ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
."-
il is H. E. BENSON, J. H. FIELD, D. BIENISTQCK, AND H. H. STORCH Synfhefic Fuels Research Branch,
U. S. Bureau
o f M i n e r , Region VIII, Brocefon, Pa.
EVELOPMENT of the oil circulat,ion process for tlie synthesis of liquid fuels by thc Fischer-Tropsch reaction is continuing a t the Federal Bureau of Mines laboratories a t Bruceton, Pa. Removal of the high exotherniic heat of react,ion (about 50,000 B.t.u. per gallon of liquid products) is achieved by sensible heating of a recycle oil that completely submerges the catalyst so that close temperature control can be maintained. The initial \vork with this type of system was'done in 1934 by Duftechniid and coworkers ( 3 ) , of the I. G. Farbenindustrie at Oppau, but. \Tap interrupted by the war. Operation of the oil circulation process in a demonstmtion plant of about 50-barrel-per-day capacity was conducted by the Bureau of Mines a t Louisiana, N o . ( 6 ) . Because cementation of a fixed bed of fused iron oxide catalyst interrupted the synthesis, a moving or expanded hed operation was developed in which the catalyst bed was slightly expandd and the particles maintained in motion by the upward flow of cooling oil. A superficial linear velocity of the oil of about 0.1 foot per second was suficient to expand the hed 5 to 10%. Higlirr linear velocities produced greater rates of catalyst disiritcgration. Results of the fixed-bed and the initial expanded-bed expcriments have been presented ( 2 ) . Operat,ing and yield data, and properties of t,he products were given when either a hydrogen-rich, 1:3: 1 hydrogen to carbon monoxide, or a 1 : 1 gas \\-as used. A gas conversion of 70% was maintained resulting in an over-all calculated conversion of 90% for two stages.
Fused iron
xide Catalysts
In the moving-bed experinients a t Bruceton with fused iron oxide catalysts described in this paper, the following process variables were studied in an attempt to improve the ratalyst activity and the versatility of the process: Carbon monoxide-rich feed gas Pressure-300 and 400 pounds per square inch gage High conversion in one stage Temperatmure High gas throughput
reactor by a pump. The gas separator served also as a sump, where t,he excess circulating oil was drained off periodically x s heavy oil product t o maintain a constant level in the reactor. ,Z stream of reflux oil from the overhead condenser flowed t o t,hc gas separator t,o maintain control of thc wax concentration in I he circulating oil. The gaseous and low boiling reaction products and unreacLtrd synthesiv gas passed upvi.ard through a condenser, wherc the stream \vas cooled. Just beiorc the condenser a bauxite wforming unit for decomposing oxygenated compounds W ~ Finserted, with by-pass valves so that it, could be placed into serviw as desired. Gases leaving the condenser were further cooled i n :I, refrigerated condcnser with a light' oil being collected and t h c x effluent gas divided into two streams. One portion p:issccl t,hrougli H hack-pressure regulator, whereby it was reduced in presaui~;Iicfore it JTas passed to a light, hydrocarbon charcoal recovery anti ii metering system; the other portion was sent to a scruhber where the carbon dioxide was removed by a 20% monoethanolamine solution before it wa.s returned to the conveitn via a recycle winpressor. Operation. In all of the expandcd-bed experiment's, a gi'unular Eucled iron oxide-synt,hetic ammonia type catalyst was 11 Catalyst, palticlc size was from 6 to 20 mesh. This materi' an alkali-promoted magnetite containing 93.5% FesOa with minor amounts of magnesia (4.6%), chrornia (0.65'3;)) and silica ( 0 . 6 ~ o ) . Before use it n-as virtually completely rcduced t o alpha iron by hydrogen; in a few experiments ;.pec.ial csatalyst pretreatmcnts such as carbiding were used. of this type was brought t o operating conditions over a 4-day period, the induction period, during \vliioh time the temperature was raist.d in steps until a desired coiiversion (usually 70%) was achieved. Since the work reported previously, eight experiments (22 to 29) using fused iron oxide catalysts have heen conducted in the
Table I.
Effect of Hydrogen to Carbon Monoxide Feed Gas Ratio on Conversion ~.
22BQ
Three Pilot Plants Are Used to Investigate Process Variables
~
Three pilot plants, two of 3-gallon-per-day (3-inch diameter reactor X 4-foot bed height) and a larger one of about l-barrelper-day (8-inch diameter reactor X 8-foot bed height) capacity, were operated. T h e flow diagram (Figure 1) is basically the same for all units, but the larger plant is more highly instrumented. Fresh synthesis gas mixed with recycle gas was preheated and fed t o the bottom of the converter along with the recycle oil. In large scale operation the heat of reaction could be recovered from the recycle oil by generating high pressure steam. After passing through the catalyst bed, the reaction products, unreacted gas, and circulating oil flowed t o a gas separator from which the gaseous products passed overhead and the oil was recycled to the 2278
Feed m s rntio. H2: CO Catalysl aye a t Pnd of condition, lir. S n a r e velocitv. h r . - 1
1:1
I!kgerinient S o . 30B .. .. 26.1 I : 1 O 7 : 1 0.7:1 0.7:1
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..
31C I:l
45s 602 1:l 24$
506 BOI
'61
1:l 235
l:i 251
cu. 111. converted Product distyibution, a t .
36.1
32 i
29 6
24.8
20.2
20 6
Ga$
