ETBE英文工艺

l nive (et on n s Key word word文档格式规范word作业纸小票打印word模板word简历模板免费word简历 s: wn to components in the formulation of automotive gasolines, ctane r as reducers of carbon monoxide (CO) and unburned hydro- Alcohols and ethers are the oxygenated compounds most ethers are MTBE and ETBE. It is worth pointing out that ETBE production – ethanol – is derived from biomass [7]. nonreacted products [13,14]. Nowadays, to minimize implemen- F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 1 1 4 8 – 1 1 5 2 ava i l ab l e a t www.sc i enced i r ec t . com om commonly used as additives in automotive gasolines, since they possess the desired characteristics of octane ratings and CO emission reductions [7]. Some countries prefer ethers rather than alcohols due to theirmixing characteristics, such as lowvolatility and compatibility with the hydrocarbons of gasoline [8,9]. tation and operating costs, reactive distillation (also called catalytic distillation) is proposed as an alternative route for ETBE synthesis, offering high conversion and low implementa- tion/operating costs in comparison with conventional synthesis [15–17]. The reactive distillation process combines the reaction carbons (HC), minimizing the emission of volatile organic compounds [3–6]. The introduction of a minimal percentage of oxygenated compounds in the formulation of gasolines has been required by law in most countries which have areas of low air quality. ETBE is produced by reacting a C4 stream containing isobutene with ethanol over an ion-exchange resin catalyst. On an industrial scale, the conventional process of ETBE synthesis consists basically of the following stages: pretreatment of the C4 hydrocarbon feed flow, reaction, purification, and recovery of not only as enhancers of gasoline o Alcohols are substantially more polar th hydrocarbons of gasoline, and may cause the presence of a small amount of water in and distribution system [10,11]. ⁎ Corresponding author. Tel.: +55 51 3308 6306 E-mail address: rcv@ufrsgs.br (R. Cataluña) 0378-3820/$ – see front matter © 2008 Elsevi doi:10.1016/j.fuproc.2008.05.006 atings [1,2] but also is considered semi-renewable, since the raw material for its 1. Introduction Oxygenated compounds are kno which hinders the recycling of nonreacted ethanol in the process. The purpose of thiswork is to optimize the synthesis of ETBE eliminating the introduction of water into the system to break the ETBE/Ethanol azeotrope. The production process model proposed here eliminates the recycling of ethanol and suggests the use of the azeotropic mixture (ETBE/Ethanol) in the formulation of gasolines. The direct use of the azeotrope in the formulation of automotive gasolines reduces the implementation and production costs of ETBE. © 2008 Elsevier B.V. All rights reserved. be important as Tertiary ethers offer advantages over ethanol due to their low Reid vapor pressure (RVP), low latent heat of vaporization, and low solubility in water [7,12]. The most commonly used of these ETBE Azeotropic mixture (ETBE/EtOH) Gasoline Accepted 14 May 2008 displace the equilibrium towards the products. ETBE and ethanol forman azeotropicmixture Optimization of the ETBE (ethy production process Eliana Weber de Menezes, Renato Cataluña⁎ Department of Physical Chemistry, Institute of Chemistry, Federal U CEP-91501-970 Porto Alegre, RS, Brazil A R T I C L E I N F O A B S T R A C T Article history: Received 14 August 2007 Received in revised form 14May 2008 The synthesis of ETBE an exothermic reacti operating the reactio www.e l sev i e r. c an the ethers and phase separation in the gasoline storage ; fax: +55 51 3316 7304. . er B.V. All rights reserved tert-butyl ether) rsity of Rio Grande do Sul, Avenida Bento Gonçalves, 9500, hyl tert-butyl ether) from the reaction of ethanol with isobutene is of equilibrium. To increase the conversion of isobutene requires ystem at low temperatures and with excess ethanol in order to / l oca te / fup roc and purification stages in a single unit of the process [18]. In the ETBE production process, nonreacted ethanol forms an azeotropic mixture with ETBE, which cannot be separated by distillation. The process of ETBE purification occurs through the . introduction of water into the system and involves the separa- tion of the ETBE, the C4 hydrocarbonmixture, ethanol andwater. The introduction ofwater into the purification process augments the costs of implementation and production of ether. For this reason, some technologies use pervaporative separation of the ethanol from the ETBE/alcohol mixture through special mem- branes [19–23]. It has been demonstrated that the azeotropic mixture (ETBE/ ethanol) is less volatile than ethanol and that its octane rating is higher and its production cost lower than ETBE, thus presenting promising potential for application in gasoline formulations [8]. The synthesis model proposed here eliminates the recycling of ethanol and suggests the use of the azeotropic mixture (ETBE/ ethanol) as a direct additive in the formulation of automotive gasolines. 