Ind. Eng. C h e m . Res. 1992,31,1045-1050 6: apparent density, g,,/cm3 6 c ~expansion per mole of reference component CL e: porosity &L: Weisz
modulus for component CL
Registry No. CH30H, 67-56-1;CH3C1, 74-87-3.
Literature Cited Allison, V. C.; Meighan, M. H. The Determination of Methyl Chloride in Gas Mixtures. Znd. Eng. Chem. 1919, 7,943. Boudart, M.; Mears, M. E.; Vannice, M. A. Kinetics of Heterogenous Catalytic Reactions. Znd. Chim. Belge 1967,32 (Special Issue, Part l),281. Froment, G. F.; Bischoff, K. B. B. Chemical Reactor Analysis and Design; Wiley: New York, 1979. Jain, J. R., Pillai, C. N. Catalytic Dehydration of Alcohols Over Alumina. Mechanism of Ether Formation. J . Catal. 1967,9,322. Kitrell, J. R. Mathematical Modeling of Chemical Reaction. Adu. Chem. Eng. 1970,8,97. Magoren. Catalysta for Manufacturing Methyl Chloride. Japanese Patent 58-27644,1983. Marquardt, D. W. An Algorithm for Least-Squares Estimation of Nonlinear Parameters. J . SOC. Znd. Appl. Math. 1963,ll(2), 431.
1045
Ponzi, M.; Ardissone, D.; Castro Luna, A. Dimensionamiento de un Reactor para la Produccion de Cloruro de Metilo. Reu. Petroquim. 1991,9 (77),5138. Schlosser, E. G.; Rossberg, M. J.; Lendle, W. Zur Kinetik der Methylchlorid-Bildung aus Methanol und Chlorwasserstoff an Aluminiumoxid. Chem.-Zng.-Tech. 1970,42 (19),1215. Svetlanov, E. B.;Flid, R. M. Catalytic Interaction of Hydrogen Chloride with Methanol. 11. Kinetics of the Dehydration of Methanol and Hydrochlorinationof Methyl Ether on Catalysts for the Vapor-Phase Synthesis of Methyl Chloride. Russ. J. Phys. Chem. 1966,40 (12),1638. Svetlanov, E. B.; Flid, R. M.; Gareeva, D. A. Catalytic Interaction of Hydrogen Chloride with Methanol. I. Kinetics of the VaporPhase Catalytic Interaction of Methanol with Hydrogen Chloride. Russ. J . Phys. Chem. 1966,40(9), 1236. Thyagarajan, M. S.; Rajinder, K.; Kuloor, N. R. Hydrochlorination of Methanol to Methyl Chloride in Fixed Catalyst Beds. Znd. Eng. Chem. Process Des. Den 1966,5 (3),209. Weisz, P. B.; Prater, C. D. Interpretation of Measurements in Experimental Catalysis. Adu. Catal. 1954,6,143.
Received for reuiew March 27, 1991 Revised manuscript receiued September 24, 1991 Accepted October 3,1991
MATERIALS AND INTERFACES Acidic Oxygen Compounds in the Irati Shale Oil Jtilio C. Afonso and Martin Schmal* Federal University of Rio de Janeiro, COPPEIEQIUFRJ, C.P. 68502, 21945 Rio de Janeiro, Brazil
Jari N. Cardoso Zmtitute of ChemistrylUFRJ, Centro de Tecnologia, bloco A, sala A-603, 21910 Rio de Janeiro, Brazil
This work reports the principal alkylphenols (4 wt %) and carboxylic acids (1.2 wt %) present in the Irati Shale oil ( S b Mateus do Sul, Paranl) by means of a combination of gas chromatography-mass spectrometry (GC-MS) and retention time data of standard compounds. It appears that the phenols are essentially monocyclic in nature with methyl groups as the main substituents. Carboxylic acids are principally linear and predominantly of the range Cl4-Cp0. After catalytic hydrotreatment (400"C, 125 atm) high hydrodeoxygenation levels were obtained (87 wt %) for phenols and carboxylic acids, although the relative distribution of the various compounds was not significantly changed. Oxygen is present in the carbonaceous residue as several functionalities (xanthenes, phenols, aryl ethers, carbonyl compounds, and furanic structures). The remaining acidic compounds may cause instability of the treated shale oil. 1. Introduction It is well-known that shale oils typically have a much higher content of oxygen than petroleum (Bett et al., 1983; Van Meter et al., 1952),which is distributed into several functional classes: phenols, carboxylic acids, aldehydes, ketones, ethers, and furanic compounds. In effect, the major acidic components found in shale oils have been phenols (Bett et al., 1983),predominantly monocyclic in nature (Bett et al., 1983;Guenther et al., 19811,although other phenol-type compounds (naphthols (Bettet al., 1983; Regtop et al., 1982; McCreham and Brown-Thomas, 1987); indanols and fluorenols (Bett et al., 1983))have also been reported. Carboxylic acids are precursors and intermediates in biological processes and have geological significance, as they have been widely found in coals, shale bitumens, and petroleums and have also been reported as products of
