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Macromolecular Structure of Coals. 6. Mass Spectroscopic Analysis of Coal-Derived Liquids Donald T. Hooker, 11, Lucy M. Lucht,+ and NfkolaosA. Peppas' School of Chemical Engineering, Purdue University, West Lafayeffe, Indiana 47907
The macromolecular structure of coal networks was analyzed by depolymerizing coal samples using the Sternberg reductive alkylation and the Miake alkylation techniques. Electron impact mass spectra showed peaks of greater abundance at 125-132, 252-260, 383-391, and 511-520 mlz ratios. Based on analysis of the patterns of the spectra, the cluster size of the cross-linked structure of bituminous coals was determined as 126-130. Various chemical species were identified.
Introduction Coal as a Macromolecular Network. Early investigations of the coal structure were aimed predominantly at characterizing the types of functional groups that occur in the organic portion of coal. Some of these functional groups are important as sites where the coal structure can react and/or be degraded by appropriate reaction conditions. It is now accepted that coals have a macromolecular structure. Van Krevelen (1961) and Sanada and Honda (1966, 1967) were the first to propose that the organic portion of bituminous coals can be considered as a "cross-linked polymer". Since then, both Larsen and Kovac (1978) and Lucht and Peppas (1981a) have developed methematical, topological, and physicochemical models that represent the network structure of coals. Lucht and Peppas (1981a,b, 1985) proposed that the organic phase of coal consists of an effectively cross-linked macromolecular structure that does not dissolve at low temperatures unless reaction and degradation occur and of a portion of un-cross-linked macromolecular chains that can be extracted at low or moderate temperatures if an appropriate solvent is used. To further simplify the macromolecular structure in order to make it tractable for statistical analysis, Lucht and Peppas (1981b) and Peppas and Lucht (1984) proposed a cross-linked coal structure, in which each chain consists of groups of aromatic clusters and connecting bonds. The cluster may be a structure of two or more aromatic or heterocyclic rings fused together whereas the connecting bonds are simple groups such as 0, S-S, and CH2. In addition, the macromolecular chains which constitute a large portion of the coal do not contain a repeating unit, as defined in coventional polymers. Thus, coal does not have a polymer structure but a macromolecular
structure. A hypothetical repeating unit may be defined, solely for purposes of application of topological statisticid mechanical and swelling theories, for the determination of Mc, the number-average molecular weight between cross-links. One of our objectives was to characterize the size and chemical nature of the cluster bonds which form the macromolecular chains. This paper presents an interpretation of mass spectrometric analysis of !Sternberg-alkylated or depolymerized chains from the coal network, 'Present address: Lawrence Livermore Laboratory, Livermore,
CA.
Miyake-alkylated chains from the coal network, pyridine extractables, and the residue from a pyridine-extracted coal network structure. Invasive Techniques for the Study of the Macromolecular Structure of Coals. Most attempts to determine the functional groups, chemical stability, molecular weight, etc., of the organic phase of bituminous coals have been based on chemical degradation (depolymerization) techniques. Larsen and Kummerle (1976) and Wender et al. (1981) have published excellent reviews of various alkylation and depolymerization reactions of coal. The method chosen to degrade coal in this research was developed by Sternberg et al. (1971) and Sternberg and Delle Donne (1974). It is a reductive alkylation of coal using potassium metal, first forming a "coal anion" and then alkylating the coal anion with an alkyl halide. Sternberg's reaction has been used by many investigators to degrade the coal matrix for analysis by various methods (Ignasiak et al., 1978; Wachowska et al., 1979; Wachowska, 1979; Ignasiak and Pawlak, 1977; Wachowska and Pawlak, 1977). While Sternberg et al. (1971) claim that this procedure does not affect the aliphatic linkages between the aromatic clusters, Alemany et al. (1978) and Lazarov and Angelova (1980) have shown that this reductive alkylation does indeed break the methylene bridges as well. In addition, Miyake et al. (1980) have modified Sternberg's procedures by eliminating naphthalene as a possible source of contamination of the alkylated coal and have