I have developed an interest in ZeaChem’s technology platform. ZeaChem is a venture-backed biofuels company located in Menlo Park, California. They are backed by Mohr Davidow Ventures, a silicon valley venture firm that focuses on investing in high impact companies that can continue to be relevant 30 to 40 years into the future. Their website states the following about their process:
The ZeaChem technology will produce fifty percent more ethanol per ton of feed than the current best-in-class technology. Our higher yield dramatically improves process economics, allowing farmers to get more ethanol out of each acre of biomass crop.
The ZeaChem website notes that they can, through three primary processes, produce ethanol (and presumably other bio-alcohols) with the entirety of plant material – not just the fermentable sugars. Their diagram above, from the ZeaChem web site, shows this proposed pathway. While I don’t know anything about their company’s technology, I have some good guesses on what they are proposing.
The separation step on the left appears to be a separation between lignin and cellulose materials from a plant. It’s not clear how this would be achieved either through a chemical steeping or a mechanical grinding and extraction (wet or dry milling). However, given the upstream processes, I would guess that a wet milling process would be used. This is because you can more easily break up and separate the starches from lignin from a chemical extraction than with a mechanical grinding process. So this sounds like a good guess.
The top process appears to be a standard fermentation of starches and sugars. This could be accomplished directly after the (liquid) separation of lignins. This could essentially be managed continuously in a semi-batch fashion. The output of this fermentation process is an alkyl-ester. Acetic acid is a good option for this, but I presume, given the right organism, a number of alkyl esters/acids could be produced. The molecular diagram of acetic acid is below:
The bottom process appears to be a thermoprocessing of the lignins. This appears to be a rather straight-forward gasification process. Admittedly, I don’t have any first-hand experience with gasification processes (unlike with corn milling). However, I would presume that a Pyrolysis and gasification of the lignins should break down this biomass into hydrogen and a carbon monoxide (syngas). While this would be better managed with a solid form, a liquid form as I suggest above would probably be pretty manageable too. A mechanical filtration or dewatering/mechanical press might be adequate for this process too. This explains the production of steam, hydrogen, methane, and other high-value gases. Apparently, ZeaChem wants to use the hydrogen as an input into the final process and use the rest as an energy source (which is a great idea).
The right process, hydrogenolysis, seems to be the butt kicker. I don’t know anything about this process. But as I have read in my research, it refers to the addition of hydrogen molecule across a C-O bond. This is a solid-catalyzed process, as most hydrogen gas processes are. Pd is a good bet. However, a better, cheaper catalyst could be the real IP that makes this process work. The alkyl esters produced in the fermentation process are the substrate of this process. From what I can presume, the hydrogen produced in the bottom thermoprocess is used to remove the acidic oxygen group from the alkyl ester and to add a hydrogen to the C=O bond. If acetic acid is the alkyl ester then the resulting product is ethanol. If the ester is propanoic acid, then the end product is propanol. If the ester is butanoic acid, then the end product is butanol. This is a great feature in that it would give a ZeaChem plant the ability to produce one of these products given the market demand for each one.
So I would surmise there are a few points of development that ZeaChem will be focusing on:
1) A set of catalysts that is inexpensive, but efficient at facilitating the hydrogenolysis process for potential alkyl esters to make a variety of end alcohols
2) A robust manufacturing process to quickly and cleanly separate starches and lignins from a variety of sources.
3) A set of biological organisms that will easily and efficiently ferment starches and sugars into a variety of alkyl esters (acetic, propanoic, n-butanoic acids)
If I’m at all accurate in this analysis, then ZeaChem is on to something really big. These points of difficulty – catalysts, integrated manufacturing, biotech organisms – have a huge intellectual development efforts behind them. I would surmise that the founders of this company have developed something intriguing to make this process happen (I’d imagine in the fermentation organism, catalysis, or success in the overall pathway). Their future should be bright if they are able to scale this up efficiently and cost-effectively.
