Prediction of coal liquefaction reactivity by solid state 13C NMR spectral data

A method for the deconvolution of ¹³C NMR spectra of coals has been developed by using coal-like model compounds and various lithotypes separated from Yallourn brown coal which is rich in various types of oxygen-functional groups. The spectrum of coal was resolved into 24 peaks which were classified into nine types of carbon-functional group. This analytical method can be applied to all ranks of coal from lignite to anthracite. In addition, the liquefaction data of seven kinds of coal collected from five different countries were obtained by the operation of 1 t/d process support unit and 150 t/d pilot plant NEDOL process liquefaction plants. A good correlation was obtained for every reaction product between structural data derived from solid state ¹³C NMR spectra and liquefaction data of coals. This means that the yields of liquefaction products could be predicted from ¹³C NMR spectral data of coal.     

高惰质组分五彩湾煤直接液化性能研究

以新疆五彩湾煤为研究对象,进行了煤质和热解分析,考察了溶煤比、反应时间、氢初压和反应温度对其加氢液化效果的影响.结果表明,尽管五彩湾煤惰质组含量高达81.5%,镜质组最大反射率达到0.73%,挥发分低于37%,H/C仅为0.59,但在氢初压仅为6.0MPa,溶煤比1.75和反应时间60min条件下,其最佳液化温度为450℃,油产率和转化率分别达到55.20%和76.76%,仍然具有良好的液化性能.     

Liquefaction of subbituminous coals with a basic nitrogenous model process solvent

Liquefaction reactions in a tubing-bomb reactor have been carried out as a function of coal, coal sampling source, reaction time, atmosphere, temperature, coal pre-treatment, SRC post-treatment and process solvent. Pyridine as well as toluene conversions ranging from 70 to > 90 wt% involving both eastern bituminous and western subbituminous coals are obtained. 1,2,3,4-Tetrahydroquinoline (THQ) has been extensively used as a process solvent under optimized liquefaction conditions of 2:1 solvent: coal, 7.5 MPa H₂, 691 K and 30 min reaction time. Comparisons of THQ with other model process solvents such as methylnaphthalene and tetralin are described. Liquefaction product yield for conversion of subbituminous coal is markedly decreased when surface water is removed from the coal by drying in vacuo at room temperature prior to liquefaction. The effect of mixing THQ with Wilsonville hydrogenated process solvent in the liquefaction of Wyodak and Indiana V coals is described.     

Effect of pre-swelling of coal on its solvent extraction and liquefaction properties

Effects of pre-swelling of coal on solvent extraction and liquefaction properties were studied with Shenhua coal. It was found that pre-swelling treatments of the coal in three solvents, i.e., toluene (TOL), N-methyl-2-pyrrolidinone (NMP) and tetralin (THN) increased its extraction yield and liquefaction conversion, and differed the liquefied product distributions. The pre-swollen coals after removing the swelling solvents showed increased conversion in liquefaction compared with that of the swollen coals in the presence of swelling solvents. It was also found that the yields of (oil + gas) in liquefaction of the pre-swollen coals with NMP and TOL dramatically decreased in the presence of swelling solvent. TG and FTIR analyses of the raw coal, the swollen coals and the liquefied products were carried out in order to investigate the mechanism governing the effects of pre-swelling treatment on coal extraction and liquefaction. The results showed that the swelling pre-treatment could disrupt some non-covalent interactions of the coal molecules, relax its network structure and loosened the coal structure. It would thus benefit diffusion of a hydrogen donor solvent into the coal structure during liquefaction, and also enhance the hydrogen donating ability of the hydrogen-rich species derived from the coal.     

