R
TEN
E. W. NICHOLSON, J. E. MOISE, AND M. A. SEGURA ESSO Laboratories, Baton Rouge, La. Standard Oil Deoekoprnent Company, Elizabeth, N.J . to staff the pilot plant organization with selected personnel from these companies. The technicd personnel were furnished by the Esso Standard Oil Company (Louisiana Division) (then known as the Standard Oil Company of Louisiana), Standard Oil Development Company, Shell Chemical Corporation, Sinclair Rubber, Inc., Cities Service Refining Corporation, and the Neches Butane Products Company. Because of a growing national shortage of critical materials and the press for time, it was necessary to select a site that would require a minimum of change, and, further, to utilize only such additional equipment as could be furnished by the participating companies. The site chosen was on the premises of the Ethyl Corporation a t Baton Rouge, La. The choice of this location was influenced by the availability there of two high temperature coil furnaces and a complete light hydrocarbon purification system. Furthermore, a suitable butene feed stock could be obtained from an existing nearby plant operated for Rubber Reserve b y the Rsso Standard Oil Company; the Esso Standard Oil Company owned and operated a butadiene extraction plant that could be made available for recovering the butadiene produced. Even with such an excellent nucleus as a starting point, ingenuity in design was essential to provide the necessary additional facilities for the pilot plant from surplus materials that were available. An electiic timer and motor-operated valves were obtained from the demonstration hydroforming unit at the Bayway refinery of the Esso Standard Oil Company; a large heat exchanger and water circulating pumps were sccurrd from another Jersey affiliated refinery; the 25-20 chrome-nickel alloy steel transfer line for the high temperature steam was fabricated from old equipment from a commercial hydrogen production plant; t,he pilot plant reactor shclls were constructed from an available 10 X 30 foot drum; and a number of instruments, meters, and pumps weIe obtained from the Baton ltouge Esso Laboratories
Government plans, formulated soon after Pearl Harbor, for expanding the synthetic rubber industry placed great importance on obtaining large quantities of butadiene from petroleum sources. Catalytic dehydrogenation of n-butene appeared to be the most promising process. To obtain sound verification of the practicability of the process and information necessary to guide the operation of commercial units then being designed, a pilot plant with a capacity of 10 tons per day was built and operated at Baton Rouge, La. lncluded herein are descriptions of the process, the pilot plant mechanical features and failures, operating procedures, personnel requirements, and the process results.
HE Standard Oil Company (N. J.) has been investigating the catalytic dehydrogenation of Cd hydrocarbons s h c e about 1932 (8). Hence, in early 1942, when it became essential t o produce butadiene in large quantities to provide the base material for synthetic rubber for the war effort, the details of the catalytic process worked out in the laboratories of Jersey Standard affiliated companies were immediately made known to the Rubber Reserve Company and to other interested oil companies. The laboratory studies had shown that t h - catalytic dehydrogenation of butene gave satisfactory conversion and selectivity to butadiene, and ample quantities of butenes could be obtained readily from the petroleum industry as a result of the recent development of the fluid catalytic cracking process. The government’s over-all synthetic rubber program included the commercial production of butadiene from both agricultural and petroleum products. For the bulk of the production of butadiene based on petroleum, the Jersey process for catalytic dehydrogenation of butene was selected. At that time, Jersey already bad under way detailed plans for the construct;on of commercial units. However, some phases of the designs required confirmation, and it was desirable that a demonstration be made of the process in a sufficiently large pilot plant to obtain reliable data for guidance of commercial units soon to be constructed. Catalyst life, the length of reaction and regeneration cycles, the effectiveness of the proposed method of quenching the reactor products were all mattcrs of vital importance. It was desirable to determine on scale models the operating characteristics of proposed new equipment such as steam-butene mixing nozzles and waste heat boilers. At the request of the Rubber Reserve Company, several members of the oil industry contracted to operate the commercial butene dehydrogenation plants. T o consolidate pilot plant efforts, i t was decided to employ a single large pilot plant and
