Liquefaction Of Low-rank Coals Research Articles

Low-Calorie Coal Liquefaction Products as an Alternative Fuel Oil

Liquefaction of low-rank coal has been done to optimize the utilization of low-rank coal, which is less economical for obtaining alternative fuel oil. Coal samples were taken from the Bukit Pinang coal mine, Samarinda Ulu, East Kalimantan. Coal was liquefied using the NEDOL procedure at PUSPITEK, Serpong, South Tangerang, Indonesia. This Bukit Pinang coal liquefaction produces five fractions consisting of Naphta, Light Oil (LO), Middle Oil (MO), Heavy Oil (HO), and Coal Liquid Bottom (CLB) fractions. The liquefaction yield was dominated by the HO and CLB fractions (> 50% by weight). The naphtha, MO and LO fractions were fractionated using SiO2 GF254 Thin Layer Chromatography (TLC) plate. It produced aliphatic and aromatic hydrocarbon fractions. Aliphatic hydrocarbon fractions were analyzed using a Gas Chromatography-Mass Spectrometer (GC-MS), while the aromatic hydrocarbon fractions were not analyzed. Mass spectrum studies showed that the components consisted of n-alkanes, isoalkanes (branched alkanes), cycloalkanes and alkyl cycloalkanes. The aliphatic hydrocarbon components resulting from the liquefaction of low-rank coal showed its equivalence with the components that make up fuel oil. Therefore, this coal liquefaction can be suggested as an optimization for low-rank coal, which is less economical.

Experimental study on rotary triboelectric separation of low-rank coal macerals with surface modification

The enrichment of vitrinite can enhance the oil yield and conversion rate in low-rank coal liquefaction. The work evaluated the effects of surface modification on the rotary triboelectric separation of macerals. Permittivity and charge–mass ratio analysis of vitrinite and inertinite under various modified conditions demonstrated that kerosene and diesel were excellent modifiers since they keep the permittivity of macerals at a low level. The largest difference in triboelectric charge of vitrinite and inertinite was obtained when 3.0 kg/t kerosene was adopted as modifier. Rotary triboelectric separation of untreated low-rank coal indicated that the optimal separation, i.e., a vitrinite content of 65.45% and a recovery of 69.89%, was obtained at a feed rate of 1.5 g/s, a friction wheel speed of 3000 rpm, and a separation voltage of 30 kV. Under the optimum operating conditions, the optimal rotary triboelectric separation under surface modification, i.e., a vitrinite content of 69.78% and a recovery of 73.52%, was achieved when the coal was treated by 3.0 kg/t kerosene. The results demonstrated that surface modification significantly improved the rotary triboelectric separation by changing the surface electrical properties of macerals, while the excessive dosage of the modified reagent was unfavorable to achieving optimal separation.

Effects of hydrogen transfer by exchanged cobalt upon liquefaction of low rank coal

Effect of hydrogen transfer from the pressurized gas or solvent upon liquefaction (with elemental sulfur as an accelerator at 420°C for 1h) of cobalt exchanged Adaro coal was discussed. Further, catalytic effect of exchanged cobalt upon liquefaction of cobalt exchanged coal was also discussed in comparison with the results after liquefaction of demineralized coal or complex [(C5H5)2Co or Co2(CO)8] added demineralized coal.The amounts of transferred hydrogen from tetralin and the pressurized hydrogen gas upon liquefaction of cobalt exchanged coal with the pressurized hydrogen gas plus any solvent (tetralin, decalin or naphthalene) were almost equal to those of complex added demineralized coal. However, upgrading of cobalt exchanged coal occurred preferentially in comparison with that of complex added coal. In particular, the yield of residue was only 0.3% after liquefaction of cobalt exchanged coal with tetralin plus the pressurized hydrogen gas.Accordingly, liquefaction of cobalt exchanged coal was enhanced significantly by the following two reasons. It was considered that cobalt dispersed finely into the coal macromolecules with attached carboxyl groups irrespective of the size of coal molecule, and hydrogen shuttling through solvent was enhanced by catalytic effect of the dispersed cobalt.

