Biochemical mechanisms for the desulfurization of coal-relevant organic sulfur compounds

Two microbial strains (Brevibacterium sp. DO, Pseudomonas aeruginosa OS1) were isolated for their ability to desulfurize dibenzothiophene (DBT) and benzyl methyl sulfide (BMS). Enrichment was achieved by a sulfur-selective screening system using the model compounds as the sole source of sulfur for bacterial growth. Brevibacterium sp. DO utilizes DBT as a sole source of sulfur, carbon and energy for growth, whereas Pseudomonas aeruginosa OS1 metabolizes BMS to only a small extent under sulfur-selective conditions. Investigations of the regulation of enzymes involved in the desulfurization of coal-relevant sulfur compounds indicate that in nature at least two mechanisms exist: ‘carbon regulation’ and ‘sulfur regulation’. The biochemical mechanisms leading to the desulfurization of BMS and DBT are similar. The sulfur atom of both compounds is initially oxidized to the corresponding sulfone, and cleavage of the C---S bond proceeds via the formation of a chemically unstable hemimercaptal (S-oxidized form) by oxidation of the carbon atom adjacent to the sulfur atom. These results indicate that oxidation of sulfur to its highest oxidation state may be the precondition for the oxidative cleavage of the covalent C---S bonds. By isotope-labelling experiments using ¹⁸O₂, the initial enzymes were identified as sulfoxygenases that use molecular oxygen. Cleavage of the C---S bond of DBT and BMS leads to the formation of organic sulfinic acids as intermediates. With DBT the sulfinic acid is desulfurized probably by hydrolysis; this results in the formation of sulfite and benzoate. The desulfurization of BMS proceeds by sulfonic acid-oxidation. The applicability of these biochemical mechanisms to the microbial desulfurization of coal is discussed.     

脱硫菌R-8的生长及其生物降解水中二苯并噻酚

以二苯并噻酚（DBT）为唯一硫考察了pH，温度，碳源，氮源等对德氏假单胞菌（Pseudomonas delafieldii)R-8生长的影响，结果表明，该菌的最适生长pH范围为6－9，最适生长温度为30℃，甘油是细胞生长的最好碳源，最佳浓度范围为10－15g/L，最佳无机氮源乙酸铵的浓度为1．6g/L，有机氮源能促进细胞的生长，但对从DBT脱硫却产生抑制作用，硫酸钠，二甲基亚砜，胱氨酸和蛋氨酸等硫化物都可以作为R－8生长的硫源，但对R－8脱硫活性的表达没有诱导作用。     

不同硫源对小球诺卡氏菌R-9生长和脱硫活性的影响

用氯化钡沉淀结合傅里叶变换红外光谱法，证明小球诺卡氏菌（Nocardia globerula）R-9从二苯并噻吩中脱除的含硫产物以硫酸盐的形式存在于水相.比较了R-9分别以二苯并噻吩、硫酸钠和二甲基亚砜作为惟一硫源时的生长和脱硫活性.结果表明，二苯并噻吩、硫酸钠和二甲基亚砜均可以作为R-9的生长硫源，且高浓度（25 mmol•L^-1）硫酸钠和二甲基亚砜对细胞的生长不产生抑制作用.2 mmol•L^-1左右的硫酸钠或二甲基亚砜作为硫源时培养的细胞脱硫活性最高.提高硫源和碳源浓度可以提高R-9在发酵罐中的比生长速率和细胞浓度(OD600).     

Diffusion as a rate controlling step in heavy-oil biodesulfurization processes

Microbial degradation of hydrocarbons depends on various chemical and physical factors (viz, temperature, electron acceptors, nutrients, pH, substrate characteristics) and on the presence of degrading microorganisms. Even if all these factors are optimized, oil biodegradation can still be retarded by diminished availability of the compound. Setti et al. (1992) have shown that n-alkanes affect the biodegradation of aromatic sulfur compounds by an aerobic Pseudomonas sp.

This communication illustrates further investigations into the diffusion effect that controls the biodegradation of aromatic sulfur compounds.

