liquefaction pathways of bituminous subbituminous coals andtheir

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PROMOTION OF DEUTERIUM INCORPORATION FROM D2 INTO COAL MODEL COMPOUNDS BY BENZYLIC RADICALS Robert D. Guthrie Buchang Shi Rustem Sharipov Department of Chemistry University of Kentucky. Lexington, KY 40506 Burtron H. Davis Kentucky Center for Applied Energy Research 3572 Iron Works Pike, Lexington, KY 40511 Keywords: D2, hydroliquefaction, diphenylethane INTRODUCTION A large number of revealing mechanistic investigations have been carried out dealing with the thermolysis of coal and compounds which model its structure. Perhaps because of experimental difficulties, much less attention has been given to the reaction with molecular hydrogen. It seems fair to say that the detailed mechanism by which molecular hydrogen, separately or in combination with "donor solvents", is able to effect the reductive simplification of coal is not completely understood. An obvious approach to following the reaction with Hz is to substitute D The literature contains ample evidence that deuterium is incorporaxed into reaction products when thermolysis of coal and coal models is carried out under D2 gas.' It has also been shown that D-labeled substrates, such as tetralin-a,,, transfer D atoms back to dihydrogen such that HD is produced from H,.' Similarly it is clear that once incorporated into a molecule of organic substrate, transfer of D atoms between molecules is often fa~ile.~ Several mechanisms can be involved in the scrambling process. Molecule-induced homolysis and symmetry-allowed, pericyclic mechanisms have been documented by Brower and Pajak.4 A demonstration of radical-promoted exchange was provided by King and Stock' who showed that the presence of species which undergo facile homolysis increases the rate of transfer of deuterium between benzylic positions in different molecules. The mechanisms suggested seem reasonable, however, most of the proposed schemes do not address the question of how the initial transfer from H2 occurs. The facility of the scrambling reactions makes the question of how the hydrogen is transferred from Hq gas into the coal structure in the first place, a particularly difficult one to answer because the initial landing site of the hydrogen atoms is rendered uncertain. Because the H-H bond is quite strong, this initial step would seem likely to be a major obstacle to the process of interest and slower than subsequent events. A scheme put forward by Vernon6 proposes hydrogen abstraction from H2 by benzyl-type radicals. This suggestion was later supported by Shin.7 Vernon's suggestion is based on the observation that the cleavage of i,Z-diphenylethane, DPE, gives an increased yield of benzene when the reaction is carried out under H2. The phenomenon is more pronounced when the reactions are run in the absence of a hydrogen atom donor (tetralin or 9,lO-dihydrophenanthrene). It is suggested that benzyl radicals react with dihydrogen, producing toluene and 526
hydrogen atoms. The hydrogen atoms thus generated are responsible for the hydrogenolysis of the DPE to give benzene. In the presence of hydrogen donor solvents, the benzyl radicals react to give toluene and the production of H atoms is reduced. The latter part of this scheme seems quite reasonable based on the observed facility of reaction between benzyl radicals and compounds with structures similar to donor solvents.a Likewise, the reaction of hydrogen atoms with the aromatic ring of DPE seems reasonable both on energetic grounds and in consideration of the results of Price' who showed that H-atoms generated in the thermolysis of toluene above 500 'C react with toluene to produce CH and H2 with nearly equal rates. The reaction between benzyl radicals and H2 seems the most uncertain part of the scheme in that the C-H bond energy of toluene is 85 kcal/mole where as that of H-H is 104 kcal/mole." The reaction of benzyl radical with dihydrogen to form toluene and hydrogen atoms is thus likely to have an activation enthalpy of more than 20 kcal/mole. This would seem to make it an unlikely competitor with various other potential reactions of benzyl radicals which are possible in the system studied. An additional uncertainty regarding these reactions, is that most of the reported exchange studies using D2 as a source of deuterium had utilized metal reactor vessels. This raised the question of whether the initial process for introduction