LABORATORY WQRK
Fortunately, experimental laboratory work i n the production of butadiene by the catalytic dehydrogenation of butenes had made considerable progress prior to the development of hostiMes. A successful process had been demonstrated on a laboratory scale, with a catalyst of satisfactory activity and selectivity, by the Standard Oil Development Company. This catalyst, imlike most dehydrogenation catalysts, was only mildly sensitive t o steam, thus steam dilution could be used rather than some other diluent, or vacuum operation, to obtain the low hydrocarbon partial pressure necessary for satisfactory yields (8). A number of studies involving catalyst life as well as process variables bad 646
March 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
been completed. By March 1942 the small pilot units were employed chiefly in control work for testing the quality of catalysts being produced on a commercial scale. PILOT UNIT DESCRIPTION
Process Features. At the site chosen for the butene dehydrogenation pilot plant, there were available a commercial propane cracking unit equipped with two coil furnaces suitable for operation a t the required temperatures (one for steam, one for hydrocarbons), and fractionating equipment including distillation towers, condensers, heat exchangers, drums, compressors, and refrigeration unit. Rearrangement of the piping was all that was necessary to obtain the desired flow t o the equipment chosen for the pilot plant. The two reactors, cooling tower, pumps, alloy piping, motor-operated valves, controls, and instruments were for the most part obtained from refineries of the Esso Standard Oil Company and adapted for this plant. The pilot plant was designed to produce about 10 tons per day of butadiene. A butadiene extraction plant (vapor phase, copper ammonium acetate solution type) located on the adjoining property of the Chemical Products Division of the Esso Standard Oil Company was connected by pipe lines to this plant. It was operated to extract the butadiene from the Cd cut and t o return the unconverted butenes t o the fresh feed stream ahead of the reactor. The feed for the plant was the raffinate obtained from a nearby isobutene extraction plant operated for Rubber Reserve by the Esso Standard Oil Company. The normal approximate composition of the feed was: 80% normal butenes, 3% isobutene, 5% butanes, 2% butadiene, 8% propane and propylene, and 2% pentane and higher boiling hydrocarbons.
641
Butadiene was produced in the process almost entirely from n-butene. The butanes and isobutene reacted slightly but tended to build up in concentration in the recycle stream. The Cs compounds were removed in the pilot plant fractionation section and hence did not build up in the system. Butadiene in the fresh feed was partly lost through decomposition. The Cb and heavier material were removed in the feed rerun tower before being fed to the unit. The fresh feed also was washed with caustic to remove esters. The process is illustrated in Figure 1. The heated total hydrocarbon feed (fresh plus recycle) was mixed with superheated steam and passed downflow through one of the two reactors. The reaction stream was quenched with water in the bottom part of the reactor to prevent loss of butadiene by thermal decomposition. It was further cooled by direct contact with circulated water in a packed cooling tower. While one reactor was being used for dehydrogenation, the catalyst in the other reactor was being regenerated by steam alone, passed through the vessel a t reduced rates of flow. One-hour periods were used for both operations. All valve changes involved in the cyclical operation were accomplished electrically, and the cycle was electrically controlled through a timer mechanism. Temperatures in the reactor during dehydrogenation were increased from about 1100" F. when the catalyst was fresh to about 1250" F. as the run progressed and the catalyst lost activity. The regeneration temperatures were kept a t about the same level as the reactor temperatures. During reaction, the superheated steam supplied some heat to the hydrocarbons which were held a t a lower temperature than the reaction temperature to minimize thermal cracking. Since the furnaces were maintained a t constant outlet temperatures, it was necessary t o bleed saturated steam in with the superheated steam during regeneration to prevent excessively high catalyst temperatures. Reactor outlet pressure during dehydrogenation was about 4 pounds per square inch gage and regeneration
