Ind. Eng. Chem. Process Des. Dev. 1983, 22, 681-684
w, = weight fraction of component n
x , = mole fraction of component n in the liquid phase y, = mole fraction of component n in the gas phase a = probability of chain growth pL T,,
= oil density, g/cm3 = time constant for component n, min Registry No. CO,630-08-0.
Literature Cited American Petroleum Institute Research Project 44. Thermodynamics Research Center, Department of Chemistry, Texas A&M Unhrerslty, College Station, TX, 1971. DeRiester. C. L. Chem. €ng. Rog. Symp. Ser. 1953, 49, 7. Gaube, J.; Hochstadt, 0.; Schllebs, B.: Sudhelmer, 0. Klnetlsche und reaktions-technlsche Untersuchungen zur Flscher-Tropsch-Synthese von I-Alkenen(C,-Cm). Report ET I O l O A to the Bundesmlnlsterlum fi# Forschung und Technologic, West Germany, 1982. Hall, W. K.; Kdtes, R. J.; Emmett, P. J. J . Am. Chem. Soc. 1 9 0 , 82, 1027. Henr1cK)lIvB. 0.; OlhrO, S. Angew. Chem. Int. Ed. Engl. 1976, 15, 136.
68 1
Kellner, C. S.; Bell, A. T. J . Catal. 1981, 70, 418. Madon. R. J. J . Catal. 1978, 57, 183. Madon, R. J.; Taybr, W. F. J . Catal. 1981, 60, 82. Pannell, R. B.; Klbby, C. L.; Chung, K. S. Proceedings of Advances in Catalytic Chemlstry 11, Salt Lake Clty, UT, May 18-21, 1982. Sanerfleld, C. N.; Huff, G. A.. Jr. J . Catal. 1982, 73, 187. Satterfleld. C. N.; Huff, G. A., Jr.; Longwell, J. P. Ind. Eng. Chem. Process Des. Dev. 1982, 21, 465. Schultz, J. F.; Hall, W. K.; SeHgman, B.; Anderson, R. B. J . Am. Chem. Soc. 1955, 77, 213.
Materials and Molecular Research Division Lawrence Berkeley Laboratory and Department of Chemical Engineering University of California Berkeley, California 94720
Ronald A. Dictor
Alexis T.Bell*
Received for review September 27, 1982 Accepted March 11, 1983
Kinetics of Alkylation of Toluene by Acetylene with Concentrated Sulfuric Acid/Mercuric Sulfate as Catalyst in a Four-Phase System The kinetics of alkylation of toluene with acetylene with sulfuric acid and suspended mercuric sulfate a s a catalyst was studied in the temperature range of 8-20 O C . I t was found that above a certain speed of agitation mass transfer resistance can be eliminated. The effects of concentration of toluene, partial pressure of acetylene, strength of sulfuric acid, and loading of mercuric sulfate have been reported. I t was found that an increase in the strength of sulfuric acid from 90 to 95 % w/w Increased the pseudo-first-order rate constant by a factor of 8.5.
Introduction Ditolylethanes, DTE [bis(methylphenyl)ethane] are synthesized by the reaction of toluene with acetylene in the praence of concentrated sulfuric acid/mercuric sulfate as catalyst (Reichert and Nieuwland, 1923). The reaction is as follows.
