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INTRODUCTION INTRODUCTION

Vinyl acetate is a colorless, flammable liquid that also has a characteristic smell that can quickly become Vinyl acetate is a colorless, flammable liquid that also has a characteristic smell that can quickly become irri-tating. This monomer is used principally in the production of polyvinyl acetate (PVAc) and other vinyl acetate tating. This monomer is used principally in the production of polyvinyl acetate (PVAc) and other vinyl acetate co-polymers. Polyvinyl acetate is a precursor of polyvinilyc alcohol and polyvinyl acetate resins (PVA). Vinyl co-polymers. Polyvinyl acetate is a precursor of polyvinilyc alcohol and polyvinyl acetate resins (PVA). Vinyl acetate is also copolymerized as a minor raw material for vinyl chloride and ethylene to form commercial acetate is also copolymerized as a minor raw material for vinyl chloride and ethylene to form commercial  polym

 polymers and acrylers and acrylic fic fibersibers..11

Vinyl acetate is completely soluble in organic liquids but not in water. At 20º C a saturated solution of the Vinyl acetate is completely soluble in organic liquids but not in water. At 20º C a saturated solution of the monomer in water can contain between 2-2.4% of vinyl acetate, while a saturated water solution in vinyl monomer in water can contain between 2-2.4% of vinyl acetate, while a saturated water solution in vinyl ace-tate contains 1% of water. At 50ºC the solubility of the monomer in water increases in 0.1% in regards to tate contains 1% of water. At 50ºC the solubility of the monomer in water increases in 0.1% in regards to 20ºC, while

20ºC, while the solubilthe solubility ity of water iof water in n vinyvinyl l acetacetate doubles ate doubles at 50ºCat 50ºC

The most important reaction of vinyl acetate is the polymerization by free radicals which is fast and The most important reaction of vinyl acetate is the polymerization by free radicals which is fast and exo-thermic. Due to the fact that the vinyl acetate is an Esther, it presents the reactive properties of said group. thermic. Due to the fact that the vinyl acetate is an Esther, it presents the reactive properties of said group. Keeping in mind that the corresponding chain of alcohols is unsaturated, the compound presents some Keeping in mind that the corresponding chain of alcohols is unsaturated, the compound presents some differ-ences in regards to the Esther group. The speed of hydrolysis of the vinyl acetate is 1,000 times greater than its ences in regards to the Esther group. The speed of hydrolysis of the vinyl acetate is 1,000 times greater than its saturated analogous in a alkaline medium, and it was researched that its speed of hydrolysis is significantly saturated analogous in a alkaline medium, and it was researched that its speed of hydrolysis is significantly lower at a p.H. of 4.4. lower at a p.H. of 4.4. 1 1 Kirk-Othmer, (1978), Vol 23, pp 817. Kirk-Othmer, (1978), Vol 23, pp 817.

Vinyl Acetate from ethylene, acetic acid and oxygen Industrial Plant

Vinyl Acetate from ethylene, acetic acid and oxygen Industrial Plant

Simulation.

Simulation.

J.P. Contreras, J.C. Naranjo, S. Ramírez & D.M. Martínez

J.P. Contreras, J.C. Naranjo, S. Ramírez & D.M. Martínez

Chemical Engineer department, Los Andes University, Bogotá, Colombia. Chemical Engineer department, Los Andes University, Bogotá, Colombia.

I.D. Gil

I.D. Gil

Chemical Engineer department, National University of Colombia, Bogotá, Colombia. Chemical Engineer department, National University of Colombia, Bogotá, Colombia.

 Pa

 Pa er # 134650er # 134650

ABSTRACT ABSTRACT

The production of vinyl acetate monomer (VAM) represents one of the largest industries with a growth The production of vinyl acetate monomer (VAM) represents one of the largest industries with a growth es-tima

timate ote of a near 2.7% per year startf a near 2.7% per year startining in 2008. g in 2008. In recent times, thanks to diffIn recent times, thanks to different studies and the ierent studies and the importancemportance of said product

of said product, one , one process has been developed based on the process has been developed based on the reaction of ethylenreaction of ethylene, acete, acetic acid, and oxygen us-ic acid, and oxygen us-ing a Pd/Au catalyst. In this work, a detailed study was made based on a simulation of the process usus-ing the ing a Pd/Au catalyst. In this work, a detailed study was made based on a simulation of the process using the Aspen Plus v2006 program and establishing the correct operation conditions. The simulated process involves, Aspen Plus v2006 program and establishing the correct operation conditions. The simulated process involves, from the preparation of the raw materials until the dehydration of the monomer. The restrictions set for the from the preparation of the raw materials until the dehydration of the monomer. The restrictions set for the simulation corresponds to the VAM composition restriction in the extractive distillation column using glycerol. simulation corresponds to the VAM composition restriction in the extractive distillation column using glycerol.

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VAM PRODUCTION PROCESS VAM PRODUCTION PROCESS

The first available process for the synthesis of vinyl acetate was the acetoxilation of acetylene in gaseous The first available process for the synthesis of vinyl acetate was the acetoxilation of acetylene in gaseous form over a zinc acetate catalyst supported on carbon. This process consisted in the reaction of acetylene with form over a zinc acetate catalyst supported on carbon. This process consisted in the reaction of acetylene with acetic anhydride in a catalyzed medium and high temperature to form dietilene diacetate. This product passed acetic anhydride in a catalyzed medium and high temperature to form dietilene diacetate. This product passed through a cracking tower which in result gave as products acetic acid and vinyl acetate.

through a cracking tower which in result gave as products acetic acid and vinyl acetate.22 This type of reactionThis type of reaction had a

had a high production percentage (92-98%), high production percentage (92-98%), but due but due to to the increasithe increasing value of acetylenng value of acetylene, new te, new technologiechnologies andes and methodologies needed to be

methodologies needed to be research in the 60’s.research in the 60’s.

