Znd. Eng. Chem. Process Des. Dev. 1986, 25, 270-273
270
peak at about 180 "C (characteristic of some hemicelluloses or celluloses), the outstanding feature was a large exothermic effect between 360 and 500 "C, with a magnitude of -40.6 kcal/kg. This reaction also corresponds to the region of maximum yield of organic liquids and so must represent the primary thermal decomposition process to yield gases, liquid, and char. It is probable that secondary reactions are minimzed in the fluid-bed reactor because of both the short residence times and the relatively low pyrolysis temperature at maximum liquid yield. As a general comment on the degree of uncertainty in the values given for pyrolysis product yields, it should be realized that all values are actual experimental data and have not been normalized or adjusted in any way. In most of the bench-scale runs, material balances closed within 95-100%. Some of the losses are probably volatiles boiling under 100 "C,with normal experimental error accounting for the rest. In general, any given yield is estimated to be accurate to within about *5% of the value given and, for most of the data, accurate to within *2%. Reproducibility was good, with replicate runs falling usually within the 2-5% error limit. Tests were normally done in random order, also. Work done with the same apparatus as that employed in this work but using biomass (wood) feed has shown that at the conditions used, the reactions occurring are not limited by heat-transfer processes and probably not by mass transport. Inasmuch as the desired oil product is largely an intermediate component in the pyrolytic decomposition process, the results probably demonstrate a kinetically controlled system of reactions. In summary, short residence time fluid-bed pyrolysis of dried raw sewage sludge, or raw plus activated sludge, can give a high yield of liquids of up to 53% of the organic matter fed. The oil produced appears to be largely ali-
phatic with a moderate oxygen content (10-15%) but with 5-7 70nitrogen. The solid residue is about 80% inorganic matter but could be burned if desired. Because this appears to be one way of disposing of excess sludge and because the oil appears to have some promise as a source of hydrocarbon fuels, further investigation of the flash pyrolysis of dried sewage sludges and of the pyrolysis products would seem t o be worthwhile. Acknowledgment We express our thanks to the Canada Centre for Inland Waters, Environment Canada, for the financial support of this work. The encouragement and assistance of Trevor Bridle and of Herbert Campbell of the Canada Centre for Inland Waters is also acknowledged with appreciation. Registry NO.Hz, 1333-74-0;CO, 630-08-0; COP, 124-38-9;CH,, 74-82-8; CzH4, 74-85-1; CZH,, 74-84-0.
Literature Cited Bayer, E.; Kutubbudin, M. Proc. Int. Recycl. Congr. 1982, 1. Bridle, T. R. Environ. Technol. Lett. 1982,3 , 151-156. Bridle, T. R.; Campbell, H. W. ENFOR Third CanadIan Biomass Liquefaction Experts Meeting, Sherbrooke, Quebec, Sept 1983a (National Research Council of Canada, Ottawa). Bridle, T. R.; Campbell, H. W.; Sachdev, A.; Marvan, I. Prepr.-Ann. Conf. Can. Soc . Chem. Eng . 1983b, 1. Chem. Eng. 1981,88(25), 14. Prober, K. W.; Bauer, H. F. "Fuels from Waste"; Anderson, L. L., Tillman, D. A., Eds.; Academic Press: New York, 1977; pp 73-85. Scott, D. S.; Horllngs, H. Environ. Sci. Technol. 1975, 8 , 849-855. Scott, D. S.; Piskorz, J. "Fuels from Biomass and Wastes"; Klass. D. I., Emert, G. H., Eds.: Ann Arbor Scientific: Ann Arbor, MI, 1981; Chapter 23, pp 421-433. Scott, D. S.: Piskorz, J. Can. J. Chem. Eng. 1982a,6 0 , 666-673. Scott, D. S.; Piskorz, J. Ind. Eng. Chem. fundam. 1982b,27, 319-322. Scott, D. S.; Piskorz, J. Can. J. Chem. Eng. 1984, 62, 404-412.
Received for review November 9, 1984 Revised manuscript received June 11, 1985 Accepted July 24, 1985
Catalytic Treatment of Lube Base Stock for Improving Oxidation Stability Tsoung-Yuan Yan Mobll Research & Development Corporation, Central Research Laboratory, Princeton, New Jersey 08540
Two approaches have been successfully demonstrated to convert hydroaromatics present in typical lube oil base stocks to more stable products. The first approach involves catalytic treatment of lube base stocks over HZSM-$type catalysts via catalytic dehydrogenation and opening of the naphthenic rings. The second approach is via oxidative dehydrogenation of the naphthenic rings using molecular oxygen in the presence of base catalysts at low temperatures. Both treatments are effective in improving the oxidation stability and could be useful in upgrading marginal base stocks to acceptable products. The operating conditions can be chosen to minimize darkening of the oil.