(The product formed by this process constitutes 70% 0,p-DTE and 30% p,p isomer). This reaction involves four phases: gas, organic liquid, aqueous sulfuric acid, and suspended mercuric sulfate. DTE can also be synthesized by reacting toluene with acetaldehyde in the presence of concentrated H$04 or HF as catalyst (Baeyer, 1872). However, in the case of toluene the product distribution with respect to the isomers is more favorable when acetylene is used. DTE are used as a raw material for the manufacture of methylstyrenes, as a heat transfer fluid, and as a solvent. The synthesis of DTE by the alkylation of toluene with acetylene has been reported by Reichert and Nieuwland (19231, Dixon and Saunders (1954), Hoffenberg et al. (1964),and Telegin et al. (1967). The kinetics of this reaction has not been reported. The effect of variables, such as, speed of agitation, concentration of toluene and acetylene, loading of HgS04, strength of sulfuric acid, and temperature has not been systematically studied. Experimental Section Materials and Methods of Analysis. Toluene and chlorobenzene used were of laboratory reagent grade. Acetylene cylinder was supplied by a reputed firm. Sulfuric acid used was of C P grade and it was diluted to the desired concentration with distilled water. The analysis of the reactant (toluene) and the product (DTE) was performed on a gas chromatograph. The column material used was Apiezon L supported on Chro0196-4305/a3/1122-0t38 I$0 Iso10
mosorb W NAW. The oven temperature was maintained a t 220 "C. Apparatus and Procedure. The contactor used was the same as that used by Vasudevan and Sharma (1983). The reaction was carried out in the temperature range of 8 to 20 "C. The experimental setup is as shown in Figure 1. Acetylene from a cylinder was passed through a series of bubblers containing chilled water and sulfuric acid to remove acetone and moisture, respectively. The acetone and moisture-free acetylene gas was then bubbled into the reactor which was operated a t the desired speed of agitation. Two hundred fifty milliliters of organic phase, 25 mL of aqueous phase, and 1g of mercuric sulfate were added to the reactor and agitated a t a known speed. A coolant from a cryostat was passed through the cooling coil and the temperature of the reaction was maintained by keeping the circulation of coolant on and off manually. After a specified interval of time the flow of acetylene and agitation were stopped and organic phase was sampled out for analysis. This sample was given a water wash to remove traces of sulfuric acid.
Results and Discussion The mechanism of the reaction has not been reported. It is probable that both mercuric ions and solid mercuric sulfate act as catalyst. Acetylene dissolved in the aqueous solution may react with mercuric ions to form an intermediate complex; in the case of solid mercuric sulfate particles this complex formation may occur a t the solid surface. The dissolved intermediate complex now reacts with two molecules of toluene to form the product, ditolylethane. Toluene and acetylene diffuse from the organic phase into the aqueous phase where the reaction occurs. It has also been observed by us (Vasudevan and Sharma, 1983) that in the related case of alkylation of xylene with acetaldehyde in the presence of concentrated 0 1983 Amerlcan Chemical Society
882
1.
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 4, 1983
ACETYLENE CYLINDER
2. WATER
(ACETONE TRAP)
3. SULFURIC ACID I M O I S T U R E T R A P )
4. REACTOR
7.
COOLING C O I L
5.
ACETONE
8.
GAS I N L E T
6.
STIRRER
9.
BELT D R I V E
I
Figure 1. Experimental setup for the alkylation of toluene with acetylene.
X103 gmol/cm3
[Ao],,
__C
Figure 3. Effect of concentration of toluene on the volumetric rate of reaction: temperature = 8 "C; w = 0.343% (w/w); strength of H2S04= 95% (w/w).
t
-0.1 1000
2000
3000
4000
SPEED OF A G I T A T I O N , rpm ---c
Figure 2. Effect of speed of agitation on the volumetric rate of reaction: temperature = 8 "C;w = 0.343 % (w/w); strength of H 8 0 4 = 95% (w/w); [&I, = 9.4 x g-mol/cm3.
