Ind. Eng. Chem. Process Des. Dev. 1980, 25, 265-270
which implies
= -1
0,
t
(B.5)
Assuming, however, that r = 0 (the worst case), we see that (B.5) is still a good approximation. Consider that for 7 = 0, the crossover frequency is determined explicitly by
For C / O
> 1.7,
>> (1/212 and therefore w, r
1
E
265
Brosilow, C.. personal communication, Case Western Reserve University, Cleveland, OH, 1983. Cohen, G. H.; Coon, G. A. Trans. ASME 1953, 75, 827. Doyle, J.; Stein, G. IEEE Trans. Autom. Control 1981, AC-26, 4. Frank, P. M. "Entwurf von Regelkreisen mit vorgeschriebenem Verhaken"; G. Braun Verlag: Karlsruhe, 1974. Garcia, C. E.; Morari, M. Ind. Eng. Cbem. Process Des. Dev. 1982, 27, 308. Holt, 8 . R.; Morari, M. Chem. Eng. Scl.. in press. Holt, B. R.; Morari, M. Chem. Eng. Scl. 1985, 4 0 , 59. Lau, H. K.; Balhoff, R. A. personal communication, Sheii Development, Houston, TX, 1984. Rivera, D. M.S. Thesis, University of Wisconsin, Madison, 1984. Rosenbrock, H. H. "Computer-Aided Control System Design"; Academic Press: New York, 1974. Shinskey, F. G. "Process Control Systems"; McGraw-Hill: New York, 1979. Smith, C. L. "Digital Computer Process Control"; Intext Educational Publishers: Scranton, PA, 1972. Wiberg, D. M. "State Space and Linear Systems"; Schaum, T., Ed.; McGrawHill: New York, 1971. Ziegler, J. G.; Nichols, N. E. Trans. ASME 1942, 6 4 , 759.
Received for review July 10, 1984 Revised manuscript received July 22, 1985 Accepted August 1, 1985
L i t e r a t u r e Cited Astrom, K.; Hagglund, T. IFAC Workshop on Adaptive Control, Sari Francisco, 1983.
Flash Pyrolysis of Sewage Sludge Jan Piskorz, Donald S. Scott," and Ian B. Westerberg Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G 1
A dried mixture of raw and activated sewage sludge was pyrolyzed in a bench-scale fluidized-bed reactor at residence times of less than 1 s over the temperature range 400-700 O C . Organic liquid yields of up to 52% maf were obtained at the optimum temperature of 450 OC and 0.55-sresidence time. Shorter reaction times gave slightly higher liquid yields. The effects of reaction atmosphere, char accumulation, and deashing on liquid yields were also investigated. A test in a larger unit at a feed rate of 2 kg/h duplicated the bench-scale result. From elemental analyses, the char appears to be aromatic in character, while the liquid tar product has a H/C atomic ratio of about 1.77. A certain amount of water-soluble alcohols, ketones, etc., appear to be present also.
Treatment of municipal and industrial wastewaters generates significant quantities of sludge, particularly if biological processes are used. The cost of disposal of these sludges, whether treated or untreated, has increased greatly in recent years, and it has been estimated that the disposal cost is now 50% of the total wastewater treatment cost. Some recently used disposal methods may become more restricted in future years, for example, landfill, water, or ocean disposal and agricultural use. In 1980, sludge disposal costs were estimated to be $208/ton in Canada, $182/ton in the United States, and $162/ton in the European Economic Community (Bridle, 1982). There is an urgent need for alternate solutions to the sludge disposal problem, and one of these may be the conversion of sludge to a liquid fuel. Sludge combustion has been practiced for a long time in a variety of processes but is normally a net consumer of fuel and often encounters severe problems with ash clinkering or slagging and with air pollution. The possibility of converting municipal waste to a useful fuel oil was demonstrated several years ago by the development of the Occidental pyrolysis process, which used a hot circulating flow of ash or char to rapidly decompose organic material (Prober and Bauer, 1977). More recently, German work has demonstrated that a synthetic crude oil could be produced from sewage sludge by heating at 300 0196-4305/86/1125-0265$01 .SO10