Comparison of Catalytic Effects of Metals Derived from Cation-Exchanged Coal and Oil Soluble Complex upon Liquefaction of Low Rank Coal

During cation exchange treatment of low rank coals, carboxyl groups in the coal structure are exchanged with the desired cations. In this study, the liquefaction reactivity of cation (Fe2+, Co2+, or Ni2+)-exchanged Adaro sub-bituminous coal in tetralin solvent with sulfur promoter was compared with the reactivity of demineralized coal plus the oxide, sulfide, or oil soluble complex (metallocene or metal carbonyl) of any one of Fe, Co, Ni, Mo, or W. The findings are as follows: (1) Upgrading of demineralized coal is not enhanced by addition of oxide or sulfide of any one of Fe, Co, Ni, Mo, or W because these metal powders do not easily disperse into coal macromolecules during liquefaction. (2) In comparison with liquefaction of demineralized coal plus the complex of Co or Ni, liquefaction of Co- or Ni-exchanged coal significantly increases by catalytic activity of sulfurized Co or Ni. (3) Catalytic activity of exchanged Co or Ni is almost equal to that of Mo or W derived from the respective carbonyl complex.

Highly active limonite catalysts for direct coal liquefaction

The properties of limonite in Australia and Indonesia were examined by using X-ray diffraction, Mössbauer spectroscopy, Thermal gravimetric analysis (TGA) and TEM–EDX in relation to the catalytic activities in the liquefaction of low-rank coals. The molar ratio of H 2O/Fe in limonite was determined from the weight loss resulting from the dehydration reaction of FeOOH to Fe 2O 3 during heating from 120 to 400 °C in TGA. The H 2O/Fe molar ratio varied from 0.06 for hematite to 0.60 for limonite YY, depending on the hematite content. Results from the pulverization tests showed that the higher value of H 2O/Fe molar ratio resulted in lesser abrasion of medium balls. A unique limonite YY in Australia, containing no hematite, was easily pulverized to sub-micron particle size and showed an excellent oil yield in coal liquefaction. It appeared that H 2O/Fe molar ratio could be one of the most important factors to select the better limonite catalyst for coal liquefaction. Moreover, it was found that Ni containing limonite SO in Indonesia exhibited a higher liquefaction activity than YY catalyst, because of transformation into a smaller crystallite size of pyrrhotite (Fe 1− x S). The agglomeration of pyrrhotites may be suppressed by a strong interaction between FeOOH and Al(OH) 3 such as Fe–O–Al. TEM–EDX analysis suggests that Ni may be located near the Fe 1− x S structure. Oil yield was significantly increased from 43 to 62 wt% daf by CLB addition to the coal slurry in the liquefaction of Banko coal. Finely pulverized limonite catalyst (SO) can be advantageously used in a commercial plant for coal liquefaction in Indonesia due to the low catalyst cost and a high liquefaction activity to obtain a high oil yield.

Biosynthesis of polyhydroxyalkanoates from low-rank coal liquefaction products by Pseudomonas oleovorans and Rhodococcus ruber

A screening identified several bacteria that were able to use chemically heterogeneous low-rank coal liquefaction products as complex carbon sources for growth. Pseudomonas oleovorans and Rhodococcus ruber accumulated polyhydroxyalkanoic acids (PHA) amounting to 2%-8% of the cell dry weight when the cells were cultivated on these liquefaction products in the absence of any other carbon source. R. ruber accumulated, in addition to PHA, small amounts of triacylglycerols. The accumulated PHA consisted of 3-hydroxyhexanoate, 3-hydroxydecanoate, and 3-hydroxydodecanoate (P. oleovorans) or 3-hydroxybutyric acid and 3-hydroxyvaleric acid (R. ruber). Low-rank coal liquefaction products obtained from Trichoderma atroviride were better substrates for P. oleovorans than chemically produced fulvic acids.

