Microbial reduction of sulfur dioxide and nitric oxide

Two process concepts have been developed for a microbial contribution to the problem of flue gas desulfurization and NO_x removal. We have demonstrated that the sulfate-reducing bacterium Desulfovibrio desulfuricans can be grown in a mixed culture with fermentative heterotrophs in a medium in which glucose served as the only carbon source. Beneficial cross-feeding resulted in vigorous growth of D. desulfuricans, which used SO₂(g) as a terminal electron acceptor, with complete reduction of SO₂ to H₂S in 1–2 s of contact time. We have proposed that the concentrated SO₂ stream, obtained from regeneration of the sorbent in regenerable processes for flue gas desulfurization, could be split with two-thirds of the SO₂ reduced to H₂S by contact with a culture of sulfate-reducing bacteria. The resulting H₂S could then be combined with the remaining SO₂ and used as feed to a Claus reactor to produce elemental sulfur. However, the use of glucose as an electron donor in microbial SO₂ reducing cultures would be prohibitively expensive. Therefore, if microbial reduction of SO₂ is to be economically viable, less expensive electron donors must be found. Consequently, we have evaluated the use of municipal sewage sludge and elemental hydrogen as carbon and/or energy sources for SO₂ reducing cultures. Heat and alkali pretreated sewage sludge has been successfully used as a carbon and energy source to support SO₂ reduction in a continuous, anaerobic mixed culture containing D. desulfuricans. The culture operated for nine months with complete reduction of SO₂ and H₂S. Another sulfate-reducing bacterium, Desulfotomaculum orientis, has also been grown in batch cultures on a feed of SO₂, H₂ and CO₂. Complete reduction of SO₂ to H₂S was observed with gas-liquid contact times of 1–2 s. We have also demonstrated that the facultative anaerobe and chemoautotroph, Thiobacillus denitrificans, can be cultured anoxically in batch reactors using NO(g) as a terminal electron acceptor with reduction to elemental nitrogen. We have proposed that the concentrated stream of NO_x, as obtained from certain regenerable processes for flue gas desulfurization and NO_x removal, could be converted to elemental nitrogen for disposal by contact with a culture T. denitrificans. Two heterotrophic bacteria have also been identified which may be grown in batch cultures with succinate or heat and alkali pretreated sewage sludge as carbon and energy sources and NO as a terminal electron acceptor. These are Paracoccus denitrificans and Pseudomonas denitrificans.     

Selective catalytic reduction of sulfur dioxide with hydrogen to elemental sulfur over Co---Mo/Al2O3

The selective reduction of sulfur dioxide with hydrogen to elemental sulfur was studied over Co---Mo/Al₂O₃. When the feed conditions were properly optimized (SO₂/H₂ mole RATIO = 1:3), a sulfur yield of about 80% was achieved at temperatures around 300°C. The temperature is the lowest that has been reported so far for any catalyst for this reaction. The catalytic activity remained high and stable after presulfiding with 10% H₂S in hydrogen. Little influence on the catalytic activity was observed if the water content in the feed was kept below 11 vol.-%. The overall reaction consisted of two individual steps occurring on two different sites; sulfur dioxide was first hydrogenated to hydrogen sulfide on the metal sulfide phase, then followed by the Claus reaction of hydrogen sulfide with sulfur dioxide to produce elemental sulfur on the acidic sites of the alumina support.     

CATALYTIC PRODUCTION OF ELEMENTAL SULFUR FROM THE THERMAL DECOMPOSITION OF H2S IN THE PRESENCE OF CO2

The feasibility of using a cobalt-molybdenum (Co-Mo) sulfide catalyst that was prepared from a commercial Co-Mo oxide catalyst for the production of elemental sulfur from hydrogen sulfide (H₂S) and carbon dioxide (CO₂) in a packed bed catalytic reactor was studied. It was demonstrated that the desired sulfide catalyst could be prepared by first reducing, then sulphiding the corresponding oxide. The results showed that the prepared catalyst was capable of producing elemental sulfur from the thermal decomposition of H₂S in the presence of CO₂ over a temperature range of 465-700°C and at atmospheric pressure. A specific rate coefficient was calculated as well as the Arrhenius parameters for the non-equilibrated reaction. The H₂S decomposition reaction was found to be a second order reaction and have an activation energy of 114.4kJ/mol(27.3kcal/mol).     