Polycyclic aromatic hydrocarbons (PAHs) can be converted in the dissolved state only. This implies that mass-transfer from the solid phase to the aqueous phase might be rate-limiting. Dibenzothiophene (DBT) biodegradation is a good example of this model.

The presence of a fatty acid (hexadecanoic acid, aC16) during the fermentation affects DBT degradation. We propose a model in which aC16 surrounds the DBT molecule forming a micelle which favors a co-metabolic process between the fatty acid and the aromatic sulfur compound.

Similar behavior is seen when DBT is dissolved in n-dodecane (C12) and n-hexadecane (C16). There are two important parameters that affect DBT degradation in this system: the surface area of the substrate and the DBT concentration in C12. DBT degradation is limited by the diffusion of the sulfur compound from the organic phase to the adsorbed microorganism on the hydrocarbon. Diffusion increases with the DBT concentration, and the DBT degradation rate is significantly higher than that reported for DBT alone. In this case, a carrier effect of the n-alkane in the DBT degradation is shown. A barrier effect is suggested when the DBT concentration is below the limit for which the degradation rate is lowest.

Our investigations show that the presence of a co-substrate, such as fatty acids or n-alkanes, affects the bioavailability of the aromatic sulfur compound in aerobic conditions.     

微杆菌ZD-M2降解二苯并噻吩的特性及其生长条件优化

分离得到的微杆菌(Microbacterium sp.)ZD-M2是一株专一性脱硫菌,GC-MS分析表明该菌能选择性地脱除二苯并噻吩(DBT)中的硫,沿“4S途径”代谢的终产物2-羟基联苯(2-HBP)会进一步氧化为2-甲氧基联苯(2-MBP),同时降解产物中还有联苯（还原产物）存在.在水溶液中降解DBT的结果表明：该菌的适宜生长pH范围为6.5～9.5,最适生长温度为30 ℃,氯化铵为最佳氮源,生长的最佳浓度为1.0 g•L^-1.该菌能利用多种碳源和硫源进行生长,但以甘油和DBT为最佳,最适浓度分别为2.0 g•L^-1和0.2 mmol•L^-1.     

红平红球菌LSSE8–1的培养及其对二苯并噻吩中硫元素脱除的影响

红平红球菌(Rhodococcus erythropolis)LSSE8-1是一株新分离的专一性脱硫菌，HPLC分析表明该菌能选择性地脱除二苯并噻吩(DBT)中的硫，最终代谢产物是2-羟基联苯(2-HBP). 适宜的初始pH为6.5~9；能利用多种碳源，其中以甘油为最佳，适宜的甘油浓度为8 g/L；2 g/L的乙酸铵是菌体生长和脱硫的合适氮源；二甲基亚砜是提高该菌细胞收率和脱硫比活性的有效硫源.     

燃料油的生物脱硫

从大港油田的污泥中分离出一株能以二苯并噻吩(DBT)为唯一硫源而生长的菌株(Rhodococcussp.EBT-2)。HPLC分析结果表明,EBT-2可专一性降解DBT,生成2-羟基联苯(2-HBP)。以DBT为唯一硫源考察了培养基的初始pH、温度、碳源和氮源等因素对EBT-2生长和脱硫的影响。结果表明,EBT-2的最适初始pH为7.5,最适温度为30℃,最佳碳、氮源分别是葡萄糖和氯化铵。在最适条件下,EBT-2能够在48 h内将DBT从0.25 mmol/L降解到0.03 mmol/L,同时生成0.19 mmol/L 2-HBP。     

ISOLATION AND CHARACTERIZATION OF BACTERIA FOR REMOVAL OF SULFUR IN ORGANIC COMPOUNDS

Four bacterial strains have been isolated for their ability to growth on dibenzothiophene (DBT), dibenzothiophene sulfone (DBTO2). The results show that different bacteria strains oxidize the DBT to different products through different pathways. R-6 and R-16 metabolize DBT to DBTO2 and HBP; they are identified as species of Bacillus brevis and Bacillus sphaericus. For long time storage, R-9 identified as Nocardia globerula oxidizes DBT to DBT-sulfone (DBTO2) and benzenamine n-phenyl. The optimum temperature and pH for growth of R-16 are 32℃ and 7.02 respectively. The pH of broth decreases during the processes.     

