1. DEPARTMENT OF CHEMICAL ENGINEERING
By A.V. Baloyi
Subject : Chemical Process Design
Project : Methane Oxidation to Acetic Acid
2. 1
ABSTRACT
The main objective of this project is to produce acetic acid from methane. This project will show
the industrialization or commercializing of this process by using Unisim design software.
The objective of the development of new acetic acid processes has been to reduce raw material
consumption, energy requirements, and investment costs. Significant cost advantages resulted
from the use of carbon monoxide and of low-priced methanol as feedstock’s. At present,
industrial processes for the production of acetic acid are dominated by methanol carbonylation.
The kinetic reactor has therefore been efficient for the operation. Material and energy balances
were constructed effectively using the data generated from the simulated unit operations. The
commercialization the production acetic acid from methane oxidation it is a success. The
production occurs in three major steps. In the process another method is introduced to maximize
the production without any loss of the raw material. The carbonylation stage makes sure that no
byproducts are discharged everything is converted to acetic acid.
The scope of work covered in the project includes:
Designing a simulation of the plant using UniSIM
Constructing a process flow diagram of the entire process
Calculating mass and energy balances
Equipment design and sizing
Project investment and costs
Carry out HAZOP study on the process
3. 2
Table of Contents
Abstract 1
1. Introduction 3
2. Literature Review 4
2.1 Theoretical Background 4-5
2.2 Experimental 6-8
3. Technical 9
3.1 Process Flow Diagram 9
3.2 Material and Energy Balance 10-11
3.3 Process Description 12-13
3.4 Design and Description of each Unit 14
4. Hazards & Safety Considerations 20
5. Economic Analysis 21-22
6. Conclusions and Recommendations 23
7. References 24
8. Appendix 25-28
4. 3
1. INTRODUCTION
Acetic acid is an important commodity used in chemical industries, with about 9 million tons of
world demands per year. The primary use of this chemical is in the manufacture of assorted
acetate esters, fungicide, organic compounds, organic solvents and the preparation of
pharmaceuticals, cellulose acetate that is important in making film and plastic wares, perfumes
and synthetic fiber. Methane is the most abundant reactive trace gas in the atmosphere and arises
from both natural and anthropogenic sources. It is a valuable gas and is usable at a wide range of
concentrations, down to 5%. The main objective of this process is to produce acetic acid from
methane. Methane oxidation to acetic acid catalyzed by Pd2+ cations in the presence of oxygen
is the objective of this project but for total conversion other methods will be used because the are
some byproduct in the reaction, which is methanol. This project will show the industrialization or
commercializing of this process by using Unisim design software. This method it inverted in the
lab by Mark Zerella, Argyris Kahros and Alexis T.Bell
The conversion of methane to acetic acid is currently carried out in a three-step process. Methane
is first reformed in a heterogeneously catalyzed process that is energy and capital-intensive to
produce synthesis gas, a mixture of CO and H2. The CO and H2 then react at high pressure in a
second step to produce methanol, and finally, in the third step, acetic acid is produced by
homogeneous-phase carbonylation of methanol. This process is also carried in three major
stapes. The present method to the liquid phase oxidation of methane with an oxidant in a strong
acid in the presence of a catalyst comprising palladium combined with a promoter. However, this
process displayed a serious drawback. During the reaction particles of palladium black were
formed due to the reduction of Pd (II) to Pd. This invention comprises a process for the
production of acetic acid, or derivatives such as methyl acetate and acetyl sulphate, from
methane, by contacting a methane-containing feed with an oxidant in the presence of a
5. 4
palladium- containing catalyst, a promoter, and an acid selected from concentrated sulfuric acid
and fuming sulfuric acid.
2. LITERATURE REVIEW
2.1. Theoretical Background
This invention relates in general to an improved process for the production of acetic acid or a
derivative thereof by liquid phase oxidation of methane. In particular the present invention
relates to the liquid phase oxidation of methane with an oxidant in a strong acid in the presence
of a catalyst comprising palladium combined with a promoter. The primary process route used
today for production of acetic acid is by catalytic reaction of methanol and carbon monoxide.
Such a process, typically termed “carbonylation”, is described in a number of patents and
publications. Rhodium, palladium or iridium-containing catalysts have been found especially
useful for conducting this reaction. The approach for the direct synthesis of acetic acid from
methane has been reported by Periana et al., who describe the oxidation of methane to acetic acid
catalyzed by Pd2+ cations in 96 wt% sulfuric acid.