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.     

Selective oxidation of H2S to elemental sulfur over chromium oxide catalysts

CrO_x and CrO_x supported on SiO₂ have been found to be active for the selective oxidation of hydrogen sulfide to elemental sulfur. The catalysts show maximum sulfur yield at a stoichiometric ratio of O₂/H₂S, 0.5. Amorphous Cr₂O₃ exhibits higher yield of sulfur and has stronger resistance against water than supported Cr/SiO₂, especially at low temperatures. At high temperatures above 300°C, the sulfur yield over the supported catalyst becomes similar to amorphous Cr₂O₃ because the Claus reaction occurring on the silica support removes SO₂ to increase the sulfur yield. Active sites are the amorphous monochromate species that can be detected as a strong temperature programmed reduction (TPR) peak at 470°C. Catalytic activity can be correlated with the amount of labile lattice oxygen and the strength of Cr–O bonding. The reaction proceeds via the redox mechanism with participation of lattice oxygen.     

High capacity absorption of SO2 using imidazole ionic liquid mixtures

The capture of sulfur dioxide (SO₂) with readily available and cost-effective ionic liquids (ILs) is one of the challenges for the application of ILs. Here, we synthesized the ILs mixtures with different molar ratios (3∶1, 2∶1, 1∶1, 1∶2, and 3∶1) of 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]) and 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) to study their SO₂ absorption capacities. The SO₂ solubilities in these mixtures were investigated under different conditions. The SO₂ absorption capacities of [Emim][Cl]_x[OAc]_1-x at different temperatures and SO₂ partial pressure were measured. The results show that ILs can effectively capture SO₂. There exists a synergistic promotion effect between [Emim][Cl] and [Emim][OAc], resulting in quite high SO₂ absorption capacity. The [Emim][Cl]_0.33[OAc]_0.66 mixture can capture SO₂ (1.34±0.08) and (0.74±0.05) g/g at 1.0 and 0.2 atm(1 atm=101325 Pa), respectively. Comparing with the reported data, [Emim][Cl]_x[OAc]_1-x mixtures show obvious advantage for SO₂ capture. In addition, these ionic liquid mixtures have good reversibility for the absorption and desorption of sulfur dioxide.     

咪唑类离子液体混合物用于二氧化硫高效吸收

开发易制备、价格便宜、面向SO₂气体高效分离的离子液体(ILs),是当前ILs从实验探索迈向工业应用的难点与重大挑战。合成了不同摩尔比(3∶1、2∶1、1∶1、1∶2和1∶3)的1-乙基-3-甲基咪唑氯盐([Emim][Cl])和1-乙基-3-甲基咪唑乙酸盐([Emim][OAc])的离子液体混合物[Emim][Cl]x[OAc]1-x,在测定其密度、黏度、热稳定性等基本物性数据的基础上,研究了[Emim][Cl]x[OAc]1-x混合物在不同温度和SO₂分压下的SO₂吸收能力。结果表明,[Emim][Cl]x[OAc]1-x能够有效地捕获SO₂。[Emim][Cl]与[Emim][OAc]之间存在协同促进作用,有利于实现SO₂高效吸收。[Emim][Cl]0.33[OAc]0.66混合液在1.0和0.2 atm(1 atm=101325 Pa)下捕获SO₂量分别为(1.34±0.08)和(0.74±0.05) g/g,与现有结果相比,混合物在SO     

