Behavior of phenolics in coal liquefaction: adduction tendency and coal conversion capability

A series of coal liquefaction reactions has been carried out at 450°C to examine the adduction tendency and the coal liquefaction efficiency of 1-naphthol using a product extraction scheme which minimizes co-solvent effects. An additional set of experiments was conducted to provide information on the relative effectiveness of substituted phenols compared with the parent compound.The results indicate that 1-naphthol is a better solvent than phenanthrene, but a significantly poorer one than tetralin with regard to total conversion. Mixtures of this compound with tetralin do not promote conversion above that available from tetralin alone. In all cases, loss of naphthol by adduction to the coal liquids is a major problem.The three cresols effect higher degrees of coal conversion when used 1:1 with tetralin than does phenol, but the mixtures are not as effective as tetralin alone. The single-ring phenolic species were found to exhibit only a very moderate tendency for adduction.     

Effect of cresol as a co-solvent in coal liquefaction and product analysis

The influence of o-cresol on conversions of Bruceton coal to tetrahydrofuran (THF) extract was determined over the full range of composition for mixtures of o-cresol with either tetralin, phenanthrene, anthracene or pyrene. A maximum was found in both of the plots of coal conversion versus cresol content for mixtures with phenanthrene or pyrene. By comparison, the conversion found in pure tetralin was significantly higher than those found in the polynuclear aromatics and was not increased by addition of o-cresol. The enhancement of conversion by addition of cresol to the polynuclear aromatics was determined to be due to its action during the liquefaction itself, and not due to any influence exerted on post-liquefaction product separation. The relationship of these results to other studies showing the effect of cresol on both liquefaction chemistry and on post-liquefaction product work-up is discussed.     

煤直接液化初始阶段反应特性的研究

以杨村煤为例,在490℃和2倍四氢萘溶剂的条件下,反应仅5min煤直接液化总转化率就达到84．47％,表明煤在直接液化的过程中具有初始高反应活性的特点。在纯氢气气氛下随着初始压力从1．5MPa增大到7MPa,转化率从66．38％上升为83．27％,表明压力大小对煤液化转化率有较大影响。1．5MPa下溶煤比提高到4：1以后,转化率增大到79．0％就不再增长,表明用添加过量供氢溶剂的方法弥补由于降低系统压力所带来的转化率损失不可行。     

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.     

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.     

A semi-continuous flow reactor technique for coal liquefaction studies

A novel semicontinuous tubular reactor flow technique was used to study liquefaction of a typical Venezuelan coal. The technique allows a simple procedure to calculate coal liquefaction conversion. This was found to be increased by various catalysts only if the appropriate amount with the proper particle size was employed. Nickel—molybdate and cobalt—molybdate catalysts were found to be better catalysts than copper—chromite for desulfurizing the coal; however, the latter catalyst produced the largest liquefaction conversion.     

Alcohols as H-donor media in coal conversion. 1. Base-promoted H-donation to coal by isopropyl alcohol

Isopropyl alcohol can act as a hydrogen donor to coal, as can tetralin. In contrast to tetralin, however, the transfer of hydrogen by the alcohol can be promoted by the presence of either potassium isopropoxide or KOH. Acetone is formed from the alcohol in quantities that accord with the amounts of hydrogen transferred to the coal. In runs at 335 °C for 90 min, coal was converted with isopropyl alcohol in the presence of either the alkoxide or KOH to a fully pyridine-soluble product with $\text{H}\text{C}$ ratios from 0.88 to 1.13, in contrast to coal (0.79). The organic sulphur content of the coal was reduced from 2.1% to 1%. Model-compound studies with anthracene and diphenyl ether showed that the anthracene was reduced in the system to 9,10-dihydroanthracene, but the ether was recovered unchanged. The coal products from the alcohol/base treatment are very rich in aliphatic hydrogen and have number-average molecular weights in the 450–500 range. The scheme suggested to explain the conversion at 335 °C includes initial hydrogenation of anthracene-like structures in the coal, followed by thermolysis of the dihydro-intermediate.     

Coal liquefaction using indene-tetralin and indene-decalin mixtures as solvent

Indene-tetralin and indene-decalin mixtures were used as the solvent for coal liquefaction. The effect of mixing on conversion for Yallourn coal was observed under nitrogen pressure at 400 and 440 °C. Conversion to benzene-soluble material in an indene-decalin mixture (50:50, wt) at 440 °C for 1 h was 73.0% and was only 9% lower than that in 100% tetralin. The reaction of indene with tetralin or decalin may provide the active species for coal dissolution. Simultaneously, coal radicals may be scavenged by indene.     

