Fuel for Legacy Vehicles in a “Carbon-free” Environment

Electric vehicles will not solve our emissions problem: there are over a billion petroleum driven vehicles, and they will not go away any time soon. Additionally, people have a current investment, and while billionaires might throw away their vehicles, most ordinary people will not change unless they can sell what they have, which in turn means someone else is using it. This suggests the combustion motor is not yet finished, and the CO2emissions will continue for a long time yet. That gives us a rather awkward problem, and as noted in the previous posts on global warming, there is no quick fix. One of the more obvious contributions could be biofuels. Yes, you still burn carbon, but the carbon came from the atmosphere. There will also be processing energy, but often that can come from the byproducts of the process. At this point I should add a caveat: I have spent quite a bit of my professional life researching this route so perhaps I have a degree of bias.

The first point is that it will be wrong to take grain and make alcohol for fuel, other than as a way of getting rid of spare or spoiled grain. The world will also have a food shortage, especially if the sea levels start rising, because much of the most productive land is low-lying. If we want to grow biomass, we need an area of land roughly equivalent to the area used for food production, and that land is not there. There are wastelands, but they tend to be non-productive. However, that does not mean we cannot grow biomass for fuel; it merely states there is nowhere nearly enough. Again, there is no single fix.

What you get depends critically on how you do it, and what your biomass is. Of the various processes, I prefer hydrothermal processing, which involves heating the biomass in water up to supercritical temperatures with some additional conditions. In effect, this greatly accelerates the processes that formed oil naturally. Corresponding pyrolysis will break down plastics, and in general high quality fuel is obtainable. The organic fraction of municipal refuse could also be used to make fuel, and in my ebook “Biofuel” I calculated that refuse could produce roughly seven litres per week per person. Not huge, but still a contribution, and it helps solve the landfill problem. However, the best options that I can think of include macroalgae and microalgae. Macroalgae would have to be cultivated, but in the 1970s the US navy carried out an exercise that grew macroalgae on “submerged rafts” in the open Pacific, with nutrients from the sea floor brought up from wind and wave action. Currently there is work being carried out growing microalgae in tanks, etc, in various parts of the world. In principle, microalgae could be grown in the open ocean, if we knew how to harvest it.

I was involved in one project that used microalgae grown in sewage treatment plants. Here there should have been a double benefit – sewage has to be treated so the ponds are already there, and the process cleans up the nitrogen and phosphate that would otherwise be dumped into the sea, thus polluting it. The process could also use sewage sludge, and the phosphate, in principle, was recoverable. A downside was that the system would need more area than the average treatment plant because the residence time is somewhat longer than the current time, which seems designed to remove the worst of the oxygen demand then chuck everything out to sea, or wherever. This process went nowhere; the venture needed to refinance and unfortunately they left it too late, namely shortly after the Lehman collapse.

From the technical point of view, this hydrothermal technology is rather immature. What you get can critically depend on exactly how you do it. You end up with a thick brown fluid, from which you can obtain a number of products. Your petrol fraction is generally light aromatics, with a research octane number (RON) of about 140, and the diesel fraction can have a cetane number approaching 100 (because the main components are straight chain C15 or C17 saturated hydrocarbons. Cetane is the C16 equivalent.) These are superb fuels, however while current motors would run very well on them, they are not optimal.

We can consider ethanol as an example. It has an RON somewhere in the vicinity of 120 – 130. People say ethanol is not much of a fuel because its energy content is significantly lower than hydrocarbons, and that is correct, but energy is not the whole story because efficiency also counts. The average petrol motor is rather inefficient and most of the energy comes out as heat. The work you can get out depends on the change of pressure times volume, so the efficiency can be significantly improved by increasing the compression ratio. However, if the compression is too great, you get pre-ignition. The modern motor is designed to run well with an octane number of about 91, with some a bit higher. That is because they are designed to use the most of the distillate from crude oil. Another advantage of ethanol is you can blend in some water with it, which absorbs heat and dramatically increases the pressure. So ethanol and oxygenates can be used.

So the story with biofuels is very similar to the problems with electric vehicles; the best options badly need more research and development. At present, it looks as if they will not get it in time. Once you have your process, it usually takes at least ten years to get a demonstration plant operating. Not a good thought, is it?

