liquefaction pathways of bituminous subbituminous coals andtheir

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CO PRETREATMENT AND LIQUEFACTION OF SUBBITUMINOUS COAL S. C. Lim, R. F. Rathbone, E. ti. Givens and F. J. Derbyshire, University of Kentucky Center for Applied Energy Research, 3572 Iron Works Pike, Lexington, KY 40511-8433. Keywords: coal liquefaction, Pretreatment, Carbon Monoxide, Water Abstract A Wyodak subbituminous coal was pretreated at 3OO0C at various CO partial pressures in aqueous NaOH. Up to one-third of the oxygen is removed both in the presence and absence of CO. Oxygen-rich, water soluble humic acids are formed in the absence of or at low CO pressures; at 800 psig CO, water soluble product is absent. Higher CO conversions to hydrogen via the water gas shift (WGS) reaction was observed at lower pressures with higher H consumption occurring at the higher pressures. Pyridine solubility and optical microscopy of the pretreated material indicate major reconstruction of the coal structure. Liquefaction of the pretreated material at 4OO0C in hydrogen/tetralin indicates that pretreated coal reacts faster giving higher conversion and lower hydrogen consumption than raw coal. INTRODUCTION Pretreating coal prior to liquefaction has been shown to result in higher yields of product through a net reduction of retrograde reactions. The methodology can vary from treatment of coal throu h demineralization,'*2 acid-washing, solvent ~welling,'.~ alI~ylation,~-~ dissolution with strong acids and bases,'.' catalytic reactions," or by the presence of hydrogen." Solomon et al." identified at least two distinct cross-linking events when coals are heated; one applies primarily to low-rank coals and occurs at lower temperatures simultaneous with CO, and H,O ev~lution'~ that correlates with loss of carboxyl groups and occurs prior to bridge breaking or depolymerization reactions. A second event that is exhibited by higher rank coals occurs at moderate temperatures simultaneous with methane formation subsequent to the initial bridge breaking reactions and correlates best with methane formation. For lignites, these cross-linking reactions begins at about 2OO0C while the corresponding reaction for higher rank coals begin at temperatures above 40OoC. l2 Aqueous treatment around the supercritical temperature of water, i.e. -372OC, is also known to cause significant changes in coal which enhance coal conversion under a variety of process conditions.l4,l5 Illinois No. 6 coal, pretreated with steam at 50 atm between 320-360°C, provided a two fold increase in liquid yields and a 20% increase in total volatile yields when pyrolyzed at 740°C.16 Pretreated coal had lower oxygen content, exhibited reduced hydrogen bonding, had increased pore volume,17 and had twice as many hydroxyl groups than the starting coal.18 Steam inhibited retrograde reactions of the phenolic groups that were evolved. l7*' Generally, coal conversion in aqueous systems to which CO and base are added, is higher than in straight aqueous s stems or in hydrogen/donor solvent,20 especially for lower rank In the CO/H O/base system the water-gas shift Conversion OCCUrS" (CO+H,O+H,+CO,) whick involves the intermediacy of the formate anion, HCO -.27 In the study reported here the effect of this reaction system on subbituminous coal at temperatures around 3OO0C has been investigated. Substantial changes to the coal 618
substructure have been identified and the liquefaction of the pretreated coal in hydrogen donor solvent has been evaluated. EXPERIMENTAL Materials - Reagents were purchased as follows: 99% purity W grade tetralin, high purity tetrahydrofuran (THF), and high purity pentane were Burdick & Jackson Brand from Baxter SIP; UHP 6000# hydrogen was supplied by Air Products and Chemicals, Inc. A sample of Wyodak Clovis Point coal was supplied by the Wilsonville Advanced Coal Liquefaction Research and Development Facility and had been ground to -200 mesh, riffled and stored in a tightly sealed container. Analysis of the coal is presented in Table 1. Procedures - Pretreatment experiments were conducted by adding the specified amounts of coal, distilled water, and NaOH to a 25 ml vertical reactor which was sealed and pressurized with CO. The pH of the starting solution was between 13-14. After leak testing. the reactor was submerged in a fluidized sandbath at 3OO0C and shaken at a rate of 400 cycles per minute. At the end of the reaction period, the reactor was rapidly quenched to room temperature. Gaseous products were