H2S04the locale of the reaction is the aqueous phase. Since the rate of reaction is independent of interfacial area (as the rate is independent of agitation speed and hence interfacial area of mass transfer) an interfacial reaction is ruled out. Also, the solubility of toluene in the aqueous phase increases dramatically as the acid concentration is increased (Strachan e t al., 1980). Thus the locale of the reaction is in the aqueous phase. The agitation speed was varied from 2000 to 3500 rev/min and was found to have no effect on overall rate of reaction (Figure 2) and therefore the reaction is kinetically controlled. Solubility of Toluene in the Aqueous (Acid)Phase. The solubility of toluene in concentrated sulfuric acid solutions is difficult to evaluate as toluene gets sulfonated in the acid medium. However, an approximate estimate of solubility can be made on the basis of data reported by Strachan et al. (1980) for the solubility of m-bis(trifluoromethy1)benzenein higher strengths of sulfuric acid. It was found by Strachan e t al. that the solubility of mbis(trifluoromethyl) benzene increased by more than two hundred times when the strength of sulfuric acid was increased from 0 to 100 mol %. The above observation, when extended to toluene, may account for the absence of mass transfer resistance although the volumetric rate of reaction is high (of the order of 2 X lo4 g-mol/(cmS dispersion s); if we were to take the solubility of toluene in water and make an estimate of KLRu (= RAu/[A*]) we 8-l) and hence find that ~ L R u>> kLu (kmu N 10 and ~0.30 we might erroneously conclude that mass transfer plays an important role in the reaction). Since an exact value of the solubility of toluene in concentrated H2S04is difficult to evaluate, it was found convenient to group the distribution coefficient of toluene along with the intrinsic rate constant to give a pseudo rate constant. Effect of Concentration of Toluene. The effect of concentration of toluene (diluted by using chlorobenzene) is shown in Figure 3. It can be seen that over a wide range
-2 7
' [ u ;6
/5
li OO
I
0.2
0.6
I
I
0.6
0.8
P A R T I A L PRESSURE, pr , a t m
,
1.0
+
Figure 4. Effect of partial pressure of acetylene on the volumetric rate of reaction: temperature = 8 "C; w = 0.343% (w/w); strength g-mol/cm3. of H2S04= 95% (w/w);[&,Ii = 9.4 x
of concentration of toluene (2.6 to 9.4 M (pure toluene)) the rate is proportional to the concentration of toluene indicating that the reaction is first ordei. with respect to toluene. Effect of Concentration of Acetylene. It is found that the partial pressure of acetylene (nitrogen was used as a diluent) has no effect on the rate of reaction (Figure 4) which indicates that the reaction is zeroth order in acetylene. It is important to know whether there is any resistance associated with gas-liquid mass transfer. There is no effect of the speed of agitation varied over a wide range (2000-3500 rev/min) on the rate which clearly indicates that gas-liquid mass transfer resistance is insignificant. This observation can be further checked by estimation of values of parameters ( k ~ a ) and , ~ RAU/[C*],, ([C*],, = 2.7 X g-mol/cm3). The value of (kLu),L at the operating conditions will be around at least 0.03 s-l. Taking a value of RAu of 2 X lo4 g-mol/(cm3 dispersion s), we find that the R~u/[c*], value comes to about 0.0074 s-l. From the foregoing we can assume that the organic phase should be essentially saturated with acetylene, and since the value of (kLu)LLa t the operating conditions is very high ( N 0.3 s-l), it can be assumed that the transfer of acetylene from organic phase to aqueous phase is also not important. Some acetylene will be directly absorbed in the acid phase. Effect of Loading of Mercuric Sulfate. The effect of loading of mercuric sulfate on the volumetric rate of reaction is shown in Figure 5 (Table I). In the range of loading of mercuric sulfate of 0.171 wt % to 0.685 wt % , the volumetric rate of reaction is proportional to the loading of mercuric sulfate, indicating that the formation of an intermediate complex involving mercuric ion may be controlling the overall rate and hence the overall rate is surface reaction controlled. As mentioned earlier, both
Id.Eng. Chem. Process Des. Dev., Vol. 22, No. 4, 1983 683
Table I. Effect of Loading of Mercuric Sulfate on the Volumetric Rate of Reaction"
[AoliX no. 1 2 3 4 5b
% ' loading
of &SO,
0.0857 0.171 0.343 0.685 1.371
RA'
[Ao lav X
IO3 g-mol/
l o 3 g-mol/
4.70 4.70 4.70 4.70 1.50
4.660 4.560 4.455 4.175 1.435
cm3
cm3
lo6 g-mol/(cm3 disp s) 0.123 0.532 0.920 1.990 0.650 X
RA"/[& ,1 x 103 5 - 1
RA" x 105
g-mol/(cm3 (cm3 org phase)/
disp phase s ) (cm3 aq phase)
0.29 1.28 2.27 5.24 4.98
0.135 0.585 1.011 2.187 0.714
a System: toluene +- acetylene; diluent: chlorobenzene;catalyst: conc. H,SO, + HgSO,; temperature = 8 " C ; volumetric holdup of dispersed phase, $I = 0.091;strength of sulfuric acid = 95% (w/w);time of reaction = 240 8. Time of reaction = 90 s.