Approach for promoting liquid yield in direct liquefaction of Shenhua coal

Single and multi-stage liquefaction of Shenhua (SH) bituminous coal and re-liquefaction of its liquefaction residue (SHLR) were carried out in an autoclave reactor to investigate the essential approach for promoting oil yield and conversion in SH coal direct liquefaction (SHDL). The multi-stage liquefaction includes pretreatment, keeping the reactor at 250 °C for 40 min before heating up to the reaction temperature, and two-stage liquefaction processes consisting of low temperature stage, 400 °C, and high temperature stage, 460 °C. The results show that the pretreatment has slight effect on oil yield and conversion of SHDL, especially for liquefaction at 460 °C. There is a positive function of two-stage liquefaction in shortening reaction time at high temperature. Increasing ratio of solvent to SHLR can promote the oil yield and abate reaction condition in SHLR re-liquefaction, that is, it can promote the conversion from preasphaltene and asphaltene to oil. The primary factor to inhibit coal liquefaction is the consumption of hydrogen free radical (H·) from solvent or H₂ and condensation of free radicals from coal pyrolysis after a period of reaction. So the essential approach for increasing oil yield and conversion of SHDL is to provide enough H· to stabilize the free radicals from coal pyrolysis.     

Solvolytic liquefaction of coals with a series of solvents

Solvolytic liquefaction of coals of different rank was studied with a variety of solvents at 370–390 °C under nitrogen in order to elucidate the role of solvent in coal liquefaction of this kind and to find a suitable solvent for the highest yields of liquefaction. The yield was found to depend strongly upon the nature of the coal as well as the solvent under these conditions. Pyrene and a SRC-BS pitch were excellent solvents for Miike coal, which was fusible with high fluidity at these temperatures. However, the former was less efficient for Itmann and Taiheiyō coals which were fusible at a higher temperature and non-fusible, respectively. The mechanism of solvolytic liquefaction is discussed, including nature of coal and solvent at reaction temperatures, in order to understand the properties required for high yields with non-fusible coals in solvolytic liquefaction. It is found that for liquefaction with a high yield if the coal is non-fusible, solvolytic reaction should take place between solvent and coal, so giving a liquid phase of low viscosity at the reaction temperature. The solvolytic reaction may be one of hydrogen transfer when SRC-BS is used as the solvent.     

Kinetics of coal liquefaction during heating-up and isothermal stages

Direct liquefaction of Shenhua bituminous coal was carried out in a 500 ml autoclave with iron catalyst and coal liquefaction cycle-oil as solvent at initial hydrogen of 8.0 MPa, residence time of 0–90 min. To investigate the liquefaction kinetics, a model for heating-up and isothermal stages was developed to estimate the rate constants of both stages. In the model, the coal was divided into three parts, easy reactive part, hard reactive part and unreactive part, and four kinetic constants were used to describe the reaction mechanism. The results showed that the model is valid for both heating-up and isothermal stages of liquefaction perfectly. The rate-controlled process for coal liquefaction is the reaction of preasphaltene plus asphaltene (PAA) to oil plus gas (O + G). The upper-limiting conversion of isothermal stage was estimated by the kinetic calculation.     

Differences in the behaviour of US bituminous and subbituminous coals during short contact time liquefaction

The short contact time (SCT) liquefaction of Belle Ayr subbituminous coal has been compared with that of Illinois No. 6 and Pittsburgh seam bituminous coals. Each bituminous coal was highly solubilized (90 wt%, daf coal) in 3–4 min at 450 °C and 13–16 MPa hydrogen pressure. More than 80 wt% of each coal was converted to solvent-refined coal (SRC, pyridine-soluble residuum), with only small quantities of distillate oil and C₁–C₄ gas being formed. A longer reaction (up to 30 min) gave only a small increase in total conversion, but gas and distillate yields increased significantly. Iron sulphides did not appear to catalyse coal solubilization. By contrast, only 65 wt% of the Belle Ayr coal dissolved rapidly in SCT liquefaction and pyrite addition catalysed the conversion of the remaining insoluble organic matter (IOM). With an equivalent amount of pyrite present the Belle Ayr coal also gave more C₁–C₄ gas and substantially more distillate in SCT liquefaction than the bituminous coals. These differences in product distributions obtained from bituminous and subbituminous coals in SCT liquefaction can be rationalized on the basis of differences in the structures of the starting coals. However, the origin of high IOM yields with the Belle Ayr coal remains unclear.     