COOLER TOWER
REACTORS
REACTION SECTION
REGENERATING
REACT1 N G
Y
AIR FOR S T A R T I N G
o
TO POLYMER R E C O V E R Y - J
INDICATES VALVE IN "OPEN" P O S I T I O N INDICATES
VALVE IN "CLOSED"POSITION
RECOVERY SECTION
S T A 0 l L l Z E R TOWER
500 PSIG
PRODUCT RERUN T O W E R
110 P S l G
A0SORBER TOWER
1
f
r--
DEHYDROGENATION GAS TO R E F I N E R Y FUEL
HZ0
Figure 1. Process Flow Plan of Butene Dehydrogenation Pi lot Plant
___ ACCUM.
FROM REACTION
b+
I
C 4 CUT T O EXTRACTION FACILITIES
2-000 h.P, COMPS. CRACKED POLYMER b CONDENSATE
DISCARD
TO POLYMER RECOVERY
648
INDUSTRIAL AND ENGINEERING CHEMISTRY
pressure was varied betL7een 7 and 50 pounds per square inch gage,, T o keep the dehydrogenation reactor pressure as low as possible, it was necessary to minimize pressure drop in the reactor outlet piping. As motor-operated valves larger than 8 inches were not obtainable, two 8-inch lines were used in parallel. The cooled product gas stream from the reaction section was compressed and passed to the fractionation section. The fractionated material was reduced to a Ca cut, which contained 16 to 18% butadiene, and was sent to the off-site extraction unit for removal of the butadiene. Recycle material was returned in part to the feed make-up system. Part of the recycle stream was flared to prevent a build-up of inerts in the feed stream. Mechanical Features. From the general flow plan, it is apparent that much of the equipment used in the pilot plant study was conventional and does not require a detailed description; the equipment, not found as frequently in laboratories 01' pilot plants, is described in more detail. ELECTRIC TIMER. The automatic timer consisted of a slowly rotating, motor-driven arm which made contact successively with 300 individual buttons per revolution. Any of these buttons could be connected to deliver an electrical impulse when contacted which, through a relay, would open or close a motoroperated valve. The total cycle time for the pilot plant was 2 hours, whereas the master timer, if operated continuously, would make a coinplete revolution in 30 minutes. T o lengthen the timer period to 2 hours, a dormant timer was installed; this would stop the master timer operation during the major portion of the reaction and regeneration periods and then reactivate the master timer for the short periods during which valve changes were necessary. I n Figure 2 the location and names of the motor-operated valves are given. A typical sequence of valve operation is as follows: Sequence 1
2 8 4 5
6 7 8 9 10 11 12 13
14 15 16
17
Valve D-I, product out E-1, product o u t F-1 regeneration vent A-I; oil inlet B-2, steam quench C-2, water quench C-1. water ouench B-1; steam quench -4-2, oil inlet F-2, regeneration vent E-2, product out D-2 product out Chebk uosition of D-2 Start dormant timer period Reset dormant timer D-2. oroduct out E-2,' product out F-2, regeneration vent A-2, oil inlet A-1 steam quench C-1: water quench C-2, water quench B-2, steam quench A-1. oil inlet
18 19
20 21
22
Reactor South South South South Korth h-orth South South h-orth North North North
Operation Open Open Close Open Open Close ODen ciose Close Open Close Close
North North North North South South North h-orth South South South South
O'd& Open Close Open Open Close Open Close Close Open Close Close
.. . ..
