504
Ind. Eng. Chem. Process Des. Dev. 1981, 20, 504-508
Stabilization of Hydrocracked Lubricating Oils by Catalytic Treatment Tsoung Y. Yan" and Wllton F. Espenscheld Mob11 Research and Development Corporation, Central Research Divislon, Princeton, New Jersey 08540
A novel catalytic treating method for stabilizing hydrocracked lubricating oil is presented. According to this process the hydrocracked lubricating oil mixed with normal paraffins or waxy hydrocracked oil is passed over a proprietary shape-selective zeolite. Starting with waxy oil, both stabilization and pour point reductlon can be accomplished in this process simultaneously. The process c a n be integrated with the hydrocracker to save processing steps and cost. The reaction sequence involved in the process is believed to be: shape selective cracking of normal paraffins or slack wax to form olefinic intermediates, which in turn alkylate the sludge precursors and aromatics in the oil. The mechanism of hydrocracked oil stabilization remains obscure, but it is believed that the sludge precursors are deactivated and made more soluble by alkylation of aromatic components with the olefins resulting from normal paraffin cracking.
Introduction The manufacture of lubricating oils by hydrocracking heavy vacuum gas-oils or propane deasphalted residual oil has been reviewed by several authors (Gilbert and Walker, 1971; Vlugter and Van't Spijker, 1971; Bryer and Didot, 1973; Steinmetz and Reif, 1973). There are 10 hydrocracking and hydrotreating facilities in the US.with a t ~ t a l lubricating oil capacity of 47 000 bbl/day (Hydrocarbon Process., 1978). This is a small fraction of the nation's total lubricating oil capacity of 423 500 bbl/day. However, recent advances in hydrocracking technology, coupled with dwindling choices of crude for lubricating oil manufacturing, have renewed some interests in lubricating oil hydrocracking. Hydrocracked oils are superior to solvent refined oils in many respects, e.g., higher viscosity index, lower carbon residue, lower sulfur content, higher thermal stability, and better response to chemical additives for oxidation stability. However, hydrocracked oils have one distinctive deficiency-their sensitivity to sunlight or ultraviolet radiation in the presence of oxygen. On exposure to light and oxygen, the oils darken, from a haze, and finally deposit heavy sediments. This problem is well known and several methods have been proposed to stabilize hydrocracked oils (Franz and Smilski, 1971; Orkin and Braid, 1969; Langlois et al., 1969; Assef, 1970). All of these methods are expensive because they involve losses in yields, costly processing steps, or expensive chemical additives. Above all, these methods do not yield products having long-term stability. Recently, a novel catalytic treating process to stabilize the hydrocracked oils (Yan, 1978; Yan and Bridger, 1975,1980) was reported. Instead of removing the sludge forming precursors from the oils, the method involves reacting the oils with olefins over acidic catalysts at temperatures of 100-200 "C. Under favorable operating conditions, the products were found to be stable for at least a year. Notwithstanding this significant progress, the method can be further improved. It uses costly external olefins and cannot be conducted satisfactorily in a hydrocracking unit. In addition, the range of operating temperatures is narrow and the catalyst requires frequent regeneration. When acidic resin catalysts are used, the regeneration procedure becomes particularly lengthy and costly. In this paper a novel catalytic method is presented which circumvents most of these undesirable features. 0196-4305/81/ 1120-0504$01.25/0
Current Approach In order to circumvent the undesirable features of the catalytic olefin treating process, a research program was undertaken to uncover an improved catalytic process for stabilization of hydrocracked lubricating oils. This new process has the following additional features: no external olefin requirement; process stability for long term operation; compatability and integration with the hydrocracking process itself; simultaneous quality upgrading of the lubricating oil in terms of pour point reduction. The basic chemical principles for stabilizing the hydrocracked oils are the same as those of the catalytic olefin treating process. They are (1) to alkylate the sludge precursors to render them inactive to photooxidation, and the oxidized product soluble in the bulk oil, and (2) to alkylate the bulk oil to improve its solvency for polar, oxidized products. To accomplishe these objectives, we chose to treat the hydrocracked oil over a proprietary, shape selective acidic zeolite catalyst at high temperatures in the presence of paraffins (e.g., slack wax) (Espenscheid and Yan, 1974). The acidic zeolite produces the olefins needed in situ by cracking the paraffins in the feed. When paraffin A is cracked into two fragments of different sizes (reaction I),
