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Extraction of tar acids with glycols
Fuel Processing Technology, 28 (1991) 287-300
287
Elsevier Science Publishers B.V., Amsterdam
Extraction of tar acids with glycols K. K. Tiwari and D. K. Sen Central Fuel Research Institute, PO FRI, Dhanbad-828108, Bihar (India) (Received April 18th, 1990; accepted in revised form December 24th, 1990)
Abstract Recovery of tar acids from low temperature tar oil fraction boiling up to 270 ° C was investigated using glycols as solvent. AR grade ethylene glycol, diethylene glycol and triethylene glycol effected a recovery of 89%, 95.5% and 93.5%, respectively, of tar acids in two stages of extraction using a feed-solvent ratio of 1 : 1 by weight. Considerable amounts of neutral oil and tar bases were also extracted with solvents. Aqueous ethylene glycol (80 wt% ) in the solvent-feed ratio of 1 : 1 was found to effect a recovery of 84% of the tar acids present in the tar oils in two extraction stages with 82% purity of tar acids. The purity of the extracted tar acids could be improved by the use of petroleum ether as a counter-solvent. The phase-equilibrium characteristics of the system, tar acids-neutral oil-80% aqueous ethylene glycol were studied. It has been shown that two theoretical extraction stages could effect the recovery of 98% of tar acids from a feed oil containing 45% of tar acids at the feed-solvent ratio of 1 : 2 (by weight) and the highest degree of purity that could be achieved for tar acids is 87%.
INTRODUCTION
The major feedstocks for the production of organic chemicals are petroleum and coal. In the context of a global oil crisis, coal is bound to stage a comeback as a more dependable reserve which will provide primary feedstock to chemical industries for at least another century. The byproducts from coal carbonisation and oil from coal will be the major future feedstock for the organic chemical industry. In India, low temperature carbonisation (LTC) of coal has definite future. Even on a very moderate estimate at least 15 million tonnes of coal per annum will have to be carbonised by LTC to provide domestic fuel for the urban sector. This will give rise to a very sizeable amount of tar, about 7-8% of the total quantity of coal carbonised: 20-25 % of low temperature tar (LTT) constitutes tar acids. It has been shown that the economy of LTC is linked up with the profitable recovery of byproducts, such as tar acids, aromatics, etc. [ 1-3 ]. Bearing in mind the techno-economic aspects of the problems involved in the utilisation of tar acids, different methods of recovery, purification and subsequent processing of higher tar acids have been investigated in this laboratory 0378-3820/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved
288 TABLE 1 Comparison of solvents for extraction of tar acids from low temperature tar oil fraction boiling up to 270°C Solvent
Oil-solvent % Extraction of ratio components by two successive extractions
Advantages/disadvantages of the processes
Tar Tar Neutral acids bases oil Methanol (70%) Monoethanolamine (70%) Ethylene diamine (70%) Acetic acid (60%) Acetamide (saturated soln.) Formamide (100%) Dimethylformamide (70%)*
1:1 1:2 1:2 1:1 l: 1 1:1 1:1.2
Sodium hydroxide (10%)
1:1
Ammonia solution (4%)*
1:7
89.6 93.3 96.0 91.9 95.8 88.0 92.0
100
56.4 30.4 22.3 97.0 53.1 19.3 79.3
30.6 16.9 15.4 20.4 12.0 14.7 35.9
The solvents have high extraction efficiency for tar acids, but they also extract tar bases and neutral oil so that the desirable product purity is not obtained. Hence the processes are unattractive for industrial scale operations.
12.9
7.2
This is a batch process practised on a commercial scale. Recovery of tar acids requires consumption of reagents in the extraction, springing and regeneration cycles. The disadvantages are the problems of recausticisation of the carbonate liquor, corrosion and high cost of operation.
77.0 18.5 20.5
Extraction of tar acids is lower than for other solvents but all the phenol, cresols and some xylenols are extracted by the solvent. Contaminations by neutral oil and tar bases make the process unattractive.
*Results given are for one extraction. *Results given are for three extractions. [ 4 - 6 ]. T h e p r e s e n t p a p e r is c o n c e r n e d w i t h e x a m i n i n g g l y c o l s a s s e l e c t i v e s o l v e n t s f o r t h e e x t r a c t i o n o f t a r a c i d s f r o m L T T oil f r a c t i o n b o i l i n g u p t o 270 ° C. In an effort to replace the conventional process of extracting tar acids using caustic soda which has inherent disadvantages, various solvents have been tried o u t i n d i f f e r e n t p a r t s o f t h e w o r l d b u t a n i d e a l s o l u t i o n t o t h e p r o b l e m is y e t t o be found. R e c o v e r y o f t a r a c i d s f r o m t a r oil f r a c t i o n s h a s b e e n i n v e s t i g a t e d f r o m v a r -
289 ious angles. An account of all the processes used with L T T oil fraction boiling up to 270 ° C has already been presented elsewhere [ 1 ]. A comparison of the solvents under optimum conditions as mentioned in literature was made and the results are presented in Table 1. Organic solvents such as methanol [8-11], ethanol [ 12 ], fatty acids [ 13 ], etc., have been used mostly in conjunction with counter-solvents for suppressing the entrainment of neutral oil into the extract phase. The possibilities of using glycols and glycerols as solvents were examined by Cumming and Morton [14,15 ]. Triethylene glycol was found to have good selectivity for phenol. Aqueous triethylene glycol was claimed to extract almost all phenols from a high temperature tar oil fraction boiling up to 201°C, in three theoretical counter-current stages using a solvent ratio of 1:1. The solvent-free extract consisted of 82% phenols and 18% hydrocarbons. Dry glycerol was claimed to be the best extractant for phenol. However, a high degree of selectivity and extraction efficiency was not obtained when working with a phenolic mixture and commercial fractions. Aromatic hydroxy compounds present in low temperature pyrolysis coal tar have been recovered recently using a nonaqueous anionic exchange process [ 16-17 ]. The process has been claimed to be a rapid and simple method for the characterization of the acidic components of a coal tar. This paper contains results which show that ethylene glycol, diethylene glycol and triethylene glycol are appreciably effective for the extraction of tar acids from L T T oil fraction boiling up to 270 ° C. The phase-equilibrium characteristics of the system, tar acids-neutral oil-80% aqueous ethylene glycol are reported. EXPERIMENTAL DETAILS Feed material
Feedstocks were obtained by distillation of tar derived from the LTC pilot plant of the Central Fuel Research Institute, Dhanbad. The tar oil fraction boiling up to 270°C was collected. This oil had a specific gravity of 0.9535 at 30 ° C and a percentage composition as follows: tar acids - 41.3; tar bases - 3.5; and neutral oil - 55.2. For phase-equilibrium studies, tar acids and tar bases were separated from the above tar oil fraction using the standard method of alkali and acid treatment. Tar acids obtained were further extracted with saturated sodium bicarbonate solution to remove any aliphatic acid present. Both the purified tar acids and neutral oil were distilled under reduced pressure. The phenols were analysed by gas chromatography in a Perkin-Elmer 810 gas chromatograph with a flame ionisation detector using nitrogen as carrier gas (flow rate, 30 m l / min) and employing the method described by Bhattacharjee and Bhaumik [ 18 ].
