We develop the CelloFuel Portable Biomass Refinery, for producing low-carbon bioethanol from sugar beet, sugarcane, sweet sorghum, softwood forestry residues, corn/wheat stover and cassava/topinambur/potatoes. Our goal is to make bioethanol at a lower cost than existing technogies while at the same time producing bioethanol with less carbon intensity. Key markets for ethanol are California, Germany, Sweden and Finland, which have a 70% higher market price for low-carbon bioethanol. Our goal is to also make rare sugars from softwood and topinambur and nanocellulose from stover.
We reduce the cost and carbon intensity of producing bioethanol by reducing fossil fuels used for:
The CelloFuel Portable Biomass Refinery produces bioethanol from carbohydrate-rich biomass by:
Solid-state fermentation of size-reduced biomass lets sugars diffuse from the interior of the biomass to the yeast where it is then fermented to ethanol. Diffusion and fermentation are relatively slow, but integrating diffusion and fermentation is twice as fast as doing these steps one at a time. The key to cost-efficiency is distilling the ethanol using the biomass itself as the packing material without requiring any squeezing of the biomass (see US Patent 10,087,411). Another significant contributor to cost-efficiency is using dilute oxalic/maleic acid hydrolysis with softwood and stover instead of enzymatic hydrolysis or dilute sulphuric acid hydrolysis.
The CelloFuel modules produce hydrous ethanol at 80% to 95% Alcohol By Volume (ABV). This can be used to produce potable ethanol, fuel for motors and fuel for cooking. This hydrous ethanol can be transported to a central refinery for further production of transportation fuels or higher-value chemicals.
The residual biomass from sugar beet, corn/wheat stover and cassava/topinambur/potatoes are rich in protein and minerals and can be used as animal feed. It's better to use maleic acid instead of oxalic acid with hydrolysis of hemicellulose, starch and inulin because calcium oxalate, if not completely neutralized, can cause kidney stones in cattle. Calcium maleate is a healthy feed supplement, so maleic acid is better if producing animal feed.
Our patented pressure cycling technologies (US Patent 9,194,012) are useful for extracting rare sugars from softwood (mannose, arabinogalactan and galactoglucomannan) and from topinambur (inulin). These sell for more than $10/kg, making these a more valuable product than ethanol.
The residual stover after dilute oxalic/maleic acid hydrolysis contains nanocrystalline cellulose that has been carboxylated, and thus degrades at a much higher temperature than nanocellulose produced with sulphuric acid. We are working on extracting this high-temperature nanocellulose from the residual stover for use in drilling mud. See Schlumberger and Halliburton patent applications for more info about this application.
Oxalic acid is more acidic than maleic acid, so less is needed to achieve a given pH. Oxalic acid is also significantly less expensive than maleic acid. However, maleic acid produces more sugar monomers and fewer sugar degradation products than oxalic acid. After neutralizing with calcium hydroxide, calcium maleate is better for animal consumption than calcium oxalate, because of the risk of kidney stones.
The CelloFuel modules have a very low cost of capital per liter (or gallon) of ethanol produced per year, mainly because everything is assembled from mass-produced HDPE pipes, scaffolding, cooling fans and induction heaters. HDPE is easy to weld so other pipes are inexpensive to connect.
The CelloFuel Portable Biomass Refinery is made from multiple CelloFuel modules, each made of a vertical HDPE pipe. There are a variety of options for loading the HDPE pipes - screw conveyers, conveyer belts, front-loaders, etc.
The bottom of the HDPE pipe is joined with a grade 444 stainless steel plate, sufficiently thick to withstand a vacuum inside the tube. The top cap is an aluminum plate with brazed heat sinks and a fan for distillation cooling. The top cap is joined to the HDPE pipe with a gasket, and can be lifted off the HDPE pipe for biomass loading. The bottom cap can be lowered into a chute and the residual biomass dumped down the chute, with a variety of options for conveying the residual biomass. An induction heater or steam heater is used to apply heat to the bottom cap. HDPE, and grade 444 stainless steel are all resistant to corrosion by oxalic acid. The aluminum top cap is sufficiently resistant to corrosion, since there will only be occasional splatters of oxalic/maleic acid on it.
Multiple HDPE pipes are mounted in rows so that they can be loaded and unloaded efficiently. The loading time is 5 to 30 minutes, depending on whether the biomass is being size-reduced while loading. The unloading time is 5 minutes and the processing time is 3 to 4 days, so the time spent loading and unloading is a small fraction of the total time.
When using steam or 95 C water, one should be careful of a failure that leads to pressure build-up in the HDPE pipe leading to an explosion. The top cap is fairly heavy (75 kg) and is held onto the top of the HDPE pipe with gravity and/or vacuum. If there's an unexpected steam pressure build-up, the top cap raises up and releases steam. When using the HDPE pipe under vacuum, a failure simply leads to implosion, which is quite safe (and unlikely).
When performing dilute oxalic/maleic acid hydrolysis with 0.110 M oxalic acid the pH is 1.2. A leak of this oxalic acid or maleic acid solution can easily be neutralized with a dilute solution of calcium hydroxide and the resulting calcium oxalate or calcium maleate is biodegradable. Calcium hydroxide is also very safe to handle.
Burning biomass that has been infused with oxalic/maleic acid is environmentally friendly, since this only releases CO2 and water vapor.
The top cap can be winched to the ground for maintenance. The various connections to the HDPE pipe are easily accessible.
If a vandal shoots bullets into an HDPE pipe, the bullet holes are often self-sealing. In the event of a very determined vandal, the worst case is that a hole in the HDPE wall causes a leak or loss of vacuum. This can easily be repaired in the field by plastic welding.
A CelloFuel module is a single vertical HDPE pipe held up by a scaffold. Scaling up to larger scales involves simply replicating the HDPE pipes in arrays.
Mounting and dismounting the HDPE pipes and top caps is done with a winch at the top of scaffolding. The scaffold contains at least two rows of HDPE pipes. The HDPE pipes, winches and scaffolding are transported in standard 20 ft. shipping containers. An air-cooled ethanol condenser, vacuum pump, IBC containers for chemicals, and an IBC container for ethanol are located in a 20 ft. shipping container.
We are doing lab-scale tests of dilute oxalic/maleic acid hydrolysis with this test apparatus:
We are currently constructing a mechanical mockup of the pilot-scale reactor that we will test with loading and unloading biomass. The pilot-scale HDPE pipes have been received. The HDPE pipes have been tested for vacuum with steel plate end-caps.
There are four families of CelloFuel patents that have been granted in the US and around the world, including the EU, Canada, Russia, China and Brazil. We are now licensing these technologies and providing engineering consulting for profitable implementation of these technologies.