An opportunity and challenge of by-product phosphorous acid industry?

 

One of the producing methods of phosphorous acid is to recycle and utilize high-boiling-point mother liquid left in reactor’s bottom boiler during dimethyl phosphite production. The major components of the mother liquid are phosphorous acid, phosphite ester and other insoluble inorganic-polymers which have P-P bonds. The strong corrosive mother liquid has a black or dark-brown appearance and has syrup-like fine solid precipitation and suspension which could be seen by naked eye. It possesses a scent of alcohol and has a density of 1.4g/ml. The dimethyl phosphite is majorly used for production of herbicide glyphosate and other agricultural chemicals, and is widely produced by Chinese pesicides companies such as Wynca, Xingfa, Fuhua Etc

According to Chinese enacted laws and policies, the mother liquid of dimethyl phosphite should be treated as dangerous liquid waste. The principle of dangerous waste management is that the waste needs to be treated to harmless status on where it is generated. Long distance transportation, and resell is strictly forbidden. However, the law is not effectively executed on the industry of phosphorous recycling, probably because that local government thinks that the mother liquid of dimethyl phosphite has somewhat economic benefit and to sell the mother liquid to the business outside their own governing area could sever the goal to decrease the total phosphorus (TP) emission locally.

Nevertheless, this grey-area industry is not commercially sustainable. If the local government faces the pressure coming from the central government or other local offices, the possibility of transporting mother liquid to distant positions may gradually diminished. Actually, local processing of mother liquid has advantages on transportation cost since it requires approximately 1.1 to 1.2 tons of mother liquid to produce 1 ton of solid phosphorous acid. Moreover, the transportation of corrosive solid is much safer than that of corrosive liquid and doesn’t have empty barrels recycling problem.

The author believes that in the long-run the manufacturers of phosphorous acid must cooperate capitally with those giant dimethyl phosphite suppliers for sake of reducing systematic risks. By constructing recycling factories close to the mother liquid tanks, connecting two units (storage tanks and recycling equipments) with pipes and pumps and meanwhile sharing the same utility system for example heating and cooling facilities, the cost delivered to eastern ports could be cut down by 5% to 10%.

 

---Written by QZ. Copy Right Reserved. 2018/12/20