Energy & Fuels 2002, 16, 1337-1342
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Methanol-Mediated Extraction of Coal Liquid (5). Conceptual Design and Mass Balance of a Continuous Methanol-Mediated Extraction Process Shinya Sato,* Akimitsu Matsumura, Ikuo Saito, and Koji Ukegawa National Institute of Advanced Industrial Science and Technology, Institute for Energy Utilization, 16-1 Onogawa, Tsukuba, Ibaraki, 305-8569, Japan Received November 6, 2001
A total process for methanol-mediated extraction was designed. The process consisted of (1) methanol-mediated extraction, (2) neutral oil removal, (3) methanol recovery, (4) water treatment, and (5) washing. The recovery ratio of each process was determined with the naphtha fraction derived from Tanito Harum coal produced in a 150 t/day NEDOL coal liquefaction pilot plant under the conditions of a feedstock/methanol/water ratio of 1:1:1. The mass balance of the total system was calculated from the recovery ratios. In the total process, slight losses were found in methanol, water, heptane, and toluene, requiring 2-21 g of addition per 1000 g of feedstock, which were insignificant compared to the amount of feedstock. Based on the results, the entire extraction process was mostly closed. Overall, 197 g of crude phenol containing 138 g of phenols and 877 g of product oil were recovered from 1000 g of feedstock containing 206 g of phenols.
1. Introduction Coal liquids generally include quantities of phenols,1 which are converted to naphthenes by hydrotreatment.2 This conversion requires a significant amount of hydrogen, which is one of the reasons why it is expensive to produce liquid fuel from coal. However, it is possible to considerably reduce the amount of hydrogen required for refining by separating these phenols prior to hydrotreating. Further cost reductions are expected if separated phenols can be sold commercially as chemicals. Alkali extraction is in commercial use as a method to collect phenols from coal tar. However, it has several disadvantages: its extraction rate is limited due to the limited surface area between both phases, and a considerable quantity of wastes is produced. The authors have developed a methanol-mediated extraction method,3 which consists of two steps, adding methanol and water in this order, and has proved successful in separating phenols from various types of coal liquids.4-6 This method has several advantages. For example, the extraction proceeds quite rapidly at ambient temperature and pressure, and the process requires only inexpensive solvents such as methanol and water. In addition, a closed process is easily designed. * Corresponding author. Tel: +81-298-61-8436. Fax: +81-298-618436. E-mail:
[email protected]. (1) Saito, I.; Yamamoto, Y.; Sato, Y.; Imuta, K. Kogai Shigen Kenkyusho Iho 1986, 16, 1. (2) Fairbridge, C. Proc. Int. Conf. Coal Sci. 1983, 778. (3) Kodera, Y.; Ukegawa, K.; Mitoh, Y.; Komoto, M.; Ishikawa, E. Fuel 1991, 70, 765. (4) Kodera, Y.; Matsumura, A.; Ukegawa, K. Fuel 1993, 72, 57. (5) Sato, S.; Matsumura, A.; Kodera, Y.; Saito, I.; Ukegawa, K. Nippon Enerugi Gakkaishi 1997, 76, 1054. (6) Matsumura, A.; Sato, S.; Kodera, Y.; Saito, I.; Ukegawa, K. Nippon Enerugi Gakkaishi 2000, 79, 236.
This paper discusses the conceptual design of such a closed process of the methanol-mediated extraction method, then estimates the material balance in the process. 2. Conceptual Flow Diagram of a Methanol-Mediated Extraction Process The present authors described in a previous report6 that oil after methanol-mediated extraction contained several percent of methanol, and that the methanolwater phase trapped a small amount of neutral oils such as aromatics during continuous methanol-mediated extraction. Methanol must be removed from extracted oil in order to reduce hydrogen consumption in the next process, a hydrogenation process, by preventing hydrogenation of methanol to methane. Neutral oils must also be removed from the methanol-water phase in order not to disturb the further purification of crude phenol to produce phenol and cresols as chemicals. To solve these issues, we proposed a total process shown in Figure 1, which consists of the following five unit processes. (1) Methanol-mediated extraction process. This process consists of two line mixers and an extractor. Methanol and water are added into feedstock (FS) in this order, which are then mixed with line mixers, respectively. The mixture is separated into phenolextracted oil (EO) containing a small amount of methanol, and a methanol-water phase (MWN) containing phenols and a small amount of neutral oils. Prior to the extraction, the neutral oil fraction (NF) recovered in the neutral oil removal process described below is added to FS. EO is sent to a water washing process to eliminate methanol, while MWN is sent to a neutral oil removal process.
