C4 - NH3 synthesis (+syngas production)

Question 1

What are the 6 steps of the steam reforming route?

Answer 1

1. Desulfurization
2. Reforming steam
3. Water gas shift reaction
4. CO2 removal
5. methanation/ final purification
6. dewatering

Question 2

What is the Linde Process, when is it used?

Answer 2

Used: in the partial oxidation route
What: Cryogenic distillation using the Joules-Thompson step. 2x distillation columns , 2x J-T, heat of reboiler from one column used from heat of condensation in the other column, P gradient adjusted and T gradient = driving force

Question 3

What are the steps of partial oxidation route?

Answer 3

1. Air seperation using the Joules-Thompson step 2 in the Linde-Process
2. Partial Oxidation
3. Soot removal
4. Sulfur removal
5. WGS
6. CO2 removal (liquid wash + N2) = purification step

Question 4

What is the main difference between S-Ref and partial oxi?

Answer 4

The way the final purification is performed. In partial oxi, pure liquid N2 is present –> will condense everything but H2 (N2 wash) = high purity reaction mixture with no inerts. + better control of stoechio because a pure N2 feed is available

Question 5

What are the products of partial oxidation - desired?

Answer 5

3H2:1N2

Question 6

Advantages of partial oxi

Answer 6

less dependance on feedstock, pure liquid N2 available = no O-compounds left, easier to control stoechio ratio, no inerts in synthesis loop, all C-containing can be used

Question 7

Steps of J-T ?

Answer 7

gas –> compression (^T) –> heat exchanger (lower T) –> expension (lowers T + liquifaction of air)

Question 8

What is the WGS reaction?

Answer 8

CO + H2O(steam) <–> CO2 + H2 (exo)

Question 9

Does the partial oxi reactor loop need a purge?

Answer 9

no bc no inerts left

Question 10

What is the industrial use of ammonia production?

Answer 10

fertilizers, nitrogenous compounds, house cleaning, removal of NOx (environmental)

Question 11

What is the name of the simple ammonia process, and what is the reaction?

Answer 11

Bosch process, less energy required:
N2 + 3H2 <-c-> 2NH3 (exo: 92,4 kJ/mol)

Question 12

What is the problem with ammonia synthesis?

Answer 12

1. Permanent deactivation of the catalyst (S poisoning)
2. Non-permanent screening effect: O-comp must be removed (<5 ppm)
   3 Low yield = recycle loop

Question 13

What does the Chatelier impose in the Bosch process?

Answer 13

Exothermic = low T, High P
but can’t be reached because kinetic limitation (max T = 670K –> rxn rate becomes very low past that pooint), catalyst works at high T, low P –> need compromise

Question 14

What is syngas

Answer 14

HC + CO

Question 15

steam reforming reaction / partial oxi

Answer 15

HC + steam –c–> syngas
HC + O2 –> syngas

Question 16

Explain the first step of steam reforming

Answer 16

Desulfurization:
remove S for NH3 synthesis with ZnO beds at T>350°C

Question 17

Explain the 2nd.1 step of steam reforming

Answer 17

Reforming of steam :
primary reformer: produces syngas, no N2 involved

i. CH4 + H2O <-c-> CO + 3H2 (endo)
ii. CO + H2O <-c-> CO2 + H2 (exo)

we need high T for a high CO yield, low CO2 yield

high steam - CH4 ratio = favour both conversion

high steam - C ration = prevents C deposit on cat

Question 18

Explain the 2nd.2 step of steam reforming

Answer 18

secondary reformer = only step with N2 introduced –> Packed bed, adiab reactor

Combustion rxn occurs = favors the endothermic rxn, air is introduced, O2 consummed to burn of CH4, dries out CH4 (T=1000°C), boost H2:N2 ratio–> still not 3:1 + too much O2 left = need more H2

Question 19

Explain the 3rd step of steam reforming

Answer 19

Water Gas shift reaction

CO + H2O <—> CO2 + H2 (exo)

Tempered catalyst: low P gas enters a HT packed bed, then is cooled down, then enters a LT packed bed (market based decision) Conatins a guard bed of ZnO because of the Sulfur remaining

Question 20

Explain the 4th step of steam reforming

Answer 20

CO2 removal:

mostly removed in bulk + stripping (physical scrubbing, will dissolve in methanol solvent)

we now have H2/N2, CO/CO2 = 50ppm, inerts

Question 21

Explain the 5th step of steam reforming

Answer 21

Methanation 1 final purification:

CO2 + 4H2 <-c-> CH4 + 2H2O
CO + 3H2 <-c-> CH4 + H2O

both exo, T = 350-400°C
Co/CO2 <5 ppm
3H2:1N2 ratio
inerts = purge loop
use small qty of H2

Question 22

Explain the 6th step of steam reforming

Answer 22

Dewatering:
H2O in liquid form because reactive stream = screening poison for cat (seperate)
+ recovery of solvent/ reagent needed

Question 23

How can CO2 be valorized in this process?

