INTENSIFICATION OF THE PERFORMANCE OF A GASOLINE ISOMERIZATION UNIT

Transcription

1 UDC INTENSIFICATION OF THE PERFORMANCE OF A GASOLINE ISOMERIZATION UNIT ИНТЕНСИФИКАЦИЯ РАБОТЫ УСТАНОВКИ ИЗОМЕРИЗАЦИИ БЕНЗИНА The objective of reducing the content of aromatic hydrocarbons in gasoline decide to participate in their structure oxygenates, alkylbenzene and isomerization and isomerization catalysts selection. Evaluation of selectivity and stability of catalysts carried out laboratory tests in a pilot plant. Development of methods of mathematical modeling to evaluate the effectiveness of the method of calculation of the catalysts. The object of this study is to compare IP 632 zeolite catalyst in mediumtemperature process conditions and C-2 zirconium catalyst in low-temperature process conditions. Systems of kinetic equations with the corresponding rate constants were selected for them. With the help of a mathematical model the component-wise isomerizate composition for the basic and design variants was obtained, with the increase in the product yield up to 98% and the decrease in the content of aromatic hydrocarbons down to minimum 0,02% with SI-2 catalyst. As a result, the expediency of zirconium catalyst application was proved. When selecting a formalized process diagrams taken into account the condition that the isomerization process proceeds with high selectivity, so hydrocracking side reactions are minimal. The octane number of the replacement of the catalyst is increased by 2.89 points. As a result, it was proved the usefulness of the zirconium catalyst. Thus, the possibility of solving the actual problem of reducing the aromatics isomerization catalyst to the selection method of mathematical modeling isomerization, zeolite, catalyst, mathematical model, aromatic hydrocarbons, benzene, octane number. In connection with toughening of requirements to the content of aromatic hydrocarbons (benzene) and sulfur compounds in commercial gasolines, gasoline stock arises, which can be solved through the modernization of the existing production, and mainly by the introduction of new processes and catalysts [1]. The main method to solve the problem of obtaining high-octane gasolines with a low content of aromatic hydrocarbons is the inclusion of oxygenates, alkylate and isomerizate in their composition. In the process of isomerization of pentane-hexane fractions, some isocomponents are produced with the octane characteristics allowing a noticeable reduction in the share of aromatic hydrocarbons in gasoline. Isomerizate is characterized by a research octane number of 83-86, low sensitivity, absence of aromatics and minimal sulfur content [2]. Currently, the choice of isomerization catalysts is limited by three types of processes: «low-temperature» isomerization with the use of chlorinated catalysts, «medium-temperature» isomerization based on zeolite catalysts and sulfated zirconium oxide - based isomerization [3] (Table 1). These methods are among the basic refining processes now. The level of technology, technical and economic efficiency of these processes largely predetermine the efficiency of commercial gasoline production in general, and the determining factor of the efficiency of isomerization process is the stability and activity of Pt-catalysts. For this reason, the attention paid by the economically developed countries to the improvement of isomerization technology and the development of more efficient catalysts is quite understandable. The introduction of the third generation polymetallic 165

2 Pentane and hexane isomer compositions produced by «per pass» variant on the basis of different types of catalysts No Name Index 1 Type of catalyst Pt/Al2O3 Pt/ZrO2-SO4 Pt/zeolite 2 Temperature range Composition of pentanes in isomerizate % wt: - isopentane - n-pentane Octane number of pentanes (by the research method), points ,0 Composition of hexanes in isomerizate, % wt: - 2,2-dimethylbutane - 2,3- dimethylbutane methylpentane methylpentane - n-hexane , Octane number of hexanes (by the research method), points catalysts has made it possible to produce high-octane gasolines and extend the cycle length by more than two times. However, up to the present, the comparable evaluation of activity, selectivity and stability of Pt contacts is carried out using laboratory kinetic methods with their subsequent testing at experimental and even industrial units. At the same time, the development of mathematical modeling methods while using the kinetic and technological analysis of the processes provides for the possibility to evaluate the kinetic parameters of different contacts by using a method of solving the inverse kinetic problem and predict the current and stationary activity indicators, selectivity and duration of the cycle in conditions of industrial operation with the specific design features of the reactor unit and raw material composition taken into account. Thus, it became possible to solve the actual problem of the reasonable selection and comparative evaluation of the efficiency of Pt catalysts on the basis of the nonstationary kinetic model of isomerization process developed, considering physico-chemical regularities of hydrocarbon transformation on the surface of the contact and technological features of the industrial unit, as well as the in-plant database on this process [4]. Temperature is the main factor affecting the process of isomerization. As temperature increases, the hydrocracking processes are accelerated, resulting in coke deposition on the catalyst. Also, a decrease in temperature makes hydrocarbons more branched and, correspondingly, leads to an increased octane number. The temperature influence on the research octane number is shown in Figure 1 [5]. Physicochemical properties of straight-run gasoline mixture fraction (IBP-75) Parameter Unit Value Content in oil % wt 7.4 kg/m Raw mixture composition Name Content Composition, %mass: isobutane - n-butane isopentane n-pentane cyclopentane ,2-dimethylbutane methylpentane methylpentane n-hexane methylcyclopentane cyclohexane Sulfur content, mg/kg 4.30 Density at 20, kg/ m Octane number (by the research method) 70 Temperature influence on the octane number of isomerizate Depending on the type of the catalyst used, hightemperature ( ), medium-temperature ( ) and low-temperature ( ) isomerization processes are distinguished. In accordance with the task, IBP-75 straight- 166