Oxidation stability and resistance to form sludge are the most important quality parameters of lubricants. It is true that the lube oil acceptability is primarily judged by performance of the formulated product, but base stock properties can play an important role in determining the quality of the finished product. There are great differences in oxidation stability of lube base stocks derived from different crude origins. These differences result from variations in chemical composition 0196-4305/86/1125-0270$01.50/0
due to the genesis and the nature of the reservoir as well as refining conditions. Oxidation stability of mineral oil has been the subject of many investigations (Burns and Greig, 1972; Furby, 1972). It is generally recognized that certain aromatics, particularly polycyclic, contribute to the natural oxidation stability of the base oil and that there is an optimum concentration of such aromatics for maximum base oil stability (Von Fuchs and Diamond, 1942; Zimina et al., 1974). With model systems, Mahoney found 0 1985 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986 271
Table I. Catalytic Treatment of Base Oil" feed run no. operating conditions temp, "F LHSV, v/v h product yield, wt % h2 gas I t productb lube product quality color 1.5 B-10 AKV, % 269 ANN, mg of KOH/g of oil 21 lead loss, mg 320 bromine no. 0.6
1
la
2
3
3a
4
600 1.0
600 1.0
575 1.0
600 0.5
600 1.5
575 0.5
C
C
C
0.2 11.3 88.5
0.2 7.5 92.3
0.2 3.7 96.1
0.01 0.2 5.0 94.8
0.003 0.2 9.8 90.0
0.2 3.4 96.4
2.5
2.25
3
3
2.25
3
78 9.0 19 1.4
102 10.6 18 0.8
84
76 9.8 8 1.0
71 8.4 21 0.7
67 8.7 5 1.0
34 0.8
c
aBase oil, Mid-Continent heavy neutral; catalyst, HZSM-5; pressure, 0 psig; H2 flow, none. bIncludes losses due to handling. 'Not determined.
that inhibition by polynuclear aromatics increases exponentially with the linearity of ring conjugation (Mahoney, 1964,1965), and that the mechanism of antioxidation is primarily via scavenging of free radicals. Bridger et al. (1974) discovered that some lube oils are particularly unstable to oxidation in the presence of base and metal catalysts. They attributed the instability of these oils to the presence of the hydroaromatics. Hydroaromatics are partially hydrogenated aromatics. Such molecules are particularly susceptible to oxidation and are the leading causes for the formation of corrosive acids and sludge. To test and apply the latter theory, we studied two methods for improving the oxidation stability of lube base stock by using the following mechanisms: 1. catalytic dehydrogenation and ring openings of hydroaromatics; 2. oxidative dehydrogenation of hydroaromatics with oxygen. Experimental Section The base stock was a heavy neutral obtained by furfural extraction. Its pertinent properties were as follows: API gravity, 30.0'; pour point, 5 O F ; flash point, 425 O F ; sulfur, 0.27 wt %; nitrogen, 28 ppm; aniline point, 219.1 O F ; S.U.S. viscosity at 100 O F , 232 s; viscosity index, 97; and ASTM color, 1.5. The catalysts examined were as follows. 1. HZSM-5. The synthesized catalyst was converted to the acid form by ion exchange with NH4NO3and by air calcination. Properties of the finished catalyst were Si02/A1203= 70 and a cracking activity = 150. 2. NaX. The commerical Linde 13X was calcined at 800 O F . In some experiments, the NaX was sulfided with H2S before use. 3. Rb-NaX. NaX was impregnated with CH3COORb to 5% level and calcined. 4. CsY. NaY was exchanged exhaustively with Cs+ and calcined. 5. Rb-Na/Silica Gel. Davidson silica gel was impregnated with Rb2C03and Na2C03,each to 5% level and calcined. 6. Potassium/Zinc Ferrite. Zinc ferrite was impregnated with K2C03to 5% level and calcined. 7. Sodium/B-Alumina. 0-Alumina was impregnated with Na2C03to 5% level and calcined. The impregnation levels reported were based on metal content. The calcination temperature for the catalysts was 1000 O F . Experimental Procedure. Catalytic Treatment. Catalysts (20 cm3) were packed into a microreactor and heated to the desired reaction temperature. The base stock feed was pumped downflow through the reactor at the desired rate. After lining out for a period of 5 h, the gas
