Regulation of radicals by hydrogen-donor solvent in direct coal liquefaction

Radicals are important intermediates in direct coal liquefaction. Certain radicals can cause the cleavage of chemical bonds. At high temperatures, radical fragments can be produced by the splitting of large organic molecules, which can break strong chemical bonds through the induction pyrolysis of radicals. The reaction between the formation and annihilation of coal radical fragments and the effect of hydrogen-donor solvents on the radical fragments are discussed in lignite hydrogenolysis. Using the hydroxyl and ether bonds as indicators, the effects of different radicals on the cleavage of chemical bond were investigated employing density functional theory calculations and lignite hydrogenolysis experiments. Results showed that the adjustment of the coal radical fragments could be made by the addition of hydrogen-donor solvents. Results showed that the transition from coal radical fragment to H radical leads to the variation of product distribution. The synergistic mechanism of hydrogen supply and hydrogenolysis of hydrogen-donor solvent was proposed.     

Chemistry of solvents in coal liquefaction: Quantification of transferable hydrogen in coal-derived solvents

Hydrogen was evolved as hydrogen sulphide when coal-derived solvents for liquefaction were heated with sulphur (dehydrogenation method) and their naphthene contents were quantified by titration and ¹³C n.m.r. analysis to estimate the amount of transferable hydrogen from hydroaromatics present in the solvent. Examination of synthetic solvents consisting of model compounds confirmed the validity of both approaches. The content of transferable hydrogen, thus measured, in the various solvents correlated well with their liquefaction activities using Morwell brown coal. This suggests that the sufficient stabilization of radical fragments derived thermally from the coal at the initial stage of its liquefaction leads to high conversion. It was also shown that the dehydrogenation method was applicable to non-distillable heavy fractions of coal-derived liquids such as SRC which are difficult to measure by n.m.r. because of their limited solubility.     

A kinetic investigation of coal liquefaction at short reaction times

Coal liquefaction kinetics have been studied at very short reaction times (less than 250 seconds) in order to emphasize the initial underlying physical and chemical processes involved. These studies were made possible by the use of a continuous flow stirred tank reactor (CSTR) which avoids the problems of slow heat up and cool down associated with the massive equipment required for running high-temperature and high-pressure liquefaction reactions. Preliminary physical (NMR and ESR) and chemical analytical results are presented on the coal liquids and reaction residues from Illinois No. 6 hv bituminous and Wyodak Black Thunder subbituminous coals.

ESR results showed that radical concentration in the solid residue changed during coal liquefaction. These changes were accompanied by changes in the NMR-derived aromaticity. The rate of decrease of organic-based radicals was different for Wyodak Black Thunder and Illinois No. 6 coals, perhaps indicating a different mechanism for the quenching of radicals in these bituminous and subbituminous coals. NMR spectra of the liquid products indicated that the initially produced material was relatively aromatic, and that subsequent products had lower aromatic content. This is consistent with secondary hydrogenation of the primary liquefaction products. Finally, the total oxygen contents of the coal residues decreased gradually during the first three minutes of coal liquefaction at 390°C. A corresponding decrease in the hydroxyl content of these residues was also noted.     

