典型宁东煤热解阶段硫迁移路径的分子动力学模拟

以典型宁东煤为研究对象,采用工业分析、元素分析、X射线光电子能谱(XPS)分析和¹³C固体核磁共振(¹³C-NMR)等手段研究了煤样的元素组成、原子比、官能团类型及含量等分子结构特征,构建了含硫原子的宁东煤有机化学结构。通过反应力场分子动力学(ReaxFF MD)模拟,考察了热解温度和升温速率对典型宁东煤热解产物的影响,结果表明:热解温度低于1500 K时,热解产物中气体组分较少,重质焦油较多;随着热解温度升高(1500 K~2500 K),大分子化合物和活性自由基均会发生二次反应产生小分子碎片,气体产物快速增加;增大升温速率会减少C1~C4有机气体的生成,促进重质焦油的产生;16 K/ps和2500 K分别是合适的模拟升温速率和热解温度。污染性元素S的迁移路径分析结果表明:宁东煤热解过程中S原子容易迁移到相对分子质量小的有机碎片中,最终将以硫氢根的形式与H自由基结合生成H₂S参与后续燃烧反应。     

丙炔基双酚A醚硼聚合物热解过程的ReaxFF分子动力学模拟

聚合物的热解过程涉及的化学反应较为复杂,难以通过测试表征的手段深入探究其机理。本研究在实验表征的基础上,结合ReaxFF分子动力学(ReaxFF-MD)模拟方法,研究了丙炔基双酚A醚硼聚合物(PB)的热解过程。通过观察升温过程中PB的结构变化,可得到其热解过程中的断键顺序。此外,采用ReaxFF-MD模拟,其研究结果不仅验证了实验中热重-红外光谱联用(TG-FTIR)分析所得的PB热解生成小分子的主要组成为CH₄、H₂O、H₂ 和 CO,并且通过追踪上述小分子的生成过程可得到其主要的生成途径。以上研究结果表明,ReaxFF-MD模拟方法不仅有助于理解PB聚合物的热解机理,直观地反映出其热解产物生成途径,而且对聚合物耐热性能的研究有所借鉴。     

CaO催化PE热解及H2O对催化过程影响的ReaxFF MD研究与机理分析

结合反应分子动力学（ReaxFF MD）模拟方法和自行开发的全自动ReaxFF反应机理分析软件（automatic reaction mechanism analyzer, AutoRMA）深入探究了CaO催化聚乙烯（PE）热解及H₂O对催化过程的影响,通过热解产物分析、热解过程反应路径追踪和C―C键及C―H键时序变化分析来揭示反应机理。结果显示,CaO作为催化剂提高了PE的热解反应速率,有效降低了PE热解过程中C―C键和C―H键断裂的活化能,使其分别从316.88 kJ/mol和430.13 kJ/mol降低到22.24 kJ/mol和30.87 kJ/mol,并促进了PE向轻质油和气体分子的转化;CaO对自由基和碳链上的非饱和碳原子的吸附及解离可以有效促进PE的热解;但H₂O存在时由于其自身与CaO结合会抑制CaO的催化作用,同时H₂O主要通过取代反应以羟基的形式存在于烃类产品中,水分含量（质量分数）为PE的50%时导致10%的油品中含有氧元素,降低产品质量,也会导致液相产品中存在大量的水分, 因此应避免热解的废PE携带水分。研究表明,ReaxFF MD结合AutoRMA有助于对PE等聚合物催化热解机理的深入理解,进而优化反应体系。     

Resistance to sulfur poisoning of hot gas cleaning catalysts for the removal of tar from the pyrolysis of cedar wood

In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H₂S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO₂/SiO₂ using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H₂S. Steam reforming Ni catalyst was effective for the tar removal without H₂S addition, however, the addition of H₂S deactivated drastically. In contrast, Rh/CeO₂/SiO₂ exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H₂S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO₂/SiO₂, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis.     