shortened the reaction time considerablyby doing the reaction under refluxing tetrahydrofuran at approximately 66 O C instead of 25 "C. The techniques used to analyze coal-derived products in this work were mass spectrometry and gel permeation chromatography. Field ionization produces mostly molecular ions with very little fragmentation and reaction. St. John et al. (1978), Bodzek and Marzec (1981), and Anbar (1977) have employed this ionization technique to the investigation of coal products and have obtained useful molecular weight profiles and, in some cases, compound identification. Recently, we have analyzed some samples with MIKES (mass ion kinetic energy spectrum), a tandem MS system (Peppas, 1980). The type of mass spectrometry used in this work was electron impact mass spectrometry. This type of ionization causes much fragmentation of the molecule. Thus, many peaks may be caused by the same molecule. Also, peaks owing to different molecules may lie on top of each other and may be impossible to resolve. In spite of these problems MS has been used in many investigations of coal-derived products (Sharkey et al.,
0196-4313/86/1025-0103$01.50/00 1986 American Chemical Society
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Table 11. Determination of the Completion of the Sternberg Alkylation Reaction
sample blank PSOC-418 PSOC-416 PSOC-266 PSOC-212 PSOC-772 PSOC-341 PSOC-384
t-
t-
: i' E 3
1 -
E
E
W
ri
ri
normality 23rd day 27th day 0.695 0.684 0.947 0.956 0.965 0.974 0.991 0.998 0.857 0.864 0.733 0.742 0.842 0.851 0.928 0.936
diff in normality 0.009 0.009 0.009 0.007 0.007 0.009 0.009 0.008
neg charges per 100 C atoms 15.0 14.8 16.0 8.75 2.93 7.32 10.28
1959; Lumpkin and Aczel, 1978). Experimental Section Table I shows the analysis of the seven coals studied in this work as supplied by the Pennsylvania State University Coal Bank. All coal samples were subjected to flotation in a solution of benzene/CCl, with a specific gravity of 1.3 g/cm3 a t room temperature. The portion of the coal which floated was then recovered, dried, and used for all subsequent experiments (Lucht, 1983; Lucht and Peppas, 1985). After flotation the coal samples were extracted in a Soxhlet extraction apparatus with pyridine at its boiling point (115 "C). The pyridine extracts of seven vitrinites were condensed by rotary evaporation under vacuum obtained by an aspirator in order to allow for better analysis by mass spectrometry. The boiling points of the extracts were in the range from 27 to 32 "C. In all cases, approximately 120 mL of extract was condensed to a volume of about 2 mL. The previously extracted, dry, coal matrix samples were alkylated by the Sternberg reduction alkylation method (Sternberg et al., 1971; Sternberg and Delle Donne, 1974). The samples were ground under nitrogen to pass through a U.S. Standard sieve no. 70 (mesh size 210 pm). The ground coal samples were then placed in a vacuum oven, evacuated to 23 mmHg absolute, and kept at 25 "C for 2 days. Upon complete drying, the samples were weighed to hO.1 mg. To each 100-mL reaction flask, 48 mL of tetrahydrofuran, 0.5 g of naphthalene, and 2 g of potassium were added. The mixture was stirred, under nitrogen, with a glass-enclosed, magnetic stirring bar for 20 h prior to addition of the approximately 1.5-g coal sample. An additional reaction flask was set up to run along with the coal samples and to serve as a blank for later titrations. The flasks were stoppered and stirred for 23 days, at which time small samples (approximately 1 mL) were withdrawn from each flask. Additional samples were also taken after 27 days. All samples were diluted to 25 mL with distilled water and kept for 48 h before titration. The diluted samples were titrated with HC1, and a pH meter was used t o determine the end point. The rate of reaction was determined by comparing the titers of samples taken on days 23 and 27. By comparing the rate of reaction in each flask with the blank, one could determine when the reaction of the coal was complete. Table I1 summarizes the titration data for the various coal samples. Total reaction time was 34 days for samples PSOC-416, -212, and -772 and 36 days for samples PSOC-418, -266, -341, and -384. In order to terminate the reaction, the flasks were cooled in an ice bath and the excess potassium was removed. To each flask, a solution consisting of 5 mL of n-iodobutane and 15 mL of tetrahydrofuran was added over a period of 30 min. A pressure-equalizing funnel was used to introduce the solution to minimize the admission of air to the reaction flask. After the n-iodobutanejtetrahydrofuran
Ind. Eng. Chem.