10.1021/ef010260h CCC: $22.00 © 2002 American Chemical Society Published on Web 08/31/2002
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Figure 1. Simplified flow diagram for methanol-mediated extraction instruments: (A), (B) Line mixer, (C) Oil separator, (D) Neutral oil extractor, (E) Methanol distillation tower, (F) Phenol extractor, (G) Toluene distillation tower, (H) Oil washer, (I) Heptane distillation tower.
(2) Neutral oil removal process. This process consists of a neutral oil extractor and n-heptane distillation unit. The purpose of this process is to remove NF from MWN. This process employs n-heptane as a solvent to minimize
back-extraction of phenols, to extract NF effectively, to minimize the contamination of solvent to methanolwater phase after the extraction (MW), and allow easy recovery of NF from solvent.
Methanol-Mediated Extraction of Coal Liquid
After the extraction of MWN, n-heptane solution (HN) is distilled to recover NF, which contains a small amount of back-extracted phenols. NF is mixed in FS for repeated processing. Recovered n-heptane is used in this process again after adding makeup n-heptane. The methanol-water phase after extraction (MW) is sent to the next methanol recovery process. (3) Methanol recovery process. This process consists of a distillation unit. Methanol can be completely recovered by distillation because it forms no azeotropes with water.7 Recovered methanol is used in the methanol-mediated extraction process again after adding makeup methanol. At the bottom of the distillation unit is the mixture of water and phenols. If a part of phenols is released from the residual water phase at the bottom, it is separated and collected as crude phenol. The remaining water phase (WP) is sent to a water treatment process. (4) Water treatment process. This process consists of a phenol extractor and toluene distillation unit. The unit process separates phenols from WP to recover water (WA) for a washing process. Toluene is used as a solvent because it is effective in extracting phenols from water. Phenol is easily recovered from toluene solution after extraction (TP) by distillation because no azeotropes exist between toluene and phenols,8 and their boiling points are significantly different. Recovered toluene is used in the water treatment process again after adding makeup toluene. Distillation residue is recovered as crude phenol after mixing with the released phenols in the methanol recovery process. (5) Washing process. This process consists of an oil washer. The purpose of this process is to wash out methanol in EO with WA after adding makeup water. Washed oil is recovered as product oil. The phenol content of WA must be low, or the phenol can be back-extracted by EO resulting in a higher phenol content of product oil than EO. This is a determining factor in designing the performance of the water treatment process. 3. Experiments 3.1. Properties of Feedstock. Experiments were conducted using naphtha fractions derived from Tanito Harum coal liquid, which was produced in a 150 t/d NEDOL process pilot plant operated in the Sunshine Project.9,10 Operating conditions of the plant and properties of feedstock are summarized in Table 1. The feedstock contained 264 g of polar materials per 1 kg of feed, of which 206 g were phenols including phenol, o-, m-, and p-cresols, ethylphenols, and xylenols. Phenol alone accounted for 48 g. Extra-pure methanol, heptane, and toluene provided by Wako Chemical Co., Ltd., and distilled water were used as solvents. 3.2. Extraction and Analysis. Methanol-mediated extraction was performed in separator funnels employing standard extraction conditions of the method, namely an oil/methanol/ (7) Azeotropic Data-III; Gould, R. D., Ed.; American Chemical Society: Washington, DC, 1973; p 14. (8) Azeotropic Data-III; Gould, R. D., Ed.; American Chemical Society: Washington, DC, 1973; p 319. (9) Ishibashi, H.; Kouzu, M.; Hayashi, T.; Kamei, T.; Oi, S.; Endo, M.; Miyake, M.; Nishibayashi, T.; Asano, S.; Kobayashi, M.; Kano, T.; Imada, K.; Inokuchi, K. Nippon Enerugi Gakkaishi 1998, 77, 1201. (10) Aramaki, T.; Ohi, S.; Hayashi, T.; Yoshimura, Y.; Oneyama, M.; Kouzu, M.; Koyama, K.; Satoh, E.; Ueda, S.; Kobayashi, M.; Yoshida, H.; Yamagiwa, H. Nippon Enerugi Gakkaishi 1999, 78, 110.