biodegradation of crude oils (Mackenzie et al., 1983;Beahr and Albrecht, 1984). In respect to shale oils, carboxylic acids have been characterized in retort waters (for example, Riley et al. (1979))but appear to be less commonly reported in the shale oils (Van Meter et al., 1952;Fookes and Walters, 1990). Perhaps this may be explained by the fact that carboxylic acids are much less abundant in such samples than phenols. Problems associated with the presence of oxygen arise as soon as synthetic crudes are used to produce commercial fuels (instability, odor, viscosity, etc.), making removal of O-containing compounds necessary. Phenols and carboxylic acids are among the main causes for such instability (Fookes and Walters, 1990; Furimsky, 1983;White et al., 1983). One of the strategies to solve this problem has been the conversion of oxygen functional groups into water (hydrodeoxygenation,HDO).
0888-5885192/263~1045$03.00/0 0 1992 American Chemical Society
1046 Ind. Eng. Chem. Res., Vol. 31, No. 4, 1992
Literature reported the HDO of shale oils (Harvey et al., 1986,1987),and very high HDO levels were obtained, although no reactions were indicated for the elimination of oxygen from the feedstocks. On the other hand, several other works studied the conversion of oxygen model compounds (for example, Kalurry et al. (19851, Odebunmi and Ollis (1983), Rollmann (1977),and Durand et al. (1984)). More attention has been paid to the HDO of phenols and furanic compounds, as they account for the major O-containing compounds in shale oils (Furimsky, 1983). In the case of the former, two main pathways are generally described: (i) direct elimination of the oxygen from the aromatic ring (which can be subsequently hydrogenated); (ii) previous hydrogenation of the aromatic ring followed by oxygen elimination. Less studied were the carboxylic acids due to the low contents in shale oils. However, two papers (Chiang and Itabashi, 1966; Silva, 1986) indicate that under specific hydrotreating conditions the HDO reactions involve reduction and decarboxylation of the carboxyl group, while cracking of the carbon chain is a secondary reaction. From HDO studies it is clear that oxygen compounds participate in the deactivation of catalyst through formation of 0-containing carbonaceous deposita (Furimsky, 1983),notably under conditions of limited hydrogen supPly. Nevertheless, in a general way, catalytic hydrodeoxygenation has not received as much attention as hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) because of the small amounts of oxygen normally found in conventionalcrudes. On the other hand, in order to achieve an acceptable HDO level, the knowledge of the 0-containing compounds present in a feedstock to be hydroprocessed is important since the reactivity toward HDO varies considerably among the various classes of oxygen compounds (Furimsky, 1983). Taking into account the relatively few studies on 0 elimination from shale oils and ita importance for the stability of treated oils, this work aimed to study the reactivity toward HDO of the acidic compounds (phenolsand carboxylic acids) present in a sample of the Irati shale oil, representative of the feedstock currently processed commercially (about 1000 barrels/day by Petrobrh, Paranl, Brazil),under a drastic hydrotreating condition. For this purpose, we have made a detailed characterization of the principal acidic compounds present in the sample before and after hydroprocessing. The behavior of the treated oil and the presence of oxygen in the carbonaceous residue over the spent catalyst are also presented and discussed. 