PRODUCTION HCi Process Pulls α Switch N e w continuous t w o stage solvent extraction purification process by Hooker slashes costs A NEW cost-saving method to purify by-product anhydrous hydrogen chlo ride may soon be available to chlorin ated hydrocarbon producers. The gaseous product coining from chlorination primarily contains hydrogen chlo ride, chlorine, and vapors of organic compounds. The problem is to sep arate and recover the hydrogen chlo ride and chlorine. This week, Hooker Chemical sits down to weigh licensing possibilities on its new continuous twozone solvent extraction process. Trick to the Hooker approach—ab sorb the impurities via solvent extrac tion, rather than former practice of absorbing the product in water which means carrying the highly corrosive hydrochloric acid through the system. Eliminated: costly anticorrosiou equip ment and maintenance costs. After four months of operating prove-out on the large scale unit at Hooker's Montague, Mich., causticchlorine plant, Hooker engineers are sold on the new process used here to supply hydrogen chloride gas to Du Pont*s nearby neoprenc plant. Here's how they stack it up against the widely, used muriatic acid absorptiondesorption ''nietlkfd:, •Initial outlay halved "(nearly alliron construction ). • Operating and maintenance costs pared better than 50%—less down time. Hooker recovers hydrogen chloride and chlorine in this plant. In the center is the carbon tetrachloride absorber (left) and chlorine absorber (right). Tall gray column in front of tiiese is the chlorine stripper. Heat exchangers are at bottom right, with the gunk still to their left. Purified hydrogen chloride exits through a line at top of the carbon tet absorber
• Greater flexibility—operates effectively at as low as one quarter capacity, yet has seemingly no scale-up limitations. Another plus factor is nearly complete chlorine recovery, says Hooker. In contrast» the absorption-desorption method—absorbing gaseous feed in water and later partially desorbing it by heat—can't economically recover the chlorine present as an impurity. And scale-up poses some restrictions on the water absorption scheme. Limiting factor: heat transfer. • Two Stages· In essence, the new technique is a two-stage scrubbing operation. Feed gas containing the byproduct hydrogen chloride and contaminants—primarily unreacted chlorine and organics—enters a chlorine absorber. Here, scrubbing with carbon tetrachloride (at about 35° C.) takes out chlorine and organic vapors. Then the hydrogen chloride fraction is channeled to a second scrubbing tower (zone 2 ) , where hexachlorobutadiene (Hooker calls it C-46) removes the carbon tet from the first scrubbing. About the only impurities left in the final anhydrous hydrogen chloride are inerts and trace amounts of C-46. Carbon tet shapes up as the best bet for the first zone solvent, says Hooker. Reasons: low boiling point (76.8° C.) and price, and excellent solubility for chlorine. In the second zone, hexachlorobutadiene, with its high boiling point (215° C.) and low price, stability, inertness, and strong carbon tet absorbing power, fills the bill. Trichlorobenzene boiling around £15° C. ranks next. • Little W a s t e · Carbon tet fraction from the zone 1 scrubber is cycled next to the chlorine stripper—a carbon tet purification column. Recovered carbon tet is cooled, then pumped back ;to die chlorine absjoirber. Overhead product from Ûie sBipper^î^^p|nifîng recovered chlorine, first .goeswt*$\-;a> scrubbing tower to reduce carbon tet content further. The hydrogen chloride-carbon tet over* "'ad from zone 1 enters the carbon c absorber (zone 2) at about 35° C. and is scrubbed with C-46. At this stage, purified hydrogen chloride goes off as overhead, while the mixed solvent effluent flows to a carbon tet stripper. Carbon tet-free C-46 is cooled and recycled to the zone 2 scrubber. Carbon tet is funneled back to zone 1 chlorine stripper.
Economy level for the second stage scrubber is 0° C , says Hooker, giving an anhydrous product with only 2 5 0 p.p.m. organic. But one of the new process's many refinements—a smaller auxiliary scrubber—can further refrigerate the product to reduce organic content even more. • Key to Economy. The two-solvent system is the key to operating economy, sax's Hooker. Circulation rate for a first zone solvent or a single-solvent system is about 10 times that for zone 2 solvent. Thus the higher boiling I C-46 would have to be used to keep I down solvent loss and exit gas con- I tamination. This means costly pre- I heaters and coolers and high utility I consumption. The two-solvent system I saves more than enough in utilities alone to pay for the additional equipment. Added bonus: insurance against chlorine contamination in the final product by additional scrubbing. Although suited t o almost any direct organic chlorination (particularly hydrocarbons), the new process has some I restrictions. Feed gas must be dry. This rules out by-products from alcohol chlorinations, where water is formed, unless equipment is used ahead of the process to remove tihe I water. And the method is programed to handle by-product hydro- I gen chloride where unreacted chlorine J and organics are the sole, or principal, contaminants. An interesting feature of the Hooker unit is the unusually large diameter packing towers. The zone 1 scrubber is 54 in. across and stands 5 4 ft. The chlorine stripper has a 6 6 in. diameter and is 42 ft. high. And, Hooker engineers say, they work out just fine.
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• Fuel burn-up monitoring is now added to Nuclear Science and Engineering Corp/s neutron dosimetry services. (These include supplying bare and cadmium-covered cobalt foil «and wire and sulfur pellets to get I dosimetry data for thermal, epithermal, I and fast neutrons.) NSEC*s monitor- I ing service supplies a dosimeter of enriched uranium-235 in an aluminum capsule. The company adjusts the uranium-235's enrichment to the appropriate value for the fuel being tested and makes a post-irradiation assay. NSEC is also developing dosimetry techniques for the complete neutron energy spectrum normally encountered in food irradiation facilities and nuclear reactors.
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COPPER COPPER SULFATE MON0HVDRATE0 COPPER SULFATE
CUPRIC CH10M0E CUPWC OXIDE
COPPER CARBONATE
SULFUR SULFURIC AGO V." SODIUM I.TDKOSULFITE-' LIQUID SULFUR* r PARA'TOLUEJIIE SULFOH*IC ' O I O X I D F * . ^ ' * J ACID/ANHYDROUS
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ZINC iMONQHYOKATED iZIKCiSULiATEÎ
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MANGANESE MANGANESE SULFATE MONOHYDRATED MANGANESE SULFATE
MANGANOUS OXIOE
Sarapies. specifications and detailed information upon request.
TENNESSEE
COIPORATIOH
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SEPT. 15,
1958 C & E N
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