Table 11. Effect of Temperature on the Pseudo-First-OrderRate Constant" RA'X lo6
RA" x io5
no.
temp, " C
g-mol/cm3
g-mol/ (cm3 disp s)
g-mol/(cm3 disp phase s)
1 2 3
8 15 19
4.455 4.185 4.090
0.92 1.96 2.30
1.011 2.154 2.527
[Aolav X 10'
R~''/(IAolav X x lo2 s - '
W )
(cm3org phase/ cm3 aq phase) 0.66 1.50 1.80
System: toluene -t acetylene; diluent: chlorobenzene;catalyst: conc. H,SO, + HgSO, ;initial concentration of g-ml/cn?;volumetric holdup of dispersed phase, $I = 0.09l;loading of toluene in the organic phase, [A0Ii= 4.7 x HgSO, = 0.343% (w/w);strength of H,SO, = 95% (w/w).
1
I
90 92 94 STRENGTH OF HZSO4
,'/a
1
1
96
98
(w/w)+
Figure 6. Effect of strength of sulfuric acid on the pseudo-firstorder rate constant: temperature = 8 OC;w = 0.343% (w/w); [&Ii = 4.7 x 10-~g-mol/cm3.
The rate expression in the range of loading of HgS04 between 0.171 and 0.685 wt % is given by the equation (1) RAa = RA' = @k,[&]w Effect of S t r e n g t h of S u l f u r i c Acid. The effect of strength of sulfuric acid on the pseudo-first-order rate constant (which is a combination of intrinsic rate constant and distribution coefficient of toluene between aqueous and organic phases) is shown in Figure 6. As the strength of sulfuric acid is increased from 90 to 95 w t %, the pseudo-first-order rate constant increases by a factor of 8.5. This sharp increase is probably due to the steep increase in the solubility of toluene in sulfuric acid above a strength of sulfuric acid of 85 w t % (Strachan et al., 1980). Effect of Temperature. The effect of temperature on the pseudo-first-order rate constant is shown in Table 11. It is seen that as the temperature is raised from 8 to 15 "C,the pseudo-first-orderrate constant increases by a little more than a factor of 2. This is due to the increase in both intrinsic rate constant and solubility of toluene with an increase in temperature. Our data are inadequate to allow a rational evaluation of activation energy. Yield of Ditolylethane Based on Toluene. The yield of product ditolylethane decreased sharply with an increase in the conversion of toluene (At a level of conversion of toluene of 10 % , the yield of product DTE was about 92
Ind. Eng. Chem. Process Des. Dev. 1983, 22, 684-686
884
%. As the conversion increased to 25% the yield of product dropped to about 70%). This is due to further alkylation of the product DTE with acetylene a t higher levels of conversion of toluene. Conclusions (1) The alkylation is first order with respect to the concentration of toluene and zeroth order with respect to the concentration of acetylene. In the range of loading of mercuric sulfate of 0.171 to 0.685 w t % the rate is proportional to catalyst loading. (2) The pseudo-first-order rate constant increases by a factor of 8.5 as the strength of sulfuric acid is increased from 90 to 98 w t % and this is probably due to the sharp increase in the solubility of toluene in the acid phase. Nomenclature a = interfacial area of mass transfer, cm2/cm3 [&I = concentration of toluene in the organic phase, gmol/cm3 [A*] = solubility of toluene in the aqueous phase, g-mol/cm3 [C*], = solubility of acetylene in the organic phase, gmof/cm3 k L = true liquid side mass transfer coefficient, cm/s k, = pseudo-first-order rate constant, s-l cm3org phase/cm3 aq phase R A = specific rate of reaction, g-mol/(cm2e) RA’ = volumetric rate of reaction, g-mol/(cm3disp s) RA” = volumetric rate of reaction, g-mol/(cm3disp phase s) w = loading of mercuric sulfate, % w/w