The only other products observed are methyl bisulfate and carbon dioxide. Whereas the
selectivity to the liquid-phase products is reported to be as high at 90%, Pd2+ is observed to
precipitate from solution as Pd-black, causing the reaction to stop. According to the invention,
acetic acid is produced from methane by contacting the methane, in a feed comprising methane
and optionally other components, With an oxygen containing gas in the presence of a palladium-
containing catalyst, a promoter, and an acid selected from concentrated sulfuric acid and fuming
sulfuric acid. The inclusion of a promoter, for example a copper (II) salt, increases the rate of
acetic acid formation from methane by more than a factor of five as compared With the Periana
et al. Work and, in addition, inhibits the precipitation of Pd black, it reduced the production of
the sulfur products and carbon dioxide.
6. 5
The methane that is introduced into the process may be an essentially pure methane stream, a
methane stream that contains various impurities, or a stream that contains methane as one of
several components, for example, a methane containing stream that emanates from a chemical
process unit, a natural gas stream, a methane-containing stream produced by a gas generator, a
methane-containing off-gas, a biogenic methane stream, and the like. The methane feed to the
process may also contain other materials that may be oxidized under the process conditions to
form acetic acid. Methanol, dimethyl ether, methyl acetate and methyl bisul fate may also be fed
to the process. The palladium-containing catalyst may be any palladium containing material that
possesses the necessary catalytic activity for this reaction. Preferred palladium-containing
catalysts are palladium salts such as palladium (II) and palladium (IV) sulfates, chlorides,
nitrates, acetates, acety lacetonates, amines, oxides, and ligand-modified palladium systems, for
example systems containing ligands such as phosphines, nitriles, and amines. Promoters suitable
for use in the process of this invention include materials that have a demonstrated REDOX
couple with palladium, such as salts of copper, silver, gold, vanadium, niobium, tantalum, iron,
chromates, and organic sys tems such as hydroquinone or anthraquinone complexes with such
metals. Preferred promoters for the process are salts of copper and iron, most preferably cupric
salts. Other preferred promoters include cupric and cuprous nitrate, sulfate, phosphate, acetate,
acetylacetonate, and oxide, ferric chloride and ferric sulfate.
For metals that have multiple valences, e.g. copper and iron, the promoter can be introduced as a
salt of the lower valence which becomes oxidized in situ When in contact With the oxygen-
containing gas or With H2SO4 or S03. In addition to its primary function, the promoter may also
serve to catalyze regeneration of the acid. Additionally, a salt of platinum or mercury may be
included in the process, to assist in conversion of methane to methanol and/or methyl bisulfate,
which may then be converted to acetic acid by the Catalyst/promote
8. 7
2.2. Experimental
2.2.1. Method 1
The effects of CH4 and O2 partial pressures were explored to determine the influence of these
variables on the yields of acetic acid and methyl bisulfate, the selectivity of methane conversion
to these products, and the retention of Pd2+ in solution. Unless specified otherwise, all reactions
were carried out in 96 wt% H2SO4 containing 20 mM of PdSO4 at 453 K. The initial partial
pressures of CH4 and O2 were chosen to avoid compositions that would result in an explosive
mixture during any part of the reaction. The results of these experiments are given in Tables 1
shows that for an initial CH4 partial pressure of 200 psi, the yield of acetic acid rose from 65.7 to
181 mM as the initial partial pressure of O2 increased from 0 to 125 psi. Over the same range of
O2 partial pressures, the yield of methyl bisulfate increased from 2.5 to 4.8 mM, whereas the
production of methanesulfonic acid increased from 3.0 to 29.4 mM. The are other two sulfur-
containing byproducts, sulfoacetic acid and methane disulfonic acid.
Figure 1: method 1 results
9. 8
2.2.2. Method 2 (preferred method)
In this example CH4 and 02 Were reacted at 180° C. in a high pressure, glass-lined autoclave
containing catalytic amounts of PdSO4 and CuCl2 added to concentrated sulfuric acid (96%
W/W). Reactions were carried out for 4 h, after which an equal volume of Water Was added to
the product solution in order to hydrolyze any anhydrides. Reaction products were analyzed by
1H NMR. More specially, using a 50 mL glass autoclave liner, 0.0121 g (20 mM) of PdSO4, and
0.0081 g (20 mM) of CuCl2 Were dissolved in 3 mL (5.67 g) of 96% sulfuric acid. A small
Teflon-coated stir bar Was added prior to sealing the autoclave. The reactor was purged With Ar
and then pressurized With 400 psig of CH4 and 30 psig of O2.