OC for 3 h under an inert atmosphere (Bayer and Kutubbudin, 1982). Workers at Battelle Northwest Laboratories have developed a similar process in which sludge is heated with sodium carbonate for 1h under an argon atmosphere (asquoted in "Chemical Engineering", 1981). The German process is claimed to be a net producer of energy if the sludge is dewatered. Bridle et al. (1983a, 1983b) in Canada have recently produced a good quality oil from a dried mixture of raw and waste activated sludge using a retort type of reactor at atmospheric pressure. Yields of up to 28% (dry basis) were obtained at 425 OC. A high proportion of aliphatic hydrocarbon was found in the pyrolytic oil produced. Another possible pyrolysis process which has been used successfully with various biomass materials, and with coal, for the production of liquids is the short residence time fluidized bed. The use of a fluidized bed of sand permits very high heating rates of the solid and the rapid removal of vapors formed by thermal decomposition of the feed. This process has been called flash pyrolysis and has been applied at atmospheric pressure to a wide variety of biomass materials by Scott and Piskorz (1981,1982a)with good yields of liquid products. The application of this process to dried sewage sludge will be described in the following sections. 0 1985 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986 267 Table I. Feedstocks Characteristics -.,.L~
.._a
lllu~~~ulc
feedstock 1 2 3
description -250 pm, runs 3-16 -250 pm, acid-washed, run 17 pilot plant feed, as received
% as is 6.23 0.0 5.91
ash, as is 90
b
C
42.48 37.54 42.20
41.30 35.67 39.69
H%
C%
as is 4.75 5.36 4.92
maf 57.14 58.39 56.48
as is 29.31 36.47 29.31
N 90 maf 7.91 8.58 8.21
as is 2.99, 2.54 3.49 4.01
maf 5.83, 4.95' 5.59 7.73
"Moisture content determined by drying at 105 "C. *Determined by combustion at 800 "C. This value used for maf calculations. Determined during elemental analysis (Perkin-Elmer 240C). Determined by micro-Kjeldahl. A 0
A
2 30-
40 CHAR YIELD TAR + C,' YIELD PILOT PLANT TAR YIELD U2
FEEDSTOCK NO I N2 ATMOSPHERE 0 555 S RESIDENCE TIME 60p -30 *6D OTT4WA SAND FLUIDIZED BED
A H,O
20t
s U
NI ATMOSPHERE 0555 I RESIDENCE
400
TEMPERATURE ('C)
Figure 2. Char and organic liquid yields.
mately 45% by weight of the dried sludge was less than 250 pm in size. On the other hand, the pilot plant test was done by using the entire feed as received with no screening and therefore used a much wider range of particle size than did the bench-scale runs. The fluidized bed in the bench-scale apparatus used spherical Ottawa sand, normally-595+250 pm in size (-30+60 mesh), although both larger and finer sand sizes were used when residence times were varied. The pilot plant reactor contained -841+595 pm (-20+30 mesh) sand. All tests were done at essentially atmospheric pressure, that is, from 102 to 110 kPa absolute. The residence time was defined as the pet empty reactor volume (reactor volume minus sand volume) divided by the total volumetric inlet gas flow rates expressed at reaction conditions. It is therefore an apparent vapor residence time. Actual reaction times would be slightly less (about 15%) because of the volume of volatile material generated during pyrolysis. Normal run time was 30-60 min. Figures 2-4 show the bench-scale results in a nitrogen atmosphere and at a constant residence time of 0.55 s plotted as a function of temperature. The maximum tar yield obtained was 51.9% maf basis at 400-450 "C. The maximum yield of organic liquids (tar + C4+)was 52.8% at 400 "C. A distinct and fairly strong maximum yield of organic liquids was obtained over the fairly narrow temperature range of 400-450 "C. The char yield, on the other hand, decreased steadily with increasing temperature, while the gas yield increased. This behavior is typical of fast pyrolysis of biomass materials in fluidized beds with short residence times. The water produced (product water only) showed much less variation with temperature (Figure 3) although a maximum water yield was obtained at about 550 "C. Figure 4 shows that all gases increased steadily in yield with temperature, a behavior which is typical of peat or lignite as well as cellulosic biomasses. Ethylene yields were significantly higher than methane yields at all but the lowest temperatures which is in contrast to results from biomass or coal, in which the reverse is generally the
YIELD
40
500 600 TEMPERATURE ("C)
700
Figure 3. Total gas and product water yield.
