HYDROCHLORINATION OF METHANOL T O METHYL CHLORIDE IN FIXED CATALYST BEDS M. S. T H Y A G A R A J A N , R A J I N D E R K U M A R , A N D N. R. K U L O O R Department of Chemical Engineering, Indian Institute of Science, Bangalore, India The vapor phase hydrochlorination of methanol to methyl chloride in fixed beds with silica gel-alumina (88 to 12) and y-alumina catalysts was studied in a glass tubular reactor in the temperature range of 300" to 390" C. Of the two catalysts studied, y-alumina gave nearly equilibrium conversions under the experimental conditions. The data are expressed in the form of second-order irreversible rate equations for both the catalysts studied. CHLORIDE is an important starting material in the manufacture of silicone high polymers. Apart from this, it finds applications in the low temperature polymerization of butyl rubbers and as intermediate in the manufacture of methylene chloride, which is extensively used in industry. The methods used for the production of methyl chloride are chlorination of methane and hydrochlorination of methanol ( 3 ) . The first method suffers from the disadvantage that it results in
METHYL
the formation of a group of compounds which have to be fractionated in order to obtain pure methyl chloride. Very little information is available on the hydrochlorination of methanol. The present investigation was undertaken to study the reaction in fixed beds of silica gel-alumina (88 to 12) and y-alumina catalysts. Thermodynamic Considerations
The stoichiometric equation for the preparation of methyl chloride from methanol and hydrogen chloride is given as CH3.OH
s
1
0
~
ZOO
Figure 1.
+ HC1
--t
CH3.Cl
+ H20
The equilibrium constants a t various temperatures were evaluated from the available thermodynamic data (4). The equilibrium conversions were then evaluated from the equation 8
1 400
-
11
I
I
1
e00
600
I
1
1000
TBHPERATURE, *K
Effect of t'emperature on equilibrium conversion
and are shown in Figure 1. The equilibrium conversion decreases from 99% a t 300' K. to 85% a t 1000" K. T o produce
WATER
I
Figure 2. 1. 2.
3. 4. 40. 5.
Experimental setup
Constant overhead tank Aspirator bottle Hg manometer Methanol storage HCI generator Mixer
6.
Reactor
7. Thermocouple 8. Condensers 9. N a O H bubbler 10. Mariotte system
VOL. 5
NO. 3
JULY 1966
209
methyl chloride in high conversions and in reasonably high rates the temperature range of 600’ to 700’ K. is explored for kinetic studies.
I
/ A
Experimental
Equipment a n d Operation. A flow diagram of the apparatus is shown in Figure 2 . The reactor is a borosilicate glass tube of 15-mm. i.d. and 700 mm. long. A thermowell is provided for inserting the calibrated iron-constantan thermocouple. Care is taken to keep the tip of the thermowell at the center of the catalyst bed when the catalyst is packed inside the reactor tube. The reactor is also packed with porcelain beads which serve as the preheater for the reactant gases and as a distributor. The reactor is provided with a radiation heater and the energy input to the heater is controlled by a Dimmerstat. Arrangements are made for the admission of the reactants a t the bottom of the reactor and for withdrawal of the products through a side tube a t the top. Reactants. METHANOL, analytical reagent grade, is metered through a calibrated all-glass rotameter and fed into the preheater. A steady feed rate is obtained by the pressure of air displaced by water from a constant-level tank. HYDROGEN CHLORIDE.An all-glass apparatus for the preparation of hydrogen chloride is a modified form of the apparatus developed by Bhatnagar and Kuloor ( Z ) , so that dry hydrogen chloride could be produced a t pressures slightly higher than atmospheric. The gas is dried by passing it through a calcium chloride tube and is metered using a calibrated glass capillary flowmeter. The manometric liquid used in this flowmeter is concentrated sulfuric acid. (88 to 12) Preparation of Catalysts. SILICAGEL-ALUMINA CATALYST.Aluminum foil is dissolved in potassium hydroxide solution to yield potassium aluminate solution. Silica gel (obtained from water glass) is then dispersed in potassium aluminate solution. Carbon dioxide is passed into the solution until all the alumina is precipitated. Then a 15Oj, solution of ammonium chloride is added to maintain the required pH. After some time the precipitate is washed free of chloride, filtered, and then dried. 7-ALUMINACATALYST.y-Alumina is prepared by dissolving aluminum foil in a solution of potassium hydroxide solution and bubbling carbon dioxide into the resulting potassium aluminate solution until all the alumina is precipitated. T h e precipitate is washed and then dried. The alumina thus obtained is then activated a t 400’ C. for about 16 hours and then used as such. Characteristics of Catalysts. SILICAGEL-ALUMINA. Par48 Tyler mesh. Surface area, 775.0 sq. meters ticle size, -28 per gram. ?-ALUMINA.Particle size, cylinders of 2.1 -mm. length, 1.0-mm. diameter. Surface area, 169.0 sq. meters per gram. Experimental Procedure. The preheaters, mixer, and reactor are heated to the desired temperature. Methanol and hydrogen chloride in predetermined proportions are then fed into the reactor through the mixer by applying the constant pressure device. When steady state of temperatures and feed rates is reached, the product coming out of the reactor is condensed, scrubbed through sodium hydroxide solution, and finally collected over brine solution in a Mariotte system. Each run is conducted for 10 minutes and a sample of product is analyzed immediately. Analysis. The methyl chloride content in the product gas is determined by absorption in glacial acetic acid (7).