化学链燃烧中H2S对NiFe2O4氧载体活性的影响机理

采用密度泛函理论方法研究H₂S与NiFe₂O₄（001）完整表面和氧缺陷表面的相互作用机理。结果表明,H₂S在NiFe₂O₄氧载体表面Ni原子位的吸附能比其在Fe原子位的吸附能大。氧缺陷的形成会使H₂S在氧载体表面金属原子位的吸附能增大,并且Ni原子位吸附H₂S的吸附能增加更为明显。因而,NiFe₂O₄氧载体表面的Ni原子位是H₂S的主要吸附位。同时采用热力学方法进一步研究含H₂S的合成气与NiFe₂O₄氧载体之间的反应,发现H₂S与氧载体的反应产物与氧载体的还原程度密切相关。由于铁氧化物的深度还原过程受到热力学限制,H₂S与NiFe₂O₄氧载体反应的主要产物为Ni₃S₂。密度泛函理论方法与热力学方法研究结果均表明H₂S倾向于与NiFe₂O₄氧载体中Ni发生相互作用,这将对NiFe₂O₄氧载体的反应性能产生不利影响。     

基于分子动力学模拟的轮胎橡胶气相热解产物反应机理

运用分子动力学的方法,对轮胎橡胶的热解过程进行了模拟,并结合模拟结果和密度泛函数对其气相产物的反应路径进行推测计算。模拟结果表明,热解过程主要分为两个阶段,低温热解阶段发生的主要反应是橡胶长链断裂形成单体,主要产物为异戊二烯、苯乙烯和1,3-丁二烯;高温热解阶段发生的主要反应是单体进一步生成小分子气体,产物中CH₄、H₂、C₂H₄占大部分,还有少量C₂H₆、C₃H₆。其中CH₃·攻击异戊二烯和苯乙烯单体夺取特定位置的H·是生成CH₄的最优路径,H·攻击苯乙烯单体夺取特定位置的H·是生成H₂的最优路径,CH₂CH·攻击1,3-丁二烯单体夺取特定位置的H·是生成CH₂CH₂的最优路径。本文还将热解产物分别跟天然橡胶单独热解和天然橡胶与丁苯橡胶共热解的热解产物做对比,为废旧轮胎橡胶热解得到特定的气相产物和催化热解提供理论依据。     

基于分子反应动力学模拟的六甲基二硅氧烷热解机理研究

六甲基二硅氧烷是燃烧合成高纯二氧化硅纳米颗粒的重要前体,采用ReaxFF分子动力学模拟方法研究其高温热解过程,讨论了三种不同反应力场对模拟的影响并分析其可靠性,选择其中最合适的力场开展不同温度与压力下的热解产物分析,结合气相色谱实验,揭示六甲基二硅氧烷的热解路径和机理。结果表明,反应力场对ReaxFF分子动力学模拟有重要影响,通过比较分析获得了最佳反应力场,六甲基二硅氧烷的初始热解反应为Si—C键断裂导致的CH₃脱离,温度升高会加剧解热反应的发生且使产物趋向于碎片化,热解的主要产物为CH₃、CH₄、C₂烃、H₂、CH₂O等小分子以及SiH₄、SiH₂、CH₄Si等含硅化合物。压力的改变会造成热解体系浓度的改变,从而影响分子间相互碰撞概率和反应的发生,压力越大则越容易形成稳定的热解产物。     