煤直接液化制油技术研究现状及展望

煤直接液化制油技术是促进煤炭清洁高效利用、缓解石油供需矛盾、保障我国能源安全的重要途径。为全面了解煤液化反应机理、动力学、催化剂及工艺的全过程,促进煤直接液化技术基础研究的快速进步和新工艺的开发,笔者综述了国内外在煤加氢液化反应机理、反应动力学、催化剂以及液化工艺方面取得的研究成果,重点介绍了德国IGOR、日本NEDOL和我国的神华煤液化工艺,分析了这些典型煤液化工艺的开发历程和特点;指明了煤直接液化制油技术发展趋势。煤的加氢液化反应是自由基反应机理,是一系列顺序反应和平行反应的综合结果,包含煤的热解、自由基加氢、脱杂原子和缩合反应等,总体上以顺序反应为主。借助同位素示踪、原位实时检测、等离子体技术以及微波快速加热技术等现代分析方法和试验手段,重点研究自由基的产生速率、活性氢产生速率及定量传递机理,有助于深入认识和精准阐明煤加氢液化反应机理。各国学者利用不同的研究方法,针对不同煤种、催化剂、工艺条件和供氢溶剂等,建立了各种各样的动力学模型。动力学模型从单组分到双组分和多组分,从连续反应、平行反应到复杂的网络反应,从最初的一步反应到后来较为合理的多段反应,模型越来越复杂,越来越接近工业应用。根据反应阶段不同进行分段处理的多组分"集总"反应动力学模型将是今后煤加氢液化反应动力学发展的主要方向。借助先进分析手段及科学的处理方法,建立真正揭示不同条件下煤液化动力学规律的通用型动力学模型是未来的发展趋势。借助纳米合成、等离子体等高新技术,调控组分配伍、降低催化剂粒径、优化制备方法是制备高活性催化剂的有效手段。强化系统合理配置和优化集成,重视煤的温和液化和分级转化,优化产品结构,发展直接液化-间接液化耦合技术是煤直接液化未来的发展趋势。     

Performance indices for coal liquefaction solvents

Most coal liquefaction processes are based on the thermal cleavage of activated bonds giving reactive carbon and oxygen radicals which abstract hydrogen atoms from the donor solvent. The role of oil is approximated in this study by using a simple standard reaction. A series of five representative solvents react with phenyl and phenyloxy radicals generated by thermolysis of benzoyl peroxide at 87 °C in tetrachloroethylene. The n.m.r. analysis of the reacting mixture defines four performance indices, i.e. the hydrogen-donor, the efficiency, the recycle and the scavenger indices, which characterize the ability of these solvents as efficient recycle oils in coal liquefaction processes. 9,10-dihydrophenanthrene proves to be by far the most appropriate solvent for this purpose.     

由煤制取芳烃化合物的研究进展

综述了国内外由煤制取芳烃化合物的三种思路：一是通过将煤直接进行液化获取,或者先将煤液化再从产物中获得芳烃化合物;二是先对煤进行溶剂抽提,然后对产物分类加工制取芳烃化合物;三是将煤进行氧化处理来获得高价值的芳烃化合物。分析了由煤制取芳烃化合物的所面临的产物分离困难、污染环境等问题,并指出了今后需要在分离工艺和催化剂以及如何实现煤的定向转化等方面进行重点研究。     

Improvement in coal liquefaction solvent quality by dewaxing

Recycle oils from the Integrated Two-Stage Liquefaction (ITSL), H-Coal and Solvent Refined Coal (SRC) processes were dewaxed by variants of commercial dewaxing processes—the ketone and the urea adduction techniques — yielding up to 47 wt % ‘wax’. Feed oils and product fractions were characterized by elemental analysis, ¹H n.m.r. and gas chromatography. The clean waxes were nearly pure mixtures of n-paraffins. The dewaxed oils were substantially better coal liquefaction solvents than the original (non-dewaxed) oils in batch liquefaction tests. For example, in one case, dewaxing improved the conversion of a bituminous coal to tetrahydrofuran-solubles under standard reaction conditions from 71 wt% (dafb) with the original oil to 87 wt % (dafb). These data provide a direct indication of the inimical effect of paraffinic components on solvent quality. The impact of solvent quality is particularly relevant to liquefaction processes in which thermal reactions proceed in a recycle solvent. In addition, the results indicate the technical feasibility of dewaxing coal liquefaction recycle oils by commercially available technology to improve solvent quality and to produce a useful by-product. Dewaxing could be applied in any liquefaction process that uses a deasphalted (preferably distillate) recycle stream.     

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.     

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.     

