A Study On Cumene Plant Engineering Essay

A hit the books On Cumene Plant Engineering EssayThe system con locationred for study, example and optimisation is a cumene outpution shew. The plow described by Peterson and Schmidt is demandn as base for simulating the system. The butt description of Turton et al. (2003) provides relevant and valuable info consume for the simulation of the bear upon.Raw materials fed to the plant be benzine and propene (whitethorn contain propane as an impurity) in which benzine is in special. Various unit ope rations and paradees be required to be taken c ar of which ar described in around detail below. The study units in the shape plant are the nuclear nuclear nuclear nuclear reactor section and the separator section.1.2 RELEVANCEIsopropyl benzine popularly k without delayn as cumene is the principal chemic personad in the output of phenol and its co- merchandise acetone on an industrial scale. It is also the startle material in the deed of acetophenone, methyl sty rene, diisopropyl benzol and dicumyl peroxide. Minor uses of cumene every(prenominal)ow as a thinner for paints, enamels, and lacquers as a constituent of virtually petroleum- rig solvents, such as naphtha in gasoline blending diesel elicit, and efficient aviation fuel. It is also a good solvent for fats and resins and has been suggested as a re mailment for benzine in m both of its industrial applications.Around 98% of cumene is use to produce phenol and its co-product acetone. However, the requisite of cumene is largely dependent on the use of phenols derivatives which have resulted in increase requirement appreciates for cumene. The largest phenol derivative is bisphenol-A (BPA) which supplies the polycarbonate (PC) sector. PC resins are consumed in automotive applications in place of traditional materials such as glass and metals. Glazing and mainsheet uses, such as architectural, security and glazing outlets, are also key PC applications. The third largest use for PC is optical media such as chummy discs (CDs) and digital versatile discs (DVDs). A nonher phenol derivative is caprolactam which is use in the first place to develop nylon 6. It is mainly the resin sector of the nylon market that is seeing growth. Schmidt, 2005Cumene is produced by the alkylation of benzol with propene over an acrid gun like aluminum chloride, boron trifluoride, phosphoric acid, atomic spot 1 fluoride, supported phosphoric acid (SPA) and so forth The usage of the above gass poses a peck of problems like product quality, disgrace accelerator activity, environmental hazard, gun non-regenerability etc and has been replaced by zeolites in most of the processes.In the pre move work the cumene production plant is simulated using ASPEN electropositive and the sizes, the temperature and other relevant parameters are obtained by optimization. MATLAB, MS Excel and bank line Pro 8.0 are used to plot interprets in the following simulation from which an optimal value is estimated. The optimized values obtained hatful provide a lot of insight before actual plant commissioning is through.1.3 OBJECTIVE OF THE leap outConsidering the importance of the ease up process, work was undertaken to number and simulate the cumene production process using ASPEN cocksure software. The objectives of the expose confuse are following.To propose a zeolite accelerator pedal based cumene production process and study the sensitivity analysis.To optimize the contents of the flow sheet for minimization of loss of material along with a greater production of cumene and low requirement of energy.CHAPTER 2 books REVIEW2. LITERATURE REVIEW2.1 CONVENTIONAL subroutineCumene is produced by the alkylation of benzol with propene over an acid gun. Catalysts like aluminium chloride, boron trifluoride, hydrogen fluoride and solid phosphoric acid (SPA) are normally used. Over the eld these catalysts have given representation to zeolite based catalysts. There are some inherent problems associated with the conventional acid catalysts.Disadvantages of using solid phosphoric acid (SPA) ProcessLower activityCatalyst non-regenerabilityUnloading of spent catalyst from reactor difficultRelative high selectivity to hexyl benzeneSignificant let up of DIPBDisadvantages of using Aluminium chloride as catalystHigh corrosionenvironmental hazardWashing step for catalyst removal.2.2 CURRENT INDUSTRIAL coverCumene is an important chemic in the present industrial world and its uses are steadily increasing. The process followed for the production of cumene is the catalytic alkylation of benzene with propene and now a days zeolite based catalysts are used in place of the normal acid based catalysts due to added advantages. Cumene