The chemical compound, acetic anhydride, is also used in purifying heroin.
Customs Preventive Deputy Collector Moazzam Raza told the media that customs authorities on January 9 seized 21.7 metric tons of acetic anhydride in a 20-foot container which had arrived from Tanzania's Dar es Salaam.
"The amount of the contraband confiscated is said to be worth more than 860 million rupees (USD 8 million)," he said.
He said the container arrived at Port Qasim in November last year. The law enforcers profiled the shipment and shifted it to the NLC's container terminal in Karachi.
The buyer of the shipment is in Sialkot.
Because of its use in the synthesis of heroin, acetic anhydride's (C4H6O3) movement is restricted in many countries.
However, the compound is largely used in the manufacture of fibres, plastics, pharmaceuticals and dyes.