3 run gasoline fraction is used as a raw material for isomerization unit. Its physicochemical properties are given in Table 2. Raw mixture composition is given in Table 3. The process conditions are accepted based on the literature data. The process conditions are given in Table 4. Process conditions Parameter Unit Value 1 Inlet temperature º 250 Hydrogen concentration in circulating hydrogenation gas % vol. 80 Hydrogen containing gas circulation ratio in relation to raw material nm 3 / m Volumetric feed rate h Reactor pressure mpa Inlet temperature º 150 Hydrogen concentration in circulating hydrogenation gas % vol. 80 Hydrogen containing gas circulation ratio in relation to raw material nm 3 / m Volumetric feed rate h Reactor pressure mpa 2.8 Medium temperature IP 632 isomerization catalyst and new SI-2 hydroisomerization catalyst are used. The properties of the catalysts selected are given in Tables 5, 6. Properties of the IP-632 catalyst Parameter Value Platinum content, % wt 0.35±0,02 Bulk density, g/ m 3 0.7±0.1 Extrudate diameter, mm 2.1±0.3 Properties of SI-2 catalyst Parameter Value Platinum content, % wt 0.30±0.02 Bulk density, g/ m Extrudate diameter, mm 2.8±0.3 Modeling as a method for studying technological processes includes the following main stages: - modeling task determination - model building - the use of the model in order to study the properties and behavior of the object [6]. The stage of mathematical model building begins with the preparation of a formalized scheme of transformation of reactants on the active catalyst surface. It is necessary to formalize the mechanism of transformation of reactants and consider those reactions that have the greatest impact on product yield (overall reactions). The formalization process begins with an analysis of the mechanism and thermodynamic calculations of the reaction probability by the magnitude of the Gibbs free energy [7]. The target reactions that have the greatest impact on product yield and should be considered in the modeling process are presented in Table 7. where Target reactions for mathematical modeling of pentanehexane fraction isomerization Type of reaction Equations Primary reactions n- 4 = i- 4 n- 5 = i-c 5 6 = 2- MP 6 = 3- MP Isomerization reactions: 2-MP = 3- MP 2-MP = 2,3- DMB 2,3- DMB = 2,2- DMB n- 7 = i-c 7 CH = MCP. Secondary reactions Hydration reactions: CH + H 2 = n- 6 H 14 MCP + H 2 = 2-MP MCP + H 2 = 2,3- DMB MCP + H 2 = 2,2- DMB BZ + 3H 2 = CH BZ + 3H 2 = MCP. MP methylpentane, DMB dimethylbutane, CH cyclohexane, MCP methylcyclopentane, BZ benzene, MCH methylcyclohexane, i, n hydrocarbons with an iso- structure and those of normal structure. The Gibbs energy in dependence to temperature was calculated according to the formula [1] and Table 8 G 0 0 T = H T T S (1) where 0 H T, S are enthalpy and entropy changes at standard pressure. The Gibbs energy values for pentane-hexane fraction isomerization process reactions Reactions The Gibbs energy n n- 6 H n- 6 H , n , CH +H 2 6 H MCP +H , MCP +H 2 DMB MCP +H 2 DMB BZ+3H 2 MCP BZ+3H 2 CH