Conversion of sulfur dioxide to sulfate and hydrogen sulfide by Desulfotomaculum orientis

The autotrophic, sulfate-reducing bacterium, Desulfotomaculum orientis, grew in batch culture with molecular hydrogen (H₂) as an energy source, carbon dioxide (CO₂) as a carbon source and sulfur dioxide (SO₂) as the terminal electron acceptor. At high H₂ partial pressure, SO₂ was stoichiometrically reduced to hydrogen sulfide (H₂S). At low partial pressures of hydrogen (< 0.025 atm), SO₂ was both oxidized to sulfate and reduced to hydrogen sulfide. These results indicated a new mode of sulfur metabolism for D. orientis.     

污泥与高硫煤共水热碳化过程中硫氮形态转化规律

采用高温高压反应釜进行了污泥(SS)和高硫煤(CS)的共水热碳化实验。分别考察了混合比和温度对水热炭中硫氮元素形态转化规律的影响。研究结果表明,经过水热处理后,SS中蛋白质氮(N-A)转化为杂环类氮,CS中吡咯氮(N-5)和吡啶氮氧化物(N-X)转化为吡啶氮(N-6)和季氮(N-Q);SS与CS中硫元素逐渐转化为噻吩硫和硫酸盐。随着CS混合比例和温度的升高,水热炭中含氮芳族杂环(例如N-6、N-5和N-Q)占比增加。另外,随着CS混合比例和温度升高,水热炭中噻吩硫含量分别逐渐增加至22.61%和24.98%;升高温度提高了水热炭中硫酸盐含量,而增加CS混合比例却降低了硫酸盐含量。本研究可为后续SS和CS的资源化清洁利用提供理论基础。     

Ti-MSU催化过氧化氢氧化模拟柴油深度脱硫

分子筛催化H2O2氧化脱硫的反应,由于具有反应条件温和、操作费用低、可实现深度脱硫和催化剂可回收再利用等优点,受到国内外研究者的重视。以烷基聚氧乙烯基醚（AEO9）为模板剂,以有机钛硅为原料,合成中孔分子筛（Ti-MSU）。用FTIR、XRD和BET等分析手段对合成的分子筛样品进行了表征。以Ti-MSU为催化剂和30%（质量分数）H2O2为氧化剂,对模拟燃料的氧化脱硫进行了研究,考察了不同n（Si）/n（Ti）比及反应条件对催化剂活性的影响。试验结果表明,在适宜反应条件下,Ti-MSU对二苯并噻吩（DBT）的转化率最高达58%。     

Chemical desulfurization of petroleum fractions for ultra-low sulfur fuels

An improved desulfurization process for removing sulfur from hydro treated diesel oil based on the oxidation of thiophenic type sulfur-containing compounds with H₂O₂ and acetic acid (AcOH) using H₂SO₄ as catalyst has been studied. The experimental results show that the sulfone content in the oxidation product increased rapidly with an increase in acetic acid and sulfuric acid ratios from 1:0 to 2:1 mole ratios. The maximum DBT conversion (wt.%) was at 2:1 mole ratio of acetic acid/sulfuric acid. This oxidation process is found to be capable of removing up to 90% of the sulfur compounds in hydro treated real fuels and can provide an alternative way to meet the future sulfur environmental requirements.     

Ultra-deep catalytic adsorptive desulfurization of diesel fuel using Ti-silica gel adsorbent at low Ti-loading

In this work, the effective ultra-deep catalytic adsorptive desulfurization (CADS) using titanium-silica gel (Ti-SG) adsorbent at low Ti loading (<1 wt.%) was investigated. The superior CADS capacity (37.3 mg-S/g-A) and high TOF value (432 h⁻¹) for dibenzothiophene (DBT) of Ti-SG adsorbent were achieved at Ti loading of 0.6% with high dispersion and low titanium coordination. The rate equation of catalytic DBT oxidation was described as , where the TiOOR was determined as the intermediate to enable the DBT oxidation to form the corresponding sulfone (DBTO₂). The effectiveness of CADS using Ti-SG adsorbents was verified in real diesels with varied sulfur concentrations and O/S ratios in the dynamic adsorption and multicycle regeneration. This work provides insights on using low-cost bifunctional catalytic adsorbents at low Ti loadings for effective CADS to realize ultra-deep desulfurization of transportation fuels.     