Figure 2: lab results
10. 9
2.3. Carbonylation of methanol to acetic acid
Novel acetic acid processes and catalysts have been introduced, commercialized, and improved
continuously sincethe1950s.The objective of the development of new acetic acid processes has
been to reduce raw material consumption, energy requirements, and investment costs. Significant
cost advantages resulted from the use of carbon monoxide and of low-priced methanol as
feedstock’s. At present, industrial processes for the production of acetic acid are dominated by
methanol carbonylation.
The carbonylation of methanol is catalyzed by Group VIII transition metal complexes, especially
by rhodium, iridium, cobalt, and nickel. All methanol carbonylation processes need iodine
compounds as essential co-catalysts, the reaction proceeding via methyl iodide, which alkylates
the transition metal involved. Apart from acetic acid, the carbonylation of methanol also gives
rise to the formation of methyl acetate, . In some carbonylation processes methyl acetate is also
used as a solvent. The determination of reaction rate parameters, equilibrium constants, CO
solubility and rate constant, can give rise to develop a reaction rate expression that could be used
to design and to scale up the process. So can the study of the determined parameters in the
reaction modeling and simulation by commercial simulators such as HYSYS.Plant. Because of
the lack of information on homogeneous catalysts in this field, this study focuses on the kinetics
of the homogeneous Rh-catalyzed methanol carbonylation (CH3I: promoter; water content: ~ 11
wt. %) using experimental tests and applying theoretical methods such as ab initio method with
the help of Gaussian-98 program. In the following section, the experimental apparatus of the
research are discussed. Then, the kinetics, modeling and simulation of the carbonylation of
methanol are developed
14. 13
3.3 Process Description
The design models a process based on a three-part system containing the following systems: The
methane oxidation reactor, flash distillation system and the carbonylation reactor.
The reaction requires high pressure and temperatures, from the lab report it required 1800
C and
400Psi of pressure. A compressor and heater were introduced to system. The system consists of
a kinetic reactor containing palladium sulphate as catalyst. The reactor feed is 900 kmol of
methane and 1490 kmol of air. The methane to oxygen ration is 0.3. The methane conversion is
100% (calculated value). The reaction is highly exothermic and therefore water will be used as a
cooling medium, which would then be used as a steam utility.
A separator was introduced to remove the excess of air to make the flash distillation column to
converge faster. The product where cooled down to -500
C for the separator. The liquid products
were transferred to the flash distillation column where only the two components had to be
separated, methanol the byproduct and acetic acid the required product. They feed at temperature
of -500
C and pressure of 1atm.Them boiling points where very low, high pressure and low
temperatures were used at the flash distillation column. The top came out methanol and bottom
was acetic acid.
Realizing that a lot of methanol is produced another method was found to convert methanol to
acetic acid. This method was introduced to maximize production of acetic acid to make sure no
raw material goes to waste. The new reaction was called carbonylation of methanol.
Carbonylation of methanol is when methanol reacts with carbon monoxide to produce acetic
acid. It is a homogenous reaction where rhodium is used as catalyst. A packed bed reactor was
used for this reaction. The 98kmol of was converted to acetic acid (97.37% conversion). The
reaction occurs in 20MPa and temperature of 2510
c. A compressor was introduced to system.
the reaction was endothermic no cooler was required .
15. 14
Carbonylation of methanol
Kinetics of reaction
COOHCHOHCHCO K
33
CKr eq
)/102.9exp(105.2 410
RTKmethane
There is only one reaction in the reactor which carbonylation of methanol to acetic acid and
methanol. The E and A for the arrinhius equation were found in one of references of the
research. All the assumptions were in UNIFAC and 97.3% conversion was achieved
Catalyst
The production of acetic acid by the Monsanto process utilizes a rhodium catalyst and operates at
a pressure of 30 to 60 atmospheres and at temperatures of 150 to 200°C. During the methanol
carbonylation, methyl iodide is generated by the reaction of added methanol with hydrogen
iodide. The infrared spectroscopic studies have shown that the major rhodium catalyst species
present is [Rh (CO)2I2]
16. 15
3.3 Design and Description of each Unit
3.4.1 Mixer
Function: A mixer is used to manipulate a heterogeneous physical system, with the intent to
make it more homogeneous.
Figure 4 mixer
A mixer was introduced to the system to combine the in feed streams to so they can be heated
and compressed for reactor.