290
The percentage composition of tar acids was: phenol - 13.7; o-cresol - 9.4; mcresol - 10.8; p-cresol - 12.8; xylenols and other high boiling phenols - 53.3.
Solvent Ethylene glycol, diethylene glycol and triethylene glycol, all Fluka AR grade chemicals and their aqueous solutions were used as solvents. Petroleum ether (boiling range, 6 0 - 8 0 ° C ) was used as a counter-solvent.
Extraction procedure Most extractions were done in separating funnels or jacketed columns provided with thermostat and axial stirrers. The temperature was maintained at 30 °C for all extractions. The procedures of operations are presented in Schemes 1-4.
Determination of phase-equilibrium data For phase-equilibrium studies, neutral oil and tar bases obtained from feed tar oil were mixed together in the proportion in which they occur in this oil. To this mixture were added tar acids and solvent in different proportions to obtain a series of mixtures. These were shaken for 30 min in a separating fun-
E~
"i Back-washing ~REFfNEDEXTRACT
TAROIL - S°'vent ' _30rain (I:( W la /w ] i_ R~ Solvent Shaking
(FE2-~" Petroleum.__ether, I.
(I Vol. per Vol. Tar oil / [
Settling 1 h
as(aLij
~PETROL.ETHERSOLN.
~2
E= EXTRACT
R = RAFFINATE
Scheme i. General extraction procedure.
- AIIUEOUSSOLVENT (b} Water (1:1~v) & Settling 1 h
EXTRACT Shaking
I
-VERYDILUTED SOLVENT Wafer aslb) I ~ ORSANI[PHASE
Scheme 2. Elimination of the solvent.
~OLVENT-FREE EXTRACT
291
m
-~
rY I--
w
w
t~ __J
z
- L___]
f2: b--
i
,,=,
b--z
z
,e,
--~°
t~
i
_>
a~
w ~
~ z
292 RAFFINATE ETHER ADDED{I: I V/v ) ETHER( LAYER EXTRACTION,10°/o NaOH
ALKALI~EXTRACT { a}
SOLVEN~ LAYER ( ENTRAINEDIN RAFFINATE
ETHER~OLUTION EXTRACTION,25 °/o HzS0
ACID EXTRACT Ib)
ETHER SOLUTION Ic]
Scheme 4. Raffinate treatment (estimated for acids, tar bases and neutral oils from (a), (b) and (c), respectively as described under scheme 3 ).
nel provided with water circulation to control the temperature at 30 ° C. The extract and raffinate phases were allowed to settle (1 h), separated and then analysed.
Determination of ternary solubility data These were determined by the titration method described below. A number of mixtures were made containing tar acids and solvent forming a miscible layer. Then neutral oil was added dropwise from a burette, while shaking, until a permanent turbidity point {immiscibility point) appeared. In this way, the maximum quantity of neutral oil soluble in the system was recorded. Similarly various mixtures of tar acids and neutral oil were prepared, and solvent was added to the mixture as above until two phases appeared. Lastly a series of known mixtures of neutral oil and solvent, which form immiscible layers, were made. To each of the mixtures, tar acids were added dropwise, while shaking, till the miscibility point was reached and the solution became homogeneous. All the above experiments were performed in a constant temperature bath at 30 ° C, provided with an arrangement for light to facilitate easy observation of turbidity-miscibility points. RESULTS AND DISCUSSION
Mass balances of the extraction The results for two successive extractions using a feed-solvent weight ratio of 1 : 1 are presented in Table 2. It is seen that the recovery of tar acids with ethylene glycol, diethylene glycol and triethylene glycol are respectively, 89.1%, 92.5% and 93.5%, the corresponding figures for neutral oil being 24.6%, 42.2% and 44.1%. The tar bases, though a minor component gave 75.9% recovery with diethylene glycol and triethylene glycol whereas 40% of tar bases were extracted with ethylene glycol. Thus with diethylene glycol and triethylene glycol
293 TABLE 2 Extraction of tar acids from L T T oil fraction (boiling up to 270 ° C ) with glycols at 30 ° C. (Feedsolvent weight ratio 1 : 1; two successive extractions) Solvent
1. Ethylene glycol (AR) 2. Diethylene glycol (AR) 3. Triethylene glycol (AR)
Feed (tar oil ), g
% Recovery in the extract, based on the components originally present in the feed
% Composition of extract (solvent-free)
Tar acids
Tar bases
Neutral oil
Tar acids
Tar bases
Neutral oil
22.89
89.1
40.0
24.6
72.3
2.7
25.0
23.47
92.5
75.9
42.2
59.5
4.2
36.3
23.47
93.5
75.9
44.1
58.8
4.1
37.1
the purity achieved for tar acids is around 59% whereas the corresponding figure with ethylene glycol is 72.3%. Considering the recovery as well as purity of tar acids in the solvent-free extract, ethylene glycol appeared to be a better solvent than the other two glycols. A detailed study, therefore, was undertaken with ethylene glycol.
Effect of concentration of the solvent Ethylene glycol was diluted with distilled water to obtain concentrations of 90, 80, 70 and 60 wt% of solvent. The extraction of tar acids from L T T oil fraction was carried out with the above concentrations of solvent in two successive stages maintaining the feed-solvent weight ratio of 1:1 throughout. The results are presented in Fig. 1. It is seen that the recovery of tar acids is 85% with 90% ethylene glycol, the corresponding figure with 80% solvent strength being 84%. However, at 70% and 60% concentrations of ethylene glycol, the recovery decreased significantly, the respective values being 55.5 and 50.8% of tar acids. The solvent-free extract contained 2-2.5% base over the entire range of extractions, while the contamination by neutral oil in the extract varied in the range 16-21%. It is observed that with 80% ethylene glycol the neutral oil contamination (defined as percentage of neutral oil in the extract) was minimum at 16% and the degree of purity of extracted tar acids was highest at ca. 82%. Hence, 80% solvent strength was considered optimum.
