6 mass transfer on catalyst the gasliquid reactants

This preview shows page 19 - 28 out of 47 pages.

6
Image of page 19

Subscribe to view the full document.

Mass Transfer on Catalyst The gas/liquid reactants on solid catalyst 1. Reactants transfer to the boundary 2. Reactants into the porous 3. Absorb on the active sites on catalyst 4. Reactions happen 5. Products desorption 6. Products diffuse out from porous 7. Products diffuse out from film to the bulk 20
Image of page 20
Reaction Analysis Example – Process Safety Which reaction is more dangerous? Endothermic or Exothermic? Runaway reaction: Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. Heat management in reactor design Dilution solution or carrier gas …… 21
Image of page 21

Subscribe to view the full document.

Reaction Analysis Example – Process Safety Avoid toxic chemicals in reaction routes Bhopal disaster, 1984, methyl isocyanate (MIC) gas release, 3787 deaths (video) Reaction process safety design: avoid MIC in reaction route: 1-naphthol + phosgene naphthyl chloroformate Naphthyl chloroformate + methylamine urethane carbamate 22
Image of page 22
Reactor Synthesis Objectives Screening and selection of the best reactor type for the reaction under consideration What are the desired reactor attributes or characteristics? Which reactor type will provide the best performance while meeting all the process constraints? Other factors: phase distribution; flow pattern; mixedness; heat management; Catalyst; Economics; Operation; Safety, etc. e.g. catalyst size 2~5 mm. Gas distribution. Pressure drop. Mechanical strength. 23
Image of page 23

Subscribe to view the full document.

Reactors Types – Variety of Choices 24
Image of page 24
Basic Reactor Types Batch Semi-batch CSTR (Continuous- stirred tank reactor) Plug flow (Plug- flow reactor) A, B A B A, B A, B 25
Image of page 25

Subscribe to view the full document.

Example Reactor Concentration Profiles A + B P P + B X A B P X time A B P X time A B P X residence time A B P X time Batch Semi-batch CSTR PFR Match the concentration profiles to the reactor type 26
Image of page 26
How to Select Reactor Type - CSTR vs. PFR CSTR PFR Reactants have gas NO. (low residence time) YES. (hydrogenation) Reactants/products have solid YES. (more robust for solid) NO. (plug the tube) Solid catalyst with low deactivation rate OK. But the flow pattern within the catalyst is not ideal YES. (fixed bed) Solid catalyst with high deactivation rate YES. Easy to stir frying catalyst (turbulent, sprout reactor) OK. But need high cost reactor (moving bed, fluid bed) Products have gas YES. (urea to ammonia) YES.(ammonia synthesis) Need mixing of liquid YES. (add agitator, but difficult for high pressure) OK. (need flow path design) 27
Image of page 27

Subscribe to view the full document.

Example: CSTR The irreversible reaction A B is carried out in a continuous-stirred tank reactor. The inlet and outlet flow rates are 4.0 m3/hr, with an inlet concentration of A to be 1.2 kmol/m3. The reaction is first order, with reaction rate constant k = 5.0 hr-1. Initially, the tank contains 5.0 m3 of solution with a concentration of A to be 0.6 kmol/m3. Calculate the outlet concentration of A after 0.6 hr.
Image of page 28
You've reached the end of this preview.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern