Clariant Corporation - Mount Holly Plant
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 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
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.
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
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.
Details of Reductions