Effect of using petroleum ether as counter-solvent The process generally referred to as back-washing has been detailed elsewhere [ 19 ]. The counter-solvent, being more selective towards neutral oil rather
294
9O
30
.~
.,..:
80
d
! 2o
,~ 70
>- 60
to
~ 5o 1
60
I
I
70
80
I
90
STRENGTH OF SOLVENT, °/olW/W)
Fig. 1. Effect of e t h y l e n e glycol c o n c e n t r a t i o n on t a r acids recovery: ( Q ) recovery of t a r acids, a n d ( & ) neutral oil c o n t a m i n a t i o n .
than tar acids, extracted considerable amounts of neutral oil and to some extent tar bases contaminated with tar acids of the extract, thus improving the overall purity of the desired product. The results are presented in Table 3. It can readily be seen that re-extraction of the ethylene glycol extracts using petroleum ether improved the purity of tar acids by about 11% whereas reextraction of diethylene and triethylene glycol extracts resulted in an increase in the purity of tar acids to around 75.5% from about 59% (when no countersolvent was used). At 80% ethylene glycol concentration, the purity of the solvent-free extract could be improved from 82% to about 93%. It is further seen that the recovery figures for tar acids are somewhat less than the original, indicating that some acids are lost in the counter-solvent stream. Since the counter-solvent may be reused, however, these losses are expected to be minimised in a continuously operated process and can, at any rate, be recovered from the finally exhausted stream also. From the foregoing, it is inferred that 80% aqueous ethylene glycol in conjunction with petroleum ether can effect 84% extraction of tar acids with 93 % purity in a continuous counter-current extraction process in two stages. Comparing the results of the present study with those of the processes described in Table 1, it may be concluded that the present process is devoid of the disadvantages encountered with other solvents. The process is very attractive and has good scope for commercial exploitation.
Phase-equilibrium studies In these experiments, the tar acids formed one component and neutral oils
295 TABLE3 Effect of using petroleum ether (boilingrange, 60-80 °C ) as counter-solventin the extract*. Tar oil-petroleum ether volumeratio, 1 : 1 Solvent
Feed (tar oil), g
% Compositionof extract (solvent-free)after one petroleum ether washing Tar acids
Tar bases
Neutral oil
% Recoveryof tar acids (based on tar acids in originalfeed)
1.
Triethylene glycol (AR)
25.25
75.6
3.3
21.1
83.3
2.
Diethyleneglycol {AR)
25.29
75.8
3.3
20.9
82.4
3.
Ethyleneglycol (AR)
25.23
83.7
1.9
14.4
80.4
4.
Ethylene glycol (90 wt%)
25.12
89.9
0.6
9.5
79.2
5.
Ethyleneglycol (90 wt% )
25.15
93.0
0.7
6.3
79.1
*Extracts obtained in two successiveextractions using feed-solventratio of 1 : 1. with a small quantity of tar bases was classified as another. A solvent of 80% aqueous ethylene glycol formed the third component of the ternary system. In order to plot tie lines phase-equilibrium data determined earlier were used. The percentage compositions of the extract and raffinate phases were calculated for each case. The calculations were made on a base-free basis to avoid complications in representation, particularly because tar bases form a very minor constituent in the system. T h u s a number of conjugate points were obtained which were plotted to give the equilibrium diagram for the system (Fig. 2). From the phase-equilibrium diagram it can be seen t h a t the tangent SE drawn from S meets the binodal curve at Em which represents the m a x i m u m purity of tar acids obtainable in the system under the given experimental conditions. Thus the highest degree of purity t h a t could be achieved for tar acids works out to be 87% on a solvent-free basis. A feed of 100 g tar oil comprising 45% tar acids and 55% neutral oil is represented by the point F. (The feed was so chosen because the average tar acids content of low temperature carbonisation tar oil fraction boiling up to 270 °C is around 45%. ) On adding solvent to F the overall composition of the ternary mixture moves along the line FS. The tie line Rm Em cuts FS at M which represents the composition of the feed-solvent mixture and M splits up into extract phase, Em and raffinate phase, Rm. Em represents the extract phase containing 87% of tar acids (after solvent removal) which is the m a x i m u m concentration possible in the system. The cor-
296 TAR ACIOS
90
R~IO,--~-------~o,~ " ~' ~ \ ~o eo
NEUTRAL
~I
~o,
~
60
~q
*
so
~'
~o
"
30
"
zo /
/ ' 'w~
SOLV~XT
~
"
/
Fig. 2. Extraction of tar acids from tar oils by 80% aqueous ethylene glycol {Hunter and Nash construction ).
responding raffinate phase is Rm and the raffinate composition corresponds to a tar acid content of 2% on a solvent-free basis. By measuring the line sections SM and MF the feed-solvent ratio SM: MF was found to be 1 : 2. From measurement of line sections MR,~ and MEre it was evaluated that 50.7 g of solvent-
297 free extract could be obtained containing 87% of tar acids. This corresponds to 98% recovery of the tar acids from the feed.
Calculation of the number of theoretical stages The extraction stages required for counter-current operation were derived using a construction following the Hunter and Nash method [20 ], the application of which has been described by Alders [21]. It can be seen from Fig. 2 that five tie lines have been obtained by the analysis method described earlier. The end-points of a tie line ( conjugate points) represent two coexisting phases on the binodal curve. Through each of the conjugate points of a tie line, lines parallel to the sloping sides of the triangle were drawn (not shown in the figure) which intersected at points lying above and below the baseline of the triangle. Thus ten points of intersections obtained from ten conjugate points of five tie lines were connected to obtain the conjugate line which intersects the binodal curve at p. This is referred to as the critical mixing point or plait point. As mentioned earlier, Rm, the final raffinate, is taken to contain 2% of tar acids. The lines RmS and FQ (Q lying in immediate proximity to Era) were drawn to intersect at operation point H. Rm S intersects the binodal curve at P1 which represents the final raffinate phase. Through P1, a line parallel to the sloping side of the triangle was drawn which intersects the conjugate line at a point. From this intersecting point a line parallel to the other sloping side of the triangle was drawn which meets the binodal curve at Q1. P1 and Q1 are coexisting phases and the line PIQ~ is a tie line. Q1 was connected to H and the line HQ1 extended till it reintersected the binodal curve at P2. The tie line P2 Q2 was drawn repeating the construction from Pz as above. The two tie lines P1 Q1 and P2 Q2 drawn in the ternary diagram to effect separation into P1 and Q2 indicate the number of theoretical extraction stages needed with a feedsolvent ratio of 1 : 2. It is thus seen that two theoretical stages are required to effect 98% recovery of tar acids from a feed oil containing 45% tar acids.