Hydrogels as adsorbents of organosulphur compounds currently found in diesel

Hydrogels of chitosan were synthesised using glutaric dialdehyde as the crosslinking agent in an acetonitrile/water solution (1:4, v/v). These hydrogels recognised and adsorbed the dibenzothiophene sulfone (DBTS) against other related compounds found in diesel, e.g. dibenzothiophene (DBT), fluorene (FLE) and 4,6-dimethyl DBT (DMDBT). In order to improve the recognition and adsorption of DBTS, the latter compound served as a template for the building of recognition sites inside the hydrogel matrix through the use of the molecular imprinting technique (MIT). Despite the adsorption capacity of the molecular imprinted hydrogel (MIH) was not increased, the imprinting process of chitosan allowed both an enhancement of two orders of magnitude in ligand affinity constant and material homogeneity as seen by SEM. The change in swelling degree (Q) suggested the presence of a conformational memory of the hydrogel that might allow the design of stimuli-response but also tailored-made hydrogels responding at a required factor as temperature. The imprinting process improved ligand recognition and consequently hydrogel’s specificity as shown by a monolayer adsorption. In contrast, the adsorption isotherm of DBTS by the non-imprinted hydrogel showed a multilayer adsorption due to non-specific interactions.     

基于阻滞扩散模型估算柴油脱硫吸附剂的适宜孔径分布

通过GC-PFPD色谱分析国Ⅱ、国Ⅲ、国Ⅳ标准0^#柴油中的主要含硫组分,发现苯并噻吩(BT)、二苯并噻吩(DBT)及其烷基取代衍生物是0^#柴油中的主要含硫化合物,C₂-DBT、C₃-DBT是国Ⅳ柴油中的主要含硫化合物。以BT、DBT、4,6-DMDBT为模型化合物,计算含硫化合物在不同大小孔道内的扩散阻滞因子,结合氧化铝堆积孔模型,估算氧化铝基柴油脱硫吸附剂的适宜孔径分布。结果表明,当氧化铝的平均孔径为4～10 nm时,含硫化合物的扩散阻滞因子为0.24～0.65,氧化铝的比表面积为100～250 m²·g^-1,可同时满足较低的扩散阻力和足够大的比表面积。对比分析不同氧化铝的孔分布及其吸附脱硫性能,结果表明氧化铝中4～10 nm范围内的孔面积占总孔面积的百分比与其吸附脱硫性能存在显著的正相关关系,初步推测氧化铝基脱硫吸附剂的适宜孔径分布范围为4～10 nm。     

MCM-41分子筛负载金属酞菁在氧化脱硫反应中的催化性能

采用浸渍法将8种金属酞菁分别负载到MCM-41分子筛上制得负载型金属酞菁,通过红外光谱进行表征。以二苯并噻吩（DBT）为反应底物,空气为氧化剂,己内酰胺四丁基溴化铵离子液体为溶剂考察了这8种催化剂在氧化脱硫反应中的催化活性,筛选出较优催化剂,并对工艺条件进行优化。结果表明,合成的8种负载型金属酞菁催化剂中,MCM-41分子筛负载钴酞菁具有较好的催化性能,最优工艺条件为：剂油比1：1,催化剂用量0.004 g·（10 ml模型油）^-1,空气流速50 ml·min^-1,反应时间1 h,室温,DBT脱硫率最高可达97.56%。DBT的氧化产物为DBT砜。又考察了此催化氧化系统对不同硫化物的催化氧化效果,发现不同硫化物的脱硫率均在90%以上。该催化剂在重复利用4次后脱硫率无明显的降低。     

固定化Pseudomonas delafieldii R-8细胞同时脱除噻吩和二苯并噻吩(英文)

