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.     

Apparent enhancement of coal conversions using cresol — tetralin solvents

Conversions are measured for coal hydrogenations using various solvent mixtures of p-cresol and tetralin. Compared with experiments in which tetralin alone was used as solvent, the addition of p-cresol yielded apparent increases in the observed conversions, by as much as 24%. In contrast to earlier studies, it is concluded that the effects of p-cresol occur during evaluation procedures rather than during the conversion reactions.     

The roles of vehicle and gaseous hydrogen during short contact time coal liquefaction

The roles of the vehicle and gaseous hydrogen during short contact time liquefaction (SCTL) in microreactors were examined by using a number of synthetic vehicles. The importance of vehicles during SCTL was evaluated on their ability to convert coal to tetrahydrofuran (THF)-soluble products. Reaction conditions were three minutes at 425 °C following a one minute heat-up. Although the consumption of hydrogen (hydrogen donor or gaseous hydrogen) by reactive coal fragments is minimal during the early stages of liquefaction (as in SCTL reactions), hydrogen donors were important and could be ranked according to the extent of conversion to THF-soluble products (tetrahydroquinoline > hydrogenated pyrene > dihydroanthracene = dihydrophenanthrene > tetralin). The importance of gaseous hydrogen was also studied. Gaseous hydrogen was needed if either quality or quantity of hydrogen donor was not adequate in a SCTL reaction. With certain synthetic vehicles, the SCTL stage of an integrated two-stage liquefaction process could be conducted in the absence of hydrogen. Solubility properties that might enhance solubilization of coal-derived products, and therefore the extent of liquefaction, were examined by varying the concentration of certain components (m-cresol and quinoline) of the synthetic vehicle mixtures. Solubility effects were minimal.     

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.     

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.     

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.     

Adsorptive separations of alkylphenols using ion-exchange resins

Separation of close boiling point mixtures of alkylphenols, such as p-cresol/2,6-xylenol, m-cresol/2,6-xylenol and p-cresol/m-cresol has been attempted using commercially available ion-exchange resins. The basic resins selectively adsorb the cresol isomers from their mixtures with 2,6-xylenol. The separation seems to be decided by the thermodynamic selectivity in the ion-exchange resin framework with diffusional selectivity also contributing to the separation.     

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.     

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.     

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.     

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.     

Free radicals in coal and coal conversions. 8. Experimental determination of conversion in hydroliquefaction

The results of conversion determinations on the products from Powhatan No.5 coal liquefied in an autoclave and in a high-pressure, high-temperature e.s.r. cavity are reported. Oil, asphaltene and preasphaltene yields, and overall conversion have been determined for Powhatan No.5 coal samples liquefied in tetralin, SRC-11 heavy distillate, and naphthalene at temperatures from 400 to 480 ° C in both reactor systems. The concept of reaction severity is introduced and used to formalize the relation between the effect of temperature and reaction time on oil yield and conversion. Oil is the predominant product in liquefaction in tetralin or naphthalene, asphaltene is the major product of liquefaction in SRC-II heavy distillate. Retrogressive reaction (THF-insoluble product formation) becomes severe when SRC-II heavy distillate is the liquefaction solvent and residence time of >10 min are used at temperatures >450 °C. Preasphaltenes appear to be the only intermediate species in Powhatan No.5 liquefaction.     

Catalytic liquefaction of coal with supercritical water/CO/solvent media

This paper describes studies of the catalytic activity of cobalt molybdenum sulphide, cobalt molybdenum oxide, iron sulphate, iron acetate dibasic and H₂S during the reaction between supercritical CO and water, and during liquefaction of coal using supercritical CO-water-solvent mixtures. The kinetics of the water gas shift reaction was studied first and was found to be first order in all the catalysts studied. The activity of the catalysts decreased in the following order: cobalt molybdenum sulphide > cobalt molybdenum oxide > iron salts. The presence of toluene, tetralin, and THQ decreased the CO conversion on the cobalt catalysts but increased CO conversion in the presence of iron salts catalysts. Moderate coal conversion of toluene soluble products (25%–35%) were obtained in the presence of supercritical water and water/CO mixtures. Addition of organic solvents to a supercritical water/CO medium increased conversion of toluene soluble products to 70–80% for THQ, to 50–60% for tetralin, and to 35–40% for toluene. Addition of H₂S to the solvent/water/CO medium increased conversion to toluene soluble products even further. In the presence of H₂S/solvent/water/CO, the presence of catalysts had only a minor effect on coal conversion and were not required to achieve high coal conversions. The optimum operating conditions for an Illinois No. 6 coal were obtained using a H₂S/THQ/CO/water medium at 3600 psi, and 400 °C. Higher conversions were attained with a subbituminous Wyodak coal. These studies clearly demonstrate that high conversions to soluble products can be attained using a supercritical water/Co/solvent medium.     

Novel process cycle for para-substituted benzene derivatives

A novel cyclic process produces p-cresol from toluene; toluene with iodosotoluene (derived from iodo-toluene) gives the intermediate ditolyliodonium salt converted by catalysed hydrolysis into cresol and iodotoluene (which is recycled as ‘catalyst’.) In the final product, o-cresol content is low and m-cresol is undetectable. The process reaches a steady state independent of the o-/p-isomer ratio of the iodotoluene ‘catalyst’. In a similar way, p-chloronitrobenzene can be made by reaction of di-(p-chlorophenyl)iodonium salt (derived from chlorobenzene and chloro-iodosobenzene) with nitrite ions.     

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.