Ternary solubility data In order to speculate the relative effectiveness of different aqueous glycols at 80% solvent strength, binodal curves for the system tar acids-neutral oils80% aqueous glycols were obtained using the ternary solubility data determined earlier by the titration method (Fig. 3). Several points of the binodal curves were obtained calculating the composition of the turbidity-mixing points. In this system, the liquid pairs tar acids-neutral oils and 80% aqueous glycols-tar acids are miscible in all proportions at a prevailing temperature of ca. 30 ° C, whereas neutral oils and solvent are partially miscible. Hence the system under question is one containing a pair of partially miscible compo-
298 TAR A[iDS
Y 60
~0
SO
SO
~,0
6O
30
7O
20
gO
10
I
NOILS'
90
BO
70
J
I
60
SO
I
~,0
30
20
I0
SOLVENT
Fig. 3. Distribution curves for the system tar acids-neutral oils-aqueous glycols (80% by weight) at 30 °C: ( Q ) 80% triethylene glycol, ( & ) 80% diethylene glycol,and ([]) 80% ethylene glycol. nents. The nature of the binodal curves shown in Fig. 3 is fairly common in literature [22]. It is evident from the areas of heterogeneity of the binodal curves that 80% aqueous solutions of triethylene glycol, diethylene glycol and ethylene glycol are very effective solvents for extracting tar acids from L T T oil fraction boiling up to 270 oC. CONCLUSIONS 1. Ethylene glycol, diethylene glycol and triethylene glycol alone or in aqueous solutions (80 wt.% ) are effective solvents for tar acids and can be used for the separation of tar acids from low temperature tar oil fraction boiling up to 270°C. 2. Ethylene glycol, diethylene glycol and triethylene glycol can effect a recovery of 89%, 92.5% and 93%, respectively, of tar acids in two stages of extraction using a feed-solvent weight ratio of 1 : 1. Considerable amounts of tar
299
bases and neutral oil are also extracted with the solvent. The purity of the extracted tar acids can be improved by about 11-17% using petroleum ether as a counter-solvent. 3. Aqueous ethylene glycol (80 wt.% ) can effect a recovery of 84% of the tar acids in two extraction stages using a feed-solvent weight ratio of 1 : 1. The purity of tar acids obtained is 82%, the impurities being neutral oil and tar bases. Re-extraction of the extract with petroleum ether can raise the purity of tar acids to 93%. 4. The tar acids in the extracts can be separated from the solvent simply by dilution with water. 5. From the phase-equilibrium studies of the system tar acids- (neutral oil + tar bases )-80 wt% aqueous ethylene glycol, it has been found that two theoretical stages are required to effect a recovery of 98% tar acids using a feedsolvent ratio of 1:2 from a feed (tar oil) containing 45% tar acids. The process, being very attractive, has good scope for commercial exploitation. ACKNOWLEDGEMENT
The authors wish to express their gratitude to Dr Asit Bhattacharjee, Scientist, for his assistance in analysing the samples by gas chromatography.
REFERENCES 1 Karr, C.J., 1963. In: H.H. Lowry (Ed.), Chemistry of Coal Utilization. John Wiley and Sons, Inc., New York, NY, Supplementary Volume, pp. 539-579. 2 Herman, W.A.O., 1972. Oils and basic organic chemicals from coal by hydrogenation. In: A.R.N. Rao, Samir Sen and S. Ranga Raja Rao (Eds.), Proceedings of the Symposium on Chemicals and Oil from Coal. CFRI, Dhanbad, pp. 23-43. 3 Lahiri, A. and Mukherjee, D.K., 1972. Technoeconomic feasibility of production of oil from coal in Upper Assam. In: A.R.N. Rao, Samir Sen and S. Ranga Raja Rao (Eds.), Proceedings of the Symposium on Chemicals and Oil from Coal. CFRI, Dhanbad, pp. 51-88. 4 Bhaduri, T.J., Sen, D.K., Tiwari, K.K. and Nair, C.S.B., 1972. Recovery of phenols from coal tars. In: A.R.N. Rao, Samir Sen and S. Ranga Raja Rao (Eds.), Proceedings of the Symposium on Chemicals and Oil from Coal. CFRI, Dhanbad, pp. 373-381. 5 Tiwari, K.K., Kumar, P.R. and Bhaduri, T.J., 1978. Extraction and hydrotreatment of phenolics from coal hydrogenation. Indian J. Technol., 16: 457-464. 6 Tiwari, K.K., Banerjee, S.N., Bhattacharjee, Asit and Bhattacharya, R.N., 1988. Catalytic hydrodealkylation of tar acids. App. Catal., 45: 39-51. 7 Tiwari, K.K., 1981. Studies on the recovery and dealkylation of tar acids, PhD thesis, Indian School of Mines, Dhanbad. 8 Higuchi, K., Osa, T., Takeuchi, T. and Kanetaka, J., 1960. Aqueous methanol extraction of phenols ( 1 ) - - Fundamental consideration for aqueous methanol extraction of phenols. J. Fuel Soc. Jpn., 39: 33-41. 9 Treybal, R.E., 1961. Liquid extraction. Industrial Engineering Chemistry, 53: 161-165.
300 10 11 12 13 14
15 16
17
18 19 20
21
22
Neuworth, M.B., Hofmann, V. and Kelly, T.E., 1951. Fractional extraction process for recovery of pure tar acids. Ind. Eng. Chem., 43: 1689-1694. Batchelder, H.R., Filbert, R.B., Jr. and Mink, W.H., 1960. Processing low temperature lignite tar. Ind. Eng. Chem., 52: 131-136. Kowalski, J. and Szczurek, J., 1958. Experiments about phenol extraction from tar oils by means of organic solvents. Extraction by means of ethyl alcohol. Koks Smola Gaz., 3:11-19. Kowalski, J. and Los, B., 1959. 0ber die Entphenolung yon TeerSlen mittels Milchs~iure. Brennst. Chemie, 40: 198-201. Cumming, A.P.C. and Morton, F., 1952. Solvent extraction of phenol from coal-tar hydrocarbons: The use of glycerol, triethylene glycol and their aqueous solutions as solvents. J. Appl. Chem., 2: 314-323. Cumming, A.P.C., 1953. Separation of phenols from coal-tar hydrocarbons by means of glycerol and aqueous triethylene glycol: Development of a process. J. Appl. Chem., 3: 98-106. Zanella, I., Weber, J.V., Gruber, R. and Cagniant, D., 1988. Study of hydroxyaromatic compounds from coal-derived liquids: Global characterisation by distillation, anion exchange separation, titration, 1H NMR, mass spectrometry and functional group determination. Fuel Processing Technol., 20: 33-42. Zanella, I., Weber, J.V., Gruber, R. and Cagniant, D., 1988. Study of hydroxyaromatic compounds from Coal-derived liquids. 1. An anion exchange method of extraction. Analysis, 16: 287-291. Bhattacharjee, A. and Bhaumik, A., 1977. Analysis of low-boiling isomers of phenols by gas chromatography. J. Chromatogr., 136: 328-331. Nair, C.S.B., Sen, D.K. and Basu, A.N., 1965. Extraction of tar acids from low-temperature tar oils by acetic acid. J. Appl. Chem., 15: 505-512. Hunter, T.G. and Nash, A.W., 1934. The application of physicochemical principles to the design of liquid-liquid contact equipment. II. Application of phase-rule graphical methods. J. Soc. Chem. Ind., 53: 95T. Alders, L., 1955. Phase equilibria: Determination of the critical mixing point by construction. Determination of the number of stages by construction. In: L. Alders (Ed.), Liquid-Liquid Extraction. Elsevier, Amsterdam, pp. 20-92. Treybal, R.E., 1963. Formation of one pair of partially miscible liquids. In: R.E. Treybal {Ed. ), Liquid Extraction. McGraw-Hill, New York, NY, 2nd edition, pp. 15-17.