catalyst
paraffin A B (saturate) + C (olefinic) (1) the larger fragment B is generally saturated and the smaller fragment C is olefinic. The fragment C effectively becomes the alkylating agent in place of the external olefins used in the previous method. When the molecular size of paraffin A is large (e.g., slack wax), the fragment B is still in the lubricating oils' range so that the e loss in yield of the lubricating oil due to this catalytic treating process is minimized. All paraffins, both iso- and normal, and naphthenes are potential molecules for in situ generation of olefins via catalytic cracking. However, the isoparaffins and naphthenes are excellent lubricating oil components and should be preserved in this process to prevent loss in yield and downgrading in quality of the lubricating oil product. On the other hand, the normal paraffins must be removed from the waxy hydrocracked oil to lower the pour point to 20 OF or 0 O F specifications. Currently, this dewaxing is done by methyl ethyl ketone dewaxing at great expense. Consequently, a proprietary shape selective zeolite was used to generate olefins by cracking the normal paraffins 0 1981 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 3, 1981 505 Table I. Physical Properties of Hydrocracked Oil
KV at uv 210 'F, viscos. aromatics stability, oil source cSt index wt % 11 W Midcontinenta 10.50 b 8 40 M Midcontinent 10.00 125 40 47 (-10) K 1 Kuwait 4.20 115 8.2 K2 Kuwait 7.93 131 77 K3 Kuwait 12.62 107 14.9 93 a
Wax content: 20 wt 7%.
Not measurable.
selectively. By use of this shape selective catalyst, three things were achieved, namely: (1) The loss in yield of hydrocracked lubricating oil was minimzed. (2) High quality (such as visc ity index) of hydrocracked lubricating oil was obtaine ? . I(3) The pour point of the hydrocracked lubricating oil via catalytic dewaxing was lowered. In other related research work, catalytic treatment over this proprietary catalyst has been shown to improve the oxidation stability of the treated lubricating oil (Yan, 1976). To carry out catalytic cracking of paraffins, the incipient reaction temperature required is about 450 O F . Above this temperature, the severity of the treating process can be varied by increasing the reaction temperature or decreasing the space velocity. Preliminary investigations showed that at about 450 OF, the proprietary catalyst is also an excellent alkylation catalyst. Therefore, this single catalyst can be used to generate olefins from normal paraffins in situ, and alkylate sludge precursors and bulk oil with the olefins generated. Above 450 O F catalyst deactivation by polymerization of o l e f i is minimized. Olefin concentration is maintained at a low level by the rapid alkylation reaction. Previous research also indicated that the aged catalyst can be subjected to many cycles of the oxidative regeneration to recover its activity. Experimental Section Material. A. Hydrocracked Lubricating Oils. The hydrocracked waxy and dewaxed oils were derived as follows. (1) Feed W. Propane deasphalted residuum from Midcontinent crude was hydrocracked. The 650 O F waxy hydrocracked feed, W, was obtained by topping the hydrocracked product. The properties are shown in Table I. 2. Feed M. The waxy feed W was dewaxed using methyl ethyl ketone as the solvent. The properties are shown in Table I. 3. Feed K. Propane deasphalted Kuwait residuum was hydrocracked. The 650 O F + bottoms were fractionated into three fractions of different viscosity grades using vacuum distillation, and the resulting fractions were solvent dewaxed. The properties of these products, K1, K2, and K3 are shown in Table I. B. Paraffin. Normal hexadecane of high quality, 98+ % purity, was used as received. Normal hexadecane was chosen in the experiment because the unreacted feed can be easily identified from other hydrocarbons in the hydrocracked oil by gas chromatography and can be stripped from the hydrocracked oil by distillation. C. Catalyst. The catalyst used was Mobil's proprietary catalyst HZSM-5. I t was prepared according to the method described previously (Argauer and Landolt, 1972). The NaZSM-5 as the synthesized was ion exchanged with NH4Cl and finally calcined to obtained the HZSM-5 catalyst. The catalyst had the Si02/A1203ratio of about 70. The structure of ZSM-5 zeolite has been elucidated (Kokotailo et al., 1978). The crystal size of the zeolite was
Table 11. Stabilization of Hydrocracked Oila run no.
