Znd. Eng. C h e m . Res. 1995,34, 4118-4121
4118
RESEARCH NOTES Removal and Recovery of Quinoline Bases from Methylnaphthalene Oil in a Semicontinuous Supercritical C02 Separation Apparatus with a Fixed Bed of Supported Aluminum Sulfate Kinya Sakanishi, Hiroaki Obata, Isao Mochida,* and Tsuyoshi Sakakii Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816, Japan
Capture and recovery of quinoline bases from methylnaphthalene oil were examined using a semicontinuous supercritical C02 extraction apparatus equipped with the f x e d bed of supported aluminum sulfate as a solid acid adsorbent. A model methylnaphthalene oil (quinoline and isoquinoline in 1- and 2-methylnaphthalenes) mixed with supercritical COS (323 K, 80 atm) was continuously fed over the fixed bed of the adsorbent. The nitrogen compounds were selectively adsorbed on the solid acid, giving purified methylnaphthalenes by the feeding of 120 min. Quinoline and isoquinoline started to elute by 140 and 180 min, respectively, with the composition at the outlet gradually approaching to the initial one by 220 min. After the feeding was stopped and then the adsorbent was washed with supercritical CO2 at 353 K for 25 min, the adsorbed nitrogen compounds were effectively recovered by mixing a small amount of tetrahydrofuran (THF) as a n entrainer to the supercritical COZto regenerate the adsorbent a t the same time. The adsorbent was confirmed to be repeatedly used by the above adsorption/ desorption cycle, with purified methylnaphthalenes and concentrated quinoline bases being alternatively recovered at the adsorption/desorption steps, respectively.
Introduction
dissolving ability of supercritical C02 is easily controlled by changing its temperature and pressure; that is, the adsorption and desorption of the substrates can be designed by using the supercritical solvents (Wilhelm and Hedden, 1986). In previous papers (Sakanishi et al., 1994, 19951, a batch-type extraction of methylnaphthalene oil using the supported sulfate adsorbent under the supercritical C 0 2 flow was reported t o be one of the promising ways for the selective removal and recovery of quinoline bases in addition to the purification of methylnaphthalenes. The solubilities of aromatic hydrocarbons in the supercritical CO2 should be carefully taken into account for the effective supercritical extraction and separation procedures (Dandge et al., 1985;Arai et al., 1988; Mitra and Wilson, 1991; Sheng et al., 1992). In the present study, a novel process for the removal and recovery of quinoline bases in CMNO is proposed in Figure 1,where Alz(SO& supported on silica gel as an adsorbent and supercritical C02 as an eluent are applied. A polar solvent such as tetrahydrofuran (THF) as an entrainer solvent in supercritical CO2 may enhance the desorption to regenerate the adsorbent. Such a cycle of adsorption and desorption in a reversible manner using a semicontinuous flow apparatus under supercritical COz conditions can be one of the industrially alternative procedures for recovering the useful nitrogen compounds and purified aromatic hydrocarbons at the same time.
Crude methylnaphthalene oil (CMNO)is produced as a distillation residue of naphthalene oil (bp 483-533 K)of coal tar after the recovery of crude naphthalene as shown in Figure 1. CMNO contains quinolines and isoquinolines as the contaminants in methylnaphthalenes. Purification of CMNO is currently accomplished by extraction of the oil with a sulfuric acid solution; however, this process consumes large amounts of both acid and base and produces troublesome sludges during the phase separation (Horita et al., 1987). Such procedures will be no longer feasible in modern industry; hence, alternative procedures are needed. The present authors have proposed application of metal sulfates as an acidic adsorbent which is fairly acidic when dehydrated, while neutral when hydrated (Mochida et al., 1990, 1991). Nonpolar solvents appear to play a role of antisolvent, accelerating the adsorption of bases on the adsorbent (Sakanishi et al., 1992). The authors also reported that a consecutive extraction with methanol and hexane concentrates pyrroles and phenols in the hexane insoluble-methanol soluble fraction (Fei et al., 1990). The problems of such a wet process are handling of a large amount of solvents, control of the dissolving ability of the solvent, and the limited capacity of the adsorbent. Supercritical fluids have been reputed to be a unique solvent for the selective and energy-saving extraction and separation procedures (Gere et al., 1982; Campbell and Lee, 1986; Nishioka et al., 1986). In addition, the
Experimental Section
Kyushu National Industrial Research Institute, Tosu, Saga 841, Japan.
