Handbook of Solvents - George Wypych - ChemTech - Ventech!

22.1 Absorptive solvent recovery 1537
Carbon disulfide
Adsorptive removal on activated carbon and recovery by steam desorption. For simultaneous
H 2S and CS 2 removal the Sulfosorbon-process uses adsorbers packed with two different
activated carbon types
• Iodine impregnated wide-pore activated carbon for H 2S oxidation in the bottom part
(gas inlet) of the adsorber
• Medium-pore activated carbon for the adsorption of CS 2 in the upper layer of the
fixed bed.
As soon as the CS 2 concentration in the treated air approaches the emission limit, the
exhaust air stream is directed to a regenerated adsorber. After an inert gas purge, the carbon
disulfide is desorbed with steam at 110 to 130°C. The resulting CS 2/steam mixture is routed
through a condenser and cooler, before entering a gravity separator where phase separation
occurs.
At the usual CS 2 and H 2S concentrations in viscose production exhaust air, the CS 2 adsorption/desorption
cycles can be run for a prolonged periods before the first layer loaded
with elemental sulphur has to be regenerated.
The regeneration process of the sulphur loaded activated carbon involves the following
steps:
• washing out of sulphuric acid with water
• extraction of elemental sulphur with carbon disulfide
• desorption of carbon disulfide with steam
• air drying and cooling of activated carbon
The elemental sulphur present in the carbon disulfide in dissolved form can be separated
by distillation and recovered as high-purity sulphur.
Design example 34
In the production of viscose filament yarn a Supersorbon � -system combined with a
NaOH-scrubber system (Figure 22.1.21) has been in use since 1997. A very high standard
of safety engineering is implemented in the treatment system owing to the flammability of
the CS 2 and the toxic nature of the constituents to be removed from the exhaust air.
System concept
First treatment stage:
Absorption of H 2S in two NaOH jet scrubbers and one water-operated centrifugal
scrubber.
Second treatment stage:
Fixed-bed adsorption for purification of exhaust air and CS 2 recovery.
Treated air stream
Exhaust air from viscose filament yarn plant.
Design data:
Exhaust air flow rate 12,000 Nm 3 /h
Solvent capacity 27 kg CS 2/h and 7.5 kg H 2S/h
Exhaust air temperature 15 - 30°C
Clean air solvent concentration
CS 2: max. 100 mg/Nm 3 (24-hour mean)
H 2S: max. 5 mg/Nm 3 (24-hour mean)