temp, "F
reaction time, h
product stability, h
450 500 550
15 15 15
> 200 > 200
feed M
1 2 3
40
>200
a Batch reaction; feed: M, dewaxed hydrocracked oil; paraffin added: n-hexadecane, 7 wt 7%; catalyst/oil: 0.02; pressure, psig: 0.
about 0.5 pm and its pore size about 5.5 A. The constraint index of the zeolite was about 10 at the reaction temperature indicating that it is a "shape" selective catalyst. The constraint index as defined approximates the ratio of cracking rate constants for n-hexane and 3-methylpentane (Frillette et al., 1981). The catalytic activity of the catalyst was characterized by cracking n-hexane. Its activity was found to be 200 times that of 46 AI silica alumina cracking catalysts. Procedure. A. Batch Reaction. Seven weight percent n-hexadecane was mixed with the freshly filtered, dewaxed hydrocracked lubricating oil and the catalyst in a flask equipped with a stirrer and a reflux condenser. The well-agitated mixture was held at the reaction temperature for the desired period of time. The product was recovered for stability testing by removing the catalyst fines using a centrifuge and the excess n-hexadecane and light ends using vacuum distillation. B. Continuous Flow Reaction. In the continuous flow reaction the waxy hydrocracked oil or the mixture of n-hexadecane and dewaxed hydrocracked oil was pumped upflow through a fixed bed of catalyst at the desired pressure, temperature, and space velocity. The excess n-hexadecane and light ends were removed from the effluent by distillation and 650 O F + bottoms were recovered for testing. C. Product Analysis and Testing Procedure. The extent of catalytic cracking was measured by the yield of light ends derived from cracking of both n-hexadecane and the paraffms in the hydrocracked oil. However, the extent of alkylation is more difficult to measure. A gas chromatograph was used to assess qualitatively the proceeding alkylation by comparing the boiling point distribution of the treated oil with untreated oil. In general, it was found that the fraction boiling at about 800 OF was increased over that in the feed (untreated oil) at the expense of fraction boiling at about 700 O F . The 650 O F + oil was tested for light stability by use of the ultra violet light test. Test tubes were half filled with oil, loosely stoppered, and then placed in a Rayonet Photochemical reactor which contained 16 UV lamps of 2537-A wavelength. The temperature in the box was regulated at 37 "C with a cooling fan. The oil was inspected periodically for haze and deposit formation. The 650 O F + bottoms were also tested for pour point according to ASTM D97. The color of the 650 O F + bottoms was determined using ASTM D1500 or by measuring its optical density at 546 pm. Results and Discussion Stabilization of the Oil. As shown in Table 11, the dewaxed oil (feed M) was stabilized by reacting with nhexadecane in the presence of the zeolite catalyst between 450 and 550 OF, in a batch reactor. The stability of the oil was increased from 40 h to over 200 h. In a flow reador, this feed (M) was stabilized to over 400 h at 500 OF (see Table 111). The waxy hydrocracked oil (feed W) in the absence of added external paraffins was stabilized to over
508
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 3, 1981
Table 111. Stabilization of Dewaxed Hydrocracked Oils in the Presence of Added Paraffinsa reactor yield of light temp, "F LHSV ends, wt % b stability, h feed 400 500 550 450 500
0.33 0.33 0.33 1.00 1.00
3 17 32 3 7
40 214 418 72 44 202
Flow reactor; feed: M, dewaxed hydrocracked oil; paraffin added: n-hexadecane, 7 wt %; pressure, psig: 0. b Weight percent of materials boiling below n - C 1 6 . Table IV. Stabilization of Hydrocracked Oils without Added Paraffinsa run no.
feed stock
temp, "F
light end, pour pt, "F stability, h wt % b
1 W control 120 40 2 W 450 5 45 500+ 3 W 500 13 25 500+ 4 W 550 25 0 575+ 5 K1 control -5 24 6 K1 500 63 7 K2 control 0 24 8 K2 500 360t 9 K3 control -10 36 10 K3 500 1300+ a Reactor: continuous flow; LHSV VlV h: 0.33. Light end, 650 OF-, produced.