The process was modified until acetoxilation in a gaseous phase of ethylene over palladium and gold The process was modified until acetoxilation in a gaseous phase of ethylene over palladium and gold cata-lyst supported on silica gel was capable. The catacata-lyst used potassium acetate to help the reaction in a lyst supported on silica gel was capable. The catalyst used potassium acetate to help the reaction in a tempera-ture range of 423 – 463 K and a pressure range of 600 to 1,000 kPa. This is how ethylene acetoxilation with ture range of 423 – 463 K and a pressure range of 600 to 1,000 kPa. This is how ethylene acetoxilation with oxygen, acetic acid and Pd as a catalyst was developed. This process consists of two parts: a process in a oxygen, acetic acid and Pd as a catalyst was developed. This process consists of two parts: a process in a ho- ho-mogeneous liquid phase that is used to produce 25% of the production of vinyl acetate, and another mogeneous liquid phase that is used to produce 25% of the production of vinyl acetate, and another heteroge-neous gaseous phase process used to produce the last 75% of the product.

neous gaseous phase process used to produce the last 75% of the product.

The synthesis of vinyl acetate from ethylene, acetic acid and oxygen over a Palladium catalyst is a very The synthesis of vinyl acetate from ethylene, acetic acid and oxygen over a Palladium catalyst is a very im- portant

 portant indusindustrial process, but trial process, but its selectiits selectivity ivity is affected by the s affected by the production oproduction of COf CO22 due to the combustion of thedue to the combustion of the

ethylene. Various factors affect the synthesis of vinyl acetate, like for example, the dispersion of Pd, partial ethylene. Various factors affect the synthesis of vinyl acetate, like for example, the dispersion of Pd, partial  pressures from the react

 pressures from the reactives that are ives that are the catthe catalyalyst additives (near 80% st additives (near 80% if iif it is Pd/SiOt is Pd/SiO22and greater to 94% if it isand greater to 94% if it is

Pd-Au/SiO

Pd-Au/SiO22) and contact ) and contact time. time. The invThe investigatiestigation done by Han, H. F., et al. (2004) shows that the ethyon done by Han, H. F., et al. (2004) shows that the ethylene lene isis

the principal cause for the production of CO

the principal cause for the production of CO22 due to the fact that combustion kinetic does not change if thedue to the fact that combustion kinetic does not change if the

acetic acid is taken out of the medium. acetic acid is taken out of the medium.33

The process that involves ethylene, acetic acid, oxygen over a Pd catalyst medium proves to be the best The process that involves ethylene, acetic acid, oxygen over a Pd catalyst medium proves to be the best op-tion to de

tion to develop. velop. This iThis is evident because for the last thirty ys evident because for the last thirty years it has ears it has been applied been applied in in the industry. In thethe industry. In the U.S.A. alone, the production of ethylene is around 11.533x10

U.S.A. alone, the production of ethylene is around 11.533x1033 tons per year, which more than 30% is used ontons per year, which more than 30% is used on the product

the production of vinyion of vinyl acetate.l acetate.

 Productio

 Production Process n Process using Ethyusing Ethylene, Acetic Alene, Acetic Acid and Oxygencid and Oxygen..

The process is centered on the reaction between ethylene, oxygen and acetic acid in order to produce vinyl The process is centered on the reaction between ethylene, oxygen and acetic acid in order to produce vinyl acetate and water.

acetate and water. There is a second unwanThere is a second unwanted reaction in the process ted reaction in the process based on the ethybased on the ethylene lene oxidioxidization tozation to  produce

 produce water water and and carbon carbon dioxidioxide. de. The The gaseous gaseous effeffluents from the luents from the reactor reactor are are cooled cooled tryitrying tng to o have a have a partialpartial condensation of the stream. Next, the gas is separated from the liquids in a phase separator. The gas is washed condensation of the stream. Next, the gas is separated from the liquids in a phase separator. The gas is washed with acetic acid from a recycle stream. This helps to recover the vinyl acetate in the absorber. Afterwards, with acetic acid from a recycle stream. This helps to recover the vinyl acetate in the absorber. Afterwards, there is a process to eliminate the CO

there is a process to eliminate the CO22 from the gas phase and recycle it back in to the reactor the Ethylene isfrom the gas phase and recycle it back in to the reactor the Ethylene is

necessary. necessary.

The liquids that come out from the separator and the acetic acid used in the washing process enter an The liquids that come out from the separator and the acetic acid used in the washing process enter an azeo-tropic distillation tower. In this part of the process, the main objective is to separate the acetic acid (bottoms) tropic distillation tower. In this part of the process, the main objective is to separate the acetic acid (bottoms) form the water and vinyl acetate mixture (distillate). The distillate enters to a decantation process in which its form the water and vinyl acetate mixture (distillate). The distillate enters to a decantation process in which its organic product (mainly vinyl acetate) divides into a reflux stream that heads back to the distillation column organic product (mainly vinyl acetate) divides into a reflux stream that heads back to the distillation column

2 2

Kirk-Othmer,

Kirk-Othmer, Concise enciclopedia of Chemical Technology, John Wiley & Sons, 1985 (USA), pp. 1227Concise enciclopedia of Chemical Technology, John Wiley & Sons, 1985 (USA), pp. 1227 .. 3

3

Han, Y.F., et

Han, Y.F., et al, Kinetics of ethylene combustion in al, Kinetics of ethylene combustion in the synthesis of vinyl acetate over Pd/SiOthe synthesis of vinyl acetate over Pd/SiO22catalyst, Journal of Catalyst, Vol.catalyst, Journal of Catalyst, Vol. 224, 2004, pp. 60-68.

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and another stream that enters a separation train process where the proper concentration level of vinyl acetate and another stream that enters a separation train process where the proper concentration level of vinyl acetate is achieved to comply with the wanted specifications. The aqueous stream from the decanter is discarded.

is achieved to comply with the wanted specifications. The aqueous stream from the decanter is discarded.

A portion of the bottoms stream from the distillation column (mainly acetic acid) is used in the washing A portion of the bottoms stream from the distillation column (mainly acetic acid) is used in the washing proc-ess in the absorber, while the other portion of the bottom stream is mixed with pure acetic acid from the feed ess in the absorber, while the other portion of the bottom stream is mixed with pure acetic acid from the feed streams to

streams to later on enter later on enter to to an evaporation process. Tan evaporation process. The gaseous acetic acid obtained is mihe gaseous acetic acid obtained is mixed with the recyclexed with the recycle gas, oxygen and ethyl

gas, oxygen and ethylene to ene to form the feed to the reactform the feed to the reactor.or.

