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SYNTHESIS OF DIMETHYL ETHER Bachelor of Chemical Engineering CAPSTONE I SUBMITTED BY: GROUP 7 AIGERIM BAKYTZHANOVA ID 201100705 DINARA GAPEYENKO ID 201101210 RUSLAN MARTEMYANOV ID 201102238 AZAT YERKINOVA ID 201103889 SUBMITTED TO: PROFESSOR COSTIN-SORIN BILDEA 2015 DECLARATION I/We hereby declare t...

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SYNTHESIS OF DIMETHYL ETHER

Bachelor of Chemical Engineering

CAPSTONE I

SUBMITTED BY: GROUP 7 AIGERIM BAKYTZHANOVA

ID 201100705

DINARA GAPEYENKO

ID 201101210

RUSLAN MARTEMYANOV

ID 201102238

AZAT YERKINOVA

ID 201103889

SUBMITTED TO: PROFESSOR COSTIN-SORIN BILDEA

2015

DECLARATION

I/We hereby declare that this report entitled “Synthesis of Dimethyl Ether” is the result of my/our own project work except for quotations and citations which have been duly acknowledged. I/We also declare that it has not been previously or concurrently submitted for any other degree at Nazarbayev University.

Names:

Signature:

Aigerim Bakytzhanova Dinara Gapeyenko Ruslan Martemyanov Azat Yerkinova Date: 27.11.2015

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ABSTRACT This project considers the design of dimethyl ether (DME) production plant that is aimed to produce 200,000 tons of DME annually. In order to reach that production rate methanol should be fed at a rate of 280,000 tons per year. The DME production process is done by indirect method that includes only methanol dehydration and that reaction is known to be catalytic therefore process is done by presence of γ-Al2O3 catalyst in adiabatic reactor. Methanol with 99.5% purity is heated to 2900C before it goes to reactor. Since the methanol dehydration is an exothermic reaction, the reactor outlet mixture flows out at 3900C. Adiabatic reactor provides 66% of methanol conversion. Reactor outlet mixture is then sent to distillation columns, where DME with 99% purity is separated from water/methanol mixture. In the second distillation column methanol is removed from water and returns back at a recycle at rate of 566.7 kmol/hr, while water is drown out from process at rate of 550 kmol/hr. Aspen Plus software will be used for designing the reactor, heater and two distillation columns. Also project considers the preliminary economic evaluation and safety consideration of a chemical plant.

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TABLE OF CONTENT 1. INTRODUCTION ................................................................................................................. 1 2. DME APPLICATION ............................................................................................................ 1 3. PROCESSES TO OBTAIN DIMETHYL ETHER ................................................................ 3 3.1 Direct method of DME synthesis ..................................................................................... 4 3.2 Indirect method of DME synthesis................................................................................... 5 3.2.1 Reactor types for DME synthesis in Gas Phase ...................................................... 11 3.2.2 Reactor types for DME synthesis in Liquid Phase .................................................. 14 4. MARKET ANALYSIS ........................................................................................................ 16 5. BASIS OF DESIGN ............................................................................................................. 18 5.1 Chemistry ....................................................................................................................... 19 5.2 Thermodynamics ............................................................................................................ 19 5.3 Kinetics........................................................................................................................... 20 5.4 Mechanism ..................................................................................................................... 22 5.5 Physical Properties of Mixture ....................................................................................... 22 5.6 Thermodynamic Model .................................................................................................. 25 6. CONCEPTUAL DESIGN .................................................................................................... 26 6.1 Input/ Output analysis .................................................................................................... 26 7. REACTOR-SEPARATION ................................................................................................. 28 7.1 Reactor choice ................................................................................................................ 28 7.1.1 Isothermal and Adiabatic Reactors for Methanol Dehydration .............................. 28 7.1.2 Reaction Condition .................................................................................................. 30 7.2 Separation Process.......................................................................................................... 31 8. PRELIMINARY MASS BALANCE ................................................................................... 33 9. HEAT INTEGRATION ....................................................................................................... 35 10. HEALTH AND SAFETY CONSIDERATIONS .............................................................. 36 10.1 DME ............................................................................................................................. 36 iv

10.2 Methanol....................................................................................................................... 36 10.3 Sustainability ................................................................................................................ 37 11. ECONOMIC EVALUATION............................................................................................ 37 11.1 Capital Cost .................................................................................................................. 37 11.2 Operating Cost.............................................................................................................. 38 11.3 Profit ............................................................................................................................. 38 12. FUTURE PLANS ............................................................................................................... 39 REFERENCE ........................................................................................................................... 41 APPENDIX .............................................................................................................................. 45

