Study of C5/C6 isomerization on Pt/H-zeolite catalyst in industrial conditions

Transcription

1 Ovidius Univesity Annals of Chemisty Volume, Numbe, pp. -6, Study of / isomeization on Pt/H-zeolite catalyst in industial conditions Claudia Iina KONCSAG*, Ioan Alexandu TUTUN and Cistian SAFTA Ovidius Univesity of Constanta, Depatment of Chemisty and Chemical Engineeing, 4 Mamaia Blvd, 957 Constanta, Romania Abstact. This is an expeimental study of / isomeization on Pt/H- zeolite conducted in industial conditions. The goal of the wok was to find the kinetic paametes of the main isomeization eactions, by consideing the industial eacto as an ideal plug flow eacto. This assumption is fai, taking into account the high pessue and low linea velocity of the effluent in the eacto. The kinetic model can be used fo the pediction of isomeizate poduction and quality. Keywods: kinetic paametes, isomeization, LSRG. Intoduction The inceasing demand fo gasoline pool with high octane numbe, cost-effective and envionmentally sound, led to the development of new technologies but also to the impovement of old solutions, such as the isomeization of light staight un gasoline (LSRG [,, 3]. With the goal of maintaining the gasoline pool octane, without adding lead compunds and having in view the eduction of benzene concentation, the isomeization of light staight un gasoline- LSRG - is a vey attactive solution. Light naphtha cuts esult in good yield at oil pocessing, so a high quantity of impoved octane naphtha can be obtained. The banched molecules esulting in the pocess incease the octane numbe of the LSRG with appox. units. The esulting gasoline faction has a highe vapou pessue than the feed, so ignition will be impoved. The pesent study of / isomeization on Pt/H- zeolite was conducted in industial conditions. The goal of the wok was to find the kinetic paametes of the main isomeization eactions, by consideing the industial eacto as an ideal plug flow eacto. The yield and composition of obtained poducts in the pocess ae of highest impotance. The knowledge of the mechanism and a good model based on it, pedicting the poduction and the quality of the isomeizate is useful fo the poduction foecast of the industial unit.. Theoetical aspects Staight light un gasoline with boiling points ange of 7-7 o C is mainly composed of n-paafins : n-pentane and n-hexane. The main eactions ae pesented in Fig.. n-hexane nhexane n-pentane -Methyl,-Dimethyl i-pentane Fig.. Main eactions at the isomeization of / naphtha on zeolitic catalyst The seconday eactions with neglictible yield ae: hydogenation of olefins and hydocacking. The isomeization eactions occu on alumina o zeolites based catalyst. New catalysts ae bifunctional with metallic and acid centes [3], and the mechanism descibed in [4, 5] involves the following steps: o o 3-Methyl,3-Dimethyl ISSN-3-7 Ovidius Univesity Pess

2 C.I.Koncsag et al.,. / Ovidius Univesity Annals of Chemisty (, -6 ( 3.Dehydogenation: the n-paaffinic molecule is adsobed on a metallic cente and an olefinic molecule is fomed. Isomeization: the fomed molecule is tansfeed on an acid cente whee it gains a poton, the hydocabon chain is banched and the esulting i- Olefin eleases the poton 3. Hydogenation: the i-olefin is tansfeed back on the metallic cente whee it is fast hydogenated. The kinetics of the isomeization eaction depends on the catalyst type. Beme et al [6] consideed the main eactions as pseudo-fist ode eactions fo bifunctional catalyst NiH/NaY zeolite.othe authos found diffeent ode fo the main eactions. Spivey and Byant [7] modelled the isomeization on Pt/CaY zeolite with the Eq. and : = ( +.94 P P ( 34 H 366 PH C 6 ( +.4 PC 6 = ( Whee is the eaction ate [kmol/h], P, P and P H ae the patial pessue of C 5, C 6 and H espectivelly, in ba. In [8], Ahai et al found moe complicated equations fo the catalyst Pt/H zeolite whee the eaction ate of evey hydocabon depends on the patial pessue of all the othe compounds in the eacto. Also, Ahai et al poduced two sets of equations, one fo the tempeatue 6 o C and one fo the tempeatue 7 o C. The goal of this study was to find kinetic equations valid fo the Pt/H zeolite in the ange of unning paametes of the industial eacto, taking into account that the tempeatue vaies in naow limits. 3. Expeimental The expeiment was conducted in an industial eacto on Pt/H zeolite catalyst. The installation is pesented in Fig.. The paametes of the eacto wee collected duing a month. The main fluxes indicated in Fig. ae: - feed, -eciculated paaffins, 3- effluent and 4- isomeizate. The fluxes wee analysed by GC-FID daily and chomatogaphic data seved to calculate convesions and yields. The + n- paaffin content in feed vaied between 55-68% as seen in Fig.3. % (n C 5 + n C 6 in fe e d Day No. Fig.3. n-paaffin content in feed duing the test un The paametes of the eacto duing the test un ae pesented in Table : Table. Paametes of the isomeization eacto duing the test Paamete Unit Value (limits Reaction zone volume m 3 Flowate m 3 /h 9- Liquid Houly Space h Velocity (LSHV Aveage tempeatue in o C the eacto Pessue ba -4 Mola atio H /feed Results and Discussions The data collected in the test seved to calculate the convesion of Paaffin in the eacto (Fig.4. The convesion of nc 5 +nc 6 vaied between %. Since the catalyst was a pefomant one, the feed had the ecommended composition and all the paametes in the eacto wee those indicated by the designe, this low convesion should be due to the poisoning of the catalyst with H S pesent in the hydogen flow; usually, the H used in this pocess is esidual fom efiney.