溶剂对依兰煤液化反应特性的影响

不同的溶剂对煤直接液化过程产生不同的影响，其组成和性质决定了反应进行的途径。本文介绍了进行该项研究的试验装置和工艺过程，从试验结果得出了三种不同溶剂即ＨＡＯ，ＤＡＯ和循环溶剂对煤液化产物及各项收率的影响。     

The behavior of n-paraffins under coal liquefaction conditions

In order to evaluate the concentration and the distribution of n-paraffins in recycle solvent of coal liquefaction processes, the behavior of n-paraffins under coal liquefaction conditions was investigated. Four coals (Wandoan, Taiheiyo, Wyodak, Illinois No. 6) were liquefied and n-paraffins produced were analyzed. For example, n-paraffins, produced from liquefaction of Wandoan coal at 450°C for 1 h, contain approximately 5.2 wt.% (dry coal base) hydrocarbons in the range C₁₀C₃₆.Furthermore, cracking reactions of n-paraffins were carried out and their behavior under coal liquefaction conditions was analyzed. The cracking conversions of n-paraffins increased with increasing carbon numbers of n-paraffins, and the rate constants for cracking of n-paraffins were directly proportional to carbon numbers. The product distribution in the cracking of n-paraffins was evaluated by using bond dissociation energy. On the basis of these results, the concentrations of n-paraffins in the recycle solvents were calculated and these calculated values agreed well with those observed in the coal liquefaction process.     

煤炭直接液化溶剂的研究

讨论了煤炭直接液化过程中溶剂的特点、作用及质量要求,煤液化溶剂具有一般溶剂的功能,同时还具有良好的供氢和传递氢的功能特点,起到溶解、分隔煤裂解生成的自由基的作用,溶剂必须具有一定的分子结构和分子大小。初步讨论了表征煤液化循环溶剂供氢性的指标,指出普通溶剂如四氢萘和二氢萘等部分饱和的芳香化合物可直接用作煤液化溶剂,多环芳烃含量较高的煤焦油和石油系重质油,经过预加氢处理提高溶剂的供氢性后,可作为煤液化过程的起始溶剂或替代溶剂。     

模型化合物在煤液化研究中的应用

本文主要论述了目前世界上应用模型化合物研究煤液化过程的概况。研究内容包括：全煤结构模型化合物的研究，煤液化时桥键裂解过程的作用，氢转移及煤和溶剂之间的相互作用，以及利用模型化合物考查煤液化中缩聚反应的研究等。并指出利用模型化合物研究煤液化的局限性。     

Free radicals in coal and coal conversions. 10. Kinetics and reaction pathways in hydroliquefaction

The development is reported of a point rate model for the solubility fractions obtained from Powhatan No.5 coal liquefaction in terms of free-radical concentration. Stepwise regression procedures were used to determine rate constants for general hypothetical rate models. Chemical principles were used at each stage to eliminate terms and to fix others. Rate constant expressions were obtained by fitting In k to the inverse absolute temperature for each solvent. Generalized reaction paths were determined from these individual reactions by combining various reactions. These reactions described the conversion of material between solubility fractions via free-radical interactions. In all three solvents progressive liquefaction reactions that did not involve measured radicals (conventional reaction terms) predominated in the rapid break-up of coal, while free-radical reactions are predominant in retrogressive changes. At higher radical concentrations retrogressive reactions predominated. More reactions of all types became significant with increasing temperature.     

The nature of the synergistic effect of binary tetralin-alcohol solvents in Kansk-Achinsk brown coal liquefaction

Kansk-Achinsk brown coal hydrogenation and swelling in tetralin, in low molecular alcohols, in other solvents and in binary mixtures were studied. Tetralin was found to be the most effective liquefaction solvent, but methanol and ethanol were the active ones in coal swelling. Synergistic effects were observed when the mixtures of tetralin and methanol or ethanol were used for liquefaction and swelling. The effect of binary solvents was shown to be due to the ability of alcohol components to cause brown coal to swell improving the availability of the fragments of coal matter for the reactive hydrogen donor tetralin molecules.     