2. Experimental Section 2.1. Analytical Conditions. The origin and the main properties of the Irati shale oil, the separation method utilized and the analytical conditions employed (highresolution gas chromatography, HRGC, and gas chromatography-mass spectrometry, GC-MS) have been given elsewhere (Afonso et al., 1991a). The whole unfractionated sample was used in the search for phenol and cresols. For heavier compounds, we employed the "polar" cut (retention factor below 0.25) obtained from fractionation (thin-layer chromatography, SiOz, n-hexane) of the samples for characterization. After isolation, the acids were esterified using diazomethane and subsequently purified using thin-layer chromatography @ioz, n-hexane/dichloromethane 7/3). 2.2. Catalytic Hydrotreatment. The catalytic hydroproceasing of Irati shale oil was performed on a three-phase fluidized-bed reactor (400 "C, 125 atm, space velocity 1h-l, H2/oil ratio 600 (v/v), time on stream, 71
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h) with a sulfided Ni-Mo/AlP03 catalyst (Shell 324). The above experimental conditions lead to a maximum production of diesel fraction (n-C13-n-Cm(Souza et al. (1985)). Details of the apparatus, the reactor, the catalyst, and the experiments are given elsewhere (Afonso et al., 1991a; Souza et al., 1985). Acidic compounds were analyzed at the end of hydroprocessing in the same way as described above for the natural oil. 3. Results and Discussion 3.1. Phenol Distribution. Figure 1 shows all the phenols identified in this work. Phenolic structures were suggested by direct comparison of the mass spectra with reference data (Stenhagen et al., 1969; Cornu and Massot, 1975; Aczel and Lumpkin, 1960). Mass spectral identification was quite simple (some representative spectra are presented in Figure 2): the general features suggested the compounds up to C4-alkyl to contain only methyl groups. An alkyl attachment other than methyl appears only in the case of the C5-alkyl homologue. Cresols and xylenols were identified on the basis of their retention time data determined from GC and GC-MS analyses (Correa, 1991).
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The characterization of the tri- and tetramethylphenols was obtained on the basis of their retention data on GC phases of behavior similar to the one used in this work, reported in the literature (HF'Analytical Supplies Catalog, 1989; Zweig and Sherma, 1972). The C5-alkyl homologue was tentatively characterized by mass spectral interpretation. All the characterizations are presented in Figure 1.
Phenol itself was not found (m/z 94 mass fragmentogram). Phenols higher than C5-alkyl could not be evidenced in any sample. Similarly, other phenol-type compounds (naphthols, indanols, phenols with two OH groups) were not detected on the basis of their diagnostic mass fragmentograms (Stenhagen et al., 1969; Aczel and Lumpkin, 1960; Budzikiewicz et al., 1964). The characteristicsof the phenol distribution in the Irati shale oil are summarized in Table I. When compared to the characteristics reported for other shale oils in the literature, we observe that the general trends found are very similar (e.g., no particular characteristic was found for the phenol distribution in the Irati shale oil). This fact suggests that the appearance of phenols in kerogen-derived oils may follow the same reactional pathways in all cases and may reflect specific moieties in kerogens in which phenols are liberated/formed under pyrolysis.