500 h (see Table IV). Thus, the feasibility of stabilizing the hydrocracked oil in the presence of paraffins and the proprietary zeolite catalyst was demonstrated. hcidently, the improvement in stability obtained in this process is greater than that claimed in the literature for other processes and the treated oil is acceptable for commercial applications. It is noted that this improvement is somewhat less than can be expected from the olefin treating process disclosed previously. The reason is not clear but it may be due to the following factors: (1) There are less favorable conditions for alkylation at higher temperatures. (2) The olefinic fragments are less abundant as compared with added external olefins. In the olefin treating method, it was shown that the concentration of olefins added should be greater than 5 w t 5% in order to obtain best results. (3) The alkylation reaction is less selective to the sludge precursors under the conditions employed. With the aid of new analytical methods, such as elution chromatography, 'H NMR and 13C NMR, the reaction products could be examined more critically to better elucidate the mechanism of reaction. Possible Reactions Involved. Since the oil is a complex mixture, and the degree of reaction is rather small, it is difficult to elucidate all the reactions involved with certainty. However, the reaction sequences proposed in the previous section appear to be taking place. These reactions are: (a) shape selective catalytic cracking of the normal paraffins to generate olefins in situ; (b) alkylation of the sludge precursors and perhaps some of the aromatic compounds in the oil as well as by the olefins. The evidence to support the above reaction sequence is as follows. A t the reaction temperature effective for the process, the cracking of paraffms is demonstrated by the formation of light ends (cracked products) (see Table 111). At too low a temperature, say below 400 O F , the procedure is not effective for stabilizing the oil. Cracking of paraffins, particularly, in the absence of hydrogen and hydrogenation catalyst, results in one olefin per carbon-carbon scission
as dictated by stoichiometry. The cracking is selective for normal paraffins. The pore size of the catalyst is too restrictive to accommodate isoparaffins and naphthenes. Consequently,normal paraffins are seleetively cracked to produce the necessary olefins for alkylation. Furthermore, the greatly reduced pour point of the product when the waxy hydrocracked oil was treated according to our procedures is further evidence of shape selective cracking (see Table IV). This pour point reduction is an important beneficial side effect of the present process because the expensive solvent dewaxing step is minimized or eliminated altogether. Alkylation of the sludge precursors and aromatics in the oil appears to take place. By comparing the boiling point distribution of the treated and stabilized "waxy" oil with the untreated waxy oil feed using gas chromatography, it was shown that the fraction boiling around 800 O F is increased over that in the feed at the expense of fraction boiling around 700 O F . To test the validity of this mechanism, equal amounts of aromatics and paraffinic middle distillate cuts boiling between 550 and 700 O F were reacted over the proprietary zeolite at 500-600 O F . It was found that substantial amounts of heavier product were formed which boil above 700 O F . Those heavier products were undoubtedly alkylation products. Other indirect evidence, such as the effect of processing conditions and nature of hydrocracked oil feed on the quality of treated oils, are all consistent with the above postulate. The effects of these variables are discussed below. Effect of Hydrocracked Oil. As discussed in the previous paper (Yan, 19781, the more viscous the oil the more stable it is to light (Table I). I t is probable that it takes longer to agglomerate the oxidized product to form sludge in a more viscous oil. It is also possible that the more viscous oil is an intrinsically better solvent for the oxidized products than the lighter oils. I t should not be overlooked that more viscous oils generally contain more aromatics than the lighter oils when they are derived from the same crude (see Table I). Assef (1970) has reported that the formulated hydrocracked oil is more stable to light and air than the base oil itself. This observation is consistent with what is described above. In the formulation, the oil is thickened or made more viscous by addition of viscosity index improver. Furthermore, the viscosity index improver itself, and other additives such as dibutyl-p-cresol (DBPC) antioxidant, are more polar and better solvents for the oxidation products than the base oil itself. These two factors, viscosity and increased solubility of the oxidized compounds in the base oils, seem to remain important in the catalytic stabilization process. As shown in Table IV, the difficulty of stabilization increases in order: K 3 < K2 < K1, which is also the decreasing order of viscosities and boiling ranges. One other possible contributing fador is that the more viscous oils are more easily alkylated and the degree to which they can be alkylated is also more favorable thermodynamically. From a practical point of view, this result suggests that the hydrocracked oil should not be cut to yield base stocks of lower boiling point than the desirable lowest boiling point product so as to avoid or minimize light and air instability. Effects of Paraffinic Reactants. The heavier the normal paraffins, the more readily they are cracked to produce the olefinic fragments for alkylation. In addition, the heavier the normal paraffin, the better the chance for saturated fragments to remain in the lubricating oil range and, upon isomerization, to constitute a lubricating oil
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 3, 1981 507
Table V. Effect of Hydrogen Pressure on Stabilization of Waxy Hydrocracked Oila
run no.