Model methylnaphthalene oil (quinoline (Q), 8 wt %; isoquinoline (IQ), 8 wt %; 1-methylnaphthalene and 2-methylnaphthalene (1-MN and 2-MN),42 wt %; each
+
0888-588519512634-4118$09.00/0
0 1995 American Chemical Society
Ind. Eng. Chem. Res., Vol. 34, No. 11,1995 4119
n tight Oil
Carbolic Oil
p&zzzip bp80'2M'C
Wash Oil
Anlhracene Oil Pitch
Figure 1. Separation scheme of quinoline bases from crude methylnaphthalene oil (CMNO). 2.0 mVmin
co1
1. C(h cylinder 2. Feed reservoir
6. Static mixer 7. Needle valve
IO.Back pressure regulator 11. Condenser 12. Sampling vessel
3. Entrainer reservoir 8. Heater 4, pump 9.Packed mlumn 13. Trap (9.8mm inncr diameter. 75.1 mm lengh in a hanlonfal direction ) 14. Flow meter 5. Cwler unit
Figure 2. Semicontinuous supercritical COz separation apparatus.
of the guaranteed grade used) was prepared as a model feed. A commercial crude methylnaphthalene oil (CMNO) was also used as a feed for comparison. Aluminum sulfate (Alz(S04)3-14HzO) supported on a silica gel (MB-4B, Fuji Davison Chemical, Ltd., 30-200 mesh) was used as an adsorbent. Aluminum sulfate of 10 wt % was supported by impregnation from an aqueous solution on silica gel, of which surface area and mean pore diameter were 500 m2/g and 64 A, respectively. The adsorbent was calcined a t 623 K for 3 h in air before its use. Figure 2 shows the semicontinuous supercritical COz extraction apparatus used in the present study. The model CMNO was fed a t the flow rate of 0.02-0.05 m Y min to the fixed bed of 3.4 g of Alz(S04)3/SiOz with the supercritical COz (323 K, 80 atm; COz flow rate, 11.8
g/min at room temperature and 1atm). The fured bed is a stainless steel tube column (5.5 cm3 capacity, in a horizontal direction, 9.8 mm inner diameter, 75.1 mm length) capped with two sintered stainless steel filter disks (20 pm pore size). The adsorbent was densely packed in the tube column by using a vibrator. The eluted compounds were sampled in 20 min intervals and analyzed by GC-FID (50 m capillary OV-101 column, 383 K). The elution profile of the feed was recorded with the feeding times of 20-300 min in the first run. In case of recovery of adsorbed compounds, the feeding was stopped at 240 min when the adsorbent was saturated with nitrogen compounds. The column temperature was raised to 353 K, and THF was introduced at a level of about 4 vol % to the supercritical COz flow, t o recover the adsorbed species and to regenerate the adsorbent
4120 Ind. Eng.Chem. Res., Vol. 34, No. 11, 1995 Table 1. Effects of C02 Preextraction of Saturated Adsorbent on the Concentration of Recovered Nitrogen Compounds" preextraction conditions recovered N compds in run pressure time wt by THF the recoveryb by no. (atrn) (h) phase addition (g) THF addition (%) 1 2 3 4 LO 40 60 80 100 120 140 160 180 200 220 240 260 280 300 Feeding time (min)
Figure 3. Elution profile of model feed using a semicontinuous extraction apparatus under supercritical COz conditions. Conditions: pressure, 80 atm; temperature, 323 K adsorbent, Al2(SO4)3/SiO2(3.4 9); COz flow rate, 11.8g/min; feed flow rate, 0.035 mumin; feed composition, 1-MN 42%, 2-MN 42%, quinoline (Q) 8%,isoquinoline (IQ) 8%.
-
2x 0
'I/] I--,I*
50 65 80
1 gas 1 subcritical 1 supercritical
2.02 1.51 1.33 0.50
36.5 45.5 47.7 97.3
a Adsorption conditions: 323 K, 80 atm; 240 min; C02 flow rate, 11.8 g/min; N compounds in the feed, 16.8%. Desorption conditions: supercritical COz with 4% THF a t 323 K, 80 atm.
*
Table 2. Yields and Elemental Analysis of Effluents in the Adsorption of CMNO under Supercritical COZ sampling time (min) recovery of CMNO 80 160 240 300 adsorbate(g1 yield (g) H (%I C (%) N (%I
6.83 90.23 1.48
0.23 0.30 0.37 0.69 7.12 7.06 6.93 6.90 91.83 91.26 91.39 90.85 0.08 0.26 0.61 0.79
1.19 10.44 82.33 7.22
OAdsorption conditions: 323 K, 80 atm; C02 flow rate, 11.8 g/min; feed flow rate, 0.03 mumin until 240 min. The feeding was stopped a t 240 min, and the supercritical COz was flowed until 300 min. Desorption conditions: supercritical C02 with 4%THF at 323 K and 80 atm after 300 min.
----
1 I
u o
0.03
0.04
0.05
Feed speed (ml/min) Figure 4. Influence of model feed speed on the recovery of purified MN under supercritical C02 conditions (other conditions are the same as in Figure 3).
for its repeated use. In some experiments, C02 of gas, subcritical or supercritical at 323 K, was used for washing out the remaining methylnaphthalenes before introducing THF.