钙基脱硫剂用于冶炼烟气脱硫的模拟与实验

提出了一种应用钙基脱硫剂脱除冶炼烟道气中高浓度SO₂并回收硫单质的方法。通过热力学模拟多种硫化物与SO₂之间的反应,筛选得出硫化钙（CaS）适合作为化学链脱硫技术的脱硫剂,它在400～650℃范围内可将SO₂还原为单质硫,生成的固相产物为CaSO₄而非CaO。通过固定床反应器内的脱硫实验,发现温度对脱硫率和硫单质回收率影响较大。在400～650℃范围内温度越高,脱硫率和硫单质回收率越大;当温度高于600℃时,脱硫率和硫单质回收率基本相等。提高空速,则会降低脱硫率和硫单质回收率,但两者的差值随空速增大逐渐减小。当烟气中SO₂浓度小于1%时,脱硫率维持在99.8%基本不变;SO₂浓度升至3.45%后,平均脱硫率急剧下降至92.1%;SO₂浓度越高,平均脱硫率越低。硫单质回收率随SO₂浓度增大存在一最佳范围。在脱硫反应后期,粒径较大的脱硫剂颗粒脱硫性能较低。SEM照片表明了脱硫剂颗粒随反应温度的升高团聚现象更为明显,XRD表征证明了反应中SO₂气体被还原为升华硫颗粒。     

Microwave-assisted desulfurization of NOx storage-reduction catalyst

The activity of NO_x storage-reduction (NSR) catalysts is greatly reduced by sulfur poisoning, caused by the SO₂ present in the exhaust stream. Desorption of sulfur species from poisoned NSR catalysts occurs at temperatures in excess of 600 °C using reducing atmospheres and conventional heating. In this work, microwave (MW) heating has been used to promote desulfurization of poisoned NSR catalysts. The experiments were carried out by heating the catalyst with MW radiation and using hydrogen as the reducing gas. Desorption of H₂S at 200 °C was observed. Desorption at even lower temperatures (150 °C) was observed when water was introduced to the system. In the presence of water, sulfur species desorbed as both H₂S and SO₂. An overall reduction of sulfur species of about 60% was obtained. The use of MW heating proves to be an efficient way to achieve regeneration of poisoned NSR catalysts.     

Catalytic reduction of sulfur dioxide using hydrogen or carbon monoxide over Ce1−xZrxO2 catalysts for the recovery of elemental sulfur

This study focuses on the direct sulfur recovery process (DSRP), in which SO₂ can be directly converted into elemental sulfur using a variety of reducing agents over Ce_1−xZr_xO₂ catalysts. Ce_1−xZr_xO₂ catalysts (where x = 0.2, 0.5, and 0.8) were prepared by a citric complexation method. The experimental conditions used for SO₂ reduction were as follow: the space velocity (GHSV) was 30,000 ml/g_-cat h and the ratio of [CO (or H₂, H₂ + CO)]/[SO₂] was 2.0. It was found that the catalyst and reducing agent providing the best performance were the Ce_0.5Zr_0.5O₂ catalyst and CO, respectively. In this case, the SO₂ conversion was about 92% and the sulfur yield was about 90% at 550 °C. Also, a higher efficiency of SO₂ removal and elemental sulfur recovery was achieved in the reduction of SO₂ with CO as a reducing agent than that with H₂. In the reduction of SO₂ by H₂ over the Ce_0.5Zr_0.5O₂ catalyst, SO₂ conversion and sulfur yield were about 92.7% and 73%, respectively, at 800 °C. Also, the reduction of SO₂ using synthetic gas with various [CO]/[H₂] molar ratios over the Ce_0.5Zr_0.5O₂ catalyst was performed, in order to investigate the possibility of using coal-derived gas as a reducing agent in the DSRP. It was found that the reactivity of the SO₂ reduction using the synthetic gas with various [CO]/[H₂] molar ratios was increased with increasing CO content of the synthetic gas. Therefore, it was found that the Ce_1−xZr_xO₂ catalysts are applicable to the DSRP using coal-derived gas, which contains a larger percentage of CO than H₂.     