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LIST OF TABLES Table 1. Table of commercial methanol production catalysts ................................................... 8 Table 2. Physical properties of DME and Methanol ................................................................ 10 Table 3. Properties of DME in comparison with diesel fuel, propane and butane................... 11 Table 4. DME plants ................................................................................................................ 17 Table 5. Physical properties of the main chemical materials ................................................... 19 Table 6. Equilibrium constants and free energies for DME synthesis ..................................... 19 Table 7. The properties of γ-Al2O3 catalyst ............................................................................. 20 Table 8. The reaction rates for the DME synthesis using γ-Al2O3 catalysis ............................ 20 Table 9. The properties of 3-mm γ-Al2O3 catalyst for Bercic model ...................................... 21 Table 10. Binary interaction parameters .................................................................................. 26 Table 11. Mass balance equations list. ..................................................................................... 33 Table 12. Breakdown of Capital cost ....................................................................................... 45 Table 13. Breakdown of Total Operating Cost ........................................................................ 45 Table 14. Date for Figure 17 .................................................................................................... 46

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LIST OF FIGURES Figure 1: DME applications ....................................................................................................... 3 Figure 2: Scheme of routes to produce DME ............................................................................ 3 Figure 3: The single-step DME synthesis .................................................................................. 5 Figure 4: Methanol production flow diagram ............................................................................ 9 Figure 5: The chemical structure of DME ............................................................................... 10 Figure 6: Indirect DME synthesis from natural gas in adiabatic fixed-bed reactor ................ 12 Figure 7: Comparison of different types of DME reactors ...................................................... 14 Figure 8: CD with Distillation Column .................................................................................... 15 Figure 9: Schematic presentation of DWC .............................................................................. 16 Figure 10: Global DME market ............................................................................................... 18 Figure 11: Residue curve for Dimethyl/Water/Methanol ........................................................ 23 Figure 12: T-xy diagram for Dimethyl/Methanol at 1 and 10 bar ........................................... 24 Figure 13: T-xy diagram for Methanol/Water at 1 bar............................................................. 24 Figure 14: Production Path ....................................................................................................... 26 Figure 15: Separation section ................................................................................................... 27 Figure 16: Scheme of adiabatic DME reactor .......................................................................... 29 Figure 17: Scheme of isothermal DME reactor ....................................................................... 29 Figure 18: Conversion versus Temperature profile for 15 bar ................................................. 30 Figure 19: Three components separation sequence.................................................................. 31 Figure 20: Diagram of separation process................................................................................ 32 Figure 21: Preliminary Process flowsheet. ............................................................................... 33 Figure 22: Preliminary flowsheet with stream data for ideal conditions ................................. 35 Figure 23: Flowsheet with heat integration .............................................................................. 36 Figure 24: Decision tree of DME production........................................................................... 40

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ABBREVIATIONS Ci - Concentration of chemical (kmol/m3) Ki - Adsorption constant (m3/kmol) Pi - Partial Pressure k, kr, k1,k2 – Thermodynamic equilibrium constant ks - Reaction Rate constant (kmol/kg*h) E/DME – Dimethyl Ether M - Methanol W – Water rA– Rate of reaction T – Temperature Fw– Working capital Fc – Fixed cost Kp – process constant Cei– Equipment individual cost Cei,0 – Equipment reference cost Fm,t,p – correction factor

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1. INTRODUCTION In recent years alternative energy sources have received large attention due to the fact that oil, gas and coal resources are limited and environment pollution is increasing. Biofuel is one of the promising alternative sources of energy synthesized from alcohols by chemical reaction. The idea of implementation of biofuel found a wide spread throughout the world. One of such green fuels is Dimethyl Ether (DME). DME is the organic compound with chemical formula CH3OCH3. DME is non-toxic, colorless gas, non-corrosive and environmentally friendly. DME is an excellent clean fuel, capable for easy transportation, and could be applied in such fields as transport, household, power generation. It can be synthesized from such feedstocks as natural gas, crude oil, coal, waste mass and biomass (Kiss, 2012, p. 74). The synthesis of DME occurs in presence of different commercial solid catalysts such as γ-Al2O3 in liquid or gas phase. Moreover, DME production considers either direct or indirect method (ibid.). This project will consider the production of DME with purity 99.5% through the indirect method implying the methanol dehydration in a gas phase using the adiabatic reaction and two distillation columns for separation part. Additionally, this project will cover the market analysis, the process of DME synthesis, kinetics of the methanol dehydration and safety considerations.

2. DME APPLICATION The largest consumer of DME is China, using about 90% of the world consumption. The main application of DME in China is residential heating and cooking. Moreover, the Shanghai city administration is going to use DME as fuel for buses, taxis and commercial trucks. This is made aiming to reduce the emissions and become less dependent on oil imports. Several announcements were done that 85% of China vehicles will use DME as a fuel (Shana, 2011). In Europe, Volvo has engineered the DME fleet and is testing the trucks with low emissions from DME. For this purpose, the black liquor (wood pulp byproduct) is turned into DME at four Sweden plants. The trucks are used in the whole Sweden to lessen the emissions. The Volvo pilot program continues in Texas with union of several companies to meet EPA standards for economy of fuel and air pollution. Summing up, the main stakeholders in Europe are Volvo group, Chemrec and Preem from Sweden, Haldor from Denmark and Total from France (Kauffman, 2014).