H, press., psig
10 11 12 13 14 15 16
0 50 350 1800 1800 1800
conditions temp, "F LHSV, V/V h control 500 500 550 700 750 750
0.35 0.35 0.35 5 5 10
ASTMC
0.599 0.770 0.252 0.205
6.5
5 5 6
Reactor: continuous flow; feed: W; H, circulation: 4000 SCF/B.
component resulting in lower yield losses. Consequently, heavier normal paraffins are preferred in this process. It should be noted that the "normal" paraffins we mean are those paraffm that can be converted by the shape selective catalyst. These include slightly branched isoparaffm, such as those found in the slack wax. Consistent with this postulate, the slack wax, as present in the waxy feed, is more effective than n-hexadecane in stabilizing the hydrocracked oil (cf. Tables 111and N).All the components in the slack wax boil above 650 O F , while n-hexadecane boils at 548 OF. It is fortunate that the slack wax can be used effectively as the paraffinic feed which enables the process to accomplish both oil stabilization and dewaxing simultaneously. Effect of Process Variables. A. Reaction Temperatures. The reaction temperature is the most important process variable. It has to be higher than the incipient cracking temperature so that the necessary olefm can be produced from the paraffinic reactants. This incipient temperature is about 400-500 OF depending on the nature and boiling range of the paraffinic reactants. At the optimum temperature, the rate of cracking is just sufficient to produce the necessary level of olefins at the given space velocities. This optimum range of operation temperature appears to be between 450 and 550 OF (see Tables I11 and IV). At higher temperatures, the equilibrium constant for alkylation becomes less favorable. In addition, the cracking rate becomes excessive, resulting in loss of yield. Furthermore, the coking tendency increases resulting in rapid catalyst aging. The wide optimum temperature range of 125-150 O F is very important is process operations. The process temperatures can be gradually increased as the catalyst ages to maintain the constant reactivity. The wider the optimum temperature range the longer the operation cycle and the less frequent catalyst regeneration. B. Space Velocity. Within a reasonable range, the space velocity and reaction temperature are interchangeable for attaining the desirable severity. When the reaction temperature is increased from 400 to 450 OF, the space velocity can be increased from 1/3 to 1 v/v h (see Table 111). Even though more extensive studies are yet to be done, this result suggests an apparent activation energy of 19 kcal/mol. This figure is comparable with that for cracking of paraffins of 30 and 15 kcal/mol for kinetic and diffusion controlled reactions, respectively. In fact, it is quite close to that expected for a diffusion-controlled case as can be expected for small pore size zeolites. It is noted that the typical activation energy for alkylation of aromatics with olefins over acidic catalysts is much lower at about 12 kcal/mol. These facts imply that the overall reaction rate is controlled by cracking of paraffins. C. Concentration of Paraffinic Reactants. In order to provide enough olefinic intermediates to assure more complete alkylation, the concentration of the paraffinic reactants should be as high as practical. As shown in Table
product stability, h
color ODb
40 48 115 goo+ 500+ 500+ 500+
Optical density at 546 pm.
pour pt, O
F
115
0 -30 -5
ASTM D1500.