SULFUR RECOVERY WITH REDUCED EMISSIONS, LOW CAPITAL INVESTMENT AND HYDROGEN CO-PRODUCTION

The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H₂S and C0₂ by liquid- or vapor-phase hydrolysis. Unreacted H₂S and C0₂ are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be controlled to very low levels by increasing stripper boil-up. Process operating costs depend on the level of sulfur recovery required and can also be much lower than those of the modified Claus Process.

The process chemistry depends on a shift in the equilibrium of H₂S decomposition caused by reaction of hydrogen with C0₂ by the reverse of the water-gas-shift reaction. Catalysts for this chemistry have been identified. Reactor conversion is further improved by rapid cooling of the reactor effluent gas. Other aspects of process design and operation confer further advantages with respect to the Claus process; however, the process equipment used is similar to that used in a Claus plant. Retrofit of existing plant to the new technology can therefore be considered.     

苯酚型低共熔溶剂中硫酸钛作为催化剂高效氧化脱硫

低共熔溶剂广泛应用于氧化脱硫过程,开发新型的低共熔溶剂并进一步提升脱硫效果具有重要的意义。 以氯化胆碱为氢键受体,苯酚为氢键供体合成了ChCl/2Ph型低共熔溶剂。通过FT-IR和¹H NMR证实了苯酚和氯化胆碱之间存在氢键作用。以苯酚型低共熔溶剂为萃取剂,双氧水为氧化剂,硫酸钛为催化剂氧化脱除模拟油中的二苯并噻吩。考察了反应温度、V(ChCl/2Ph)/V(Oil)、n(H₂O₂)/n(S)、催化剂用量以及硫化物类型对脱硫率影响。实验表明最佳反应条件如下：模拟油量为5 ml,V(ChCl/2Ph)/V(Oil)=2∶10, n(H₂O₂)/n(S)=6,催化剂用量为0.01 g,反应温度为40℃,反应时间180 min。在此条件下脱硫率可以达到98.2%。求得体系的表观活化能为41.9 kJ/mol。含有催化剂的低共熔溶剂相可以重复使用5次且活性没有明显降低。机理研究表明形成钛的过氧化物和Br?nsted酸性是具有较高脱硫活性的关键。     

二氧化硫在脱钙后海水体系中的溶解平衡

CO₂脱钙后海水与标准海水相比,具有更少的Ca²⁺和更多的HCO₃^-,理论上HCO₃^-可与SO₂溶于水后产生的亚硫酸氢根反应,促进SO₂的溶解.为此本文以N₂为惰性载气,研究了1atm下,温度变化范围为34.0~63.9℃,SO₂在标准海水、NaHCO₃含量增多的海水以及钙离子减少的海水中的溶解性能,以期实现海水CO₂脱钙与烟道气脱硫的耦合.结果表明SO₂在标准海水中的溶解度随着温度的升高显著降低,且SO₂溶解度的数值与温度呈近似线性关系;海水中HCO₃^-含量的增加会提高SO₂在此水体系中的溶解度;而海水中钙离子的减少对SO₂在此水体系中的溶解性能并无显著影响.因此与标准海水体系相比,CO₂脱钙后海水体系对SO₂具有更好的溶解性能,为利用CO₂脱钙后海水进行烟气脱硫,从而实现海水脱钙与烟气脱硫的耦合提供了理论支持及基础数据.     