Humic acids and methylated humic acids as models for reactions of brown coal with CO/H 2O and with H 2

Humic acid derived from Loy Yang coal and the product of mild O-methylation of this humic acid have been reacted with CO/H 2O/sodium aluminate (NaAlO 2) and H 2/Ni/Mo in 35 ml autoclaves at 365°C and 400°C. The O-methylated humic acid gave lower conversions for CO/H 2O/NaAlO 2 reactions than the original humic acid but similar conversions for H 2/Ni/Mo reactions. These results provide strong evidence in support of the mechanistic proposals of Ross for the involvement of phenols in the initial stages of low rank coal liquefaction with CO/H 2O/NaAlO 2 but much less evidence for their involvement in H 2/Ni/Mo reactions. The humic acid and methylated humic acid have also been reacted with H 2/MeOH both with and without added ZnCl 2 catalyst. The results are compared with previous work of Kuznetsov et al. and confirm that the autoclave constitutes a well-mixed system and that the H 2/MeOH/ZnCl 2 system more closely resembles the H 2/Ni/Mo rather than the CO/H 2O/NaAlO 2 system.

99/00225 A new process for catalytic liquefaction of low-rank coal using dispersed MoS 2 catalyst generated in-situ with added H 2O

99/00225 A new process for catalytic liquefaction of low-rank coal using dispersed MoS 2 catalyst generated in-situ with added H 2O

98/03653 Liquefaction of low-rank coals with hydriodic acid and microwaves

98/03653 Liquefaction of low-rank coals with hydriodic acid and microwaves

98/02843 Apparatus and process for purification of high-temperature and high-pressure reducing gases: Tatani, A. et al. Jpn. Kokai Tokkyo Koho JP 09,271,625 [97,271,625] (Cl. B01D53/14), 21 Oct 1997, Appl. 96/79,867, 2 Apr 1996, 9 pp. (In Japanese)

Three United States low-rank coals are investigated at 250–450° C using tetralin and a molybdenum sulfide catalyst. Donor solvent provides high conversions and prevents retrogressive reactions throughout the temperature range investigated. Catalytic hydrogenation provides better product quality at low temperatures but is not effective at preventing retrogressive reactions at high temperatures. Up to 400°C, the donor solvent and catalyst are equally effective for providing high conversion. At 450°C, catalytic hydrogenation in the absence of donor solvent is not as effective as donor solvent reaction in the absence of catalyst. The temperature gas-phase hydrogen (H2) is not sufficient, even in the presence of catalyst, to prevent retrogressive reactions. Solvents have two major effects on noncatalytic liquefaction of low-rank coals: dissolution of coal-derived radicals to reduce their local concentration and prevent recombination and participation in the chemical depolymerization of the coal. Below 350°C, physical solvation appears to be more important than the chemical nature of the solvent. Catalysis by ammonium tetrathiomolybdate (ATTM) is clearly beneficial in enhancing conversion. At 400° C, nearly comparable conversions are obtained from either ATTM without a donor solvent or tetralin with no catalyst. At 450° C, the donor solvent is vital in preventing retrogressive reactions. The highest conversions and highest oil are obtained at 450° C for reactions with both ATTM and tetralin.

98/02830 Mineral matter effects in low-temperature liquefaction of low-rank coals: Martin, S. C. and Schobert, H. H. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 25–30

Demineralization by successive HCl/HF treatments of a low rank coal has demonstrated that removal of the inherent mineral matter imparts no serious detrimental effect upon low temperature liquefaction. It appears that elimination of such species allows for better access for gaseous H{sub 2}, as suggested by previous studies.