vented into a collection vessel and analyzed by gas chromatography. Solid and liquid products were scrapped and washed from the reactor using water and then filtered, and 'freeze dried'. The pH of the aqueous layer was between 5 and 6. Subsequently the sample was dried at 8OoC/25 mm Hg for 60 min. In several experiments the insoluble material was placed in a Soxhlet thimble, extracted with THF for 18 hours, and dried overnight at 8OoC/25 mm Hg. Ashing of the water and THF insolubles indicated >95% of the Na fed as NaOH reported to the aqueous layer. Soluble material was concentrated by removing excess THF to which was added a 50:l excess volume of pentane and the mixture placed in an ultrasonic bath for 3 min. The insolubles were removed by filtering and the solubles recovered after evaporating the pentane. The water soluble fraction was acidified with HC1 to precipitate humic acids which were centrifuged, collected and dried. The aqueous layer was extracted with ether. Recoveries and products are reported on an maf basis calculated by subtracting the coal ash from the total THF insolubles. Na product is assumed to report completely to the aqueous phase. Liquefaction experiments were performed by placing raw or pretreated coal and tetralin (2:l tetra1in:coal) in the reactor described above and submerging the reactor in a sandbath at 4OO0C for periods from 15 to 60 min in 800 psig (cold) H2. The reactor was rapidly cooled and gaseous products collected. The solid/liquid products were separated into THF insoluble (IOM plus ash), THF soluble/pentane insoluble (PA+A) and pentane soluble (oils) fractions. Conversions and product yields are reported on an maf basis by assuming complete recovery of the ash in the THF insolubles. Analyses - FTIR transmittance spectra were obtained on a Nicolet Model 20SXC spectrometer using KBr pellets of the parent and demineralized coals. Carbon, hydrogen and nitrogen were determined on a Leco Model 600 combustion analyzer. Total sulfur was determined according to ASTM D4239-84 with a Leco Model SC32 combustion-IR analyzer. Optical Microscopy - Samples of coal, pretreated coal, and liquefaction residues were prepared for microscopical examination by mixing with epoxy resin, placing the mixture into a small cylindrical mold, and allowing the epoxy to harden. A sample surface was then ground and 619
Page 1 and 2:
LIQUEFACTION PATHWAYS OF BITUMINOUS
Page 3 and 4:
the conversion of A+P and O+G with
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Asphaltcncs PrCasphaltenCS Cwr%, da
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NEW DIRECTIONS TO PRECONVERSION PRO
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ecause of incorporation of the coal
Page 11 and 12:
should be considered more. The step
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17 18 Run no. 0 cys I ToS-CyS TS-To
Page 15 and 16:
INTRODUCTION Effects of Thermal and
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apid decline in modulus. The loss m
Page 19 and 20:
-0.01- . 04 5 -0.03- E 6 -0.0s- c)
Page 21 and 22:
Assessment of Small Particle Iron O
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yields are calculated by subtractin
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conversion is greater than the corr
Page 27 and 28:
Table 3. Effect of Superfine Iron O
Page 29 and 30:
EFFECT OF A CATALYST ON THE DISSOLU
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inherent volatility of Mo(CO), perm
Page 33 and 34:
Analysis of the quantity and compos
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$ EO .- 0 m L 0 c 0 0 > 40 300 350
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0 0 0 0 0.000 0.005 0.010 0.015 0.0
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of these studies indicate that cont
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Different levels of adsorption occu
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Nominal 2 Table 1. Concentration of
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- iF m 1.6 1.4 1.2 - - - 1- 0 0.8 -
Page 47 and 48:
RESULTS AND DISCUSSION Swelling of
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. . % . . 9 'HF 0 0 0 *. . 0 . . 0
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1.50 KQ 1.00 0.50 I / ' 02 525 I 1
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hydrogen atoms. The hydrogen atoms
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D to generate more D atoms. It is r
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12. a. Poutsma, M. L.; Dyer, C. W.