+
Results and Discussion
Influence of Variables on Conversion. The pressure of operation was considered to be of negligible effect because the number of moles of the reactants is equal to that of products. Hence, all of the experiments during the present investigation were conducted at nearly atmospheric pressure. Separate design equations are developed for each of the two catalysts studied-silica gel-alumina and y-alumina. The composition of the feed was not very important and only a few experiments were conducted by changing the composition of the feed. 210
l&EC PROCESS DESIGN A N D DEVELOPMENT
I
/m
Catalyst: r-Alumlna Ratio of rcrctants=l:l (HCI:CHaOH)
I
1
I
I
I
I
I
1
0.1
0.3
0.5
0.7
0.9
11
1.3
1.5
W/F, gm
Figure 3. peratures
I
of crtalyrt/gm mole of fccdlhr
Conversion vs. time factor at various temCatalyst. y-Alumina Ratio of reactants 1:l
The effect of the other variables- WJF and temperature-is dependent on the levels of each. To take these interactions into account, a complete factorial design approach was resorted to. Thus, for each level of temperature, four levels of space velocity were studied. The amount of catalyst was mqintained the same throughout the investigation, but was changed for a few runs in order to ascertain whether diffusion or chemical reaction rate constitutes the rate-controlling mechanism. EFFECTOF TIMEFACTOR. The time factor ( W J F ) in the present case was varied by changing the feed rate while maintaining the weight of the catalyst constant. The data obtained by varying the time factor on both the catalysts a t temperatures of 300°, 330°, 360°, and 390’ C. are shown in Figures 3 to 6. The fact that the curves do not register fall or sudden rise indicates that the rates of side reaction are negligible. The manner in which the temEFFECTOF TEMPERATURE. perature increases the conversion is shown in Figure 7, where the conversion has been plotted against temperature for various WJFvalues as parameters. This increase is expected from the Arrhenius equation, which gives the effect of temperature on homogeneous reactions. For catalytic reactions, the final apparent effect of temperature is due to both the effect on adsorption constants and specific reaction rate constants. I n the present case, as the change in conversion with temperature is high for both the catalysts, the effect of adsorption constants appears to be less. No fall in the activity of the catalyst was observed with rise in temperature within the range of temperatures studied. Higher temperatures, however, could not be employed because of the lowering of the equilibrium conversion and the higher probability of formation of side products like ether. E ~ F E COF T COMPOSITION OF REACTANTS.I t is seen (from Figures 4 and 5) that a t lower temperatures the effect of change
E 30.3 U
-
-
a?