3.2. Carboxylic Acids. The characterization of these compounds by GC-MS was easier than in the case of phenols. The acids are essentially linear, from n-C6 to n-C= (m/z74 mass fragmentogram, see Figure 3), although homologues up to mC36 have been found in the Irati bitumen (Carvalhaes and Cardoso, 1986a). The assignment shown in Figure 3 was determined from retention time data of standard c16 and C18methyl esters. Fatty acids (CI4-Cm)are the most abundant components, with maxima at c16 and C18. The high predominance of c16 and C18acids in the pyrolysate seems to indicate that the fatty acids released on pyrolysis are essentially bound to kerogen as such (Tissot and Welte, 1984). The characteristicsof the distribution of carboxylic acids are summarized in Table 11. The data presented agreed well with those for other geological samples. From the abundance profile shown in Figure 3, it is interesting to observe that the even-carbon-number acids in the shale oil strongly predominate over the oddcarbon-number ones (Cl4+?6range), with a carbon preference index (CPI (Bray and Evans, 1961)) of about 8.5. The data are at variance with results for the Irati bitumen (Carvalhaes and Cardoso, 1986a),where a CPI of 2.5 was found (C14-Cxrange). These results for a kerogen-derived oil are of geochemical importance since they provide a
1048 Ind. Eng. Chem. Res., Vol. 31, No. 4,1992
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much clearer case for the contribution of higher plants (Eglinton and Hamilton, 1967) to the Irati oil shale. Additionally, our results challenge published estimates of the relative contribution of different biota (Carvalhaes and Cardoso, 1986b) to the Irati depositional environment, based solely on extractable organic matter (the bitumen, which corresponds to 3 wt % of the organic matter in the Irati shale). 3.3. Catalytic Hydrodeoxygenation (HDO).As pointed out in the Introduction, the removal of oxygen from shale oils is of great interest (notably in view of the stability of treated samples). For this reason, we have studied the HDO of the Irati shale oil under a drastic hydrotreating condition. Phenols and carboxylic acids were removed to an extent of 87 wt % . This result agrees with the high HDO levels that have been reported during hydrotreatment of other shale oils (Harvey et al., 1986, 1987) under similar conditions. Nevertheless, no preference in removal related to structure type, molecular weight, or substitution pattern was observed. Thus, the chromatographic profiles presented in Figures 1and 3 were not significantly altered; e.g., the distribution of the acidic compounds in the hydrotreated oil is very close to that of the original oil. In the case of phenols, this result agrees well with data on HDO of model cresols and xylenols (Kalurry et al., 1985) under similar hydrotreating conditions (with a Ni-Mo oxide catalyst) and has also been observed after hydroprocessing of a coal liquid (McClennen et al., 1983), although in some cases the ortho-substituted phenols have been found less reactive due to their steric hindrance (Rollmann, 1977; Odebunmi and Ollis, 1983). Probably the drastic hydrotreating conditions employed can account for a similar degree of reactivity of all phenolic sites. In the case of the carboxylic acids, our data strongly suggest that reduction of the carboxyl group is the effective reaction; decarboxylation appears to occur to much less extent. This could perhaps be expected as a result of the strong reducing conditions employed (high hydrogen pressure) in this work.
. Y .
Alkylbenzenes/cyclohexanes and n-alkanes are the end HDO products of phenols and carboxylic acids, respectively. No cyclic and linear alcohols were detected as HDO intermediate products. This result could be expected in view of the drastic experimental conditions and in keeping with some previous studies (Furimsky, 1983; Durand et al., 1984; Satterfield et al., 1985). The proposed HDO reactions are presented in Figure 4. Noteworthy is the fact that previous hydrogenation of the aromatic ring appears not to be necessary to oxygen elimination from phenols. The same degree of reactivity found in this work for phenols and carboxylic acids does not agree with the tentative classification given by Furimsky (19831, where phenols would need much stronger conditions for complete oxygen elimination than carboxylic acids. This disagreement is, a t present, difficult to rationalize but justifies further studies in order to well establish a more accurate stability trend for 0-containing compounds. 3.4. Sensitivity of HDO toward Hydrotreating Conditions. The data presented in this work were obtained under a fixed experimental condition (see section
