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Znd. Eng. Chem. Res. 1996,34, 2138-2141
Dehydrochlorination of Waste 1,1,2=Trichloroethane Eugeniusz Milchert,* Waldemar Pazdzioch, and Jerzy Myszkowski Department of Organic Technology, Technical University of Szczecin, ul.Putaskiego 10, 70-322 Szczecin, Poland
The best results of the waste 1,1,2-trichloroethane dehydrochlorination by 10 wt % NaOH are obtained in temperature 70-80 ‘C at NaOWl12-TCE molar ratio 1.1:l and flow rate 270 g/(dm3 h). In these conditions 98.3 wt % vinylidene chloride and aqueous layer (13 wt % NaCl 0.07 wt % NaOH) are obtained. Vinylidene chloride yield is 97.5 mol %.
+
Introduction Vinylidene chloride has several important applications in production of packing films, synthetic fibers, and l,l,l-trichloroethane. Its copolymers with allyl esters of acrylic acid are applied in the production of water-soluble paints. Of technical importance are also copolymers with vinyl chloride, acrylonitrile, and ethylene. Vinylidene chloride can be obtained from residuary waste 1,1,2-trichloroethane (112-TCE), a byproduct of the chlorination of ethylene to 1,2-dichloroethane (Malinowska and Szczeszek, 1975). Catalytic dehydrochlorination of 112-TCE in gaseous phase is characterized by a low selectivity (Shelton et al., 1971; Z6l.tdski et al., 1990). Industrial methods are based on dehydrochlorination of 112-TCEwith alkaline aqueous solutions (Milchert et al.,1992). These methods are constantly being developed due t o the possibility of recycling the residual brine back to the electrolysis system. This work presents the results of dehydrochlorination of waste 112-TCE,the byproduct in the production of vinyl chloride by “dichloroethane method”.
Experimental Section Raw Materials. In the reaction, technical 112-TCE containing (in wt %) 112-TCE, 95.8; perchloroethylene (PER), 2.6; 1,2-dichloroethane (12-DCE), 0.8; l,l,ltrichloroethane (111-TCE), 0.5; and 1,1,2-trichloroethylene (TRI), 0.3, was fed. It was obtained from the tails after 12-DCE distillation. The tails composed of (in w t %) 112-TCE, 73.5; 12-DCE, 14.1; 1,1,1,2-tetrachloroethane (UNS TET), 6.7; PER, 3.5; 1,1,2,2-tetrachloroethane, (SYM TET), 1.5; pentachloroethane (PENTA), 0.4; trans-1,2-dichloroethylene(TRANS), 0.1; TRI, 0.1; and 111-TCE, 0.1, were supplied by ZaMady Azotowe “Wodawek”, Poland. Laboratory distillation was carried out on a 20-plate Brunn column. Sodium hydroxide (pure) from Zaklady Chemiczne “08wiqcim”,Poland, was used. Dehydrochlorination Method. The equipment shown in Figure 1 was purged with nitrogen, and its flow was kept over the reaction. Reactor 1 was filled with aqueous solution containing 11.8 wt % NaCl and 0.08 w t % NaOH. It corresponds to the content of aqueous layer assuming 100% conversion of 112-TCE. 112-TCE and 10% sodium hydroxide solution were added to the reactor in a continuous way with the use of peristaltic pumps 2. The temperature of the reactor was kept constant with an ultrathermostat. The volume of reaction mixture was 0.25 dm3. In the temperature range under investigation the product evaporated from the reactor, passed through the dephlegmator 3, distillation head 4,and reflux condenser 5, and flew off into receivers 6, cooled to -20 “C, and filled with mono-
Figure 1. Scheme of the apparatus: 1, reactor; 2, peristaltic pump; 3, dephlegmator; 4, distillation head; 5, reflux condenser; 6, receivers for vinyl chloride; 7, brine receiver; 8, container for 1,1,2-trichloroethane; 9, container for sodium hydroxide solution.