Advertisement

Liquid Fuels from Algae

In the previous post, I discussed biofuels in general. Now I shall get more specific, with one particular source that I have worked on. That is attempting to make liquid fuels from macro and microalgae. I was recently sent the following link:

https://www.fool.com/investing/2017/06/25/exxonmobil-to-climate-change-activists-chew-on-thi.aspx

In this, it was reported that ExxonMobil partnering Synthetic Genomics Inc. have a $600 million collaboration to develop biofuels from microalgae. I think this was sent to make me green with envy, because I was steering the research efforts of a company in New Zealand trying to do the same, except that they had only about $4 million. I rather fancy we had found the way to go with this, albeit with a lot more work to do, but the company foundered when it had to refinance. It could have done this in June 2008, but it put it off until 2009. I think it was in August that Lehmans did a nosedive, and the financial genii of Wall Street managed to find the optimal way to dislocate the world economies without themselves going to jail or, for that matter, becoming poor; it was the lesser souls that paid the price.

The background: microalgae are unique among plants in that they devote most of their photochemical energy into either making protein and lipids, which in more common language are oily fats. If for some reason, such as a shortage of nitrogen, they will swell up and just make lipids, and about 75 – 80% of their mass are comprised of these, and when nitrogen starved, they can reach about 70% lipids before they die of starvation. When nitrogen is plentiful, they try to reproduce as fast as they can, and that is rapid. Algae are the fastest growing plants on the planet. One problem with microalgae: they are very small, and hence difficult to harvest.

So what is ExxonMobil doing? According to this article they have trawled the world looking for samples of microalgae that give high yields of oil. They have tried gene-editing techniques to grow a strain that will double oil production without affecting growth rate, and they grow these in special tubes. To be relevant, they need a lot of tubes. According to the article, if they try open tanks, they need an area about the size of Colorado to supply America’s oil demand, and a corresponding lot of water. So, what is wrong here? In my opinion, just about everything.

First, you want to increase the oil yield? Take the microalgae from the rapidly growing stage and grow them in nitrogen-starved conditions. No need for special genetics. Second, if you are going to grow your microalgae in open tanks (to let in the necessary carbon dioxide and reduce containment costs) you also let in airborne algae. Eventually, they will take over because evolution has made them more competitive than your engineered strain. Third, no need to consider producing all of America’s liquid fuels all at once; electricity will take up some, and in any case, there is no single fix. We need what we can get. Fourth, if you want area, where is the greatest area with sufficient water? Anyone vote for the ocean? It is also possible that microalgae may not be the only option, because if you use the sea, you could try macroalgae, some of which such as Macrocystis pyrifera grow almost as fast, although they do not make significant levels of lipids.

We do not know how ExxonMobil intended to process their algae. What many people advocate is to extract out the lipids and convert them to biodiesel by reacting them with something like sodium methoxide. To stop horrible emulsions while extracting, the microalgae need to be dried, and that uses energy. My approach was to use simple high pressure processing in water, hence no need to dry the algae, from which both a high-octane petrol fraction and a high-cetane diesel fraction could be obtained. Conversion efficiencies are good, but there are many other byproducts, and some of the residue is very tarry.

After asking where the best supply of microalgae could be found, we came up with sewage treatment ponds. No capital requirement for building the ponds, and the microalgae are already there. In the nutrient rich water, they grow like mad, and take up the nutrients that would otherwise be considered pollutants like sponges. The lipid level by simple extraction is depressingly low, but the levels that are bound elsewhere in the algae are higher. There is then the question of costs. The big cost is in harvesting the microalgae, which is why macroalgae would be a better bet in the oceans.

The value of the high pressure processing (an accelerated treatment that mimics how nature made our crude oil in the first place) is now apparent: while the bulk of the material is not necessarily a fuel, the value of the “byproducts” of your fuel process vastly exceeds the value of the fuel. It is far easier to make money while still working on the smaller scale. (The chemical industry is very scale dependent. The cost of making something is such that if you construct a similar processing plant that doubles production, the unit cost of the larger plant is about 60% that of the smaller plant.)

So the approach I favour involves taking mainly algal biomass, including some microalgae from the ocean (and containing that might be a problem) and aiming initially to make most of your money from the chemical outputs. One of the ones I like a lot is a suite of compounds with low antibacterial activity, which should be good for feeding chickens and such, which in turn would remove the breeding ground for antibiotic resistant superbugs. There are plenty of opportunities, but unfortunately, a lot of effort and money required it make it work.

For more information on biofuels, my ebook, Biofuels An Overview is available at Smashwords through July for $0.99. Coupon code NY22C