Greek Letter
4 = volumetric holdup of dispersed liquid phase, cm3 aq phase/(cm3 aq phase cm3 org phase)
+
Subscripts i = initial value f = final value av = average value g-L = gas-liquid L-L = liquid-liquid Registry No. Toluene, 108-88-3;acetylene, 74-86-2;mercuric
sulfate, 7183-35-9; sulfuric acid, 7664-93-9. Literature Cited Baeyer, A. Ber. 1872, 5 , 1094. Dixon, J. K.; Saunders, K. W. Ind. Eng. Chem. 1954, 46, 852. Hoffenberg, D. S.; Smolln, E. M.; Matsuda, K. J . Chem. Eng. Data 1984,
9(1),104. Reichert, J. S.;Nieuwland, J. A. J . Am. Chem. Soc. 1923, 45, 3090. Strachan, A. N.; Field, J. P.; Fleming, K. A. “Proceedings, International Solvent Extraction Conference”; Assoc. Ing. Univ. Liege, Belgium, 1980 Vol. 11, 80-82. Telegh. V. G.; Sidorov, V. A.; Kharchenko, A. A.; Biryukova, L. M. Khlm. Tekhnol. Topl. Masel. (in Russian) 1987, 72(5), 19;Cbem. Abstr. 1967. 67, 83936. Vasudevan, T. V.: Sharma, M. M. Ind. Eng. Chem. Process D e s . D e v . i 9 8 3 , 2 2 , 161.
Department of Chemical Technology T.V. Vasudevan University of Bombay Man Mohan Sharma* Bom bay-400019, India Received for review August 9, 1982 Accepted April 11, 1983
CORRESPONDENCE Comments on “Analytkal Form of the Ponchon-Savarit Method for Systems with Straight Enthalpy-Composltlon Phase Lines”
Sir: Recently, Govind (1982) proposed an equation to compute the number of theoretical stages in binary distillation when the enthalpy-composition phase lines are straight but not parallel. I feel that this publication needs some comment.
you get
Number of Theoretical Plates In principle, the solution to this problem has been known for some time. You only need to combine the methods proposed by Smoker (1938), assuming straight and parallel phase lines, and of Peters (1922), who d e f i e d ‘‘caloric concentrations” to be able to use the equations of the McCabe-Thiele method with systems having different heats of vaporization of the components. These ‘‘caloric concentrations” can be defined as follows (see also Hausen (19421, Stein (1970))
Enthalpies and heats can be transformed in the same manner. For instance to account for nonsaturated feed, the difference of specific enthalpies is
0196-4305/83/1122-0684$01.50/0
u = (1- C)x/(l - CX)
(5)
u = (1 - C)y/(l
(6)
- Cy)
Ah~,cor/X~ = A~F/X(XF)
(7)
Together with the familiar equations of the McCabeThiele method and the equation of Smoker (1938), assuming constant pressure and relative volatility, it is now easy to compute the number of theoretical stages by substituting x , y, and A h p by u, u, and AhF,eor. You have
0 1983 American
Chemical Society