methyl ether of hydroquinone to prevent the polymerization of vinylidene chloride. The excess of the aqueous layer was passed through the siphon to the container 7. Analytical Control. During the process the concentration of sodium hydroxide was determined by acid-base titration method every 10 min. It was necessary due to maintaining the constant molar ratio of sodium hydroxide to 112-TCE. After the process had been completed the sodium hydroxide concentration was determined in the aqueous layer from the reactor. The composition of raw vinylidene chloride was determined by gas chromatography. The determinations were carried out using a Chrom 5 apparatus, equipped with a 3 m x 4 mm steel column, filled with 15 wt % SE 30 on Chromosorb W AW DMCS 80/100 mesh connected with the identical column filled with 10 wt % FFAP on Chromosorb W AW DMCS 80/100 mesh. The detector was a flame ionization detector, the carrier gas was nitrogen at 28 cm3/min,the temperature of the injection chamber and detector was 200 “C, the oven temperature was 10 min at 80 “C, increase of 5 “C/min up to 160 “C, and 22 min at 160 “C. The experiments allowed determination of the influence of various factors on the
0888-5885/95/2634-2138$09.00lO 0 1995 American Chemical Society
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1.06
o 112-TCE conversion (?/o
1.08
1.10
1.12
1.14
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Figure 2. Influence of NaOW112-TCE molar ratio on formation of VDC. Temperature 90 "C, 10 wt % NaOH solution, 112-TCE flow rate 110 g/(dm3 h).
course of dehydrochlorination of 112-TCE. The sensitivity of the vinylidene chloride (VDC) detection was lov3 mV cm3/mg.
Results and Discussion Purity of 112-TCE. Dehydrochlorination was carried out with 10% sodium hydroxide solution, applied in excess of 10 mol % with respect to the reacting compounds. The reaction temperature was 85 "C. Pure 112-TCE (99.9 wt %) gives the mixture composed of (wt %) VDC, 98.9; TRANS, 0.5; cis-1,2-dichloroethylene (CIS), 0.4; chloroacetylene (AC), 0.1; and 112-TCE, 0.1. In this mixture there is no vinyl chloride monomer (VCM). The main reaction and more important side reactions occurs according to the scheme 3CHClz-CH,C1
-
CC1,=CH2
cis-
+
CC12=CH2 cis- trans-CHCl=CHCl+ 3HC1
+
-
CClECH
+ truns-CHCl=CHCl-
+ HCI
2CCl=CH
+ 2HC1
1,2-DCE (0.5 wt %) in pure 112-TCE (99.5 w t %) caused an increase in VCM concentration up to 0.04 mol %. The unchanged 1,2-DCEwas present in the product. In pure 112-TCE, UNS TET (1.5 w t %) or SYM TET (1.0 wt %) undergoes dehydrochlorination much easier. In both cases TRI is formed and tetrachloroethanes are not observed. TRI and PER do not undergo transformation when dehydrochlorination is carried out with aqueous solutions of NaOH. A small increase in PER concentration (weight percent) in the product in comparison to its concentration in raw material results from decrease of molecular weights of the products. The impurities mentioned above do not influence the yield of VDC calculated with respect to the amount of 112TCE used. The yield is 94-97 mol %.
Molar Ratio of Sodium Hydroxide to 112-TCE. An increase in molar ratio of NaOW112-TCE causes the lowering the VDC concentration. However, the degree of 112-TCE transformation increases. This results also in the increase of VDC yield in relation to 112-TCE introduced to the reactor (Figure 2). The decrease in VDC concentration results from its further dehydrochlorination to AC. The changes in concentrations of byproducts are insignificant, 0.1-0.2 wt %. Chloroacetylene is formed from 1.051 molar ratio of NaOW 112-TCE and maximum value (0.05 w t %) is obtained at 1.14:l molar ratio. The concentrations of PER, TRI, and 112-TCE are kept at constant level and are respectively 0.03, 0.18, and 0.12 wt %. The concentrations of VCM, CIS, and TRANS increase in the given range with the increase of NaOW112-TCE molar ratio. Increase of CIS and TRANS is nearly the same, from 0.26 to 0.38 wt %, and the increase of VCM is from 0.07 to 0.23 wt %.
Temperature. The investigations of the influence of the temperature show that at 50 "C the VDC yield is approximately 83 mol %. At 80 "C it increases up to 93 mol %, and above this temperature no further increases of yield are observed (Figure 3). The increase in the yield is caused by a higher reacting of 112-TCE a t practically the same selectivity of the transformation to VDC. This is confirmed by the course of changes in byproduct concentrations (Figure 4). As previously, the changes in byproduct concentration are insignificant. AC becomes detectable (0.02-0.03 wt %) at 70 "C. Its amount doubles with each temperature increase of 10 "C. Also, with the increase in temperature the concentration of VCM increases. Concentration of NaOH Aqueous Solution. The standard dehydrochlorination was carried out with 10 w t % NaOH solutions. Several tests were performed applying 20 w t % NaOH solution. In order to maintain constant NaOW112-TCE molar ratio of 1.1and the time of remaining 112-TCE in the reaction zone, the rate of
2140 Ind. Eng. Chem. Res., Vol. 34, No. 6,1995
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ro
85
80
75
80
85
90
Temperature (‘C)
* VDC yield (% mol),
0 112-TCE
conversion (% md),
VDC concentration (“3 wt.)
