Ch5.1 inorganic bulk acids - HNO3

Question 1

What are the 3 reactions to produce HNO3

Answer 1

1. oxidation of NH3
2. 2NO +O2 <-> 2NO2
3. Absorbtion

Question 2

Explain the graph relatin burner efficicency and T

Answer 2

There is an optimum at around T = 900
If T is too low, does favors the side reaction(++ + exo )
If T is too high, will not favor the reaction at all bc it is exo
We want low T for exo rxn (Chatelier)

Question 3

Do we want fast or long residance time

Answer 3

Fast ! avoid side reaction / reaching T>900

Question 4

4NH3 + 5O2 –> 4 NO + 6 H2O
What P do we wwant

Answer 4

Low P bc more moles on left side –>

Question 5

What happens if reaction 2 and 3 have same kinetics (low T, ^P)

Answer 5

They will happen simulatneously

Question 6

Name the 4 steps of the process

Answer 6

1. Reactor w/ excess air
2. heat exchanger (lower T)
3. Condensor (^P)
4. Absorber with water inlet

Question 7

Do you need a water inlet for absorber? why

Answer 7

yes for better heat exchange (here it is to cool)

Question 8

Describe weak nitric acid

Answer 8

high gas velocity = don’t need catalyst
usel alloy of Rh and Pt

Question 9

Do we need a catlyst?

Answer 9

no

Question 10

Explain the absorber principle of step 4

Answer 10

1. water flows counter-current
2. oxidation between trays, absroption on trays
3. Cooled bc of exo

Question 11

Describe the distance between the trays

Answer 11

at the bottom: they are closer
at the top; higher distance –> slower oxidation of No

Question 12

Why use a single P plant?

Answer 12

smaller equipment size = save money
possible to recover energy at higher value

Question 13

Describe the conditions of single P plant

Answer 13

^P
7-12 bar

Question 14

Describe the steps of single P plant

Answer 14

1. reactor
2. condensor
3. seperator
4. stripper with air
5. absorber

Question 15

What are the pressures for dual P plant?

Answer 15

reactor 1: 4-5 bar
absorber: 10-15 bar (need a compressor before)

Question 16

What are the differences between single and dual P plant?

Answer 16

1. absorption more efficient at higher P
2. if P too high (single P): more Pt loss, shorter gauze life
3. smaller conversion at ^P
4. NH3 –> NO smaller
5. NH3–> HNO3 smaller

Question 17

Which molecules form an azeotrope?

Answer 17

HNO3 and water

Question 18

What is the problem of an azeotrope?

Answer 18

hard to seperate the 2 molecules

Question 19

What is the deal with NOx

Answer 19

environmental regulations: remove NOx from gas bc can go in atmosphere

Question 20

What are the concentration of NOx in absorber

Answer 20

2000-3000 ppm

Question 21

What is the max concentration required for NOx

Answer 21

200 ppm

Question 22

What are 3 NOx removal types

Answer 22

1. SCR (selective catalyst reduction)
2. non-SCR
3. extended absorption

Question 23

Describe SCR

Answer 23

NOx –> N2 by reaction with cat (NH3)
any P
single or dual P plants

Question 24

CON’s of SCR

Answer 24

catalyst is $$$
40-60% of OPEX
replace every 2-3 years

Question 25

Describe non-SCR

Answer 25

absorber tail gas heated to ignition T and fuel is added mix --> cat reduction unit --> fuel (CH4) reacts with cat w/ NOx non-selective: fuel depletes O2 first flexible produces heat

Question 26

why is non-SCR not selective?

Answer 26

non-selective: fuel depletes O2 first

Question 27

Describe extended absorption

Answer 27

^efficicency: install larger tower or add 2nd towe for ^P : NOx<200 ppm achievable

Question 28

Why are azeotrope not seperable

Answer 28

relative volatility = 1

Question 29

5 methods to seperate NH3/Water azeotrope

Answer 29

1. membrane 2. PSDistillation 3. Extractive distillation 4. Azeotropic distillation 5. salting

Question 30

What are the steps of exctractive distillation

Answer 30

1. azeotropic distilation 1 2. water removal 3. recycle loop, use H2SO4 = dry air

Question 31

What are the steps of PSDistilation

Answer 31

0. feed mix with recycled stream (azeotrop) 1. distillation 1 at P1 2. pump --> P2 3. Distillation tower 2 2 pure products at bottom = less volatile

Question 32

What do you use for the extractive distillation

Answer 32

aqueous solution of MgNi effective dehydrating agent : H2SO4

Question 33

What are the 3 steps for the extractive distillation

Answer 33

1. dehydrating column 2. Bleacher + condensor 3. Absorption column

Question 34

Is the material choice important for the extractive distillation, why?

Answer 34

Has an effect on corrosion speed by nitric acid metal alloys that form adherant film are protected by oxide films from corrosion H2 embrittlement (production at metal/acid surface)

Question 35

What is the material choice for the exctractive distillation

Answer 35

nitric acid = strong oxidizing material

Question 36

T or F: Nitric acid is the largest N2O emission in industry

Answer 36

T