Liquefaction of subbituminous coals under apparently non-hydrogenative conditions

Reactivities of several coals of different ranks have been examined in degrading extractions with aromatic solvents under apparently non-hydrogenative reaction conditions. Pyrene and A240 pitch liquefied the fusible coals in high yields and the slightly-fusible coals in moderate yields, indicating the importance of fusibility in such liquefaction processes. A240-LS pitch is a powerful solvent for slightly-fusible coals. Considerable amounts of pyridine- or THF-soluble fractions were produced especially with A240-LS pitch. A240 pitch is a better solvent than pyrene for some slightly-fusible coals. However, the extent of depolymerization of liquefied coal, pyridine- or THF-solubility, was definitely inferior. Yields of such fractions are higher for lower-rank coals. The mechanism of coal liquefaction under apparently non-hydrogenative conditions is discussed with emphasis on the stabilization of thermal fragments 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.     

Carbonization and liquid-crystal (mesophase) development. 15. A common stage in mechanisms of coal liquefaction and of coal blends for coke making

This paper discusses the processes of coal liquefaction and co-carbonization of coal/pitch blends in terms of physical and chemical properties of the fluid phases found in both pyrolysis systems. Mechanisms of development of thermal plasticity in coals are outlined. In coal liqudfaction the importance is stressed of hydrogen-donor vehicles interacting with the products of thermal depolymerization of coal. The concept of variations in the facility of solvation and solvolysis of additives in co-carbonizations can explain the variations observed in degrees of interaction of a single coal with several additives. Possibly, the hydrogen-donor facility of an additive may be as important in assessments of modifying ability as an average molecular structure. The possibility exists of using an analysis of optical texture of cokes resulting from the fluid coal/solvent pyrolysis systems to characterize the effectiveness of solvents in coal liquefaction systems as distinct from coal blending co-carbonization studies.     

An investigation of the role of hydrogen sulphide in coal liquefaction catalysis by high-temperature and high-pressure e.s.r.

The role of hydrogen sulphide (H₂S) as a coal liquefaction catalyst was tested using two typical coals having different ash content and mineral matters by means of high-temperature and high-pressure e.s.r. For Illinois No. 6 coal having pyrite as minerals, a slight increase in radical concentration in a coal/H₂S system was observed at about 500 K and then drastic increase in radical concentration at above 620 K. On the other hand, in a coal/N₂ system, the increase in radical concentration was much smaller.The effect of H₂S on the change of radical concentration for Yallourn coal which has little ash content was not remarkable. It was concluded that H₂S is a promoter of liquefaction in presence of iron, but has little inherent catalytic function itself. High-temperature and high-pressure e.s.r. is found to be a useful tool to understand the synergistic effect of H₂S-iron sulphide in a coal liquefaction catalyst.     

催化裂化（FCC）油浆作煤直接液化溶剂的研究进展

煤制油工艺等煤炭清洁高效转化技术是能源化工领域的研究热点,溶解性好、提供/传递氢能力强且热稳定性高,其溶剂选择、使用是影响煤制油工艺经济运行的关键。本文以煤液化溶剂作用为基础,通过对液化自身产物、废塑料及FCC油浆等煤直接液化溶剂的组成、性质及作用效果的综合评述,指出煤、溶剂、氢气间的混合并非理想混合,与煤H/C适宜、极性相近的溶剂在共处理过程表现出良好的协同作用,液化过程的转化率、轻质产物选择性明显提高。分析表明,协同作用的大小取决于煤、溶剂的组成、性质匹配。煤-重质烃共处理工艺利用富芳烃油浆溶解性好、提供/传递氢能力强的特点强化了煤热解加氢反应的进行,同时煤加氢液化产生的多孔残煤具有吸附性强的特点,有助于重质烃改质,使共处理转化率显著提高、轻质产物选择性增大。最后指出,煤-重质烃共处理的协同作用为改善煤、中质/重质芳烃的综合利用提供了可能。