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INDUSTRIAL PROCESSES. We try to obtain max. efficiency (min. waste, min. input of energy, and as rapid rxn as possible) in these processes. Max efficiency is possible through 2 ways: A-) kinetics ( how fast the products are made from the reactants)

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industrial processes
INDUSTRIAL PROCESSES
  • We try to obtain max. efficiency (min. waste, min. input of energy, and as rapid rxn as possible) in these processes.
  • Max efficiency is possible through 2 ways:

A-) kinetics ( how fast the products are made from the reactants)

B-)equilibrium (how much of the desired product is obtained)

1 haber process

1.Haber Process

Ammonia is produced industrially by the Haber process which involves the catalytic reduction of nitrogen by hydrogen at temperatures of 450-500 ºC and pressures of 35-40 MPa.Fe(s) is used as a catalyst for the reaction.

The process provides an excellent illustration of Le Chatelier's Principle, and is a favourite of examiners!

1 haber process3
1.Haber Process
  • How can we increase the efficieny of production of ammonia?

1. Lower temp is needed.

- But it will decrease the rate of the reaction.

- so, a compromise temp is chosen. Take a look at the graph on P. 189.

1 haber process4
1.Haber Process
  • How can we increase the efficieny of production of ammonia?

2. Finely grinded catalyst will increase the rate.

1 haber process5
1.Haber Process
  • How can we increase the efficieny of production of ammonia?

3. High pressure is needed.

- It will be between 200 – 1000atm (20- 100MPa) since the cost is considered.

1 haber process6
1.Haber Process
  • How can we increase the efficieny of production of ammonia?

4. Min amount of waste:Remaining N2 and H2 are recycled.

- 20% of N2 and H2 mixture is converted to ammonia.The remaining N2 and H2 mixture isn’t wasted. The mixture of N2 , H2 , and NH3 are coolled down until all NH3 liquifies. NH3 is separated & N2 and H2 are recycled.

1 haber process9
1.Haber Process
  • Ammonia is used in obtaining HNO3, some fertilizers, and nylon.
2 contact process
2.Contact Process
  • Sulphuric acid is produced in industry by first oxidising sulphur dioxide gas (SO2) to sulphur trioxide (SO3):
  • The reaction is exothermic, and results in a reduction in volume. In practice, a temperature of about 450 °C and a pressure of 100-200 kPa are used.
  • A catalyst, vanadium pentoxide, V2O5, is used, thus increasing the rate of the reaction at the relatively high temperature used.
2 contact process11
2.Contact Process
  • How to increase the efficiency of the rxn?
  • 1. high Pressure is needed.

- Excellent conversion is obtained with only about 2 atm which is required to obtain the flow rate of the gases in the reactor.

2 contact process12
2.Contact Process
  • How to increase the efficiency of the rxn?
  • 2. using pure oxygen instead of the air.
2 contact process13
2.Contact Process
  • How to increase the efficiency of the rxn?
  • 3. lower temp is needed.

- However, the temp cannot be too low.Otherwise, the process will be too slow.A compromise temp is chosen: 700-800 K.

2 contact process14
2.Contact Process
  • How to increase the efficiency of the rxn?
  • 4. finely grinded catalyst can be used.
2 contact process15
2.Contact Process
  • How to increase the efficiency of the rxn?
  • There are many converters sued for this process, making the initial temp high so as to increase the rate of the rxn but when the rxn is about to reach the equilibrium, the converters make the temp low so as to increase the yield.The resultis well over 90 %coversion to SO3.
2 contact process16
2.Contact Process
  • How to increase the efficiency of the rxn?
  • After the absorbance of SO3, the gases are passed through another converter to separate SO2 so that it won’t be released into the air.
2 contact process17
2.Contact Process
  • The obtained SO3:
  • SO3 (g) + H2O(l)  H2SO4(l)
  • Sulfuric acid is used in many areas: manufacture of fertilizers,polymers, detergents,paints, car batteries, etc.
  • The annual usage of sulfuric acid of a country shows a good extent of chemical industry of that country.
question 1
Question 1

Two gases A and B in a container at a constant temperature, T, and pressure, P, reach equilibrium after a time t1 s. They react according to the reaction

A + B C (ΔH < 0)

The diagram shows the change in the concentrations [X] ofA, B and C with time t. What stress is applied at time t = t2 s?

A) [A] is increased at constant P and T

B) T is increased at constant P

C) P is decreased at constant T

D) [B] is decreased at constant P and T

E) [C] is increased at constant P and T

answer
Answer
  • The stress is a sudden increase in [A] at constant pressure and temperature. Applying Le Chatelier's Principle, this must cause a shift of the equilibrium to the right.
  • A shift in the equilibrium to the right results in a decrease in [B] (since B is used up to react with A) and a consequent increase in the concentration of the product C.
question 2
Question 2

Which set of conditions will optimize the yield of ammonia in the Haber process, which takes place according to the reaction below?

N2(g) + 3H2(g) 2NH3(g) (ΔH < 0)

A) High temperature and low pressure

B) Low temperature and high pressure

C) Low temperature and low pressure

D) High temperature and high pressure

answer21
Answer

Low temperatures (since ΔH < 0)

and high pressures (since a decrease in volume will occur) will favour the formation of NH3.

references
References
  • http://www.chem.purdue.edu/gchelp/liquids/vpress2.html
  • http://intro.chem.okstate.edu/PLE482701/ExpertVaporPressure.html
  • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swf
  • http://ibchem.com/IB/ibsyllabus-2009.htm
  • http://www.physchem.co.za/OB12-che/chatelier.htm
  • http://www.chem-toddler.com/index.php