I
H. G. BOYNTON,' E. W. LEWIS,2 and A. T. WATSON3 Humble
Oil &
Refining Co., Baytown, Tex.
A High Pressure Photochemical Reactor This reactor design permits investigation of photochemical reactions at elevated pressures while providing for good temperature control, efficient mixing, and ready scale-up to commercial size
A suitable for operation a t elevated pressures over PHOTOCHEMICAL
REACTOR
a wide range of temperatures, while allowing for efficient light transmission and heat removal and maintaining a high degree of turbulence for contacting hvo phase systems, is presented. Because glass or quartz is used to obtain suitable light transmission, most photochemical reactors have had to operate at or near atmospheric pressure (3,72). Also, in annular bubble tube-type reactors. satisfactory contact between gas and liquid phases is difficult ( 6 ) . Heat removal is a problem in large scale operation (72). The reactor described here overcomes these difficulties (2). Description of Reactor
The reactor system (Figure I) has a nominal capacity of about 2 barrels per day. The reactor consists of a spiral coil tube about 12 inches in diameter fabricated from 200 feet of heay-Xvalled borosilicate glass tubing (I '4 and l , ' ~ inch in inside and outside diameter. respectively) enclosed in an 8-foot section of 18-inch Schedule 40 carbon steel pipe flanged a t both ends. Reactor inlet and outlet lines pass through the bottom flange. The light source consists of 12 General Electric H400 E-1 400-watt mercury vapor lamps arranged in three tiers within the spiral coil. Electrical connections to the lamps from Tulamp transformers 1 Present address, Market Development Division, Enjay Go., Inc., 1141 East Jersey S t . , Elizabeth, Tu'. J. 2 Present address, Marketing Department. Humble Oil & Refining Co., P.O. Box 2180, Houston, Tex. 3 Present address, Research Department, Chemstrand Corp., Decatur, Ala.
are made through Conax elements at the top of the steel shell. The glass coil reactor is supported from the outer periphery by a cylinder rolled from stainless steel sheet. This steel both supports the reactor coil and reflects the light which passes through the coil. Jacketed lights are selected because high pressure mercury l a m p will not operate a t the temperatures desired for the reaction without outer jackets. The reactor has also been used with blacklight fluorescent lamps arranged in a bundle inside the reactor coil. The reactor spiral coil and lamps are completely immersed in a boiling liquid hydrocarbon Xvhich absorbs the heat of reaction from the coils. The hydrocarbon vapor is condensed by a xvater cooled condenser a t the top of the reactor shell. The hydrocarbon coolant is selected such that its vapor pressure and, consequently, the pressure exerted externally on the coils is sufficiently high a t the operating temperature to allow the desired pressure operation within the reactor tube. Actually, the reactor system is generally operated with external pressure on the glass piping slightly higher than that of the reactants inside the coil. Thus, in the event of a slight amount of leakage in the flange connections of the glass piping, the light hydrocarbon that would flow into the reaction system would not be detrimental to the reaction and could easily be removed from the final product. O n the other hand, if the pressure differential were reversed, small leaks would result in considerable corrosion of the steel vessel and chlorine would react with the hydrocarbon bath. For the work described in this paper the reactor shell was filled with hutanepentane mixtures.
3
rC-
'
--?
~
'11
Figure 1. Details of high pressure photochemical reactor
Outer skin temperarures measured a fekv inches doivnstrcam from the reactor inlet were a few degrees higher than rhe inlet temperature during normal operations, the variation depending on the operating conditions cmployed (see table), Estimates based on these temperatures and approximate heats of reaction indicate that rate of heat removal from the system is limited by thermal conductivity of the glass \Val1 of the reactor. Thus, this rate could have been increased significantly by using thinner walled tubing. This tvould be possihle VOL. 51, NO. 3
MARCH 1959
267
7:
VENT
A
"d SC4LES
Figure 2.