U
-u
I
Catalyst: r-Alumina Ratio of reactantr=l:2 (HCI:CH3OH)
I
I
0
Figure 4. peratures
0.5
1.0 WIF, gm o f c a l s l y r l / g m mole of.feed/hr
1.5
Conversiori vs. time factor at various temCatalyst. y-Alumina Ratio of reactants 1 :2
I
I
I
1
2
3
W/F, grn of catalyrt/gm mole of fced/hr
Figure 6. peratures
Conversion vs. time factor at various temCatalyst. Silica gel-alumina Ratio of reactants 1 :1
> U
0.5-
m
U r
I
0.4-
0
u
: 0.3
x
.-$- 0.2-
Catalyst : r-Alumina
E
W/F, gm of catalyst/gm
Figure 5. peratures
mole of feed/hr
Conversion vs. time factor at various temCatalyst. y-Alumina Ratio of reactants 1 :3
> C
8
0.1
0,0
-
Ratio of reactants=l:l (HCi: CH30t
300
330
360
390
410
TemperatUrQ *C
Figure 7.
in molal ratio is not considerable but a t higher temperatures it is more significant. Thus, conversion can be increased mainly by increasing the temperature. Comparison of Catalysts. Comparison of Figure 4 with Figure 7 shows that y-al.umina catalyst gives higher conversions throughout the range of temperatures and time factors considered. However, it s e e m unreasonable to compare the catalysts in the above fashion because their densities are not the same. As a result, the volume of the catalyst possessing a lower density will be much greater than that of the other and the number of particles of this catalyst is greater than that of the other. Thus, for the same weight, the catalyst having lower density offers
Effect of temperature on conversion Catalyst. y-Alumina Ratio of reactants 1:l
higher surface area for the reaction, thereby making it possible to achieve higher conversions even if its activity is slightly less than the other. In the present case, the density of y-alumina is very low compared with that of silica gel-alumina, so much so that the volume of 1.O gram of silica gel-alumina catalyst is smaller than 0.5 gram of y-alumina. The bulk densities of silica gel-alumina and y-alumina are, respectively, 0.6302 and 0.2857 gram per cc. VOL. 5
NO. 3
JULY 1966
211
Rate Equation
The method employed for expressing the results quantitatively is based on the order of reaction approach. The design equation for a catalytic flow reactor can be put in the form
W/F' =
[
(2)
dXA/T
Arrhenius plots were made for both y-alumina and silica gel-alumina catalysts. The plot for y-alumina is presented in Figure 8, and that for silica gel-alumina is presented in Figure 9. The values of k employed in these graphs are averaged values which are considered to be more representative than any arbitrary chosen value. From the slopes and intercepts the values of E and A are calculated for both the catalysts and are given below:
I n Equation 2 r is a function of x A because the concentrations of unreacted materials vary with conversion. The secondorder rate equation for the reaction can be expressed as
y-Alumina E = 19,178 cal./gram mole A = 1.816 X lo7
r = k CA C B
Silica Gel-Alumina E = 18,860 cal./gram mole A = 2.615 X l o 3
(3)
By substituting this in Equation 2 and making substitution and integration, the final equation obtained is
W/F' = n$/k
-
1 --nAo
+
n.4
- nBo
In 0
- XA
nAo
1 nAo
- nBo
In
nBo nBo - XA
(4)
Employing these values of E and A , the final integrated rate equation is written by expressing k of Equations 4 and G in terms of E and A . Thus for 7-alumina, the final rate equations are : Where the feed does not contain equimolal quantities of methanol and hydrogen chloride :
This equation applies only when the initial moles of the reactants are not equal. For the special case when nAo = n B o , Equation 3 becomes
(5)
r = k CAz
Substituting Equation 5 in Equation 2 and integrating we obtain
pV/F'
= D k.nAo n 2
( ~
nAu
- xA
)
(6)
The known values of %A, nAo, n B o ) no, and p!'/F' are substituted and the values of k calculated a t various conversion values. T h e resulting values of k are given for y-alumina and silica gel-alumina catalysts in Table I. Table I shows that a t 300' C. the values of k are nearly equal for feeds of various molal ratios. Similar is the case with values of k a t 330" and 360' C. These observations confirm that the reaction is definitely of first order with respect to each of the reactants, methanol and hydrogen chloride. Reaction velocity constants for silica gel-alumina catalyst a t various temperatures are also presented in Table I. Effect of Temperature on Reaction Velocity Constants. The reaction velocity constant is related to the reaction temperature, in accordance with the Arrhenius equation, as follows : k =A
,--E/RT
- E/RT
(8)
Reaction Velocity Constants at Various Ternperatures Mole Ratio of
NO. 1
2 3 1
212
( HCl : CHaOH)
1.0
-
0.8
-
0.6
-
.x
Table 1.