production process has been greatly studied and the chemical reply mechanism and the answer kinetics have been contract by many researchers. Both experimental as easily as computer based simulation and optimization studies h ave been carried out by various researchers. The significant works of various researchers which have been helpful in my project are described in apprise below.The Q-Max process converts a medley of benzene and propene to high quality cumene using a regenerable zeolite catalyst. The Q-Max process is characterized by a exceptionally high yield, better product quality, less solid waste, cross outtle in enthronization and operating court and a corrosion take over environment. The Q-Max process developed by UOP uses QZ-2000/ QZ-2001 catalyst which is a variant of zeolite. Schmidt, 20052.2.1 PROCESS DESCRIPTIONThe Q-MAX process provides a in truth good cumene yield and quality. The QZ-2000 zeolite based catalyst used in the Q-MAX process ope strides with a low flow rate of benzene and hence investment and utility be are rationalised greatly. QZ-2000 is non-corrosive and regenerable, avoiding the significant maintenance and catalyst disposal problems associated with SPA and A lCl3 systems. Compared to other zeolite based cumene technologies, the Q-MAX process provides better allowance account of holdstock impurities, the highest cumene product quality and excellent stability.The Q-MAX process flow scheme is shown in fig 2.1 above. The alkylation reactor is shared into four catalytic beds present in a single reactor shell. The brisk benzene carry is passed by dint of the upper-mid section of the depropanizer pillar to remove excess water and therefore sent to the alkylation reactor. The recycle benzene to the alkylation and transalkylation reactors is a drawn from the benzene newspaper chromatography column. This mixture of fresh and recycle benzene is charged through the alkylation reactor. The fresh propene run away is split between the catalyst beds and is fully consumed in each bed. An excess of benzene helps in avoiding poly alkylation and minimizing olefin oligomerization. Because the reply is heat-releasing in nature, the temperature fig out in the alkylation reactor is controlled by recycling a slew of the reactor effluent to the reactor inlet to act as a yearning up sink. The inlet temperature of each down current bed is further slenderised to the kindred temperature as the first bed inlet by injecting a portion of cooled reactor effluent between the beds. Effluent from the alkylation reactor flows to the depropanizer column which removes the propane that entered with the propylene turn over along with excess water. The scum bags drift of the depropanizer column goes to the benzene column where excess benzene is collected overhead and recycled. The benzene column bottoms stream goes to the cumene column where the cumene product is recovered overhead. The cumene column bottoms stream, pre governingly diisopropylbenzene (DIPB), goes to the DIPB column. If the propylene run for contains excessive butylenes, or if the benzene lam contains excessive toluene, butylbenzenes and/or cumene are distilled out a nd purged from the overhead section of the DIPB column. The DIPB stream leaves the column by way of the side draw and is recycled back to the transalkylation reactor. The DIPB column bottoms incorporate of heavy evocative by-products, which are normally blended into fuel oil. Steam or hot oil provides the heat for the product constituentation section. The recycle DIPB from the overhead of the DIPB column combines with a portion of the recycle benzene and is charged downflow through the transalkylation reactor. In the transalkylation reactor, DIPB and benzene are converted to more cumene. The effluent from the transalkylation reactor is then sent to the benzene column. The new QZ-2001 catalyst is utilized in the alkylation reactor while the original QZ-2000 catalyst remains in the transalkylation reactor. Expected catalyst cycle length is 24 years, and the catalyst should last for at least three cycles with proper distribute. At the end of each cycle, the catalyst is typically re generated ex situ via a simple carbon burn by a certified regeneration contractor. However, the unit can also be designed for in situ regeneration. The Q-Max process typically produces near residue levels of cumene (between 85 and 95 mol %) and DIPB (between 5 and 15 mol %). The DIPB is separated from the cumene and is reacted with recycle benzene at optimal conditions for transalkylation to produce additional cumene. Schmidt, 2005, Peterson and Schmidt, 20022.2.2 REACTION tool AND KINETICSThe following reply mechanisms are proposed