Energy independence
So you want to produce all the fuel you need without importing it in from other countries, with all the messy politics that that can involve. Here’s how:
Use the carbon dioxide generated from the first step of Cquestrate’s process to allow you to grow algae (the availability of carbon dioxide is the rate limiting constraint if you have even a moderate amount of sunlight). Vent off any oxygen generated from photosynthesis and then decompose the algae in anoxic conditions (no oxygen) - this will generate methane. With solar irradiation at 20MJ per m2 per day and an efficiency of converting sunlight to chemical energy of 1%, you are able to generate 730GJ per ha per year. Wholesale prices for methane are ~USD10 per GJ, so you have a per hectare yield of ~USD7,300. Farmers would be delighted with that kind of yield.
Now, it isn’t quite that simple - there are high capital and operational costs involved in growing algae - but there are reasons to believe that producing methane will be far cheaper than producing biodiesel (although biodiesel sells for more). For a start, if you want to produce biodiesel you have to get it out of the algae cells, by breaking down the cell walls and using solvents, which involves energy and expense. Methane by contrast is a gas, which will separate out without the need for any expensive processing.
Another benefit is that algae don’t by choice produce much of the lipids that you need to produce biodiesel. You have to stress the algae, by making the conditions in which they grow abnormal. Photoynthesis yields sugars - the algae then have to go through a series of biochemical steps to convert those sugars into lipids - and each step reduces the overall energy efficiency conversion from sunlight to chemical energy. By contrast, to produce methane all you need to do is to allow the algae to do what they do most naturally - produce sugars - and then allow them to decompose (this is helped by two sets of organisms - the first set breaks sugars down into acetic acid and the second set breaks acetic acid down into methane and carbon dioxide). The energy efficiency of this decomposition process is, in theory 95%, but in practice is closer to 80%.
Current projects which seek to produce biodiesel from algae use the flue gases from power stations as they are a concentrated source of carbon dioxide. This means that the algae needs to be grown near the power station and that tends to mean high land prices. Cquestrate’s process can be performed on cheap land far away from a power station as its source of carbon dioxide is from the calcination of limestone.