Effects of solvent and iron-compounds on the liquefaction of brown coal

Hydrogen-donor solvents such as hydrophenanthrene are the most effective aromatic solvents for the liquefaction of brown coal. The hydrogen-donating ability of the solvent is more important for brown coals than for bituminous coals, because the thermal decomposition and subsequent recombination of the structure of the brown coals occurs rapidly. Three-ring aromatic hydrocarbons are more effective solvents than two-ring aromatics, and polar compounds are less effective solvents with brown coals than with bituminous coals. The thermal treatment of brown coal, accompanied by carbon dioxide evolution at temperatures > 300°C, in the presence of hydrogen-donating solvent did not affect the subsequent liquefaction reaction. However, thermal treatment in the absence of solvent strongly suppressed the liquefaction reaction, suggesting that the carbonization reaction occurred after the decarboxylation reaction in the absence of hydrogen donor. To study the effect of various iron compounds, brown coal and its THF-soluble fraction were hydrogenated at 450°C in the presence of ferrocene or iron oxide. The conversion of coal and the yield of degradation products are increased by the addition of the iron compounds, particularly ferrocene, and the yield of carbonaceous materials is decreased.     

溶胀煤制备及煤加氢液化性能的研究

在自然和微波条件下,对五彩湾煤进行溶胀处理,进行煤质、电镜、热解、煤的结构-化学指数分类、加氢液化产率和液化残渣热解的分析。实验结果表明:五彩湾煤自然溶胀煤样和微波溶胀煤样的层状和裂纹显著增加,失重量明显增大。煤加氢液化测试结果表明,在氢初压6.0 MPa、溶煤比1.75:1、反应温度450℃和反应时间60 min条件下,气产率由原煤的9.7%,降低到两种溶胀煤均在3.4%左右;油产率由原煤的55.2%,提高到自然溶胀煤的70.1%和微波溶胀煤的74.0%;转化率由原煤的76.8%,增加到自然溶胀煤的82.1%和微波溶胀煤的84.8%。可见,经过溶胀处理,煤加氢液化效果显著。     

Catalytic hydrocracking of primary maceral concentrate extracts prepared in a flowing solvent reactor

Differences between the behaviour of coal macerals during liquefaction and catalytic hydrocracking were investigated. The liquefaction experiments were carried out in tetralin, using a flowing solvent reactor. The extracts were catalytically hydrocracked in a micro-bomb reactor, using a commercial catalyst. Extracts and hydrocracked products were characterised by size exclusion chromatography (SEC), UV-fluorescence spectroscopy (UV-F), probe-mass spectrometry and thermogravimetric analysis. Conversions of the vitrinite and the liptinite concentrates during liquefaction were high (∼89%), while inertinite samples yielded a little over 20% extract. For inertinites, the emerging picture was consistent with high cross-link density. Liptinite was extracted less completely at lower temperatures and more slowly at high temperatures compared to corresponding vitrinites and vitrinitic coals. Long chain aliphatics released from the liptinite concentrate between 340 and 390°C appeared likely to have originated in lower-molecular mass material occluded in the sample matrix and dissolving in tetralin prior to the onset of massive covalent bond scission. SEC chromatograms showed material of larger MMs in liptinite and vitrinite extracts than in the inertinite extract. The molecular mass distributions broadened with increasing extraction temperature. Catalytic hydrocracking experiments were carried out in a micro-bomb reactor for 10 and 120 min at 440°C, under 190 bar of hydrogen. In hydrocracking, the liptinite was the slowest extract to react at short reaction times (∼10 min). However, at longer reaction times, its products showed the smallest MM-distribution. Smaller differences were observed between the chromatograms of the 10 and 120 min hydrocracked products of the inertinite extract. Differences between spectra of the three extracts would strongly suggest the presence of larger (and apparently irreducible) polycyclic aromatic ring systems, in the hydrocracked products of the inertinite extract.     

