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Clariant Corporation - Mount Holly Plant

Year Submitted: 2007

Process: Dyeing

Industry: Chemical Manufacturing

Wastes Reduced: Sulfuric Acid

Location: Mount Holly NC

No. of employees: 352

Contact: Michael Teague

Phone: (704) 331-7104


The Clariant Corporation's Mount Holly Plant is located on either side of the Catawba River. The East plant is located in Mecklenburg County and the West plant is located in Gaston County. The facilities have a combined employment of 352 people and operate seven days a week 24 hours a day.
The East plant manufactures dyes and textile chemicals, including sulfur black dye, a major product at the plant. For every pound of sulfur black dye that the East plant produces, 1.11 pounds of co-product are produced. This co-product is composed of 0.60 pounds of 25% sodium thiosulfate, 0.38 pounds of 75% sulfuric acid and 0.13 pounds of 20% ammonium sulfate.

P2 Application:

Sulfuric Acid The East plant generates roughly 15 million pounds per year of 75% sulfuric acid as co-product. This co-product is generated during the separation of the organic phase from the aqueous phase after the nitration of monochlorobenzene. The organic phase is the product, dinitrochlorobenzene, and the aqueous phase is the co-product, 75% sulfuric acid with a small percentage of nitric acid, nitrochlorobenzene, and dinitrochlorobenzene. All of this co-product was previously shipped to a sulfuric acid furnace in Baton Rouge, LA, for incineration and regeneration of the acid. Although this was an environmentally sound management practice, the facility, concerned with the lost product in the aqueous phase and the expense of treatment, sought an alternative disposal method. In recent years, the nitration plant was renovated and, as part of the project, engineers designed and installed a 26-stage extraction vessel. The extraction vessel, or washer, counterflows the sulfuric acid co-product against virgin monochlorobenzene. The small percentage of nitrochlorobenzene and dinitrochlorobenzene in the acid stream dissolve into the monochlorobenze stream and subsequently enter the next reaction vessel for the nitration process. The 75% sulfuric acid co-product, with the organics removed below the level of regulatory concern, is collected for distribution. By removing the organics in the sulfuric acid waste stream, the facility eliminated the classification of this co-product as a D-listed hazardous waste. With a relatively clean sulfuric acid co-product, the facility began seeking potential markets. The facility began working with TexasGulf (now Potash Corporation of Saskatchewan) in Aurora, North Carolina. After all parties were satisfied that there were no regulatory issues, the East plant began shipping the 75% co-product to Aurora to be used in ore beneficiation. By installing the extraction vessel, the plant increased product yield of the dinitrochlorobenzene by an estimated 3%. In addition to the increased revenues from yield increases, this project resulted in the avoidance of $750,000 in annual treatment costs. Revenues from the sale of the 75% sulfuric acid are minor.
Sodium Thiosulfate The East plant generates an estimated 20 million pounds per year of 25% sodium thiosulfate as co-product. This co-product is generated during the filtration of black crudes to remove the actual sulfur dye from the reaction mass. The dye solids are removed and the co-product filtrate is collected. All of this co-product was previously passed to the wastewater treatment system. Plant personnel determined that the addition of the sodium thiosulfate to the wastewater was causing several problems with the treatment system, including:

  • Contributing to an estimated 60% of the biological oxygen demand (BOD) in the aeration basin
  • Nuturing the development of microorganisms favoring degradation of inorganics over organics
  • Increasing the density of the activated sludge
  • Generating excess alkalinity demand

The East plant found it difficult to comply with existing requirements under its National Pollutant Discharge Elimination System (NPDES) permit and knew eliminating a significant amount of the sodium thiosulfate from the wastewater stream would have a beneficial impact on this effort. Sodium thiosulfate is commonly used for dechlorination, but markets for the coproduct were limited due to its strong color and the presence of ammonia. After aggressively seeking potential users, Clariant found a facility that was using virgin sodium thiosulfate to dechlorinate its wastewater prior to entering a public wastewater treatment system. After evaluating the co-product, the facility began purchasing the 25% sodium thiosulfate from Clariant. Clariant collects the coproduct and adjusts the pH before shipment. The facility is now purchasing roughly 12 million pounds per year from Clariant, with demand potentially increasing. After removing 60% of the sodium thiosulfate entering the effluent, Clariant was able to take several aerators totaling 400 horsepower out of service. Meeting the NPDES permit requirements has become easier for the facility. Combining the internal savings (electricity for aeration, purchase of lime, etc.) and external revenues from the sale of this co-product, recycling of sodium thiosulfate saves the plant about $200,000 annually.
Ammonium Sulfate The East plant generates an estimated 5 million pounds per year of 20% ammonium sulfate. As part of the plant's compliance plan under the new air toxic standards listing ammonia as an air toxic, the facility installed a three-stage air scrubber to remove ammonia emissions from several sulfur dye production areas. The first stage of the scrubber removes a significant portion of the steam. The second stage uses 34% sulfuric acid to react with the ammonia, forming ammonium sulfate and removing the ammonia from the air stream. The third stage uses 20% caustic to remove any H2S formed in the process. Because discharging the ammonium sulfate to the wastewater system would cause significant compliance problems, the facility decided to seek an alternative solution. The facility considered shipping the co-product off-site to a treatment plant designed for nitration, but the estimated cost was high, $120,000 to $150,000 per year. Instead, the facility began seeking recycling options for the co-product. The East plant contacted a hay farm in South Carolina whose owner was interested in the product from a crop nutrient standpoint. The East plant has developed a successful working relationship with this farm, which picks up and transports the ammonium sulfate to the farm. Although the East plant receives minimal revenues from this sale, it does avoid the potential cost of treatment.

  • Total Cost Savings: $1,100,000.00

Details of Reductions

  • Sulfuric Acid
  • Sodium Thiosulfate
  • Ammonium Sulfate
Source: WRRC

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