For a detail analysis, the process has been divided in to three parts: reaction, distillation and dehydration. It is For a detail analysis, the process has been divided in to three parts: reaction, distillation and dehydration. It is shown in figure 1.

shown in figure 1.

Figure 1. VAM pr

Figure 1. VAM production process flow diagram.oduction process flow diagram.

 Reactio

 Reaction systemn system

The reaction that produces the vinyl acetate takes place in a P.B.R. reactor where a gaseous mixture of The reaction that produces the vinyl acetate takes place in a P.B.R. reactor where a gaseous mixture of eth-ylene, acetic acid, and air (with small presence of CO

ylene, acetic acid, and air (with small presence of CO22 and water from the recycle streams) are fed to the reac-and water from the recycle streams) are fed to the

reac-tor.

tor. To To obtain an annual production oobtain an annual production of 5,000 tf 5,000 tons (amount detons (amount determiermined for the Colombined for the Colombian market) of vinan market) of vinyl ace-yl ace-tate, 2,197.3 mol per minute with a molar composition of 0.5 of ethylene, 0.07 of oxygen, 0.15 acetic acid and tate, 2,197.3 mol per minute with a molar composition of 0.5 of ethylene, 0.07 of oxygen, 0.15 acetic acid and 0.263 o

0.263 of nitrogen have to f nitrogen have to be fed. An excess of ethybe fed. An excess of ethylenlene over acete over acetic acid (3:1) music acid (3:1) must be guaranteed. t be guaranteed. The concen-The concen-tration of oxygen must be kept below 8 % molar because at higher concenconcen-trations it breaches the explosive tration of oxygen must be kept below 8 % molar because at higher concentrations it breaches the explosive limit of the mixture.

limit of the mixture.

The reactions that take place are: The reactions that take place are:

(1) (1) (2) (2)

These reactions are highly exothermic and the standard heat of reaction for the first reaction is 42.1 Kcal per  These reactions are highly exothermic and the standard heat of reaction for the first reaction is 42.1 Kcal per  mol of vinyl acetate, while the heat of reaction for the second reaction is -316Kcal per mol of ethylene.

mol of vinyl acetate, while the heat of reaction for the second reaction is -316Kcal per mol of ethylene.

The heat of reaction is removed by generating vapor in the shell section of the tubes. This vapor is used in The heat of reaction is removed by generating vapor in the shell section of the tubes. This vapor is used in other part of the process. This is the same for the reaction catalyzed by palladium and gold supported by silica. other part of the process. This is the same for the reaction catalyzed by palladium and gold supported by silica.

O O  H   H  O O  H   H  C  C  O O O O  H   H  C  C   H   H  C  C 22 44 22 44 22 22  Pd  Pd  44 66 22 22 2 2 1 1 + +    →→       + + + + O O  H   H  CO CO O O  H   H  C  C 22 44 ++33 22      → Pd  Pd →22 22 ++22 22

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The temperature must be below 200ºC because at this temperature the catalyst suffers irreversible mechanical The temperature must be below 200ºC because at this temperature the catalyst suffers irreversible mechanical damages. The catalyst is activated with a temperature over 140º C. This allows to take an inferior operation damages. The catalyst is activated with a temperature over 140º C. This allows to take an inferior operation limit temperature of 150ºC.

limit temperature of 150ºC.

The recommended operation pressure is between 8 and 10 atm (Dimian y Bildea, 2008) because higher  The recommended operation pressure is between 8 and 10 atm (Dimian y Bildea, 2008) because higher   pressures favor the

 pressures favor the productivityproductivity, but , but affaffect negatively ect negatively the selectivthe selectivity due to ity due to the adsorption othe adsorption of the ethylenf the ethylene in toe in to the active sites of the catalyst benefiting the unwanted combustion reaction.

the active sites of the catalyst benefiting the unwanted combustion reaction. The rate law for this reaction (1) is given by:

The rate law for this reaction (1) is given by:

(3) (3) Where

Where is is the the partpartial ial pressure pressure of of the the ethylene ethylene and and is is the the partpartial ial pressure pressure of of the the oxygen:oxygen: (4) (4) The values of the activation energy E

The values of the activation energy E11depend on the operation temperature. At temperatures between 120ºdepend on the operation temperature. At temperatures between 120º

C and 140º C (1

C and 140º C (1stst region) activation energies of 40 kJ/mol can be obtained keeping in mind a dependency of region) activation energies of 40 kJ/mol can be obtained keeping in mind a dependency of  Arrhenius law. At temperatures between 140º C and 160º C (2

Arrhenius law. At temperatures between 140º C and 160º C (2ndnd region) the mean activation energy is 15region) the mean activation energy is 15 kJ/mol, there for reaction rates higher than those of the first region can be observed. This is the same for  kJ/mol, there for reaction rates higher than those of the first region can be observed. This is the same for  αα11,,

which values are 0.38, 0.35, and 0.35 for temperatures of 120º C, 140º C, and 160º C respectively. From this which values are 0.38, 0.35, and 0.35 for temperatures of 120º C, 140º C, and 160º C respectively. From this observation comes the preferen

observation comes the preference for temperatures over 140º ce for temperatures over 140º C in the process.C in the process. The values of 

The values of ββ11reported are 0.20, 0.20, 0.21 for temperatures of 120º C, 140º C and 160º C respectively.reported are 0.20, 0.20, 0.21 for temperatures of 120º C, 140º C and 160º C respectively.

A molar relation of ethylene/acid higher than 3 is used. A molar relation of ethylene/acid higher than 3 is used.

