Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment

Transcription

1 J. Chem. Chem. Eng. 7 (2013) D DAVID PUBLISHING Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment S. Aruna Kumari 1, Goruganthula Venkata Subrahmanya Sarma 1*, G. M. J. Raju 1, J. V. S. Murty 2 and C. Bhaskara Sarma 3 1. Department of Chemical Engineering, College of Engineering (A), Andhra University, Visakhapatnam , India 2. Department of Chemical Engineering, G V P College of Engineering (A), Visakhapatnam , India 3. Gayatri Vidya Parishad College of Engineering for Women, Visakhapatnam , India Received: September 02, 2012 / Accepted: September 28, 2012 / Published: April 25, Abstract: Experiments were conducted for the extraction of phenols from the phenol fraction obtained from the coal tar distillate. The phenol fraction for the present investigation has been procured from Visakhapatnam Steel Plant, Visakhapatnam whose composition is known. The phenol fraction from coal tar distillate can be treated for extracting phenols using caustic soda. An attempt has been made to find out whether the existing practice of using only 8%-15% can be modified by increasing the strength of sodium hydroxide and also explore the possibilities of substituting the sodium hydroxide with KOH as an extractant. The different streams of liquids obtained during experimentation have been analyzed by gas chromatograph. Salient features of the study are that higher concentrations of the alkali significantly improved the separation efficiencies of phenols and also regenerate the phenolate with higher phenol content. Increase in the alkali strength has greatly improved the separation as well as the phenol content in the regenerated phenols. Disposal of effluents containing phenols may lead to environmental problem of ground water pollution and the study throws a light on the removal of phenols from the effluents to the extent possible by using higher strength alkali solutions. Key words: Alkali treatment, phenol, phenol fraction, recovery efficiency, coal tar. 1. Introduction Phenols derived from coal tar have traditionally been used as monomers for the production of phenol formaldehyde resins such as indene-coumarone resins, novalak, resoles and novalak fibers are used in flame and chemical resistant textile and paper industries. These are also used as reinforcement in composite materials, as a precursor for carbon composites and carbon fibres. Resoles are used in the production of decorative laminates. Bis-phenol A and bis-phenol C are two important monomers for the synthesis of polycarbonate resins. The phenols and their derivatives find wide range of applications in household as well as * Corresponding author: Goruganthula Venkata Subrahmanya Sarma, Assistant Professor, research fields: biosorption, corrosion, beach morphology and sedimentology. gvssarma@yahoo.com. in the production of drugs and pharmaceuticals, dye stuffs, and in the agro-chemicals industry. Multivalent phenol is used in the manufacture of black paints, photographic developers and also as wood preservatives. Several investigations have been carried out on the extraction of phenol from phenol fraction by using various treatment methods such as chemical reaction method, solvent extraction, pyrolysis, biological treatment. Among the alternatives, isolation of crude phenol by alkali (sodium hydroxide) extraction is also very popular commercially. Bhattacharya et al. [1, 2] investigated on the industrial applications of phenols and also studied in detail the factors augmenting the recovery of phenols from ammoniacal liquor and its effluents and tar-oil cuts. The author reported that the recovery of phenols from tar-oil cuts was best when