2. Experimental 2.1. Reaction system and purification 2.1.1. Reaction The ETBE production process was carried out in a flow, using as reagents a mixture of C4 hydrocarbons with 36 mol% of isobutene (i-C4) and 99.5 mol% of anhydrous ethyl alcohol. Table 1 presents the mean molar composition of the industrial load of C4 hydrocarbons. Amberlyst® 15 resin was used as catalyzer. The schematic diagram in Fig. 1 depicts the production process. The reaction system consists of an adiabatic fixed bed reactor fed by two cylinders, one containing the reagent ethanol (EtOH) and the other the C4 hydrocarbon mixture under a pressure of 20 bar. The composition of the reagent mixture and the reaction system are controlled by two electronic liquid flow gauges, one for ethanol, with a capacity of 405mL/h, and the other for the C4 hydrocarbons mixture, with a capacity of 1380 mL/h. These gauges allow the EtOH/i-C4 ratio and space velocity to be set as desired. The reagent mixture is heated and fed into the reactor's lower portion. The temperatureof the catalytic streambedandat the exit is monitored with thermocouples inside and outside the reactor toensure the reaction is in thesteadystate condition.The reactor's effluent is flashed into a distillation column under Table 1 – Mean molar composition of the industrial hydrocarbons load of the C4 cut Compounds Concentration (molar%) Isobutane 1.7 n-butane 7.6 2-transbutene 16.9 1-butene 33.2 Isobutene 36.0 2-cisbutene 4.6 1149F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 1 1 4 8 – 1 1 5 2 Fig. 1 –Flowchart of the ETBE synthesis. (1) Nitrogen; (2) and (3) Re PI: Pressure Indicator; TI: Temperature Indicator; TR: Temperatu Indicator Controller. agents; (4) Adiabatic fixed bed reactor; (5) Distillation column. re Recorder; TIC: Temperature Indicator Controller; FIC: Flow atmospheric pressure, separating the C4 hydrocarbons into vapor phase and the ethanol, ETBE and byproducts into liquid phase. The isobutene conversionwas evaluated as a function of the composition of the C4 hydrocarbons in the vapor phase. The concentration of liquid C4 at the bottom of the column is negligible. The conversion of isobutene was determined by gas chroma- tography from the molar balance in the reactor. The calculation methodology considered normalization of the isobutene in relation to the saturated hydrocarbons (isobutane and n-butane), which are considered inert and do not participate in the reaction. The conversion of isobutene was calculated according to Eq. (1)): The composition of the C4 hydrocarbon (reagent) load and the C4 in the vapor phase (reaction products) was determined by gas chromatography using a thermal conductivity detector (GC-TCD, Shimatzu 17A), a “plot” type fused silica capillary column with a stationary phase of Al2O3/Na2SO4 (50 m×0.53 mm) and Helium (5.0) as carrier gas. The analytical conditions were: isotherm at 40 °C for 20min, a heating ramp-up of 20 °C/min up to 190 °C, and holding at this temperature for 10min. The injector and detector temperatureswere 180 °C and 220 °C. The split ratiowas 1:20 and products of the reaction (tert-butyl alcohol and C8 hydro- carbons). The product of this bottom flow column is directed to a second distillation column (under identical conditions as those of the first). The bottom flow consists of ETBE with a high degree of purity, together with byproducts of the reaction, while the top flow consists of the azeotropic ETBE/ EtOH mixture. The composition of the bottom flow was analyzed by gas chromatography with flame ionization detector (CG-FID, Varian 3. Results and discussion i�C4 conversion ¼ Normalization of the i�C4 loadð Þ�Normalization of the i�C4 reactors exitð ÞNormalization of the i�C4 loadð Þ � 100 ð1Þ 1150 F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 