In what's being called the largest biofuel financing ever, and one of the top five single investments in a renewable energy company, Seattle biofuel company Imperium Renewables has closed a Series B round and debt totaling $214 million USD.

The company closed a total of $113 million of private equity. At the same time, it mandated Société Générale Corporate & Investment Banking to act as sole book-runner and lead arranger of a $101 million Senior Secured Credit Facility.

The company, one of the largest biodiesel producers on the west coast, is to operate the nation’s largest biodiesel plant when its Port of Grays Harbor facility opens this July.

This new investment allows the company to pursue plans to open additional facilities around the world, including Hawaii, the Northeast United States and internationally.

Imperium's Grays Harbor facility on the coast of Washington state is expected to have the capacity to produce up to 100 million gallons of biodiesel per year, making it the largest biodiesel production facility in the United States.

Additional planned facilities are to increase the company's capacity to 400 million gallons, or about 10 million barrels of biodiesel annually, by the end of 2008.

Existing investors Technology Partners and Nth Power were joined by a number of new investors, including Ardsley Partners, Attractor Investment Management, BlackRock Investment Management (UK), Capricorn Management, Ecofin, Robeco C.V., Silver Point Capital, Southport Energy Alternatives, Stark Biodiesel Investments and Treaty Oak Capital Management.

Imperium says its process and technology innovations enable it to deliver improvements in product quality and throughput while significantly reducing capital and operating expenditures.

Read Cleantech.com's coverage of Imperium Renewables, including an in-depth interview with CEO Martin Tobias, here.