Answer 23

Direct use:
1. Enhanced oil recovery of CO2 at critival point = dissolves remaining oil
2. Supercritical fluid
3. Coffee –> decaf
4. Coke/ beverages
5. Urea

Indirect use:
1. Fuels
2. Plastics

Question 24

What are the 3 types of reactors used for the amonia synthesis?

Answer 24

1. Bosch reactor (before)
2. Quench reactor - horizontal
3. Intermediate cooling multiple adiabatic packed beds

Question 25

Describe the Bosch reactor.

Answer 25

Sacriditial liner, Carbon based steal, H2 diffused through liner and escapes through holes to avoid embrittlement of jacket linear and external heating

Question 26

Explain a quench reactor + why use it horizontally?

Answer 26

Better T controle Try to operate reactor as close as possible to maximum curve rate = minimize volume Horizontal = Ergun design = less P drop smaller V. note: outlet still contains N2 H2 and NH3 = reaction loops to recycleseperate

Question 27

Explain Intermediate cooling multiple adiabatic packed beds

Answer 27

Intercooling = maximal rate curve + minimize volume

Question 28

Explain the reaction loop of the NH3 reactor

Answer 28

1. Steam reforming --H2, N2, CH4, Ar--> 2. Quench reactor --NH3, N2, H2, CH4, Ar -->3. seperator -1---> NH3/// -2---> H2, N2, CH4, Ar -- purge --> feed to quench reactor

Question 29

Why use the purge after the seperation step?

Answer 29

Less product losses, removes excess inerts = avoid tart production

Question 30

What are the 4 different synthesis loop scenarios?

Answer 30

1. Purge after seperator, Seperation right after the reator 2. Seperation before reactor, Purge after reactor 3. Seperation before reactor, 1 compression after sep, purge after reactor 4. Seperation before and after reactor, purge after 2nd seperation

Question 31

P/C of 1. Purge after seperator, Seperation right after the reator

Answer 31

:) Ammonia Recovery, Minimized Hydrogen/Nitrogen Loss, Control of Inert Buildup, energy consumption because unreacted gases are recycled immediately :( Ar will build up in the recycle loop = lowers N2/H2 P = lower NH3 prod Hydrogen/Nitrogen Loss Through Purge , compressor work increases due to larger volumetric flow.

Question 32

P/C 2. Seperation before reactor, Purge after reactor

Answer 32

:) Removal of Undesired Components Before Reaction Control of inerts :( Ammonia Loss in Purge (because not all seperated) energy and product loss. not allow for effective recycling of unreacted gases lacks the economic and technical efficiency

Question 33

P/C 3. Seperation before reactor, 1 compression after sep, purge after reactor

Answer 33

:) removing ammonia before the reactor = Shifts equilibrium toward more NH₃ formation Efficient Use of Compressor :( Ammonia Loss in the Purge Waste of Product and Energy not fully exploit heat recovery from the reactor outlet.

Question 34

P/C: 4. Seperation before and after reactor, purge after 2nd seperation

Answer 34

:) remove impurities before gas enters reactor Higher Efficiency via Multi-stage Compression High Ammonia Recovery good Inert Management :( higher cost More units = more potential for wear/failure. Complex Control System

Question 35

How do you process downstream (syngas production?)

Answer 35

Fischer-Trops: (2n+1)H2 + nCO --> CnH(2n+2) + nH2O converts natural gas --> liuqid fuels in gas-to-liquids (GTL), coal-to-liquids (CTL), and biomass-to-liquids (BTL) processes. Valorizes NG that would get flared

Question 36

Explain Fischer-Trops process

Answer 36

Cat = sensitive to S --> need purified Syngas highly exo see diagram

Question 37

What 3 reactors to deal with highly exothermic reaction of F-T?

Answer 37

1. Multi-tubular fixed-bed reactor 2. Rise reactor 3. Slurry reactor

Question 38

Advantages of F-T versus standard refinery

Answer 38

Clean fuels (no S) Feedstock flexibility (Coal, gas, biom, waste) Fuel compatibility Carbon management potential High-quality products Energy independence

Question 39

Disadvantages of F-T versus standard refinery

Answer 39

high $ lower overall efficiency (bc multiple steps) highly exo = T management, avoid cat deactivation Larger volumes, slower kinetics H2 needed = can produce CO2 Climate impact for Coal Less maturity

Question 40

Differences of Ft and refineries

Answer 40

FT is a synthesis route from gases, enabling fuels from non-petroleum sources. Refineries directly upgrade crude oil via separation and catalytic conversion different feedstock: FT: Syngas (CO + H₂) derived from coal, natural gas, biomass vs Ref: Crude oil (complex mixture of hydrocarbons) FT = cat synthesis of gas (obalt or iron-based catalysts) Ref = phys and chem seperation + conversion, different catalyst used reactions are different Products: FT: waxes, diesel, naphtha, jet fuel Ref: Gasoline, diesel, jet fuel, lubricants, petrochemicals