L1

Copyright Information

• This material is made available by the University of Melbourne under Section 113 P of the Copyright Act 1968 and may be subject to copyright. For further details, visit the University Copyright website.

Module Overview

• The plan for today's session is to:
    - Complete the discussion on material balances involving chemical reactions.
    - Introduce the next module on vapor pressure and humidity.

Safety Discussion

• Emergency Stop Buttons
    - The session begins with a briefing on safety regarding the use of fluid pumps in industrial settings.
    - Emergency Stop Button:
      - Designed to immediately shut down fluid pumps.
      - Usual placement is conspicuous (red button) to ensure visibility during emergencies.
    - Start Mechanism:
      - Involves a delay mechanism where a start button has to be held for 3 to 5 seconds before the pump can be restarted.
      - This precautionary measure ensures operators think thoroughly before restarting potentially dangerous equipment.

Material Balances in Chemical Reactions

• Case Study: Reaction of Ethylene and Oxygen to produce Ethylene Oxide
    - Initial inputs: 120 moles of ethylene and 60 moles of oxygen with a conversion rate of 10%.
• **Calculations:
    - Ethylene consumed = 120 moles * 10% = 12 moles
    - Oxygen consumed = 6 moles (stoichiometric ratio: 2:1 with ethylene)
    - Products: 12 moles of ethylene oxide
    - Remaining reactants after reaction:
      - Ethylene: 120 - 12 = 108 moles
      - Oxygen: 60 - 6 = 54 moles
• Total Moles in Product Stream:
    - Total = Unreacted Ethylene (108) + Unreacted Oxygen (54) + Ethylene Oxide (12) = 174 moles.

Efficiency Concerns

• The reaction efficiency is low, as only 12 moles of product are produced from 120 moles of reactants.
• Improvement Strategies:
    - Use of a Recycle Stream:
      - Incorporating a recycle stream helps improve the overall conversion rate.
      - A separator is used to differentiate products from unreacted reactants, allowing for the recycling of reactants.
      - Single Pass Configuration: Only 10% conversion is achieved without recycling.
• Recycle Configurations:   - Stream Numbers:
      - Stream 1: Fresh feed of reactants.
      - Stream 2: Mixture going into the reactor.
      - Stream 3: Outputs from the reactor before separation.
      - Stream 4: Product stream after separation.
      - Stream 5: Recycled stream of unreacted reactants.

Detailed Web of Stream Calculations

• Assuming a 20% separation efficiency:
    - Stream Calculations:
      - Stream 2 input total of ethylene = 120 moles + moles from recycle (m).
      - Stream 3 leaving the reactor: 0.9 * (120 + m)
      - Stream 4 (products): 20% of Stream 3 total,
      - Stream 5 (recycled unreacted): 80% of Stream 3.
• Recycle loop variable = m (moles of ethylene in stream 5).
    - Equations governing the balance can then be established and solved to find quantities in different streams.

Material Accounting and Reaction Products

• Using a previously established conversion: 42.8 moles of ethylene consumed yields the same amount of ethylene oxide produced due to the stoichiometric ratio (2:1 for oxygen). The number of moles confirmed for different streams to maintain a steady state was established through checking balance equations:
    - Overall conversion of ethylene = 35.7%.

Example of the Sodium Iodide Reaction with Seaweed

• Reaction Process:
    - Sodium iodide from seaweed reacts with manganese oxide and sulfuric acid, generating sodium sulfates and iodine.
    - The conversion for this reaction is 75%.
• Inputs include seaweed containing 5% sodium iodide and 30% water.
• Stream Processing Setup:
    - Stream 1: Seaweed input to the mixer (total 3100 kg/hr).
    - Identifying key reactants and process behavior and calculation of resulting flow rates by implementing a series of material balances around the reactor.

Vapor Pressure and Humidity Module Introduction

• Vapor Pressure Defined:
    - The pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature.
    - Important in determining saturation and condensation points across varying temperatures.
• Phase Changes:
    - Phase diagrams show the relationship between temperature, pressure, and the states of matter (solid, liquid, gas).
    - Critical points and supercritical phases where properties merge between gas and liquid states create mixed substances.

Comparison to Ideal Gas Behavior

• In chemical engineering, understanding the variabilities of real gases is critical. The Clausius-Clapeyron Equation connects vapor pressure to latent heat and temperature:
    - $dP/dT = L/(T(V_g - V_l))$
    - On applying assumptions regarding specific volumes, we derive simplified expressions helpful for practical calculations in thermal systems and energy balances.

Conclusion

• Overview of complex material balances and reaction efficiencies highlighted how reuse and recycling improve output in chemical processes. The next session will focus on vapor pressure and humidity to delve deeper into phases, equilibrium, and practical chemical engineering applications.