化學工藝學Chapt_6 Hydrogenation and dehydrogenation process

1、Hydrogenation and dehydrogenation process一、一、Hydrogenation reaction types(1) Hydrogenation of double bond of unsaturated alkyne and alkene(2) Aromatic hydrogenation (3) Hydrogenation of the compound containing oxygen CH=CH2 C2H5C2H5CuNiSelectivity hydrogenationH24H2(4) Hydrogenation of the compound

2、containing nitrogen (5) Hydrogenolysis二、二、Dehydrogenation reaction types(1)Dehydrogenation of alkanes to produce alkenes, dienes and aromatics(2) Dehydrogenation of alkenes to produce dienes(3) Dehydrogenation of alkyl aromatics to produce alkenyl aromatics(4) Dehydrogenation of alcohols to produce

3、aldehydes and ketones6.2 General rules of hydrogenation, dehydrogenation reactions一、一、General rules of catalytic hydrogenation reactions 1. Thermodynamic analysisTable 6-1 Thermal effect value of hydrogenation reaction at 25 （1）Temperature H 0， T ，K P . KP is large in a wide temperature range, almos

4、t irreversible reaction. KP is large at medium temperature, KP decreases at high temperature, thermodynamics is dominant KP is large at low temperature, but KP deceases in the available temperature range, thermodynamics unfavorable, chemical equilibrium becomes a key factor. 20)ln(RTHdTKdPP（2）Pressu

5、re For hydrogenation reaction， n0， P ，Kp ，balance yield （3）hydrogen ratio A +H2 B H2 Advantages: conversion (X) increases, and it is favorable to remove reaction heat Disadvantages: concentration of product (yB) decreases, and separation difficult, a large amount of H2 cycle, large energy consumptio

6、n.2HABNyyyKXyyyKABHN22. Kinetic analysisFactors affecting the reaction rate has temperature, pressure, hydrogen ratio, and the structure of reactants. （1）Influence of reaction temperature Irreversible reaction： KP is large enough，T ， r, but T ，S (because side reaction activation energy is large as t

7、emperature increasing). H0 0，P ，r r n C6H5CH3C6H4(CH3)2C6H3(CH3)3 Comparison of hydrogenation rate for different hydrocarbon When the hydrogenation reaction independently proceeds on the same catalyst, their rate sequence is:When the hydrogenation reaction simultaneity proceeds on the same catalyst,

8、 their rate sequence is: Hydrogenation of the compounds containing oxygen RCHO R2CO； RCOOR RCOOH Hydrogenation of organic sulfides 3Hydrogenation catalysts (1) Metal catalysts Ni,Pd,Pt/Carrier (2) Skeleton catalysts (3) Metal oxide catalysts MoO3,Cr2O3,ZnO,CuO,NiO low activity, high reaction tempera

9、ture, anti-poisoning(4) Metal sulfide catalysts MoS2, NiS2, Co-Mo-S, anti-poisoning, low activity, high reaction temperature(5) Metal complex catalysts Ru, Rh, Pd, Ni, Co, Fe high activity, good selectivity, mild conditions, recovery difficult.二、二、General rules of catalytic dehydrogenation reaction1

10、. Thermodynamic analysis（1）Influence of temperatureEndothermic reaction H0The equilibrium constant increases, and equilibrium conversion increases with the reaction temperature increasing. （2）Influence of pressureThe equilibrium concentration of the products increases with decreasing total pressure.

11、 2Dehydrogenation catalysts Requirement for dehydrogenation catalysts:Good selectivity.The reaction can produce at low temperature.Good thermal stability of catalyst.No deactivation at high temperature. Good chemical stability.Enough mechanical strength.Good anti-coking and easy regeneration propert

12、ies.Cr2O3-Al2O3, Fe2O3-Al2O3 6.3 Synthetic ammonia preparation by nitrogen hydrogenation P ，T ， HR 0.5N2 + 1.5H2 NH3 -46.22KJ/mol (298K) 一、一、Reaction principle1. Reaction thermodynamics of ammonia synthesisThe reaction is exothermic reaction, and the reaction heat is related to the temperature and p