287
Elsevier Science Publishers B.V., Amsterdam
Extraction of tar acids with glycols K. K. Tiwari and D. K. Sen Central Fuel Research Institute, PO FRI, Dhanbad-828108, Bihar (India) (Received April 18th, 1990; accepted in revised form December 24th, 1990)
Abstract Recovery of tar acids from low temperature tar oil fraction boiling up to 270 ° C was investigated using glycols as solvent. AR grade ethylene glycol, diethylene glycol and triethylene glycol effected a recovery of 89%, 95.5% and 93.5%, respectively, of tar acids in two stages of extraction using a feed-solvent ratio of 1 : 1 by weight. Considerable amounts of neutral oil and tar bases were also extracted with solvents. Aqueous ethylene glycol (80 wt% ) in the solvent-feed ratio of 1 : 1 was found to effect a recovery of 84% of the tar acids present in the tar oils in two extraction stages with 82% purity of tar acids. The purity of the extracted tar acids could be improved by the use of petroleum ether as a counter-solvent. The phase-equilibrium characteristics of the system, tar acids-neutral oil-80% aqueous ethylene glycol were studied. It has been shown that two theoretical extraction stages could effect the recovery of 98% of tar acids from a feed oil containing 45% of tar acids at the feed-solvent ratio of 1 : 2 (by weight) and the highest degree of purity that could be achieved for tar acids is 87%.
INTRODUCTION
The major feedstocks for the production of organic chemicals are petroleum and coal. In the context of a global oil crisis, coal is bound to stage a comeback as a more dependable reserve which will provide primary feedstock to chemical industries for at least another century. The byproducts from coal carbonisation and oil from coal will be the major future feedstock for the organic chemical industry. In India, low temperature carbonisation (LTC) of coal has definite future. Even on a very moderate estimate at least 15 million tonnes of coal per annum will have to be carbonised by LTC to provide domestic fuel for the urban sector. This will give rise to a very sizeable amount of tar, about 7-8% of the total quantity of coal carbonised: 20-25 % of low temperature tar (LTT) constitutes tar acids. It has been shown that the economy of LTC is linked up with the profitable recovery of byproducts, such as tar acids, aromatics, etc. [ 1-3 ]. Bearing in mind the techno-economic aspects of the problems involved in the utilisation of tar acids, different methods of recovery, purification and subsequent processing of higher tar acids have been investigated in this laboratory 0378-3820/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved
288 TABLE 1 Comparison of solvents for extraction of tar acids from low temperature tar oil fraction boiling up to 270°C Solvent
Oil-solvent % Extraction of ratio components by two successive extractions
Advantages/disadvantages of the processes
Tar Tar Neutral acids bases oil Methanol (70%) Monoethanolamine (70%) Ethylene diamine (70%) Acetic acid (60%) Acetamide (saturated soln.) Formamide (100%) Dimethylformamide (70%)*
1:1 1:2 1:2 1:1 l: 1 1:1 1:1.2
Sodium hydroxide (10%)
1:1
Ammonia solution (4%)*
1:7
89.6 93.3 96.0 91.9 95.8 88.0 92.0
100
56.4 30.4 22.3 97.0 53.1 19.3 79.3
30.6 16.9 15.4 20.4 12.0 14.7 35.9
The solvents have high extraction efficiency for tar acids, but they also extract tar bases and neutral oil so that the desirable product purity is not obtained. Hence the processes are unattractive for industrial scale operations.
12.9
7.2
This is a batch process practised on a commercial scale. Recovery of tar acids requires consumption of reagents in the extraction, springing and regeneration cycles. The disadvantages are the problems of recausticisation of the carbonate liquor, corrosion and high cost of operation.
77.0 18.5 20.5
Extraction of tar acids is lower than for other solvents but all the phenol, cresols and some xylenols are extracted by the solvent. Contaminations by neutral oil and tar bases make the process unattractive.
*Results given are for one extraction. *Results given are for three extractions. [ 4 - 6 ]. T h e p r e s e n t p a p e r is c o n c e r n e d w i t h e x a m i n i n g g l y c o l s a s s e l e c t i v e s o l v e n t s f o r t h e e x t r a c t i o n o f t a r a c i d s f r o m L T T oil f r a c t i o n b o i l i n g u p t o 270 ° C. In an effort to replace the conventional process of extracting tar acids using caustic soda which has inherent disadvantages, various solvents have been tried o u t i n d i f f e r e n t p a r t s o f t h e w o r l d b u t a n i d e a l s o l u t i o n t o t h e p r o b l e m is y e t t o be found. R e c o v e r y o f t a r a c i d s f r o m t a r oil f r a c t i o n s h a s b e e n i n v e s t i g a t e d f r o m v a r -
289 ious angles. An account of all the processes used with L T T oil fraction boiling up to 270 ° C has already been presented elsewhere [ 1 ]. A comparison of the solvents under optimum conditions as mentioned in literature was made and the results are presented in Table 1. Organic solvents such as methanol [8-11], ethanol [ 12 ], fatty acids [ 13 ], etc., have been used mostly in conjunction with counter-solvents for suppressing the entrainment of neutral oil into the extract phase. The possibilities of using glycols and glycerols as solvents were examined by Cumming and Morton [14,15 ]. Triethylene glycol was found to have good selectivity for phenol. Aqueous triethylene glycol was claimed to extract almost all phenols from a high temperature tar oil fraction boiling up to 201°C, in three theoretical counter-current stages using a solvent ratio of 1:1. The solvent-free extract consisted of 82% phenols and 18% hydrocarbons. Dry glycerol was claimed to be the best extractant for phenol. However, a high degree of selectivity and extraction efficiency was not obtained when working with a phenolic mixture and commercial fractions. Aromatic hydroxy compounds present in low temperature pyrolysis coal tar have been recovered recently using a nonaqueous anionic exchange process [ 16-17 ]. The process has been claimed to be a rapid and simple method for the characterization of the acidic components of a coal tar. This paper contains results which show that ethylene glycol, diethylene glycol and triethylene glycol are appreciably effective for the extraction of tar acids from L T T oil fraction boiling up to 270 ° C. The phase-equilibrium characteristics of the system, tar acids-neutral oil-80% aqueous ethylene glycol are reported. EXPERIMENTAL DETAILS Feed material
Feedstocks were obtained by distillation of tar derived from the LTC pilot plant of the Central Fuel Research Institute, Dhanbad. The tar oil fraction boiling up to 270°C was collected. This oil had a specific gravity of 0.9535 at 30 ° C and a percentage composition as follows: tar acids - 41.3; tar bases - 3.5; and neutral oil - 55.2. For phase-equilibrium studies, tar acids and tar bases were separated from the above tar oil fraction using the standard method of alkali and acid treatment. Tar acids obtained were further extracted with saturated sodium bicarbonate solution to remove any aliphatic acid present. Both the purified tar acids and neutral oil were distilled under reduced pressure. The phenols were analysed by gas chromatography in a Perkin-Elmer 810 gas chromatograph with a flame ionisation detector using nitrogen as carrier gas (flow rate, 30 m l / min) and employing the method described by Bhattacharjee and Bhaumik [ 18 ].