Reactants
Similarly for silica gel-alumina catalyst the final integrated rate equation is
(7)
or In k = In A
When feed contains equimolal quantities of methanol and hydrogen chloride:
01
0
0.4-
0.2
-
0.0
-
7,s
-
Aaerage Value of k 300'C.
33'0'C.
36OOC.
1:l 1:2 1:3
?-Alumina Catalyst 1.034 2.202 3.404 1.032 2.198 3.403 1.036 2.206 *..
1:l
Silica Gel-Alumina Catalyst 0,2573 0,6415 1.4010
390'C.
1
7.714
...
... 2.8180
I&EC PROCESS D E S I G N A N D DEVELOPMENT
1
0.15
1
I
0-17
0-16
1
0.18
+*lo2
Figure 8. stants
Effect of temperature on reaction velocity conCatalyst. y-Alumina Ratio of reactants 1 :1
Conversion X
0.05 0.075 0.10 0.15
0.20 0.30 0.35
0.40
Temlberature 300" C. W/F' calcd. W/F' exptl. 0.2546 0.2220 0.4044 0.3510 0.5729 0.5000 0.9820 0.9050
... ... ...
...
...
...
...
I
.
.
Table II. Validity of Rate Equations Catalyst. ?-Alumina Ratio of reactants. 1 : 1 (CHaOH:HC1) Temperature 330" C. Temperature 360' C. W/F' calcd. W/F' exptl. W/F' calcd. W/F' exptl. 0.1101 0.1170 0.5160 0.7600
0.2477 0.4245 0.6603 1.4853
0.2520 0.4120 0.6270 1.2740
...
...
...
0 .'1.162 0.1988 0.3092 0.6956 1.0816 *..
...
0 .'l620 0.2660 0.3950 0.8250 1.1600
...
Temperature 390" C. W/F' calcd. W/F' exptl. 0.0260 0.0280 0 0582 0.0997 0.1551 0.3488 0.5425 0.9293
0,0660 0.1330 0.1780 0,3900 0.5950 0.9230
silica gel-alumina catalyst showed that Equation 11 expresses the data well. Acknowledgment
The authors thank the authorities of the Council of Scientific and Industrial Research, New Delhi, for the award of a Junior Research Fellowship to one of them (M.S.T.).
0.50-
0.30
-
0.10
-
?so
-
7-70
-
K
T.50
-1.30 -
2
JL 0 cn
Nomenclature
A CA,
E F F'
CB =
k
nAo, nBo
Effect of temperature on reaction velocity Catalyst. Silica gel-alumina Ratio of reactants 1:l
= = = = = = = = =
r T
=
XA
= =
X
=
w
Figure 9. constants
=
frequency factor, gram moles/hr. (atm.*) (gram cat.) concentration of species A and B activation energy, cal./gram mole feed rate, gram moles/hr. feed rate, gram/hr. reaction velocity constant, gram moles/(hr.) (atrn.2) (gram cat.) equilibrium constant number of moles of species A and B initially present, gram moles per unit mass of feed total moles of feed per unit mass of feed universal gas cmstant rate of reaction, gram moles/(hr.) (gram cat.) absolute temperature, O K. weight of catalyst, grams moles of hydrogen chloride converted per unit mass of feed moles of methyl chloride formed per mole of total feed
literature Cited
(I) Allison, V. Reliability of Equsrtion. T o verify that the equations derived represent the data adequately, calculations were made for W/F' values Iby putting various values of conversions x A in the equations. A. set of values calculated through Equation 10 as well as experimentally determined values is given in Table I1 for y-alumina catalyst. Table I1 shows that the calculated values agree well with the experimental ones. Similar calculations conducted for
C., Meighan, M. H., J. Znd. Eng. Chem. 7, 943 (1919). (2) Bhatnagar, R. K., Kuloor, N. R., J . Sci. Znd. Res. (India) 12A, No. 11, 520 (1953). (3) Kirk, E. R., Othmer, D. F., "Encyclopedia of Chemical Technology," Vol. 3, p. 741, Interscience Encyclopedia Inc., New York, 1949. (4) Kobe, K. A,, Crawford, H. R., Petrol. Rejner 37 (7), 125 (1958).
RECEIVED for review January 18, 1965 ACCEPTEDJanuary 24, 1966
VOL. 5
NO. 3
JULY 1966
213