3 4 Study of / isomeization.../ Ovidius Univesity Annals of Chemisty (, -6 ( 3 4 Fig.. The industial / isomeization unit.. - feed; -eciculated paaffins; 3- effluent; 4- isomeizate

4 C.I.Koncsag et al.,. / Ovidius Univesity Annals of Chemisty (, -6 ( 5 C o n v e s i o n, % Day No. Fig.4. The convesion of n-paafin in the eacto, duing the test The feed only contained n-paaffin, i-paafin and cyclo-paaffin, without aomatics. Based on ou expeimental data, a mathematical model is poposed (Eq.3 and 4, close to Spivey and Byant s model but even simplie: = k P P (3 H = k P P (4 H The meaning of the tems in Eq.3-4 is the same as in Eq.-. k and k ae the kinetic constants fo the C 5 tansfomation and fo espectivelly [kmol h - ba -3 ]. The goal of the wok was to find the kinetic paametes of the main isomeization eactions (k and k, by consideing the industial eacto as an ideal plug flow eacto. This assumption is fai, taking into account the high pessue and low linea velocity of the effluent in the eacto. So, the chaacteistic ecuation of the plug flow eacto (Eq.5: = c X A A τ A, (5 was customized fo the said eactions (Eq.6 and 7: = k X C 5 ( X τ (6 PC 5PH = k X C 6 ( X τ (7 PC 6PH In Eq. 5, τ is the esidence time in the eacto, A denotes the eactant (n o n, c A is the concentation of the eactant in the feed and X denotes the convesion (as faction. Equations (6 and (7 wee integated and the mathematical expession of k and k (Eq.8-9 esulted: k = /[τ. p.. p H (-X ] (8 k = /[τ. p. p H. (- X ] (9 The paametes k and k [ kmol h - ba -3 ] wee calculated fo each set of expeimental data and the mean value and elative eos wee detemined: k =.7 with a medium eo 6.5% and a maximum eo.%; k =.877 with a medium eo 6.% and a maximum eo 7.%; The eos ae acceptable. This conclusion was dawn taking into account that simila study [8] gave highe eos (medium eo.% and maximum eo 6.3% and, in geneal, in chemical engineeing studies, such eos ae fequent and acceptable. 5. Conclusions This expeimental study of / isomeization on Pt/H- zeolite conducted in industial conditions had the goal to find the kinetic paametes of the main isomeization eactions. The kinetic constants wee found with easonable eos. The kinetic model is valid fo the ange of paametes in the test peiod: tempeatue 6 C±3 C, LHSV=.99-. h, pessue -4 ba, H /feed mola atio:.-.7. This ange of paametes is tight but the industial pocess doesn t exceed it. The pactical esult of this study is that the kinetic equations poposed hee can be used fo the pediction of isomeizate poduction and quality.

5 6 Study of / isomeization.../ Ovidius Univesity Annals of Chemisty (, -6 ( 6. Refeences * addess: ckoncsag@univ-ovidius.o []. *** UOP Penex TM Pocess, 7 []. G.C.Andeson, R.R.Rosin and M.A.Stine, New Solutions fo Light Paafin Isomeization, UOP LLC Repot AM-4-6, 4 [3]. A.Coma Canos, J.M.Fontela Delgado and J.J. Lazao Munoz, US Patent 5,64,648, 993 [4]. A.Hollo, J.Hancsok and D.Kallo, Applied Catalysis A:Geneal, 9(-, 93- ( [5]. P.B.Weisz and E.W.Swegle, Science, 6, (956 [6]. H.Beme, W.P.Reschetilowscki, F.Vogt and K-P Wendladt, Studies in Suface Science and catalysis, 8, 3-38 (984 [7]. J.J.Spivey and Ph.A.Byant, Ind. Eng. Chem. Poc. Des. Dev. (4, (98 [8]. J.S.Ahai, K.Khosand, A.A.Hosseini and A.Fashi, Petolem&Coal, 48(3, 4-5 (6