... . . I
Reset dormant timer
The approximate time required for the motors t o open or close each of the various valves in the system was as follows: Valve c-1, c - 2 -4-1,A-21 B-I, B-2 E-1, E-2 F-1, F-2 D-1, D-2
i
Time Required, See. 2
15 30
-4s each reactor was switched from regeneration to dehydrogenation operation, it was necessary to depressure i t slowly. Rapid depressuring might badly damage the reactor brick lining and also cause undesirably large surges in conditions. Therefore, one of the two reactor outlet motor-operated valves on each reactor (D-1 or D-2) was arranged to open by a series of impulses from the timer. The total time for opening this valve was about
SUPERHEATED STEAM
Vol. 41, No. 3
3 minutes. The second product outlet valve (E-1 or E-2) did not start opening until D-1 SATURATED or D-2 was comSTEAM ,/-) pletely opened. R/f 1XIh.G NozzLns. One of the important requisites for QUENCH WATER successful catalytic dehydrogenation of R L G C ? E r ~ ~ , O ? ~ ~ ~ - U L C N l i A T I O I : butenes was the %T\* @w thorough mixing of the butene feed w o UCT with superheated 0 U T L E.l steam as it entered Figure 2. Arrangement of Valves Controlled by Timer t h e reactor. A number of mixing nozzle designs were submitted and three of these designs were tested under operating conditions. It was found that all three provided excellent mixing of steam and butenes. The principal process differencc was the pressure drop across the nozzle. In Figure 3 the Ingersoll-Rand type mixing nozzle is shown; this was used in all of the Jersey plants. Steam was injected through a nozzle and the steam aspirated hydrocarbons into a Venturi-type throat where mixing occurred. A splash plate on the outlet of the mixer served to direct the flow through the four slots provided as directional outlets to prevent impingement on, and possible movement of, the catalyst bed. REACTORS.The reactors used in the butene dehydrogenation pilot plant are shown in Figure 4. Because of the high temperatures required in the process, the reactors were lined with refractory. The thickness of insulation used was greater than that required by the temperatures employed because it was necessary to reduce the internal reactor diameter to about 6 feet to correspond to the desired pilot plant production capacity. T o guard against spalling of the brick lining by quench water, a 0.5-inch carbon steel liner was installed over the brick on the bottom head and an 18-8 chrome-nickel alloy steel liner was installed on the side walls of the quench zone. 111 the original construction, six thermocouple wells were brought through the firebrick walls of the reactor. During t'he first run, by-passing of tlhe gases occurred and caused localized overheating of the outer shell. It was believed t'hat a large amount of the bypassing occurred around the thermocouples. During the first turnaround these couples were removed and the holes sealed. Two new horizont'al wells were installed to traverse the entire catalyst bed area. Each well contained several couples of different lengths which served to indicate temperatures a t different points in the bed. Subsequent operation, however, indicated that by-passing of gases around the catalyst bcd and down the shell was still occurring. The installation of an alloy steel liner during the next turnaround ultimately prevented the by-passing. The liner is shown in Figure 4. The water quench system to prevent t'he thermal decomposition of the but,adiene was inst,alled in the bottom part of the reactor. It consisted of fifteen carbon steel spray nozzles equally spaced on a ring made of 2-inch alloy steel pipe. IJ'ater was pumped to these nozzles from the bottom of the cooling tower. I n order that the effect on process results of reactor catalyst bed depth could be studied, the catalyst bed support was designed so that it could be easily raised or lowered. This was done by supporting the bottom bed grid by means of sections of pipe the length of which could be readily adjusted. When the bed depth was changed, the height of the ring carrying the water spray nozzles for quenching the reactor product was also adjusted.
(k,
bbdJ
March 1949 STARTING-UP PROCEDURE
INDUSTRIAL AND ENGINEERING'CHEMISTRY
t 17
HYDRCCAREON
INLET
\
2" --._.
-
! S T E A M INLET
/
I
