Q.Explain a process in which a biocatalyst is used in the industrial preparation of a compound.

The key idea is biocatalysis — using a living organism's own enzymes to carry out an industrial-scale chemical transformation under mild conditions. The process directly relevant to this chapter is the industrial manufacture of ethanol by fermentation.

Reasoning:

1. Substrate: Sugars (from molasses or starch-derived syrup) provide the sucrose/glucose feedstock.
2. Biocatalysts: Yeast supplies two enzymes — invertase, which hydrolyses sucrose into glucose and fructose, and zymase, which converts glucose and fructose into ethanol and carbon dioxide. …

Why a Biocatalyst?

Many industrial reactions need high temperature, strong acids/bases, or metal catalysts. Biocatalysts — enzymes, usually supplied by a living microorganism such as yeast — offer a mild, highly specific alternative: they work near room temperature and neutral pH, with very little unwanted side product.

The process examined here is the fermentation of sugars to ethanol, one of the oldest and largest-scale biocatalytic processes, and the one this chapter's own account of 'manufacture of ethanol' is built around.

Step-by-Step Process

1. Feedstock preparation

   A sugar source — molasses (which contains sucrose) or a starch-derived syrup — is diluted with water to give a fermentable solution.

2. Enzyme action — invertase

   Yeast cells secrete the enzyme invertase, which hydrolyses sucrose into glucose and fructose:

3. Enzyme action — zymase The same yeast also supplies zymase, a complex of enzymes that converts glucose and fructose into ethanol and carbon dioxide:

4. Fermentation conditions

   The mixture is kept anaerobic (excess CO2 excludes air) at about 293–298 K for one to three days. The enzymes are deactivated once the ethanol concentration rises to roughly 10–14%, which caps the yield of this step.

5. Recovery

   The fermented 'wash' is distilled and rectified to concentrate the ethanol; further dehydration (e.g. with quicklime, or azeotropic distillation) is needed to get anhydrous ('absolute') ethanol beyond the 95.6% ethanol–water azeotrope. …

Concept: Biocatalysis in Industrial Chemistry

Biocatalysis uses natural catalysts — enzymes (proteins) or whole cells — to perform chemical transformations. In industry, this offers high specificity, mild reaction conditions (low temperature, neutral pH), and reduced by-products compared to traditional chemical catalysts.

Method: Enzyme-Catalysed Hydrolysis for Acrylamide Production

Method name: Nitrile Hydratase Biocatalysis

Relevant compound: Acrylamide ($\text{CH}_2=\text{CHCONH}_2$)

Steps of the process

1. Feedstock preparation

   Acrylonitrile ($\text{CH}_2=\text{CHCN}$) is dissolved in water to form a dilute solution (typically 2–5% w/v). This prevents enzyme inhibition at high substrate concentrations.

2. Biocatalyst selection

   The enzyme nitrile hydratase (from Rhodococcus rhodochrous J1 or Pseudomonas chlororaphis) is immobilised on a solid support (e.g., polyacrylamide gel or alginate beads). Immobilisation allows reuse and continuous operation.

3. Reaction conditions

   • Temperature: 10–20°C (mild, preventing unwanted polymerisation)
   • pH: 7.0–8.5 (buffered with phosphate)
   • Continuous stirred-tank reactor (CSTR) or packed-bed reactor

4. Biocatalytic conversion

   Nitrile hydratase selectively adds water to the nitrile group ($-\text{CN}$) without affecting the carbon-carbon double bond:

5. Product recovery

   The reactor effluent is passed through a charcoal column to remove residual acrylonitrile and colour. The solution is then concentrated by evaporation and crystallised.

6. Enzyme recycling

   Immobilised enzyme is filtered and reused for multiple batches (up to 200 cycles in some industrial setups).

Why this method is preferred …

Common Mistakes: Biocatalysts in Industrial Preparation

Students often lose marks on this question due to a few recurring errors. Here’s a breakdown of each mistake and how to avoid it.

✗ Mistake 1: Confusing "biocatalyst" with "chemical catalyst"

What happens: Students describe a process using a metal catalyst (e.g., Pd, Pt) or an acid/base catalyst, thinking any catalyst qualifies.

Why it’s wrong: A biocatalyst is specifically an enzyme or a whole microbial cell — not a synthetic chemical.

How to avoid:

• Always check: Is the catalyst a protein (enzyme) or a living microorganism?
• If the catalyst is not biological, it is not a biocatalyst.

✗ Mistake 2: Describing a lab-scale reaction instead of an industrial process

What happens: Students write about a reaction done in a test tube or a small flask (e.g., "add enzyme to glucose solution in a beaker").

Why it’s wrong: The question explicitly asks for industrial preparation — meaning large-scale, continuous or batch production in a bioreactor.

How to avoid:

• Use terms like fermenter, bioreactor, immobilised enzyme column, continuous flow, large-scale.
• Mention downstream processing (separation, purification) if relevant.

✗ Mistake 3: Vague or incomplete process description

What happens: Students write only the name of the process (e.g., "glucose isomerase converts glucose to fructose") without explaining how it is done industrially.

Why it’s wrong: The question asks to explain a process — you must include:

• The biocatalyst (name the enzyme or microbe)
• The substrate (starting material)
• The product
• Conditions (temperature, pH, immobilisation method)
• Why it is used industrially (advantage)

How to avoid:

Use a structured answer:

1. Biocatalyst: e.g., glucose isomerase (immobilised on a support)
2. Substrate: glucose syrup
3. Product: high-fructose corn syrup (HFCS)
4. Process: continuous flow through a packed-bed reactor at 60°C, pH 7.5
5. Industrial significance: higher yield, lower cost, no by-products

✗ Mistake 4: Choosing a process that does not use a biocatalyst

What happens: Students pick the Haber process (ammonia) or contact process (sulfuric acid) — these use chemical catalysts, not biocatalysts.

How to avoid:

Memorise 2–3 standard examples of industrial biocatalysis: