Just as ethanol can be produced from corn, so, too, can butanol. The main disadvantage to butanol production is that yields are significantly lower. But recall that the advantages include a better interaction of butanol with gasoline than ethanol, as well as the higher energy content of butanol. If all of the available residues of the corn along with the corn are converted to acetone-butanol (AB), the result would be the production of 22.1 x 109 gallons of AB biofuel – this is a yearly amount. In 2009, 10.6 x 109 gallons of ethanol were produced from corn – this would be equivalent to 7.42 x 109 gallons of butanol on an equal energy basis. Recall that butanol production is accomplished in a similar fashion to ethanol production; it uses different enzymes. The figure below shows the schematic of wheat straw processing that was shown in Lesson 7. A description of the process and some information on production using wheat straw and other feedstocks can be found at the end of Lesson 7.
A schematic diagram of acetone butanol ethanol (ABE) production from wheat straw.
This image presents a flowchart detailing the bioconversion of wheat straw into butanol, a valuable biofuel and industrial solvent. The process begins with milling, where wheat straw is mechanically broken down to increase surface area and improve downstream processing efficiency.
Next, the milled straw undergoes chemical treatment with sulfuric acid (H₂SO₄), which helps to break down the lignocellulosic structure and release fermentable sugars. This is followed by enzymatic hydrolysis, where enzymes further degrade the pretreated biomass into simpler sugars. During this step, lignin, a non-fermentable component, is separated as a byproduct.
The resulting sugar-rich hydrolysate is then subjected to fermentation, during which microorganisms convert the sugars into butanol (BuOH), along with carbon dioxide (CO₂) and hydrogen gas (H₂) as gaseous byproducts. After fermentation, solids are separated from the liquid phase.
The liquid undergoes a recovery process, which includes distillation and possibly other purification steps. During this stage, butanol, water, and other components labeled A & E (unspecified in the diagram) are recovered.
The final output of the process is butanol, with several byproducts including lignin, CO₂, H₂, and distillation residues, making this a comprehensive representation of a lignocellulosic biomass-to-butanol conversion pathway.
So, how much investment might be necessary to build a plant for butanol production? An extensive computer simulation was done to determine costs, payback time and return on investment – we will not discuss the details of the computer simulation because it is beyond the scope of this course. However, I will provide a summary of the study to give you an idea of the related costs. An estimate was done for producing butanol from wheat straw (BEEMS Module B6). The estimate was based on a plant size of 150 x 106 kg/year, or 48 x 106 gallons of butanol per year, and the following costs were determined:
- Equipment purchase cost $27.66 x 106
- Total plant direct cost (TPDC) $88.08 x 106
- Total plant indirect cost (TPIC) $52.85 x 106
- Total plant cost (TPC = TDPC + TPIC) $140.93 x 106
- Contractor’s fee & contingency (CFC) $21.14 x 106
- Direct fixed capital cost (DFC = TPC+CFC) $162.06 x 106
It would take ~$162 million to build a butanol plant that produces 48 million gallons of butanol. Operating costs must also be taken into consideration, which would be more than $200,000,000. The major factors in the operating costs are utilities (59% of the costs) and raw materials (21%). With these costs in mind, it was estimated that for a grassroots plant, the butanol production cost would be $1.37/kg, or $4.28/gal. For an annexed plant, the cost of butanol production would be lower, or $0.82/kg, or $2.55/gal. The researchers doing this work have been successful at producing AB from lignocellulosic substrates, though there are some challenges ahead. In conclusion, these are the overall estimates:
- The cost of production of butanol from WS is $1.37/kg (distillative recovery)
- Return on investment is 19.87% and payback time is 5.03 years
- Expansion of an existing plant would result in a production cost of $1.07/kg (distillative recovery), and $0.82/kg (membrane recovery)
- Utilities affect butanol production costs most
This kind of information may convince a venture capitalist to contribute to the building of a butanol plant, especially if the payback is in 5 years and the return on investment is 19.87%. However, this was a computer simulation and would have to be updated for current prices. That could alter the numbers.