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Table 111. Data of Miyake Reductive Alkylation Studies w t of
sample PSOC-418 PSOC-212
potassium, g 1.98 2.10
initial wt of coal sample, g 1.9857 2.0015
wt of recovered alkylated coal, g 1.7326 1.4295
mixture was added, the flasks were warmed to room temperature and their contents stirred for 2 h. To recover the alkylated coal by precipitation, the contents of each flask were poured into a flask containing 200 mL of 50 vol % aqueous ethanol. The solids were separated by vacuum filtration and washed with 50 vol % aqueous ethanol to remove traces of iodide ion. The recovered solids were dried to a constant weight in a vacuum oven at 23 mmHg and 40 'C. The contents of the -blank" reaction flasks were also carried through this complete procedure, and no solids were recovered. Table I1 shows the number of negative charges per 100 carbon atoms calculated from the titration data. This numher shows the relative amount of anion formed on the coal molecules. Miyake et al. (1980) have developed a modified reductive alkylation procedure. The coal samples used in this procedure were PSOC-418 and -212. The samples were prepared in the same manner as for the Sternberg alkylation. Into each reaction flask there were added 50 mL of tetrahydrofuran, approximately 2 g of potassium, and about 2 g of the coal sample. Table I11 summarizes pertinent information ahout this procedure. Again, preparation of the reaction mixture was done under nitrogen. Each flask was fitted with a condenser and placed in a water bath a t 85 "C to reflux the tetrahyhofuran (bp 67 "C) for 6 h. The contents were stirred with a glass-enclosed, magnetic stirring bar. The flasks were then cooled in an ice bath, and a solution of 10 mL of n-iodobutane and 20 mL of tetrahydrofuran was slowly added over a 30-min period. The flasks were warmed to room temperature and stirred for 3 h. A t this time the excess potassium was removed and the reaction mixture was evaporated under vacuum in a rotary evaporator. The solids were washed and filtered with 50 vol % aqueous ethanol to remove traces of iodide ion. The solids were dried in a vacuum oven at 23 mmHg and 40 OC t o a constant weight. All alkylated coal samples and condensed extracts were analyzed by electron impact mass spectrometry. The unit used was a Consolidated Electrodynamics Corp. mass spectrometer (Type 21-llOB) with an electron impact ionization source. The ionizing voltage of the source was 70 eV. The source temperature was adjusted to 195-230 "C for analysis of the extracts and to 300-350 "C for analysis of the alkylated coal samples. In addition, one extract sample (PSOC-418) was run from 70 to 310 "C and one alkylated coal sample (PSOC-384) was run from 120 to 310 "C in order to investigate the effect of temperature on the MS spectra. Finally, a nonalkylated, extracted, solid coal sample was analyzed at 310 "C. Results and Discussion Mass Spectrometry of Alkylated Coals. Ten coal samples alkylated by Stemberg's technique were analyzed by electron impact mass spectroscopy in the range of mass/charge ( m / z )ratio of 20-600. The ion source temperature varied between 300 and 350 OC. One coal sample (PSOC-384) was analyzed at four different ion source temperatures, notably 120, 200, 270, and 310 "C. Figure 1 presents a typical mass spectrum of the Sternberg-alkylated coal sample from PSOC-384. The mass spectrum is plotted in terms of relative abundance in arbitrary units vs. the m/z ratio. T o determine the
I . .
i"/llCE
e-710
Figure 1. Electron impact mass spectrum of Sternberg-alkylated coal (expandedscale): coal sample PSOC-384, ion source temperature T,= 310 "C. Table IV. Conditions of Mass Spectroscopic Analysis of Coal Samples Alkylated by the Sternberg Method and Maximum m l z Ratios Detected sample
ion source temp, "C
P.SOC. -. ~. IR .