13、ressure285108961.14108987.25log5105. 18534. 0322.2250logTTTTKfH2-N2-NH3 system2 Influence factors on equilibrium concentration 25 . 12)1 ()1 (33mmPKyyyPINHNHTemperature、pressure、ratio of H2/N2, content of inert gas (1) T ，or P ，KP， (2) Ratio of H2/N2：m3， is the biggest； in fact, best value is m=2.68

14、 2.90 (3) inert gas in system, 3NHy3NHy3NHyy(H2)、y(N2)、y(NH3)、yi is mole fraction of H2、N2、NH3、inert gas (CH4 and Ar) in raw materials. m=yH2/ yN23. Reaction kinetics of ammonia synthesisInfluence of various factors on reaction rate:（1） P ， （2） Reversible exothermic reaction Top temperature（3）Influe

15、nce of H2/N2 ratio: Initial reaction：H2/N2=1.5， biggest H2/N2 ratio change to 3 with the reaction proceeding.3NHr3NHr（4）inert gas ， 3NHr4. Catalysts of ammonia synthesis（1）Catalyst composition Iron-based catalysts Before reduction FeO+Fe2O3 (Fe3O4) Al2O3: Structure type promoter can improve the stru

16、cture of reduced iron. K2O : Electron type promoter is favorable for the adsorption and activation of N2.（2）Catalyst reduction Fe3O4 -Fe Reduction temperature： Actual reduction temperature cannot exceed normal using temperature Water can produce in reduction reaction. Water vapor content in the outl

17、et gas cannot exceed 0.5-1.0g/m3 , and the reduction space velocity is higher than 1500030000h-1 H2、N2 mixture gas as reducing gas.reduced二、二、Selection of technological conditions1. Pressure P ，equilibrium conversion and reaction rate 2. TemperatureAmmonia synthesis reaction is reversible exothermic

18、 reaction, so there is the most appropriate reaction temperature (Top) The most appropriate temperature curve is affected by the equilibrium temperature, catalyst performance, the pressure, inert gas content and the internal diffusion (內(nèi)擴內(nèi)擴散散). 3. Initial composition of make-up gas （1）H2/N2 = 2.82.9

19、 Initial reaction ，the best H2/N2 = 1.5 With reaction proceeding, the best H2/N2 The best equilibrium ammonia content, H2/N2 = 3（2）It is not favorable for the chemical equilibrium and reaction rate when there is inert gas in the reaction system. Space velocity ，production capacity Space velocity ，Sy

20、stem resistance Cycle power consumption Low pressure method: space velocity 5000 -10000h-1 Middle pressure method: space velocity 15000 -30000h-1 High pressure method: space velocity 60000h-1 4. Space velocity 5. Catalyst particle size 三、三、Process flow and converter1. Process flow of ammonia synthes

21、isProcess flow of large-scale synthesis ammonia plant1-離心式合成氣壓縮機；2,9,12-換熱器；3,6-水冷器；4,7,8,10,15-氨冷器；5-水分離器；11-高壓氨分離器；13-氨合成塔；14-鍋爐給水的加熱器；16-氨分離器；17-低壓氨分離器；18-開工爐Typical ammonia synthesis loop arrangementsFlow sheet of an integrated ammonia plantFuelAirProcess airProcess steamNatural gasAmmoniaAmmoni

22、a synthesisAmmonia recoverySulfur removalPrimary reformingSecondary reformingPurge High pressure（10MPa） High temperature（400 500 ）2Ammonia synthesis converter 多層軸向冷激式氨合成塔多層軸向冷激式氨合成塔 Ammonia converter of multi-layer axial quench type 徑向多段冷激式氨合成塔徑向多段冷激式氨合成塔 Ammonia converter of radial multi-stage quen

23、ch type 內(nèi)部間接連續(xù)換熱式氨合成塔內(nèi)部間接連續(xù)換熱式氨合成塔 Ammonia converter with internal indirect continuous heat exchanger 多層軸向冷激式氨合成塔多層軸向冷激式氨合成塔Ammonia converter of multi-layer axial quench typeQuech gas (material gas)徑向多段冷激式氨合成塔徑向多段冷激式氨合成塔Ammonia converter of radial multi-stage quench typeFeed-effluent heat exchangerQ

24、uech gas (material gas)軸向徑向混合型氨合成塔軸向徑向混合型氨合成塔Ammonia converter of axial and radial mixture type6.4 Methanol synthesis一、一、Basic principle of methanol synthesisCO2+ 3H2CH3OH(g) + H2O(g)CO2+ 3H2CO+ H2OThe reactions are strong exothermic reactionsCO+ 2H2CH3OH催化劑催化劑Main reactionsSide reactins:2CO+ 4H2(CH