Conventionally, the application area included the propellant function in a variety of personal care products, such as foams, shaving creams, antiperspirants, etc. (Nexant Inc., 2008). The main cause of the usefulness as propellant is high water solubility (DuPont, 2000). In the 1970s and 1980s, the increase of the oil prices and oil embargos took place. The consequences of that was the need to conversion of oil resources to liquid fuels that are easily transported (Fleisch et al., 2012). Global research and development was aimed to reach that goal. As a result, the patent that described methanol fuel that included DME was introduced in Germany (Manjunke & Mueller, 1984) and the USA presented patent that investigated the diesel engine operability on 95 percent to 99 percent DME based fuel (Levine, 1990). Nevertheless, as DME had to be modified as well as engine constructed for diesel, the further development was needed. The DME potential as fuel continued to grow as the LPG had similar properties to DME. The main application DME became the blending with LPG in 20 to 80 ratios to meet the household heating and cooking use (Fleisch et al., 2012). In late 1990s, Electric Power Development, General Electric Co. and Amoco performed the experimental use of DME as gas turbine fuel that showed efficient performance and low emissions level (Fleisch et al., 2012). Summing up, the DME can be used as: 

A substitute for liquefied petroleum gas in heating and cooking purposes.



A substitute for chlorofluorocarbon during the production of paint-aerosols cans and cosmetics as a propellant.



A substitute for diesel fuel. If the engine is modified to operate on DME basis, high cetane number DME is used as a fuel.



A precursor during the acetic acid and dimethyl sulfate synthesis.



A refrigerant.



A rocket propellant.



A carrier in foggers and sprays against insects.

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A solvent during the extraction of compounds that are organic.

More applications are listed below in the Figure 1.

2

CH4

SNG

H2

Fuel Cell

Centralized Power Generation

Boiler/Turbine

Distributed Power Generation

Diesel Engine/Micro Gas Turbine

Reforming

Fuels

DME

Combustion Diesel Vehicle Propellant, Solvent Home Use Device

Chemicals Raw material for CI chemistry Figure 1: DME applications

3. PROCESSES TO OBTAIN DIMETHYL ETHER There are two routes to produce DME: a two-step (indirect) and a one-step (direct) method. DME is typically produced through indirect method using syngas as a feedstock. DME can be synthesized from any stock materials containing methane such as natural gas, biogas, water treatment gas, and coal gasification. Water supply requirements and wastewater quantities are minimal (Ohno, et al., 2005, p. 4).

Figure 2: Scheme of routes to produce DME (Adapted from Pourazadi, et al., 2011, p. 1211)

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3.1 Direct method of DME synthesis Synthesis of dimethyl ether can be done directly from syngas with (Equation 3.1) or without water-gas shift reaction (Equation 3.2): 3CO + 3H2 → CH3OCH3 + CO2

△ 𝐻 = -246.0 kJ/ mol

(3.1)

2CO + 4H2 → CH3OCH3 + H2O

△ 𝐻 = -205.0 kJ/mol

(3.2)

The overall reactions imply initially, conversion of syngas into methanol (Equation 3.3) and next, dehydration of methanol into dimethyl ether (Equation 3.4). Those two major chemical reactions are made in one reactor and therefore the given method is called ‘single-step’ synthesis of DME (Peng, et al., 1999). Hybrid catalysts are used in direct process. Hybrid catalysts are produced by combination of commercial methanol synthesis catalyst and methanol dehydration catalyst (Ohno, et al., 2005, p. 5). 2CO + 4H2 → 2CH3OH

△ 𝐻 = -182 kJ/mol

(3.3)

2CH3OH → CH3OCH3 + H2O

△ 𝐻 = -23 kJ/mol

(3.4)

Additionally, to decrease the water level and to increase the rate of methanol dehydration in the system a water-gas shift reaction takes place (Equation 3.5). CO + H2O → CO2 + H2

△ 𝐻 = -41 kJ/mol

(3.5)

It was deducted that methanol produces in higher rate from the CO/CO2/H2 mixture rather than from the mixture consisted only from carbon monoxide and hydrogen (Kalala, 2012, p. 15). The conversion of syngas into dimethyl ether is made into slurry or fixed bed reactors by using bi-functional catalyst obtained by mixing CH3OH synthesis and CH3OH dehydration catalysts resulting in the high level of activity for the chemical reactions (ibid., p.16). Taking into account that in direct methods two reactions occur simultaneously, the direct route has some economic benefits such as elimination of methanol purification, reducing operation costs, etc. In addition, one step method of DME synthesis also can give high purity of dimethyl ether (99.5 %), and since it uses only one reactor for the chemical reactions it results in lower dimethyl ether production cost. However, due to the fact that overall process of the DME production is too exothermic it requires constant temperature control to overcome the system damage. Moreover, the separation process of DME and carbon dioxide becomes difficult and

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costly due to the presence of methanol in the system (Azizi, et al., 2014, p. 152).

Figure 3: The single-step DME synthesis

Moreover, direct process of DME synthesis has not been examined on large-scale production. The indirect method has advantages in terms of operation control because of reactor types that are used and optimal operation conditions for each step can be easily selected. As a result it is easier to remove heat from the reactor due to less heat generation compared to direct synthesis. Therefore, conventional method of DME prod...