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Fermentation of sugars obtained from hydrolysis of starch or cellulosic biomass is an alternative to using petrochemicals as the feedstock in production of ethanol. One of the many commercial processes to do this \(^{16}\) uses an enzyme to hydrolyze starch in corn to maltose (a disaccharide consisting of two glucose units) and oligomers consisting of several glucose units. A yeast culture then converts the maltose to ethyl alcohol and carbon dioxide: $$\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{O}(+\text { yeast }) \rightarrow 4 \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}+4 \mathrm{CO}_{2}\left(+\text { yeast }+\mathrm{H}_{2} \mathrm{O}\right)$$ As the yeast grows, \(0.0794 \mathrm{kg}\) of yeast is produced for every \(\mathrm{kg}\) ethyl alcohol formed, and \(0.291 \mathrm{kg}\) water is produced for every kg of yeast formed. For use as a fuel, the product from such a process must be around 99.5 wt\% ethyl alcohol. Corn fed to the process is 72.0 wt\% starch on a moisture-free basis and contains 15.5 wt\% moisture. It is estimated that 101.2 bushels of corn can be harvested from an acre of com, that each bushel is equivalent to \(25.4 \mathrm{lb}_{\mathrm{m}}\) of corn, and that \(6.7 \mathrm{kg}\) of ethanol can be obtained from a bushel of corn. What acreage of farmland is required to produce 100,000 kg of ethanol product? What factors (economic and environmental) must be considered in comparing production of ethanol by this route with other routes involving petrochemical feedstocks?

Step by step solution

01

Determine the Conversion Factor from Ethanol to Corn

From the problem statement, it is known that \(6.7 \mathrm{kg}\) of ethanol can be obtained from a bushel of corn. Therefore, to find the amount of corn needed for \(100,000 \mathrm{kg}\) of ethanol, divide \(100,000 \mathrm{kg}\) by \(6.7 \mathrm{kg/bushel}\) to get \(14,925.37 \mathrm{bushels}\) of corn.

02

Calculate the Required Acreage of Farmland

Now that the amount of corn in bushels is known, convert this to acreage of farmland required. Since 101.2 bushels can be harvested from a single acre of farmland, divide \(14,925.37 \mathrm{bushels}\) by \(101.2 \mathrm{bushels/acre}\) to get about \(147.48 \mathrm{acres}\) of farmland.

03

Consideration of Economic and Environmental Factors

While not a mathematical calculation, the problem also asks for factors to consider when comparing this method of ethanol production with others. Economic factors could include cost of corn production versus petrochemical feedstocks, pricing and availability of land for farming, and labor costs. Environmental factors might include sustainability of resource use, carbon footprint of ethanol production, and possible negative impacts on local biodiversity. These factors will vary depending on geographic location, local regulations, and other context-specific variables.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fermentation

In the quest to produce alternative fuels, fermentation serves as a powerhouse process. It’s a biological method where microorganisms like yeast convert sugars and starches into alcohol and other chemicals. In ethanol production, yeast fermyet the sugar maltose, derived from corn starch, into ethyl alcohol and carbon dioxide. This reaction looks something like this: \[\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} + \mathrm{H}_{2}\mathrm{O} (+ \text{ yeast }) \rightarrow 4 \mathrm{C}_{2} \mathrm{H}_{5}\mathrm{OH} + 4 \mathrm{CO}_{2}(+ \text{ yeast } + \mathrm{H}_{2}\mathrm{O})\].
Fermentation naturally produces other by-products including yeast biomass and water. The efficiency of this biological conversion and the quality of the final ethanol product are critical factors. In our scenario, achieving 99.5 wt% ethyl alcohol is essential for its use as a fuel.

Enzyme Hydrolysis

Before fermentation can occur, corn starch needs to be broken down to simpler sugars that yeast can consume. This process is known as enzyme hydrolysis, and it's a pivotal step in bioethanol production. Enzymes like alpha-amylase and glucoamylase act on starch molecules, converting them into maltose (two glucose units) and oligomers. This enzymatic splitting of complex carbohydrates into fermentable sugars is not only efficient but also allows for the use of corn, a renewable biomass, in lieu of non-renewable petrochemicals.

Agricultural Land Use for Ethanol

Converting corn to ethanol demands significant agricultural resources. To calculate land use, a yield of 101.2 bushels of corn per acre and the conversion ratio of 6.7 kg of ethanol per bushel are key figures. For the production of 100,000 kg of ethanol, around 147.48 acres of farmland are needed. This conversion shows the substantial land area necessary for bioethanol production, underlining the importance of considering land availability and the competition with food production. It also highlights the need for sustainable agricultural practices to ensure that the land can continue to be productive in the long term.

Economic and Environmental Factors in Ethanol Production

Ethanol production from corn rivals petrochemicals economically and environmentally. The cost of corn production, land pricing, and availability, along with labor costs, comprise the economic aspect. Conversely, the environmental impact encapsulates sustainability of resource use, the carbon footprint of bioethanol, and potential effects on biodiversity. Each factor can heavily influence the viability and desirability of ethanol as an alternative fuel, making it imperative to strike a balance that supports both the economy and the ecosystem.