3 e2 ~
1
0FEEDSTOCK HZ 5 5 ATMOWHER/ 5 RESIDENCE NO I TIME 6 0 p -30 t 6 0 OTTAWA SAND FLUIDIZED BED
.k
n
z
0
403
500
600
700
TEMPERATURE ('C)
Figure 4. Yields of individual gases.
case (Scott and Piskorz, 1982). However, at the conditions for maximum liquid yield, the gas production is relatively small, about 8% only on an maf basis, with the great majority (over 80% by weight) being carbon dioxide. Pyrolysis was carried out in three different atmospheres at 500 and 650 "C,in nitrogen, methane, and hydrogen. Results are shown in Table 11. At 500 O C , there are no very pronounced influences of reaction atmosphere, although higher tar yields and lower gas yields were obtained in a hydrogen atmosphere and lower char yields and higher gas yields in a methane atmosphere. More significant differences are apparent in the results at 650 OC,as might be expected. In a hydrogen atmosphere, tar yields are sharply reduced and gas yields increased, particularly yields of light hydrocarbon gases. This is a typical result also observed in the pyrolysis of other types of biomass in hydrogen atmospheres a t higher temperatures (Scott and Piskorz, 1981). On the other hand, a methane at-
268
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986
Table 11. Effect of Reaction Atmosphere on Product Yields" 500 "C yields, % 650 "C yields, % maf maf reaction atm reaction atm H2 NZ CH4 H2 NZ CH4 run no. 3 11 12 10 7 13 20.2 10.7 8.8 char 14.7 11.1 11.0 tar 51.7 19.4 46.5 46.0 28.8 26.0 14.6 16.0 46.4 gas 12.4 40.7 37.4 15.3 18.0 HZO 13.5 17.2 12.5 14.1 HZ N.A. 0.25 0.19 N.A. 0.51 0.49 co 1.82 2.27 3.79 11.37 9.04 10.39 8.61 9.10 COZ 7.33 10.42 11.60 12.00 0.37 N.A. 4.07 CH4 0.42 2.21 N.A. 0.27 0.24 C2H4 0.22 4.84 4.10 3.58 1.92 0.16 0.24 C2H6 0.20 0.75 0.71 0.51 0.47 c3 0.55 4.24 3.18 2.73 c4+ 1.81 2.13 1.95 9.52 9.32 7.49 98.2 95.2 % recovered 96.0 95.7 96.5 94.1 ONote: all product yields expressed as % maf. The percentage recovered is based on the total amount of sewage sludge fed. Conditions: feedstock 1 [42.48% ash (as is), 6.23% H,O], 0.55-s vapor residence time.
Table 111. Effect of Gas Residence Time on Product Yields at 450 OC" yields, '70 maf, gas residence time, s 0.30 0.55 1.00 run no. 15 5 14 char 21.18 20.72 28.34 tar 53.70 51.88 43.53 9.95 11.51 gas 10.13 15.22 18.16 H20 10.44 0.12 0.08 HZ 0.26 co 1.07 1.16 1.45 7.21 8.14 6.53 COP 0.21 0.18 CH4 0.22 (!ZH4 0.11 0.11 0.11 C!2H6 0.12 0.11 0.09 0.27 0.28 c3 0.30 c4+ 1.52 0.77 1.19 % recovered 97.66 98.86 100.79 a Note: all product yields expressed as % maf. The percentage recovered is based on the total amount of sewage sludge fed. Conditions: feedstock 1 [42.48% ash (as is), 6.23% H,O], N2 atmosphere.
moshere showed much smaller differences from a nitrogen atmosphere than did hydrogen at 650 "C. Although at these temperatures, reaction of H2 or CH4 with ash components might occur, or the ash might be expected to show some catalytic effect on liquid production, neither of these possibilities appears to take place to any significant degree. However, at 650 "C, the presence of an atmosphere which can supply hydrogen appears to be somewhat detrimental to tar production. Table 111shows the effect of apparent gas residence time on the yields of various products at 450 "C in a nitrogen atmosphere. Tar yield and total organic liquids yield are both at a maximum at the shortest residence time of 0.30 s. This result is in agreement with other work carried out in our laboratories with a variety of biomass and coal feeds. Char yield increases sharply at long residence times at the expense of liquid yield, suggesting that the char or ash may exert a catalytic polymerization effect on pyrolysis fragments. The only significant change in volatiles is a substantial increase in pyrolytic water yield at long residence times, possibly a byproduct of condensation reactions. The increase in water production does not appear to be primarily due to secondary gas-phase reactions, such as the water gas reaction, inasmuch as there is a relative increase
Table IV. Effect of a Fluidized Bed of Hamilton Char on Product Yields at 450 "Ca fluidized-bed material -30+60 Ottawa sand +30 Hamilton char run no. 5 16 char 20.7 17.8 tar 51.9 40.3 10.0 14.6 gas 15.2 15.8 HZO 0.12 0.38 HZ co 1.16 1.46 7.21 9.41 COZ 0.21 0.33 CH4 0.11 0.14 CZH, 0.11 0.16 CZH6 0.27 0.40 c3 0.77 2.31 c4+ '70 recovered 98.9 94.0 Note: all product yields expressed as % maf. The percentage recovered is based on the total amount of sewage sludge fed. Conditions: feedstock 1 [42.48% ash (as is), 6.23% H,O], N2 atmosphere, 0.55-9 vapor residence time, fluidized bed, run 5, 60 g, -30+60 Ottawa sand, run 16, 39.96 g, +30 Hamilton char.