1 1 4 8 – 1 1 5 2 e lo e in v e r le v f 2 T d h r c Fig. 2 – Isobutene conversions as a function of the temperature a molar ratios (MR) and a space velocity of 0.52 h−1. the volume of injected sample was 20 µL. The conversions obtained in the reaction system were valuated as a function of the EtOH/i-C4 molar ratio (MR) in the ad and the temperature at the reactor's exit. The molar ratios valuated were 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5. The temperature terval of the reaction was 48 °C to 88 °C, using a single space elocity of 0.52 h−1, which was chosen on the basis of previous xperiments, in order to ensure sufficient residence time of the eactants in the catalytic stream bed to enable the products aving the reactor tomeet theequilibriumcondition.This space elocity corresponds to the minimum limit of operation of the low control of the reactants using a 340 cm3 reactor. .1.2. Purification of the reactor's effluent he effluent from the reaction system was fractionated in a istillation column to remove the light compounds (C4 excess ydrocarbons of the reaction). In this first column that eceives the effluent from the reactor, the bottom flow onsists of a mixture (ETBE/EtOH) together with secondary 3.1. Evaluation of the parameters of the reactional system Fig. 2 presents the isobutene conversion profiles adjusted as a function of the temperature at the exit from the reactor and the EtOH/i-C4 molar ratios of the feed. The conversions shown here represent the results of three consecutive assays for each reaction condition evaluated. 39XL), using a fused silica capillary column (CP sil PONA CB) with a 100% dimethylpolysiloxane active phase (100m×0.25mm) and Helium (5.0) as a carrier gas. The analytical conditions were isotherm at 40 °C for 20min, a heating ramp-up of 5 °C/min up to 190 °C, and holding at this temperature for 10 min. The injector and detector temperatures were 250 °C and 300 °C, respectively. The initial split ratiowas of 1:300, passing on to 1:20 after 2min of analysis. The volume of injected sample was 20 µL. t the exit from the reactor, considering the distinct EtOH/i-C4 the bottom flow is composed of ethanol plus the secondary O L As indicated in Fig. 2, at a space velocity of 0.52 h−1, the reaction attains the maximum conversion in the temperature interval of 61 to 67 °C. Because it is a reversible and exothermic reaction, the increase in temperature exerts a negative effect on the displacement of the chemical equilibrium; hence, the higher the temperature the lower the conversion of isobutene in equilibrium. At temperatures of 50 to 61 °C, the conversion is directly proportional to the increase in temperature due to the faster reaction. At temperatures below 61 °C, the conversion is kinetically controlled while at higher temperatures, the con- version is controlled by thermodynamic equilibrium. The increase in ethanol concentration with the increase in the EtOH/i-C4 molar ratio in the system's feed directly reduces the velocity of the reaction (according to the Eley-Riedel kinetic mechanism), but increases isobutene conversion. These results are compatible with the values reported by Françoisse & Thyrion [24]. As Fig. 2 indicates, for molar ratios (MR) of 1.0 to 1.2, the maximumconversions vary from88 to 90%,while atmolar ratios of 1.3 to 1.5 the conversions vary from 91 to 92%. At a tem- perature of 65 °C, the molar ratios above 1.2 present practically the same isobutene conversions. For MR=1.0, the best operational temperature for maximum conversion is 59 to 63 °C. As the MR increases, so does the temperature ofmaximumconversion. This behavior is caused by the reaction mechanism. When the ethanol concentration increases, the reaction rate decreases due to the adsorption of Table 2 –Mass balance of ETBE productionwith a 100 kg of C4 hydrocarbons load for the molar ratios (MR) of 1.0 and 1.5 at a temperature of 62 °C MR i-C4 conversion, (%)⁎ Load (kg) Products (kg) mEtOH mAzeotrope mETBE 1.0 88 30 20 43 1.1 89 34 36 30 1.2 90 36 50 20 1.3 91 40 66 8 1.4 91.5 42 80 – 1.5 92 46 97 – ⁎ Results extracted from Fig. 2. F U E L P R O C E S S I N G T E C H N ethanol in the active sites of the catalyst, making diffusion of the isobutene inside the particle catalyst difficult, and thus present- ing a negative reaction order for the ethanol concentration. According to our chromatographic analysis, the