Stvrene Production bv J
J
Catalytic Dehydrogenation OPERATION AT ORDINARY PRESSURES WITH BENZENE AS DILUENT Julian PI. Mavity, Earl E. Zetterholm, and George L. Hervert Universal Oil Products Company, Riverside, Ill.
Two block furnace assemblies were described in a previoub paper (4). The simulated recycle runs were made with the unit containing the stainless steel reaction tube of 1.25-inch inside diameter. The 16.4-mm. i.d. quartz tube unit, was used for all other tests,
Laboratory data are presented on the catalytic dehgdrogenntion of ethylbenzene over a chromia-alumina catalyst in the presence of benzene. Reduction of the partial preslure of ethj-lbenzeneby the diluent has the same favorable efrects as subatmospheric pressures; in addition, the benzene serves as a heat carrier for the endothermic dehydrogeuation reaction. Benzene is relatively stable under the conditions used and has no deleterious effect on the catalyst. Teight ratios of benzene to ethylbenzene varyi n g from about 10 to 0 were investigated. Dilution decre>tsedconl-ersion a t high ethylbenzene space velocities, increased it a t low- space velocities. 4 t a given conversion, dilution improved styrene ultimate yield and reduced carbon formation. Reduction of pressure below atmospheric, in addition to the use of benzene diluent, further improved the selectivity of the dehydrogenation reaction. Cinder preferred conditions (benzene t o ethylbenzene w-eight ratio of 5 , atmospheric pressure, 3.8 ethylbenzene epace velocity, and 581" C. a t the catalyst bed inlet) the average conversion in a series of simulated recycle runs was 34.8%, styrene ultimate yield, 89.7 weight %.
50
z
9 40 u?
a w
>
5
30
3 20
PREVIOUS paper (4)presented laboratory scale data on the catalytic dehydrogenation of ethylbenzene to styrenc and denionstrated the advantages of carrying out the reaction at piesw e s below atmospheric. Another method which has been used bo produce similar effects but which avoids the necessity of subatmospheric pressures involves carrying out the dehydrogenation in the presence of some added material; the partial pressure of rhe ethylbenzene is thereby reduced. This method has an added sdvantage in that the diluent can be used as a heat carrier for the endothermic dehydrogenation reaction. The use of various inert gases, such as carbon dioxide @,e,I O ) , nitrogen ( 2 , 6, I O ) , and methane (Pf, has been cited in a number af patents, both domestic and foreign. The Dow process ( I , 6) now in extensive commercial use employs steam. The use of benzene for this purpose has been suggested by Smith (6). Benzene was well adapted for present n-ork, since i t has no deleterious effect on the chromia-alumina type of catalyst employed, is relatively stable under the conditions covered, and is readily separated from styrene and ethylbenzene by virtue of its lower boiling point. This work comprised a laboratory scale study of some of the factors involved in the use of benzene diluent, with particular regard to the effect of the process variables on yields. Dow ethylbenzene n-as fractionated in a fifty-tray, bubble-cap glass column, a small forerun and residue being discarded. The benzene n as Merck's reagent grade. Fresh C.O.P. dehydrogenation catalyst (I/* X inch cylindrical pellets) Tas used in each of the simulated recycle runs. In all other runs the catalyst had been preaged by 21 days of jervice in pilot plant dehydrogenation of butane. Separate qamplr? r e r e used for rnch run.
IO
I
too I
10
I
I
20
30
I
40
%
I
I --T--7
50
€4
70
80
CONVERSION
Figure 2. Effect of Ethylbenzene Concentration on Ultimate Yield of Styrene a t 600" C., Atmospheric Pressure, and 30-3Iinute Process Period
829
by bromine number (8). I n most cases samples larger than the customary 1 ml. were used in order to obtain increased accuracy. Carbon on the used catalyst from each run was obtained from
E *
eo
Y 745 MM.
August, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
succeeding run. Three methods cif deterniiiiiiig yic.ltl-: (1 c’re employed. h k t h o d A was used in the process variable investigation and was described under the heading “Analyscs a,nd
i b l i h h more accurate yic,lc! data under g coiiditions and to determine by w t u a l fr:ictionation the ex