2 Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment % caustic soda was used for the separation of dephenolized phenol and water soluble crude phenolates. In the early days of coal carbonization, only coal tar used to be recovered from the gas. Later, it was discovered that the light oil derived from coal tar contains significant quantities of benzene and this discovery established that coal tar can be used as a raw material for the production of phenols. The phenol constituent of the tar was given as 0.7% by weight of dry tar and this laid a sound foundation to the recovery of phenols from coal tar chemicals. Investigations on tar acids and naphthalene were carried out by Volkman and Rhodes et al. [4]. Coal tar was distilled at 270 o C and the distillate was treated with 15% of NaOH solution. A review of the work done on the solvent extraction of phenols from coal tar fraction was presented by Fenske [5] and Bhaduri et al. [6, 7]. Recovery of phenols from the effluents of coal carburization processes was reported by Chaudhuri [8]. All these investigations carried out phenol recovery process by alkali treatment and a concentration of 15% NaOH was found to be the most optimum. No investigations for the concentration of caustic soda beyond 15% were reported in the literature. Besides this, no attempt has also been made by the earlier investigators to compare the recovery efficiencies when the treatment is carried out using KOH as a substitute for NaOH. The present study envisages recovering the phenols from phenol fraction obtained from coal tar distillation process through employing higher concentration of NaOH as well as a few concentration of KOH. Raw phenol fraction was procured from the tar distillation unit of Visakhapatnam Steel Plant (RINL). The middle oil fraction of the tar distillation unit contains phenols, cresols, xenols and naphthalene. Two methods for recovery of phenols from coal tar are in practice: (1) recovery from ammonical liquor and its effluents; (2) recovery from tar oil cuts. The process involved in the second method is the regeneration of phenol fraction by alkali treatment. The phenol fraction is first treated with alkali solutions (sodium or potassium hydroxide) to form the corresponding alkali phenolate. Subsequently, the water soluble phenolates are separated from dephenolized oil. Then the water soluble crude phenolates are treated with 98% sulphuric acid to obtain the phenols. The reactions during recovery are: Stage 1: Reaction between phenol fraction from coal tar and alkali to get sodium phenolate is shown as: C 6 H 5 OH + NaOH + other oils C 6 H 5 ONa (sodium phenolate) + H 2 O + (dephenolized oils). (1) Stage 2: The regeneration reaction as given: 2C 6 H 5 ONa + H 2 SO 4 2C 6 H 5 OH + Na 2 SO 4. (2) 2. Experimental Procedure Known weight of phenol fraction was treated with various concentrations of NaOH (sodium hydroxide) on weight basis. The weight of NaOH used in the present study were 10%, 15%, 20%, 25%, 30%, 35% and 40%. Experiments were also repeated for comparison using potassium hydroxide. However, the results were obtained only with three concentrations of KOH 15%, 25% and 35%. The entire process involved two stages viz., dephenolisation and regeneration. 100 ml each of RP (regenerated phenols) obtained from all experimental runs were taken, 1,000 ml of toluene added to the RP sample and charged into the distillation unit and distillation carried out. The condensate was collected till temperature rose to 110 o C and slightly more. The condensate contained water and toluene that were separated using a separating funnel. The residue, rich in regenerated phenols, almost completely free of moisture was weighed and used for subsequent analysis. The process flow followed during experimentation is shown in Fig Dephenolisation Stage 50 g of each phenol fraction were treated with sodium hydroxide solutions of a given concentration in

3 336 Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment Phenol fraction NaOH Chemical reaction Mixture H 2 SO 4 Dephenolised oil Sodium phenolate Chemical reaction Regenerated phenol Effluent Fig. 1 Process flow sheet. a separating funnel to convert all phenols into phenoxides. In all the runs, maximum conversion was assured by the addition of sodium hydroxide solutions of desired concentration 20% in excess than those required stoichoimetrically. The contents of the separating funnel are rigorously stirred for 1 h to convert all phenols into phenoxides. The mixture is allowed to settle for about 1 h till two layers (oil and aqueous) are formed. The bottom layer (sodium phenoxides) is drained into another conical flask and top layer is drained into a beaker separately. The oil in the top layer is dephenolized oil. 2.2 Regeneration Stage The bottom layer is treated with 98% sulphuric acid in sufficient amounts (slightly over and above the stoichiometric quantities) to release the phenol from sodium phenoxides. This step involves vigorous exothermic reaction and is carried out slowly and continuously. As soon as the reaction is complete, the mixture is stirred and allowed to settle for about half an hour. Two layers are observed one being organic and the other aqueous. Top layer is rich in phenol (regenerated) and the bottom layer contains sodium sulphate dissolved in water along with some soluble hydrocarbons and phenols. The different streams of solutions/layers on separation were analyzed for their phenol content using the gas chromatograph and the data were given in the Table 1. The compositions of crude phenol, regenerated phenol fraction and dephenolized oil obtained from gas chromatographic analysis was given in the Table Results and Discussion Higher concentrations up to 40% of alkali were attempted during the present investigation to evaluate the recovery efficiencies. Table 1 Composition of phenol fraction. Phenol fraction sample taken g Phenol content in phenol fraction g Cresols content in phenol fraction g Naphthalene content in phenol fraction g Others Remaining

