Lecture 6 - Mass and process balancesOb

Define system boundary

Seperate the matter identified for investigation from the surrondings, the remainder of the universe. The system boundary may be real and tangible, such as the walls of a beaker or fermenter, or it may be virtual or notional (existing based on estimation)

Define stoichiometry

Stoichiometry is the calculation of relative quantities of reactants and products in chemical reactions (CHEMICAL CHANGE). Stoichiometry is founded on the law of conservation of mass and conservation of atoms.

What is the general mass balance equation during the process (not start or finish) of a batch and fed-batch process?

(mass in through system boundaries) - (mass generated within system) = (mass out through system boundaries) - (mass consumed within system)

Discuss how mass balances enable you to check the consistency in your process and spot deviations.

- Biologists say cells look happy. Bioengineers could measure glucose concentration and conclude the state of cell health.

Discuss how mass balances enable you to support the design, sclae up/down and optimisation of processes.

- By identifying limiting factors for exmaple.

Should cell growth and its requirements for substrate be considered in mass balances?

- It depends on the cell type. - If cells used in procere are nongrowing you do not have to take it into consideration. Non growing cells means that the cells are not components of any stream flowing into or out of the process, nor are they generated in reaction. Therefore cell mass did not need to be included in the calculation (it remained constant). - For cells with viable growth, growth and other metabolic activity must be taken into account in the mass balance.

Is it a reasonable assumption to assume that the liquid phase of slurry is water only?

- It is reasonable, as the concentration of dissolved substances (for example residual carbohydrate, minerals, vitamins and amino acids, as well as additional fermentation products) in fermentation broths is typically very small; water in spent broth usually accounts for more than 90% of the liquid phase.

Discuss how mass balances enable you to estimate things about your system which you want to know but cannot measure.

- Requires you to have data for at least one side of the balance

Discuss how mass balances enable you to check the consistency/reliability of your data

- Requires you to have data for both sides of the balance.

Is it reasonable to assume that unreacted oxygen and nitrogen leave a system as off-gas rather than components of a product stream?

- This assumption IS REASONABLE, due to the very poor solubility of oxygen and nitrogen in aqueous liquids: although any product stream most likely contains some dissolved gases, the quantities would be relatively small. - This assumption may be need to be reviewed for gases with higher solubility, such as ammonia.

What is the mass balance of the overall process?

- You need to make/calculate mass balances for each and every variable of the process.

What quantitity is not conserved during chemical reactions?

1. Number of moles/molecules. Moles are not conserved - the moles can and will change depending on the reaction type. This is because the size (relative molecular mass) of the products is different to that of the reactants, as by definition, the identity of components change during a chemical reaction. As moles = (mass in grams) / (mass/realtive atomic mass), the number of moles, must therefor also change.

What are the 2 general types of systems? List and define them.

1. STEADY STATE SYSTEM: - A system in which all properties (e.g. temperature, pressure, concentration, volume, mass and so on) do NOT very with time. >> Thus if we measure any variable of a steady-state system, its value will be unchanging with time - Can occur during a reaction (continous process), or when there is no reaction 2. TRANSIENT or UNSTEADY PROCESS: - A system in which PROPERTIES (e.g. temperature, pressure, concentration, volume, mass and so on) VARY WITH TIME. >> Thus if we measure any variable of a unsteady-state system, its value will be changing with time.

What are the steps for calculating mass balances?

1. Select a unit to work in - mass/moles, hours/days etc. - Calculations are easier when all quantities have the same units (shold be indicated on diagram). 2. Draw a clear process flow diagram - Showing all streams entering and leaving the system - All quantitative info should be shown - In mass balances, we are interested in masses (integral equation), mass flow rates (differential equation), and mass composistions. If info is given in volumes or molar quantities, mass flow rates and compositions should be calculated before labelling the flow sheet. 3. Define the reaction equation(s) + system boundary 4.Select a basis for the calculation (i.e. period of time) - It is helpful to focus on a specific quantity of material entering or leaving the system. For continous processes at steady state you usually base the calculation on the flow rate at a particular time. For batch or semi-batch processes, it is convenient to use total amount of mass fed to the system or the amount withdraw at the end. 5.Identify which components of the system, if any, are involved in reaction: - Neccesary in order to determine which mass balance equation is approprite (which species to include). 6. State/define any assumptions or limitations of your balances - Real life is complex, to simplify we make assumptions. - i.e. conclusions will only hold true for a system operating under the conditions specified (including e.g. temperature).

Objectives of lecture: 1. Understand how to calculate mole and mass fractions of components 2. Be familiar with stoichiometry and reaction equations 3. Understand types of process and balance equations 4. Be able to calculate mass and process balances

1. Understand how to calculate mole and mass fractions of components 2. Be familiar with stoichiometry and reaction equations 3. Understand types of process and balance equations 4. Be able to calculate mass and process balances

For the breakdown of glucose to ethanol (anerobic respiration), calculate the grams of each component.