基于分子反应动力学模拟的六甲基二硅氧烷热解机理研究

六甲基二硅氧烷是燃烧合成高纯二氧化硅纳米颗粒的重要前体,采用ReaxFF分子动力学模拟方法研究其高温热解过程,讨论了三种不同反应力场对模拟的影响并分析其可靠性,选择其中最合适的力场开展不同温度与压力下的热解产物分析,结合气相色谱实验,揭示六甲基二硅氧烷的热解路径和机理。结果表明,反应力场对ReaxFF分子动力学模拟有重要影响,通过比较分析获得了最佳反应力场,六甲基二硅氧烷的初始热解反应为Si—C键断裂导致的CH₃脱离,温度升高会加剧解热反应的发生且使产物趋向于碎片化,热解的主要产物为CH₃、CH₄、C₂烃、H₂、CH₂O等小分子以及SiH₄、SiH₂、CH₄Si等含硅化合物。压力的改变会造成热解体系浓度的改变,从而影响分子间相互碰撞概率和反应的发生,压力越大则越容易形成稳定的热解产物。     

高含有机硫天然气的净化研究与探索

在使用单一甲基二乙醇胺（MDEA）溶液脱除天然气中H₂S的过程中,随着有机硫含量不断地增加,常常造成出料气中H₂S和总硫含量均不能满足国家二类天然气质量要求。在改变关键参数后,脱硫效果仍然不能改善。因此,本文针对高含量的有机硫,开展了MDEA+DIPA、MDEA+DEA、环丁砜+MDEA、环丁砜+DIPA 4组高效脱硫剂的复配研究,通过对比H₂S及有机硫在溶液中的吸收分压,筛选出了吸收效果较优的脱硫剂组合为：环丁砜+MDEA。随后再利用BBD响应面分析法,以环丁砜、MDEA、H₂O的不同配比为变量,以H₂S和总硫脱除率最高为目标函数进行寻优,经过混料实验与复合优化,最终得出最优脱硫剂配比为：23.3%环丁砜+54.6%MDEA+22.1%H₂O。最优配比脱硫剂经现场装置使用后的效果表明,H₂S脱除率达到99.964%,总硫脱除率达到99.833%,出料气中H₂S含量为14.4mg/m³,总硫含量为78.5mg/m³,满足二类气标准。     

Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts

The interactions of H₂ and H₂S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H₂ and H₂S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H₂ and H₂S were enhanced, but the adsorption energy of H₂ increased more than that of H₂S, indicating that the adsorption of H₂S became less favorable compared with H₂ on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst.     

Kinetics of dibenzothiophene hydrodesulfurization over MoS2 supported catalysts: modelization of the H2S partial pressure effect

The influence of H₂S partial pressure over the catalytic activity of MoS₂, supported on three different oxides: Al₂O₃, TiO₂ and ZrO₂, was studied in the hydrodesulfurization of dibenzothiophene (DBT). A complex inhibiting effect is observed and two orders of reaction relative to H₂S were determined: −1/2 and 0, as a function of H₂S partial pressure. The experimental results are in good agreement with the kinetic models whereby the DBT transformation takes place through a dihydrogenated intermediate (DH-DBT). The associated mechanism considers that the heterolytic dissociative adsorption of H₂ and H₂S occurs over an unsaturated Mo ion and over a stable sulfur ion.     

高硫石油焦热解过程及硫形态的变化特性

在管式炉实验装置上进行不同温度高硫石油焦N₂气氛热解实验,并利用X射线光电子能谱分析（XPS）技术进行表征,深入分析高硫石油焦热解过程中硫形态变化特性,同时采用热重-红外联用（TG-FTIR）技术深入分析热解过程。热重分析结果表明,高硫石油焦热解经历了干燥脱水阶段,长链脂肪烃、稠环芳香烃等组分分解阶段,在430℃和635℃失重速率达到最大形成失重峰。红外分析结果表明,高硫石油焦热解释放气体主要包括CO₂、CH₄、H₂O、SO₂、芳烃化合物和脂肪族化合物等,并且在不同温度区间释放气体组成有着巨大的差异。XPS分析结果表明,高硫石油焦表面硫含量及存在形态与热解温度紧密关联,随着热解温度的不断升高,高硫石油焦表面硫含量在700℃达到最大值,不同硫形态之间发生相互转化。     