25、3)2O+ H2OCO+ 3H2CH4+ H2O 4CO+ 3H2C4H9OH + 3H2OCO2+ H2HCHOProducing hydrocarbon2CO+ 2H2CH4+ CO2CO2+ 4H2CH4+ 2H2O2CO+ 5H2C2H6+ 2H2OnCO+ (2n+1)H2 Cn H2n+2+ nH2OProducing alcohol2CO+ 4H2C2H5OH+ H2OProducing formaldehydeProducing etherOther carboxylic acids 、ester Reaction thermodynamics of methanol synt

26、hesisH0298K = - 90.8 kJ/mol1) P , T , H ;2) The change of the reaction heat is large with the pressure when the temperature is lower than 200 ; ;3) The change of the reaction heat is less with the pressure when the temperature is higher than 300, and the pressure is lower than 30MPa. In general, the

27、 reaction occurs at 20MPa, 300-400. 10 20 30 40 MPa25100200300400600- HTPReaction heat effect:Equilibrium constant:Low temperature, high pressure Methanol synthesis二、二、Catalysts for methanol synthesis1）Cr-Zn based catalyst（ZnO/Cr2O3）: high pressure catalyst Low activity，reaction at high temperature

28、and high pressure (590K-670K，25 -35MPa). 2）Cu based catalyst（CuO/ZnO/Al2O3）: low pressure catalyst High activity，reaction at low temperature and low pressure (500K-530K，5 -10MPa). Temperature, Pressure: relate to catalyst activity ZnO-Cr2O3: most favorable temperature about 380 ， 30MPahigh pressure

29、method； CuO-ZnO-Al2O3: 230-270 ,5-10MPalow pressure method Space velocity：influence on conversion and selectivity Cu-Zn-Al catalyst, space velocity 10000/h Cu-Cr catalyst, space velocity 2000040000/h Raw material gas components: According to stoichiometry (化學計量法化學計量法) H2/CO=2:1，in general hydrogen i

30、s excess，it is favorable for H2/CO=2.2-3.0。 The reaction heat can be decreased due to CO2 in raw material gas, and the methanol yield is the highest when CO2 content is 5%. The gas partial pressure and the conversion can be decreased due to the inert gas (N2 and CH4) in the reaction system, so the i

31、nert gas should be regularly removed. 三、三、Process conditions for methanol synthesis四、四、The process flow and reactor of methanol synthesisProcess flow sheet of methanol synthesisPurgecompressureRecycle gasSyngaspurgeLight components（H2,CO,CO2,CH3OCH3)Light ends Aldehyde, ester雜醇油雜醇油fusel oilAlcohol w

32、ith high boiling point、H2OMethanol synthesis process flow sheet by low pressure methodResidue light endsSeparatorFlash separatorRemoval light components towerRectification tower 6.5 Styrene preparation from ethylbenzene dehydrogenation Main reactionSide reactionsCatalysts of ethylbenzene dehydrogena

33、tion t OFe32 OCr32 一、一、Reaction conditions selecting for ethylbenzene dehydrogenation(1) Temperature The reaction of the ethylbenzene dehydrogenation is reversible endothermic reaction. Ethylbenzene conversion and reaction rate increase, and styrene selectivity decreases with temperature increasing.

34、Styrene selectivity increases, but reaction rate decreases, and ethylbenzene conversion decreases with temperature decreasing.Change of styrene yield with temperature has a maximum point, the corresponding temperature is the most appropriate temperature. (2) Pressure (3) Space velocity Low space vel

35、ocity, selective decrease. High space velocity, improve selectivity, but conversion is not high, the unreacted material gas must be recycled, energy consumption increases, so it is necessary to consider comprehensively so as to select the best space velocity. (4) Influence of catalyst particle size

36、The selectivity of dehydrogenation reaction decreases with thecatalyst particle size increasing.(5) Steam dosage 1. Process of multi-tubular and isothermal ethylbenzene dehydrogenation二、二、Process flow and reactor of ethylbenzene dehydrogenationMulti-tubular and isothermal reactor （列管等溫反應器）（列管等溫反應器）R