Schematic diagram of photochemical pilot unit
because of the pressure counterbalance technique ivhich allows the use of glass tubing a t high reaction pressures. To ensure that hydrocarbons used in the bath Tvould not absorb the \\-ave length of light needed to initiate the photochemical reaction, these hydrocarbons \vere percolated through silica gel before being introduced into the shell. This removed traces of unsaturates that might have decreased the light transmission through the hydrocarbon bath and also removed the last traces of water to ensure proper operation of the electrical connections. A steam coil a t the bottom of the reactor system provided heat for the initial start-up operations and was used to maintain the desired operating tem-
perature. Cooling ivater in excess of that needed to remove the heat of reaction was supplied to the condenser coil. T h e steam supply \vas regulated by a pressure controller (Figure I ) to maintain a constant shell pressure predetermined from the vapor pressure of the selected hydrocarbons. The teinperature-pressure relationship \vas varied during operations simply by lvithdrawing a portion of the liquid hydrocarbon bath and replacing it Lvith a lighter or heavier hydrocarbon depending upon the conditions desired. The shell of the reactor system is fitted \vith a 2.5-inch diameter glass windoiz- for observation of the lights and flow patterns. The reactor coil pressure was controlled by use of a pressure con-
Reactor Inlet, Middle, and Outlet Temperatures Lie Very Near Bath Temperature. Per Cent of Chlorine Reacted Is a Function of Light Intensity at 175" F. Operating Conditions
Number of lamps (GE H400 E-lj Reactor temperatures, F. Inlet Inlet skin" Middle skinb Outlet Bath Reactor pressures, p.s.i.g. Inlet Outlet Feed rates, lb./hr. Oil Chlorine Sulfur dioxide Product inspections Wt. % RSO? C1 Wt. % C1 a s RC1 Yc of Clz charged reacted Cln selectivity to SOsC1, %"
Run IYurnl)er 70 60
76
-7-
,a
71
0
4
9
9
176 177 176 175 175
175 177 176 175 175
175 176 175 174 174
100 63
98 60
102 61
55
54
9
9
9
162 162 161 160 160
192 196 191 190 190
188 195 190 190 190
198 207 201 200 200
97 80
95 56
102 50
103 62
Applications The high pressure photochemical reactor described above was used to study the sulfochlorination reaction first reported by Reed (70, 77). This reaction presumably proceeds in the following manner :
h
c1, --+
21.7 7.1 9.6
22.1 7.2 9.6
22.6 6.9 8.6
22.4 7.0 9.1
21.9 8.6
22.6 9.3 7.9
22.6 9.1 7.5
7.0 6.7 73.0 6.4
18.9 8.7 90.3 12.5
30.0 9.8 95.8 16.8
20.6 9.0 90.5 13.1
33.4 10.9 97.5 16.8
34.9 14.0 98.6 14.1
32.5 13.3 97.6 13.8
7.5
Outside skin temperature on reactor coil taken G iiicliei tlownstream from junction of C'I? Outside skin temperature on reactor coil taken ar>proxiniatelymid-way and oil-SO1 streams. (C'l in ItSOzCl X 100j/total C1 in prodnct. between reactor inlet and outlet.
*
268
trol valve on the reactor outlet. T I I O pressure taps for the controller were manifolded so that either the inlet or the outlet pressure could be the primar)controlled variable. Because of high lag in the system through the 200 feet of reactor coil, hon.ever, the controller operated satisfactorily only as an outlet pressure controller. Because pressure drop through the reactor coil varied only a few pounds per square inch during operarion a t a given set of conditions, it \\-as possible to maintain the approximate desired inlet pressure by controlling the outlet pressure. Although the long path length photochemical reactor described above involtred a considerable portion of glass material for the fabrication of the spiral reactor coil, no difficulties were encountered as to ruggedness of construction and ease of maintenance. .4 service factor of about 80Yc \vas obtained during the last periods of operation. This is felt to be exceptionally high for pilot units and indicates that a satisfactory srrvice factor could be obtained on larger units. This reactor probably lends itself much more readily to scale-up to commercial size than many photochemical reactors which have been pre\,iously described. This is particularly true Lrith respect to the problem of heat removal \\-here bulk reactors with large holdups make heat removal difficult for highly exothermic reactions. .4reactor of this q p e can be used for reactions ivhich require very short wave lengths if a quartz or other q p e coil is used to obtain the desired transmission and greater care is taken for the purification of the hydrocarbon bath.
INDUSTRIAL AND ENGINEERING CHEMISTRY
R. + HCI + SO? +RSO?.
+ C1. --+
RH
R. RSO?.
2 c1.
+ C11 +RSOiCl + C1.
Competing rvith this sulfochlorination reaction is the direct chlorination reaction R.
+ Cl! +RCl + C1.