The reaction rates were reported like TOF (turnover frequency). This type of data indicates the number of  The reaction rates were reported like TOF (turnover frequency). This type of data indicates the number of  reactions or catalytic cycles done by a unit of the activated center by unit of time (molVA/(molPd seg):

reactions or catalytic cycles done by a unit of the activated center by unit of time (molVA/(molPd seg):

(5) (5)

Were w

Were wPdPdis the fraction of palladium in the catalyst (0.01), D is the palladium dispersion coefficient (withis the fraction of palladium in the catalyst (0.01), D is the palladium dispersion coefficient (with

which the fraction of atoms of active palladium can be calculated) and PM

which the fraction of atoms of active palladium can be calculated) and PMPdPdis the molecular weight of Pd inis the molecular weight of Pd in

kg/mol. The value of D is reported with a value of 0.4 by Han et al. (2005), the value of A

kg/mol. The value of D is reported with a value of 0.4 by Han et al. (2005), the value of A11 calculated with thecalculated with the

data reported by Han et al., (2005) is of 9.7 x 10

data reported by Han et al., (2005) is of 9.7 x 10-3-3molVA/(kgCat seg) (For partial pressures expressed in kPa).molVA/(kgCat seg) (For partial pressures expressed in kPa). For reaction (2)

For reaction (2) the same authors report the same authors report a sima simililar rate ar rate reaction law (Han et al., 2004):reaction law (Han et al., 2004): (6) (6) (7) (7)

α

α22was determined with values of -0.27, -0.31 and -0.27 for temperatures of 140º C, 160º C and 180º C re-was determined with values of -0.27, -0.31 and -0.27 for temperatures of 140º C, 160º C and 180º C

re-spectively. Besides this, an increase of 50% of the production of CO

spectively. Besides this, an increase of 50% of the production of CO22 was observed when the temperature in-was observed when the temperature

in-creased from 140ºC to 160ºC. The values found for 

creased from 140ºC to 160ºC. The values found for ββ22 were 0.88, 0.82, 0.89 for temperatures of 140ºC, 160ºCwere 0.88, 0.82, 0.89 for temperatures of 140ºC, 160ºC

and 180ºC respectively. The activation energy E

and 180ºC respectively. The activation energy E22 obtained from data was 21 kJ/mol (higher than the activationobtained from data was 21 kJ/mol (higher than the activation  Pd   Pd   Pd   Pd   PM   PM   D  D w w TOF  TOF   KgCat   KgCat  molVA molVA r  r 



==

 

 

 

 



 

 

 

 

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energy of reaction (1) which is 15 kJ/mol). No dependency was observed by the partial pressure of the acetic energy of reaction (1) which is 15 kJ/mol). No dependency was observed by the partial pressure of the acetic acid in the rate law. This confirms that the production of CO

acid in the rate law. This confirms that the production of CO22is due basically to the oxidation of the ethylene.is due basically to the oxidation of the ethylene.

The value of A

The value of A22calculcalculated taking in to accoated taking in to account the datunt the data reported a reported by Han et al., (2004) resulted in a value of by Han et al., (2004) resulted in a value of 

5.13 x 10

5.13 x 10-4-4molVAmolVA/(kgCat seg). /(kgCat seg). (For par(For partial pressures expresstial pressures expressed in kPa).ed in kPa).

VAM distillation and dehydration. VAM distillation and dehydration.

It is based on the outlet homogeneous gaseous reactor stream in which the high temperature and pressure It is based on the outlet homogeneous gaseous reactor stream in which the high temperature and pressure guarantee its state, favoring the reaction conditions. This shows that through manipulating factors like guarantee its state, favoring the reaction conditions. This shows that through manipulating factors like tem- perature

 perature and and pressure, pressure, it’s poit’s possissiblble e to to generate generate changes changes that that allallow ow the the separation separation of of the the components, components, princi princi-- pall

 pally vinyy vinyl acetatl acetate. e. The effluenThe effluent t reactor reactor stream is costream is composed by 45,mposed by 45,9% 9% mol of mol of ethylethylene, 6,ene, 6,7% 7% of watof water, er, 5,7%5,7% of VAM, 5,4% of o

of VAM, 5,4% of oxygenxygen, 1% o, 1% of Carbon Dioxif Carbon Dioxide, 12,5% de, 12,5% of Acetic Aciof Acetic Acid y 34,3% od y 34,3% of Nitrogen.f Nitrogen.

The general description of this system consists of an effluent reactor stream that is cooled with cooling The general description of this system consists of an effluent reactor stream that is cooled with cooling wa-ter with the objective of generating two phases: the gaseous phase which contains principally oxygen, ethylene, ter with the objective of generating two phases: the gaseous phase which contains principally oxygen, ethylene, carbon dioxide, and ethane when the feed of ethylene is not pure. The second phase consistis of a liquid phase carbon dioxide, and ethane when the feed of ethylene is not pure. The second phase consistis of a liquid phase that contains principally vinyl acetate, water and acetic acid. The vapor phase passes to a compressor while the that contains principally vinyl acetate, water and acetic acid. The vapor phase passes to a compressor while the liquid phase passes to an azeotropic distillation column. The gas stream passes from the compressor to an liquid phase passes to an azeotropic distillation column. The gas stream passes from the compressor to an ad-sorption column with the objective of extracting the remaining vinyl acetate, while the liquid stream exits the sorption column with the objective of extracting the remaining vinyl acetate, while the liquid stream exits the azeotropic distillation column in the form of distillates which later on are condensed to form two liquid phases azeotropic distillation column in the form of distillates which later on are condensed to form two liquid phases in a decanter. The heavier of the two phases is recycled back in to the distillation column and the other passes in a decanter. The heavier of the two phases is recycled back in to the distillation column and the other passes on to the purification process to obtain the vinyl acetate, while the other is mainly water. The bottoms stream is on to the purification process to obtain the vinyl acetate, while the other is mainly water. The bottoms stream is fed back to the absorption tower. With these conditions, the column gets to generate three currents: the fed back to the absorption tower. With these conditions, the column gets to generate three currents: the bot-toms which are mainly acetic acid, the distillate which is composed by two immiscible phases that allow the toms which are mainly acetic acid, the distillate which is composed by two immiscible phases that allow the separation of the VAM and the water. This is the most important process due to its difficulty to separate separation of the VAM and the water. This is the most important process due to its difficulty to separate (wa-ter-VAM mixture). The liquid bottoms of the separator are mixed with the liquid stream of the separator so it ter-VAM mixture). The liquid bottoms of the separator are mixed with the liquid stream of the separator so it can head later on to a distillation column.

can head later on to a distillation column.

