Oily algae

Algae, as well as other biologically sourced feed stocks, has been the subject of a lot of research in oil production, for what should be obvious reasons. There are several things about using some bio-sources that concern me, however. Using food cropland to grow corn or soy intended for conversion to fuel, for one, resulting in less food production (and contributing to higher food prices).

The bio-sources that don't bother me in this way are things like manure or other waste to bio-fuel. Even wood waste and scrap paper can be turned into either oil or syngas (which can be turned into oil, among other things).

But, an interesting comment in a recent press release about oil from algae caught my eye: "byproduct stream of material containing phosphorus that can be recycled to grow more algae."


If the phosphorus that the algae incorporates into their cells as they grow can indeed be separated from the carbon that is converted into oil, well enough that it's a nutritious source to further algae growth, this could be a very good thing. Add to that, algae can be grown in tanks on non-arable land and pumped around, instead of occupying farmland and requiring diesel-powered equipment to grow and harvest it, and it looks even better.

(Fortunately, algae are not self-aware and thus won't eventually realize that they're being fed the equivalent of Soylent Green.)

Algae feed; Figure 3 in Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor, Elliott et. al.

The general process of hydrothermal liquefaction has been around for a few decades now. On looking more closely at the actual paper, it looks to me like there are two new and interesting parts to it.

(I could be wrong about what is new and interesting of course; making oil is not my area of expertise.)

The first is the recycling of nutrients. Unfortunately, as press releases tend to do, this was exaggerated. Where the press release said "byproduct stream of material containing phosphorus that can be recycled to grow more algae", the actual paper indicated only that some phosphorus was detected in one of the byproducts. They didn't even have the distribution of phosphorus (or ammonia, another recyclable nutrient) fully characterized yet, and pointed out that this needs more research. So, it could be a partial nutrient recycle, which is better than nothing, but will still need fertilizer inputs.

The second is that they didn't need to use a special solvent to separate the oil from the water. It sounds odd, since most people's experience is that oil and water don't mix, but apparently most hydrothermal liquefaction processes (as described in both papers linked above) don't separate naturally but need a solvent to assist. It's important to not have water in your product oil, but if you're going to recycle the water back to grow the algae which this group mentions as a possibility, it's also important to not have oil in your water.

I guess something in the other systems acts as a surfactant, allowing either the oil to disperse in the water or vice versa, and the solvent is needed to break that up. Since the paper draws attention to removing solids before trying to separate oil from water, it's possible that those are the culprit.

It will be interesting to see how this performs once the nutrient and water recycle loops are connected.

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