111, apparently 7 wt % of n-hexadecane is sufficient to stabilize the oil. Since the waxy hydrocracked oil generally contains about 15-20% of wax, it should be sufficient to stabilize the oil. Good results were obtained in stabilizing the waxy hydrocracked oil (Table IV). In this investigation, no attempt was made to find the minimum concentration of paraffinic reactants required, but it was estimated to be 5-6 wt %, which is considerably lower than typical waxy hydrocracked oils. D. Hydrogen Pressure. Most of the experimenh were conducted in the absence of hydrogen at a reactor pressure below 150 psig. The results from runs with hydrogen pressures at 350 and 1800 psig are shown in Table V. I t looks as if the reaction temperature has to be increased in the presence of hydrogen, particularly at higher pressures. This is consistent with the fact that hydrogen inhibits catalytic cracking, the rate-controlling step in this overall treating process. In fact, when the pressure was increased to 1800 psig, comparable to that of the hydrocracker itself, the reaction temperature for this catalytic stabilization process had to be increased to 720-750 O F , which is again the typical reaction temperature of the hydrocracker. Thus, it appears feasible to integrate this catalytic treatment with the hydrocracker to minimize the processing cost. This integration could be accomplished by addition of a reactor with the proprietary catalyst operating as a second stage reactor at essentially the same conditions as the hydrocracker. Alternatively, the catalyst in the last zone of the hydrocracker could be replaced with the proprietary zeolite catalyst. Since the typical hydrocracker is operated at 0.5 to 1 LHSV, and since stabilization is achieved at 5-10 h-' space velocity att 720-750 OF (Table V), the volume of the zeolite catalyst needed is about 10% that of the hydrocracking catalyst. Effects of Catalytic Treating on Product Quality as Lubricating Oil Base Stock. The catalytic treating process is effective in stabilizing hydrocracked lubricating oils as described above. This stabilization effect is achieved in mild conditions without affecting basic characteristics of the oil. Nevertheless, its effects on other pertinent properties as lubricating oil base stock are also assessed. A. Color. The color of the catalytic treated products were the same as the feed or lighter, particularly when it was conducted in a hydrogen atmosphere. B. Oxidation Stability. Oxidation stability of the oil as measured by B-10 test was generally improved by this catalytic treatment (Yan, 1976). In this test, the oil is heated in the presence of aluminum and lead wires and air for an extended period of time. The change in the neutralization number, or increase in acidity and increase in viscosity of the oil are measured. The increase in acidity and viscosity of the treated oil were generally decreased by 20 to 50%,indicating that the oxidation stability of the oils was improved in the catalytic treating. C. Viscosity Index. Since the n-paraffins (the high viscosity index components) are selectively cracked, the
508
Ind. Eng. Chem. Process Des. Dev. 1981, 20, 508-511
viscosity index of the products is decreased, in the manner similar to that occurring in conventional solvent dewaxing. Removal of waxes is needed to decrease the pour point of the oil to meet the specification as lubricating oil. The dewaxing selectivity defined as the decrease in viscosity index per degree of pour point lowering for the catalytic treatment was found to be about the same as the solvent dewaxing. Conclusions It is well known that hydrocracked lubricating oils are unstable and form sediment upon exposure to light and air. Such unstable oils can be stabilized by catalytically treating them with paraffins over shape selective proprietary zeolite catalysts. In practice, the waxy hydrocracked oils which contain slack wax can be treated directly over the catalyst to simultaneously stabilize them and decrease their pour point to specification. This catalytic treating process can be integrated with the hydrocracker by adding a second stage reactor or replacing the catalyst in the last zone. The reaction sequence includes shape selective cracking of the normal paraffins (or slack wax) to form olefinic intermediates, which in turn alkylate the sludge forming precursors and aromatic compounds in the oil. Both catalytic cracking and alkylation reactions are catalyzed by the proprietary zeolite catalyst. The mechanism of hydrocracked oil stabilization involved in this catalytic stabilization process has not yet been ascertained, but it
is postulated that the sludge precursors are deactivated and the base oil itself is improved in its ability to dissolve the oxidized product by alkylation with olefins obtained in the course of normal paraffin cracking.
