Closed-loop Biodiesel

I think Robert Rapier has made it explicitly clear that switching to biofuels with our current gas guzzling enterprise is largely a non-starter. I have said this in the past, "that we should not dismiss biofuels simply because their lobby groups are stupid." Biofuels provide very high utility due to the fact that they are high-density liquid fuels, ideal for long distance transportation. However, the paradigm needs to change: we need to get serious about both conservation and efficiency. We need smaller, lighter cars that incorporate all the efficiency advantages of hybrids and diesels. We also need to offset load to electricity rather than liquid fuels through the plug-in concept.

Over at the Oil Drum, Heading Out wonders why the big emphasis on ethanol from the USA corn farmers? You mean aside from their money-grubbing mendacity? As he points out biodiesel is a much better idea. The problem with ethanol obviously lies in distillation. I am not very high on cellulose ethanol either due to this simple problem. Separating the product from the water requires a whole lot of heat input.

Biodiesel is fatty acids which have been esterified by the addition of an alcohol, typically methanol. This greatly improves the flow properties of biodiesel compared to straight vegetable oil (triglycerides). Vegetable oil is relatively easy to separate from the plant. The most common method is to basically squeeze it out mechanically. This requires vastly less energy than distillation.

There is still the problem of the methanol input. My potential solution to this problem was to run an anaerobic reactor with the remaining material (i.e. cellulose) in order to produce methane. Methane production by anaerobic bacteria requires some very low grade heat inputs that could certainly be supplied by passive solar if the system was well designed and insulated. Producing methane is this fashion is relatively wasteful of the carbon you've managed to sequester -- the output is roughly half CH₄ and half CO₂.

However, the key point is that through this integrated approach there is no destruction of the soil nutrients. From an energy perspective it makes more sense to simply burn the dry biomass but then all your fertilizer becomes fly ash. In a methane reactor, the fixed nitrogen, phosphorous, and potassium will still be in the sludge left over once the bacteria are done with it. The sludge can be used as a fertilizer (with some soil issues). Overall it is a much more 'permaculture' solution than anything else I've seen.

The biodiesel/biogas approach is nearly a closed-loop. It produces diesel fuel and methane to power the farm machinery needed to grow the crop, and it also preserves the majority of the nutrients in the soil. Ethanol is constantly hammered because it essentially transforms natural gas into ethanol. It should be clear to everyone that if the integrated biodiesel/biogas approach isn't energy positive it simply won't be able to run.

In the past I haven't been able to find sufficient information to analyze this problem. I hope to take a second look at the issue and see if a reasonable back of the envelope approximation can be done now that there's so much more ethanol information out there.