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Figure 3. Minimum Steps to Explin D
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Apoaratus and Procedure Microflow R
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Model ComDound Test Figure 5 shows
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Figure 1. High resolution gas chrom
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Figure 5. Product distribution for
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THQ at somewhat higher temperatures
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areas of the particles and the SEM
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Experimental Catalyst Precursors an
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impregnating solvent. Table 3 shows
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of MoCo-TC2 at the level of 0.5 wt%
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Table 4. Effect of Temperature Prog
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In the past, chemical treatments in
Page 83 and 84:
The effect of Corn20 preaatment on
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Reaction Time Figure 1 - Schematic
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DISSOLUTION OF THE ARGONNE PREMIUM
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A much more def~tive trend is seen
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EFFECT OF CHLOROBENZENE TREATMENT O
Page 93 and 94: same conditions and an extraction t
Page 95 and 96: ACKNOWLEDGEMENT The authors thank t
Page 97 and 98: THE STRUCTURAL &=RATION OF HUMINlTE
Page 99 and 100: to be originally derived from demet
Page 101 and 102: 145 30 I --/---Jh I , , I I , 250 2
Page 103 and 104: THE EFFECTS OF MOISTURE AND CATIONS
Page 105 and 106: 1 for the Zap lignite. These result
Page 107 and 108: content of the samples ion-exchange
Page 109 and 110: Table 1. F'yrolysis Results of Vacu
Page 111 and 112: 585 I
Page 113 and 114: EFFECT OF TEMPERATURE, SAMPLE SI2E
Page 115 and 116: of some of the thermobalance runs.
Page 117 and 118: 2. The mechanism of drying is a uni
Page 119 and 120: Influence of Drying and Oxidation 0
Page 121 and 122: "c gives W conversion mpared to the
Page 123 and 124: Table 1. Products dismbutions (dmmf
Page 125 and 126: - 50 45 40 E 35 2 30 E T) 25 ap 20
Page 127 and 128: Influence of Drying and Oxidation o
Page 129 and 130: FTIR . . of the L m To investigate
Page 131 and 132: CONCLUSIONS The characexizntion of
Page 133 and 134: A b S 0 r b a n C e A b s 0 r b a n
Page 135 and 136: An NMR Investigation of the Effd of
Page 137 and 138: for determining the area of the pea
Page 139 and 140: of the ronl roniponcnte nnd (2) the
Page 141 and 142: 2w 180 160 9 140 120 P loo f 80 P O
Page 143: 25 I 20 ' + 0 Drying lime, hours Fi
Page 147 and 148: Pyridine extraction showed that 60
Page 149 and 150: Figure 1. Reflected white-light pho
Page 151 and 152: Table 3. Pyridine Extraction Sample
Page 153 and 154: A bang-bang control strategy was us
Page 155 and 156: increased from 120°C to 135”C, r
Page 157 and 158: * wt% based on the amount of naphth
Page 159 and 160: Use of Biocatalysts for the Solubil
Page 161 and 162: Results Enzyme Modification with Di
Page 163 and 164: Conclusions Reducing enzymes can be
Page 165 and 166: Dynamics of the Extract Molecular-W
Page 167 and 168: where yi = (x-xi !/pi. The zero mom
Page 169 and 170: satisfactory agreement between theo
Page 171 and 172: 0.8 0.6 0.4 0.2 “E \ bo Y, - 1 0
Page 173 and 174: The Use of Solid State C-13 NMR Spe
Page 175 and 176: differences lie in the fact that th
Page 177 and 178: I- z W 0 K W n PROTONATED AROMATIC
Page 179 and 180: ZAP WIO SIDE CHAINS IN PYRIDINE EXT
Page 181 and 182: ORGAFlIC VOLATILE MATER AND ITS SUL
Page 183 and 184: (Figure 1). They indicated that the
Page 185 and 186: Table 3. Elemental analysis of arom
Page 187: 1- 700'C Figure 3. GClFID chromatog
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