Sometime shortly after 7 a.m. PST on Monday, execs at algae oil company Solazyme, members of the media and others will board a plane at Houston’s Bush Intercontinental Airport and take off on the first commercial U.S. domestic flight to use Solazyme’s algae-based jet fuel. United Airlines will operate the flight, which will land at Chicago O’Hare International Airport a couple of hours later and is set to carry 189 passengers.  The event is significant: While companies have spent years looking to scale next-generation biofuel products, few are producing fuels that can scale large enough to sell to the airline industry, let alone the auto industry. Solazyme’s jet fuel, dubbed Solajet, isn’t a widely commercialized product yet, but it has a few deals, including with the Navy and Australian carrier Quantas.