of D atoms into the thermolysis milieu might be metal catalyzed. Either the walls of the reaction vessel or metal species contained in common reactor vessel sealants are possible stopover points for D atoms prior to their introduction at the seminal sites for the scrambling process. If these were involved, the well-precedented process of double bond reduction by metal-bound deuterium would then be a likely entry route for D atoms. In cases where liquefaction is accomplished by the deliberate addition of hydrogenation catalysts, this would be the expected mechanism.'' As we wished to understand the noncatalyzed reaction and to use it as a base line for further studies of catalytic agents, we designed and employed a suitable glass reaction vessel. RESULTS AND DISCUSSION Using the glass reactor vessel described in the experimental section, we have carried out the thermolysis of 1,2-diphenylethane, DPE, under 2000 psi of D gas at 450 OC. DPE disappeared following a first order rate law as &own in Figure 1. The resultant mixture showed products reported earlier by Poutsma" for this reaction in the absence of D2: toluene, benzene, ethylbenzene, stilbene, 1,l-diphenylethane, phenanthrene and diphenylmethane. We also found what appeared to be diphenylpropane and trace amounts of other materials. For comparison, we carried out the reaction at the same pressure of N, and found most of the same products except, as reported by Vernon,b greatly reduced relative amounts of stilbene, benzene and ethylbenzene. These results are shown in Table I. Representative GC\MS data on the mixture obtained from the D2 reaction are shown in Table 11. The data suggest that deuterium introduction is taking place both at aliphatic positions and in the aromatic rings (note both benzene-dl and -d are formed.) To assess the relative amounts of aromatic and alisatic substitution, the reaction mixture was subjected to gas chromatographic separation and the individual components analyzed by both 'H-NMR and 'H-NMR. Typical results are shown in Table 111. Interestingly, as seen in Table 11, the pattern is very similar for 527
Page 1 and 2: LIQUEFACTION PATHWAYS OF BITUMINOUS
Page 3 and 4: the conversion of A+P and O+G with
Page 5 and 6: Asphaltcncs PrCasphaltenCS Cwr%, da
Page 7 and 8: NEW DIRECTIONS TO PRECONVERSION PRO
Page 9 and 10: ecause of incorporation of the coal
Page 11 and 12: should be considered more. The step
Page 13 and 14: 17 18 Run no. 0 cys I ToS-CyS TS-To
Page 15 and 16: INTRODUCTION Effects of Thermal and
Page 17 and 18: 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
Page 23 and 24: yields are calculated by subtractin
Page 25 and 26: 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
Page 31 and 32: inherent volatility of Mo(CO), perm
Page 33 and 34: Analysis of the quantity and compos
Page 35 and 36: $ EO .- 0 m L 0 c 0 0 > 40 300 350
Page 37 and 38: 0 0 0 0 0.000 0.005 0.010 0.015 0.0
Page 39 and 40: of these studies indicate that cont
Page 41 and 42: Different levels of adsorption occu
Page 43 and 44: Nominal 2 Table 1. Concentration of
Page 45 and 46: - iF m 1.6 1.4 1.2 - - - 1- 0 0.8 -
Page 47 and 48: RESULTS AND DISCUSSION Swelling of
Page 49 and 50: . . % . . 9 'HF 0 0 0 *. . 0 . . 0
Page 51: 1.50 KQ 1.00 0.50 I / ' 02 525 I 1
Page 55 and 56: D to generate more D atoms. It is r
Page 57 and 58: 12. a. Poutsma, M. L.; Dyer, C. W.
Page 59 and 60: Figure 3. Minimum Steps to Explin D
Page 61 and 62: Apoaratus and Procedure Microflow R
Page 63 and 64: Model ComDound Test Figure 5 shows
Page 65 and 66: Figure 1. High resolution gas chrom
Page 67 and 68: Figure 5. Product distribution for
Page 69 and 70: THQ at somewhat higher temperatures
Page 71 and 72: areas of the particles and the SEM
Page 73 and 74: Experimental Catalyst Precursors an
Page 75 and 76: impregnating solvent. Table 3 shows
Page 77 and 78: of MoCo-TC2 at the level of 0.5 wt%
Page 79 and 80: Table 4. Effect of Temperature Prog
Page 81 and 82: In the past, chemical treatments in
Page 83 and 84: The effect of Corn20 preaatment on
Page 85 and 86: Reaction Time Figure 1 - Schematic
Page 87 and 88: DISSOLUTION OF THE ARGONNE PREMIUM
Page 89 and 90: A much more def~tive trend is seen
Page 91 and 92: 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 and 144:
25 I 20 ' + 0 Drying lime, hours Fi
Page 145 and 146:
substructure have been identified a
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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