On completion of L the mechanical work, \ti%the unit was thoroughly pressure tested with air. Each section that operated at a different pressure was isolated and tested a t a pressure in excess of the design operating pressure. Whenever possible, this was followed by flushing with water to remove any loose material that might clog orifices or cont r o l v a l v e s . A11 pumps were run with Figure 3. Steam-Butene either oil or water to Mixine Nozzle ensure their satisfactory operability. All instruments and instrument lines were checked and the automatic valves were operated with the timer. All safety valves, the emergency pulldown system, and fire protection facilities were checked. Sample lines were checked for location, and sampling apparatus for adaptability. The off-site tie-in lines were checked and coordination with off-site operators was established. Prior to actual operation, i t was deemed advisable to dry the brick-lined reactors at a low rate. Natural gas burners were installed in the bottom of each reactor and temperatures were maintained at 250" F. for a period of 8 days. After drying the reactor brick lining, catalyst was charged to each reactor and the Ingersoll-Rand mixing nozzles were placed in position. The entire reactor system was then purged with inert gas (carbon dioxide, 10%; carbon monoxide, 2%; nitrogen, 88%) until an Orsat analysis showed less than 0.5 oxygen in the gas stream. Natural gas was cut into the suction of the product compressors and vented a t the cooling tower knockout drum until the inert had been replaced with natural gas. Recycle of natural gas then was established through the same system a t a flow of 1200 to 2500 cubic feet per minute. Circulation of quench water to the cooling tower was started a t a low rate. After starting circulation of natural gas to the reactors and circulation of water to the cooling tower, the furnaces were fired to give a reactor inlet temperature of 150" F. Firing was continued in this manner until the bottom of the catalyst bed had reached 90" F. Temperatures then were increased to 250' F. reactor inlet until the catalyst bottom temperatures reached 150" F. The entire catalyst bed temperature was slowly brought up in this manner until a minimum bed temperature of 500' F. was reached. At this temperature, it was felt safe to introduce steam to the furnaces to complete the heating-up step. As the flow of steam was increased, natural gas circulation was stopped and the compressors unloaded. Catalyst bed temperatures were raised 50' F. per hour until a bed temperature of 1100" F. was reached, and then held at this temperature until hydrocarbon feed was introduced. Other correlated operations were in progress during this heating-up period. The fresh feed rerun tower was brought on stream and the &free product was stored in the feed drum for later introduction into the dehydrogenation section. The reactor quench system also was started as soon as the temperature of the gases leaving the reactor reached 700" F. As the
ll
-
649
reactor temperatures rose, the quench water was increased to hold 700" to 750' F. in the carbon steel exit lines. The timer system was first tried out before any gas flow was introduced to the reactors. It was then stopped and not put on again until the heating had progressed to the point where steam was introduced. When the catalyst bed temperature had reached 1100" F. and it was apparent that the timer system and the quench system were operating satisfactorily, the hydrocarbon feed pump was started up on by-pass to suction. Hydrocarbons then were introduced into the hydrocarbon furnace at as rapid a rate as possible while still maintaining a coil outlet temperature of 1050" F.; the high initial rate was necessary to hold down conversion. The compressors were attended carefully to avoid any pressure build-up in the system. The dehydrogenated hydrocarbons were sent from the compressors to an absorber tower where the butadiene and diluent Cq were absorbed in a lean oil a t 525 pounds per square inch gage pressure. The fat oil was sent to a stabilizing tower. This stabilization system consisted of a 2&plate, 2.5-foot diameter tower operating a t 500 pounds per square inch gage pressure. It was equipped with suitable reboiling and refluxing facilities. Propane and lighter gases were taken overhead and partially condensed in exchangers cooled by evaporation of a hydrocarbon stream principally composed of propylene. The C4 and heavier bottoms were sent to a product rerun tower for final purification before being sent to the off-site butadiene extraction unit.
J Figure 4.
W
Butene Dehydrogenation Pilot Plant Reactor
The product rerun tower consisted of a 39-pIate, 2.5 foot diameter tower operated at 110 pounds per square inch gage pressure. Heat was supplied by open steam in the bottom section. The butadiene and diluent C4 were taken overhead through water-cooled condensers and sent to the product accumulator. The bottoms were withdrawn through a bottoms cooler and sent to a water separator where water 'was removed from the lean oil. The lean oil was recycled to the absorber. MECHANICAL FAILURES AND OPERATING DIFFICULTIES
Reactor Spoolpiece Failure. After 4 months of operation a crack appeared in the 20-inch diameter spool piece a t the exit, of the north reactor. Observation showed that losses of product could be minimized by holding a constant reactor outlet temperature on both the reaction and regeneration cycles. Losses were
INDUSTRIAL AND ENGINEERING CHEMISTRY
MINUTE9
Figure 5.