Rsn ...
PSOC-416 PSOC-266 PSOC-212 PSOC-772 PSOC-341 PSOC-384
310 320 300 320 300 310
max m j z ratio detected 51 .9 ~. 520 594 520 525 530 462
relative abundance, the data were normalized with respert to the most abundant peak (species), assumed to be 100 arbitrary units. Some general qualitative conclusions are immediately evident. Relative ahundances greater than 10 were ohserved only to a 130 mfr ratio. However, in order to show the full range of speries detected, Figure 1 shows the data in expanded scale with a maximum relative abundance of IO arbitrary units for clear identification of the peaks. Table IV Dresents the maximum m. z ratio observed for each sample. A. Determination of Cluster Size. The maximum m / z ratio observed was 594 for coal PSOC-266 with an ion source temperature of 320 "C. Most of the maxima were observed in the range of 520-594 m / z ratios. However, higher maxima may exist since, under the conditions of volatilization and ionization of the mass spectroscopicunit, it is likely that (i) the high molecular weight portions of the coal sample did not volatilize, (ii) some additional repolymerization (polycondensation) occurred, leading to high molecular weight species which could not be volatilized, and (iii) the maxima in the mass spectra represent species produced by repolymerization during the reductive alkylation of the coal. The data for alkylated products from coal sample PSOC-266 are different than the data for all other samples tested. Coal extracts of this particular sample have a number-average molecular weight, M., considerably higher than all other samples tested, as shown by Hill-Lievense et al. (1985). In addition, Lucht and Peppas (1985) reported that this was the only sample that swelled much less than other samples of comparable rank. All of these results may be due to the fact that this sample was the only one that had "weathered" for over a month. The m/z ratios observed are characteristic of similar molecular weights of original coal chains in the matrix, since Sternberg et al. (1971) claim that his reductive al-
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Table V. Analysis of Mass Spectra of Sternberg-Alkylated Coals ion coal source regions of elevated abundance in mass sample temp, O C spectrum (in m/z)" PSOC-418 350 77-80, 127-132, 384-392, 514-519 PSOC-416 310 127-132, 252-262, 375-392 PSOC-266 320 77-79, 115-117, 126-132, 152-157, 252-263, 326-335, 384-392, 456-461, 514-520, 588-594 PSOC-212 300 115-117, 127-133, 252-263, 383-392, 455-460,511-519 PSOC-772 320 75-79, 115-118, 126-133, 141-143, 252-263, 383-393, 516-524 PSOC-341 300 78-80, 127-132, 252-263, 288-291. 384-393 PSOC-384 310 125-133, 141-145, 151-159, 250-260, 282-289, 326-331, 354-359, 376-391 Only regions with m / z
> 75.
kylation is a "mild" degradation. Sternberg's technique involves cleavage of ether bonds, elimination reactions, carbon-carbon bond cleavage, and reduction of carbonyls to semiquinones or ketyls, but it is believed that few rearrangements take place. However, whether or not the observed molecular weight of 594 corresponds to the highest molecular weight species existing in these coal products is not as important as is the molecular weight of the aromatic clusters present. This can be obtained by interpretation of the mass spectra presented. We identified regions of high abundance at certain regions of characteristic m / z ratios. We used those peaks which occurred in groups larger than four peaks and which had a distinctly greater abundance than the surrounding peaks. Table V shows these data for seven samples tested at approximately the same ion source temperature. It was determined that m / z ratios of 125-132 and 383-393 appeared in all of the spectra. In addition, the m/z range of 252-520 was observed in all the samples but PSOC-384. Regions of elevated abundance appear in all the samples in multiples of the mass/charge ratio of 126-130. This recurring pattern would be observed if the alkylated coal sample contained