     

Prediction of Selective Extraction of Cresols from Aqueous Solutions by Ionic Liquids Using Theoretical Approach

This work reports the prediction of selective extraction of cresol from aqueous solutions using ionic liquids (ILs) as the solvent. Judicious screening of various ILs was carried out for all the three forms of cresol (i.e., o-cresol, m-cresol, and p-cresol). A quantum chemical based theoretical model “conductor-like screening model for real solvents” (COSMO-RS) was used to predict the selectivity of cresol in aqueous medium at infinite dilution. A screening of 360 possible ILs from 15 cations and 24 anions was carried out to determine the best IL for the removal of cresol from water. Amongst the phosphonium and imidazolium based cations, trihexyl tetradecylphosphonium [THTDP] and 1-octyl-3-methylimidazolium [OMIM] gave the highest selectivity other than the anions bromide and chloride. The selectivities for different cresols followed the pattern: m-cresol > p-cresol > o-cresol. Similarly for pyridinium and quinolium based cations, 1-ethylpyridinium [EPY] and 1-octylquinolium [OQU] gave the highest selectivity. Amongst the two cations studied for pyrrolidinium based cations, 1-hexyl-1-methylpyrrolidinium [HMPL] was the best. Trihexyl tetradecylphosphonium salicyclate [THTDP][SAL] gave the highest selectivity of 662 amongst all the ILs screened.     

Chemistry of Texas lignite liquefaction in a hydrogen-donor solvent system

To study the nature of chemical cleavage and resultant product transfer from solid lignite phase to liquid phase, autoclave (300 cm³) experiments have been carried out at pressures ranging up to 34 MPa and temperatures of 380–390 °C. The charge to the autoclave was freshly mined wet lignite, tetralin and hydrogen or helium. To obtain an indication of the reaction mechanisms underlying the liquefaction process, liquid and gas samples from the reactor at different time intervals were analysed. The gas samples were analysed by use of a multi-column, multi-valve automated gas Chromatograph, a system specially fabricated for coal-derived gas analysis. The liquid sample was filtered through Millipore filters and separate into three fractions by gel permeation chromatography. Fraction 1 is mostly colloidal carbon and high-molecular-weight species which cannot be separated on a g.c. Fractions 2 and 3 were analysed by gas chromatography — mass spectrometry (g.c.-m.s.). Fraction 2 represents the liquid products released from lignite and fraction 3 is mostly the tetralin and tetralin-derived products. Gel permeation chromatography (g.p.c.) followed by gas chromatography (g.c.) was used to devise a method for monitoring the extent of liquefaction. The production of carbon dioxide is at a maximum before the liquefaction reactions are at a significant rate. The source of carbon dioxide appears to be the carboxylic groups in lignite. The liquefaction reactions consume hydrogen from tetralin which undergoes dehydrogenation to form naphthalene. Once the lignite has undergone depolymerization, the tetralin to naphthalene conversion slows down. The continued heating of lignite conversion products in excess of tetralin does not appear to alter the molecular size distribution of the liquid product. The distillable fraction of lignite-derived liquid is composed of various alkylated phenols and aromatics and alkanes, and they are formed simultaneously.     

Catalytic effects of MoCl3- and NiCl2-containing molten salts in hydroliquefaction of Akabira bituminous coal with and without hydrogen-donor vehicle

Catalytic effects of MoCl₃-LiCl-KCl and NiCl₂-LiCl-KCl molten salts in hydroliquefaction of Akabira bituminous coal were studied. In the absence of solvent, both catalysts showed high coal conversion activity and high selectivity for the formation of hexane-soluble oil product. Oil yields from the catalytic runs were 3.4–3.0 times that from a non-catalytic run. Addition of hydrogen-donor tetralin considerably increased the oil yield and conversion and reduced the total hydrogen consumption. About 95 and 91 wt% daf coal was converted into pyridine-solubles and 59 and 54 wt% into oil with relatively low total hydrogen consumption (3.5 and 3.1 wt% daf coal) with the MoCl₃ and NiCl₂ catalysts respectively, in the presence of tetralin. Thermogravimetric analysis indicated that these catalysts enhanced the depolymerization of the coal organic matrix. Analysis of the liquefaction products suggested that the catalysts effectively catalysed the hydrocracking of polyaromatic structures contained in heavy products to hydroaromatics with relatively small ring sizes, explaining the high oil selectivity.     

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。     

Direct hydroliquefaction of a low rank soft brown coal

The behaviour of the soft brown coal from the Kostolac Mine (Serbia, Yugoslavia) was investigated during hydroliquefaction carried out in a batch reactor by direct catalytic hydrogenation of the pulverized coal (−160 μm) dispersed in tetralin. The effects of temperature (ranging from 365 to 440°C), pressure (13.5 to 15.0 MPa) and residence time (1 to 8 h) on the yield of individual liquefaction products as well as the petrographic composition of the coal residues were closely followed by separation and analysis of the products. These consisted of liquid products soluble in n-heptane (light oils), n-heptane insoluble products (asphaltenes), the solid coal residue and gaseous products. A good reactivity of this soft brown coal was observed. The yield of liquid products varied from 23 to 64 wt.% (based on dry ash-free coal). A total coal conversion of 80 to 86% was achieved. Petrographic composition and optical properties of the solid coal residues were analyzed microscopically in order to establish the character and intensity of the coal changes. The solid residues were found to consist of 12 various grain categories. The low proportions of unreacted or partly reacted coal grains confirmed the good reactivity of the Kostolac soft brown coal in the applied liquefaction process.