1. Write down correct reaction formula. 2. Calculate the relative molecular masses of each component (using relative atomic weights)

Discuss the important characteristics of a CHEMICAL change in regards to: 1.) Arrangement of particles 2.) Conservation of mass 3.) Energy changes 4.) Reversibility

1.) Arrangement of particles: During a chemical change, the particles themselves are changed in some way. In the example of hydrogen peroxide that was used earlier, the molecules were split up into their component atoms. The number of particles will change because each molecule breaks down into two water molecules and one oxygen molecule. 2.) Mass conservation: Mass is conserved during a chemical change, but the number of molecules may change. 3.) Energy changes: The energy changes that take place during a chemical reaction are much greater than those that take place during a physical change in matter. During a chemical reaction, energy is used up in order to break bonds and then energy is released when the new product is formed. 4.)Reversibility: Chemical changes are far more difficult to reverse than physical changes.

Discuss the important characteristics of a PHYSICAL change in regards to: 1.) Arrangement of particles 2.) Conservation of mass 3.) Energy changes 4.) Reversibility

1.) Arrangement of particles: When a physical change occurs, the compounds may re-arrange themselves, but the bonds in between the atoms will not break 2.) Conservation of mass: In a physical change, the total mass, the number of atoms and the number of molecules will always stay the same. 3.) Energy changes: Energy changes may take place when there is a physical change in matter, but these energy changes are normally smaller than the energy changes that take place during a chemical change. 4.) Reversibility: Physical changes in matter are usually easier to reverse than chemical changes. Methods such as filtration and distillation can be used to reverse the change. Changing the temperature is another way to reverse a physical change.

What are the two types of the general mass balance equation?

1.) Differential balance - For CONTINOUS proceses AT A PATICULAR POINT IN THE PROCESS, where the information about the system is specified in flow RATES at a PARTICULAR INSTANT in time. 2.) Integral balance: - For BATCH and SEMI-BATCH processes between their INITIAL AND FINAL STATES, where the information about the system is specified in QUANTITY OF MASS (not rate) and collected over a PERIOD OF TIME rather than at a particular instant (e.g. 100 kg of substrate is added to reactor, after 3 days, 45 kg product is recovered).

What 4 terms are used to define the composition of mixtures and solutions. List them. When would you use one and not the other?

1.) Mole fraction of component X 2.) Mole percent and 3.) Mass fraction of component X 4.) Mass percent You use one and not the other, depending on the question and what you are trying got calculate (for example you use mass fraction, when the it is difficult to know the exact composition of the compound (e.g. complex proteins), and therefore not possible to calculate the mole fraction).

Why are mass balances important/what do you use them for?

1.) They enable you to estimate things about your system which you want to know but cannot measure - Requires you to have data for at least one side of the balance 2.) They enable you to check the consistency/reliability of your data - Requires you to have data for both sides of the balance (and compare the calculated/theoretical calues it to the data collected) 3.) They enable you to check the consistency in your process and spot deviatons 4.) They support deisng, scale up/down and optimisation of processes. - By identifying limiting factors for example.

What mass of oxygen is required to produce 15g of glutamic acid? C6H12O6+ NH3+ 1.5O2 + -> C5H9NO4+ CO2+ 3H2O

4.9g of oxygen is required to produce 15g of glutamic acid.

Define physical change

A change that can be seen or felt, but that doesn't involve the break up of the particles in the reaction. During a physical change, the form of matter may change, but not its identity For example melting, boiling and freezing of water. The water molecules still remain bonded as they are, with 2 hydrogens bonded to one oxygen atom, but the observed state changes. BUT PARTICLE REARRANGEMENT OCCURS (with water molecules being more or less loosley packed).

What are the 4 specific types of processes? List them.

A process is anything that causes changes in the system or surroundings. 1. A BATCH process 2. A SEMI-BATCH process 3. A FED-BATCH process 4. A CONTINOUS process

Discuss a fed-batch process

A process that allos input of material to the system but not output.

Define system

A system can be anything, so long as it can be defined by a BOUNDARY. >> "A system consists of any matter identified for investigation, and is set apar from the surrondings, which are the remainder of the universe, by a system boundary" For example, cells, machines, flasks, petri dishes etc.

What types of balances can we do? And which can we not do?

CAN do: 1. Mass or materials balances 2. Energy balances CANT do: Moles balances, because moles are not conserved during a chemical reaction

What are the 2 types of systems?

CLOSED: Closed system is one in which the boundary is non-permeable, it does not allo mass to pass from the system to the surrondings and vice versa. In this case MASS IS CONSERVED. OPEN: Open system is one in which the boundary allows exchange of mass between the surroundings and the system. MASS IS NOT CONSERVED.

