Fluidized Bed Work at Fuel Research Board

Work on the fluidized synthesis process has been done in an internally baffled reactor having an internal diameter of 1” and a length of 10 feet. The unit operates at 20 atmospheres, 300°C., linear velocity (based on empty tube) 0.6 ft./sec. Work has been done on an impregnated mill scale catalyst and on a synthetic ammonia catalyst. The fresh gas SVH was 1000 based on the volume of the volume of the settled bed. All work was done with 2H₂:1CO gas.

The following results were obtained in some of the early runs to determine the effect of scrubbing the recycle gas:

	Synthetic Ammonia Catalyst		Mill Scale Catalyst
	End gas Stripped	End gas unstripped	End gas stripped	End gas unstripped
CH₄, g./m.³ fresh feed	44	55	25	33
C₂-C₄, g./m.³ fresh feed	100	60	80	60
C₅₊, g./m.³ fresh feed	41	65	65	90
Total	185	180	170	183
Water sol. Oxygenated	2	5	14	10
CO going to C, %	1.3	1.9	1.8	3.0

The increase in the C₅₊ fraction recycling unstripped gas indicates that propylene and butylenes are entering into the reaction to form higher hydrocarbons. The increased methane yield under these conditions is an indication of cracking of some of the recycled C₂-C₄ fraction.

One experiment was begun with 400 cc. Of unreduced synthetic NH₃ catalyst weighing 1 Kg. and containing 720 g. of iron. During a 40 day run, 10000 cc. Of solids (catalyst + carbon + adsorbed wax) having an average carbon content of 65% by weight were withdrawn from the system. Throughout this period the CO conversion was 90% or greater in spite of the fact that the iron remaining in the reactor was only about 5% of its initial value.

To obtain further information on the synthesis over used catalysts containing low concentrations of iron, the following comparison was made between fresh mill scale and a mill scale catalyst that had been used in the synthesis:

Catalyst	Fresh Mill Scale	Mill Scale Catalyst containing carbon deposited in synthesis1/
Duration, days	7	12
Initial volume of catalyst, cc.	380	400
Final volume of catalyst, cc.	1683	1354
Fe, grams	720	70
Temperature, °C.	300	340
Initial SVH	1040	1030
Final SVH	743	317
Liters of synthesis gas/g. Fe/hour	0.57	5.9
Yield stabilized C₅₊ g./m.³ fresh feed	74.2	90
1/ Carbon 50% by weight; bulk density 0.42 g./ml.

It will be observed that the initial volume of catalyst, initial space velocity, and temperature were the same with both fresh and used catalyst but the iron present in the reactor containing used catalyst was only 10% of that with the fresh catalyst. Consequently, the rate of synthesis gas feed per gram of iron with the used catalyst was 10 times that with the fresh catalyst. In spite of this the yield of liquids plus solids was greater with the used catalyst of low iron content.

Hall has on his program the determination of the minimum content of iron necessary for the synthesis in a fluidized bed.

The details of a run (Run 13) with mill scale catalyst is a fluid bed are as follows:

Pressure	20 atmospheres
Temperature	300-320°C.
H₂:CO	2:1 in fresh feed
H₂:CO, usage ratio	1.88:1.9
Velocity of gas	0.65 ft./sec. (based on empty tube)
Recycle ratio	5:1
CO converted	98.5%
CO à CO₂	4.5%
CO à CH₄	14.3%
CO à C	1.6%
CO à C₅₊
CH₄, g./m.³ fresh feed	32-38
C₃+C₄, g./m.³ fresh feed	63
Liquids + solids, g./m.³ fresh feed	90
C₂	?
Distillation of liquids + solids:
below 150°C.	64% by weight
below 200° C.	76.6% by weight
below 300°C.	92.5% by weight
residue	5.8% by weight
loss	1.7% by weight
Alcohols in water layer	5.3-9 g./m.³ fresh feed
Fatty acids(calculated as acetic)	2.0-3.8 g./m.³ fresh feed

The minimum CH₄ that Hall has observed in fluidized operation is 25 g./m.³ of fresh feed.

The synthetic ammonia catalyst gives less oxygenated compounds than the mill scale catalyst.