Aromatics Production from Shale Gas Ethane

Added on - 16 Sep 2019

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Spring 2017IDE Project:Ethane to AromaticsAromatics Production from Shale Gas Ethane
Table of ContentsNOTitlePage No1Abstractiii2Introduction13Process Overview24Methods of Implementation35Results186Conclusion257Recommendation268References27List of FiguresNOTitlePage No1Figure 1: Block diagram of Aromatic Production from ShaleGas Ethane22Figure 2: Working process Flow Diagram after Recycle43Figure 3: First Reactor5, 184Figure 4: First Separation Distillation Column12, 195Figure 5: Membrane13, 206Figure 6: Distillation Column-114, 217Figure 7: Distillation Column-215, 228Figure 8: Distillation Column-316, 239Figure 9: Column used for Recycle and Purge streams17, 24i
List of TablesNOTitlePage No1Table1.a: The estimated reaction rate constants forconcentrations in M (or moles/liter = kmoles/m3)iii, 62Table 1.b: the rates of reversal reactions73Table 2: Results of stream 3184Table 3: Results of stream 5, 30195Table 4: Results of stream 7, 8206Table 5: Results of stream 11, 17217Table 6: Results of stream 19, 20228Table 7: Results of stream 35, 39239Table 8: Results of stream 27, 2824List of GraphsNOTitlePage No1Graph 1: Pressure Drop in Conversion of Ethane82Graph 2: Pressure Drop in Formation of BTX83Graph 3: Formation of BTX vs. size of Reactor10ii
1.AbstractIn this report, we showed the aromatic production from shale gas ethane, the motivation forthis is to economical production of aromatic from ethane. This process will produce 500 x 106lb of benzene, toluene, and xylene (BTX) per year from a feedstock of fractional-grade ethane.The conversion of ethane to BTX occurs in a steam reformer reactor operating at 700°C, 1 atm,catalyzed by Zn-ZSM-11 zeolite. After the reaction occurs, the light components are separatedfrom the product stream using a multistage compressor and flash followed by the separationsystem. The light hydrocarbons (ethylene, ethane, propylene) are recycled to the reactor andthe hydrogen and methane are burned. The final BTX product is separated from the heavystream using two distillation columns, and the remaining heavy components are sold for use ingasoline. The financials for this venture are highly sensitive to the price of catalyst componentsand catalyst lifetime. A few major reasons that make this venture unprofitable are the high costof catalyst, the high equipment cost, and the short catalyst lifespan. After the in-depth analysisof the financials, we recommend that this project only be executed if market prices for inputcomponents significantly decrease, prices for BTX significantly increase, or catalyst lifetimesignificantly increases. The software we used for the simulation of process flow diagram ofaromatic production from shale gas ethane is ASPEN plus.Table 1.a: The estimated reaction rate constants for concentrations in M (or moles/liter = kmoles/m3)ReactionNoForward reaction rateconstant, k at Tref(1/sec)Equilibrium constant, Kc112.10.227059043214.50.688829581316.5187.521333459.2214920.65547.23.32E+1663.95.65498E+1374.57505.94797iii
2.IntroductionDue to the recent increase in fracking in the United States, there is a high availabilityof light paraffinic hydrocarbons to be used as feedstock, especially ethane. Whileresearch into alkanes-to-aromatics processes was more popular in the 90s, theseprocesses fell out of favor due to the difficulty in finding a suitable catalyst. However,H-ZSM-5 and H-ZSM-11 zeolites catalyze the transformation of light paraffins intoaromatic hydrocarbons with great success [1-3]. Zn-ZSM-5 zeolite is more active andmore selective than H-ZSM-5 in the production of BTX [2,4-6]. But it is reported thatZn-ZSM-11 shows excellent aromatization behavior for C3, C5and C6paraffins [7,8].The conversion of ethane into aromatic compounds at 700°C and atmospheric pressureover Zn-ZSM-11 zeolite has been studied in a flow reactor at different 1 atm pressuresof ethane. The observed products at different ethane conversion levels were formedthrough a variety of processes including ethane dehydrogenation, producing ethylene asthe only primary unstable product. Ethylene underwent very rapid reactions throughcarbenium ion intermediates, producing aromatic hydrocarbons and C1-C4hydrocarbonsas secondary products.This project is also motivated by the decrease in traditionalsources of BTX, leading to a demand for new methods of production. BTX is typicallymade through catalytic naphtha reform or by extracting from naphtha-fed ethylenecrackers, both of which require relatively expensive crude oil. As ethane is a commonby-product of fracking, it is much cheaper, thus allowing for very high potential profitsfrom this process1
Figure1: Block diagram of Aromatic Production from Shale Gas Ethane3.Process OverviewThere are many different processes for producing aromatics from ethane. We will be usingthe process shown in the figure above. This process consists of a single catalytic, gas-phasereactor, in which four major reactions occur. The reactor effluent is fed through a series of unitoperations in order to separate and purify the products. The first operation is to separate thelighter components (hydrogen, methane, ethylene) from the heavier components. The lightercomponents are fed to a membrane which selectively removes the hydrogen gas. Themembrane retentate is fed to two distillation columns in series. The first column separates outmost of the methane. The 2ndcolumn distillate is mostly ethane and ethylene, which is recycledto the reactor. The bottoms from the 2ndcolumn is waste. A fraction of the distillate is purgedbefore it is mixed with the fresh feed. The heavy stream leaving the first separation system is2
fed to another distillation column. The distillate stream contains the remaining lightcomponents and is waste. The bottoms stream contains the desired products of benzene,toluene, xylenes, and C9aromatics. This stream is then sent to another series of distillationcolumns to separate these products. [9]4.Methods of ImplementationWe used the feed stream data from CHE 307 calculations. To begin with, allcalculations have been done using a basis of 100 gmol/s in Stream 0, with compositiongiven in Table 2. Afterwards, we scaled up the process to produce 500106lbaromatics/year. SI units were used for all calculations (C, MPa, mol, s, kJ). The unitand stream labels as shown in the figure on page 4 have been used. For naming theliquid mole fractions (for benzene in stream 30, for example) as x30,B was used andvapor mole fractions as y5,B. Mole fractions of vapor/liquid mixtures should be labeledwith z’s. Total molar flow rate of stream 5 is S5. Molar flow rate of benzene in stream5 is B5.Mass units should have ’ (e.g., B’5). Species abbreviations are shown in the table. Flow rateshave been recorded to 3 decimal places.For the implementation of the whole process on Aspen, the first and foremost is the decision oftaking the property method. Due to the presence of hydrocarbons and the wide range ofpressures of operation (ranging from 1 bar to 26 bar) an equation of state method was used,more specifically, PENG ROBINSON method was used which not only works for generatingdata for high pressure systems, but also works with hydrocarbon and gas refining systems.3
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