KGT 00 Kemisk Reactionsteknik I, 5p - KGT 00 Chemical Reaction Engineering I, 5p KGT 00 Kemisk Reactionsteknik I, 5p - KGT 00 Chemical Reaction Engineering I, 5p Instructors KGT 00 Kemisk Reaktionsteknik I, 5p KGT 00 Chemical Reaction Engineering I, 5p Welcome Prof. Jonas Hedlund - Lectures Dr. Göran Olofsson - Lectures Lic.Eng. Mattias Grahn - Tutorial sessions M.Sc. Alessandra Mosca Tutorial sessions and Laboratory exercise General Course Topics:.Numerical methods and Material balances.conversion and simple reactor design equations 3.Rate laws and stoichiometry 4.Isothermal reactor design 5.Pressure drop and unsteady-state reactor operation 6.Selectivity and multiple reactions 7.Nonisothermal reactor design 8.Multiple steady-states and bifurcation analysis Course Literature: Elements of Chemical Reaction Engineering, 4th Edition H. Scott Fogler Full IT support: http://www.ltu.se/web/pub/jsp/polopoly.jsp?d59 Parts of Course: It is primarily a knowledge of chemical kinetics and reactor design that distinguishes the chemical engineer from other engineers. H. Scott Fogler, Professor of Chemical Engineering, University of Michigan. Lectures. Tutorial sessions (räkneövningar). Assignment problems Laboratory exercise. Exam. KGT 00 Kemisk Reactionsteknik I, 5p - KGT 00 Chemical Reaction Engineering I, 5p 3 Introduction to Chemical Reaction Engineering - 4 Introduction to Chemical Reaction Engineering Date Pass Activity, Teacher Literature 9/ 3. Introduction and numerical methods, Jonas Lecture notes 0/ 4. Material balances, Jonas Lecture notes 3/. Material balances, Jonas.-.4additional 7/ Tutorial Session, Topic, Alessandra Problems 7/ 3-4 Computer Lab Matlab tutorial, Mattias Matlab tutorial 3/ Tutorial Session, Topic, Alessandra Problems 3/ 3. Conversion and design equations, Jonas.-.5 / 3 Tutorial Session, Topic, Alessandra Problems / 3 3. Rate laws and stoichiometry, Jonas 3.-3.4 3/ 4 Tutorial Session, Topic 3, Mattias Problems 6/ 4. Isothermal reactor design, Jonas 4.-4.3 7/ - Computer Lab Matlab tutorial, Mattias Matlab tutorial 7/ 3 Tutorial Session, Topic 4, Mattias Problems 0/ 3-4 Laboratory exercise, group &, Alessandra Lab. comp. 3/ Tutorial Session, Topic 4, Mattias Problems 4/ -3 Laboratory exercise, group 3&4, Alessandra Lab. comp. 5/ 3 5. Pressure drop and unsteady-state, Göran 4.4-4.7additional 7/ 4 Tutorial Session, Topic 5, Mattias Problems 0/ 6. Selectivity and multiple reactions, Göran 6.-6.6 / 3 Tutorial Session, Topic 6, Mattias Problems 4/ 7. Nonisothermal reactor design, Fredrik 8.-8.3,8.7 4/ 3-4 Laboratory exercise, group 5&6, Alessandra Lab. comp. 7/ 7. Nonisothermal reactor design, Göran 8.-8.3,8.7 8/ 7. Nonisothermal reactor design,göran 9.-9.,8.4 /3 3-4 Tutorial Session, Topic 7, Mattias Problems 6/3 8. Multiple steady-states, Göran 8.6 7/3 4 Tutorial Session, Topic 8, Mattias Problems 0/3 3 Tutorial Session, exam consultation, Mattias Assignments: Assignment # 3 4 Topic - 3-4 5-6 7-8 Chemical Reaction Engineering Typical questions that CRE may answer: Is a batch or a continuous process preferred? What kind of reactor should be used? How large reactor is necessary to produce wanted amount? What factors influence the yield? How is the process optimized? How should the process be controlled? How is the reactor affected by a change in the operating conditions? KGT00 Chemical Reaction Engineering I, 5p gives the fundamentals. KGT003 Chemical Reaction Engineering II, 5p, gives deeper understanding.