aromatic clusters of molecular weight 126-130. Recent work supports this hypothesis. Makabe and Ouchi (1979) and Ouchi et al. (1979) deduced that low-rank coals, up to 80% C (daf), have tetralin-like unit structures, that in coals with 8045% C (daf) an average cluster consists of two to three condensed aromatic rings fused with 0.5 naphthenic ring, and that for coals with 86.7% C the average coal cluster has four condensed aromatic rings fused to two naphthenic rings. Thus, for the coals of 7045% C (daf), one would expect to see an abundance of molecules with molecular weights close to 130. These clusters could be bonded together by bridges, resulting in production of peaks in multiples of 2-4 times the molecular weight of the clusters. These conclusions are in qualitative agreement with data obtained by Lucht and Peppas (1985), which indicate a structure of aromatic clusters connected by small bridges. Swelling data obtained by Lucht and Peppas indicate that the number of aromatic clusters at 35 "C in the presence of pyridine between two cross-links is seven to eight for coals of approximately 70432% C (dmmf). Similar evidence was reported by Iwata et al. (1980), who examined the average chemical structure of some Japanese coals by mild hydrogenolysis. They reconstructed chemical species of molecular weight between 320 and 622, consisting of aromatic clusters of benzene, naphthalene, anthracene, phenanthracene, and higher order polyaromatic compounds,
Table VI. Identification of Important Chemical Compounds in Mass Spectra of Alkylated Coal Products compd major peak at m / z ratio benzene 78 pyridine 79 toluene 91 ethylbenzene 91 xylenes 91 phenol 93 diethylbenzene 105 xylene derivatives 105 117 phenol derivatives 128 naphthalene 132 quinoline 141 2-n-butylnaphthalene 141 methylnaphthalene 178 anthracene 178 phenanthracene 180 acridine 191 9,lO-dimethylanthracene
E e A :
9
'
6
I
fi I\
I
C 4
*B
E
u
2
I
s a
200
10a
400
300
600
500
MRSS/CHRRGE R R T I O
Figure 2. Electron impact mass spectrum of Miyake-alkylated coal (expanded scale): coal sample PSOC-212, ion source temperature T, = 320 "C.
and connected them with methylenic or etheric bonds. Our conclusions disagree to some extent with older literature, notably the work of Reed (1960), who obtained "repeating units" of molecular weight of about 180. Note, however, that Reed was working with coals in the range of 85-90% C (dmnd basis). The effect of source temperature was investigated for coal sample PSOC-384. A t the lowest temperature (120 "C) there wm little volatilization of the sample. However, at 200 O C a fairly good spectrum was obtained for the lower molecular weight compounds. The observed m/z maxima for these samples indicated that higher temperatures were needed to analyze for high molecular weight components. B. Identification of Important Chemical Species. The data obtained from the mass spectra enable us to provide some general information about chemical compounds found in our coal samples. Using previous literature on identification of mass spectra peaks (Holden and Robb, 1960a,b; Bodzek and Marzec, 1981) and the peaks observed in our research, we constructed Table VI which includes important compounds and their characteristic peaks at certain mlz ratios, Mass Spectrometry of Coals Alkylated by the Miyake Method. Mass spectra were run on products of the modified alkylation proposed by Miyake et al. (1980). Figure 2 shows the spectrum of PSOC-212. Again, the spectra were very similar to each other. However, the observed mass spectrum presented some differences from the spectrum obtained on the coal alkylated by the Sternberg technique. There were some peaks in the range of 121-130 and its multiples, but they
Ind. Eng. Chem. Fundam., VOI. 25, No. 1. 1986 IB
:e i s
107
---
E
Y I
--
"a
10 EB
68
188
IlS
I
1.8
ea
lea
n45515"merE Z * T , Y
- . . I I C . I I m
i.iTIU
Figure 3. Electron impact mass spearum of mal matrix (expanded scale): coal sample PSOC-418, ion source temperature T,= 310 OC.