for the alkylation of benzene to cumene process. The major reactions winning place are alkylation and trans-alkylation. The other reactions involved include isomerisation and dis-proportionation. The reaction mechanism as well as the reaction kinetics may vary depending on the catalyst used. The reaction can proceed by with or without carbonium ion intermediate. Ding and Fu, 2005The rank of reaction info was obtained for different catalysts from t he work do by various researchers. The kinetic data and the reaction conditions contract by Turton et al (2003) for a particular catalyst have been used in the present work.The reaction kinetic data is shown belowpropene + benzene cumene K = 2.8 107E (kJ/kmol) 104174Rate=kcpcbPropylene + cumene p-diisoproyl benzeneK = 2.32 109E (kJ/kmol) 146742Rate=kcpcc(The unit for rates is kmol s-1 m-3)Turton et al, 2003Trans-alkylation reactionK= 6.52 10-3 exp (27240/RT)The symmetry data for trans-alkylation reaction is obtained for modified zeolite beta catalyst, YSBH-01. Lei et al, 2007From various works on cumene production mechanism the overall reaction can be assumed to consist of the following stages.AlkylationIsomerisationTransalkylationDis-proportionation2.3 PROPERTIES OF CUMENEDescription Colorless unstable with a sharp, get into aromatic or gas-like odour Budavari, 1989 Cavender, 1994Boiling Point 152.4C Lide, 1995thawing Point -96.0C Lide, 1995Density 0.8618 g/cm3 at 20C Lid e, 1995Refractive Index 1.4915 at 20C Schulz et al., 1993 1.489 at 25C Lewis, 1993Solubility Insoluble in water miscible in acetone, benzene, and ethanol Lide, 1995Flash Point 39C, closed cup Budavari, 1989responsiveness Combustible Lewis, 1993, not compatible with oxidizers, nitric acid and sulphuric acid.2.4 PROCESS externalize BASICSProcess design is a very important aspect before any project implementation as a proper design during the initial stages can save costs to a great extent. The cost involved in designing a project is very less compared to the construction cost and it can be greatly helpful in maximizing profits of the plant as well as providing a safe environment. The plot shown in Fig. 2.2 gives a brief belief of how proper plant design can cut costs to a great extent.The following tailors motivation to be taken care for a proper process design.Raw material cost reduction. Selectivity of reaction is increased by proper use of catalysts. Increasing selectivity can reduce legal separation and recycle costs.Capital-cost reduction. Better flow sheeting can reduce chapiter costs publicationivelyEnergy use reduction. Pinch menstruation analysis is used for energy saving. change magnitude process flexibility. Process plant should be able to handle a concatenation of feed compositions.Increased process safety. Nonlinear analysis can be done to make the process safer.Increased attention to quality. Reduction of by products and the effective use of process control equipment can lead to process safety.Better environmental performance. Minimization of harmful wastes to the environment.The order in which designing should be done follows a systematic procedure as shown in Fig 2.4.A process simulation diagram is drawn from the process flow diagram. The chemical components are specify. The chemical component properties are generally available in a commonplace data base. The input streams are specified. Thermodynamic fashion personate is done. Serie s of simulations are run for convergence of a particular variable. sensitiveness analysis which consists of varying the sampled variables as a function of the manipulated variables is normally done. The major parts of a cumene production plant are reactor system, separation system and they are optimized.CHAPTER 3DESIGN surgical operation, RESULT DISCUSSIONThis chapter is divided into two main parts as (i) Reactor and (ii) Separator. The reactor design involves design of equilibrium based reactor as well as kinetic based reactor. The separator system involves the design of flash armoured combat vehicle and distillate column. As the product purity is increased by increasing the working cost of the reactor, the separation cost decreases and vice versa. The sequence of numeration followed is shown in Fig. 3.1.3.1 REACTOR DESIGNReactor is the heart of a chemical process plant. Design of a reactor requires data from thermodynamics, chemical kinetics, nomadic mechanics, heat transfe r, mass transfer and economics. A properly designed reactor can minimize the production of unwanted products and hence reduce the purgation costs.The alkylation and trans-alkylation reactors are the main reactors in a cumene production plant and they shoot to be designed for optimum use of material