4 Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment Yield of Regenerated Phenol (Crude Phenol) Phenols or regenerated phenol yields are expressed as gm of crude or regenerated phenol l/50 g of phenol fraction and the calculated data for NaOH were plotted (plot A) and shown in Fig. 2. The increase in the regenerated phenol yield was found to be very significant upto 50% with increase in NaOH concentration from 10% to 35%. Phenol fraction of 50 g yield 15.4 g of crude phenol with 10% NaOH and 22 g with 35% NaOH (Table 2). Increasing trend in the yield is consistent and gradual with increasing NaOH concentration. Plot B in the same figure gives the comparison with KOH treatment. The trends observed in both the cases are the same. At concentration of 15% alkali (either NaOH or KOH), the yield of regenerated phenol is almost the same in both the cases while at an alkali strength of 35%, the yield of RP with NaOH was 35% higher than that obtained with KOH. This may be rightly attributed to the higher affinity of sodium over potassium to phenolate group. The higher ionization potentials for Na + over K + that give the measure for affinity might increase the tendency for relatively strong bonding of sodium ion with the phenolate group In view of this, encouraging efficiency of NaOH, a few more experimental runs were conducted at 40% NaOH solution. The first stage of the reaction was smooth as expected while in the second stage of regeneration with sulphuric acid exhibited a certain drawback. A close inspection of the reaction mixture showed that use of NaOH beyond 35% showed a tendency to form emulsion formation of distinct layers of RP and sodium sulphate and hence 40% alkali treatment was Table 2 Effect of concentration of NaOH and KOH (50 gm) with the yield of regenerated phenol, dephenolised oil, loss of phenol and weight of effluent. Sl. Conc. (%) Wt. of RP (gm) Wt. of DO (gm) Wt. Loss of phenol (gm) Wt. of effluent (gm) No. NaOH KOH NaOH KOH NaOH KOH NaOH KOH NaOH KOH Table 3 Effect of sodium hydroxide with phenol content in RP, in DO, Wt.. Loss of phenol, phenol content in effluent (results from gas chromatograph analysis) Wt. of phenol fraction = 100 gm; column temperature = 100 o C; sample injected = 0.2 L; phenol content in raw phenol fraction = 13.9 gm. Sl. No. Conc. of NaOH (%) Wt. of RP (gm) Wt. of phenol content in Wt. of phenol content in Wt. loss of phenol RP (gm) DO (gm) (gm) not considered for subsequent analysis. 3.2 Yield of Dephenolized Oil (DO) Fig. 2 Effect of concentration of NaOH and KOH. Yield of dephenolized oil expressed as g/50 gm of PF (phenol fraction) for different concentrations of NaOH is shown in Fig. 3 and the values are given in the Table 2. Obviously a downward trend was observed in DO yield with increasing strength of NaOH. As expected an increase in the regenerated phenol resulted

5 338 Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment in a decrease in the formation of dephenolized oil. Results are compatible with the yield of RP as discussed above, while 35% NaOH gave the lowest yield, 10% NaOH gave highest yield of DO. Thus, 35% concentration of NaOH was found to be more effective in reducing the dephenolized oil content as this increased the content of regenerated phenol in the phenol fraction. Similar observations were noted with KOH, but in this case the amount of dephenolized oil observed was more with concurrent low yields of regenerated phenol compared to NaOH for any given concentration of alkali. 3.3 Losses in the Experiments Phenols from regenerated phenol layer were lost into the effluent as they are sparingly soluble in water. More the effluent generation and more the loss of phenols into the effluent has been observed from the Table 2 and Fig. 4. Losses appear to follow a specific trend. Treatment with 10% NaOH gave a maximum loss of 2.56 gm/50 g of raw phenol fraction, whereas 35% NaOH gave a minimum loss of 1.37 gm/50 gm, which is almost 50% of the maximum loss with 10% NaOH. The effluent generation was found to be more in case of 10% NaOH, therefore, losses were found to be more at Fig. 3 Effect of concentration of NaOH and KOH. lower concentration of NaOH. Similar trends were also observed with KOH, but the magnitude of losses were found to be 26%-35% lower compared to that of NaOH treatment while the magnitudes of losses, however, were found to be lower by 26%-35% compared to those with NaOH. 3.4 Generation of Effluent As larger amount of water is present in solutions at low concentrations, generation of effluent containing the sulphates of sodium or potassium is supposed to be more at low concentrations of either of the alkalis compared to that at higher concentrations. Amounts of effluent generated are shown in Table 2 for both the cases of NaOH and KOH and the plots of the data on effluent are shown in Fig. 5 for different concentrations of NaOH and KOH. Effluent generation was found to be the least at 35% concentration of either of the alkalis. Compared between the two alkalis, more amount of effluents were obtained in the case of KOH perhaps due to the lesser to the lesser affinity of sulphate of potassium in the effluent stream to regenerated phenol and dephenolized oil. So separation of effluent from phenol fraction appears to be more efficient in the case of KOH than NaOH. Phenol content in RP showed that it increased along with an increase in the concentration of NaOH Table 2 and Fig. 6. Yield of phenol with 30% NaOH was approximately 40% higher than that with 15% NaOH. In the case of phenol content in DO, no specific trend was observed with respect to the NaOH concentration used Table 2 and Fig. 7. Quantity of phenol present in DO was about 8% to 10% of the original Fig. 4 Effect of concentration of NaOH and KOH on weight loss of phenol in effluent. Fig. 5 Effect of conc. of NaOH and KOH on effluent weight.