The effects of morphological changes and mineral matter on H2S evolution during coal pyrolysis

The H₂S release profiles of five important Colombian coals have been monitored using temperature programmed pyrolysis. It was found that there was no correlation between the amount of H₂S and the sulphur content of the original coals. Coals which had been treated to remove all of the mineral matter and inorganic sulphur showed a good correlation with the free swelling index of the coals. This was explained by the physical trapping of H₂S in closed porosity formed during pyrolysis. A similar result was found for demineralised coals with pyrite present. The H₂S for untreated coals showed no systematic variation with rank, the coal sulphur content or free swelling index. This was because certain coals were rich in finely dispersed calcium which could chemically prevent H₂S release.     

Sulfur exchange on Co---Mo/Al2O3 hydrodesulfurization catalyst using S radioisotope tracer

A commercial Co---Mo/Al₂O₃ catalyst was labeled with the radioisotope ³⁵S in hydrodesulfurization (HDS) of ³⁵S-labeled dibenzothiophene (³⁵S-DBT) in a high-pressure flow reactor at 50 kg/cm². Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H₂S were carried out on the labeled catalyst at 50 kg/cm² and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of ³⁵S---H₂S released from the ³⁵S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT> 4-MDBT> 4,6-DMDBT. In the sulfur exchange reaction with H₂S, the adsorption of H₂S on the catalyst reached saturation above a H₂S partial pressure of 0.36 kg/cm². It was suggested that the release of H₂S from the labile sulfur may be the rate determining step of the HDS reaction.     

Theoretical study on the mechanism of sulfur migration to gas in the pyrolysis of benzothiophene

The release and control of sulfur species in the pyrolysis of fossil fuels and solid wastes have attracted attention worldwide. Particularly, thiophene derivatives are important intermediates for the sulfur gas release from organic sulfur, but the underlying migration mechanisms remain unclear. Herein, the mechanism of sulfur migration during the release of sulfur-containing radicals in benzothiophene pyrolysis was explored through quantum chemistry modeling. The C₁-to-C₂ H-transfer has the lowest energy barrier of 269.9 kJ·mol^–1 and the highest rate constant at low temperatures, while the elevated temperature is beneficial for C−S bond homolysis. 2-Ethynylbenzenethiol is the key intermediate for the formation of S and SH radicals with the overall energy barriers of 408.0 and 498.7 kJ·mol^–1 in favorable pathways. The generation of CS radicals is relatively difficult because of the high energy barrier (551.8 kJ·mol^–1). However, it can be significantly promoted by high temperatures, where the rate constant exceeds that for S radical generation above 930 °C. Consequently, the strong competitiveness of S and SH radicals results in abundant H₂S during benzothiophene pyrolysis, and the high temperature is more beneficial for CS₂ generation from CS radicals. This study lays a foundation for elucidating sulfur migration mechanisms and furthering the development of pyrolysis techniques.     

Catalytic activity of iron compounds for coal liquefaction

The catalytic activity of pyrite and synthesized -FeOOH in coal liquefaction was investigated using batch autoclaves with the aim of developing an industrial iron catalyst. The results indicate that the presence of H₂S helps gaseous hydrogen transferring and prevents deactivation so that the catalyst promotes hydrocracking of coal and hydrogenation of the products. The activity converges with excess H₂S and sulfur addition equivalent to an S/Fe molar ratio of 2.0 being reasonable for the activation. The active site is located on the outer surface, with finely divided catalysts exhibiting high activity. Both pulverized pyrite and synthesized -FeOOH are sufficiently fine as to exhibit high activity in the process. Pulverized pyrite is an industrially feasible iron catalyst for coal liquefaction process, because it is inexpensive and does not require sulfur addition.     