Energy & Fuels, Vol. 16, No. 6, 2002 1339 Table 1. Properties of Feedstocka operating condition of NEDOL process temperature at the top of reactor, °C pressure at the top of reactor, Mpa gas/liquid volume ratio catalyst slurry, wt % coal slurry, wt % properties of naphtha fraction specific gravity (@15/4 °C) boiling range, °C gas pentane ∼ 200 °C 200 ∼ 220 °C 220 ∼ 260 °C 260 ∼ 350 °C composition, wt % neutral phenol cresols other phenolsb other polar compoundsc
460 17 700 3 45 0.8608 26.9-265.9 1.5 61.9 20.7 15.2 0.7 73.6 4.8 9.1 6.7 5.8
a Naphtha fraction of Tanito Harum coal liquid. b Mainly ethylphenols and dimethylphenols. c Mainly nitrogen-containing compounds.
water ratio of 1:1:1 (by weight). The experimental conditions and procedure were detailed in our previous report.6 The chemical composition of the feedstock and each phase after extraction were determined by the following procedure. A 150 mg sample was held on top of a column of 250 mm length and 4.6 mm inner diameter, in which silica gel No.923 (Davison Inc.) was packed. First, the sample was flushed of hydrocarbons with 20 mL of n-hexane and then of phenols with 20 mL of ethanol. Phenols contained in the ethanol solution were determined using a gas chromatograph (Shimadzu GC14A) equipped with a capillary column (DB-5, 30 m × 0.25 mm φ) and a flame ionization detector (FID). The temperature range was 40-240 °C at a heating rate of 10 °C/min, with 3 min of holding time at the start. 3.3. Distillation Experiments. Some of the unit processes in the extraction process employ distillation to recover solvents. Recoveries of solvents in the unit processes were estimated as follows. A 100 mL sample was set in a 200 mL three-neck flask with a 250 mm long Vigreaux distillation column having at the top a Claisen fractional distillation head with a cock. The sample was stirred and heated while a thermometer attached to the second head of the flask monitored liquid temperatures. First, 40 mL of distillate was removed and the cock at the top was adjusted to remove distillates slowly. Distillates and bottoms were collected periodically, then analyzed according to the procedure described above.
4. Results and Discussion 4.1. Methanol-Mediated Extraction. The compositions and extraction rates of EO and MWN are shown in Table 2. EO contained 3.8 and 0.8 wt % of methanol and phenol, respectively, while MWN contained 1.3 wt % of neutral oil. 4.2. Neutral Oil Removal. Preliminary experiments with MWN and n-heptane revealed that they separated swiftly when their volumes were equal, but separation took a very long time if only half the volume of n-heptane was mixed with MWN. Therefore, n-heptane volumetrically equal to methanol-water solution was used in the main experiment. Extraction lowered the concentration of neutral oil in MWN down to 0.1 wt % (Table 3). Distillation of HN to recover n-heptane produced small amounts of NF as distillation residues (Table 4). Residual neutral oil and
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Table 2. Results of Methanol-Mediated Extractiona feedstock phase amountc
total compositionc neutral phenol cresols other phenols other polar compounds methanol water
recovered
feedstock
solvent
treated oil
methanol-water
1000
2000
835
2165
1000 1000
707 7 25 24 37 32 4
29 41 66 43 21 968 996
736 48 91 67 58
recovery,%b
3.9 85.4 72.5 64.2 36.2 96.8 99.6
a Extraction was carried out using methanol and water equal to feedstock by weight. b The percentage of compound in methanolwater phase to that in feedstock. c g per kg of feedstock.