Results Figure 3 shows the elution profile of the model methylnaphthalene oil. No nitrogen compounds were eluted until the feeding time of 120 min, with only denitrogenated methylnaphthalenes being recovered in the separation vessel. Quinoline first started to elute at 140 min, while isoquinoline appeared at 180 min, suggesting that quinoline and isoquinoline may be separated by optimizing the elution conditions. After 180 min, the base concentration of the eluate gradually increased to reach that of the feed. The feeding was continued until 300 min in this case. Figure 4 shows the influence of the feed flow rate on the recovered amounts of purified methylnaphthalenes. The recovered amount of methylnaphthalenes without nitrogen compounds was the largest at the feed speed of 0.03 mumin or smaller. Based on the calculation of the solubility of naphthalene derivatives (Arai et al., 1988; Sheng et al., 19921, the feed rate of 0.03 mumin corresponds to the maximum solubility of about 0.08 mol % in the supercritical C02 under the conditions of 323 K, 80 atm, and 11.8 g/min. Hence, the feed at higher flow rates than 0.03 mumin in the C02 solvent cannot be homogeneous. The feed rate should be carefully controlled based on the feed solubility in order t o
maintain the homogeneous supercritical phase as well as to achieve the highest adsorption efficiency. The adsorbent was successfully regenerated under supercritical C 0 2 flow mixed with 4 vol % THF as an entrainer at 353 K before the following runs. About 2 g of purified methylnaphthalenes was steadily recovered in the repeated runs, although the recovered amount in the fourth run was slightly decreased probably due t o the changes of adsorbent packing and conditions. The desorbed nitrogen compounds were steadily recovered based on the atomic ratio of N/Al (acid site of the adsorbent) as high as unity in the repeated runs. Table 1 shows the effects of C02 preextraction of saturated adsorbent with nitrogen compounds by the feeding time of 240 min on the concentration of recovered nitrogen compounds by THF-added supercritical C02. Supercritical C02 with THF liberated the adsorbed compounds from the adsorbent, although the concentration of nitrogen compounds in the adsorbate was twice that of the original feed as indicated by run no.1 of Table 1. It is suggested that methylnaphthalenes remaining in the dead space of the adsorbent column come out with the solvent. Gaseous and subcritical C02 at 323 K washed out such remaining methylnaphthalenes before the entrainer was flowed, leaving the nitrogen compounds of 45.5 and 47.7%, respectively, on the adsorbate. Supercritical COn concentrated nitrogen compounds of 97% on the adsorbate, and they were effectively recovered by the supercritical C02 with THF entrainer. Table 2 shows the separation results of the crude methylnaphthalene oil using Al2(SO4)3/SiO2under supercritical COSflow. The nitrogen compounds in CMNO were effectively adsorbed on the adsorbent, with denitrogenated fractions being obtained by 80 min. The nitrogen content in the effluent gradually increased in the time course to 0.26 wt % at 160 min, 0.61 wt % at 240 min, and 0.79 wt % at 300min. After the feeding was stopped at 240 min, supercritical C02 was flowed for 60 min at 323 K and 80 atm and then the adsorbed compounds were desorbed by adding THF as an en-
Ind. Eng. Chem. Res., Vol. 34, No. 11, 1995 4121 trainer. A total of 1.19 g of the nitrogen compounds was recovered at the higher nitrogen content of 7.22 wt % by this two-step recovery procedure. According to the compositions of CMNO analyzed by GC before and after the supercritical COS separation (sampled at 160 min), nitrogen compounds such as quinoline, isoquinoline, and methylquinolines (their total content: about 8 wt %) were completely removed and recovered by the above supercritical C02 separation procedure.