A schematic diagram of the pilot unit used in these studies is shown in Figure 2. Liquid sulfur dioxide and chlorine were pressured from charge tanks tvith nitrogen and the chlorine was vaporized in a steam jacketed vaporizer. Flow rates of both compounds were controlled by hand valves and monitored by flow indicators, but final determination of the rates \vas
CHEMICALS F R O M PETROLEUM made by means of scales on which the charge tanks were mounted. I n order to minimize the possibility of oil backing u p into the liquid chlorine charge tank, the chlorine was passed through two check valves. Also, a n alarm actuated by a hlercoid pressure switch was mounted on the chlorine line just downstream of the vaporizer to warn the operator if the pressure a t this point should increase to Ivithin about 10 p.s.i. of the pressure on the tank. I n addition, a low-temperature alarm was mounted on the chlorine line just upstream of the reactor to guard against charging liquid chlorine to the reactor due to failure of the steam supply. A phenol-extracted lubricating oil having a molecular Jveight of 460 ivas pumped from a barrel mounted on scales by means of a proportioning pump to the reactor. T h e oil and sulfur dioxide streams were combined and passed through a pressure control valvr: undergoing a drop of about 50 pounds in order to obtain tnising of the streams. The combined stream \vas then preheated to the reactor temperature before joining the chlorine charge inside the lighted zone of the reactor. T h e total product from the reactor system passed to a gas stripper Lvhere the hydrogen chloride and unreacted sulfur dioxide and chlorine 1vei-e removed by countercurrent scrubbing \vith natural gas. T h e liquid product \vas m-eighed and analyzed for sulfonyl chloride and chlorine both chemically and by infra-
red absorption. T h e tail gas was sampled by absorption in 20" BC. caustic and analyzed by titration. I t is not the purpose of this report to give a detailed process variable study of the reaction, but to use certain portions of such a study to illustrate the application of the reactor described and to illustrate typical operating conditions which were employed. Effect of Light Intensity. 4 brief study \vas made on the effect of light intensity at 175' F. The conversions obtained ivith O j 4: and 9 lamps are shoivn in Figure 3 . Also plotted in this figure are the chlorine selectivities. Conversion is defined as the weight per cent RS0,CI in the oil product and selectivity is defined as the per cent chlorine present in the product as R S 0 2 C1 divided by the total per cent chlorine in the product. A s these curves are still ascending sharply a t the highest light intensih: it appears that light intensit) is a limiting factor and that a further increase in conversion and selectivity could be obtained by a further increase in light intensity. ShoLvn in the table (runs '6, 75, and 71) is the per cent of the total chlorine charged which reacted with the oil feed in these esperiments (called chlorine utilization). T h e per cent chlorine reacted a t 175' F. is a function of light intensity. T h i s is not the case a t 190' F. as utilization at that temperature is about 95 to 98y0even in the absence of light with the particular feed stock employed. Holvever. a t 190' F.
conversion to the desired product, RS02C1, is a function of light intensity even though chlorine utilization is not. Effect of Reactor Temperature. Several runs illustrating the effect of varying the reactor temperature are also shown in the table (runs 71, 70, 60, 55, and 54) and the conversions a ~ e plotted in Figure 4.. The conversions to sulfonyl chlorides appear to reach a maximum a t about 190" P'. rhough a more detailed study would probably indicate a slightly lower temperature to be actually the optimum operating level. As mentioned previously, temperature could be varied easily by simply removing a portion of the reactor bath and adding a lighter 01- heavier paraffinic hydrocarbon depending upon whether operation at a lowet, or higher temperature \vas desired.
Consideration of Pressure Drop and Flow Pattern
Of paramount importance in the design of this photochemical reactor \vas the necessity to produce a flow pattern conducive to intimate mixing of the hvo phases, hitiall>-there was considerable concern as TO the gas floiv velocities required to obtain froth floi\,-type phenomena. Literature discussions ( 7 , 4, 5, 7-9) on gas-liquid floiv systems indicarcd that to obtain intimate mixing of the two phases would require gas velocities far in excess of those which could feasibly he obtained in the photochemical sulfo-
4 Figure 3. Conversion and chlorine selectivity are functions of light intensity
Figure 4.
Conversion to RSOsCl i s maximized at about
190" F.
I 4 60
LAMPS
-9
180
170 REACTOR
voL.
TEMPERATURE,
51, NO. 3
190
200
OF.