Adsorption of sulphur dioxide onto activated carbon prepared from oil-palm shells with and without pre-impregnation

Adsorption of sulphur dioxide (SO₂), a common gaseous pollutant, on oil-palm-shell activated carbon in a fixed bed was studied in this paper. Oil-palm shell is an abundant agricultural solid waste in tropical countries like Malaysia and Thailand. The effects of fixed-bed length, SO₂ gas superficial velocity, adsorbent particle size and internal pore structure on fixed-bed performance were investigated. Some characteristic parameters such as the breakthrough time, τ_0.05, exhaustion time, τ_0.95, length of mass transfer zone, L_MTZ, adsorptive capacity, W, and adsorption rate constant, K, were derived from the breakthrough curves. Tests of SO₂ adsorption onto activated carbons prepared from oil-palm shells pre-impregnated with potassium hydroxide (KOH) and phosphoric acid (H₃PO₄) of different concentrations were also carried out. It was found that the fixed-bed performance was not only dependent on the operating conditions and the textural properties of the adsorbent but was also influenced by the surface chemistry of the adsorbent, which was related to the type and concentration of the impregnating agent. In general, the quality of oil-palm-shell activated carbon prepared by CO₂ activation is comparable to that of a commercial product, and the samples prepared from oil-palm shell with KOH pre-impregnation are more suitable for the removal of SO₂ gas.     

载体结构对锡铁负载型催化剂脱硝性能的影响

利用凹凸棒土（ATP）、活性炭（AC）、介孔硅（MCM-41）、二氧化钛（TiO₂）这4种孔结构不同的载体,通过水热法制备了以Fe₂O₃为催化剂主活性组分、SnO₂为辅活性组分的锡铁负载型催化剂。催化剂的微观结构通过BET和SEM测试,并在催化剂评价装置中模拟烟气组成,考察锡铁负载型催化剂在反应温度为80～280℃、脱硝空速为32000～48000h^-1范围内的选择性催化还原（SCR）性能。同时考察了SO₂与H₂O对1/2SnFe/ATP催化剂的影响。实验表明,载体可能为催化剂提供大量Brønsted酸性位点,有利于反应气体吸附。1/2SnFe/ATP催化剂表现出最佳的SCR脱硝性能,在200℃时实现最高96.4%的NO转化率,而且由其抗硫性及其抗水性实验表明：SO₂单独作用于催化剂时,脱硝效率降低迟缓,切断二氧化硫后仍能恢复到85%以上。同时加入水和二氧化硫后,将会导致脱硝效率急剧下降。停止加入后,催化剂效率又开始慢慢恢复,效率可以恢复达到70%以上。     

Effects of SO2/redox exposure on the microstructure of cerium–zirconium mixed metal oxides

Cerium–zirconium solid solutions were prepared and characterized to determine the effects of SO₂/redox exposure on the microstructure of the crystallites. The mixed oxides were prepared via co-precipitation of cerium(IV) ammonium hydroxide and zirconium oxynitrate using ammonium hydroxide. The oxides were characterized prior to and after SO₂ exposure to discern the effects of temperature and SO₂ on crystallite properties. The samples were treated at 673 and 1073 K with a flow of 100 ppm SO₂/balance N₂ with a concomitant redox pulse of 5% H₂/balance N₂ and 5% O₂/balance N₂ on 10 s intervals. The cubic crystalline structure (CaF₂) was observed and maintained for compositions ranging from 100 to 25 at.% cerium without indication of a separate tetragonal phase. While the cubic structure was maintained, the addition of zirconium in the cubic lattice reduced the cubic lattice parameter (a₀) and the crystallite grain size. Under identical redox conditions and temperatures, exposure to SO₂ resulted in smaller grain sizes, as calculated by X-ray diffraction (XRD) and confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In addition, higher exposure temperatures resulted in larger crystallite grain sizes without altering the cubic lattice parameter. Auger electron spectroscopy (AES) confirmed the absence of surface sulfur species, indicating sulfur dioxide alters the microstructure of the crystallites under redox conditions without the formation of cerium–zirconium chemisorbed sulfur species.     