How many significant figures/decimal places shold your final answers have in balance calculations?

Cant avoid carrying excess significant figures: - In some processes you have to subtract a very small number from a large one and carrying more significant figures than in the given data (because some mixtures contain very little compound A for eaxmple). >> This is an unavoidable feature of most mass balances for biological processes, which are characterised by dilute solutions, low product concentrations, and large amounts of water. HOWEVER, alothough excess significant figures were carried in the mass balance table, the final answers were reported with due regard to data accuracy.

What form is oxygen supplied in to cells?

Cells use oxygen in the DISSOLVED FORM, so oxygen must be transfered into the reactor in a liquid phase (water).

What 2 pieces of information do you need to calculate the mass and molar relationships of a reaction?

Do this using stoichiometric calculations. We need: 1. Correct reaction equation 2. Relevant atomic weights

State the law that number of atoms are conserved

During a chemical reaction the number of atoms in the reactants is the same as the number of atoms in the product. Relates to the mass being retained as the atoms make up the mass.

What are the two assumptions made when working with stoichiometric calculaitons are reactions?

During a chemical reaction: 1. Mass is conserved 2. Number of atoms of each element is conserved

What two quantities are conserved during chemical reactions? In other words, what are the 2 laws upon which stoichiometry is built?

During chemical and biochemical reactions, the following 2 quantities are conserved: 1.) Total mass: The sum of all relative atomic masses that comprise the components of the reactants, should equal that of the products) 2.) Number of atoms of each element: the number of atoms of each element on the reactanct side should equal that on the product side.

Give an example of a system and process. In general how would you calculate the mass balance for it?

FLASK

What is the general mass balance equation for a STEADY STATE system WITH NO reaction? Give an example.

GENERAL MASS BALANCE EQUATION: Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) In steady state systems, the mass accumulated is equal to zero (all parameters, including mass, is constant). Therefore, 0 = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) (mass in through system boundaries) - (mass generated within system) = (mass out through system boundaries) - (mass consumed within system) If there is no reaction, then the generation and consumption terms are zero. Therefore, (mass in through system) = (mass out through system) e.g. making up a bottle of complete medium and putting it in the freezer.

What is the general mass balance equation for a STEADY STATE system WITH reaction? Give an example.

GENERAL MASS BALANCE EQUATION: Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) In steady state systems, the mass accumulated is equal to zero (all parameters, including mass, is constant). Therefore, 0 = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) (mass in through system boundaries) - (mass generated within system) = (mass out through system boundaries) - (mass consumed within system) e.g. continous process. > It is a differential equation

When was the law of mass conservation first discovered?

Historically, mass conservation was discovered in chemical reactions by Antoine Lavoisier in the late 18th century,

In general, what are we looking at in mass balances? / What underpins mass balances?

In steady-state material balanes, masses entering a process are summed up and compared with the toal mass leaving the SYSTEM: the term BALANCE implies that the masses entering and leaving should be equal (MASS IS CONSERVED - underpins mass balances) Essentially, material balances are ACCOUNTING PROCEDURE: the total mass entering must be accounted for at the end of the process, even if it undergoes a physical change.

Define process

Is anything, process, that CAUSES CHANGES in the SYSTEM or SURROUNDINGS.

Define mass percent /weight percent.

Is mass fraction times 100. Mass percent = ((mass of A)/(total mass)) X 100

What is the mass balance equation for calculating total mass? and atomic species?

Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) Because total mass can neither be created or destroyed except by nuclear reaction, the generation and consumption terms must also be zero in balances applied to total mass (same for atoms). Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) Because you are considering the totoal mass, the mass of the system will stay the same (conservation of mass) (atoms are also conserved). Therefore, 0 = (mass in through system boundaries) - (mass out through system boundaries) (mass in through system boundaries) = (mass out through system boundaries)

What is the general mass balance equation?

Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) The accumulation term can either be positive or negative; negative accumulation represents depletion of preexisting reserves. The mass reffered to in the equation can be: 1. TOTAL MASS, 2. MASS OF A SPECIFIC MOLECULAR or ATOMIC SPECIES, 3. MASS OF A PARTICULAR COMBINATION OF COMPOUNDS such as cells or biomass.

What is a key application of the conservation of mass in biochemical engineering?

Mass balances A mass balance, also called a material balance, is an APPLICATION OF CONSERVATION OF MASS to the ANALYSIS of PHYSICAL SYSTEMS. By accounting for material entering and leaving a system, mass flows can be identified which might have been unknown, or difficult to measure without this technique.

Define mass fraction / weight fraction

Mass fraction of component X, is the ratio of mass X to the mass of the entire solution or mixture. The sum of all mass fractions of the solution/mixture should equal 1.

When does the law of mass conservation not hold true?

