The rat’s nest of pipes and columns snaking across the desert harbors a secret process that will use cobalt to turn natural gas into a powerful, clean-burning diesel fuel.

By next year, rulers of this tiny desert sheikdom hope, these gas-to-liquids (GTL) reactors under construction will bring in and buses.

Petroleum experts who have sniffed vials of gin-clear GTL diesel speak of it with reverence.

“It’s a beautiful product,” says Jim Jensen, a Massachusetts-based energy economist. “The kerosene smells like perfume.”

In all, some $20 billion has been committed to build an unprecedented array of clean diesel plants in this Gulf shore industrial park.

Those chipping in include oil titans Royal Dutch/Shell Group, ChevronTexaco Corp. and Exxon Mobil Corp., which is making a $7 billion bet on GTL, the largest investment in the corporate history of America’s largest company.

Smaller plants in Malaysia, South Africa and the United States have proved the technology works, but none is nearly as large as those planned here. In a few years, says Andy Brown, who heads Shell’s office in Qatar, the country will be “the GTL capital of the world.”

“This really is where GTL will come of age, where the industry will be born,” he said.

By 2011, the Qatar plants should be producing 300,000 barrels of liquid fuels and other products daily. The largest GTL plant now producing is Shell’s plant in Bintulu, Malaysia, churning out 14,700 barrels per day.

The investments amount to a big gamble on a clean alternative to pollutant-rich crude oil, based on an obscure “synthetic fuel” process developed to make fuel from coal Germany in the 1920s.

The clean-burning fuel, with almost none of the smelly sulfur soot belched by engines firing on conventional diesel, appears tailor-made for countries looking to reduce emissions in line with the Kyoto Protocol on global warming.

Faisal al-Suwaidi, chief executive of Qatar Liquefied Gas Co., said Japan, Canada, Korea, Europe and the United States, the world’s largest polluter, have expressed interest in the fuel. Although Washington has refused to sign the Kyoto protocols, state and local caps on emissions are pushing refiners to clean up diesel.

As far as carbon emissions go, green diesel appears to offer only a modest dent, partly because natural gas contains less carbon than oil-based diesel. The big difference is in sulfur.

Sulfur emissions from diesel engines cause as many as 10,000 deaths a year among Americans with heart and lung ailments, said William Becker, who represents state and local air pollution control agencies in the United States.

“It’s a matter of life and death,” Becker said. “And the solution depends on removing the sulfur.”

Emissions can be cut further by adding better filters that remove up to 90 percent of remaining particulates, said Richard Kassel, a fuels expert at the Natural Resources Defense Council in New York. Sulfur-laden diesel gums up these finer filters, he said.

“Clean fuels open the door to the most advanced emission controls,” Kassel said.