Introduction to Chemical Reaction Engineering - 5 Some chemicals, plant sizes and waste produced: Introduction to Chemical Reaction Engineering - 6 Chemical reactors: Category Plant capacity Price Waste/product Petroleum 0 6-0 8 tons/y $0./lb 0. Refining Commodity Chemicals 0 4-0 6 0.- -3 Fine Chemicals 0-0 4-0 -0 Thermodynamics Kinetics Fluid flow CHEMICAL REACTOR Mass transfer Heat transfer Foods -50 Materials 0- Pharmaceuticals 0-0 3 0-0-00 Design CHEMICAL PROCESS Process control Chemical processes A generic flow diagram of a chemical process: Economics Raw Materials Separation Process Chemical Reactor(s) Separation Process Products By-products Chemical process: Natural Gas Methane Syngas Methanol Acetic acid Acetylsalicylic acid. Numerical Methods and material balances - 7 b Integration: S f ( x) dx a Analytical solution SF(b)-F(a), where F is a primitive to f. Numerical solution, trapeze formula S h(0.5*f a f f 0.5*f b) The function values are calculated at equal distance h. Example π S sin( x)dx Analytical solution S-cos(π)cos(0) 0 Numerical solution, with hπ/4 X SINx TRAPZ 0 0 0 0,785398 0,70707 0,7070678,570796,35694 0,70707 0,7070678 3,4593 3,3E-5,6557E-5 Sum*h,90 S,90 With hπ/00, S,9998. Numerical Methods and material balances - 8 Identical solution using Matlab: In the command window, write the following (press return after each command): clear X 0:pi/00:pi; Ysin(X); Z trapz(x,y) The Matlab will answer: Z.9998 Ordinary differential equations (ODE) Example (first order ODE): y 0. 5( x y) Suppose that we are interested of the solution for x4. A few solution curves: y(0) (boundary condition, bivillkor), selects only one of these solutions Analytical solution (will not be considered here): 0 5x y e. x y(4) 3.389056 Eulers method:
. Numerical Methods and material balances - 9. Start at the boundary condition n0 (x n,y n), in this case (0,).. Calculate x n x n h and y n y n hy n 3. Increase n (nn) and go to until x4. For h: n x n y n y n 0 0-0,5 0,5-0,5 0,5 0,5 3 3 0,375 0,6875 4 4,065,535 Reducing h to half, also reduces the error to about half: h y(4) y(4) Analytical - y(4) Euler.065.3 0.5.96.4 0.5.58 0.8 0.00 3.385 0.004 It is possible to use Richardson extrapolations to improve the result, but it is also possible to use Excel or similar with small h.. Numerical Methods and material balances - 0 Matlab solution:. Save an m-file with the name example.m and the content: clear [X,Y] ode45('diffeq',[0,4],); plot(x,y). Save another m-file with the name diffeq.m and the content: function dydx diffeq(x,y); dydx0.5*(xy)-; 3. Write example in the command window and press Enter. Matlab will now run the m-file with the name example, which will run the built in ODE solver ode45 (also a m-file). Ode45 will create a matrix (the solution) with X values in the first column and corresponding Y values in the second. The plot command will draw a figure of the solution:. Material Balances -. Material Balances Before we start designing reactors, we have to consider Material Balances (MB). MB:s can be very useful in order to calculate data which can not be measured directly. MB:s are also an essential part in reactor design. Material balances are made over a selected boundary:. Material Balances - If no generation or consumption occurs, i.e. no chemical reaction: Accumulation input - output If the is at steady state as well (accumulation0): flow streams System System boundary Output flow streams output Choice of a Basis for Calculations: Start by choosing basis for calculations, it could be: Material balance: A unit of mass/mole (solid or liquid s) A unit of volume (gas s) A unit of time (continuous processes) to Production output from Accumulation Arrival at the same solution independent of basis Poorly chosen basis can make calculations unnecessarily difficult. Units can be /time, or kg. Use the most convenient units. Problem analysis: Problem analysis increase the clarity (överskådlighet) of a MB problem and thus simplify the solution. Analyse the problem by determine the degrees of freedom: Degrees of freedom (number of independent flow variables) - (number of independent balance equations) (number of specified independent flow variables) (number of help equations). Material Balance on a can be for: Degrees of freedom 0 for a correctly specified problem. Total mass (no generation or consumption if no nuclear processes) Total (ery useful in CRE) Mass of a chemical compound Moles of a chemical compound (ery useful in CRE) Mass of an atomic species Moles of an atomic species (ery useful in CRE)