Ind. Eng. Chem. Res., Vol. 31, No. 4,1992 1049 2.2), but it is worthwhile to comment on the HDO levels obtained under other hydrotreating conditions (Schmal, 1988) with the same catalyst, the same feedstock, and the same reaction system, as measured by the amount of water and COzpresent in the gas phase. The HDO rate increased with the increasing of the temperature range (350-475 OC) and of the hydrogen pressure (50-125 atm), although the effect of temperature was not very significant above 430 OC. These data are comparable to those obtained for the HDO of model compounds (Furimsky, 1983) and of a mal-derived liquid (Ternan and Brown, 1982). It must be pointed out that the amounts of H 2 0and COz remained approximately identical during time on stream, suggesting a HDO constant level during hydroprocessing. 3.5. Oxygen in the Carbonaceous Residue. No significant deactivation was observed during time on stream (71 h (Souza et al., 1985)). In spite of this fact, a carbonaceous residue was formed over the catalyst. Thus, the spent catalyst was submitted to Soxhlet extractions with n-hexane (24 h) and benzene (24 h). IR spectra clearly show the presence of oxygen functional groups: a series of absorptions between lo00 and 1355 cm-l was observed, accounting for the presence of xanthenes, aryl ethers, phenols, and furanic structures (Silverstein et al., 1981). An absorption a t 1790-1710 cm-' is ascribed to the presence of carbonyl compounds. Also, a small band a t 3775 cm-l accounts for phenolic OH. Since phenols are the basic 0-containing constituents of the Irati shale oil, it is likely that furans, aryl ethers, and xanthenes are formed from phenols, via coupling reactions, under limited active hydrogen supply, as on the surface of a catalyst covered by carbonaceous deposits (Furimsky, 1983). On the other hand, the presence of carbonyl compounds can be attributed to carboxylic acids and ketones, already present in the feedstock. 3.6. Stability of the Treated Oil. The hydrotreated oil presented darkening and insoluble solids after several weeks in refrigerated storage. The high HDO level accomplished does not seem to indicate that residual acidic compounds could account alone for this instability. In reality, nitrogen-type compounds (indoles and carbazoles), which are also present in high amounts in the treated oil (about 2.4 wt % (Afonso et al., 1991b)),are also responsible for the instability of synthetic crudes (Fookes and Walters, 1990; Harvey et al., 1986). According to recent studies (Fookes and Walters, 19901, the instability of the hydrotreated Irati shale oil can, at least, be partially explained by the fact that nitrogen compounds and carboxylic acids would have been precipitated with the oxidation products of residual phenols, probably through formation of hydrogen bonding, during storage. It is interesting to observe that the behavior presented by phenols in this work (as in other studies) seems actually to contradict the expectation that very hindered phenols (e.g., 2,4,6-alkyl substituted) are in fact antioxidants (Furimsky, 1983). Nevertheless, such hindered phenols appear to be much less abundant than those which tend to polymerize rapidly in synthetic fuels (Furimsky, 1983). On the basii of the phenol distribution presented in Figure 1,it seems that this fact is also observed in the case of the Irati shale oil. 4. Conclusions
Phenols, the most abundant oxygen compounds in the Irati shale oil, show a distribution profile with the overall characteristics that have been reported for other shale oils: (i) predominance of C2- and C3-alkyl homologues and of polyalkyl compounds with short side chains; (ii) presence
of essentially monocyclic structures (simple alkylphenols). Carboxylic acids are dominated by linear compounds with a strong predominance of even-carbon-number acids, which suggests a contribution of higher plants to the Irati oil shale. A high hydrodeoxygenation level can be obtained under a drastic hydrotreating condition, but the remaining acidic compounds present in the hydrotreated oil are among the ones responsible for its instability. Clearly, further studies must be undertaken in order to improve HDO (and HDN) levels and, consequently, the storage properties and the commercial value of the Irati shale oil. Also, further additional insight into the reactions involved and how they respond to experimental parameters would be extremely valuable.
Acknowledgment We thank R. Frety (CNRS, Lyon, France) for many valuable suggestions and for a critical reading of this paper. We also thank R. B. Coelho, L. M. P. Damasceno, H. Freitas, and C. Cesar (Institute of Chemistry, UFW, Brazil) for GC and GC/MS analyses. We are grateful to CNPq, CAPES, and CENPES (Petrobras) for financial support.