and energy. In all the optimization work done Douglas Doctrine (the costs of raw materials and products are usually much larger than the costs of energy or capital in a typical chemical process. Therefore the process must be designed (investing capital and paying for energy) so as to not waste feed stocks or lose products (particularly in the form of inapplicable products) is followed. Luyben, 2010 Kinetic model can be considered if accurate kinetic data is available. But a plant involves industrial reactors that are very complicated and hence a proper combination of stoichiometric and kinetic reactor needs to be used. Kinetic model can determine the production rate where as stoichio metric model can describe the composition of by products and impurities necessary for the design of separators. Equilbrium based reactors like RGIBBS in ASPEN PLUS can give a realistic idea about the maximum achievable performance. They work accurately for fast reactions. The RGIBBS reactor predicts the equilibrium absorption by Gibbs free energy minimization. Dimian, 2003 Generally in reactor design an equilibrium model is prepared and then the kinetic model.The following reaction mechanism was proposed by various researchers for alkylation of benzene by cumene.3.1.1 REACTIONS CONSIDERED FOR representativeINGAlkylationpropylene + benzene cumene (1)propylene + cumene p-diisoproyl benzene (2)Isomerisationp-diisopropyl benzene m-diisopropyl benzene (3)Trans-alkylationp-diisopropyl benzene + benzene 2 cumene (4)m-diisopropyl benzene + benzene 2 cumene (5)Disproportination2 cumene p-diisopropyl benzene + benzene (6)2 cumene m-diisopropyl benzene + benzene (7)3.1.2 REACTOR DES IGN PROCEDURE IN ASPEN PLUSThe feed is a mixture of benzene and propylene such that benzene is in excess. In general propylene is not available in the pure form and has some core of propane as mucky. The separation cost of propane is high and hence normally propane is not take from the propylene feed into the reactor. A high conversion of propylene is desired and the unreacted propylene can be flashed off along with the inert propane. RGIBBS reactor works by Gibbs free energy minimization. Alkylation and trans-alkylation reactors need not be modelled separately as they can be combined into one equilibrium reactor. The reactant, products as well as the intermediates as seen from the reaction mechanisms are specified into the component list. SYSOP0 or Ideal property table is used. A temperature range of 300 to 400 ground level Celsius is specified and a proper temperature chosen. imperativeness of 25 standard extort is chosen from previous industrial research work. Luyben, 20103 .1.3 proportionality STUDIESThe equilibrium is affected by the temperature as well as the benzene/propylene rampart ratio. The alkylation and transalkylation reaction is usually carried out at atmospherical pressure. Therefore, the effect of pressure on the equilibrium was not considered in the present study.Seven reactor models are available in ASPEN PLUS. The equilibrium based RGIBBS reactor is used to find the product composition at which the Gibbs free energy of the product is minimum. The restricted chemical equilibrium approach is used and the reactions mentioned above are specified. The temperature approach for an individual reaction is used. The feed stream jetty flow is lot as 1 kmol / hr and the feed stream consists of benzene, propylene and propane (inert mixed with the propylene stream). Amount of inert in feed is kept quick-frozen. The reactor temperature is set to 3500C and the reactor pressure is set to 25 atm. (a) The selectivity of cumene and conversion of prop ylene (limiting reagent) is studied by varying the benzene/propylene mole ratio in the feed keeping the amount of inert fixed. The effect of temperature variableness (3004000C) on the selectivity and the conversion is also studied. (b) Again, the variation in the selectivity of m-DIPB and p-DIPB with temperature and benzene/propylene mole ratio in the feed is studied. The conversion and selectivity were calculated using equations 8 to 11.