Microwave-assisted hydroconversions of demineralized coal liquefaction residues from Shenfu and Shengli coals

Microwave-assisted hydroconversions of demineralized coal liquefaction residues (DCLRs) from Shenfu (SF) and Shengli coals were investigated using methanol or ethanol as the solvent for both reaction and extraction. The results show that the solubilities of hydroconverted DCLRs in methanol under 0.7 MPa of initial hydrogen pressure (IHP) follow the order: non-catalytic hydroconversion = activated carbon-catalyzed hydroconversion < Pd/C-catalyzed hydroconversion < Ni-catalyzed hydroconversion; the solubility of Ni-catalyzed hydroconverted DCLR from SF coal in methanol increases with raising temperature up to 140 °C and with increase in IHP; the solubility of Ni-catalyzed hydroconverted DCLR from SF coal in methanol under 0.7 MPa of IHP at 130 °C is higher than that in ethanol. The molecular compositions of the extractable fractions were analyzed with GC/MS and the structural features of some extractable and inextractable fractions were characterized with FTIR.     

Coal feed flexibility in the Exxon Donor Solvent coal liquefaction process

The Exxon Donor Solvent (EDS) Process has been successfully employed to liquefy coals of varying rank. Bituminous, subbituminous and lignitic coals have been processed in the continuous, integrated 40 kg day^?1Recycle Coal Liquefaction Units and 1 t day^?1 Coal Liquefaction Pilot plant located at Baytown, Texas. Recent operations show that significant improvements in total liquid yield, as well as additional flexibility in product distribution, can be achieved with recycle of liquefaction bottoms. The impact of the type of coal and mode of operation on product yield and distribution as well as pilot unit operability are discussed. Specific changes in process configuration have been explored and are desirable for different coals and can be used to produce a variety of products. The implication of these recent results on defining the coal liquefaction reaction paths is discussed.     

Efficiency of hydrogen transferring liquefaction of a subbituminous coal using hydrogenated fluoranthene for short contact time at high temperature and low pressure

An Australian subbituminous coal (Wandoan) was effectively liquefied at 490 and 510 °C under nitrogen pressure of 2.5 MPa for 1.0–7.5 min using 1, 2, 3, 3a-tetrahydrofluoranthene (4HFL) as a hydrogen-donating solvent. The yields of oil and asphalthene could be as high as 58 and 24 wt%, respectively. The content of 4HFL was very influential on the oil yield although under appropriate liquefaction conditions, a considerable amount remained after reaction. The kinetics of the reaction and analytical study of the products and the solvent suggest consecutive as well as instantaneous depolymerization in the process. The coking or recondensation reaction was very rapid after 4HFL was consumed, confirming the efficacy of the short contact time liquefaction.     

Co-liquefaction of lignite and sawdust under syngas

Individual and co-liquefaction of lignite and sawdust (CLLS) under syngas was performed in an autoclave and the effects of temperature, initial syngas pressure, reaction time and ratio of solvent to coal and biomass on the product distribution of CLLS were studied. Sawdust is easier to be liquefied than lignite and the addition of sawdust promotes the liquefaction of lignite. There is some positive synergetic effect during CLLS. In the range of the experimental conditions investigated, the oil yield of CLLS increases with the increase of temperature, reaction time (10-30 min) and the ratio of the solvent to the feedstock (0-3), but varies little with the increase of initial syngas pressure. Accordingly, the total conversion, the yield of preasphaltene and asphaltene (PA + A) and gas, changes by the difference in operation conditions of liquefaction. The gas products are mainly CO and CO₂ with a few C₁-C₄ components. The syngas can replace the pure hydrogen during CLLS. The optimized operation conditions in the present work for CLLS are as follows: syngas, temperature 360 °C, initial cold pressure 3.5 MPa, reaction time 30 min, the ratio of solvent to coal and sawdust 3:1. Water gas shift reaction occurs between CO in the syngas and H₂O from coal and sawdust moisture during the co-liquefaction, producing the active hydrogen which increases the conversion of liquefaction and decreases the hydrogen consumption.     