Table 3. Results of the Extraction of the Neutral Fraction Using n-Heptanea feed
recovered
phase
methanol-water
n-heptane
n-heptane
methanol-water
total amountc compositionc neutral phenol cresols other phenols other polar compounds methanol water n-heptane
1000
757
794
963
757
12 5 7 9 1 4 0 756
1 14 24 11 9 443 460 1
13 19 31 20 10 447 460
a
Extraction was carried out using methanol and water equal to feedstock by weight. methanol-water phase to that in feed phases. c g per kg of feedstock.
b
recovery,%b
7.7 73.7 77.4 55.0 90.0 99.1 100.0 0.1
The percentage of compound in recovered
Table 4. Results of n-Heptane Recovery by Distillationa feed phase
recovery,%b
recovered
n-heptane
neutral fraction
n-heptane
1000
44
956
15 7 8 11 0 6 0 953
15 7 8 11 0 2 0 1
0 0 0 0 0 4 0 952
amountc
total compositiond neutral phenol cresols other phenols other polar compounds methanol water n-heptane
n-heptane
0.0 100.0 100.0 100.0 33.3 0.1
a Extraction was carried out using methanol and water equal to feedstock by weight. b The percentage of compound in recovered n-heptane phase to that in feed phase. c g per kg of feedstock. d 0 means less than 0.5 g.
Table 5. Results of Methanol Recovery by Distillationa feed
recovery,%b
recovered
phase
methanol-water
methanol
water
isolated oil
total amoumtc compositiond neutral phenol cresols other phenols other polar compounds methanol water n-heptane
1000
459
495
46
1 14 25 12 10 460 477 1
1 0 0 0 1 456 1 1
0 6 9 2 4 3 471 0
0 8 16 10 5 1 5 0
water
isolated oil
0.0 42.9 36.0 16.7 40.0 0.7 98.7 0.0
0.0 57.1 64.0 83.3 50.0 0.2 1.0 0.0
a Extraction was carried out using methanol and water equal to feedstock by weight. b The percentage of compound in recovered phase to that in feed phase. c g per kg of feedstock. d 0 means less than 0.5 g.
phenols accounted for 2.6 and 4.5 wt % of feedstock, respectively. 4.3. Methanol Recovery. The concentration of methanol in the bottoms was lowered to about 0.9 wt % at the bottom temperature of above 100 °C, and the distillate contained about 0.2 wt % of phenol but no cresols nor ethylphenols (Table 5). These results con-
firmed that most methanol could be recovered from water and phenols by distillation. Cooling bottoms to room temperature resulted in phase separation of phenols. The separated oily fraction was recovered as crude phenols. 4.4. Water Treatment. WP contained 3.3 wt % of phenols, including 1.1 wt % of phenol alone. The target
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Energy & Fuels, Vol. 16, No. 6, 2002 1341
Table 6. Results of Water Treatment Using Toluenea feed phase
recovered
feed
water toluene water toluene recovery,%b
total amountc 1000 compositiond neutral 0 phenol 11 cresols 18 other phenols 4 other polar compounds 8 methanol 7 water 952 n-heptane toluene
826
947
879
0 1 0 0 1 0 0 0 824
0 0 0 0 1 1 944 0 1
0 12 18 4 8 6 8 0 823
0.0 0.0 0.0 11.1 14.3 99.2 0.1
Table 7. Results of Crude Phenol Recoverya feed total amountc compositiond neutral phenol cresols other phenols other polar compounds methanol water n-heptane toluene
recovered
total amoumtc compositiond neutral phenol cresols other phenols other polar compounds methanol water n-heptane toluene
939
61
0 14 21 5 9 7 7 0 937
0 1 0 0 1 0 0 0 937
0 13 21 5 8 7 7 0 0
0.0 92.9 100.0 100.0 88.9 100.0 100.0 0.0 0.0
a Extraction was carried out using methanol and water equal to feedstock by weight. b The percentage of compound in recovered crude phenol phase to that in feed phase. c g per kg of feedstock. d 0 means less than 0.5 g.