Effect of pre-swelling of coal at mild temperatures on its hydro-liquefaction properties

The effects of pre-swelling treatment of Shenhua coal at mild temperatures (less than 160 °C) on its hydro-liquefaction properties were determined in this paper. It was found that with the increase of pre-swelling temperature in tetralin (THN) up to 120 °C, the liquefaction conversions of swollen coals increased. However, when N-methyl-2-pyrrolidinone (NMP) was used as swelling solvent, the liquefaction conversion decreased with the increase of pre-swelling temperature. The liquefied product distributions were very much dependent on the pre-swelling pretreatment conditions, and the mechanism was discussed. Based on the results obtained, a new swelling-liquefaction combining technology (SLCT) was advanced, in which the liquefaction conversion and oil + gas yield were enhanced.     

Hydroliquefaction of low-sulfur coals using iron carbonyl complexes—Sulfur as catalysts

Hydroliquefaction of low-sulfur Australian coals (Wandoan and Yallourn) was studied using iron carbonyl complexes as catalyst. The addition of Fe(CO)₅ (2.8 wt% Fe of coal) increased coal conversion from 48.6 to 85.2% for Wandoan coal, and from 36.7 to 69.7% for Yallourn coal in 1-methylnaphthalene at 425°C under an initial hydrogen pressure of 50 kg cm^?2. When molecular sulfur was added to iron carbonyls (Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂), higher coal converions ( > 92%) and higher oil yields (>46%) were obtained, along with an increase in the amount of hydrogen transferred to coal from the gas phase (0.2 to 2.8%, d.a.f. coal basis). In the liquefaction studies using a hydrogen donor solvent, tetralin, Fe(CO)₅S catalyst increased the amount of hydrogen absorbed from the gaseous phase and decreased the amount of naphthalene dehydrogenated from tetralin. The direct hydrogen transfer reaction from molecular hydrogen to coal fragment radicals seems to be a major reaction pathway. Organic sulfur compounds, dimethyldisulfide and benzothiophene, and inorganic FeS₂ and NiS were found to be good sulfur sources to Fe(CO)₅. From X-ray diffraction analyses of liquefaction residues, it is concluded that Fe(CO)₅ was converted into pyrrhotite (Fe_1?xS) when sulfur was present, but into Fe₃O₄ in the absence of sulfur.     

超细FeS对五彩湾煤直接液化性能的影响

以硫酸亚铁为铁源,硫化钠为沉淀剂,采用液相沉淀法合成了超细FeS催化剂。以四氢萘为溶剂,反应温度430℃、氢初压6.0 MPa、反应时间60 min、溶煤比2∶1条件下,探讨超细FeS催化剂对五彩湾煤直接液化性能的影响。结果表明：硫酸亚铁基超细FeS粒子形貌均一,呈细棒状;五彩湾煤直接液化实验的油产率、液化率和转化率,以2.0%（wt,以活性金属元素计,相对于干燥无灰煤,下同）超细FeS为催化剂的实验分别达到56.15、73.29和81.21%（wt,相对于干燥无灰煤,下同）,高于相同条件下,以3.0%分析纯Fe2O3为催化剂的实验产率（分别是44.00、49.33和62.05%）。     

Catalytic hydrogen transfer due to FeSO4 and Co&z.sbnd;Mo in coal liquefaction

The liquefaction behaviour of a Kentucky coal was studied in batch autoclave experiments at 410 °C under either a H₂ or a N₂ atmosphere (≈ 13.8 MPa) for reaction times of up to 2 h. To understand the catalytic roles of FeSO₄ and a Co&z.sbnd;Mo catalyst in coal liquefaction and to assess the feasibility of using FeSO₄ as a model for coal pyrites, effects of impregnation of the coal with FeSO₄ and direct charges of a Co&z.sbnd;Mo catalyst on coal liquefaction and tetralin dehydrogenation were examined. Both catalysts increase the conversion to benzene-soluble material by 7–10%, and improve the selectivity values for conversion to oil and gas. In addition they are also active in the dehydrogenation of tetralin. The dehydrogenation activities of these catalysts correlate with their catalytic activities during coal liquefaction. Analyses of the mean chemical structures and the product distributions of the coal-derived liquid from liquefaction in H₂ and in N₂ atmospheres indicate that:

1. (1) H-transfer from tetralin is the only major mechanism of coal liquefaction; and

2. (2) both pyrrhotite, generated in-situ from FeSO₄, and Co&z.sbnd; Mo catalyst can provide a major liquefaction mechanism by catalysing the H-transfer from the donor solvent to the coal or the coal-derived liquid.

