They say this goes against Obama's declared green credentials and his commitment to battle climate change.
Liquid coal is a cleaner alternative to diesel, still the main fuel for heavy transport in the U.S. It might also be a bit cleaner than gasoline. And the coal can be found in the United States so there is much less transportation involved in its use.
Personally, I believe that solar energy is the way to in eventually finding the right "mix" for sustainable energy production. Nearly all of our energy production currently is solar although much wrapped up with carbon through photosynthesis of plant life.
However, solar can never be the sole solution and their definitely will have to stop-gap measures on the way before solar energy obtains worldwide "grid parity," the point where it matches other sources in cost.
One big short-term solution is the use of biofuels, which Obama has routinely promoted. Biofuels are also part of the long-term solution, but only on a limited scale. Too much use of biofuels could threaten rainforests as the world population continues to grow, which would be counterproductive. However these clean fuels offer a quick way of reversing current trends.
Liquid coal can also be part of an interim mix until better technologies are poised to take over. To some extent this takeover is already starting to happen with solar energy. In many locations, solar has reached grid parity. Investment is pouring into the solar energy industry. Technologies are developed that help bring down the cost of refining silicone, the primary "ingredient" in photovoltaic cells. Silicone is the second most abundant element
Obama is a pragmatic politician rather than a purist and liquid coal in his view may represent a way, probably a temporary way, to start achieving energy independence. However, it is clear from his policy statements that it is not a main solution for he doesn't mention coal at all in most of his energy papers and speeches.