On the other hand, the nearly free vinyl acetate gaseous stream goes to a carbon dioxide extraction unit in On the other hand, the nearly free vinyl acetate gaseous stream goes to a carbon dioxide extraction unit in order to take out most of this component out of the stream. The stream that had the CO

order to take out most of this component out of the stream. The stream that had the CO22 extracted is dividedextracted is divided

in to a purge and a recirculation stream that mixes with the other portion of the stream that had no CO in to a purge and a recirculation stream that mixes with the other portion of the stream that had no CO22 ex-

ex-tracted. This stream will be used to exchange heat with the outlet stream of the reactor and to serve as a base tracted. This stream will be used to exchange heat with the outlet stream of the reactor and to serve as a base feed stream for the reactor, taking in to account that this streams is added through other feed streams that are feed stream for the reactor, taking in to account that this streams is added through other feed streams that are needed for the reaction.

needed for the reaction.

PROCESS SIMULATION PROCESS SIMULATION

The development of this work began with a bibliographic compilation form which the optimum VAM The development of this work began with a bibliographic compilation form which the optimum VAM pro-duction process and its conditions were established. Starting from said process, a simulation was done with the duction process and its conditions were established. Starting from said process, a simulation was done with the ASPEN PLUS v.2006 program from where a total process material and energy balance were established. Also, ASPEN PLUS v.2006 program from where a total process material and energy balance were established. Also, the final purity of the product and the possible modifications that allow a production of a greater quality and the final purity of the product and the possible modifications that allow a production of a greater quality and lower operation cost

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 Defined Prop  Defined Propertieserties

To determine the models that would be applied in the simulation, an analysis of two articles were used as To determine the models that would be applied in the simulation, an analysis of two articles were used as strating points. These article were

strating points. These article were “Don’t gamble with physical properties for simulations”“Don’t gamble with physical properties for simulations” and the articleand the article about t

about thermodinamics hermodinamics of Galen of Galen J. Supples. J. Supples. Thanks to the information fThanks to the information found in ound in the text of the text of Alexandre D.Alexandre D. Dimian [1], it was deterimined that the model that best fitted the property’s description was the SR-Polar  Dimian [1], it was deterimined that the model that best fitted the property’s description was the SR-Polar  model because i

model because it tt takes into account akes into account the interaccion between gaseous components.the interaccion between gaseous components.

This choice was supported by the fact of the liquid phase is mainly composed by vinyl acetate (apolar), This choice was supported by the fact of the liquid phase is mainly composed by vinyl acetate (apolar), water (polar), acetic acid (polar), and supposing that there are interaction parameters due to the fact that these water (polar), acetic acid (polar), and supposing that there are interaction parameters due to the fact that these are known compounds. Finally, the NRTL and UNIQUAC models and all their variations were taken into are known compounds. Finally, the NRTL and UNIQUAC models and all their variations were taken into considerati

consideration in order to get on in order to get presitipresition with these types of on with these types of components, but afcomponents, but after researchiter researching ng the the AlAlexandre D.exandre D. Dimian book, the NRTL-HOC model was chosen.

Dimian book, the NRTL-HOC model was chosen.

 Reactio  Reactionn

Figure 2 illustrates the preparation of the raw material simulation and reaction flow diagram. Figure 2 illustrates the preparation of the raw material simulation and reaction flow diagram.

Figure 2 Reaction simulation flow diagram. Figure 2 Reaction simulation flow diagram.

To design the reactor, it was established that it had to be done isothermally trying to prevent the sections To design the reactor, it was established that it had to be done isothermally trying to prevent the sections that exceed 200°C which in turns lowers the catalyst activity. To control the temperature effect, the use of an that exceed 200°C which in turns lowers the catalyst activity. To control the temperature effect, the use of an inert gas was applied, in this case nitrogen. Besides this, the reactors are designed to achieve a low conversion inert gas was applied, in this case nitrogen. Besides this, the reactors are designed to achieve a low conversion of acetic acid by each pass (between 15 to 38% of acetic acid, and 8 to 10% of ethylene). It has to be taken in of acetic acid by each pass (between 15 to 38% of acetic acid, and 8 to 10% of ethylene). It has to be taken in to account that activation energy of the unwanted reaction is greater than the activation energy of the wanted to account that activation energy of the unwanted reaction is greater than the activation energy of the wanted reaction, so at higher temperature the selectivity will be affected.

reaction, so at higher temperature the selectivity will be affected.

The reactor is a tube and shell reactor with a tube diameter of 3.7 cm, which have inside the catalyst. The The reactor is a tube and shell reactor with a tube diameter of 3.7 cm, which have inside the catalyst. The calculations took in to account a refrigerant at a constant temperature of 5 degrees (° C) below the inlet calculations took in to account a refrigerant at a constant temperature of 5 degrees (° C) below the inlet tem- perature

 perature of the of the reactives and afterwards, treactives and afterwards, through Aspen Plus v.2006, hrough Aspen Plus v.2006, the simulthe simulation was made using saturatedation was made using saturated water in co-current through the shell at 418K and vapor was produced at 4 atm. The simulation complies with water in co-current through the shell at 418K and vapor was produced at 4 atm. The simulation complies with the specification of the reactor’s design.

the specification of the reactor’s design.

The global heat transfer coefficient calculated by Dimian y Bildea, (2008), was used (0.2KW/m

The global heat transfer coefficient calculated by Dimian y Bildea, (2008), was used (0.2KW/m22K). Like-K). Like-wis

wise, te, the physihe physical properties of tcal properties of the catalyst are the ohe catalyst are the ones reported in the US Patnes reported in the US Patent No. ent No. 5808136: a bulk densi5808136: a bulk densityty of 0.5 kg/L, partial size of 5 mm and a porous volume of 0.8 L/kg. Thanks to this data, an empty fraction of  of 0.5 kg/L, partial size of 5 mm and a porous volume of 0.8 L/kg. Thanks to this data, an empty fraction of  0.4, and a catalyst solid density of 0.833 kg/L were calculated. The operation inlet temperature for the reactor  0.4, and a catalyst solid density of 0.833 kg/L were calculated. The operation inlet temperature for the reactor  was 150ºC.