290
The percentage composition of tar acids was: phenol - 13.7; o-cresol - 9.4; mcresol - 10.8; p-cresol - 12.8; xylenols and other high boiling phenols - 53.3.
Solvent Ethylene glycol, diethylene glycol and triethylene glycol, all Fluka AR grade chemicals and their aqueous solutions were used as solvents. Petroleum ether (boiling range, 6 0 - 8 0 ° C ) was used as a counter-solvent.
Extraction procedure Most extractions were done in separating funnels or jacketed columns provided with thermostat and axial stirrers. The temperature was maintained at 30 °C for all extractions. The procedures of operations are presented in Schemes 1-4.
Determination of phase-equilibrium data For phase-equilibrium studies, neutral oil and tar bases obtained from feed tar oil were mixed together in the proportion in which they occur in this oil. To this mixture were added tar acids and solvent in different proportions to obtain a series of mixtures. These were shaken for 30 min in a separating fun-
E~
"i Back-washing ~REFfNEDEXTRACT
TAROIL - S°'vent ' _30rain (I:( W la /w ] i_ R~ Solvent Shaking
(FE2-~" Petroleum.__ether, I.
(I Vol. per Vol. Tar oil / [
Settling 1 h
as(aLij
~PETROL.ETHERSOLN.
~2
E= EXTRACT
R = RAFFINATE
Scheme i. General extraction procedure.
- AIIUEOUSSOLVENT (b} Water (1:1~v) & Settling 1 h
EXTRACT Shaking
I
-VERYDILUTED SOLVENT Wafer aslb) I ~ ORSANI[PHASE
Scheme 2. Elimination of the solvent.
~OLVENT-FREE EXTRACT
291
m
-~
rY I--
w
w
t~ __J
z
- L___]
f2: b--
i
,,=,
b--z
z
,e,
--~°
t~
i
_>
a~
w ~
~ z
292 RAFFINATE ETHER ADDED{I: I V/v ) ETHER( LAYER EXTRACTION,10°/o NaOH
ALKALI~EXTRACT { a}
SOLVEN~ LAYER ( ENTRAINEDIN RAFFINATE
ETHER~OLUTION EXTRACTION,25 °/o HzS0
ACID EXTRACT Ib)
ETHER SOLUTION Ic]
Scheme 4. Raffinate treatment (estimated for acids, tar bases and neutral oils from (a), (b) and (c), respectively as described under scheme 3 ).
nel provided with water circulation to control the temperature at 30 ° C. The extract and raffinate phases were allowed to settle (1 h), separated and then analysed.
Determination of ternary solubility data These were determined by the titration method described below. A number of mixtures were made containing tar acids and solvent forming a miscible layer. Then neutral oil was added dropwise from a burette, while shaking, until a permanent turbidity point {immiscibility point) appeared. In this way, the maximum quantity of neutral oil soluble in the system was recorded. Similarly various mixtures of tar acids and neutral oil were prepared, and solvent was added to the mixture as above until two phases appeared. Lastly a series of known mixtures of neutral oil and solvent, which form immiscible layers, were made. To each of the mixtures, tar acids were added dropwise, while shaking, till the miscibility point was reached and the solution became homogeneous. All the above experiments were performed in a constant temperature bath at 30 ° C, provided with an arrangement for light to facilitate easy observation of turbidity-miscibility points. RESULTS AND DISCUSSION
Mass balances of the extraction The results for two successive extractions using a feed-solvent weight ratio of 1 : 1 are presented in Table 2. It is seen that the recovery of tar acids with ethylene glycol, diethylene glycol and triethylene glycol are respectively, 89.1%, 92.5% and 93.5%, the corresponding figures for neutral oil being 24.6%, 42.2% and 44.1%. The tar bases, though a minor component gave 75.9% recovery with diethylene glycol and triethylene glycol whereas 40% of tar bases were extracted with ethylene glycol. Thus with diethylene glycol and triethylene glycol
293 TABLE 2 Extraction of tar acids from L T T oil fraction (boiling up to 270 ° C ) with glycols at 30 ° C. (Feedsolvent weight ratio 1 : 1; two successive extractions) Solvent
1. Ethylene glycol (AR) 2. Diethylene glycol (AR) 3. Triethylene glycol (AR)
Feed (tar oil ), g
% Recovery in the extract, based on the components originally present in the feed
% Composition of extract (solvent-free)
Tar acids
Tar bases
Neutral oil
Tar acids
Tar bases
Neutral oil
22.89
89.1
40.0
24.6
72.3
2.7
25.0
23.47
92.5
75.9
42.2
59.5
4.2
36.3
23.47
93.5
75.9
44.1
58.8
4.1
37.1
the purity achieved for tar acids is around 59% whereas the corresponding figure with ethylene glycol is 72.3%. Considering the recovery as well as purity of tar acids in the solvent-free extract, ethylene glycol appeared to be a better solvent than the other two glycols. A detailed study, therefore, was undertaken with ethylene glycol.
Effect of concentration of the solvent Ethylene glycol was diluted with distilled water to obtain concentrations of 90, 80, 70 and 60 wt% of solvent. The extraction of tar acids from L T T oil fraction was carried out with the above concentrations of solvent in two successive stages maintaining the feed-solvent weight ratio of 1:1 throughout. The results are presented in Fig. 1. It is seen that the recovery of tar acids is 85% with 90% ethylene glycol, the corresponding figure with 80% solvent strength being 84%. However, at 70% and 60% concentrations of ethylene glycol, the recovery decreased significantly, the respective values being 55.5 and 50.8% of tar acids. The solvent-free extract contained 2-2.5% base over the entire range of extractions, while the contamination by neutral oil in the extract varied in the range 16-21%. It is observed that with 80% ethylene glycol the neutral oil contamination (defined as percentage of neutral oil in the extract) was minimum at 16% and the degree of purity of extracted tar acids was highest at ca. 82%. Hence, 80% solvent strength was considered optimum.