Pressure Surge Study
reduced further by clamping a gasket over the crack with a large pipe clamp. At the end of the run then in progress, the orack was welded. Reactor Pressure Surges. At the outset of operations, it was noted that switching of the reactors from regenerat,ion to dehydrogenation caused an increase of 20 to 30% in gas rate to Che compressors. This is shonn in Figure 5 by the pressure survey a t the beginning of a typical dehydrogenation period. (The spaces indicated by flare represent unloading of the gases to a flare stack by meam of an emergency pulldown valve to prevent the pressure at the compressor suction from exceeding the value at which the compressor would stall.) This condition was analyzed furt,her wit,h the aid of special sample probes that were welded into the side wall of the reactor and extended to various sections of the reaction zone. I t was concluded from these observations t,hat the surges were the result o f the following factors: At the start of the dchydrogenatiori peiiod the catalyst was h o t and active which should result in high gas production, For a short period, hydrocarbons mere going to both reactors in parallel so that the volume of gaseous hydrocarbons per volume of catal st per hour would be lorr- and conversion high (sampling revealecfa conversion of 44.7% with a selectivity of 44% during these short periods before the switching was completed). At the time both reactor inlet valves were open t o the hydrocarbon furnace, the back prcssure on the furnace decreased and the tubes unloaded into the reactor. The speed control on the compressors was not suitable i o handle the high gas rates.
TABLE T.
vQ1.41, NQ. 3
During the f i s t run, it was necessary to vent part of the gases in order to maintain reasonable pressures. During the turnaround preceding the second run, several changes were made which greatly alleviat,ed the conditions. The principal changes were t,o make a slight adjustment in the timer cycle which eliminated the necessity of handling initial regeneration gases with the compressor, and the instnllatiori of an improved speed controller on the compressors. Following these changes, the surges were handled without difficulty. The data obt'ained on this particular problem later proved of benefit to the commercial units in niinimizing this condit'ion in their operation, Tower Deposition. About 6 weeks after thc fractionation system was put into use, a serious heat, t'ransfer coefficient drop developed in thc: stabilizer reboiler. The spare reboiler was put into service and operations continued. Shortlv thereafter, the tom& began to flood and had t i be taken out of service. On examination, it was found that a heavy deposit of rubbery polymer had plugged several of t'he downcorners and had foulcd most of the plates, The deposit increased from top t o bottom of the tower, probably a result of higher Lemperatures in i,he lower section. The reboiler bundle was pulled and found to be completely fouled with t'he same material. Several experiments were tried with commercia,l polymerization inhibitors which were added to the lean oil, but without material succcss. Latcr, in commercial operation, it, was found possible to greatly reduce polymer formation by operating the stabilizer a t a lower temperature and pressure. The polymer formed in this operation was not, the so-called popcorn polymer t'hat bas been found in butadiene purification and described in the literature ( 3 ) . It was similar t o the tj-pe described as peroxide-catalyzed, producing a high molecula,r weight plastic type of polymer ( I ) , In connection with deposition, serious thought was given to t,hc possibility of the formation of acetylides In this operation. Special inst,ructions were issued t o cover safe procedures to be used in cleaning the towers folloiving a run. Fortunately, no difficulties due to a,cct,ylideswere noted during t,he entire operstion, PERSONNEL
The operating personnel consisted of a technical shift supervisor, a first class operator, and three helpers. The operatorand a helper at,tended to the actual operation o f the unit. T h e second helper operated the control board and rrcorded tempmatures and pressures on an hourly basis. The third helper rc-
S.iniwx SCHEDULE Analyses
I.
Sample Fresh feed from sphere
Recycle feed Feed rerun tower overhead 4. Feed rerun tower bottoms 5 . hlixed feed to hydrocarbon furnace 6. Regeneration vent gas 2. 3.
7.
8. 8. 10. 11.
12. 13. I 4. a
Qverhead product t o absorber Absorber overhead gas Stabilizer overhead gas Combined orerhead gas Product, rerun tower overhead Product rerun bottoms Total polymer Water product from polymer separator Padbielniak analyses.
l y p e 9 ir.ork-np
Type
Purpose Rlaterialj balance
Frequency On roquest
Materials balance Materials balance Materials balance
Weekly 'Twice weekly TwPIce weekly
24-hr. bomb J 24-hr. bomb
Materials balance Materials balance
Daily Three daily
24-hr, bomb 8-hr., 1 gal.
Special Special Special
hlaterials balance
Materials balanre co11trol Special Materials balance Materiala balance
On request On request On requost Daily Dally
On request Daily Daily
Snap bomb Snap, 1 qt.