Literature Cited Argauer, R. J.; Landoh, G. R. (To Mobil Oil corp.) U S . Patent 3 702 888, Nov 1972. Assef, P. A. API Proc., Dlv. Ref. 1970, 50. 775. Bryer, R. P.; Dklot, F. E. SAE Pap. 730-781 (Sept 1973). Espenscheid, W. F.; Yan, T. Y. (To Mob11 Oil Corp.) U.S. Patent 3 853 749, Dec 1974. Franz, W. G.; Smilskl, M.T. (To Mobil Oil Corp.) U.S. Patent 3 562 145, Feb 9, 1971. Frlllette, V. J.; b a g , W. 0.; Lago, R. M. J. Catal. 1981, 67, 218. Gilbert, J. 0.; Walker, J. 8th WorMPet. Congr. 1971, 4, 147. l$&ocarbon Process. 1978, 57(5), 185. Kokotallo, G. T.; Lawton, S. L.; Olson, D. H.; M e r , W. M. Nature (London), 1978 272, 437. Langlols, G. E.; Cerrho, E.; Whlte, R. J. (To Chevron Research Co.) U S . Patent 3 463 724, Aug 1969. Orkin, B. A.; Braid, M. (To Mobil Oil Corp.) U.S. Patent 3 438 334, Aprl 1989. Stelnmetz, I.; Reif, H. E. API Roc., Mv. Ref. 1973, 53, 702. Vlugter, J. C.; Van't Spijker, P. 8th WorM Pet. Congr. 1971, 4, 159. Yan, T. Y. (To Mobil Oil Corp.) US. Patent 3989617, Nov 1978. Yan, T. Y. Ind. Eng. Chem. Prod. Res. Dev. 1978, 17, 368. Yan, T. Y.; Brldger. R. F. (To Mobil Oil Corp.) U.S. Patents 3 928 171, Dec 1975; 4 181 597, Jan 1980.
Received for review September 5, 1980 Accepted March 16, 1981 Presented at the Division of Petroleum Chemistry, Second Chemical Congress of the North American Continent, Las Vegas, Aug 1980.
Correlation of the SolubMty of Carbon Dioxide in Hydrocarbon Solvents Herbert M. Sebastlan, Ho-mu Lln, and Kwang-Chu Chao' School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907
A correlation is developed for the solubility of carbon dioxide in hydrocarbon solvents at temperatures from 340 to 700 K and pressures up to 170 atm. The fugacity of dissolved carbon dioxide at zero pressure is correlated as a function of solubility parameter and temperature. The high-pressure fugacity is obtained upon applying a Poynting correction for which the required partial molal volume of carbon dioxide is correlated as a function of temperature. The Henry constant of carbon dioxide is Included in the correlation. When compared with 339 experimental data points of 15 mixture systems, the correlation shows an overall average absolute deviation of 6%.
Introduction The solubility of carbon dioxide in hydrocarbon solvents is of interest to a number of industrial processes. Carbon dioxide is found in petroleum reservoir fluids, natural gases, coal gases, and liquids. Carbon dioxide flooding is a method of tertiary oil recovery. As a consequence of this interest, a substantial amount of vapor-liquid equilibrium data of C02-containingmixtures has become available in the literature. In this work we develop a correlation of the fugacity of dissolved carbon dioxide in liquid hydrocarbon solutions. The fugacity is expressed as a function of temperature, pressure, and concentration with solubility parameter 0196-4305/81/1120-0508$01.25/0
Table I. Constants in Eq 3 A, A, A3
A4
A5 A6
3.4156 7.1715 X -4.1542 X 1.4655 X -8.7574 x 10-8 -1.2158X l o 3
lo-)
employed to characterize the solutions. Correlation of Fugacity Sebastian, Lin, and Chao (1981) recently developed a correlation of solubility of hydrogen in hydrocarbon solvents. The method employed in this work for the corre0 1981 American Chemical Society