6 Studies on Recovery Efficiencies of Phenols from Phenol Fraction Using Alkali Treatment 339 Fig. 6 Phenol content in RP vs. conc. of NaOH. Fig. 7 Phenol content in DO vs. conc. of NaOH. increase in concentration of NaOH up to 35%. Use of higher concentrations of NaOH beyond 35% has not yielded any advantage in the recovery of phenol in RP. An attempt to conduct experiments with 40% NaOH revealed that the second step of regeneration of phenol posed difficulty in separation of RP from aqueous layer (effluent). This could be due to formation of an emulsion. NaOH gave better yield of regenerated phenol than KOH. Percent loss of phenol fraction from the use of the alkalis was more or less equal. Effluent generation decreased with increase in the concentration of NaOH and KOH, but the same was always lower in the case of the former than the latter. Acknowledgments Authors are thankful to Visakhapatnam steel plant for providing phenol fraction. References Fig. 8 Total wt. loss of phenol vs conc of NaOH. Phenol fraction and constitutes partly due to losses. 3.5 Weight Loss of Phenol Loss of phenol could be greatly reduced with increase in NaOH concentration Fig. 8. The loss was found to be only 1.2 g with 30% NaOH while it was 4.7 g with 15% NaOH. The yield of RP as well as the phenol content in it, increased with increase in the concentration of NaOH. However, the phenol content in RP remained around 47% in 15%, 20% and 30% concentrations of NaOH (Table 1). 4. Conclusions The conclusions are drawn based on the analysis of the experimental data of the present study. 35% concentration of NaOH gave better yield of crude phenol fraction. So 35% concentration of NaOH was found to be optimum. The yield of regenerated phenol increased with [1] Bhattacharya, R. N.; Roy, M. B.; Tiwari, K. K. Study on Chemicals from Coal Carbonisation Products. Technology Information, Forecasting and Assessment Council (TIFAC). Dept. Sci. and Technol [2] Bhattacharya, R. N.; Roy, M. B. Chem. Eng. World 1990, 25, 162. [3] Bhattacharya, R. N.; Roy, M. B. Coke Chem. USSR 1989, 4, 89. [4] Volkman, E. W.; Rhodes, E. O.; Work, L. T. A Determination of the Physical Characteristics of Coal Tar Samples, 2nd Edition; D Van Nostrand company: New York, 1935; pp [5] Fenske, M. R. Fractionation of Straight Run Pennsylvania Gasoline. Ind. Eng. Chemistry 1932, 24(5), [6] Bhaduri, T. J.; Sen, D. K.; Sen, D. K.; Tiwari, K. K.; Nair C. S. B. In Proc. Symp. on Chemicals and Oil from Coal; CFRI: Dhanbad, 1972; pp [7] Bhaduri, T. J.; Sen, D. K.; Sen, D. K.; Tiwari, K. K.; Nair C. S. B. In: Proc. Symp. on Chemicals and Oil from Coal, Central Fuel Res. Inst.; CFRI: Dhanbad, 1972; pp [8] Chaudhuri, B.; Patwardhan, A. A.; Sharma, M. M. Alkylation of Substituted Phenols with Olefins and Separation of Close Boiling Phenolic Substances via Alkylation/Dealkylation. Ind. Eng. Chem. Res. 1990, 29(6),