Effect of using petroleum ether as counter-solvent The process generally referred to as back-washing has been detailed elsewhere [ 19 ]. The counter-solvent, being more selective towards neutral oil rather
294
9O
30
.~
.,..:
80
d
! 2o
,~ 70
>- 60
to
~ 5o 1
60
I
I
70
80
I
90
STRENGTH OF SOLVENT, °/olW/W)
Fig. 1. Effect of e t h y l e n e glycol c o n c e n t r a t i o n on t a r acids recovery: ( Q ) recovery of t a r acids, a n d ( & ) neutral oil c o n t a m i n a t i o n .
than tar acids, extracted considerable amounts of neutral oil and to some extent tar bases contaminated with tar acids of the extract, thus improving the overall purity of the desired product. The results are presented in Table 3. It can readily be seen that re-extraction of the ethylene glycol extracts using petroleum ether improved the purity of tar acids by about 11% whereas reextraction of diethylene and triethylene glycol extracts resulted in an increase in the purity of tar acids to around 75.5% from about 59% (when no countersolvent was used). At 80% ethylene glycol concentration, the purity of the solvent-free extract could be improved from 82% to about 93%. It is further seen that the recovery figures for tar acids are somewhat less than the original, indicating that some acids are lost in the counter-solvent stream. Since the counter-solvent may be reused, however, these losses are expected to be minimised in a continuously operated process and can, at any rate, be recovered from the finally exhausted stream also. From the foregoing, it is inferred that 80% aqueous ethylene glycol in conjunction with petroleum ether can effect 84% extraction of tar acids with 93 % purity in a continuous counter-current extraction process in two stages. Comparing the results of the present study with those of the processes described in Table 1, it may be concluded that the present process is devoid of the disadvantages encountered with other solvents. The process is very attractive and has good scope for commercial exploitation.
Phase-equilibrium studies In these experiments, the tar acids formed one component and neutral oils
295 TABLE3 Effect of using petroleum ether (boilingrange, 60-80 °C ) as counter-solventin the extract*. Tar oil-petroleum ether volumeratio, 1 : 1 Solvent
Feed (tar oil), g
% Compositionof extract (solvent-free)after one petroleum ether washing Tar acids
Tar bases
Neutral oil
% Recoveryof tar acids (based on tar acids in originalfeed)
1.
Triethylene glycol (AR)
25.25
75.6
3.3
21.1
83.3
2.
Diethyleneglycol {AR)
25.29
75.8
3.3
20.9
82.4
3.
Ethyleneglycol (AR)
25.23
83.7
1.9
14.4
80.4
4.
Ethylene glycol (90 wt%)
25.12
89.9
0.6
9.5
79.2
5.
Ethyleneglycol (90 wt% )
25.15
93.0
0.7
6.3
79.1
*Extracts obtained in two successiveextractions using feed-solventratio of 1 : 1. with a small quantity of tar bases was classified as another. A solvent of 80% aqueous ethylene glycol formed the third component of the ternary system. In order to plot tie lines phase-equilibrium data determined earlier were used. The percentage compositions of the extract and raffinate phases were calculated for each case. The calculations were made on a base-free basis to avoid complications in representation, particularly because tar bases form a very minor constituent in the system. T h u s a number of conjugate points were obtained which were plotted to give the equilibrium diagram for the system (Fig. 2). From the phase-equilibrium diagram it can be seen t h a t the tangent SE drawn from S meets the binodal curve at Em which represents the m a x i m u m purity of tar acids obtainable in the system under the given experimental conditions. Thus the highest degree of purity t h a t could be achieved for tar acids works out to be 87% on a solvent-free basis. A feed of 100 g tar oil comprising 45% tar acids and 55% neutral oil is represented by the point F. (The feed was so chosen because the average tar acids content of low temperature carbonisation tar oil fraction boiling up to 270 °C is around 45%. ) On adding solvent to F the overall composition of the ternary mixture moves along the line FS. The tie line Rm Em cuts FS at M which represents the composition of the feed-solvent mixture and M splits up into extract phase, Em and raffinate phase, Rm. Em represents the extract phase containing 87% of tar acids (after solvent removal) which is the m a x i m u m concentration possible in the system. The cor-
296 TAR ACIOS
90
R~IO,--~-------~o,~ " ~' ~ \ ~o eo
NEUTRAL
~I
~o,
~
60
~q
*
so
~'
~o
"
30
"
zo /
/ ' 'w~
SOLV~XT
~
"
/
Fig. 2. Extraction of tar acids from tar oils by 80% aqueous ethylene glycol {Hunter and Nash construction ).
responding raffinate phase is Rm and the raffinate composition corresponds to a tar acid content of 2% on a solvent-free basis. By measuring the line sections SM and MF the feed-solvent ratio SM: MF was found to be 1 : 2. From measurement of line sections MR,~ and MEre it was evaluated that 50.7 g of solvent-
297 free extract could be obtained containing 87% of tar acids. This corresponds to 98% recovery of the tar acids from the feed.
Calculation of the number of theoretical stages The extraction stages required for counter-current operation were derived using a construction following the Hunter and Nash method [20 ], the application of which has been described by Alders [21]. It can be seen from Fig. 2 that five tie lines have been obtained by the analysis method described earlier. The end-points of a tie line ( conjugate points) represent two coexisting phases on the binodal curve. Through each of the conjugate points of a tie line, lines parallel to the sloping sides of the triangle were drawn (not shown in the figure) which intersected at points lying above and below the baseline of the triangle. Thus ten points of intersections obtained from ten conjugate points of five tie lines were connected to obtain the conjugate line which intersects the binodal curve at p. This is referred to as the critical mixing point or plait point. As mentioned earlier, Rm, the final raffinate, is taken to contain 2% of tar acids. The lines RmS and FQ (Q lying in immediate proximity to Era) were drawn to intersect at operation point H. Rm S intersects the binodal curve at P1 which represents the final raffinate phase. Through P1, a line parallel to the sloping side of the triangle was drawn which intersects the conjugate line at a point. From this intersecting point a line parallel to the other sloping side of the triangle was drawn which meets the binodal curve at Q1. P1 and Q1 are coexisting phases and the line PIQ~ is a tie line. Q1 was connected to H and the line HQ1 extended till it reintersected the binodal curve at P2. The tie line P2 Q2 was drawn repeating the construction from Pz as above. The two tie lines P1 Q1 and P2 Q2 drawn in the ternary diagram to effect separation into P1 and Q2 indicate the number of theoretical extraction stages needed with a feedsolvent ratio of 1 : 2. It is thus seen that two theoretical stages are required to effect 98% recovery of tar acids from a feed oil containing 45% tar acids.