4 A transformation scheme was adopted based on the thermodynamic calculation (Figure 2). When choosing a formalized process scheme, the high selectivity of the isomerization process was considered, so side hydrocracking reactions are minimal [8,9]. In this scheme the C 5 -C 6 fraction components are presented individually and the C 7+ fraction components are presented in a formalized way due to their low concentration in raw materials. These constants were taken from the abstract of N.V. Chekantsev [10]. The mixture octane number is calculated in accordance with the additivity law by the formula RON mix = x i i, (12) where RON mix is the multicomponent mixture octane number by the research method, x i is the i-component mass fraction in the mixture, RON i is the i-component octane number by the research method (Table 10). n-c 4 n-c 5 k 19 k 20 k 21 k 22 i-c 4 i-c 5 BZ k 1 MCP k 12 k 2 k 4 k 5 3- P k 10 k 11 k 9 CH k 3 k 6 k 7 k 8 k 13 n-c 6 H P 2.3-DMB 2.2-DMB k 1 k 15 k 1 k 16 k 1 Formalized scheme of the process transformation mechanism The formalized scheme of the transformation mechanism is described by the following system of differential equations: At =0, C i =C i0, where is the hydrocarbon number according to the transformation scheme. Data on isomerization reaction rate constants for IPM-02 and SI-2 catalysts are presented in Table

5 Pentane-hexane fraction isomerization reaction rate constants Reaction Rate constant -1 on catalysts IPM-632 SI-2 n i 4 n-c n 5 i-c i-c 5 n n 6 H 14 MP MP n 6 H n 6 H H DMB DMB DMB H DMB Comparative evaluation of the results of the basic and design calculations obtained from the L-35-11/1000 unit in Table 11. Octane numbers of individual components Component RON Component RON n MP 75.5 i-c ,2- DMB 94.0 n ,3-DMB i-c 5 92 MCP 91.3 n- 6 H CH P 74.4 BZ 113 Thus, the possibility of solving the actual problem of reducing the aromatics isomerization catalyst with the selection of the method of mathematical modeling. Using a mathematical model obtained exploded isomerate composition for the base and project variants where yield when the catalyst SI-2 is increased to 98% and aromatics content is reduced to a minimum of 0.02%. The octane number of the replacement of the catalyst is increased by 2.89 points. The expediency of using a zirconium catalyst. Evaluation of the results of the basic and design calculations obtained from the L-35-11/1000 unit Hydrocarbons Raw material, % wt Design variant Isomerizate, % (calc.)wt. Basic variant Isomerizate, % (calc.) wt. RON i-c n- C i-c n-c n-c 6 H MP MP DMB DMB MCP CH C BZ Total [1]. 169

6 1 Pt/Al 2 O 3 Pt/ZrO 2 -SO 4 Pt , , , ,0-2,5 26,0-26,5 34,0-35,0 4,5-4,8 0,3-0,4 11,5-11,0 5,2-5,7 9,0-9,5 3,5-4,5 0,3-0,4 4, ) 170

7 ,3 2, ,7 2,8 0,35± 3 0,7± 2,1± 0,30 3 1,4 2,8 IP n- 4 = i- 4 n- 5 = i-c n- 7 = i-c 7 =. 2 6 H n-c 4 k19 k20 i-c 4 n-c 5 k21 k22 i-c 5 k1 k12 k2 k4 k5 3- k10 k11 k9 k6 k7 k8 k3 k13 n-c 6H ,3-2,2- k1 k15 k16 k1 k1 171

8 i, n G 0 0 T = H T T S (1) 0 H T S [8,9]. C 5 -C 6 C 7+ =0 C i =C i0 i, 4 4-3,75-2,18-0,61 0,89 n ,46-5,89-5,32-4,75 n- 6 H 14-4,75-4,01-3,29-2,6 n- 6 H 14-1,85-0,99-0,13 0,73-0,97-2,51-4,12-5,73-5,53-4,83-4,14-3, ,38-3,02-2,64-2,26-3,92-0,9 0,23 8, ,9-3,01-3,16-3,34 +H 2 6 H 14-71,19-83,6-96,7-110,8 2-79,86-87,38-95,73-104,7 2-78,9-84,9-91,6-98, ,4-89,7-95,8-102, ,2-227,4-244,6-263, ,9-227,2-240,1-254,2 =x i i, (12) x i i i i 172