Figure 4. Electron impact mass spectrum of extracts from pyridine-extracted coal (expanded scale): coal sample PSOC-416, ion source temperature Ti = 225 "C.
were not as pronounced as in the previous spectra. There were a lot of groups of peaks at intervals of 10-15 mass units indicating the existence of CH, groups or similar groups. Alkylation following Miyake is therefore a more destructive procedure than that of Sternberg. Mass Spectrometry of Coal Matrices. One s p e d " was obtained of a coal sample (PSOC-418)which had been extracted only with pyridine and not degraded in any manner. Figure 3 shows the mass spectrum obtained. The ion source temperature was 310 "C. The coal matrix was still intact, and very little volatilization occurred. A comparison of this spectrum with the spectra of the degraded products shows that the alkylation technique did break down some of the coal matrix into smaller molecular weight components. It has been previously observed (Collins et al., 1981) that, when bituminous coals are extracted with pyridine, the extracts and the solid residues (coal matrix) retain up to 20% pyridine. Therefore, it was expected that pyridine would be detected in the mass spectrum of the coal matrix. Indeed, a strong pyridine peak was observed at an m/z ratio of 79. In fact, a strong peak a t m/z 79 was observed for every sample that was analyzed. Mass Spectrometry of Coal Extracts. Analysis of the mass spectra of coal extracts was done by the same procedure as for the alkylated coals. The same convention was used in describing relative abundance, by normalizing with respect to the highest intensity in each spectrum. Seven samples of coal extracts were analyzed. The ion source temperature for all samples was in the range of 195-230 OC. In addition, extracts of sample PSOC-418 were run at 70,100,150,250, and 310 "C for investigation of the ion source temperature effect on the mass spectra. Figure 4 presents a typical mass spectrum for PSOC-416 plotted in terms of relative abundance in arbitrary units v8. m/z ratio. Major peaks appear at m/z ratios lower than 190. There are many similarities in the mass spectra of the coal extracts, but the similarity is not as strong as it was for the alkylated coal samples. The peaks observed at 37-45,49-53, and 75-80 were also seen in the alkylates while the peaks at 155-157 and 163-170 were not seen in the alkylated coal samples. This leads us to conclude that the extracts are structurally different from the coal matrix and not similar as postulated by Lazarov and Angelova (1976). Early work by Friedel et al. (1968) had shown that the time of extraction affects the chemical structure of the products obtained. Alkylbenzenesand phenols are prominent at the early stage of coal extraction. Polynuclear aromatics are mainly extracted later. In long-term ex-
tractions (up to 17 h) they detected small amounts of three-to-six-ring cata- or pericondensed polynuclear aromatics. The time of extraction used in this work was very long (approximately 2 weeks) to ensure complete extraction of the coal matrix. Thus, based on the work of Friedel et al. (1968), there should he components with high molecular weights of approximately 328, the molecular weight of a six-ring condensed polynuclear aromatic compound. Indeed, there were components in this mass range and some amount of material of higher molecular weight. Ladner et al. (1980) analyzed the chemical structure of pyridine-soluble coal extracts, using infrared spectroscopy and NMR. They found that long alkyl side chains are prominent in lignites, occurring mainly in the low molecular weight fractions. The average alkyl chain length for extracts of the lignites was between 2.5 and 4, decreasing to 2 for those from bituminous coals. They also found that methyl groups are the main constituent of the aliphatic chains of all extracts from lignites and bituminous coals. By analysis of the degree of condensation of the lignite extracts, they found that the aromatic nuclei consist