Na2SO4共热解的特性,对热解气态产物进行了分析.结果表明,红土镍矿与硫酸钠共热解可分为5个阶段：游离水析出阶段（37-152℃）、针铁矿分解脱羟基阶段（238-278℃）、利蛇纹石和高岭土脱羟基阶段（554-602℃）、白云石分解阶段（892-914℃）和Na2SO4分解阶段（1241-1286℃）.H2O,CO2和SO2是红土镍矿与硫酸钠共热解过程析出的主要气体.根据Coasts模型,红土镍矿与硫酸钠共热解为一级反应,热解机制是Na2SO4中的Na＋取代富镍硅酸盐中的Ni^2＋,被置换出的Ni2＋与游离氧结合形成NiO,有利于下一步还原焙烧-磁选富集镍.

Regeneration of Fe_(2)O_(3)-based high-temperature coal gas desulfurization sorbent in atmosphere with sulfur dioxide

Regeneration of a high-temperature coal gas desulfurization sorbent is a key technology in its industrial applications.A Fe_(2)O_(3)-based high-temperature coal gas desulfurizer was prepared using red mud from steel factory.The influences of regeneration temperature,space velocity and regeneration gas concentration in SO_(2) atmosphere on regeneration performances of the desulfurization sorbent were tested in a fixed bed reactor.The changes of phase and the composition of the Fe_(2)O_(3)-based high-temperature coal gas desulfurization sorbent before and after regeneration were examined by X-ray diffraction(XRD)and X-ray Photoelectron spectroscopy(XPS),and the changes of pore structure were characterized by the mercury intrusion method.The results show that the major products are Fe3O4 and elemental sulfur;the influences of regeneration temperature,space velocity and SO_(2) concentration in inlet on regeneration performances and the changes of pore structure of the desulfurization sorbent before and after regeneration are visible.The desulfurization sorbent cannot be regenerated at 500℃ in SO_(2) atmosphere.Within the range of 600℃-800℃,the time of regeneration becomes shorter,and the regeneration conversion increases as the temperature rises.The time of regeneration also becomes shorter,and the elemental sulfur content of tail gas increases as the SO_(2) concentration in inlet is increased.The increase in space velocity enhances the reactive course;the best VSP is 6000 h^(-1) for regeneration conversion.At 800℃,20 vol-%SO_(2) and 6000 h^(-1),the regeneration conversion can reach nearly to 90%.

Sulfur retention efficiency of clean coke produced by co-pyrolysis of coal with CaCO_(3) to substitute household coal

Raw coal is used by many suburban and rural households for cooking and heating and results in severe air pollution,especially problematic SO_(2) emissions.A source treatment strategy was proposed to reduce SO_(2) emissions,which used the co-pyrolysis of raw coal with a CaCO3 additive to produce clean coke.The effect of Ca/S molar ratio on the SO_(2) capture efficiency of clean coke was investigated,and the SO_(2) retention efficiency was optimized at a Ca/S molar ratio of 1.5.The sulfur retention mechanism of clean coke was attributed to:(1)CaCO3 decomposition to CaO and partial reaction of CaO with H2S to generate CaS during pyrolysis.(2)Transformation of the remaining sulfur in the clean coke to SO_(2) during combustion,capture by unreacted CaO to form CaSO_(4),and direct oxidation of CaS to CaSO_(4).The feasibility of SO_(2) emission reduction by clean coke in a practical household stove was verified.