Mass is also not generally conserved in OPEN SYSTEMS. Such is the case when various forms of ENERGY ARE ALOOWED IN OR OUT OF THE SYSTEM (see for example, binding energy). However, again unless radioactivity or nuclear reactions are involved, the amount of energy escaping such systems as heat, work, or electromagnetic radiation is usually too small to be measured as a decrease in system mass.

Define mole fraction

Mole fraction is another way of expressing the concentration of a particular component of solution or mixture. It is equal to the moles of one component divided by the total moles in the solution or mixture. The sum of the mol fractions for all components of the solution is equal to 1 (think about probability)

Define mole percent

Mole percent is the percentage of the total moles that is of a particular component Mole percent = mole fraction x 100 Mole percent is equal to the mole fraction for the component multiplied by 100 The sum of the mole percents for each component in a solution will be equal to 100. mole % solute + mole % solvent = 100 %

What type of processes operate in steady-state conditions?

STEADY STATE system: - Properties of the system remain the same over time. - >> CONTINOUS PROCESSES are as close to steady-state systems as possible (the rate of input equals rate out output, and so while there is flow in the system it is constant). HOWEVER, unsteady-state conditions will exist during START-UP and for some time after any change in operating conditions.

Discuss a continous process

THERE ARE INPUT & OUTPUTS DURING THE PROCESS. A continous process allows matter to flow in and out of the system (OPEN SYSTEM). If the rates of mass input and output are equal, continous processes can be operated indefinitely. - To start with an initial volume, medium is constantly introduced, product is constantly removed - Inputs and outputs at the same rate. Volume remains the same. - Incoming stream contains substrate, leaving stream contains the product. *****More and more focus on this, because people think its more cost-effective and efficient******

Discuss a semi-batch process

THERE ARE INPUTS OR OUTPUTS DURING THE PROCESS, BUT NOT BOTH (e.g. Fed-batch) - Nutrients added intermittently. - Batch process initially and after a certain point, a feed input is introduced and the volume of the vessel increases. A process that allows either input or output of mass during the process. E.g. t-flask: put in cells in the beginning, then you do a medium exchange (you take out all the medium, usually half way through the experiment, to remove waste and put in fresh medium, then you allow the cells to grow again >> With T-flask you have both inputs AND outputs, as you remove all medium AND add new. THE BOOK DOES NOT HAVE THIS DEFINITOIN, BUT TIMES CHANGE and prof. says this is the current definition of semi-batch. **** Often used for stem cell cultures***

Discuss a batch process

THERE ARE NO INPUT OR OUTPUT DURING THE PROCESS. - A batch process operates in a closed system. - All materials are ADDED to the system at the START of the process; - The system is then CLOSED and the products removed only when the process is complete.

Of the 2 criteria that are needed to calculate the mass and molar relationships of a reaction, which is the limiting criteria?

The 2 critera: 1. Correct reaction equation >>> In real life it is VERY DIFFICULT TO DETERMINE the real reaction equation, esp. with new processes like stem cells, because there are SO MANY COMPONENTS. 2. Relevant atomic weights >> In ALL cases this is given by the PERIODIC TABLE.

Define chemical change

The formation of new substances in a chemical reaction. One type of matter is changed into something different. For example: the decomposition (breakdown) of hydrogen peroxide to form water and oxygen gas

State the law of mass conservation

The law of conservation of mass states that: "The law of conservation of mass states that the total mass of substances taking part in a chemical reaction is conserved during the reaction. MASS CANNOT BE CREATED OR DSETROYED DURING A CHEMICAL REACTION" For any SYTEM CLOSED to all transfers of matter and energy, the MASS OF THE SYSTEM must remain CONSTANT OVER TIME, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is "conserved" over time. The law implies that MASS CAN NEITHER BE CREATED NOR DESTROYED, although it may be REARRANGED in space, or the entities associated with it may be changed in form

What type of processes operate in trasient/UNsteady-state conditions?

UNSTEADY STATE system: - Properties (temp, pressure, mass etc.) of the system CHANGE over time. >> According to this definition, BATCH, SEMI-BATCH & FED PROCESSES operate in unsteady systems. - FED-BATCH and SEMI-BATCH processes: the TOTAL MASS of the system is either increasing or decreasing with time. - BATCH process: even though the mass may be constant (nothing is added or removed from the system during the process), changes occurring inside the system cause the syste properties to vary with time.

What is the general mass balance equation for an UNSTEADY STATE system? Give an example.

Unsteady = process variables (temperature, mass, pressure etc.) change with time - with reaction. GENERAL MASS BALANCE EQUATION: Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) + (mass generated within system) - (mass consumed within system) SOME STEPS. Ask lecturer. Mass accumulated = (mass in through system boundaries) - (mass out through system boundaries) - (mass converted within system) E.g. any cell culture vessel. **** This is the one that mainly happens in real life****