Discussion The present study revealed that a novel process for removal and recovery of quinoline bases from methylnaphthalene oil can be designed by using supported aluminum sulfate as an adsorbent and a semicontinuous supercritical C02 extraction apparatus. Supercritical C02 is a very unique solvent for the selective extraction and separation of aromatic hydrocarbons because it is very stable and has relatively lower critical temperature and pressure. Supercritical COZ under the present conditions of 323 K and 80 atm dissolved methylnaphthalene oil completely a t the feed flow rates below 0.03 mumin. Although it showed a low selectivity for dissolving aromatic hydrocarbons and heterocyclic aromatics to carry over both fractions onto the fmed bed filled with 10 wt % Al~(S04)3/Si02,it succeeded in selective adsorption of nitrogen compounds and purifying methylnaphthalenes. The adsorbed nitrogen compounds are effectively desorbed and recovered by adding a small amount of THF as an entrainer solvent to supercritical COz for the repeated use of the adsorbent. Supercritical COz at 323 K recovered the remaining methylnaphthalenes of the column more effectively than gas or subcritical C02, concentrating nitrogen compounds recovered by the THF-added supercritical C02. Such recovering procedures in combination with drying the fxed bed of the adsorbent by higher temperature supercritical C02 enable the repeated use of the adsorbent in the adsorptioddesorption cycle in a reversible manner. The acidity and adsorption capacity of the adsorbent are carefully designed according to the concentration and basicity of nitrogen compounds in addition to the properties of the entrainer solvent for the complete recovery of nitrogen compounds. Antisolvent behaviors can increase the capacity of adsorbent. Too strong acidity and insufficient capacity of the adsorbent may hinder the reversible adsorptioddesorption of the adsorbate and the effective capture and recovery of the separated compounds. The solubility of the adsorbates in the supercritical C02 is also important to improve the efficiency of the adsorptioddesorption profile under supercritical C 0 2 flow. As suggested by the elution profile in Figure 3, quinoline and isoquinoline can be separately recovered due to their different basicities, controlling their de-
sorption rate by optimizing the extraction conditions including temperature, pressure, and flow rate. Isoquinoline of stronger basicity is naturally desorbed later. Hydrogenation of quinoline and isoquinoline is suggested to differentiate more their basicities.
Literature Cited Arai, Y.; Iwai, Y.; Yamamoto, H. Separation of coal liquids by supercritical extraction. J . Fuel Znst. Jpn. 1988,67,822. Campbell, R. M.; Lee, M. L. Supercritical fluid fractionation of petroleum- and coal-derived mixtures. Anal. Chem. 1986,58, 2247. Dandge, D. K.; Heller, J. P.; Wilson, K. V. Structure solubility correlations: Organic compounds and dense carbon dioxide binary system. Ind. Eng. Chem. Prod. Res. Dev. 1985,24,162. Fei, Y. Q.; Sakanishi, K.; Sun, Y. N.; Yamashita, R.; Mochida, I. Concentration of pyrroles and phenols from coal tar pitch by organic solvent extraction. Fuel 1990,69,261. Gere, D. R.; Board, R.; McManigill, D. Supercritical fluid chromatography with small particle diameter packed columns. Anal. Chem-. 1982,54,736.Horita, Y.; Togari, 0.; Komoto, T.; Nakamura, M.; Tanji, H. Hydrodenitrogenation of coal tar pitch (No. 2). J . Petrol. Znst. Jpn. 1987,30,94. Mitra. S.: Wilson. N. K. An emoirical method to oredict solubilitv " in supercritical fluids. J . Ch'romatogr. Sci. 1991,29,305. Mochida, I.; Fei, Y. Q.; Sakanishi, K.; Usuba, H.; Miura, K. Capture and recovery of basic nitrogen species in coal tar pitch using nickel sulfate as adsorbent. Chem. Lett. 1990,515. Mochida, I.; Sakanishi, K.; Usuba, H.; Miura, K. Removal of basic nitrogen species in coal-tar pitch by metal sulphates supported on silica gel. Fuel 1991,70,761. Nishioka, M.; Whiting, D. G.; Campbell, M.; Lee, M. L. Supercritical fluid fractionation and detailed characterization of the sulfur heterocycles in a catalytically cracked petroleum vacuum residue. Anal. Chem. 1986,58,2251. Sakanishi, K.;Sun, Y. N.; Mochida, I.; Usuba, H. Removal and recovery of nitrogen compounds in crude methylnaphthalene oil using alminium sulfate supported on silica -gel. Fuel Process. _Techno[ 1992,32,143. Sakanishi. K.: Obata. H.: Mochida. I.: Sakaki. T. Removal and recovery of nitrogen and sulfur compounds from coal tar fractions using supported aluminium sulfate under supercritical COz conditions. Prepr.-Am. Chem. SOC.,Diu. Fuel 1994,39(31, 761. Sakanishi, K.; Obata, H.; Mochida, I.; Sakaki, T. Capture and recovery of nitrogen compounds in methylnaphthalene oil using aluminium sulfate supported on silica gel under supercritical COz conditions. J . Energy Znst. Jpn. 1995,74,109. Sheng, Y.-J.; Chen, P.-C.; Chen, Y.-P.; Wong, D. S. H. Calculations of solubilities of aromatic compounds in supercritical carbon dioxide. Znd. Eng. Chem. Res. 1992,31,967. Wilhelm, A.;Hedden, K. A non-isothermal experimental technique to study coal extraction with solvents in liquid and supercritical state. Fuel 1986,65,1209. I
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Received for review January 19, 1995 Revised manuscript received J u n e 27, 1995 Accepted July 12, 1995@ IE950059S ~~~
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Abstract published in Advance ACS Abstracts, September 15, 1995. @
