I/EC NEW ΑΛΊ)
or a combination of both techniques, to liquefy all the chlorine they can get out of the air-chlorine mixture. But this method still leaves a disposal problem for the weak gas stream. Plant engineers have tried :
INTERESTING
• Venting the w e a k gas at some high point in the plant, w i t h a n d w i t h o u t air dilution. • Absorbing the chlorine in cold water a n d then flushing the satu rated liquid into nearby rivers. • Causticizing or liming to neu tralize the chlorine to hypochlorite.
.
BORESTER® BORIC A C I D E S T E R S •·$
No. 21 Triisopropanolamine Borate (extremely stable to hydrolysis) No. 22 Triallyl Borate No. 23 Trimenthyl Borate I, II No. 24 Tri- (2, 6, 8-trimethy!-4-nonyl) Borate (very resistant to hydrolysis) No. 25 Methyl Metaborate 1 High No. 26 Methyl Polyborate Boron No. 27 η-Butyl Metaborate J content No. 28 Isopropyl Metaborate Elemental Boron: 2 Grades 90a-92a ΟΛα Q7U 33d-3/a
Also some special g ^ d e s having specific characteristics
Technical Data Sheets and Samples on Request
Please send the following: Borester
21 | 22 | 23
24 '
25
28
Bulletin Sample Boréster r
26
27
Bulletin Sample Elemental Boron, 90a-92a
/
Elemental Boron, 95a-97a Name & Position Company
,
Address
___
I *EC
United States Borax & Chemical Corporation ^
Pacific Coast Borax Company Division 100 Park Λ venue. New York 1 7, Ν. Y.
MANUFACTURERS OF FAMOUS " 2 0
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© Circle
88 A
AIR POLLUTION CONTROL
Nos. 88 A l ,
88 A-2 on Readers' page 129 A
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At times, all of these methods have their drawbacks. Vents can cause trouble when the wind.is blowing in the wrong direction. W a t e r absorp tion takes a great deal of dilution unless the saturated liquid can be tossed into a fast-moving stream nearby. Some consumers have no use for sodium or calcium hypochlorite. I n this case they have to be near a fast-moving stream of water, one that is already heavily loaded with indus trial waste or sewage (a stream with a high biochemical oxygen d e m a n d ) . Chlorine contamination has been with us a long time a n d engineers have worked u p a n u m b e r of other recovery methods. T h e weak gas can react with ferrous chloride to form ferric chloride ; ferrous chloride is then regenerated with scrap iron. But this process isn't economical unless the plant has a use for ferrous or ferric chloride. For those who have a market for sulfur chloride, this by-product can be manufactured by reacting the weak gas with sulfur. D i a m o n d Alkali engineers took a different approach. T h e y concen trated on recovering the chlorine, economically, as a gas or liquid, so it could be sold or re-used in chlorination processes. $ 2 0 - a - T o n Chlorine
D i a m o n d ' s process reclaims liquid chlorine from snift gas at a cost of less t h a n $20 per ton of chlorine, which includes all operating a n d investiment costs. T h e chlorine is absorbed differentially in carbon tetrachloride, then removed in a steam-heated stripper. Diamond engineers prefer to absorb at a pressure of 100 p.s.i. and strip at a pressure of about 35 p.s.i. ( T h e stripper operates at the pressure
INDUSTRIAL AND ENGINEERING CHEMISTRY
·
A Workbook Feature
normally carried on the m a i n chlo rine condensing plant, so that re covered chlorine can be returned directly to the main stream without further compression or pumping.) A typical recovery unit processes a chlorine-air mixture containing 3 5 % chlorine, at a pressure of 10 p.s.i.g., which is delivered to the suction of a positive displacement, horizontal, nonlubricated com pressor. W h e n compressed to 100 p.s.i.g., the mixture comes out of the compressor at 240° F. T h e gas is cooled first in a water-cooled heat exchanger, then in a refrigerated cooler. At this point, a portion of the chlorine condenses, and it can be returned directly to the m a i n stream. Gas leaving the refrigerated cooler, at a t e m p e r a t u r e of 5° F., contains approximately 3 0 % chlorine. This stream goes to the bottom of a packed column and flows countercurrent to liquid carbon tetrachlo ride. I t leaves the top of the a b sorber, stripped completely of chlo rine, t h r o u g h a back-pressure con troller. C a r b o n tetrachloride is fed into the top of the packed tower at approximately 0° F . ; it leaves the bottom at a temperature of about 50° F. T h e rich solvent goes to the center of a stripping column, heated by a thermosyphon reboiler. Lean solvent from the bottom of the stripper, at 260° F., is cooled to 0° F. before it is returned to the absorber. T h e u p p e r section of the recovery tower acts as a rectifying column that refluxes liquid chlorine in contact with chlorine vapors. It produces a solvent-free stream of gaseous chlorine. O n l y a portion of the chlorine vapor leaving the tower is condensed for reflux; the balance can be condensed a n d recovered as a liquid, or it can be returned to the main process as a gas. T h e system must be anhydrous to prevent corrosion. Gas mixtures containing water vapor have to be dried before the chlorine is recovered. T h e recovery process is covered by U . S. P a t e n t No. 2,765,873. Dia m o n d officials say t h a t licenses are available to all comers w h o w a n t to lop a few bucks off their chlorine bill a n d W y a t t C. Hedrick Engineering Corp. of Houston is available to do the engineering.
