Qatar signed a $6 billion deal with Chevron Phillips Chemical on Sunday to build a plant including the biggest ethane cracker in the Middle East, converting natural gas into polyethylene and other plastics.

The Ras Laffan Petrochemicals Complex, which will produce 2.1 million tonnes of ethylene a year along with 1.7 million tons of polyethylene derivatives, will come on stream in 2026.

The complex will have "lower waste and greenhouse gas emissions" than similar facilities around the world, said Saad Sherida al-Kaabi, Qatar's energy minister and the CEO of QatarEnergy.

QatarEnergy has a 70 percent equity share in the joint venture with Texas-based Chevron Phillips taking the other 30 percent.

"This marks QatarEnergy's largest investment ever in Qatar's petrochemicals sector and the first direct investment in 12 years," Kaabi said at a signing ceremony in Doha.

Ras Laffan will double Qatar's ethylene production capacity and increase its polymer output from 2.6 million tons to more than four million tons a year. Overall, Qatar's petrochemical production capacity will rise to almost 14 million tons a year.

The investment "marks an important milestone in QatarEnergy's downstream expansion strategy", Kaabi said.

"It will not only facilitate further expansion in the downstream and petrochemical sectors in Qatar, but will also reinforce our integrated position as a major global player in the upstream, LNG, and downstream sectors."

Ethane crackers, which convert gas into ethylene, have been targeted by environmental activists for their emissions, while ethylene and polyethylene are used in a swathe of plastic products from piping to water bottles and food packaging.

Wealthy Qatar has large reserves of natural gas including the North Field, which contains the world's biggest deposits and stretches under the Gulf sea into Iranian territory.