Ethanol Production Methods

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Questions and Answers

Which of the following is a primary reason why biochemical conversion is considered a more mature technology than thermochemical conversion for ethanol production?

Thermochemical conversion produces a wider range of byproducts, making separation and purification more complex.
Thermochemical conversion requires higher temperatures and pressures, leading to increased operational costs.
Biochemical conversion has been extensively used with sucrose and starchy materials, while thermochemical conversion is still primarily at the pilot scale. (correct)
Biochemical conversion can utilize a broader range of feedstocks, including lignocellulosic biomass without pretreatment.

In the context of ethanol production, what is a key advantage of using sucrose-containing feedstocks like sugarcane compared to starchy materials like corn?

Starchy materials require more complex fermentation processes, increasing the risk of contamination.
Starchy materials produce more valuable byproducts, offsetting the higher processing costs.
Sucrose extraction is simpler and less costly, as it does not require hydrothermal treatment or enzymatic hydrolysis. (correct)
Sucrose-containing materials have a higher sugar content per unit mass, leading to greater ethanol yields.

Why is the shift toward utilizing non-edible feedstocks, such as lignocellulosic materials, for bioethanol production considered important?

Non-edible feedstocks are more readily available and require less land for cultivation.
Non-edible feedstocks have a higher theoretical ethanol yield compared to edible sources.
The fermentation process for non-edible feedstocks is simpler and requires less energy.
Using edible sources for bioethanol production could threaten food security and increase food prices. (correct)

What is the main purpose of pre-treating lignocellulosic biomass in the bioethanol production process?

To hydrolyze hemicellulose and increase the accessibility of cellulose for enzymatic hydrolysis. (A) Signup and view all the answers

In the context of lignocellulosic biomass conversion, what is the role of enzymatic hydrolysis?

To convert cellulose into hexose sugars, primarily glucose. (D) Signup and view all the answers

Which statement accurately compares the water requirements of sugar fermentation versus thermochemical conversion in ethanol production?

Sugar fermentation requires more water due to processes like washing and fermentation. (A) Signup and view all the answers

What is a key distinction between the types of reactors typically used in sugar fermentation versus thermochemical conversion for ethanol production?

Sugar fermentation typically uses a batch reactor, whereas thermochemical conversion favors a continuous reactor. (A) Signup and view all the answers

What is the primary reason that Saccharomyces cerevisiae, commonly used in ethanol fermentation, can be 'poisoned' by high ethanol concentrations?

Ethanol inhibits cell growth and metabolic activity of Saccharomyces cerevisiae at high concentrations. (C) Signup and view all the answers

Why is distillation necessary in the production of ethanol via fermentation?

To concentrate the aqueous ethanol solution to a higher percentage (e.g., 95%). (D) Signup and view all the answers

Based on the description, what is the primary benefit of utilizing agricultural residues for bioethanol production?

Utilizing residues enhances energy resources, strengthens the rural economy, and creates and eco-friendly system. (A) Signup and view all the answers

Considering the process of converting starchy materials to ethanol, what is the purpose of the cooking stage (85-105°C)?

To gelatinize the starch, making it more accessible for enzymatic hydrolysis. (A) Signup and view all the answers

What is the key difference between oligosaccharides and polysaccharides based on their hydrolysis products?

Oligosaccharides yield a few monosaccharide molecules upon hydrolysis, while polysaccharides yield many. (B) Signup and view all the answers

What role does molasses play in ethanol production, and from which feedstock is it derived?

Molasses is a sugar-rich byproduct of sucrose extraction from sugarcane and beetroot. (C) Signup and view all the answers

What is the main reason for controlling the operating conditions of dilute acid pre-treatment during lignocellulosic biomass conversion?

To optimize the production of pentose sugars while limiting the formation of inhibitory compounds. (A) Signup and view all the answers

Which of the following best describes the role of enzymatic catalysis involving C5 and C6 sugars in lignocellulosic biomass conversion?

Two different enzymes are needed because there is no efficient technology to convert both C5 and C6 sugars. (D) Signup and view all the answers

According to the fermentation reactions described, what are the primary products generated from the conversion of one mole of glucose?

Two moles of ethanol and two moles of carbon dioxide. (C) Signup and view all the answers

In the processing of starchy materials for ethanol production, enzymatic hydrolysis is used after gelatinization. What is the main function of this enzymatic hydrolysis?

To convert starch into fermentable sugars like glucose. (C) Signup and view all the answers

Why is it important to maintain a certain level of dilution during the fermentation of pre-processed edible sources (sugar, corn) for ethanol production?

Dilution helps maintain the optimal pH, thus preventing inhibition of the microorganisms. (B) Signup and view all the answers

Within the process of ethanol production, what is the role of pyruvate?

Pyruvate is a key branching point in fermentation where it metabolizes to produce acetaldehyde and carbon dioxide. (A) Signup and view all the answers

According to the provided equation for theoretical ethanol yield (Cs x 0.51), what does 'Cs' represent?

The sugar concentration (C6 or C5) in the feedstock. (A) Signup and view all the answers

Flashcards

Chemical Ethanol Production

Uses acid to catalyze the hydration of ethylene into ethanol.

Fermentation

Uses microorganisms like yeast (Saccharomyces cerevisiae) or bacteria (Zymomonas) to convert sugars into ethanol.