飞灰对五彩湾煤低压直接液化性能影响研究

在溶煤比为2.75∶1,氢初压为6.0MPa和反应时间为60min条件下,考察了温度、飞灰加入量、CoSO4和NiSO4用量及其加入方式等因素对五彩湾煤直接液化性能的影响.结果表明,在给定的条件下,在飞灰加入量为3%(daf,质量分数)和温度为415℃时,可获得最大油产率为64.59%;当CoSO4和NiSO4与飞灰和煤样机械混合加入时,对液化油产率和转化率产生负效应;当NiSO4和CoSO4浸渍担载加入时,油产率分别达到68.01%和66.58%.尽管煤质分析结果表明该煤样加氢液化性能较差,但以飞灰、CoSO4和NiSO4为催化剂时,还是获得了良好的液化效果.     

Quantitative study on cross-linking reactions of oxygen groups during liquefaction of lignite by a new model system

Cross-linking reactions (CLR) of oxygen groups during liquefaction of lignite were quantitatively studied by a new model system. Chinese Yitai lignite (YT) was first oxidized by nitric acid at 70 °C and about 98% of the oxidized sample could be dissolved in tetrahydrofuran (THF) at room temperature. Then benzyl alcohol, PhCH₂OH (BA), as a model compound was added into the oxidized coal, also acted as solvent in the subsequent liquefaction. Temperature-programmed reactions (TPR) at liquefaction conditions under hydrogen atmosphere were performed to evaluate the CLR by quantitative analysis of THF-insoluble solid products (THFI) after reaction. Extensive CLR were observed even under high pressure of H₂ at 200-400 °C, and more than 51.7% and 81.2% of the THFS fraction was converted into the THFI at 300 °C with tetralin (TET) and BA as solvent, respectively. The THFI fraction was almost solely caused by the CLR, which makes it possible to quantitatively study the CLR by analyzing the amount of the cross-linked solid products (CSP). The pyrolysis behaviours of CSP and oxidized coal were examined by TG. Other model compounds containing oxygen-functional groups (alcohol, phenol, carboxyl, carbonyl and ether groups) can also be used in this model system to study CLR of oxygen groups in low-rank coals.     

煤炭直接液化技术研究

我国煤炭直接液化技术研究已达到国际先进水平．兖州、天祝、神府烟煤和先锋．沈北、东胜褐煤都是较好的直接液化原料煤。煤直接液化的馏分油最适宜生产高辛烷值汽油、优质喷气燃料和催化重整制取芳烃原料油．两段催化液化由1t无水无灰煤生产5bb1馏分油．煤油共炼与直接液化相比较，简化了工艺过程，改进了馏分油产率和质量。我国煤直接工艺发展方向是煤油共炼或两段催化液化工艺。     

Liquefaction of sawdust for liquid fuel

Pressurized liquefaction of sawdust was carried out in an autoclave in the presence of solvent under cold hydrogen pressure ranging from 2.0 to 5.5 MPa at the temperature range of 150C–450°C. The reaction time varied from 5 to 30 min. Investigations were made on the effects of temperature, reaction time, cold hydrogen pressure and solvent on the liquefaction process. Results indicate that liquefaction of sawdust can start at a temperature of 200°C, much lower than that for coal in a hydrogen-donor solvent, e.g., tetralin which was used in this run of experiment. Oil yield increase with the rise either in temperature and in cold hydrogen pressure or with the longer reaction time.     

煤中显微组分液化反应性研究进展

煤炭液化是目前可大规模采用的缓解我国石油资源供应紧张的有效方法.综述了国内外关于煤岩显微组分液化特性和机理的研究现状,讨论了显微组分性质对液化反应性的影响,提出了今后深化研究的方向,认为低煤级煤中惰质组的转化率和油收率不可忽视,只是反应条件与其他显微组分并不一致,且影响惰质组反应性的因素较为复杂.所以建议,不同显微组分的最佳液化条件与差异、煤中活性显微组分与惰性成分在液化过程中的相互关系、显微组分在液化反应过程中的协同效应及其表征等是值得今后深化研究的方向.