in the hydrogen content of the gases. One run was carried out to determine if the presence of large quantities of char for longer times had any significant effect on product yields. Char received from the Canada Centre for Inland Waters, which was prepared from the dried raw sewage sludge, was screened to recover a +595 Fm size fraction (14.6% of the char, density 1.65 g/cm3). This char was used in place of the sand in the fluidized bed at a temperature of 450 "C, residence time of 0.55 s, and a nitrogen atmosphere. Relatively little of the char, about 13.6%, was elutriated from the bed during the 30min run. Results obtained are compared in Table IV with those obtained when the fluidized material was sand. Tar yields are significantly reduced, while gas yields are increased. As the char is relatively high in sodium and calcium, both of which are known gasification and cracking catalysts, this result is not unexpected. It would appear that it would be advantageous to keep the char inventory in the bed low by blowing over char as it is formed, at least if maximum yields of organic liquids are desired. In order to determine if the high ash content of the feed was detrimental or advantageous in promoting the formation of organic liquids during flash pyrolysis, one run was carried out with a feedstock which had previously been acid extracted according to the methods proposed by Scott and Horlings (1975). Feed material was slurried with HC1 at an initial pH of 0.8. Additional acid was slowly added to maintain the pH at 0.8. The slurry was then heated to 90 "C and held there for 10 min, after which the slurry was filtered and the residue washed with distilled water. The filter cake was dried at 105 "C and then broken up and screened to obtain the -250-~mfraction. The acid extraction removed 41.0% of the ash and 18.7% of the organic material. Results obtained are compared to the normal feedstock in Table V. Tar yield is very significantly greater, per unit of acid extracted organic material fed, but only slightly greater per unit of original feedstock. Further, the organic liquids appeared to be rather different in character, and a much more stable fog was formed and very little condensed out in the condensers. Gas yield was also reduced somewhat, due almost entirely to a reduction in COPproduction. Similarly char yield was also reduced, so that liquid product appeared to increase at the expense of both gas and char. Hence, there appears to be a negative effect of much of the metal or alkaline cations on liquid production. In addition, it is possible that the extracted
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986 289 Table V. Effect of Acid Washing the Feedstock on Product Yields at 460 "C" yields, % maf, feedstock 1 (original) 2 (acid-washed) run no. 5 17 20.7 16.4 char 51.9 64.7 tar 10.0 7.4 gas 15.2 12.9 H20 0.12 H2 1.03 1.16 co 4.75 7.21 COZ 0.13 0.21 CH4 0.11 0.09 C2H4 0.07 0.11 C2H6 0.27 0.20 c3 1.17 0.77 c4+ 100.9 % recovered 98.9 Note: all product yields expressed as % maf. The percentage recovered is based on the total amount of sewage sludge fed. Conditions: feedstock 1 is the original feedstock [42.48% ash (as is), 6.23% H,O], feedstock 2 is the acid-washed feedstock [27.54% ash (as is), 0.0% H20], N2 atmosphere, fluidized bed, 60 g, -30+60 Ottawa sand, 0.55-9 vapor residence time.
Table VI. Comparison of Bench-Scale and Pilot Plant Pyrolysis of Municipal Sewage Sludge at 450 OC4 bench scale pilot plant PS-2 temp, "C 450 450 residence time 0.56 0.60 char 20.7 22.6 51.9 52.2 tar gas (total) 10.0 7.8 15.2 12.9 HzO H2 0.12 0.02 co 1.16 1.41 coz 7.20 5.15 CH4 0.21 0.33 C2H4 0.11 0.24 CZH6 0.11 0.11 c3 0.27 0.22 0.77 0.28 c4+ 7'0 recovered 98.9 91.7 feed rate 139.3 g/h 2.08 kg/h time, min 21.7 150.0 "Note: all product yields are expressed as % maf feed. The percentage recovered is based on the total amount of sewage sludge fed -as is". Conditions: bench scale (run 5) feedstock 1 [42.48% ash (as is), 6.23% H20], nitrogen atmosphere, fluidized bed, 60 g, -30+60 Ottawa sand. Pilot plant runs feedstock [42.20% ash (as is), 5.91% H,O], recycle gas atmosphere, fluidized bed: 2100 g, -20+30 Ottawa sand.
organic material contained carboxylate groups, which would account for the reduced C 0 2 yield, and that this extracted organic material did not readily form tars but gave high char yields in normal pyrolysis. A test was carried out at 500 "C in a larger pyrolysis unit with a dried sludge feed rate of approximately 2 kg/h.