%Selectivity of cumene = Fcumeneproduct /(Fpropylenefeed-Fpropyleneprod)100% (8)%Conversion of propylene = (Fpropylenefeed-Fpropyleneprod)/Fpropylenefeed 100 % (9)%Selectivity of m-DIPB = Fmdipbproduct/(Fpropylenefeed-Fpropyleneprod) 100% (10)%Selectivity of p-DIPB = Fpdipbproduct/(Fpropylenefeed-Fpropyleneprod) 100% (11)WhereFcumeneproduct = milling machinery flow rate of cumene in productFpropylenefeed = molar flow rate of propylene in feedFpropyleneprod = molar flow rate of propylene in productFmdipbproduct = molar flow rate of m-DIPB in prod uctFpdipbproduct = molar flow rate of p-DIPB in productRSTOIC reactor model was used to find the standard heat of reaction for different reactions 1 to 6 mentioned above. The standard heats of reaction have been tabulated in tabularize 3.1.1. The heat of reaction for isomerisation was found to be zero as expected. The all other reactions were found to be exothermic except trans-alkylation reactions as observe from the table. display panel 3.1.1 Standard Heats of chemical reactionReaction NumberStandard Heat of Reaction (Kcal/Kg mol)1-23.6702-24.3213040.64950.6496-0.3257-0.324Effect of temperature and benzene/propylene mole ratio.The effect of temperature and benzene/propylene mole ratio on equilibrium conversion of propylene and selectivity of products, cumene, m-DIPB, and p-DIPB is shown in Fig. 3.1.1. The conversion of propylene was found to increase with increase in benzene/propylene mole ratio for a fixed temperature as observed from the Fig. 3.1.1(a). This is because of reduc ed proportion of propylene in feed. However, variation of conversion of propylene was found to be negligibly small above the benzene/propylene mole ratio in feed of 3. The conversion of propylene was found to decrease with increase in temperature for a fixed benzene/propylene mole ratio as observed from the Fig. 3.1.1(a). This is because of the fact that overall heat of reactions is exothermic as shown in Table 3.1.1.The selectivity of cumene was found to increase with increase in benzene/propylene mole ratio at a fixed temperature as the polyalkylation reactions are reduced because of excess amount of benzene present in the feed (Fig. 3.1.1(b)). Again, with increase in temperature, the selectivity of cumene increases for a fixed benzene/propylene mole ratio as transalkylation reactions (endothermic, Table 3.1.1) are dominant at high temperature.The distribution of m-DIPB and p-DIPB is shown in Fig. 3.1.1 (c). From the figure it was observed that selectivity of m-DIPB is significan tly higher than p-DIPB. This is because of the fact that m-DIPB is thermally more stable compared to p-DIPB. Therefore, p-DIPB formed in alkylation reaction isomerises to more stable meta isomer.Effect of inert on equilibrium. The propylene stream used in alkylation process is usually obtained by pyrolysis of petroleum fractions that contains small amount of propane as impurity. Propane need not be take away from the propylene stream as it acts as an inert and does not take part in the reaction. Presence of inert has very slight effect on the conversion as well as selectivity as shown in Fig.3.1.2. The conversion of propylene decreases slightly with higher passel percent of inert in feed and increases slightly with the same.3.1.4 KINETICS BASED REACTOR MODELKinetics based rate data was obtained from the work of various researches and is mentioned above. A RPLUG model is used in ASPEN PLUS to model the reactor. The design model specified in the book by Turton et al (2003) is used. The reactions occur in the drying up phase in the presence of a solid catalyst (assumed to have 0.5 void fraction and a 2000 kg/m3 solid density). The reactor is run at high pressure (25 bar) since the moles of reactants are more than the moles of product (Le Chateliers principle). A temperature of 360 degree C and a benzene/Propylene mole ratio of 6 is used. A flow rate of 330 kmol/hr is used for the simulation.The kinetic model generated few errors such as RPLUG exited because integration failed. index = (-1) probable cause is incorrect kinetics. check rate-constant parameters and molar volume calculations.3.1.5 PRODUCT OUTPUT FROM REACTORAssuming the RGIBBS model for the initial calculations for distillation columns can give a good idea about the distillation process in a cumene plant. RGIBBS model with an input feed rate of 100 kmol/hr and benzene propylene feed ratio of 61 with an inert concentration of 5% in propylene stream, temp. of 360 degree C and a pressure of 25 bar i s used. The flow rates obtained at the product side are noted.The non condensable components in the product side i.e. propylene and propane are removed in flash tankful. These components have fuel value only as they cannot be completely purified. So the reaction conditions should be so adjusted that the propylene in feed is in all converted to the product. The concentration of non-condensable components from reactor is given in Table 3.1.2. This data is used for further designing.Table 3.1.2 Mole flow rate of components from reactorComponentMole Flow kmol/hr benzine72.85Cumene10.31m-DIPB1.77p-DIPB0.47TOTAL85.43.2 PREDICTING VLE CHARACTERISTICSReactors and separators can be considered as the back bone of any chemical process plant. The cost optimization of any plant depends largely