and liquid products were collected and material balances calculated. The liquid product was distilled to drive off the materials boiling below 650 O F . The bottom lube fraction was tested for color (ASTM D1500), oxidation stability (B-10 test), and bromine number (D1159). The gaseous products were analyzed by using a mass spectrometer. Oxidative Dehydrogenation. The feed was passed over the catalyst in an upflow reactor at 1 LHSV, atmospheric pressure, and the desired temperature. Air was cofed with oil at a rate of 5 cm3 of air/cm3 of oil. The product was stripped of any light product and water at an equivalent temperature of 650 O F and examined in accordance to the B-10 procedure. Substantial oxygen uptake was observed qualitatively but not quantitatively. Oxidation Stability (B-10) Test. This evaluation of the resistance of the lubrication to oxidation by air under specified conditions is measured by the changes in neutralization (ANN) number and viscosity (AKV), and the loss of lead specimen due to corrosion. The oil sample is placed in a glass oxidation cell together with iron, copper, and aluminum catalysts and a weighed lead corrosion specimen. The cell and its contents are maintained in a constant temperature bath at 325 O F (163 "C), and 10 L/h of dried air is bubbled through the sample for 40 h. At the end of the test, the oil sample is removed from the cell, and the neutralization number (NN) (ASTM D664) and kinematic viscosity (KV) at 100 "C (ASTM D445) of the oil are determined. Changes in NN and KV in comparison with the initial values of the oil, leading to ANN and AKV, respectively, are then calculated. The lead specimen was weighed to determine the loss in weight and thus measure the corrosion effects. Results and Discussion The results of the catalytic treatment over HZSM-5 and of the oxidative dehydrogenation over various catalysts are shown in Tables I and 11, respectively. Catalytic Treatment over HZSM-5. Efficacy of Catalytic Treatment over HZSM-5. The oxidation stability of the base stock as measured by B-10 was significantly improved (see below for details and definitions of terms). In comparison with the original feed, hKV decreased from 269% to 67%, the ANN decreased from 21 to 8.7 mg of KOH/g of oil, and the lead loss due to corrosion decreased from 320 to 5 mg (run 4). Such improvements should be useful in the commercial upgrading of marginal stocks. Process Conditions. In order to assess the reproducibility, runs 1 and 3 were repeated (Table I). Considering the complexity of the experiment and of the B-10 test, the
272
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986
Table 11. Catalytic Treatment of Base Oil with Air" run no. feed 11 12 13 NaX NaX catalyst description Rb (5) treatment operating conditions temp, O F product inspection color 1.5 B-10 (325 O F , 40 h) U V , Yo 269 A",mg of KOH/g of oil 21 lead loss, mg 320 bromine no. 0.6
calcined
14
calcined
calcined
550
400 300
400
6
5.5
56 7.6 132 1.0
71 57 9.3 5.4 59 0.7 0.6
2
15 16 &alumina (Na 5%)
21 zinc ferrite
20 NaX
5 (5%) sulfided calcined
200
300
200 200
200
7.25 2
2.25 2.25
3.5
2
2
2.25
64 5.4
49 8.2
47 8.2
52 8.2
64 10.1
63 8.5
38 7.1
44 7.6
0.6
0.6
0.6
0.6
0.6
0.5
0.6
0.6
200
250
17 18 19 CsY silica gel (via Ex) Rb (5%) Na (5%) calcined calcined
Base oil, Mid-Continent heavy oil; pressure, 0 psig; LHSV, 1 v/v h; 02,5 cm3/cm3 of oil.