This larger unit used a recycle product gas as the fluidizing gas-largely a C02and CO mixture-rather than nitrogen. As pointed out earlier, the whole feed was used, with no selective screening beforehand. The results of this test are shown in Table VI with a bench-scale run at comparable temperature and residence time shown for comparison. Comparison of results from the bench-scale unit and from the pilot plant, as shown in Table VI, suggests that very similar yields were obtained. The H20 and C02yields appear to be somewhat reduced in the pilot plant. However, considering the differences in operating conditions, the duplication of the results is good and supports the bench-scale results which suggest that at 450 "C the reaction atmosphere is not an important factor in determining yields. Comparison of the results from the fluidized bed with those reported by Bridle et al. (1983a, 1983b) from a kiln-type pyrolysis apparatus shows that very comparable yields are obtained for the various products although the organic liquid yield appears to be somewhat higher at optimal conditions from the fluidized bed, possibly because of its shorter characteristic residence time. In addition, the gas yield from the fluidized bed pyrolysis is much lower than that reported by Bridle et al. (1983b) and the pyrolytic water somewhat higher. Table VI1 shows the variation with temperature of some elemental analyses for the char and for both the heavier methanol-soluble tar and for the organics recovered dissolved in the aqueous condensate. The char shows the expected pattern of increasing ash and decreasing organic content with temperature as predicted from the results given in Figure 2. The very low hydrogen content is surprising, especially at higher temperatures, and the H/C ratios suggest a highly aromatic char at temperatures above 400 "C. Nitrogen and oxygen are also depleted from the char with increasing temperature. The tar has a fairly constant H/C ratio at varying temperatures and the value of 1.77 at the optimal temperature of 400-450 "C suggests aliphatic compounds, and the high nitrogen and oxygen values indicate the presence of amine or carbonyl groupings. The light water-soluble organics have high H/C ratios and high oxygen content, indicating low molecular weight alcohols, ketones, etc. The apparent high nitrogen values for these compounds are probably not due to amine formation but are more likely due to the presence of dissolved ammoniacal compounds in the aqueous phase. Although accurate elemental analyses of high ash solids are often difficult to achieve in microanalytical apparatus, such as that used in this work, because of sampling problems, the sewage sludge is a very homogeneous solid mixture, and as a result, the microsampling errors are minimized. The char analyses are therefore considered to be nearly as accurate as the tar values. A differential scanning calorimeter analysis for feedstock no. 1was carried out also. Apart from a small endothermic
Table VII. Oil and Char Elemental Analyses,O wt % effect of Dvrolvsis temD: feedstock 1. 0.55-5 residence time. N, atm char tar light organicC C H N O C H N 0 C H N 0 temp, "C ash H/C char 350 67.36 20.48 1.58 2.44 8.24 68.81 10.31 5.51 15.37 44.15 12.45 12.51 30.89 0.93 400b 75.38 15.37 1.13 1.56 6.56 71.37 10.44 5.19 13.00 44.81 8.56 13.13 33.50 0.88 0.62 450 80.27 11.96 0.62 1.22 5.93 69.42 10.23 5.85 14.50 42.25 1.17 17.27 39.31 0.52 500b 81.74 12.61 0.55 1.18 3.92 10.58 9.00 7.97 12.45 40.85 7.65 15.72 35.78 0.56 550b 83.67 10.94 0.51 0.93 3.95 69.04 8.97 7.78 14.21 45.01 9.49 18.28 27.22 0.35 650 88.09 10.27 0.30 0.69 0.65 65.15 8.92 9.83 16.10 39.40 13.37 25.69 21.54 700 89.38 10.04 0.05 0.53 0.00 72.66 6.41 15.66 5.27 35.50 10.69 28.22 25.59 Sulfur not determined; all oxygen by difference. *Average of two determinations.
H/C tar 1.80 1.76 1.77 1.53 1.56 1.64 1.06
H/C It. 0rg.C 3.38 2.29
2.25 2.53 4.07 3.61
Light organics recovered in aqueous phase.
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
