Mass Transfer 2 Section # 1

The Last Term ! Overview on subjects Graduation Project Recharge your batteries!

Mentality! What have you heard about the subject? How do you see the subject? How will you deal with the Subject?

Massophobia!

What about the section?! Please don’t change your timetable. At least 12 sections in 9 weeks! Monday Monday Monday Tuesday Tuesday Tuesday Where: Mondays: 12.15 pm (sections 1 and 2) Tuesdays: 2 pm (sections 3 and 4) The site name: www.egypteucation.org The Course name: Mass Transfer (Second Term) Enrollment Key: Masstwo2013 Office hours: a) Mondays:: (11:45-3) b) Tuesdays: (10: 2)

Year’s Work 10 marks for the section. Marks will be distributed on 2 quizzes, and a report. The attendence will be used as bonus marks.

The schedule Section Subject 1st Refreshment 2nd Sheet # 1 Psychrometry 3rd Sheet # 1 Psychrometry (cont’d) 4th Leaching Sheet 5th Leaching Sheet (cont’d) 6th Leaching Exams 7th Sheet # 2 Psychrometry 8th Psychrometry Exams (on sheet #1) 9th Sheet # 2 Psychrometry (cont’d) 10th Leaching “Solids-free coordinates” 11th Non-Adiabatic Evaporative cooling 12th Psychrometry Exams (on sheet #2)

Studied Applications of Mass transfer Absorption Distillation Crystallization Membrane Separation Mass transfer limited chemical reaction Mass transfer limited electrochemical reaction

Important Mass Transfer Concepts 1) Equilibrium Relation It is mainly got using a set of experimental data. The equilibrium relation is specific for certain system, temperature, and pressure. Mainly reaching equilibrium isn’t economically favorable. It represents one of the constraints for the chemical engineer. It defines your borders! It is vital for the design of the mass transfer equipment.

Important Mass Transfer Concepts 2) Operating Curve (Line) It is got by performing overall balance on the equipment. (mass and heat balance) We can have one or more operating curves for one equipment. It is so called because any point on this line (curve) represents the bulk concentrations of the phases at any section of the equipment (As if the equipment operates along this line!)

Important Mass Transfer Concepts 2) Operating Curve (Line) (Cont’d) (Ponchon-Savarit) method used in distillation is an example of having more than one operating line.

Important Mass Transfer Concepts 3) Number of stages Based on the overall efficiency, we have certain relation between ideal and actual stages. Ideal stages can be calculated graphically using the method shown in the figure. For packed column, we don’t have stages. But, we have a concept known as number of transfer units.

Important Mass Transfer Concepts 4) Pinch Point No separation will be affected, as there is zero driving force. Infinite number of stages is required. One of the flow rates is at its minimum value. The operating flow rates are determined based on it.

Important Mass Transfer Concepts 5) Rate of mass transfer Rate = mass transfer coefficient * Area * Driving force Driving force can be the pressure or concentration difference. The units of mass transfer coefficient depends upon the driving force. The mass transfer coefficient is very important in determining the plate efficiency, and thus in the design of the plate column. The mass transfer coefficient is very important in determining the height of transfer unit, and thus in the design of the packed column. The mass transfer coefficient is mainly got using empirical equations.

Important Mass Transfer Concepts 6) Why do we calulate number of stages graphically?! In the mass transfer applications, we mainly have mass balance and equilibrium relations only, so why don’t we solve them together to get the number of stages?! To answer this question, we will take a simple example on an absorption column: We will further assume that the equilibrium relation can be substituted by a straight line (Y= α X) The overall mass balance equation is:

Important Mass Transfer Concepts 6) Why do we calculate number of stages graphically?! (Cont’d) Substituting the equilibrium relation in the mass balance gives: The previous is known as a “First order finite difference equation”. It is solved by certain mathematical technique to get after more than 4 or 5 steps:

Important Mass Transfer Concepts 6) Why do we calculate number of stages graphically?! (Cont’d) Finally!

Multi-component Distillation Highlights Multi-component Distillation

Introduction Multicomponent Distillation Sorel Method Lewis-Matheson Method Shortcut Method Plate to plate method Empirical Methods

KEY COMPONENTS The solution is based on choice of two “key” components between which it’s desired to make the separation: “Light Key” and “Heavy Key”. Light Key: is the lightest component in the bottom product Heavy Key: is the heaviest component in the top product a