Literature Cited Aczel, T.; Lumpkin, H. E. Correlation of Mass Spectra With Structure in Aromatic Oxygenated Compounds. Aromatic Alcohols and Phenols. Anal. Chem. 1960,32,1819-1822. Afonso, J. C.; Schmal, M.; Cardoso, J. N.; Frety, R. Hydrotreatment of Irati Shale Oil: Behavior of the Aromatic Fraction. Ind. Eng. Chem. Res. 1991a,30,2133-2137. Afonso, J. C.; Cardoso, J. N.; Schmal, M. Comportamento de Compostos Nitrogenados em Condi@es Severas de Hidrotratamento. Sixth Brazilian Symposium on Catalysis, Sept 11-13 1991,Salvador-BA; Instituto Brasileiro de Petroleo: Rio de Janeiro, 1991b; pp 390-399. Baset, Z. H.; Pancitov, R. J.; Ashe, T. R. Organic Compounds in Coal: Structure and Origin. In Advances in Organic Geochemistry; Douglas, A. G., Maxwell, J. R., Eds.; Pergamon Press: Oxford, UK, 1980; pp 619-630. Beahr, F. H.; Albrecht, P. Correlations Between Carboxylic Acids and Hydrocarbons in Several Crude Oils. Alteration by Biodegradation. Org. Geochem. 1984,6,597-603. Bett, G.; Harvey, T. G.; Matheson, T. W.; Pratt, K. C. Determination of Polar Compounds in Rundle Shale Oil. Fuel 1983, 62, 1445-1454. Bodoev, N. V.; Rokosov, Y.V.; Koptyug, V. A. Aliphatic Carboxylic Acids and Ketones from Sapropelitic Coals. Fuel 1990, 69, 216-220. Bray, E. E.; Evans, E. D. Distribution of n-paraffins as a Clue to Recognition of Source Beds. Geochim. Cosmochim. Acta 1961,22, 2-15. Budzikiewicz, H.; Djerassi, C.; Williams, D. H. Interpretation of Mass Spectra of Organic Compounds; Holden-Day: San Francisco, 1964; pp 164-170. Cardoso, J. N.;Chicarelli, M. I. The Organic Geochemistry of the Paraiba Valey and Marau Oil Shales. In Advances in Organic Geochemistry; Bjoroy, M., et al., Eds.; Wiley: Chichester, UK, 1983;pp 823-833. Carvalhaes, S. F.; Cardoso, J. N. Acidos Carboxilicos do Xisto da FormaGiio Irati. An. Acad. Bras. Cienc. 1986a,58,7-15. Carvalhaes, S. F.; Cardoso, J. N. Hidrocarbonetos Lineares e Ramificados do Xisto da Formay?io Irati. An. Acad. Bras. Cienc. 1986b,58,17-25. Chiang, K. H.; Itabashi, K. Synthesis of n-dodecane by Catalytic Hydrogenolysis. Kogyokagakau Zasshi 1966,69,63-66. Cornu, A.; Massot, R. Compilation of Mass Spectral Data: Index de Spectres de Masse, 2nd ed.; Heayen & Sons LM in cooperation with SCM Publications: London, 1975;Vols. I and 11. Correa, S. M. A. Personal communication, 1991. Durand, D.; Geneste, P.; Moreau, C.; Pirat, J. L. Heterogeneous Hydrodeoxygenationof Ketones and Alcohols on Sulphided NiOMo0,l-y A1203Catalyst. J. Catal. 1984,90,147-149.
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Receiued for reuiew September 3, 1991 Reuised manuscript received November 22, 1991 Accepted December 14, 1991
Diffusion of Hydrocarbons in Polyethylene Shain J. Doongt and W. S. Winston Ho* Corporate Research, Exxon Research and Engineering Company, Route 22 East, Annandale, N e w Jersey 08801
The diffusivities of a series of aromatic hydrocarbons in semicrystalline polyethylene were obtained by the use of a modified gravimetric sorption technique with a flow system capable of a wide range of activities (or vapor pressures) and temperatures. The effects of penetrant concentration and size and temperature on the diffusivities were investigated. The experimental data can be fitted quite well by our proposed hybrid model that combines the key features of the free-volume and molecular models. In the hybrid model, polymer parameters and penetrant molecular thickness are used to determine the term equivalent to the preexponential factor of the free-volume model, and the free-volume expression is used to relate penetrant diffusivity to penetrant concentration and size. The hybrid model fitted the data better than the free-volume model, and it avoided the complexity of the molecular model. Introduction Understanding of diffusion of molecules in polymers is important for separation, packaging, and polymer processing. It also provides valuable information on molecular
* T o whom correspondence should be addressed. 'Present address: The BOC Group, Technical Center, Murray Hill, N J 07974. 0888-5885/92/2631-1050$03.00/0
motions and structures of polymers. A comprehensive review on diffusion in polymer-penetrant systems can be seen in Frisch and Stern (1983). A recent review on the theoretical models of diffusion is given by Aminabhavi et al. (1988). A widely used method to interpret the diffusion process or mechanism of penetrants in polymers above the glass transition temperature is the "free-volume model". This model assumes that the penetrants diffuse through the free 0 1992 American Chemical Society