reaction products of ethanol with isobutene are ETBE, C4 hydrocarbons (nonreacted), ethanol (nonreacted), TBA (tert-butyl alcohol), SBA (sec-butyl alcohol), C8 hydrocarbons and, in lesser proportion, C12 hydrocarbons. Higher temperatures favor the formation of reaction byproducts, leading to the increased production of compoundswith highermolarmasses, such as isobutene dimers (C8) and isobutene trimers (C12). The increase in ethanol concentration in the load requires a higher temperature to activate the reaction. This fact, allied with the presence of water in the ethanol, favors the formation of TBA and, at a lower concentration, SBA, due to the reaction of the water with the C4 olefins. Based on our experimental results, we found that the highest formation of secondary products was obtained with a molar ratio of 1.5 and at a reaction temperature of 87 °C. products of the reaction. As the data in Table 2 indicate, the stoichiometric molar ratio allows for the highest ETBE production of high grade purity,minimizing the production of the azeotropicmixture. To increase the production of ETBE with a high degree of purity, minimizing or preventing the formation of the azeotropic mixture, it is necessary to use water in the system. However, this increases the installation cost of the production plant. Moreover, the introduction of water leads to the formation of the azeotropic EtOH/H2O mixture, which makes it difficult to recycle the ethanol. Some technologies use pervaporative separation of the ethanol in the azeotropic mixture (ETBE/ EtOH) by means of special membranes. The use of ETBE in azeotropic form would eliminate the costs related to the purification stage of the ETBE production process. In high purity ETBEproduction unitswhichusewater to break the ETBE/EtOH azeotrope, the recycled ethanol contains water in its composition, increasing the formation of TBA and SBA alcohols and reducing the activity of the catalyst. 4. Conclusions In the synthesis of ETBE using an adiabatic reactor and a space velocity of 0.52 h−1, the highest isobutene conversion is obtained at reaction temperatures ranging from 61 to 67 °C. When the concentration of EtOH in the load increases, the conversion of i- C4 in the equilibrium also increases, but the reaction rate toward ETBE formation decreases. The azeotropic mixture possesses a potential for application in gasoline formulations, offering advantages over the use of ethanol (suchas lowervolatility and lower solubility inwater) and ETBE (higher octane rating and lower production costs). The production system without ethanol recycling, considering the ETBE/EtOH azeotropic mixture as an end product of the system, minimizes production costs since it does not require the ethanol purification unit. The maximum ETBE production with a high degree of purity and minimal production of the ETBE/EtOH azeotropic 3.2. Optimization of the production process Based on the experimental results summarized in Fig. 2, the highest production of ETBE (or the greatest conversion of i-C4) was found to occur with MR 1.5. However, this led to a higher production of the azeotropic ETBE/EtOH mixture. Table 2 presents the mass balance as a function of the molar ratios of 1.0 and 1.5 in the feed and a temperature of 62 °C (corresponding to themaximum conversion temperature for MR=1.0), consider- ing as base load 100 kg of C4 hydrocarbons (0.66 mol of i-C4). According to the results presented in Table 2, as themolar ratio of EtOH/i-C4 increases, so too does the conversion and the production of the ETBE/EtOH azeotropic mixture. At a molar ratio equal to or higher than 1.4, the concentration of ethanol in the reactor's effluent is higher than in the composition of the azeotropic mixture. Thus, all the ETBE produce in the reaction system is concentrated in the top flow of the fractionation column in the formof azeotrope and 1151O G Y 8 9 ( 2 0 0 8 ) 1 1 4 8 – 1 1 5 2 mixture is attained using a stoichiometric molar ratio of EtOH/i-C4. Acknowledgements The authors acknowledge to the Petrochemical Company of the Rio Grande do Sul (COPESUL), Brazil, for supplying the raw material (C4 cut) for the production of the ETBE and thanks the financial support of the CNPq. R E F E R E N C E S [1] F. Nadim, P. Zack, G.E. Haag, S. Liu, United States experience with gasoline additives, Energy Policy 29 (2001) 1–5. [2] A.K. 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