Biodesulfurization(BDS) is a promising technology for deep desulfurization.In this work,Pseudomo-nas delafieldii R-8 cells are immobilized in calcium alginate beads and used for BDS of transportation fuels.It is found that thiophene and dibenzothiophene(DBT) can be simultaneously metabolized by immobilized R-8 cells.The initial sulfur content in the model oil is 300 mg?kg?1(thiophene︰DBT 1︰1).After 10 h of treatment,the thiophene concentration is reduced by 40%,while DBT is reduced by 25%.The utilization rate of thiophene is faster than that of DBT.Moreover,the oil/water ratio of alginate immobilized cells is studied to reduce the water volume in desulfurization systems.Long-term recycling of BDS by alginate immobilized cells is carried out with oil/water ratio at 5︰1.The immobilized cells are successfully reused over 15 batch cycles.In the last batch,the desulfurization activity remains at least 75% of the first batch.     

V-Mo based catalysts for oxidative desulfurization of diesel fuel

Catalytic oxidative desulfurization (ODS) of a Mexican diesel fuel on a spent HDS catalyst, deactivated by metal deposits, was carried out during several reactive-batch cycles in order to study the catalytic performance to obtain low sulfur diesel. To explain catalytic activity results, Mo and/or V oxides supported on alumina pellets were prepared and evaluated in the ODS of a model diesel using tert-butyl hydroperoxide (TBHP) or H₂O₂ as oxidant. The catalytic results show that V-Mo based catalysts are more active during several ODS cycles using TBHP. The performance of the catalysts was discussed in terms of reduced species of vanadium oxide, prevailing on the catalysts, which increase the sulfone yield of refractory HDS compounds (DBT, 4-MDBT and 4,6-DMDBT).     

Synthesis of alumina-nitrogen-doped carbon support for CoMo catalysts in hydrodesulfurization process

More stringent environmental legislation imposes severe requirements to reduce the sulfur content in diesel to ultra-low levels with high efficient catalysts.In this paper,a series of CoMo/NDC@alumina cat-alysts were synthesized by combination of the chemical vapor deposition of nitrogen-doped carbon(NDC) using 1,10-phenanthroline and co-impregnation of Mo and Co active components.The optimal cat-alyst with additive of 25％ 1,10-phenanthroline was screened by a series of property characterization and the hydrodesulfrization (HDS) active test.The amount of "CoMoS" active phase of the optimal CoMo/C3 catalyst increased 5.3％ as compared with the CoMo/γ-Al2O3.The introduction of NDC improved the sul-fidation degree of Mo by 21.8％ as compared to the CoMo/γ-Al2O3 catalyst,which was beneficial to form more active sites.The HDS conversion of the NDC supported catalysts are higher than CoMo/γ-Al2O3 whether for the dibenzothiophene (DBT) or 4,6-dimethyl dibenzothiophene (4,6-DMDBT).Further hydroprocessing evaluation with Dagang diesel revealed that the CoMo/C3 catalyst possessed higher HDS property and the removal rate of DBTs in the diesel increased by 4％-11％ as compared to the CoMo/γ-Al2O3 catalyst.     

Microbial desulfurization of modeland straight‐run diesel oils

The desulfurization kinetics of Nocardia globerula R‐9 was investigated initially in a model system consisting of dibenzothiophene (DBT) dissolved in dodecane. The ability to desulfurize straight‐run diesel oil by resting cells of this strain was also evaluated. The course of desulfurization of DBT in dodecane could be represented by the Michaelis–Menten equation. The desulfurization of DBT and 4,6‐dimethyl dibenzothiophene (4,6‐DMDBT) in a mixture of the two proceeded simultaneously without preference for either of them. The sulfur content of the straight‐run diesel oil could be reduced from 1807 to 741 mg dm^?3 by treatment with resting cells of this strain, at a mean rate of 5.1 mmol sulfur kg^?1 h^?1. This showed that Nocardia globerula R‐9 could be a potential bacterium for reducing the sulfur content of petroleum products. Copyright © 2003 Society of Chemical Industry