3.4.2 Heater
17. 16
Figure 5 heater
From the lab results the reaction required a high pressures and temperatures. The mixed feed was
heated to 1800
c and 400Psi of pressure that was the feed to the reactor. The energy required was
1.17e7 kj/hr
3.4.3 Methane oxidation reactor
Function: A reactor is a vessel in which chemical reactions take place. Conditions of operation
are based on the nature of the reaction system and its behavior as a function of temperature,
pressure, catalyst properties, and other factors.
Kinetics of the reaction
OHCHCOOHCHOCH Keq
2324
CKr methane
)/107.1exp(1007.1 522
RTKmethane
There is only one reaction in the reactor which is methane oxidation to acetic acid and methanol.
The E and A for the arrinhius equation were found in one of references of the research. All the
assumptions were in UNIFAC and 100% conversion was achieved.
Catalyst
Palladium catalyzed cross-coupling reactions have revolutionized the way in which molecules
are constructed. The field of cross-coupling has grown to include numerous strategies for C-C,
C-N, and C-O bond formation. While a range of palladium catalysts have been developed for
each transformation, it is often difficult to determine which catalyst is best for your desired
cross-coupling application. This reaction between CH4 and 02 is reacted at 180° C. in a high
pressure, catalytic amounts of PdSO4 and CuCl2 added to concentrated sulfuric acid (96%
W/W).
18. 17
3.4.4 Cooler
Function: A cooler is a heat removal devices used to cool the working fluid.
Figure 6 cooler
The product stream was at high temperatures and pressure. It required to be cooled for
separation. It was cooled from 4000c to -500
c at that temperature air is still in gaseous phase. The
pressure was also decreased from 2809 kPa to 1atm. It required energy of 4.5e7kj/hr
3.4.5 Separator
19. 18
Function: A separator is used to separate dispersed liquid in a gas stream. It is important that the
dimension of the separator is large enough so that liquid can settle in the bottom of the tank.
Figure 7 separator
The separator was the first stage of separation where excess of air is removed from the main
product. The excess of was emitted to atmosphere where it still safe for the environment. The
emissions contained high amounts of nitrogen.
3.4.6 Distillation column
Function: A distillation column is used to separate different components in a fluid, by using their
difference in boiling point.
The design
20. 19
Figure 8 distillation column
The column has 10 stages and the feed stage is no 5. It is full reflux and the operational pressures
are between 1000kPa and 1015kPa.
Worksheet (Distillation Column)
21. 20
Figure 9 worksheet
The worksheet results show that methanol exits at the top and acetic acid at the bottom. The
UNIFAC models it is advantageous because the VLE can be predicted for a large number of
systems without introducing new model parameters that must be fitted to experimental VLE data.
The binary coefficients of acetic acid were displayed by the UNIFAC only. The first batch of
acetic acid is produced and the methanol continues to produce the second batch.
22. 21
3.4.7 Compressor
Function: A compressor converts power into kinetic energy to increase the pressure of gases.
Compressors are used for high operation from 200 kPa - 400MPa.
Figure 10; compressor
The compressor was installed because of the knowledge that was obtain from research that
carbonylation occurs in at high pressures. The compressor was compressing the methanol so the
inlet of the reactor can have high pressures.
3.4.8 Mixer 2
Figure 11 mixer
The mixer is there to combine both the reactants so they could feed to the reactor. The feed to the
reactor is at a pressure of 20MPa and temperature of 2510
C .
23. 22
4. HAZARDS AND SAFETY CONSIDERATIONS
Hazards Identification
Very hazardous in case of skin contact, of eye contact , of ingestion, of inhalation.
Hazardous in case of skin contact (corrosive, permeator), of eye contact (corrosive).
Liquid or spray mist may produce tissue damage particularly on mucous membranes of
eyes, mouth and respiratory tract.
Inhalation of the spray mist may produce severe irritation of respiratory tract,
characterized by coughing, choking, or shortness of breath.
Reacts with metals to produce flammable hydrogen gas.
First Aid Measures
Eye Contact: immediately flush eyes with plenty of water for at least 15 minutes.
Skin Contact: immediately flush skin with plenty of water for at least 15 minutes while
removing contaminated clothing and shoes. Cover the irritated skin with an emollient.
Inhalation: remove to fresh air. If not breathing, give artificial respiration. If breathing is
difficult, give oxygen.
Ingestion: Do not induce vomiting unless directed to do so by medical personnel.
Fire Fighting Measures
Dry chemical powder.
Alcohol foam.
Water spray or fog
Accidental Release Measures (Spillage)
Absorb with dry earth, sand or other non-combustible material.
Absorb with an inert material and put in an appropriate waste disposal.
Use water spray curtain to divert vapor drift.
Neutralize the residue with a dilute solution of sodium carbonate.
