CHEMICAL REACTOR CHARATERIZATION GOALS Outline basic concepts Review reaction chemistr Develop basic definitions of performance Identify important reactor variables o Review reaction thermodynamics /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 1 CHEMICAL REACTOR CHARATERIZATION GOALS: u Outline basic concepts u Review reaction chemistry u Develop basic definitions of performance u Identify important reactor variables u Review reaction thermodynamics
PURPOSE OF A CHEMICAL REACTOR The purpose of a chemical reactor is to convert less desirable feed components more desirable output components. Q Convert a cheap raw material into a more valuable products, e.g., natural gas into ammonia, ethylene into polyethylene, etc Convert hazardous compounds into ones that are environmentally benign, e.g., hydrogen sulfide into sulfur, carbon monoxide into carbon dioxide. PCB's into C02 H20 and HCl /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 2 PURPOSE OF A CHEMICAL REACTOR The purpose of a chemical reactor is to convert less desirable feed components into more desirable output components. uConvert a cheap raw material into a more valuable products, e.g., natural gas into ammonia, ethylene into polyethylene, etc. uConvert hazardous compounds into ones that are environmentally benign, e.g., hydrogen sulfide into sulfur, carbon monoxide into carbon dioxide, PCB’s into CO2, H2O, and HCl
CHEMICAL REACTIONS o a chemical reaction is an exact recipe for converting raw materials into products or byproducts o The key concept is that of the stoichiometric coefficient o The stoichiometric coefficient ai specifies the mols of the ith component produced per mol of the jth reaction. Reactions take place in mols, not mass!! /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 3 CHEMICAL REACTIONS u A chemical reaction is an exact recipe for converting raw materials into products or byproducts u The key concept is that of the stoichiometric coefficient u The stoichiometric coefficient aij specifies the mols of the ith component produced per mol of the jth reaction. u Reactions take place in mols, not mass!!
EXAMPLE #1 CH4+202->C02+2H20 CH4+11202-C0+2H20 i Componen CH4 02 2-1.5 C02 CO 5H20 22 /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 4 EXAMPLE #1 1) CH4 + 2 O2 --> CO2 + 2 H2O 2) CH4 + 1 1/2 O2 --> CO + 2 H2O i Component ai1 ai2 1 CH4 -1 -1 2 O2 -2 -1.5 3 CO2 1 0 4 CO 0 1 5 H2O 2 2
CONVERSION AND SELECTIVITY o Conversion is that fraction of component entering a reactor that is converted to products and byproducts o Conversion is generally based on one or more independent key components of primary interest in the reaction system o The selectivity of a key component with respect to a specified product is the fraction of that component converted to the specified product divided by the total conversion of the key component. /2099 Chemical reactor Characterization 5
9/20/99 Chemical Reactor Characterization 5 CONVERSION AND SELECTIVITY u Conversion is that fraction of component entering a reactor that is converted to products and byproducts u Conversion is generally based on one or more independent key components of primary interest in the reaction system u The selectivity of a key component with respect to a specified product is the fraction of that component converted to the specified product divided by the total conversion of the key component
EXAMPLE #2 Reactor material balance Mols/ hr in Component Feed Effluent Delta CH4 10020 00 02 20050 -150 N2 400400 C02 CO 20 H20 0160 160 /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 6 EXAMPLE #2 Reactor Material Balance: Mols/hr in Component Feed Effluent Delta CH4 100 20 -80 O2 200 50 -150 N2 400 400 0 CO2 0 60 60 CO 10 30 20 H2O 0 160 160
EXAMPLE #2(Contd CONVERSIONS CH4:(60+20)/00=0.80or80% 02:(120+30)200=0.75075% SELECTIVITES CH410C02:6080=0.750r75 CH4t0CO:20/80=0.250r25% Note: The sum of the selectivities for a given key component must sum to 1.0 or 100% CH4toH20:(60+20)/80=l.00r10% 02toCO2:120/50=0.8or80% 02t0CO:30150=0.2or20% /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 7 EXAMPLE #2 (Cont’d) CONVERSIONS CH4: (60 + 20)/100 = 0.80 or 80% O2: (120 + 30)/200 = 0.75 or 75% SELECTIVITIES CH4 to CO2: 60/80 = 0.75 or 75% CH4 to CO: 20/80 = 0.25 or 25% Note: The sum of the selectivities for a given key component must sum to 1.0 or 100%. CH4 to H2O: (60 + 20)/80 = 1.0 or 100% O2 to CO2: 120/150 = 0.8 or 80% O2 to CO: 30/150 = 0.2 or 20%
TYPICAL CONVERSION VS SELECTIVITY 08 ≥0.6 e0.4 02 0 02040.60.8 Conversion /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 8 TYPICAL CONVERSION VS SELECTIVITY 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 Conversion Selectivity
SERIES REACTIONS Ethylene glycols from Ethylene oxide(eo and h20 Series form: 1 C2H40 (EO)+ H20 -> C2H602(mono ethylene glycol 2)C2H602+ C2H40 - C4H1003(di-ethylene glycol 3)C4H1003+ C2H40-> C6H1404(tri-ethylene glycol Convert to parallel forms C2H40+H20->C2H602(MEG) 1)+2)2C2H40+H20->C4H1003(EG 1)+2)+3)3C2H40+H20->C6H1403(TEG 9/2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 9 SERIES REACTIONS Ethylene Glycols from Ethylene Oxide (EO) and H2O: Series form: 1) C2H4O (EO) + H2O --> C2H6O2 (mono ethylene glycol) 2) C2H6O2 + C2H4O --> C4H10O3 (di-ethylene glycol) 3) C4H10O3 + C2H4O --> C6H14O4 (tri-ethylene glycol) Convert to parallel form: 1) C2H4O + H2O --> C2H6O2 (MEG) 1)+2) 2 C2H4O + H2O --> C4H10O3 (DEG) 1)+2)+3) 3 C2H4O + H2O --> C6H14O3 (TEG)
RECOMMENDED PROCEDURE o Convert reactor requirements from a mass basis to a mol basis Convert any series reactions to parallel reactions Divide all reactions throug gh by the stoichiometric coefficient of the key component Calculate the reactor based on the conversion and selectivity specifications Convert from a mol basis back to a mass basis Check the reactor material balance(bs in=lbs out /2099 Chemical reactor Characterization
9/20/99 Chemical Reactor Characterization 10 RECOMMENDED PROCEDURE u Convert reactor requirements from a mass basis to a mol basis u Convert any series reactions to parallel reactions u Divide all reactions through by the stoichiometric coefficient of the key component u Calculate the reactor based on the conversion and selectivity specifications u Convert from a mol basis back to a mass basis u Check the reactor material balance (lbs in = lbs out)