     

Dependence of coal liquefaction behaviour on coal characteristics. 3. Statistical correlations of conversion in coal-tetralin interactions

The liquefaction behaviour of coals can vary over a wide range depending on both their chemical and petrographic characteristics. Sixty-eight coals have been studied under standard liquefaction conditions, in the presence of tetralin but with no added catalyst or molecular hydrogen. Simple correlations between conversion and individual coal parameters proved unsatisfactory. A novel approach utilizing a stepwise multiple regression analysis led to a number of linear equations relating conversion simultaneously to several coal characteristics. Such linear equations provide a basis for accurately predicting liquefaction behaviour and confirm that wise selection of appropriate feedstocks will have an important economic value. It seems permissible to infer that the behaviour of coals in any processing conditions can only be adequately accounted for by consideration of at least three coal properties; attempts to correlate coal properties solely with a rank parameter, such as carbon content, can no longer be considered adequate.     

Synergistic effects between light and heavy solvent components during coal liquefaction

As part of research to examine coal conversion in solvents containing high-boiling-point components, experimental studies were carried out with model compound solvents. The dissolution of bituminous and subbituminous coals was investigated in pyrene-tetralin and 2-methylnaphthalene-tetralin mixtures. The effects of donor level, gas atmosphere, hydrogen pressure and conversion temperature were determined. At 400 °C, in the presence of hydrogen gas, pyrene-tetralin solvent mixtures show synergism in coal conversion. At donor concentrations as low at 15 wt%, the degree of conversion was almost as high as in pure tetralin. This phenomenon was not apparent in 2-methylnaphthalene-tetralin mixtures. The relative ease of reduction of pyrene and its ability to shuttle hydrogen is considered to be a principal reason for this difference in behaviour. Conversion in pure pyrene and in pyrene-tetralin mixtures at low donor concentrations increased with increasing hydrogen pressure. At 427 °C, bituminous coal conversion was higher in a 30 wt% tetralin-70 wt% pyrene mixture than in either pure compound. It was found that in the absence of coal pyrene can be hydrogenated by H-transfer from tetralin as well as by reaction with hydrogen gas. This can provide a means to increase the rate of transfer of hydrogen to the dissolving coal through the formation of a very active donor (dihydropyrene). During coal liquefaction, several pathways appear to be available for hydrogen transfer for a given coal, the optimal route being dependent upon the solvent composition and the conditions of reaction.     

Alkanes and solvent dimers in successive extract fractions released from coal during liquefaction in a flowing-solvent reactor

Types of alkanes present in liquefaction product fractions released from coal during successive time—temperature intervals were examined by g.c.—m.s. Experiments were carried out in a flowing-solvent reactor where solubilized products are continuously removed from the reaction zone; tetralin, quinoline and hexadecane were used as the solvent. At 450°C (with 400 s holding) total conversions in tetralin, quinoline and hexadecane were 82.5, 74.7 and 24 wt% (daf), respectively. In tetralin, alkanes were released from coal more readily and at lower temperatures than in quinoline or hexadecane; m.s. signal intensities fell rapidly with increasing reaction temperature. In quinoline, lower intensities of alkane peaks were observed than in tetralin, although the trend with temperature was similar. In hexadecane however, the trend of intensity with temperature was reversed compared with liquefaction in tetralin or in quinoline; the range of alkanes detected was also smaller than in tetralin or in quinoline. The presence of alkenes in the hexadecane extracts suggested a pyrolytic mechanism for the thermal breakdown. Isoprenoid alkanes, pristane and phytane, were detected in the tetralin and quinoline extracts but not those prepared in hexadecane. Materials present in product mixtures and thought to originate with each solvent were briefly investigated: dimers were the most prominent species in tetralin extracts, with only low-intensity dimers being found in quinoline extracts and no apparent formation of higher homologues from hexadecane. These results were compared with the pattern of alkane release from coal during liquefaction in tetralin in a conventional minibomb reactor and in the pentane-soluble fraction of the total (unfractionated) extract from the F-S reactor.     