mainly of single rings. However, for bituminous coals the aromatic neuclei may include up to three rings. In analyzing the mass spectra of the coal extracts and comparing these with the spectra of the alkylated cod, we observed that the spectra of the extracted coal had many groups of peaks separated by 10-15 mass units which would indicate that the extracts had a more aliphatic character than the alkylated coal sample. This finding has also been observed by Vahrman (1970, 1972). The molecular weight of coal extracts from gel permeation chromatography analysis varies between 300 and 10 500. The number-average molecular weight is in the range of 600-760 as determined by Hill-Lievense et al. (1985). The mass spectra of the coal extracts show very few components with molecular weights greater than 400, although the mass spectrum of extracts of PSOC-418 does show a peak a t a molecular weight of 510. This discrepancy between the results of MS and GPC can be attributed to the inability to volatilize the higher molecular weight components in MS. The samples run a t various source temperatures again show that higher temperatures produce scans of higher molecular weight components. However, a lower temperature was required for the extracts than for the alkylates to obtain the complete spectrum. Conclusions By interpreting the mass spectra of Sternberg-alkylated coals, we determined that aromatic clusters with a m / z
Ind. Eng. Chem. Fundam. 1986, 2 5 , 108-115
108
ratio of 126-130 were important components of these samples. The rank of the sample had little effect on the mass spectra, as all spectra were very similar. However, the data from the alkylation procedure indicate that rank does influence the amount of "coal anion" formed and the yield of degraded product. Coal sample PSOC-266 behaved differently than the other samples probably because it was "weathered" before collection. The alkylation procedure proposed by Miyake et al. (1980) was much faster and easier than the procedure proposed by Sternberg et al. (1971). However, the reductive alkylation of Miyake is more destructive than the reductive alkylation of Sternberg. Acknowledgment This research was supported by Contract DE-FG-2280PC30222 from the Department of Energy, Pittsburgh Energy Technology Center, and by a grant from the Continental Oil Co. Literature Cited Alemany, L. E.; King, S. R.; Stock, L. M. fuel 1978,57, 1976. Anbar, M. Final Technical Report EPRI-AF-390. 1977. Bodzek, D.; Marzec A. Fuel 1981, 60, 47. Collins, C. J.; Hagaman, E. W.; Jones, R. M.; Ragen, V. F. fuel 1981,60, 359. Friedel, R. A,: Shultz. J. L.; Sharkey, A. G. Fuel 1968,47, 403. Hill-Llevense, M. E.: Lucht, L. M.; Peppas, N. A. Angew. Makromol. Chem. lg65, 734, 73. Holden, H. W.; Robb, J. C. fuel 196Oa,39, 39. Holden, H. W.; Robb. J. C. Fuel I W O b , 39, 485. Ignasiak, 8. S.;Fryer, J. F.; Jadernik, P. fuel 1978,57,578. Ignasiak, E. S.;Pawlak, M. Fuel 1977, 56, 216. Iwata, K.; Itoh, H.;Ouchi, K.; Yoshida, T.Fuel Process Techno/. 1980, 3 , 221. Ladner, W. R.; Martin, T.G.; Snape, C. E.; Bartle, K. D. fuel Chem. Prepr. 1980,25,67.
Larsen, J. W.; Kovac, J. I n "Organic Chemistry of Coal"; Larsen, J. W., Ed.; American Chemical Society: Washington, D.C., 1978; ACS Symp. Ser. No, 71. p 36. Larsen, J. W.; Kummerle. E. W. fuel 1976,55, 162. Lazarov, L.; Angelova, G. Khim. Tverd. Topl. (Moscow) 1976, 70, 15. Lazarov. L.; Angelova, G. Fuel 1980, 59, 5 5 . Lucht, L. M. R . D . Thesis, School of Chemical Engineering, Purdue University, West Lafayette, IN, 1983. Lucht, L. M.; Peppas, N. A. I n "Chemistry and Physics of Coal Utilization"; Copper, B. R., Petrakis, L., Eds.; American Institute of Physics: New York, 1981a; AIP Conf. Proc. No. 70, p 28. Lucht, L. M.; Peppas, N. A. I n "New Approaches in Coal Chemistry"; Blaustein, E. D., Bockrath, B. C., Friedman, S.,Eds.; American Chemical Society: Washington, D.C., 1981b; ACS Symp. Ser. No. 169, p 43. Lucht, L. M.; Peppas, N. A. f u e l , in press. Lumpkin, H. E.; Aczel. T.I n "Organic Chemistry of Coal"; Larsen, J. W., Ed.; American Chemical Society: Washington, D. C., 1978; ACS Symp. Ser. No. 71, p 215. Makabe, M.; Ouchi, K. fuel 1979,58, 43. Miyake, M.; Sukigara, M.; Nomura, M.; Kikhawa, S. fuel 1980,59, 637. Ouchi, K.; Iwata, K.; Makabe, M.; Itoh, H. FuelChem. Prepr. 