reproducibility of these runs was rather good. At space velocities of 0.5 and 1.0, the temperature required to achieve a significant improvement in oil stability appears to be between 550 and 600 O F . Considering both the product quality and yield, the best operating conditions appear to be 0.5 LHSV and 575 O F . Feed Conversion. It is observed that a yield loss due to cracking of about 5% or higher to the lighter product is required to achieve improvement in the product stability (cf. runs 5 and 6 and 3 and 4). For the same level of improvement in product stability, product yield loss appears to be lower with decreasing temperature and decreasing space velocity. Light Products. The light produds are mostly gasoline boiling range material with less than 0.2 wt % dry gas. In all runs, between 0.003 and 0.01 wt % H2 was produced. Since the molecular weight of the base stock was about 550, this represents 0.0083-0.0275 mol of H2/mol of feedstock. A t the lower reaction temperatures of 500-600 OF, the hydrogen production is due to dehydrogenation of hydroaromatics containing labile H2 The product tends to become darker, and the ASTM color increases from 1.5 to between 2 and 3. Possible Mechanism. The improvement of oil quality in metal catalyzed oxidation is likely to be due to the catalytic conversion of the hydroaromatic compounds in the feed. The possible reactions are as follows. Dehydrogenation. The HZSM-5 catalyst has sufficient hydrogen-transfer activity to dehydrogenate reactive hydroaromatics. This is supported by the fact that molecular hydrogen in amounts between 0.003 and 0.01 wt % was produced. The increase in the olefin content of the products as indicated by the increase in the bromine number supports the notion that the operating conditions are not hydrogenative but that dehydrogenation reactions can occur. Opening of the Hydroaromatics Ring via Cracking. Naphthenic rings are known to be susceptible to acidic cracking. Over strong acidic catalysts at low temperatures, ring-opening reactions for conversion of hydroaromatics could become comparable with dehydrogenation reactions. Oxidative Dehydrogenation. Oxidation Stability Improvement. Oxidative dehydrogenation over base catalysts improved the oxidation stability of the lube base stock. When the feed was treated with O2over NaX (run 20) and tested according to the B-10 test, the AKV decreased drom 269% to 38% and ANN decreased from 21 to 7.1 mg of KOH/g of oil. It is believed that such improvements could be sufficient to upgrade the marginal stocks to acceptable products. Effect of Catalysts. Six base catalysts, namely, NaX, Cs/Y, Rb/NaX, Na/B-alumina, Rb-Na/silica gel, and
potassium/zinc ferrite, were tested with good results (Table 11) and suggest that the important characteristic of these catalysts is their basicity. The nature of the support does not appear to be critical; NaX, Y, &alumina, silica gel, and zinc ferrite serve as the support equally well. The nature of the base or the method of deposition is not critical. Na, K, and Rb were equally active whether deposited by impregnation or ion exchange. Operating Conditions. A reaction temperature of 200 O F was effective in improving the oxidation stability of the product (run 20, Table 11). The oxidation stability of the product did not improve further as the reaction temperature was increased. This could be due to excessive oxidation. In run 11, where the reaction temperature was 550 O F , a small amount of carbonyl compounds was detected by IR. In addition, excessive oxidation darkened the product significantly. In run 14, the ASTM color of the product was 7.5. Coloration of the product is one of the most important drawbacks for commercial acceptance. For this reason, the treating temperature should be as low as possible to minimize the color deterioration of the product. Color Improvement of the Treated Product. Since oxidative dehydrogenation inherently darkens the oil product, some decolorization techniques have been considered. The darkened oil can be readily decolorized to the original level by furfural extraction. To avoid the additional solvent extraction cost, the oxidative dehydrogenation treatment can precede the furfural extraction step for aromatics removal in the lube-refining process. Another approach is selective hydroprocessing. Audeh and Bridger (1974) succeeded in using CoMo/A120, at 160 "C, 1LHSV, and 200 psig of H2to decolorize the darkened oil to lighter than the original oil (1vs. 1.5) without loss of the oxidation stability obtained by the dehydrogenation treatment. Apparently, this procedure removes the color bodies without rehydrogenating the aromatics to labile hydroaromatics. Possible Reaction Mechanism. The hydroaromatic compounds are dehydrogenated to stable aromatics as shown below: boa0 C O t O y l l
a +
/
H20
/
The base catalysts evidently allow the reaction to take place selectively at lowest temperatures. Some nonselective oxidations do occur at higher temperatures and lead
Ind. Eng. Chem. Process Des. Dev. 1986, 2 5 ,
