Problem 7 - Biomass As A Sustainable Energy Source For The Future

Question

Write out the reaction equations for syngas fermentation to acetic acid with either \(\mathrm{CO}\) or \(\mathrm{CO}_{2}\) as reacting species.

Step-by-Step Solution

Answer

Question: Write the balanced reaction equations for syngas fermentation to acetic acid with either CO or CO2 as reacting species. Answer: 1) 4 CO + 2 H2O + 2 H2 → CH3COOH + 3 CO2 2) 2 CO2 + 4 H2O + 8 H2 → CH3COOH + 3 H2O

Step 1: Reaction with CO as reacting species

To write the reaction equation for syngas fermentation to acetic acid with CO as the reacting species, we start by identifying the reactants and products. In this case, the reactants are CO, water (H2O), and a reducing agent like hydrogen gas (H2). The main product is acetic acid (CH3COOH). Next, we need to balance the reaction equation to ensure the conservation of elements. Balancing the reaction equation, we get: \[4 \mathrm{CO} + 2 \mathrm{H}_{2}\mathrm{O} + 2 \mathrm{H}_{2} \rightarrow \mathrm{CH}_{3}\mathrm{COOH} + 3 \mathrm{CO}_{2}\]

Step 2: Reaction with CO2 as reacting species

To write the reaction equation for syngas fermentation to acetic acid with CO2 as the reacting species, we start by identifying the reactants and products. In this case, the reactants are CO2, water (H2O), and a reducing agent like hydrogen gas (H2). The main product is acetic acid (CH3COOH). Next, we need to balance the reaction equation to ensure the conservation of elements. Balancing the reaction equation, we get: \[2 \mathrm{CO}_{2} + 4 \mathrm{H}_{2}\mathrm{O} + 8 \mathrm{H}_{2} \rightarrow \mathrm{CH}_{3}\mathrm{COOH} + 3 \mathrm{H}_{2}\mathrm{O}\] In conclusion, the reaction equations for syngas fermentation to acetic acid with either CO or CO2 as reacting species are: \[4 \mathrm{CO} + 2 \mathrm{H}_{2}\mathrm{O} + 2 \mathrm{H}_{2} \rightarrow \mathrm{CH}_{3}\mathrm{COOH} + 3 \mathrm{CO}_{2}\] \[2 \mathrm{CO}_{2} + 4 \mathrm{H}_{2}\mathrm{O} + 8 \mathrm{H}_{2} \rightarrow \mathrm{CH}_{3}\mathrm{COOH} + 3 \mathrm{H}_{2}\mathrm{O}\]

Key Concepts

Acetic Acid Synthesis

Acetic acid, a key ingredient in vinegar, can be industrially produced through a process called syngas fermentation. Syngas, a mixture of carbon monoxide (CO), carbon dioxide (CO2), and hydrogen (H2), is converted by microorganisms into acetic acid (CH3COOH). This is an example of bio-catalysis, where the biological components (microorganisms) help facilitate the reaction. This process is preferred in some cases because it can be carried out at lower temperatures and pressures compared to chemical catalysis, potentially reducing the overall energy costs.

In the reaction involving carbon monoxide, the balanced chemical equation is:
\[4 \mathrm{CO} + 2 \mathrm{H}_2\mathrm{O} + 2 \mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{COOH} + 3 \mathrm{CO}_2\]
Similarly, when carbon dioxide is used as a reacting species, we have:
\[2 \mathrm{CO}_2 + 4 \mathrm{H}_2\mathrm{O} + 8 \mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{COOH} + 3 \mathrm{H}_2\mathrm{O}\]
Both reactions demonstrate the transformation of gases into a valuable liquid chemical.

Chemical Reaction Balancing

To ensure the law of conservation of mass is followed in chemical reactions, every atom that enters a reaction must be accounted for in the products. Balancing chemical equations is essential in chemical engineering to predict the outcomes of reactions and design processes accordingly.

To balance an equation, the number of atoms for each element in the reactants must be made equal to the number found in the products. For the synthesis of acetic acid from syngas, we meticulously adjust the coefficients (numbers in front of the chemical formulas) so that the number of carbon, hydrogen, and oxygen atoms are the same both before and after the reaction. As presented in the syngas fermentation equations:
\[4 \mathrm{CO} + 2 \mathrm{H}_2\mathrm{O} + 2 \mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{COOH} + 3 \mathrm{CO}_2\]
and
\[2 \mathrm{CO}_2 + 4 \mathrm{H}_2\mathrm{O} + 8 \mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{COOH} + 3 \mathrm{H}_2\mathrm{O}\]
we see that the number of each type of atom balances out, fulfilling the requirement for a correct chemical equation.

Carbon Monoxide Reduction

Carbon monoxide reduction is a critical part of syngas fermentation, particularly in the context of sustainable fuel production and chemical synthesis. This process refers to the conversion of carbon monoxide (CO) into other substances through the gain of electrons - a reduction reaction.

During the fermentation process, microorganisms act as catalysts, enabling the reduction of CO to form acetic acid.
\[4 \mathrm{CO} + 2 \mathrm{H}_2\mathrm{O} + 2 \mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{COOH} + 3 \mathrm{CO}_2\]
The reaction shows that carbon monoxide (CO) is transformed into acetic acid (CH3COOH), with carbon dioxide (CO2) being another product of the reaction. This reaction is part of the broader field of gas fermentation, which offers promising routes for converting waste gases into useful chemicals.

Carbon Dioxide Reduction

Carbon dioxide reduction, also known as carbon fixation, is a process that converts gaseous carbon dioxide (CO2) into organic compounds. In syngas fermentation to produce acetic acid, reducing CO2 is another reaction pathway that can be used by specific microorganisms. The balanced equation for this process is:
\[2 \mathrm{CO}_2 + 4 \mathrm{H}_2\mathrm{O} + 8 \mathrm{H}_2 \rightarrow \mathrm{CH}_3\mathrm{COOH} + 3 \mathrm{H}_2\mathrm{O}\]
Here, CO2 undergoes reduction by combining with hydrogen (H2) in the presence of water (H2O), yielding acetic acid as the main product and water as a by-product. This not only demonstrates a valuable chemical process for creating acetic acid but also highlights an approach to utilizing CO2, which is a significant effort in mitigating the impact of this greenhouse gas.