. Material Balances - 3 Example : Titanium dioxide TiO is a white hiding pigment used heavily in the paint and paper industries. A pigment plant is to produce 000 kg h - dry TiO product. An intermediate stream consisting of TiO precipitate suspended in an aqueous salt solution, is to be purified of salt so that the final product contains, on a water-free basis, at most 00 ppm (mass basis) of salt. The salt removal is to be accomplished by washing the precipitate with water. If the raw pigment stream contains 40% TiO, 0% salt and the rest water (all mass %) and if the washed pigment is, upon settling, projected to consist of about 50% (mass) TiO solids, what will the composition of the waste wash water stream be? Determine degrees of freedom for this problem, is it solvable?. Material Balances - 4 Example : Propane is burned with 5% excess air. How many of air per second are needed to produce 00 of exhaust gas per second? Calculate the degrees of freedom and solve with three different bases for calculation. C 3H 8 5O 3CO 4H O Example 3: Solubility of barium nitrate at 00 C is 34kg/00kg water, at 0 C it is 5kg/00kg water. If you start with 00kg barium nitrate in a saturated solution at 00 C, how much precipitates after cooling to 0 C? Calculate the degrees of freedom to verify that the problem is correctly specified. Bypass flow: Reactor Possible boundaries Example 4: A process removes radioactive strontium (Sr 90 ) from milk by filtration through a bed of CaHPO 4. The process removes all Sr but also unfortunately removes 97% Ca from the milk. Milk containing 4.85 0-4 kg Sr/m 3 and 0-3 kg Ca/m 3 is fed to the process. If the milk must contain at least 5 0-5 kg Ca/m 3, what will the Sr concentration be? Process: Milk CaHPO 4 bed Fresh Feed. Material Balances - 5 Recirculation and purge: Reactor Purge Recycle Example 5: Methanol synthesis is based on the reaction between CO and H : CO 3H CH 3OH H O Separation Product. Material Balances - 6 Example 6: A stoichiometric mixture of H and N will be produced for ammonia synthesis (75% H,5% N ) by letting generator gas (78% N, 0% CO, % CO ) react with water gas (50% H, 50% CO). The reaction shall be carried out such that all CO is consumed because CO poisons the ammonia synthesis catalyst. The generator gas and water gas will react with steam so that CO and H react by the reaction: CO H 0 CO H (water gas shift reaction) All water is consumed and CO is removed in a scrubber. Calculate the ratio between the feeds of generator gas and water gas and between generator gas and steam. Process: CO and H are fed stoichiometrically to the process and the feed also contain 0.5 vol.% inert gas. 60% of CO and H are converted in the reactor to CH 3OH. The concentration of inert in the reactor feed is vol.%. Calculate (a) mol gas recycled per mol fresh feed and (b) mol gas purged per mol fresh feed. 78% N 0% CO % CO Process 4 CO Process: 50% H 50% CO 5 75% H 5% N 3 CO H I F B C A Reactor Separation CH 3OH, H O D P CO,H,I R CO,H,I H O
. Material Balances - 7 The rate of reaction A chemical reaction occurs when molecular species lose their identity and take a new form: Types of reactions: Decomposition (sönderdelning) A B C Combination (kombinering) B C A Isomerization (isomerisering) A B Reaction occurs at a certain rate or speed; If A B (decomposition). Material Balances - 8 r A is dependent on: species concentration temperature pressure type of catalyst Observe! r A may not be the same at every position in the reactor. Forms of the reaction rate equation (note that r A < 0 and k > 0): - r A kc A - r A kc A r B r A rate of formation of A per unit time per unit volume of reactor rate of formation of B per unit time per unit volume of reactor mol A s (m 3 reactor) mol B s (m 3 reactor) < 0 > 0 k CA - ra k C A dc A Note that ra is a very confusing definition of reaction rate and should be used with great care (or not at all). It is only valid for a constant volume batch reactor (consider for instance a steady state reactor). The definitions above can be used for all kinds of reactors. The General Mole Balance then - r A r B (-*(rate of formation of a) rate of formation of b) Rate can be expressed based on different units of size: 0 System r A rate of formation of A per volume reactor Mole balance on species j at any time t; r A rate of formation of A per mass of catalyst r A rate of formation of A per surface area of catalyst to Production output from Accumulation time In prod out acc. Material Balances - 9 O P j where N j is number of of j in at time t. Can express P j in terms of reaction rate:. Material Balances - 0 Batch Reactor 0 0 rjd rj (No spatial variation if well mixed) Then P j r j time time volume olume dnj rj Usually is constant Continuous Stirred Tank Reactor (CSTR) Only true if r j is constant throughout volume, i.e. if concentration, temperature, etc. are constant. If r j varies with : P j M i r ji i If divided into M infinitesimal volume elements (d) then Pj rjd Thus the general mole balance equation for any reactor becomes: Usually operated at steady state: 0 Also perfectly mixed (no spatial variation): rjd rj Then O r j 0 O rjd Fj0 Fj r j 0 The CSTR is modelled so that the concentration in the outlet stream is the same as inside the tank. C j υ υ is volumetric flow rate (volume/time) r j function of C j etc. Conc. C j0 C j Position
. Material Balances -. Material Balances - Tubular Reactor d rj d 0 Plug flow, no mixing If the reactor has constant cross-sectional area (A); Operated at steady-state: 0 then O rjd 0 d A dz dfj A rj dz END OF TOPIC Modelled so that concentration and temperature are constant radially but varies axially throughout the reactor. Mole balance for an infinitesimally thin section of the reactor with volume d: 0 d d dz to Production output from Accumulation time Material balance over d: r j d ( d )