}
Complete P o d & : unsats., i -t- nCa's, GHs, n-CaH3. 1 and 2 Same as 1 Pod: CY4- L, C,;Hs, CaRs, CIEIN, Dist. and Reid vapor p r e m Ss.me as I , include aoetylenes r\scarit,e -i Burrell f o r COz,
co,
C2,c2-i
0 2 , w1,
As requested
C:lle Same ab% 1 Dist. and Reid vapor 1)re35.
Same as 1 Burrell for CO?, C O , 112,
c1,
......
c2.t-
Ssine as 1 t o Cat Same as I from Cn iL
Same as I from Cz
Snap, 1 qt, 24-hr., 1 qt, Snap. I qt.
Same as 4 Same as 4 ClHs content
Same a8 4 CaHe content
C3
C3
4- L, Ca, C a f 4. L, C4, C6i;
0 2 ,
.....
24-hr. 3 mal. 24-hr.: 3 i a l . 24-br., 3 gal. 24-hr., 3 gal. 24-hr. bomb
...,,,.,....
,.....
. ...
-+ 1,
March 1949
651
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE 11.
IDENTIFYING
I I1 Run 3/14-28 4/11-5/9 Date 1943 186 186 Cataiyst volume, cu. ft. 79 79 Cetalvst bed denth. in. Ingersoll..Rand Type"nozz1e No h-0 KABS liner No NO Natural gas circulation 130 120 n-Butylenes V/V/hr.a 1112 Ratio, steam t o n-CaHs 1500 1400 Dehydrogenation steam V/V/hr.a 1000 375 Regeneration steam V/V/hr. a 1180 1190 Dehydrogenation inlet temp., F. 1180 1190 Regeneration inlet temp., p F. 6.5 6 Reaction pressure, lb./sq. in. gage 40 35 Regeneration press., lb./sq. in. gage a Volume of gas per volume of catalyst per hour.
I11 5/31-6/3 100 45 Neohes Yes No 210 10 1900 1900 1200 1200 6.2 7.5
CHARACTERISTICS O R P I L O T P L A N T RUNS IV V VI A-B VI C-E VI J 6/10-27 100 49 Neches Yes NO
210 13 2200 2200 1210 1210 6.4 7.5
corded flows, temperatures, and pressures in the operating area and also procured samples on the prescribed schedule. The parttime services of the shift foreman, assistant foreman, and compressor man were available when needed during start-up periods. The operating personnel were furnished by the Ethyl Corporation inasmuch as their men were familiar with the general operation of the unit. The Esso Standard Oil Company furnished an additional shift supervisor from their technical staff during initial operation. Over-all supervision of operations was furnished by the Esso Standard Oil Company. The assembly and correlation of data were handled by representatives of the various companies involved. It was customary to vest program planning and responsibility for data in someone representing the company whose operating conditions were being investigated. RESULTS
For purposes of data collection as well as government accounting, all streams entering and leaving the unit were measured, sampled, and analyzed. Whenever possible, these figures were checked by tank gagings. Material balances were made around the dehydrogenation unit alone as the extraction unit data were not readily available. Podbielniak analyses of the feed and product streams were the primary sources of analytical information. Gas density and butadiene analyses were used for control. In Table I, the nature, purpose, frequency, quantity, and analyses obtained on the various samples are shown. Because of the cyclic nature of the process, extreme care was exercised in obtaining true composite samples. Liquid Ca samples were drawn under pressure into bombs by displacement of acidified magnesium chloride brine. Gas samples were taken a t atmospheric pressure by displacement of acidified salt brine, All bottles were specially marked t o prevent misuse or contamination through erroneous use by other operating plants. Conversion and selectivity varied slightly with the different operating specifications. However, in most of the runs, process results equaled or bettered those predicted from laboratory data on which the large scale production rates were based. Some typical process results from the pilot plant operation are shown below in comparison with laboratory unit results. Pilot Plant Comp. total feed t o furnace, mole % n-C4Hs
C4H6
cs+
Operating conditions Feed rate n-CaHs V/V/hrGa Steam t o ;-c~H*, 'mole ratio Reactor pressure, lb./sq. in. Reactor inlet temperature, O F. Regeneation pressure, lb./sq. in. Regeneration steam rate, V/V/hr.a Yields Conversion of n-CaHs, mole % Seleotivity t o C4He mole % Dry gas wt % of L-GHs Carbon,'wt.'% of n-C&Ha a Volume of gas per volume of catalyst per
Laboratory Unit
74 1.2 2.7
67 2.2 0.4
214 15 7 1170 15 1160
470 20 Atmos. 1185
31 75 7.1 2.8 hour.
