Lecture 2

Question 1

what are the benefits of batch operation?

Answer 1

small production rates - a few tons/day
usually more flexible and economical
usually require less capital expenditure

Question 2

what is a disadvantage to batch operation

Answer 2

quality control is usually a problem

Question 3

what are the benefits to continuous operation?

Answer 3

adopted in all large-scale chemical processing
diminished labour costs: eliminations of operations such as emptying and filling of reaction vessels
automatic control of process, reducing labour costs but requiring greater capital outlay
greater constancy in reaction conditions leads to more uniform product quality

Question 4

what do we neglect in isothermal reactors

Answer 4

we neglect:
heat release (or uptake) by the reaction
heat transfer between parts of the reactor and/or heat exchange with the surroundings

Question 5

what is the mass balance in isothermal reactors

Answer 5

for any type of reactor, we apply the principle of mass conservation to a reactant in a certain volume ΔVr and certain time interval Δt

input to the reactor - output from the reactor - consumption due to chemical reaction = accumulation

Question 6

what is r

Answer 6

r is the rate of disappearance of reactant moles per unit volume per unit time [kmol/ m^3 s]

Question 7

why do we assume reaction starts instantly at t=0 for batch reactors

Answer 7

we assume t=0 at the start of the reaction because we assume the reactant is fully loaded and ready to react and we are neglecting loading time and time it will take to heat the reactor up. realistically not true because it takes time to fill the reactor would happen unless at very low temperature. then it would take a while to raise temperature to reaction temperature

Question 8

what volume do we use to apply the mass balance equations in batch reactors

Answer 8

we assume homogenous system with infinite stirring. therefore, we are considering the whole volume of the reactor

Question 9

what is the input and output for the batch reactor

Answer 9

the input and output are zero. at time = 0 the reactor has already neen loaded and we’re not adding anything and at the end we’re not extracting anything

Question 10

what is the general mass balance

Answer 10

input-output+production-consumption=accumulation

Question 11

what is the mass balance for a batch reactor

Answer 11

production- consumption= accumulation

Question 12

what does the mass balance in a batch reactor apply to

Answer 12

the whole volume of the reactor
teh dimension of each term is mass

Question 13

why do we assume steady state for CSTR

Answer 13

we assume steady state because that is how the reactor operates most of the time except when it stars, ends, or is there’s disturbances

Question 14

what volume do we use to apply the mass balance equation to the CSTR

Answer 14

whole reactor volume assuming homogenous system and infinite stirring rate

Question 15

what is the accumulation in CSTR

Answer 15

zero because steady state

Question 16

what is the general mass balance for steady state CSTR

Answer 16

inputc

Question 17

what does the mass balance for steady state CSTR apply to

Answer 17

the whole volume of the reactor
the dimension of each term is mass/time

Question 18

why do we assume steady state for PFR

Answer 18

generally operates at steady state except when starting, ending and if theres any disturbances

Question 19

what volume would we use to apply the mass balance equation for steady state PFR

Answer 19

an infinitesimally small slice perpendicular to the flow

Question 20

what is the accumulation in steady state PFR

Answer 20

zero because steady state

Question 21

what is the mass balance equation for steady state PFR

Answer 21

input- output +production - consumption= 0

Question 22

what does the mass balance apply to in steady state PFR

Answer 22

a differential cross section of the reactor and then integrated
the dimensions of each term is mass/time

Question 23

define rate of reaction

Answer 23

the rate of reaction is defined as the rate of net moles of a species produced or disappearing/ (unit of time)(unit of volume)

Question 24

what is the rate of reaction of a reactant A

Answer 24

rA= -1/VR * dNA/dt

minus sign because reacttant disappears
1/V represents per unit volume
negative sign ensures r is always positive

Question 25

what is the rate of reaction for product B

Answer 25

rB= 1/VR * dNB/dt

Question 26

if the reaction is carried out at constant volume what is the reaction rate for reactant A

Answer 26

rA= -dCA/dt

Question 27

why can we assume constant volume for liquid phase reactions

Answer 27

liquid phase reaction can be assumed to have constant volume because liquids are incompressible

Question 28

how do we deal with rate of reaction for gas phase reactions

Answer 28

in gas phase reactions we assume the gas presents ideal behaviour and then we can use:

NART/V =P = CART

Question 29

write the rate of reaction as a function of temperature

Answer 29

rA=-1/VR * dNA/dt = k CA ^n

where n is the reaction order

Question 30

what is n

Answer 30

n is the reaction order. it does not necessarily correspond to the stoichiometric coefficient and there not necessarily has to be a reaction order

Question 31

how are reaction rate equations determined?

Answer 31

they are determined experimentally

Question 32

what methokds are used find reaction orders and kinetic coefficients

Answer 32

there are four methods: differential, integral, half times, initial rates

slide 11 lecture 2

Question 33

what is the accumulation in a batch reactor in terms of a species A which can be a reactant or product in tems of number of moles of A within the system at time t and molecular weight of A and reaction rate of component A

Answer 33

(MANA)t+Δt- (MANA)t

where t=0 when reactor is loaded
and t+Δtis any point in time during the reaction

Question 34

what is the production- consumption in a batch reactor in terms of rate of reaction

Answer 34

(MArAVR)Δt

where production is positive and consumption is negative

Question 35

what is the derivation on slides 13 and 14 for

Answer 35

answer when figure out