Pt/TiO_2催化二甲醚部分氧化重整制氢

二甲醚是一种理想的氢载体,可用于解决氢的储存和运输。以Pt/TiO_2为部分氧化催化剂,结合Ni/Al_2O_3重整催化剂,考察钛前驱体和焙烧温度对二甲醚部分氧化重整制氢反应的影响。结果表明,以Ti(C4H9O)4为原料制备的TiO_2为金红石相,Ti(SO4)2或Ti O(OH)2为原料制备的TiO_2为锐钛矿相;以Ti(C4H9O)4为原料制备的Pt/TiO_2-E催化剂催化性能略好,转化率接近100%,H2收率约90%,表明金红石相TiO_2负载的Pt催化剂略佳;以Ti(SO4)2为原料制备的Pt/TiO_2-S催化剂500℃焙烧可获得金红石相TiO_2。与Pt/Al_2O_3催化剂相比,Pt/TiO_2催化剂具有更好的催化性能,H2收率超过90%,而Pt/Al_2O_3催化剂H2收率约80%。     

Some experimental observations of aerosol formation in the photo-oxidation of sulphur dioxide

The formation of particles in the u.v. photolysis of ppm concentrations of SO₂ in pure nitrogen and in nitrogen-oxygen mixtures has been studied in a flow system. Both the number of particles and the mass of the H₂SO₄ aerosol produced was determined over a range of SO₂ and water vapour concentrations.

In the near u.v. (λ = 290–400nm) the mass conversion of SO₂ to H₂SO₄ was too small to be measured, but particles were detected on a condensation nucleus counter above a threshold SO₂ concentration when the H₂SO₄ formation rate was sufficient to achieve an appreciable nucleation rate. The number of stable particles formed increased with water vapour concentration at a given H₂SO₄ production rate. These experimental data agree reasonably well with recent theoretical calculations of aerosol nucleation and growth rate in the H₂SO₄/H₂O system.

At short wavelengths (λ = 185 nm) a much higher H₂SO₄ formation rate was achieved. Although nucleation occurred at < 1 per cent r.h. the aerosol growth process was slow at low water vapour concentrations. A r.h. of 30 per cent was required for the incorporation of the bulk of the H₂SO₄ into the aerosol phase.     

锰基NH_3-SCR低温脱硝催化剂研究进展

锰基催化剂在低温氨选择性催化还原(NH3-SCR)脱硝反应中表现出良好的催化活性。讨论H_2O和SO_2对锰基催化剂活性的影响,综述通过制备方法改性、添加助剂和优化载体改善锰基催化剂抗H_2O和抗SO_2性能的研究进展,并对锰基低温SCR催化剂的研究方向进行展望。     

不同烟气组分对粉状活性焦吸附汞的影响机理

在模拟燃煤热烟气为热源和介质条件下，以准东褐煤为原料，通过一维沉降炉进行炭化活化（一步法）制备粉状活性焦，考察了活性焦对Hg⁰的吸附能力，探索了SO₂、H₂O、O₂、CO₂、H₂O+O₂、SO₂+O₂及H₂O+SO₂+O₂气氛对活性焦吸附Hg⁰的影响机理。结果表明：一步法获得的活性焦对Hg⁰具有较高的吸附性能。N₂气氛作对比，H₂O、H₂O+O₂、CO₂和SO₂气氛下抑制活性焦对Hg⁰的吸附；O₂、SO₂+O₂和H₂O+SO₂+O₂促进活性焦对Hg⁰的吸附。通过Hg 4f的XPS分析证明了不同气氛组成对活性焦吸附Hg⁰的抑制和促进机理。H₂O覆盖在活性焦活性位上和堵塞孔隙而抑制活性焦对Hg⁰的吸附；SO₂与Hg⁰在活性焦上发生竞争吸附而抑制对Hg⁰的吸附；CO₂ 吸附在活性焦微孔上而抑制对Hg⁰的吸附；O₂气氛下主要形成了HgO, SO₂+O₂气氛下Hg⁰被氧化成HgSO₃，进一步氧化成HgSO₄； H₂O+SO₂+O₂气氛下，Hg⁰被氧化成HgO和HgSO₄。