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Using all of the information, a 0.6 m/s rate was obtained which implies the use of 234 tubes and a pressure Using all of the information, a 0.6 m/s rate was obtained which implies the use of 234 tubes and a pressure drop of 7.28% (and outlet pressure of 7.83 bar), achieving the needed conversion of acetic acid (35%). The drop of 7.28% (and outlet pressure of 7.83 bar), achieving the needed conversion of acetic acid (35%). The  previousl

 previously mentiy mentioned parameters oned parameters are suggested are suggested in this report. A reacin this report. A reactor tor length of 6.01m was calcullength of 6.01m was calculated tated takingaking in to account the data. The calculations were made always keeping in mind the volume in liters of the reactor. in to account the data. The calculations were made always keeping in mind the volume in liters of the reactor. The volume per tube is 6.46 Lt, and t

The volume per tube is 6.46 Lt, and the total reactohe total reactor volume ir volume is 1,513 Lt.s 1,513 Lt.

VAM distillation VAM distillation

Figure 3 illustrates the distillation simulation flow diagram of the vinyl acetate monomer. Figure 3 illustrates the distillation simulation flow diagram of the vinyl acetate monomer.

Figure 3. VAM distillation simulation flow diagram. Figure 3. VAM distillation simulation flow diagram.

For the gas phase obtained from the first flash unit, a 20 stage VAM absorption tower was defined. It is in For the gas phase obtained from the first flash unit, a 20 stage VAM absorption tower was defined. It is in the range with what was found in the literature for two the scenarios mentioned earlier. Finally, the same the range with what was found in the literature for two the scenarios mentioned earlier. Finally, the same analy-sis was conducted keeping in mind the stream temperature, although the final separation showed the same sis was conducted keeping in mind the stream temperature, although the final separation showed the same be-havior as seen in the acid stream.

havior as seen in the acid stream.

Finally in the carbon dioxide extraction stage, the most important factor that was taken in to account was Finally in the carbon dioxide extraction stage, the most important factor that was taken in to account was the concentration of the absorbing agent because this stream is recycled to the reactor. It was necessary the concentration of the absorbing agent because this stream is recycled to the reactor. It was necessary keep-ing a constant CO

ing a constant CO22 concentration because it is fundamental, if not, possibly the selectivity and production couldconcentration because it is fundamental, if not, possibly the selectivity and production could

 be affected.

 be affected. To To do do thisthis, , it is imperativit is imperative e to to have a have a control ocontrol over the ver the concentration in this stage, concentration in this stage, so tso that that the con-he con-centrate of the absorbing agent increases as the internal acidity increases. At an industrial level, the absorbing centrate of the absorbing agent increases as the internal acidity increases. At an industrial level, the absorbing agents for carbon dioxide commonly used are amine solution (due to their basic characteristic) or Potassium agents for carbon dioxide commonly used are amine solution (due to their basic characteristic) or Potassium carbonates (due to their affinity)

carbonates (due to their affinity)

The liquid phase begins its separation using an azeotropic distillation column. For design purposes, the The liquid phase begins its separation using an azeotropic distillation column. For design purposes, the ef-fect of t

fect of the temperature ohe temperature over the ver the quantity of VAM in the desiquantity of VAM in the desired stream was researched and tested with a sensi-red stream was researched and tested with a sensi-tivity anal

tivity analysiysis and was found that any effect was observed in temperats and was found that any effect was observed in temperature range oure range of 0 to 1000 K. f 0 to 1000 K. A siA similmilar sit-ar sit-uation occurs with the acid concentration in the distillate stream when the temperature is varied. On the other  uation occurs with the acid concentration in the distillate stream when the temperature is varied. On the other  hand, based on the eff

hand, based on the effect of the number of ect of the number of stages over tstages over the acid concentrathe acid concentration iion in the disn the distillate stream, tillate stream, it wasit was found that a total of 23 stages is the optimum because it reaches a flow of 0.57 Kmol/h, lower than 0.85 that is found that a total of 23 stages is the optimum because it reaches a flow of 0.57 Kmol/h, lower than 0.85 that is generated with a larger number of stages. Finally, the effect of the recirculation flow over the vinyl acetate generated with a larger number of stages. Finally, the effect of the recirculation flow over the vinyl acetate  produced

 produced was studied was studied and no and no difdifference was found when ference was found when it was varied, it was varied, so it so it was kept was kept at at 74.55 74.55 kmolkmol/h for /h for thethe VAM on the distillate stream.

VAM on the distillate stream.

The decanter is the unit in which one has to be more careful due the fact that is in this unit that the two The decanter is the unit in which one has to be more careful due the fact that is in this unit that the two  phases are generated:

 phases are generated: organic and aqueoorganic and aqueous phases. Keeping ius phases. Keeping in min mind the tnd the temperature, and supposing that whenemperature, and supposing that when the temperature rises the amount of vinyl acetate varies in the outlet stream, this had no effect. Therefore the the temperature rises the amount of vinyl acetate varies in the outlet stream, this had no effect. Therefore the

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decanter’s inner temperature was varied with the objective of finding the optimum temperature that can decanter’s inner temperature was varied with the objective of finding the optimum temperature that can gener-ate the

ate the two phases. This temperature was found to two phases. This temperature was found to be 150 f and a pressure of 1 atbe 150 f and a pressure of 1 atm.m.

It was established that the process conditions were going to be 1 atm and a temperature slightly lower than It was established that the process conditions were going to be 1 atm and a temperature slightly lower than 150 f.

150 f.

 Dehydra  Dehydrationtion

Figure 4 illustrates the VAM dehydration simulation flow diagram. Figure 4 illustrates the VAM dehydration simulation flow diagram.

Figure 4: VAM dehydration simulation flow diagram. Figure 4: VAM dehydration simulation flow diagram.

The dehydration of the VAM via extractive distillation consists of adding a solvent (Glycerol) to the The dehydration of the VAM via extractive distillation consists of adding a solvent (Glycerol) to the

VAM-water mixture. This mixture is impossible to separate by normal distillation methods; it was necessary to VAM-water mixture. This mixture is impossible to separate by normal distillation methods; it was necessary to alternate the relative volatility of the components allowing the separation. Therefore a dehydration column was alternate the relative volatility of the components allowing the separation. Therefore a dehydration column was design with 20 stages.

design with 20 stages.

