HOUSTON (Reuters) - Saudi Aramco took the first steps to integrating a petrochemicals business into the United States’ biggest oil refinery, which is operated by its subsidiary Motiva Enterprises.

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Aramco's Chief Executive Amin Nasser signed memoranda of understanding (MoUs) worth $8 billion-$10 billion with Honeywell UOP HON.N and Technip FMC FTI.N to study petrochemical production technology for use in a chemical plant the company is considering building at the Port Arthur refinery.

Saudi Arabia’s Crown Prince Mohammed bin Salman, who was winding up a two-week visit to the United States, was present at the signing in Houston, Texas, on Saturday along with Saudi Energy Minister Khalid al-Falih and U.S. Energy Secretary Rick Perry.

“These agreements signal our plans for expansion into petrochemicals,” Motiva’s Chief Executive Brian Coffman said.

Aramco, which wants to develop its downstream business as the government prepares to sell up to 5 percent of the world’s largest oil firm in an initial public offering (IPO) this year, wants to use oil as a major petrochemicals feedstock.

Coffman also said Motiva was evaluating boosting the 603,000 barrel-per-day (bpd) Port Arthur refinery’s capacity to 1 million or 1.5 million bpd, which would make it the largest in the world.

The aromatics unit for which Honeywell UOP’s technology is being considered under one of the MoUs, would convert benzene and paraxylene, byproducts of gasoline production, into 2 million tons annually of feedstocks for chemicals and plastics.

The other MoU would allow Aramco to use Technip FMC’s mixed-feed ethylene production technologies in the United States. The technology would produce 2 million tons a year of ethylene, which is used to make plastics, Motiva said.

The final investment decision on setting up a multi-billion-dollar petrochemical plant at Port Arthur is not expected until 2019, and is “dependent on strong economics, competitive incentives, and regulatory support,” Aramco said in a statement.

Coffman did not provide a timeline for the possible expansion of the Port Arthur refinery’s crude oil processing capacity.

“That’s something we’re evaluating, we’re studying for in the future,” he said.

The 1.2-million bpd Reliance Industries RELI.NS refinery in Jamnagar, India, has the world's largest crude oil processing capacity.

Aramco said last year that it would invest $18 billion in Motiva to expand the refinery and move into petrochemical production.

Other U.S. companies, including Chevron Phillips Chemical Co CHEPH.UL - a joint venture of Chevron Corp CVX.N and Phillips 66 PSX.N - and Exxon Mobil Corp XOM.N, have recently opened plants, like the one Motiva is considering, to process ethane into ethylene.

Chevron Phillips is considering building a second ethane cracker on the Gulf Coast of Texas.

The price tag for a large ethane cracker is typically over $6 billion, according to analysts. In addition to taking refining byproducts, ethane crackers provide hydrogen for refineries to use in making motor fuels.