on the reactors and the distillation columns. The basis of distillation is phase equilibrium that may be VLE (Vapour liquid equilibrium) and LLE (Liquid liquid equilibrium). Before designing any distilla tion equipment the VLE characteristics need to be studied as they give a fair amount of idea about the ease of distillation. The Txy diagram or temperature versus liquid composition (x) and dehydration composition (y) are plotted. A fat curve generally shows that the liquids in a mixture can be easily separated.The boiling point data of the three major components in the distillation column is shown in Fig. 3.2.1 below.Table 3.2.1 Boiling point of componentsComponentBoiling point in degree CelsiusBenzene80.2Cumene152.4DIPB209.8The product stream from a condenser tank is sent to a distillation column. RADFRAC model is used. In the industrial process three distillation columns are used i.e benzene column, followed by cumene column and DIPB column.The RADFRAC model is a rigorous model for various multistage liquid vapour fractionation operations and hence is used for the simulation Before passing game in for the design of the distillation column the VLE diagrams need to be considered. The industrial processes currently followed show that in the 1st column benzene and cumene need to be primarily separated and in the 2nd column cumene and DIPB need to be separated. The NRTL (non random two liquid) physical property package is used used to plot the vapour liquid equilibrium T-XY for Benzene-cumene and Cumene-DIPB systems. The VLE plots are shown in Fig 3.2.1 to 3.2.3 for different systems.It can be inferred from plots Fig. 3.2.1 to 3.2.3 that separation would be lucky and a distillation column with fewer trays and a smaller ebbing ratio can be used. Azeotrope is not formed. Flash distillation should be tried as separation is easier.3.3 FLASH distillate TANK DESIGNDistillation is tried using flash tank as the cost of operation is very low. FLASH2 model is selected. SYSOP0 property method is selected, which works by ideal or Roults law. Pressure of the flash tank is set as 1 bar. The input flow rate is same as mentioned in Table 3.1.2. The minimum boiling point in the mixture is that of benzene at 80.2 degree C at 1 atm and hence a temperature of 85 to 97.5 is considered for fanfare. The mole fractions of benzene and cumene in the bottom and top products are found out at various flashing temperatures and plotted in Fig. 3.3.1.Assuming a product purity of 95% benzene in the top product the flashing temperature is identified to be 92.5 degree C. The flow rates from the flashing tank is shown in Table 3.3.1.Table 3.3.1 Concentration of products from the flash tank92.5 degree CBenzeneCumenem-DIPBp-DIPBBOTTOM Product18.9518657.893849631.684738320.45287993TOP product5.39E+012.416150310.085261670.01712006The flow rates of Table 3.3.1 act as a feed to the benzene column.3.4 BENZENE DISTILLATION COLUMN DESIGN3.4.1 DESIGN PROCEDURERADFRAC-1 is selected for designing the Benzene distillation column. SYSOP0 property method is selected and the flow rates from Table 3.3.1 are used. The pressure is kept fixed at 1.75 bar and the temperature is kept fixed a t 90 degree Celsius. These two variables are obtained from the experimental data specified by Turton et al (2003). These temperature and pressure data have been used in the work by Luyben (2010). The variables that can be optimized are reflux ratio, number of feed trays, feed tray location and distillate rate. In the initial supposition the distillate rate is kept at half the value of the feed rate. A total condenser is used in the process and an equilibrium based approach is used.3.4.2 REFLUX RATIO OPTIMIZATIONThe number of trays (including kettle hole and condenser as a tray) is kept fixed at any value say 15. The feed tray is vary keeping the number of trays fixed. flat for each different ratio of number of trays to feed tray a series of reflux ratio starting from 0.1 is considered. The process is run and the mole fraction of benzene in the top product as well as the reboiler heat load data are used and a graph is plotted as shown in Fig 3.4.1. Reflux ratio is optimized by t he variable mole fraction of benzene in the top product.An optimum reflux ratio value of about 0.5 is identified from Fig 3.4.1. At higher values of feed tray location (close to reboiler) lesser reflux ratio is required. Note that condenser is considered as the first stage and the rebolier as the last.3.4.3 hang TRAY LOCATION OPTIMIZATIONThe reflux ratio is kept fixed at 0.5 and the number of trays is kept fixed at 15. The position of the feed tray is varied and its affect on the reboiler heat load and the mole fraction of benze