Analysis of solvent extracts from coal liquefaction in a flowing solvent reactor

Point of Ayr coal has been extracted using three solvents, tetralin, quinoline and 1-methyl-2-pyrrolidinone (NMP) at two temperatures 350 and 450 °C, corresponding approximately to before and after the onset of massive covalent bond scission by pyrolysis. The three solvents differ in solvent power and the ability to donate hydrogen atoms to stabilise free radicals produced by pyrolysis of the coal. The extracts were prepared in a flowing solvent reactor to minimise secondary thermal degradation of the primary extracts. Analysis of the pentane-insoluble fractions of the extracts was achieved by size exclusion chromatography, UV-fluorescence spectroscopy in NMP solvent and probe mass. With increasing extraction temperature, the ratio of the amount having big molecular weight to that having small molecular weight in tetralin extracts was increased; the tetralin extract yield increased from 12.8% to 75.9%; in quinoline, increasing extraction temperature didn't have an effect on the molecular weight of products but there was a big increase in extract yield. The extracts in NMP showed the enhanced solvent extraction power at both temperatures, with a shift in the ratio of larger molecules to smaller molecules with increasing extraction temperature and with the highest conversion of Point of Ayr coal among these three solvents at both temperatures. Solvent adducts were detected in the tetralin and quinoline extracts by probe mass spectrometry; solvent products were formed from NMP at both temperatures.     

Free radical chemistry of coal liquefaction: role of molecular hydrogen

Model compounds containing the types of carboncarbon bonds thought to be present in coal were pyrolyzed in the presence of tetralin and molecular hydrogen at 450 °C. The relative rates of conversion of the model structures are predictable from the bond dissociation energies of the compounds. Conversion of dibenzyl in the presence of both tetralin and molecular hydrogen or in the presence of hydrogen alone proceeds along two parallel reaction paths. Toluene is produced by a thermal cracking reaction in which the rate-controlling step is the thermal cleavage of the β-bond in dibenzyl. Benzene and ethylbenzene are produced by a hydrocracking reaction. The rate of the hydrocracking reaction is directly proportional to the hydrogen pressure. The strong bond in diphenyl is hydrocracked in a system containing both molecular hydrogen and a source of free radicals. These studies on model coal structures offer firm evidence that molecular hydrogen can participate directly in free radical reactions under coal liquefaction conditions. Under some conditions molecular hydrogen can compete with a good donor solvent to stabilize the thermally produced free radicals. Molecular hydrogen can also promote some hydrocracking reactions in coal liquefaction that do not occur to an appreciable extent in the presence of only donor.     

Liquefaction mechanism of Wandoan coal using tritium and 14C tracer methods: 2. Liquefaction using 3H labelled gaseous hydrogen

Tritium labelled gaseous hydrogen was used to clarify the role of gaseous hydrogen in coal liquefaction. Wandoan coal was hydrogenated under 5.9 MPa (initial pressure) of ³H-labelled hydrogen and in unlabelled solvents such as tetralin, naphthalene and decalin at 400 °C and for 30 min in the presence or absence of NiMoAl₂O₃ catalyst. Without a catalyst, liquefaction proceeded by addition of the hydrogen from donor solvent. The NiMoAl₂O₃ catalyst enhanced both hydrogen transfer from gas phase to coal and hydrocracking of coal-derived liquids. With NiMoAl₂O₃ catalyst, liquefaction in naphthalene solvent proceeded through the hydrogen-donation cycle: naphthalene → tetralin → naphthalene. The amount of residues showed that this cycle was more effective for coal liquefaction than the direct addition of hydrogen from gas phase to coal in decalin solvent. The ³H incorporated in the coal-derived liquids from gas phase was found to increase in the following order: oil < asphaltenes < preasphaltenes < residue.     

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。     

Effect of tetralin dissociation on coal liquefaction: Tubing bomb versus batch autoclave

The extent of coal hydroliquefaction in the presence of a good catalyst (impregnated ammonium heptamolybdate) and a hydrogen-donor solvent (tetralin) can be substantially greater in a tubing bomb than in a stirred autoclave, under nominally identical liquefaction conditions. This difference may be associated with the typically lower gas:liquid volume ratio existing under reaction conditions in a tubing bomb, relative to the ratio in an autoclave. If equilibrium is reached in the catalysed dissociation of tetralin, the extent of dissociation is less, and the hydrogen partial pressure is substantially higher, in the tubing bomb than in the autoclave. Calculations and measurements have been made for the equilibrium conditions in tetralin dissociation when coal is absent but a good catalyst (ammonium heptamolybdate dispersed on alumina) is present. For the calculation, the molar volumes and vapour pressures of tetralin and naphthalene must be known, together with the dissociation constant. Agreement was good between calculated and experimental values of dissociation in both tubing bomb and autoclave. The results permit prediction that increasing the gas:liquid volume in a tubing bomb liquefaction experiment should decrease the conversion; this effect was observed.