CARBON DISULFIDE
9
Emphasis in raw materials shfts further from charcoal to methane, but impact of new processes using coke or liquid petroleum fractions remains to be seen HARRY W.
HAINES, JR.
variety of reactions are available for making carbon
A disulfide, but only two have become important commercially; one is from carbon and sulfur and the other from methane and sulfur. The classic method uses charcoal and sulfut--heat is applied with carbon electrodes to a hearth or to retorts directly fired by natural gas, producer gas, or other fuels. Recently, however, especially in the United States, production from methane and sulfur has become more common. Considerable data on carbon disulfide are available in the literature, including a description of both routes of manufacture (6). An excellent thermodynamic analysis of both the methane and charcoal routes is given (7) and, for the methane route, thermodynamic and kinetic data are available (2, 8) as well as kinetic data for plant design (7,3). Thermodynamic properties of sulfur ( 7 I), carbon disulfide (5),and hydrogen sulfide (10) are tabulated in the literature.
REACTIONS FOR MAKING CARBON DISULFIDE ( 4 )
F.
CH, + 4/nS.
=
CS,
+ 2HIS
c + z/ns. = cs, ZCO + 2/nS. = 2 c o s = cs, + CO, c + zn,s = csI + ZH, 5C
+ ZSO, = CS, + 4CO
1050-1300 1200-1550 800-850 2025-2075 2250-2300
Methane RoulhProcess Technology
T o obtain satisfactory reaction rates, most plants use temperatures above 1000° F., although stoichiometric convenion is theoretically possible at temperatures as 44
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
ow as 6OOOF. Pressures are 20 to 30 p.s.i.g. Saturated ulfurvaporat 1180°F.contains210/0diatomic,58’%hextomic, and 21y0 octatomic molecules (9). However, vailable kinetic data are correlated satisfactorily by ssuming a second order reaction between methane and diatomic sulfur which Is probably the true reactant. Activation energies of 61,920 and 68,940 B.t.u. per pound-mole have been reported. At space velocities of 600 standard cubic feet per cubic foot per hour, catalytic reactora generate 35 pounds of carbon disulfide per hour per cubic foot of catalyst. Some plants are designed to operate on the exothermic and some on the endothermic side of the adiabatic reaction temperature of about 1200’ F. Heating the reactants (neglecting heat losses) requires about 1650 to 1750 B.t.u. per pound of carbon disulfide product. Carbon disulfide can be made from methane and sulfur by either a high or low pressure purification process (Figure 1). In either case, the methane should contain less than 1% propane and heavier hydrocarbons and no more than 2% ethane. The high pressure process is especially applicable for small plants where recovery of hydrogen sulfide is uneconomical and where the hydrogen sulfide may be used elsewhere as a reactant. Coils in the sulfur vaporizer are of high-chrome steel, and the reactor also is preferably of this material. Distillation towers in the purification section can be of carbon steel. ne^ Me~hods
Although the methane route has many advantages over the charcoal method, incentives to develop new processes still exist, particularly for foreign areas where low cost methane is unavailable. An inventor of the original methane process, Carlisle M. Thacker, is work-
METHANE ROUTES FOR MAKING
3
. 2
ing on a technique for making carbon disulfide from liquid petroleum fractions, and has patents pending. His purification system is reported to be nearly the same as those in conventional plants using kerosine as lean oil. Sulfur is vaporized, but Thacker has not indicated the degree of superheat added to the petroleum fraction or reactor operating temperatures. He claims a lower raw material cost, a higher yield of carbon disulfide, less preheat, and lower purification costs. Shawinigan Chemical also has a new method based on its Fluohmic furnace, a resistance-heated fluidized bed. Sulfur or hydrogen sulfide may be used as the reactant and in laboratory tests, conversions up to 70% were produced when gaseous sulfur, or liquid sulfur which vaporizes as it enters the chamber, flowed upward through a coke bed heated to 2000O to 2200' F. Other laboratory tests showed that about 70% of the hydrogen sulfide fed to a coke bed was converted to carbon disulfide at 2700' to 2750' F., with apparent efficiencies of 90 to 100%. In some tests efficiencies actually exceeded loo%, because sulfur in the coke entered the reaction. Economic Aspects
Total carbon disulfide capacity in the United States is difficult to estimate (Table I), but the shift from charcoal to methane is marked. At one time Stauffer Chemical had seven charcoal plants in operation and DowChemical operated one at Midland, Mich. Because of this shift and lower costs, production of carbon disulfide, since 1958, has been increasing about 6 to 7% per year. One 50 million pound-per-year plant is under construction.
However, this production picture may be affected by an impending merger. Regenerated cellulose consumes about 80% of the total carbon disulfide output; this is a big factor in the planned acquisition by FMC Corp. of American Viscose, a leading rayon manufacturer which has also one fourth of the nation's cellophane capacity. FMC may have a better chance than Stauffer Chemical which was thwarted by the Justice Department last year from acquiring American Viscose. If FMC is successful, considerable plant expansion may result. TABLE 1.
CARBON DISULFIDE PLANTS
Capaity,* Millim
,J. T. Baker Chemical Penn Yan, N. Y. FMC Corp. & Allied Chemical So. Charleston, W. Va. Old Hickory Chemical Old Hickory, Tenn. Richmond, V O . ~ Pennsalt Chemical Houston, Tex. Pittsburgh Plate Glass Natrium, W. Vo." So. Charleston, W. Vo.' Stauffer Chemical Delaware City, Del. Lowland, Tenn.
Charcoal