Ternary solubility data In order to speculate the relative effectiveness of different aqueous glycols at 80% solvent strength, binodal curves for the system tar acids-neutral oils80% aqueous glycols were obtained using the ternary solubility data determined earlier by the titration method (Fig. 3). Several points of the binodal curves were obtained calculating the composition of the turbidity-mixing points. In this system, the liquid pairs tar acids-neutral oils and 80% aqueous glycols-tar acids are miscible in all proportions at a prevailing temperature of ca. 30 ° C, whereas neutral oils and solvent are partially miscible. Hence the system under question is one containing a pair of partially miscible compo-
298 TAR A[iDS
Y 60
~0
SO
SO
~,0
6O
30
7O
20
gO
10
I
NOILS'
90
BO
70
J
I
60
SO
I
~,0
30
20
I0
SOLVENT
Fig. 3. Distribution curves for the system tar acids-neutral oils-aqueous glycols (80% by weight) at 30 °C: ( Q ) 80% triethylene glycol, ( & ) 80% diethylene glycol,and ([]) 80% ethylene glycol. nents. The nature of the binodal curves shown in Fig. 3 is fairly common in literature [22]. It is evident from the areas of heterogeneity of the binodal curves that 80% aqueous solutions of triethylene glycol, diethylene glycol and ethylene glycol are very effective solvents for extracting tar acids from L T T oil fraction boiling up to 270 oC. CONCLUSIONS 1. Ethylene glycol, diethylene glycol and triethylene glycol alone or in aqueous solutions (80 wt.% ) are effective solvents for tar acids and can be used for the separation of tar acids from low temperature tar oil fraction boiling up to 270°C. 2. Ethylene glycol, diethylene glycol and triethylene glycol can effect a recovery of 89%, 92.5% and 93%, respectively, of tar acids in two stages of extraction using a feed-solvent weight ratio of 1 : 1. Considerable amounts of tar
299
bases and neutral oil are also extracted with the solvent. The purity of the extracted tar acids can be improved by about 11-17% using petroleum ether as a counter-solvent. 3. Aqueous ethylene glycol (80 wt.% ) can effect a recovery of 84% of the tar acids in two extraction stages using a feed-solvent weight ratio of 1 : 1. The purity of tar acids obtained is 82%, the impurities being neutral oil and tar bases. Re-extraction of the extract with petroleum ether can raise the purity of tar acids to 93%. 4. The tar acids in the extracts can be separated from the solvent simply by dilution with water. 5. From the phase-equilibrium studies of the system tar acids- (neutral oil + tar bases )-80 wt% aqueous ethylene glycol, it has been found that two theoretical stages are required to effect a recovery of 98% tar acids using a feedsolvent ratio of 1:2 from a feed (tar oil) containing 45% tar acids. The process, being very attractive, has good scope for commercial exploitation. ACKNOWLEDGEMENT
The authors wish to express their gratitude to Dr Asit Bhattacharjee, Scientist, for his assistance in analysing the samples by gas chromatography.
REFERENCES 1 Karr, C.J., 1963. In: H.H. Lowry (Ed.), Chemistry of Coal Utilization. John Wiley and Sons, Inc., New York, NY, Supplementary Volume, pp. 539-579. 2 Herman, W.A.O., 1972. Oils and basic organic chemicals from coal by hydrogenation. In: A.R.N. Rao, Samir Sen and S. Ranga Raja Rao (Eds.), Proceedings of the Symposium on Chemicals and Oil from Coal. CFRI, Dhanbad, pp. 23-43. 3 Lahiri, A. and Mukherjee, D.K., 1972. Technoeconomic feasibility of production of oil from coal in Upper Assam. In: A.R.N. Rao, Samir Sen and S. Ranga Raja Rao (Eds.), Proceedings of the Symposium on Chemicals and Oil from Coal. CFRI, Dhanbad, pp. 51-88. 4 Bhaduri, T.J., Sen, D.K., Tiwari, K.K. and Nair, C.S.B., 1972. Recovery of phenols from coal tars. In: A.R.N. Rao, Samir Sen and S. Ranga Raja Rao (Eds.), Proceedings of the Symposium on Chemicals and Oil from Coal. CFRI, Dhanbad, pp. 373-381. 5 Tiwari, K.K., Kumar, P.R. and Bhaduri, T.J., 1978. Extraction and hydrotreatment of phenolics from coal hydrogenation. Indian J. Technol., 16: 457-464. 6 Tiwari, K.K., Banerjee, S.N., Bhattacharjee, Asit and Bhattacharya, R.N., 1988. Catalytic hydrodealkylation of tar acids. App. Catal., 45: 39-51. 7 Tiwari, K.K., 1981. Studies on the recovery and dealkylation of tar acids, PhD thesis, Indian School of Mines, Dhanbad. 8 Higuchi, K., Osa, T., Takeuchi, T. and Kanetaka, J., 1960. Aqueous methanol extraction of phenols ( 1 ) - - Fundamental consideration for aqueous methanol extraction of phenols. J. Fuel Soc. Jpn., 39: 33-41. 9 Treybal, R.E., 1961. Liquid extraction. Industrial Engineering Chemistry, 53: 161-165.
300 10 11 12 13 14
15 16
17
18 19 20
21
22
Neuworth, M.B., Hofmann, V. and Kelly, T.E., 1951. Fractional extraction process for recovery of pure tar acids. Ind. Eng. Chem., 43: 1689-1694. Batchelder, H.R., Filbert, R.B., Jr. and Mink, W.H., 1960. Processing low temperature lignite tar. Ind. Eng. Chem., 52: 131-136. Kowalski, J. and Szczurek, J., 1958. Experiments about phenol extraction from tar oils by means of organic solvents. Extraction by means of ethyl alcohol. Koks Smola Gaz., 3:11-19. Kowalski, J. and Los, B., 1959. 0ber die Entphenolung yon TeerSlen mittels Milchs~iure. Brennst. Chemie, 40: 198-201. Cumming, A.P.C. and Morton, F., 1952. Solvent extraction of phenol from coal-tar hydrocarbons: The use of glycerol, triethylene glycol and their aqueous solutions as solvents. J. Appl. Chem., 2: 314-323. Cumming, A.P.C., 1953. Separation of phenols from coal-tar hydrocarbons by means of glycerol and aqueous triethylene glycol: Development of a process. J. Appl. Chem., 3: 98-106. Zanella, I., Weber, J.V., Gruber, R. and Cagniant, D., 1988. Study of hydroxyaromatic compounds from coal-derived liquids: Global characterisation by distillation, anion exchange separation, titration, 1H NMR, mass spectrometry and functional group determination. Fuel Processing Technol., 20: 33-42. Zanella, I., Weber, J.V., Gruber, R. and Cagniant, D., 1988. Study of hydroxyaromatic compounds from Coal-derived liquids. 1. An anion exchange method of extraction. Analysis, 16: 287-291. Bhattacharjee, A. and Bhaumik, A., 1977. Analysis of low-boiling isomers of phenols by gas chromatography. J. Chromatogr., 136: 328-331. Nair, C.S.B., Sen, D.K. and Basu, A.N., 1965. Extraction of tar acids from low-temperature tar oils by acetic acid. J. Appl. Chem., 15: 505-512. Hunter, T.G. and Nash, A.W., 1934. The application of physicochemical principles to the design of liquid-liquid contact equipment. II. Application of phase-rule graphical methods. J. Soc. Chem. Ind., 53: 95T. Alders, L., 1955. Phase equilibria: Determination of the critical mixing point by construction. Determination of the number of stages by construction. In: L. Alders (Ed.), Liquid-Liquid Extraction. Elsevier, Amsterdam, pp. 20-92. Treybal, R.E., 1963. Formation of one pair of partially miscible liquids. In: R.E. Treybal {Ed. ), Liquid Extraction. McGraw-Hill, New York, NY, 2nd edition, pp. 15-17.