MARCH 1959
269
60. 55
-
1
75
-
INLET PRESSURE 100 p s 1 g CHARGE RATES OIL 3 gph (22.5 Ib I hr ) 0 Q A SO, Ib/hr 9.0 100 7 5 GI, Ib/hr 7 0 4 5 91 LWS-9
-
70
0
a-
E
,
0
55
W
3
I50 W
0 1
a
-+ / REACTOR TEMPERATURE
45
- 190°F INLET PRESSURE 100 p s 1 g CHARGE RATES OIL - 3 g p h ( 2 2 5 I b / h r ) S O * - 0 13 8 Ib/hr 0 981b/hr LAMPS 10
-
I
170
REACTOR
190 TEMPERATURE,OF 180
200
Figure 5. Pressure drop through the reactor depends on temperature and ch!orine r a t e
chlorination reactor. Furthermore, oilair-mock-up experiments performed preliminary to the pilot unit studies further demonstrated that excessive gas velocities are required in a nonreactive system to produce a flow pattern conducive to intimate mixing of the two phases. However, the pilot unit work showed that flo\\. characteristics far different from those obtained in the oil-air system are obtained in a reactive system such as chlorine and oil. This apparently is due to liberation of hydrogen chloride in a pin point carbonation-type phenomenon Lvhich tends to transform the two-phase system into a highly turbulent froth. Thus, the desired froth or foam Aoiv pattern was obtained a t appreciablv lower gas rates under reaction conditions than those predicted from the oil-airmock-up studies and the literature. Inasmuch as a froth or foam flow pattern was obtained under nearly all conditions employed in the photochemical sulfochlorination reactor, no attempt was made t o obtain complete definition of the effect of the operating variables on pressure drop and flow pattern. Actually, complete definition of the effects of some of the major operating variables on pressure drop is somewhat complicated by interaction of these variables w.ith respect to both the physical characteristics of the system and also the reaction kinetics. For example, variations in reactor temperature and pressure resulted in changes in volume and velocity of gas in the reactor coil and in the physical properties of both gas and liquid. Such variations also caused changes in the rates of the photochemical reactions. Both of these ?pes of changes affected the pressure drop and degree of turbulence. However, general observations of the effects of
270
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I
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I
160
6
10
Figure 6. Increasing chlorine rate causes sharp increase in pressure drop
some of the major operating variables were obtained. Pressure drop appears to reach a maximum point in the region of about 175" to 180' F. as reactor temperature is varied bet\Qeen the limits of 160' and 190" F. (Figure 5). Further. pressure drop increased steadily as the rate of chlorine charged was increased. At very low chlorine charge rates, slug flow was obtained. Lowering the inlet pressure also increases the reactor pressure drop due to the increased velocity caused by the increase in volume of the gaseous material. Decreasing the inlet pressure from 100 to 80 p.s.i.g. resulted in an increase in pressure drop from 50 to 80 p s.i. Conclusion
-4 long path length photochemical reactor, which can be operated a t high pressures and is applicable to a \vide variety of gaseous phase and heterogeneous reactions, has been described. The problem of removal of high heats of reaction from photochemical reactions is simplified. and virtually isothermal conditions are obtainable. By using a bath material with the proper vapoi pressure, any desired operating pressure can be selected for a given reaction temperature. By using the proper material for the bath and quartz or various types of glasses for constructing the reaction coil, this reactor system can be adapted to many photochemical reactions requiring absorption of light of different wave lengths. Scale-up to commercial size is greatly simplified. Completely satisfactory use of this reactor system in pilot plant photochemical sulfochlorination studies has demonstrated the feasibility of commercial application.
INDUSTRIAL AND ENGINEERING CHEMISTRY
7 8 9 CHLORINE RATE, LBS / HR
Acknowledgment The authors wish to express appreciation to the management of the Humble Oil Br Refining Co., for permission to publish this work, and to I. G. Thompson, who assisted throughout the \vork described. T h e efforts of mechanical, operating, and analytical personnel are also greatly appreciated.
literature Cited (1) Bergelin, 0. P., Chem. Eng. 5 6 , 104
(May 1949).
(2) Boynton, H. G., Lewis, E. IV., Watson, A. T. (to Esso Research and Engineering C o . ) , U. S. Patent 2,848,623 (Aug. 19, 10r;Ri
( 3 ) Governale, L. J.: Clarke, J. T., Chem. Eng. Progr. 52, 281 (1956). 141 Jenkins. R.. M.Ch.E. thesis. University of Delaware, Newark, Del., 1947; Chem. Eng. Progr. 45, 45 (1949). ( 5 ) Lockhart, R. W.,Martinelli, R. C., Chem. Eng..Progr.45, 39 (1949). (6) Lockwood, W. H. (to E. I. du Pont de Nemours 8( Co., Inc.), U. S. Patent 2,193,824 (March 1 9 , 1940). (7) Martinelli, R. C., Boelter, L. X f . I;.. Taylor, T. H. M., Thomsen, E. G., Morrin, E. H., Trans. Am. Soc. .Mech. Engrs. 66, 139 (1944). (8) Martinelli, R. C., Nelson, D. B., Zbid., 70, 695 (1948). (9) Martinelli, R. C.; Putnam, J. .I., Lockhart, R. W.,Trans. Am. Znst. Chem. Engrs. 42, 681 (1946). (10) Reed, C. F. (50% Charles N. Horn), U. S. Patent 2,046,090 (June 30, 1936'1. (11) Ibid., reissue, C. S. Patent 20,968 (Jan. 3, 1939). (12) Roberts, J. B., Gage, H. B.: Brautcheck, C. H. (to E. I. du Pont d e Nemours & Co., Inc.), U. S. Patent 2,528,320 (Oct. 31, 1950).
RECEIVED for review April 2, 1958 ACCEPTED November 13, 1958 Division of Petroleum Chemistry, Symposium on Recent Developments in Chemicals from Petroleum, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