33 71 3:o
7/27-29 100 45 Neches Yes Yes 200 16 3200 1200 1180 1180 7.0 15.5
8/22-9/ ' 5 100 46 Neches Yes Yes 200 16 3200 1200 1170 1170 7.0 15.5
9/5-7 100 45 Neches Yes Yes 220 19 4160 None 1170-1220 . I .
8.5
...
9/13-18 100 45 Neches Yes Yes 160 17 2700 575 1150 1100 6.0 10.5
VI1 B-F
VI1 A 10/7-21 64 45 Kellogg Yes Yes 160 17 2700 575 1150 1-150 0.0
8.8
VI11
10/21-11/6 11/24-12/10 64 100 45 45 Kellogg Kellogg Yes Yes Yes Yea 220 335 12 15 4100 3200 500-1200 1180-1150 1200 1190-1240 1190-1240 1180-1150 7.7 8.2 15.5 15.5 '
In general, a t a conversion level of 3070, selectivities to butadiene ranging from 65 to 75% were obtained during all runs. In Table 11, the operating conditions of the various tests are shown.' There was some indication of a drop in conversion with catalyst age, but with the short runs (14t o 21 days) employed, it was possible only to indicate a trend. It was later found in the large plants that satisfactory catalyst performance could be obtained over a 6-month period of normal operation. CONCLUSIONS
The initial run in the pilot plant was completed in less than 5 months from the start of construction. Five complete sets of operating specifications were run and proved; data on equipment were obtained; and sufficient process data were secured to take catalytic butene dehydrogenation out of the laboratory stage and place it on a commercial basis. Although much of the design of the commercial units was frozen because of the emergency, and one of the plants was already 90% completed, the following information obtained in the pilot plant study was helpful to the large plant operators,
1. Catalyst disintegration and shrinkage were negligible. 2. Catalyst life under operating conditions was much greater than the previously accepted figure of 2 weeks. 3. Chlorides were extremely poisonous to the catalyst and had to be eliminated a t all costs. 4. The use of natural gas to preserve the catalyst in a reduced state during starting-up periods improved its activity during subsequent operation. 5. It was possible t o control pressure surges by proper valving and compressor control. 6. Modifications in the operating specifications for the large units improved their selectivity and activity. 7. The testing of the several proposed types of mixing nozzles proved their efficiency for use in the large plants. Good mixing was obtained with each type tested as shown by samples from probes inserted into the catalyst bed a t several locations. 8. It was shown that, with proper precautions, acetylide formation would not be a hazard in the large plants. 9. The pilot plant operating experience was valuable to the large scale operations, particularly for start-ups. 10. Finally, the pilot plant operation demonstrated beyond question that the use of the process on a commercial scale was entirely feasible, and that no major change would be required in the government's program for butadiene production. ACKNOWLEDGMENT
The generous cooperation of the Ethyl Corporation in providing their equipment, their personnel, and their operating experience contributed in a large degree to the success of the butene dehydrogenation pilot plant project. LITERATURE CITED
(1) Robey, R. F., Wiese, H. K., and M o r r e l l , C. E., IND.ENO. CHEM.,36,3 (1944). ( 2 ) Russell, R. P., M u r p h r e e , E. V., a n d Asbury, W. C., Trans. Am. Inst. Chem. Engr., 42, No. 1 (1946). (3) W e l c h , L. M., S w a n e y , M. W., G l e a s o n , A . H., B e c k w i t h , R. K., a n d H o w e , R. F., IND. ENG.CHEM.,39,826 (1947). RECEIVEDNovember 29, 1948.