to the formation of oxygenated products, such as aldehydes and acids. Such carbonyl compounds have been detected by using IR in runs at high temperatures. They can be highly colored and cause darkening of the oil. The base catalysts are believed to activate acidic hydroaromatics through a mechanism similar to base-catalyzed oxidation. Comparison of the Two Methods. Notwithstanding the differences in catalysts, reactants, and operating conditions for the two treating methods, the improvements in the oxidative stability of the products are surprisingly similar (cf. Tables I and 11). At best operating conditions, the B-10 test showed that AKV was -70; and -40%, A" was -9 and 8 mg of KOH/g of oil, and lead loss was -5 and 60 for catalytic treating and oxidative dehydrogenation, respectively. These results underscore the similarity in the overall reaction, i.e., conversion of the labile hydroaromatics leading to stable products. Additional studies aiming at elucidating the reaction mechanisms could be an interesting and rewarding research. The conditions for both methods are sufficiently mild and can be implemented readily with conventional equipment. Even though the catalyst systems in this study were stable during the 5-14 days to demonstrate the principles involved, extended aging study and further development are required to establish process viabilities for commercial processes. Summary Oxidation stability is one of the most important qualities of lube base stock and the presence of the labile hydroaromatics compounds is one of the main causes for the instability. The oxidation stability of base stocks can be
Kinetic Model of CH,-C0,-Steam
273-277
273
improved by converting hydroaromatics to more stable compounds. Two approaches for conversion of hydroaromatics have been successfully demonstrated, namely, catalytic treatment over acidic catalyst and base-catalyzed oxidative dehydrogenation. HZSM-&type catalyst was effective for conversion of hydroaromatics by catalytic dehydrogenation and ring opening of the naphthenic rings at LHSV of 0 . 5 1 and 550-600 O F . All base catalysts tested were effective for oxidative dehydrogenation at the optimum reaction temperature of about 200 O F . The catalytic treatments tested significantly improved the oxidation stability of lube oil base stocks and thus should be particularly useful in upgrading marginal stocks. The operating conditions need to be chosen to minimize colorization of the oil. Literature Cited Audeh, C. A.; Bridger, R. F. Mobil R 8 D Corp., Princeton, NJ, private communicatlon, 1974. Bridger, R. F.; Johnston, 8. E.; Heiba, E. I . Mobil R & D Corp., Princeton, NJ, private communication, 1974. Burns, A. J.; Greig, G. J . Inst. Petrol. 1972, 5 8 , 346. Furby. N. W. NASA Symposium, Interdisciplinary Approach to Liquid Lubricant Technology, Cleveland, OH, Jan 11-13, 1972, Proceedings Preprint, VOl. 1, p 2.1. Mahoney, L. R. J . Am. Chem. Sac. 1964, 8 6 , 444. Mahoney, L. R. J . Am. Chem. SOC. 1965, 8 7 , 1089. Von Fuchs, G. H.: Diamond, H. Ind. Eng. Chem. 1842, 3 4 , 927. Zimina, K. I.; Klimov, A. K.; Radchenko. E. D.; Bezhanidze, A. M.; Ivanov, V. I . Chem. Tech Fuels Oils 1979, 75, 505-509.
Received for review January 23, 1985 Revised manuscript received July 17, 1985 Accepted August 1, 1985
Reaction at High Temperature
Junhong Liu,' Fengql Wang, and Guofa Wu Department of Ironmaking, Central Iron and Steel Research Institute, Beijing, China
The catalytic reaction of CH, with CO, and steam is studied in an integral flow reactor over a nickel checkerwork catalyst and temperature range of 1218-1373 K at 1.1 atm. Conversion data based on crude catalyst and influenced by interior mass transfer are obtained for CO,/CH, = 0.9 and CO,/H,O = 1.45 (molar ratio), which are successfully f i e d to an exponential second-polynomial spline function. An approach involving stepwise regression and optimization is used to determine kinetic parameters. The model developed that reasonably represents the epxerimental data is given by eq 10. This model is based on the assumption that the mechanism for the reaction is CH, H,O = CO 3H, followed by the reaction COP H, = CO H,O. The experimental resutts demonstrate that the latter reaction is not at equilibrium and its direction is not alternated during the reaction.
+
+
+
The catalytic reaction of CH4 with steam has received much attention in recent years. Most investigators have only aimed at studying the reaction rate and mechanism of CH,; however, in order to predict the composition of products of the CHI reaction with steam or unravel the kinetic process of the reaction, at least two primary independent reactions are required to make a kinetic model. Allen et al. (1975) have studied the reaction over a nickel catalyst in a fixed-bed reactor at 911 K and have derived the kinetic model expressions
+
pcH4pH20)/( PH?
1
+ KaPH20+
PCH)'H,O + K~KsIKs~
KaKSl PH23
pCH4pHz02)/(
+
PH: PCH4PH20
* To whom
correspondence should be addressed a t the Department of Metallurgic Engineering. -. Wuhan Iron and Steel University, Wuhan, Hibei, China.
KaPHzO
+ KaKSl PH23
on the assumption that desorption of the COz and CO
0196-4305/86/1125-0273$01.50/00 1985 American Chemical Society