phenol concentration in WA is determined by the phenol concentration in EO, which was 0.8 wt %. Because the partition coefficient of phenol in the toluene/water system ranges from 2 to 4, depending on phenol concentration,11 the target must be less than 0.2 wt %. In preliminary experiments, separation of water and toluene took a very long time if only half the volume of toluene was mixed with water. Therefore, an equal volume of toluene to water was used in the main experiment. Phenol concentrations in water were 0.1 wt % or less after three extraction operations (Table 6). As a result, it was decided to use three-stage countercurrent extraction in the unit process. Next, the extraction performance of phenol was examined by tracing three-stage counter-current extraction using separator funnels. Almost all of the cresols and ethylphenols were extracted to the toluene phase because their partition coefficients in the toluene/water system are 10 or greater. TP containing less than 0.1 wt % of phenol was recovered by distillation at the top of the distillation column temperature of 110 °C, and crude phenol, in which toluene was not detected by GC, was recovered at the bottom temperature of 180 °C (Table 7). These results indicated that an efficient distillation column could effectively separate toluene and phenol. 4.5. Water Washing. Methanol in EO was extracted with an equal amount of WA, which regenerated in the (11) Tochigi, K.; Gotou, T.; Akimoto, K.; Kojima, K. Kagakukougaku Ronbunshu 1998, 24, 338.
1000
1003
956
1047
852 8 30 29 38 38 5
0 0 0 0 1 1 1000 0 1
852 6 29 29 36 1 2 0 1
0 2 1 0 3 38 1003 0 0
75.0 96.7 100.0 92.3 2.6 0.2 100.0
a Extraction was carried out using methanol and water equal to feedstock by weight. b The percentage of compound in recovered water phase to that in feed phases. c g per kg of feedstock. d 0 means less than 0.5 g.
Table 9. An Overall Material Balance
toluene toluene crude phenol recovery,%b 1000
recovered
treated product oil water oil water recovery,%b
phase
a Extraction was carried out using methanol and water equal to feedstock by weight. b The percentage of compound in recovered water phase to that in feed phases. c g per kg of feedstock. d 0 means less than 0.5 g.
phase
Table 8. Results of Water Treatment Using Toluenea
feedstock total weight neutral PhOH o-cresol other phenols other polar compounds methanol water heptane toluene
additional solvent
product oil
crude phenol
9 22 3 1
849 736 7 28 33 38 1 2 3 1
186 0 41 63 34 20 8 20 0 0
1000 736 48 91 67 58
water treatment process (Table 8). The resulting methanol concentration in product oil was approximately 0.1 wt %. Phenols in the product were slightly reduced as well. 4.6. Mass Balance in the Overall Process. Mass balance was calculated on the basis of 1000 g of FS according to the flow diagram shown in Figure 1. As there are three loops in the flow diagram, several recalculations were necessary to converge the material balance in each process. The results under 1 g were rounded (Table 9). Slight losses were found in methanol, water, heptane, and toluene, requiring 2-21 g of addition, which were insignificant compared to the amount of feedstock. Based on the results, the overall extraction process was mostly closed. In total, 877 g of product oil was recovered from 1000 g of FS. The product oil contained 22 g of solvents and 107 g of polar materials, of which 68 g was phenols. Phenol alone accounted for 7 g. The other product, crude phenol, was 190 g. It contained 157 g of polar materials, of which 138 g was phenols. Phenol alone accounted for 41 g. Neutral oil was not detected in recovered crude phenols. The overall extraction rate was therefore 67% and 85% for phenols and phenol alone, respectively. 5. Conclusion Examination of all unit processes for the methanolmediated extraction method yielded the following results. (1) The overall process was conceptually designed with unit processes of methanol-mediated extraction,
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heptane extraction to remove neutral oils, methanol recovery, water treatment, and water washing to remove methanol from product oil. (2) Experiments were conducted on each unit process following the overall process flow to determine extraction rates in each process using naphtha fractions derived from Tanito Harum coal liquid produced in a 150 t/d NEDOL process pilot plant.
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(3) Overall extraction rates were estimated on the basis of the material balance of each process. Estimated rates were 67% for phenols and 85% for phenol alone. (4) The solvent losses were so small that the whole process was almost closed. These results are useful as basic data for designing a practical process and estimating the cost. EF010260H