This dehydration column receives a stream of 93% pure VAM and a stream of glycerol composed of pure This dehydration column receives a stream of 93% pure VAM and a stream of glycerol composed of pure and recycled glycerol. This leads to a stream of 99% percent pure VAM. This stage is extremely important and recycled glycerol. This leads to a stream of 99% percent pure VAM. This stage is extremely important be-cause when the humidity is retrieve from the product, it results in a better quality product and decreases the cause when the humidity is retrieve from the product, it results in a better quality product and decreases the risk associ

risk associated with the ated with the storage ostorage of the finf the final product.al product.

ENERGY INTEGRATION ENERGY INTEGRATION

Energy integration was used with the objective of using the energy provided by the streams with high Energy integration was used with the objective of using the energy provided by the streams with high tem- perature that need t

 perature that need to be cooo be cooled or condensed so they can heat or vaporize the cold streams.led or condensed so they can heat or vaporize the cold streams.

The analysis of the energy integration for the production process of vinyl acetate was done with Aspen The analysis of the energy integration for the production process of vinyl acetate was done with Aspen Hx- Net

 Net program. The program. The streams presented in the streams presented in the table below were table below were analanalyzed. The yzed. The condensers and reheaters from thecondensers and reheaters from the distillation columns weren’t taken in to account in this analysis because it was considered that their energetic distillation columns weren’t taken in to account in this analysis because it was considered that their energetic requirements were going to be covered with the utilities intrinsic into the process.

requirements were going to be covered with the utilities intrinsic into the process.

Table 1. Stream to analyze Table 1. Stream to analyze

Inlet Streams Inlet Streams

Outlet Outlet Streams

Streams DestinatiDestination on EffectEffect 33

33 34 34 Mixer Mixer HeatingHeating

35

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37

37 2 2 Vaporizer Vaporizer CoolingCooling 6

6 7 7 Absorber Absorber CoolingCooling

10

10 11 11 SepSeparator arator CoolingCooling

Using the information of the streams and that of the Aspen Hx-Net program, a composite curve graph was Using the information of the streams and that of the Aspen Hx-Net program, a composite curve graph was made.

made.

Figure 5 Composite curve Figure 5 Composite curve

A preliminary analysis of the graph reveals that the process has an uncommon energy integration case; this A preliminary analysis of the graph reveals that the process has an uncommon energy integration case; this case is known as threshold. This type of scenario consists of only a small portion of the energy is going to be case is known as threshold. This type of scenario consists of only a small portion of the energy is going to be covered by other streams and the rest of the energy requirements have to be met with outside utilities.

covered by other streams and the rest of the energy requirements have to be met with outside utilities. The

The ∆∆ttminmin used in this analysis was of 10º C because it is the minimum standard for said analysis. In theused in this analysis was of 10º C because it is the minimum standard for said analysis. In the

composite curve graph it is il

composite curve graph it is illustrated the polustrated the portion where stream interaction can take place.rtion where stream interaction can take place. Using

Using the Aspen Hx-Net prothe Aspen Hx-Net program it was gram it was possible possible to simulto simulate the most optimum ate the most optimum designs designs for the energy for the energy in- in-tegration for the vinyl acetate process using cooling water as a refrigerant as a utility. After analyzing the tegration for the vinyl acetate process using cooling water as a refrigerant as a utility. After analyzing the op-tions given by the program, a scenario was chosen due to its low consumption of energy. Its operation cost is tions given by the program, a scenario was chosen due to its low consumption of energy. Its operation cost is lower than the rest. Taking these criteria in to account, it is clear that investment capital is higher but thanks to lower than the rest. Taking these criteria in to account, it is clear that investment capital is higher but thanks to the low o

the low operation cost peration cost and low energy consumptiand low energy consumption represents a on represents a quick capital return.quick capital return.

Table 2. Process streams used in the analysis of the heat integration. Table 2. Process streams used in the analysis of the heat integration.

Inlet

Inlet Temp. Temp. Outlet Outlet Temp.Temp. Cooling

Cooling water water 20 20 2525

High

High presspressure ure vapor vapor 250 250 249249

Table 3. Heat integration result analysis Table 3. Heat integration result analysis

Design

Design 1 1 Cost Cost index index ($) ($) Energy Energy and and UnitsUnits Heating

Heating (value/s) (value/s) 5.96E-06 5.96E-06 Heating Heating (kj/h)(kj/h) Cooling(value/s

Cooling(value/s) ) 2.51E-04 2.51E-04 Cooling Cooling (kj/h)(kj/h) Op

Opereratatioion n (v(valalueue/s/s)) 2.2.5757E-E-04 04 # # ununititss C

Capapitital al 2.2.24243.3.00005.5.030366 # # oof f sshehellllss Total

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Table 3 (continued). Heat integration result analysis Table 3 (continued). Heat integration result analysis

d

deessiiggn n 11 HHEENN Cost indexCost index ($) ($) H

Heeaattiinngg((vvaalloorr//ss)) 8 .8 .557766..112255..886 86 8 HHeeaattiinng g vvaalluuee//hh 22..1144EE--0022 C

Coooolliinng g ((vva la loorr//ss)) 4 .4 .2 52 55 .5 .6 86 81 .1 .7 27 222 CCoooolliinng g vva la lu eu e//hh 9 .9 .0 40 4EE--0 10 1 O

Oppeerraattiioonn((vvaalloorr//ss)) 99 OOppeerraattiioon n vvaalluuee//hh 9.26E-019.26E-01 C

Caappiittaall 1133 T o

T ottaal l vvaallu eu e//ss 4 .4 .0 80 88 .8 .8 78 72 .2 .1 01 099 T

Toottaal l eenneerrggy y uusseed d ((KKWW)) 11..118844..551166..006699 ttoottaall 11..8855EE++0000

CONCLUSIONS CONCLUSIONS

With a thorough bibliographic revision it was possible to determine that the optimum process to produce With a thorough bibliographic revision it was possible to determine that the optimum process to produce VAM was the acetoxilation of ethylene using acetic acid and a palladium/gold catalyst. Said process was VAM was the acetoxilation of ethylene using acetic acid and a palladium/gold catalyst. Said process was di-vided in to three: the reaction, the separation system and the VAM dehydration. In regards to the reaction it vided in to three: the reaction, the separation system and the VAM dehydration. In regards to the reaction it was evident that the temperature would determine the life of the catalyst and the selectivity of the process, was evident that the temperature would determine the life of the catalyst and the selectivity of the process, even more so in this case which presents two parallel reactions.

even more so in this case which presents two parallel reactions.