98/02847 Dry desulfurization of coal fuel gas by partial oxidation: Meyer B. et al. DGMK Tagungsber., 1997, 9704, (Proceedings ICCS '97, Volume 3), 1775–1778

Three United States low-rank coals are investigated at 250–450° C using tetralin and a molybdenum sulfide catalyst. Donor solvent provides high conversions and prevents retrogressive reactions throughout the temperature range investigated. Catalytic hydrogenation provides better product quality at low temperatures but is not effective at preventing retrogressive reactions at high temperatures. Up to 400°C, the donor solvent and catalyst are equally effective for providing high conversion. At 450°C, catalytic hydrogenation in the absence of donor solvent is not as effective as donor solvent reaction in the absence of catalyst. The temperature gas-phase hydrogen (H2) is not sufficient, even in the presence of catalyst, to prevent retrogressive reactions. Solvents have two major effects on noncatalytic liquefaction of low-rank coals: dissolution of coal-derived radicals to reduce their local concentration and prevent recombination and participation in the chemical depolymerization of the coal. Below 350°C, physical solvation appears to be more important than the chemical nature of the solvent. Catalysis by ammonium tetrathiomolybdate (ATTM) is clearly beneficial in enhancing conversion. At 400° C, nearly comparable conversions are obtained from either ATTM without a donor solvent or tetralin with no catalyst. At 450° C, the donor solvent is vital in preventing retrogressive reactions. The highest conversions and highest oil are obtained at 450° C for reactions with both ATTM and tetralin.

Liquefaction of Low-Rank Coals with Hydriodic Acid and Microwaves

A novel method for the chemical liquefaction of low-rank coals in relatively moderate conditions and short reaction times is presented. Using concentrated hydriodic acid as the reaction medium, microwaves as the energy source, and reaction times of 20 min at 230 °C, up to 50% of the organic carbon of coal can be extracted with THF. The study of the process shows that temperature of the reaction and time are the main factors affecting the desulfurization process. The redox potential and the nucleophilicity of the concentrated hydriodic acid were the driving force of the reaction as experiments with other acids or lower acid concentrations gave worse results.

97/04544 Hydrodeoxygenation in low-rank coal liquefaction systems using novel organometallic catalyst precursors: Kirby, S. R. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 466–471

Oxygen functionalities, especially phenols, are undesirable components of coal derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these functionalities, or the prevention of their formation, during the liquefaction process. Organometallic precursors of Co, Ni and Mo have been studied as catalysts. To ascertain the hydrodeoxygenation properties of these catalysts under liquefaction conditions, model compounds were investigated. Anthrone, Dibutylmethyl phenol, dinaphthyl ether and xanthene were studied to provide a comparison of conversions of deoxygenated products. Studies of the deoxygenating abilities of these catalyst precursors in coal liquefaction systems have also been performed. Improvements in conversion and product quality are observed. Both these factors are dependent on the coal used.

97/01507 Decarboxylation of coal model compounds under liquefaction conditions: Does decarboxylation lead to retrograde reactions?

In recent years, it has become clear that oxygen functional groups in low-rank coals are major actors in retrograde reactions which inhibit their efficient thermochemical processing. In the pyrolysis and liquefaction of low-rank coals, low-temperature cross-linking reactions have been correlated with the loss of carboxyl groups and the evolution of CO{sub 2} and H{sub 2}O. Pretreatments such as methylation, demineralization, or ion-exchange of the inorganic cations reduce cross-linking and CO{sub 2} evolution in pyrolysis. Cross-linking reactions also have a deleterious effect on liquefaction yields and the distribution of oils, preasphaltenes and asphaltenes. These results suggest that decarboxylation may occur by a pathway that initiates retrograde (cross-linking) reactions in the coal polymer independent of the reaction conditions. However, the decarboxylation pathways in liquefaction and pyrolysis of low-rank coals are not known, and it is not clear how decarboxylation leads to cross-linking. Radical recombination or radical addition reactions have been suggested as being involved in retrograde reactions. However, the involvement of radical pathways in thermal decarboxylation reactions has recently been brought into question. We have presented evidence that in the pyrolysis of several bibenzyls containing aromatic carboxylic acids, radical pathways are not involved in thermal decarboxylation reactions and no cross-linking or couplingmore » products are formed. Further, Manion et al. observed that decarboxylation of benzoic acid derivatives in tetralin yielded only small amounts of aryl-aryl coupling products. To gain a better understanding of the role decarboxylation plays in cross-linking reactions during liquefaction in low-rank coals, we have studied the thermal decomposition of several bibenzyls containing aromatic carboxylic acids, and their salts, in the presence of a hydrogen donor solvent (tetrahn) and a nondonor solvent (naphthalene).« less