Handling and Storage
Keep away from heat.
Keep away from sources of ignition.
Do not ingest.
Do not breathe gas/fumes/ vapor/spray.
Store in a segregated and approved area.
24. 23
5. ECONOMIC ANALYSIS
Chemical plants are built to make profit, and an estimate of the investment required and the cost
of production, are needed before the profitability of a project can be assessed. In the economic
analysis of a chemical plant, the costs for the plant are divided into investment cost and operating
cost.
The fixed capital investment is the total cost of the plant ready for start-up. The fixed capital
investment can be subdivided into manufacturing fixed-capital also known as direct cost, and
nonmanufacturing fixed capital or indirect cost. The working capital for an industrial plant
consist of the total amount of money invested in raw materials and supplies carried in stock, cash
for monthly payment of operating expenses, accounts payable, and taxes payable, etc.
The total capital investment (TCI) is the sum of the fixed capital investment end the working
capital. The ratio of working capital to total capital investment used by most chemical plants is
10-20 percent of the total capital investment. In our analysis the working capital was estimated to
be 15 percent of the total capital cost.
Estimation of Total Capital Investment
S. No. Description
Direct Costs
1 Purchased Equipment R 88 000,00
2 Purchased Equipment Installation R 30 000,00
3 Instrumentation and Controls R 54 700,00
4 Piping R 39 990,00
5 Electrical Equipment and Materials R 36 499,00
6 Buildings (Including services) R 59 999,00
7 Yard Improvements R 10 141,00
8 Service Facilities R 21 500,00
9 Land R 525 000,00
Total Direct Costs (D) R 865 829,00
Indirect Costs
10 Engineering and Supervision R 68 000,00
11 Construction Expenses R 54 600,00
12 Contractors Fee R 46 533,00
Total Indirect Costs (I) R 169 133,00
Fixed Capital Investment (FCI), D + I R 1 034 962,00
Working Capital (WC), 15% R 155 244,30
Total Capital Investment (TCI) R 1 190 206,30
Cost in R.
25. 24
Estimation of Total Product Cost
S. No. Description
Manufacturing Costs
Direct Production Costs
1 Raw Materials R 42 114,00
2 Operating Labor R 229 588,00
3 Operating Supervision R 120 411,00
4 Power and Utilities R 52 000,00
5 Maintenance and Repairs R 21 899,00
6 Operating Supplies R 18 577,00
7 Laboratory Charges R 38 999,00
8 Patents & Royalties R 0,00
9 Catalysts and Solvents R 0,00
Total Direct Production Costs R 523 588,00
Fixed Charges
10 Depreciation R 80 000,00
11 Taxes R 58 000,00
12 Insurance R 515 011,00
13 Rent R 0,00
Total Fixed Charges R 653 011,00
Plant Overhead Costs
14 Plant Overhead Costs R 205 161,00
Total Plant Overhead Costs R 205 161,00
Total Manufacturing Costs (M) R 1 381 760,00
General Expenses
15 Administrative Expenses R 6 500,00
16 Distribution & Marketing Expenses R 8 500,00
17 Research & Development R 0,00
18 Financing (Interest) R 0,00
Total General Expenses (G) R 15 000,00
Total Product Cost, M+ G R 1 396 760,00
Cost in R.
26. 25
6. CONCLUSSION AND RECOMMENDATIONS
The commercialization the production acetic acid from methane oxidation it is a success. The
production occurs in three major steps. In the process another method is introduced to maximize
the production without any loss of the raw material. The carbonylation stage makes sure that no
byproducts are discharged everything is converted to acetic acid. The yield of acetic acid, the
primary product of methane oxidation, increases with increasing O2/CH4 ratio for a fixed CH4
partial pressure and with increasing total reactant pressure for a fixed O2/CH4 ratio. Using the
Pd/Cu/O2 mixture, the effect of reaction conditions is evaluated with the aim of maximizing the
acetic acid yield. The increase in acetic acid yield as a consequence of increasing O2/CH4 ratio
is accompanied by only a modest loss in selectivity to oxygen containing organic products, and
the increase in total pressure of CH4 and O2 at a fixed O2/CH4 ratio results in a slight rise in the
yield of acetic acid. This study leads to an efficient and simultaneous estimation of the effects of
pressure, temperature, and the thermodynamic restrictions on kinetic investigation of the
homogeneously rhodium catalyzed carbonylation process. The kinetic reactor has therefore been
efficient for the operation. Material and energy balances were constructed effectively using the
data generated from the simulated unit operations.
27. 26
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