Based on the separation system, it was evident the need to separate the liquid phase from the gaseous phase Based on the separation system, it was evident the need to separate the liquid phase from the gaseous phase with the objective of purifying the final product and to recycle some raw material that did not react and are with the objective of purifying the final product and to recycle some raw material that did not react and are very expensive. To choose the most adequate properties was fundamental in order to observe and establish the very expensive. To choose the most adequate properties was fundamental in order to observe and establish the correct separation characteristics of the components based on their immiscibility and azeotropic points through correct separation characteristics of the components based on their immiscibility and azeotropic points through the simulation.

the simulation.

Finally the existence of an azeotropic point and immiscibility between water and vinyl acetate made it Finally the existence of an azeotropic point and immiscibility between water and vinyl acetate made it neces-sary to add and dehydration stage which consisted in a extraction column using glycerol as an extracting agent. sary to add and dehydration stage which consisted in a extraction column using glycerol as an extracting agent. Thanks to its polar propert

Thanks to its polar properties, Glies, Glycerol alycerol allows the water to lows the water to be extracted from the VAMbe extracted from the VAM

The analysis in regards with the total process production of VAM, it was necessary to determine the best The analysis in regards with the total process production of VAM, it was necessary to determine the best way to use the energy in the process so it could be used to exchange with other streams and by doing this way to use the energy in the process so it could be used to exchange with other streams and by doing this cut-ting back on energy expenses.

ting back on energy expenses.

 Refere  Referencesnces

[1] Han, Y. F., et al., A kinetic study of vinyl acetate synthesis over Pd-based catalysts: kinetics of vinyl [1] Han, Y. F., et al., A kinetic study of vinyl acetate synthesis over Pd-based catalysts: kinetics of vinyl acetate

acetate synsynthesithesis os over Pd-Au/SiOver Pd-Au/SiO22and Pd/SiOand Pd/SiO22catalyscatalysts, Journal of catats, Journal of catalylysisis, Vol. 232, s, Vol. 232, pp. 467-475, pp. 467-475, 2005.2005.

[2] McKetta,

[2] McKetta, J., EncyclopediJ., Encyclopedia of Chemical a of Chemical ProcessinProcessing and design, Vol. 62, g and design, Vol. 62, Marcel Dekker, INC., Marcel Dekker, INC., USA,USA, 1998, pp. 265-300.

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[5] Luyben , W. , Tyreus , B. , An industrial design/control study for vinyl acetate monomer plant ,Luyben , W. , Tyreus , B. , An industrial design/control study for vinyl acetate monomer plant , Comput.Comput. Chem. Eng.

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[6] Han, Y., et al., Particle size effects in Vinyl Acetate synthesis over Pd/SiO

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[7] Chen, M. S., et al., The nature of the active site for vinyl acetate synthesis over Pd-Au, Catalysis Today, [7] Chen, M. S., et al., The nature of the active site for vinyl acetate synthesis over Pd-Au, Catalysis Today, Vol. 17. Pp. 37-45, 2006.

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[8] Han, Y. F., et al., A kinetic study of vinyl acetate synthesis over Pd-based catalysts: kinetics of vinyl [8] Han, Y. F., et al., A kinetic study of vinyl acetate synthesis over Pd-based catalysts: kinetics of vinyl acetate

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[9] Neurock, M., First principle analysis of the catalytic reaction pathways in the synthesis of Vinyl Acetate, [9] Neurock, M., First principle analysis of the catalytic reaction pathways in the synthesis of Vinyl Acetate, Chem

Chemical Engiical Engineerinneering science, Vol. g science, Vol. 51, pp. 51, pp. 1691-1699, 1691-1699, 1996.1996. [10] McKetta,

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[11] Tacke, T., et T., et al., Catalysal., Catalyst, method t, method of its production and its use for the productof its production and its use for the product ion of viion of vinyl nyl acetate mo-acetate mo-nomer, U.S. Patent office No. 5,808,136, 15 of September of 1998.

nomer, U.S. Patent office No. 5,808,136, 15 of September of 1998. [12] Ethylene oxide (EO) and Viny

[12] Ethylene oxide (EO) and Vinyl acetate l acetate monomer (VAM) production, VaporSep® monomer (VAM) production, VaporSep® SystemSystems for Petros for Petro--chemicals, Membrane Technology & Research, disponible en <www.mtrinc.com>, consultado el [25 de Enero chemicals, Membrane Technology & Research, disponible en <www.mtrinc.com>, consultado el [25 de Enero de 2008].

de 2008].

[13] Jobson, S., et al., Integrated process for the production of vinyl acetate and/or acetic acid, U.S. Patent [13] Jobson, S., et al., Integrated process for the production of vinyl acetate and/or acetic acid, U.S. Patent office No. 6,040,474, 21 of March of 2000.

office No. 6,040,474, 21 of March of 2000. [14] Schaeffer, W., et

[14] Schaeffer, W., et al., Productal., Production of Vinyion of Vinyl Acetate from Ethylenl Acetate from Ethylene, U.S. e, U.S. Patent oPatent offffice No. 3,ice No. 3,277,158,277,158, October 4 of 1966.

October 4 of 1966. [15] Mazanec, T.

[15] Mazanec, T., et , et al., Process and apparatal., Process and apparatus for improved methods for makius for improved methods for making vinyng vinyl acetate l acetate monomer monomer  (VAM), International Publication Number WO2006/052615, May 18 of 2006.

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3.306.930, February 28 of 1967.

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July 13 of 1971.

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metathesis, Journal of molecular catalysis A: Chemical (2007), doi: 10.1016/j.molcata.2007.08.026 [21] Kragten, D.,

[21] Kragten, D., et al., A Spectet al., A Spectroscopic study of the homogeneous catalytic conversroscopic study of the homogeneous catalytic conversion of ethylion of ethylene to ene to vi- vi-nyl

nyl acetate acetate by Palby Palladiladium Acetate, Inorg. um Acetate, Inorg. ChemChem. J., . J., Vol. 38, 1999, Vol. 38, 1999, pp. 331-339.pp. 331-339.

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