97/00970 Solvent recyclability and hydrotreatment severity in direct liquefaction of low-rank coal

A multistep direct liquefaction process specifically aimed at low-rank coals (LRCs) has been developed at the Energy & Environmental Research Center (EERC). The process consists of a preconversion treatment to prepare the coal for solubilization, solubilization of the coal in the solvent, and polishing using a phenolic solvent or solvent blend to complete solubilization of the remaining material. The product of these three steps can then be upgraded during a traditional hydrogenation - step. Research was performed to address two questions necessary for the further development and scaleup of this process: (1) determination of the recyclability of the solvent used during solubilization, and (2) determination of the minimum severity required for effective hydrotreatment of the liquid product. The research was performed during two tasks, the first consisting of ten recycle tests and the second consisting of hydrotreatment tests performed at various conditions.

96/03660 Comparative roles of hydrogen gas and solvent in liquefaction of low-rank coals

96/03660 Comparative roles of hydrogen gas and solvent in liquefaction of low-rank coals

95/05774 The activity of nanoscale iron oxide for model compound reactions

Iron based catalysts have long been known to enhance the conversion in a direct coal liquefaction process. Attempts to increase the moderate activity of these catalysts have focussed on reducing particle size, enhancing and maintaining dispersion, and modifying the structure by addition of promoters. Sulfated hematites have been reported in the literature to exhibit significant activity for low rank coal liquefaction. The use of promoter metals such as molybdenum and tungsten has been shown to further enhance the catalytic effect. The superacidity of these particles has been suggested as a possible explanation for their high activity. The purpose of this study was to ascertain the effect of various promoter metals, both individually and in combinations on different types of reactions commonly associated with coal liquefaction.

Thermolysis of phenethyl phenyl ether. A model of ether linkages in low-rank coal

Currently, an area of interest and frustration for coal chemists has been the direct liquefaction of low rank coal. Although low rank coals are more reactive than bituminous coals, they are more difficult to liquefy and offer lower liquefaction yields under conditions optimized for bituminous coals. Solomon, Serio, and co-workers have shown that: in the pyrolysis and liquefaction of low rank coals, a low temperature cross-linking reaction associated with oxygen functional groups occurs before tar evolution. A variety of pretreatments (demineralization, alkylation, and ion-exchange) have been shown to reduce these retrogressive reactions and increase tar yields, but the actual chemical reactions responsible for these processes have not been defined. In order to gain insight into the thermochemical reactions leading to cross-linking in low rank coal, we have undertaken a study of the pyrolysis of oxygen containing coal model compounds. Solid state NMR studies suggest that the alkyl aryl ether linkage may be present in modest amounts in low rank coal. Therefore, in this paper, we will investigate the thermolysis of phenethyl phenyl ether (PPE) as a model of 0-aryl ether linkages found in low rank coal, lignites, and lignin, an evolutionary precursor of coal. Our results have uncovered a newmore » reaction channel that can account for 25% of the products formed. The impact of reaction conditions, including restricted mass transport, on this new reaction pathway and the role of oxygen functional groups in cross-linking reactions will be investigated.« less

95/00208 Analysis of Wilsonville low-rank coal liquefaction data

The use of both dispersed and supported catalysts for the liquefaction of low rank coals in the Wilsonville, AL facility has been evaluated using a statistical approach. This analysis was undertaken to identify the most important operating variables and their effects upon coal conversion and product distributions. The preferred two-stage configuration for the liquefaction of low rank coal consists of a slurry first-stage reactor followed by an ebullated-bed second stage reactor. The presence of a dispersed catalyst promotes the initial liquefaction steps. An ebullated-bed second stage reactor is effective for hydrocracking the coal-derived products and hydrogenating a stream to be recycled as liquefaction solvent. The effect of process configuration upon coal conversion and product distributions is significant.