thermal cracking of ethylene, propylene and light hydrocarbon

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acetylene then acetylene. B. :+Xl_gne crac+g In CoWete amlogy with propylene cracking, the two major initial reactions are : % C2fijo+C 2FI 4 -+ C~EI?O -+ c 4M 6 +HO ~ ( rno1-lsec-l) 1 7 107 ~(~ccal/mol) 7.3 8) c 2H 3 o+i:l--tC k 9 2H 2 +Ho+l,i 5 loq1 31.5 9) The vinylradical acts as a p radical. in 8) and as a 9). The kinetic parameters of Z;'nese reactions were extensive literature survey ( 1 1,15,16,17). The border line between the two zrea's is now given hy : k8(C21130)(C2H4) = k (C H O )(l.i) 9 2 3 This line is the flit1 line in Figure 18. ';;itti a second orcier initiation 1i.ke 2C H 422I.i- "+C21150 and a teir;iinatj.on involving two vinylradicals ;i2&Ii3 -+ .? , !C4Hg), an order of 2 is predicted for Conditions in the polymerization zone and a.n order of 1 for conditions in the dccoi~iposition zone. Si1:lon and Iijaclc (1 5) and Silcocks (1 8) observed seconci order kinetics, while l.:olera and Stuhbs (16) found second order 1cineti.c.s in the region 5 of Fi,mre 18 and first order kinetics in region TI, in agreement with tie proposed border line. R.m.uzi's data (11 ) ivhi.cli arc located in the transition area lead to an order of 312 for tiic ~:lolial. disa?xarrr.nc:e reaction. The pilot plant experiinento cover the transition zone. The order !ea.s shown in 'I'al:~lea 4 and 6 to evolve fron! 1 .6 to 1 .2 as the temperature is increased and the activation eiiergy from 40 to 2.boIit 75 kce?.l/iilol. I ' J?'Iie pol.yilir~i.iarttion can also lie of a J!lOleCILlar nature : .A(I mol-' sec-l) :,'(1cca,l/rnQl) iter C,ii +I ,'jC I L ---> polymer r 4 4 3 107 27 19 IC) Th.e ratio of the ra.c?ica.l. reaction and molecular condensation rates was ca3.cula.ted fron 2.n isotlierraal. non cteady state radi.ca1 siimlation of the ethylene experiinents by Sunderan & PToment (IO), to be 71 at 80GV and 1.; conversion, 15 at OOO°C and 3:~ conversion ana 10 at 825°C and 8 ;i conversion. It follows that molecular condensation cannot be neglected a.t 8CO°C and higher. This explains vlhy the experi.inenta1 Cg+ frsction was SO stroiicly correla.ted aitli the temperature. In propylene crrtcitiiie the ratios of the rates of the radical po1yl;ierisation and the moleculcir conderisation at OGCV would Le of the ordcr of IC00 because the allyl rzdical is hich and butadiene is low. It is clear also froiii Piwre 16 for ethylene ax1 from Figure 17 for propylene that tile influence of the pnr-tial and total pressure on fne order anci activation encrt27 vrill be inore or less pronounced depending u?on the distance frnrn the border line. The higher activation enerzies Given in lnbles 6 and 7 for the conditions of the classes 2, 4 and, 5 may be related to t Pinally, il; ShOii.ld be added that even less tila (1.2 wt ,:, in the etiiyleiie feed, the initiation reaction C 11 i2CI11° cannot lje ne!:lecterl, as concluded already by 2 6 1:m~ugi (I I ) unc~ BY yowell and liartin (20) . 141
From the mechanistic point of view the initiation then becomes of first order and the order of the global disappearance should vary between 3/2 and 1/2. On the other hand, the molecular reactions vtill increase the overall order. All these trends substantiate the -rariation of the order from 1.6 to 1.2 observed in the present viorl;. k n Pt R r T VE X Y z Y b E Y Notation -1 frequency factor sec or 1 rno1-lsec-l activation energy kc a1 /mol concentration IUOl/l concentration, total hydro- carbons molar flow rate of the craclced coaiponent at the inlet rate Coefficient order of reaction lJOl/l mollsec sec-’ or 1 mol-’ sec-’ total pressure atm.abs. gas constant kc a1 /mol ‘C rate of reaction mol/l sec temperature OK or ‘C equivalent reactor volume 1 conversion selectivity mol/nol tube length rn mol ratio mol/mol dilution rat io inol steam/mol hydrocarbor. expansion factor mol products/mol hydrocarbon cracked mol fraction mol /mol ethane progylene mixture initial value total mean Subscrints Table captions Table 1 : Xthylene cracking. Influence of the total pressure and the partial pressure of ethylene on the yields of the dj ffercnt groducts. Table 2 : Propylene craclrint;. Influence of the total pressure and the pnrtial pressure of propylene on the yields of the different products. Table 3 : Effect of the addition of various colnponcnts on the rate coefficient €or the cracking of ethane, propane, n-butane , i -butrine and propylene. 142 rn m m
Page 1 and 2: Thermal cracking of ethylene, propy
Page 3 and 4: TABLS 1 Influence of the partial pr
Page 5 and 6: * The-es_ulval,en4_reac4or_volwne_c
Page 7: 5. Decomposition and pol.wnerizatio
Page 11 and 12: 7) Froment G.F., Van de Steene B.O.
Page 13 and 14: .l 2 I u 1 CLASS 1 0 CLASS 2 A CLAS
Page 15 and 16: N u . I? Y - CLASS 1 0 CLASS 2 A CL
Page 17 and 18: CLASS 1 CLASS 2 CLASS 3 CLASS L CLA
Page 19 and 20: CLA5S 1 0 CLASS 2 A I,LA-\sS 3 + CL
Page 21 and 22: CLASS 1 0 CLASS 2 a CLASS 3 + CLASS
Page 23 and 24: SE 1 .a .6 .4 .2 a ECTl V IT Y Figu
Page 25 and 26: -Nb 3 -1 2 1 0 -2 ( Figure 14. I I
Page 27 and 28: I Figure 16. TERNARY MIXTURES N.BUT
Page 29: 2 , 2 D ECOM PO S I T ION ZONE .. .

thermal cracking of ethylene, propylene and light hydrocarbon

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