9 -1 IPM-632 SI-2 n ,0139 0,0717 i ,0017 0,0249 n ,1339 0,2790 i-c 5 5 0,3003 0,2100 n- 6 H 14 0,5324 0, H 14 0,1470 0,5900 n- 6 H 14 0,3630 0, H 14 0,4430 0, MP 0,0101 0,0193 0,3680 0,0288 2,3-DMB Mp 0,0138 0,0581 P DMB 0,1156 0,1270 2,3-DMB DMB 0,0387 0,0407 2,2-DMB DMB 0,1130 0,0890 MCP CH 0,0017 0,0021 CH MCP 0,0003 0,0004 CH n- 6 H 14 0,0008 0,0010 BZ MCP 0,0198 0,0210 BZ CH 0,0198 0,0210 MCP DMB 0,0015 0,0020 MCP DMB 0,0015 0,0020 MCP MP 0,0008 0,0010 n ,5 i-c 4 100,2 94,0 n ,0 i-c ,3 n 6 H 14 25, , ,55 83,06 80,19 i-c 4 0,03 0,29 1,58 n- C 4 0,18 0,51 0,48 i-c 5 12,58 42,2 28,63 n-c 5 28,58 11,2 13,64 n-c 6 H 14 18,91 4,43 6,56 2-MP 15,85 11,08 13,87 3-MP 8,37 8,12 9,13 2,2-DMB 0,54 11,32 13,15 2,3- DMB 2,26 7,71 9,08 MCP 7,24 1,83 2,14 CH 2,89 1,05 1,25 C 7+ 1,11 0,23 0,47 BZ 1,46 0,03 0,02 Total REFERENCES 1 Cole A. L. Rizenfeld F.S. Gas from the English Cleaning process gases / T. A. Semenova, I. L. Leites et al. M.: Chemistry, p. [in Russian]. 3 Rakhmonov T.Z., Hurmamatov A. M. Research absorber desulphurization installation in industrial environments // [in Russian]. 4 Surge pressure in the joint motion of oil and gas horizontal inclined tubes / A. I. Guzhov, V. G. Titov, V. S. Semenyakin, V. A. Vasiliev // Math. Universities. Oil and gas. 5 Contamination of the amine solution in the gas cleaning installations from acid components / D. A. Chudievich, G. V. Tarakanov, V. P. Kovalenko, L.S. Shpeleva, Pp [in Russian]. 6 A physical absorption process for the capture of CO2 from CO2 rich natural gas streams / E. Keskes, C.S. Adjiman, A. Gralindo, G. Jackson // Chemical Engineering Department, Imperial College London. URL: ccs/publications/keskes.pdf. 7 Holmes A.S., Ryan J. M. Cryogenic distillation separation of acid gases from methane: US patent Valencia J. A. Mentzer B. K. Processing of High CO2 and H2S Gas witn controlled Freeze ZoneTM Technology // Exxon Mobil Upstream Research Company GASEX 2008 Conference. 9 Valencia J. A., Northorp P. S., Mart C. J. Controlled Freeze ZoneTM Technology for enabling processing of high CO2 and H2S gas reserves / J. A. Valencia // ExxonMobil Upstream Research Company IPTC 12708, Chekantsev N.V. Optimization of reactor equipment and industrial conditions of the isomerization of pentane-hexane fraction // Author. dis. Ph.D. Tomsk, [in Russian].. 6 Keskes E. A physical absorption 173

10 process for the capture of CO2 from CO2 rich natural gas streams / E. Keskes, C. S.Adjiman, A. Gralindo, G. Jackson // Chemical Engineering Department, Imperial College London. URL: ed.ac.uk/ccs/publications/keskes.pdf. 7 Holmes A. S. Cryogenic distillation separation of acid gases from methane / A. S. Holmes, J. M. Ryan // US patent Valencia J. A. Processing of High CO2 and H2S Gas witn controlled Freeze ZoneTM Technology / J. A. Valencia, B. K. Mentzer // Exxon Mobil Upstream Research Company GASEX 2008 Conference. 9 Valencia J. A. Controlled Freeze ZoneTM Technology for enabling processing of high CO2 and H2S gas reserves / J. A. Valencia, P. S. Northorp, C. J. Mart // ExxonMobil Upstream Research Company IPTC 12708,