37、eactorCondenserOil-water separatorDistillation tower of EBRecovery tower of B and TSeparator of B and TRectification tower of styreneT: 580600，Conv. 4045，Sel. 9295， 2. Process of ethylbenzene dehydrogenation with adiabatic reactor Adiabatic process flow sheet of ethyl benzene dehydrogenationsuperhea

38、ted steamOil-water separatorDistillation tower of EBRecovery tower of B and TSeparator of B and TRectification tower of styreneCondenser720610660 Basic steps of process flow for ethyl benzene dehydrogenation to prepare styrene 1. Reaction types of hydrogenation and dehydrogenation, and general rules

39、 of hydrogenation and dehydrogenation.Hydrogenation reaction is reversible exothermic process, factors affecting the reaction rate have temperature, pressure, hydrogen ratio, and the structure of hydrogenation material.Dehydrogenation reaction is endothermic reaction H0, the equilibrium constant inc

40、reases, and equilibrium conversion increases with the reaction temperature increasing.Summary of key content2. Synthetic ammonia preparation by nitrogen hydrogenation, and equilibrium conversion and reaction rate increase with the pressure increasing, and ammonia synthesis reaction is reversible exo

41、thermic reaction, so there is the most appropriate reaction temperature, and the ratio of hydrogen to nitrogen (H2/N2) is 3 at the best equilibrium ammonia content, and the production capacity increases with space velocity increasing.0.5N2 + 1.5H2 NH3 -46.22KJ/mol (298K) Catalyst of ammonia synthesi

42、s is Fe3O4/ Al2O3/ K2OFe3O4 must be reduced to -Fe before using catalystAl2O3 is structure type promoter, it can improve the structure of reduced iron K2O is electron type promoter, it is favorable for the adsorption and activation of N2. Typical ammonia synthesis loop arrangements is as follows:3.

43、Basic principle of methanol synthesisCO2+ 3H2CH3OH(g) + H2O(g)CO2+ 3H2CO+ H2OCO+ 2H2CH3OH催化劑催化劑Main reactins:Side reactins:2CO+ 4H2(CH3)2O+ H2OCO+ 3H2CH4+ H2O 4CO+ 3H2C4H9OH + 3H2OCO2+ H2HCHOProducing hydrocarbon2CO+ 2H2CH4+ CO2CO2+ 4H2CH4+ 2H2O2CO+ 5H2C2H6+ 2H2OnCO+ (2n+1)H2 Cn H2n+2+ nH2OProducing

44、 alcohol2CO+ 4H2C2H5OH+ H2OProducing formaldehydeProducing etherOther carboxylic acids 、ester The reaction of methanol synthesis is exothermic reaction, low temperature and high pressure is favorable for the reaction. The reaction heat can be decreased due to CO2 in raw material gas, and the methano

45、l yield is the highest when CO2 content is 5%. The gas partial pressure and the conversion can be decreased due to the inert gas (N2 and CH4) in the reaction system, so the inert gas should be regularly removed. Process flow sheet of methanol synthesisPurgeFlow scheme of the ICI low temperature meth

46、anol process4. Main and side reactions for catalytic dehydrogenation of ethylbenzeneMain reactionSide reactionsEthyl benzene dehydrogenation reaction is endothermic reaction, ethyl benzene conversion increases, and styrene selectivity decreases with temperature increasing. Process flow sheet for eth

47、yl benzene dehydrogenation to prepare styreneethylbenzene dehydrogenation Multi-tubular and isothermal reactor of ethylbenzene dehydrogenationMulti-tubular and isothermal reactor （列管等溫反應器）（列管等溫反應器）Practice problems一、一、Write correct words or phrase in the brackets. .1. Hydrogenation reaction is rever

48、sible ( ) process, factors affecting the reaction rate have ( ), ( ), ( ), and the structure of hydrogenation material.2. Dehydrogenation reaction is ( ) reaction H0, the equilibrium constant increases, and equilibrium conversion increases with the reaction temperature ( ).3. Ammonia preparation by nitrogen ( ), and equilibrium conversion and reaction rate increase with the pressure ( ).4. Ammonia synthesis reaction is reversible ( ) reaction, the ratio of hydrogen to nitrogen (H2/N2) is ( ) at the best equilibrium ammonia content when ammonia is synthesi