Figure 3. Influence of temperature on dehydrochlorination of 118-TCE to VDC. Molar ratio NaOW112TCE l.l:l, 112-TCE flow rate 106 g/(dm3h).
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96 ...........................................
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j
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*
100
VDC yield (%mol)
150
200
250 300 350 Flow rate of raw materials (g l12TCUdm3 h)
o 112-TCE convemion (%mol)
o VDC concentration (%wt.)
Figure 4. Influence of temperature on formation of the byproducts. Reaction conditions as shown in Figure 3.
its flow was increased. It caused disadvantageous changes in the product composition. The concentration of VDC decreased and that of CIS, TRANS, and AC increased resulting in VDC yield decrease of 10-13 mol % in comparable experiments. Flow Rate of Raw Materials. The flow rate of raw materials, expressed by the flow rate of 112-TCE have been changed in the range of 73-345 g/(dm3 h). The increase of flow rate caused the lowering of 112-TCE conversion and VDC yield of approximately 2 mol % (Figure 5). The course of changes in byproduct concen-
trations show the increase in 112-TCE concentration from 0.08 to 0.82 wt % and lowering of VCM concentration from 0.15 to 0.02 wt %. The changes result from the shortening of the reaction time. The concentrations of the remaining components AC, CIS, TRANS, and PER practically do not change and are respectively 0.02, 0.25,0.24, and 0.11 w t %. In the range under investigation the system is relatively elastic. The changes in flow rate do not cause significant changes in the yield of VDC and its purity. Interfacial Catalyst. The addition of interfacial
Ind. Eng. Chem. Res., Vol. 34, No. 6, 1995 2141 0.4
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60
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AC o VCM TRANS ACIS x PER @ 112TCE Figure 5. Influence of flow rate of raw materials on 112-TCE dehydrochlorination. Temperature 70 "C, NaOW112-TCE molar ratio 1.1:l.
catalyst (tetraethylammonium chloride) or emulsifier (castor oil) slightly raises the reaction rate but does not change the VDC yield. The application of catalyst and emulsifier is not necessary. In the known industrial process of 112-TCE dehydrochlorination the yield at the level of 90 mol % is obtained at temperature 70 "C by the use of 30 mol % aqueous NaOH solution. Its main deficiency is the use of 112TCE of at least 99.8 wt %. Changing dehydrochlorination parameters, as shown below, higher VDC yield 97.5 mol % can be obtained and 112-TCE of lower purity 95.8 wt % can be used. The aqueous layer from the reactor contains NaCl (12.6 w t %), NaOH (0.07 wt %), and 10-60 ppm chloroorganic compounds (mainly 112-TCE). After the stripping by steam and concentrating NaCl to 23 wt %, it was used as the raw material in the laboratory electrolysis. VDC impurities can be easily distilled, and high purity 99.99 wt % VDC can be obtained. Its only impurity is TRANS.
in temperature 70-80 "C, and at the flow rate of 112TCE 270 g/(dm3h) allows obtaining vinylidene chloride containing (in wt %) VDC, 98.26; TRANS, 0.39; CIS, 0.36; PER, 0.26; 112-TCE, 0.18; TRI, 0.17; VCM, 0.12; AC, 0.11; 12-DCE, 0.08; 111-TCE, 0.05; and 11-DCE, 0.02. The yield of VDC with respect t o the amount of 112TCE introduced into the reactor is 97.5 mol %; 112-TCE conversion is 98.6 mol %.
Literature Cited Malinowska, B.; Szczeszek, M. Trends in search of new obtaining method for vinylidene chloride. Chemik 1975, 28, 253-256. Milchert, E.; Osiewicz, B.; Myszkowski, J. Process for the production of vinylidene chloride. Chemik 1992, 45, 119-121. Shelton, L. G.; Hamilton, D. E.; Fisackerly, R. H. Vinyl and vinylidene chloride. High Polym. 1971,24, 1205-1289. Zbltanski, A. Z.; Lach, J.; Halaburdo, N.; Pokorska, Z. Studies on catalytic dehydrochlorination of 1,1,2-trichloroethane in gaseous phase. Przem. Chem. 1990, 69, 112-115. Received for review February 9, 1995 Accepted March 27, 1995@
Conclusions The continuous dehydrochlorination of technical 112TCE of composition given in the beginning with the use of 10 wt % NaOH, at NaOW112-TCE molar ratio l . l : l ,
IE940481T Abstract published i n Advance ACS Abstracts, May 1, 1995. @