1979,24, 185. Peppas. N. A. Report on Contract DE-FG22-78 ET 13379; Department of Energy: Pittsburgh, PA, 1980. Peppas, N. A,; Lucht, L. M. Chem. f n g . Commun. 1984,30, 291. Reed, R. I.fuel 1960, 39, 341. Sanada. Y.; Honda, H. fuel 1966,45, 295. Sanada, Y.; Honda, H. fuel lS67,46, 451. Sharkey. A. G.; Wood, G.; Friedel, L. A. Chem. Ind. (London) 1959,833. Sternberg. H. W.; Delle Donne, C. L. fuel 1974,53, 172. Sternberg, H. W.; Delle Donne, C. L.; Pantages. P.; Moroni, E. C.: Markby, R. E. fuel 1971,50, 432. St. John, G. A.; Butrill, S. E.; Anbar, M. I n "Organic Chemistry of Coal"; Larsen, J. W., Ed.; American Chemical Society: Washington, D.C., 1976; ACS Symp. Ser. No. 71, p 223. Vahrman, M. Fuel 1970,49, 5. Vahrman, M. Chem. Br. 1972,8,16. Van Krevelen, D. W. "Coal"; Elsevier: Amsterdam, 1961. Wachowska, H. M. fuel 1979,58,99. Wachowska, H. M.; Nendi, 9. N.; Montgomery, D. S. fuel 1979, 58,257. Wachowska, H. M.; Pawlak, W. fuel 1977,56, 422. Wender, I.; Heredy, L. A.; Neuworth, M. E.; Dryden, I. G. C. I n "Chemistry of Coal Utilization"; Elliot, M. A., Ed.; Wiley: New York, 1961; Vol. 2, p 425.
Received for review April 26, 1984 Accepted May 6, 1985
Very Large Lattice Model of Liquid Mixing in Trickle Beds Badreddlne Ahtchl-All and Henrlk Pedersen Department of Chemical and Biochemical Engineering, Rutgers Universitjf, New Brunswick, New Jersey 08903
A three-dimensional, very large lattice model (VUM) based on percolation theory concepts is used to analyze liquid flow in trickle beds. The liquid flow distribution is a function of only a single parameter, the bed permeability. As the bed permeability increases, the model is able to account for flow transitions from rivulets to films. Correlations to the mean liquid film thickness and the dynamic holdup are derived and compared to literature values. Also, experimental data on the local liquid flow distribution are found to be in excellent agreement with the VLLM results.
Introduction Trickle bed reactors are used in the chemical processing industry for the efficient contacting of gas and liquid phases. Typically, gas and liquid phases flow cocurrently down through a loosely packed solid bed that may be a catalyst. The solid serves as a support for the liquid, as well as a means of effecting liquid mixing and radial distribution. The gas phase is always continuous in a trickle bed reactor and may contain volatile reactants or products, or the gas phase may be used as a simple means for enhancing liquid mixing. In some cases the liquid phase serves as a heat-transfer medium, and the reaction is predominantly between the gas and the solid, as in Fischer-Tropsch synthesis (Benson et al., 1954). Trickle flow conditions are observed in a packed bed over a limited range of gas and liquid flow rates as shown
schematically in Figure 1. In this diagram, the different flow regimes for the three-phase system are distinguished (Hoffman, 1978). Trickle flow prevails in the quadrant of low liquid and gas Reynolds numbers. It has been observed, however, that the trickle flow regime is in itself composed of regions with differing liquid flow texture (Prost and Le Goff, 1964; Charpentier et al., 1968a). Isolated flow prevails at low liquid flow rates, where the liquid is present primarily as drops. As the liquid flow rate is increased further, anisotropic flow predominates, changing to an isotropic flow at still higher liquid irrigation rates. These regions are characterized by rivulets and films, respectively. The complicated liquid flow patterns, plus the simultaneous existence of three phases and the random nature of the solid packing, greatly hinder tractable analysis of
0196-4313/86/1025-0108$01.50/00 1986 American Chemical Society