10MWth高硫石油焦化学链气化制合成气耦合硫磺回收新系统模拟研究

基于化学链气化技术依靠气固反应定向调控气化产物中H₂S和SO₂摩尔比为2的优势，将化学链气化与Claus工艺中的催化转化单元相结合，提出了高硫石油焦化学链气化制合成气和回收硫磺的新系统。针对系统核心单元，即化学链气化过程，基于Aspen Plus，开展热输入10 MW_th的高硫石油焦化学链气化过程模拟，以赤铁矿石为载氧体，水蒸气为气化介质，重点考察了氧碳比、气化温度对化学链气化过程及硫转化过程的影响。结果发现，氧碳比的增大导致合成气产率显著降低，但系统从需要外部提供能量逐渐转变为对外部放热，在氧碳比0.8669～0.9535区间内，系统可以达到热量自平衡。同时，气化温度的提高对合成气产率是有利的，在975℃时达到2.15 m³/kg，主要是由于CO体积分数随气化温度增加而增加。氧碳比和气化温度的提高都会导致H₂S浓度的降低和SO₂浓度的提高。并且研究了当H₂S和SO₂摩尔比为2的最佳工况时，氧碳比和气化温度为反相关，其中氧碳比为0.8669，气化温度为900℃时，冷煤气效率为64.09%。     

Selective removal of H2S from coke oven gas

The catalytic performance of some metal oxides in the selective oxidation of H₂S in the stream containing water vapor and ammonia was investigated in this study. Among the catalysts tested, V₂O₅/SiO₂ and Fe₂O₃/SiO₂ catalyst showed good conversion of H₂S with very low selectivity to undesired SO₂. Hydrogen sulfide could be recovered as harmless solid products (elemental sulfur and various ammonium salts), and distribution of solid products was varied with types of catalyst and compositions of reactant. XRD and FT-IR analysis revealed that the salt was mixture of ammonium–sulfur–oxygen compounds. It was noteworthy that V₂O₅/SiO₂ catalyst produced elemental sulfur and ammonium thiosulfate, and that elemental sulfur was principal product on Fe₂O₃/SiO₂ catalyst. Small amount of ammonium sulfate was obtained with the Fe₂O₃/SiO₂ catalyst. In order to elucidate the reaction path, the effects of O₂/H₂S ratio and concentration of NH₃ and H₂O are also studied with the V₂O₅/SiO₂ catalyst.     

Aspen Plus模拟高浓度H2S/CO2酸性气的选择性分离

以煤制氢尾气中的高浓度酸性气体H₂S和CO₂为对象,以聚乙二醇二甲醚（NHD）为吸收剂,使用PC-SAFT状态方程拟合了酸性气体CO₂和H₂S在聚乙二醇二甲醚（NHD）溶剂中溶解参数,运用Aspen Plus流程模拟软件,构建两级吸收分离工艺,实现H₂S和CO₂的高效分离,H₂S浓度由30%提升至98.7%,CO₂含量由55%提升至99.4%。由此,可以通过高效分离酸性气H₂S和CO₂,并以提浓后再资源化利用的方式实现酸性气的污染控制。     

Microbial removal of sulfur dioxide from a gas stream

A study of the feasibility of utilizing the Thiobacillus ferrooxidans or Desulfovibrio desulfuricans bacterium for microbial removal of sulfur dioxide from flue gases has been carried out. Sulfur dioxide may be readily reduced to H₂S by contact with sulfate-reducing microorganisms in which Desulfovibrio desulfuricans were dominant in the first stage. The H₂S was then oxidized to sulfur by the ferric sulfate in a second stage where ferrous ions were regenerated. These results were compared to microbial oxidation of SO₂ from flue gases to sulfate by Thiobacillus ferrooxidans. The mechanisms for the reduction of SO₂ to H₂S in the presence of Desulfovibrio desulfuricans and the oxidation of SO₂ to H₂SO₄ in the presence of ferric sulfate and Thiobacillus ferrooxidans are discussed. Sulfuric acid or gypsum CaSO₄ · 2H₂O are byproducts from microbial flue gas desulfurization.