Synthesis of n-Amyl Acetate in a Pilot Plant Catalytic Distillation

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Synthesis of n-amyl acetate in a pilot-plant catalytic distillation column with Seepage Catalytic Packing Internal Hong Li, Caichun Xiao, Xingang Li, and Xin Gao Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01980 • Publication Date (Web): 05 Oct 2017 Downloaded from http://pubs.acs.org on October 10, 2017

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Industrial & Engineering Chemistry Research

1

Synthesis of n-amyl acetate in a pilot-plant catalytic distillation

2

column with Seepage Catalytic Packing Internal

3

Hong Lia, Caichun Xiaoa, Xingang Lia, Xin Gaoa, ∗ a

4

National Engineering Research Center of Distillation Technology, School of Chemical Engineering and

5

Technology, Collaborative Innovation Center of Chemical Science and Engineering(Tianjin), Tianjin University,

6

Tianjin 300072, China

7

Abstract

8

The n-amyl acetate synthesis from the esterification reaction of acetic acid and

9

n-amyl alcohol in a pilot-plant catalytic distillation column with a decanter was

10

evaluated. A novel catalytic packing, Seepage Catalytic Packing Internal (SCPI), is

11

applied in this study. Catalytic Distillation experiments using different feed molar

12

ratios and feed modes at different pressure of column were performed to validate an

13

equilibrium stage model developed to investigate the influence of operation

14

parameters on the performances of catalytic distillation process. The results from

15

experimental runs and simulations clearly indicate that it is important to the

16

performance of catalytic distillation process by adjusting the composition and

17

temperature profiles along the reaction zone. The studies also showed that the

18

integration of reactive distillation column with a decanter is considered as potential

19

candidate to product amyl acetate. With proper operation parameters (operating

∗

Corresponding author: Tel: +86-022-27404701(X.G.); Fax: +86-022-27404705(X.G.).

E-mail: [email protected] (Xin Gao).

1

ACS Paragon Plus Environment


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pressure of 20-22kPa and mixed feeding mode)and column configuration(16-18

2

theoretical stages of reaction zone), the product purity in the bottom stream could be

3

increased to 99.3 wt% and less than 0.2 mgKOH/g acid value, meanwhile the

4

conversion of amyl alcohol could be reached more than 95%. The research

5

achievements can be applied to facilitate industrial application of SCPI and used for

6

prospective optimization studies.

7

Keywords: reactive distillation, SCPI, amyl acetate, simulation, process intensification

8

Introduction

9

The research and development of process intensification becomes a great

10

challenge for both academia and industry.1 One common application of process

11

intensification is the integration of several unit operations into a multifunctional

12

equipment, therein, the chemical process industry has paid much attention to the

13

combination of reaction and separation which called as reactive distillation (RD), also

14

known as Catalytic Distillation (CD).2 The concept of RD is first put forward in a

15

patent3 in 1921 and the demonstrated potential of RD for capital productivity

16

improvements, selectivity improvements, reduced energy consumption, and the

17

reduction or elimination of solvents has received renewed attention in recent years.4-6

18

Reactive distillation would be most efficient particularly in some systems which the

19

reactions are reversible or when the presence of azeotropes makes conventional

20

separation expensive.7

21

Amyl acetate is widely used as a solvent, an extractant or a polishing agent, also

22

used as emulsifiers in the food and cosmetic industries. The most-used method for 2


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1

amyl acetate synthesis is direct esterification of acetic acid and amyl alcohol in the

2

presence of acid catalysts. Reactive distillation has been proved to be an economical

3

and effective method in the esterification reaction.8,9 Tang et al. investigated the acetic

4

acid esterifications with five different alcohols using the reactive distillation,10 and

5

provided a generalization for the design of RD process for esterification reactions.

6

Hung et al. explored the dynamics and control of reactive distillation columns for

7

amyl acetate production using dilute acetic acid.11 Chiang et al. compared two

8

different configurations for the esterification of amyl acetate and evaluated the

9

economic advantages of different designs.12 The results clearly indicated the

10

economic advantage of reactive distillation while maintaining acetate purity for the

11

amyl acetate process. However, these researches mainly focus on the design and

12

control of the RD process, few pilot-plant RD experiments of amyl acetate synthesis

13

have been performed and few study investigate the effects of the operating factors,

14

such as the feeding mode, on the RD performance through experiments and

15

simulations.

16

The definition of type and specification of geometric features of the internal

17

devices is one of the most pivotal issues of industrial applications of CD process. The

18

most promising internals have to enhance not only the reaction rate but also the

19

separation efficiency. Therefore, catalytic packing with high catalytic efficiency and

20

good separation ability should be required, the choice of catalytic packing is crucial

21

for the overall performance of the column.13 In our previous studies, a new-type

22

internal calls Seepage Catalytic Packing Internal (SCPI) was developed.14 To better 3



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1

understand the internal, a lot of basic research works have been conducted. The

2

experiments about hydrodynamics performances in the column (600mm inner

3

diameter, 1500mm height) have been performed by Gao et al. to evaluate the liquid

4

flow behaviors and pressure drop.15,16 Compared to two other conventional column

5

internals, Sulzer Katapak-SP 1217 and catalyst bundles18, the novel structure of SCPI

6

resulted in a significantly decreased pressure drop in the column15 and the liquid

7

holdup of the SCPI was always higher within the range of acceptable performance for

8

an equivalent catalyst loading16. Based on the hydrodynamic experiments, rigorous

9

mathematical models have been proposed by Li et al.19 and Zhang et al.20 to predict

10

the pressure drop of the SCPI and composition profiles for catalytic distillation

11

process. However, no reactive distillation experiments used SCPI has ever been

12

investigated.

13

In this paper, pilot-scale RD experiments of amyl acetate synthesis were

14

performed, and the novel structured catalytic packing SCPI was used for the first

15

time for the reactive distillation process. An non-equilibrium stage model developed

16

in Aspen Plus and validated by experimental data was used to predict experimental

17

results, and the comparison of these simulated results with experimental results was

18

shown. Several simulations were performed based on the model, the effects of varied

19

operating parameter, such as the feeding position, column pressure and theoretical

20

stages of reaction zone on the process behavior were investigated.

21 22

Chemical System The chemical system investigated in this study is the heterogeneously catalyzed 4


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1

esterification of acetic acidand n-amyl alcohol into n-amyl acetate and water, as

2

shown in Eq. (1).

3

CH 3COOH(HAc)+ C5 H11OH(AmOH)← → C 5 H11COOCH3 (AmAc) + H 2 O

(1)

4

From the experimental data of Lee et al.,21 this reaction is a slightly endothermic

5

reaction with an almost-negligible heat effect. The strongly acidic ion-exchange resin

6

NKC-9 is selected as the heterogeneous acid catalyst for n-amyl acetate synthesis. An

7

experimental determining of NKC-9 for the esterification of acetic acid and n-amyl

8

alcohol has been performed and discussed in an earlier paper.22 A main challenge of

9

this system is the potential of n-amyl alcohol to polymerize, resulting in a possible

10

side product, amyl ether. In preliminary experiments at atmospheric pressure, this

11

byproduct is detected occasionally in the product. Therefore, the use of an RD process

12

to operate at vacuum pressure was deemed suitable.

13

Experimental Investigations

14

Chemicals and materials

15

The chemical, acetic acid, was supplied by Tianjin Chemical Reagent Supply

16

Company and n-amyl alcohol was obtained from The Dow Chemical Company. The

17

purity was 99.5% for acetic acid and 99.8% for n-amyl alcohol. The heterogeneous

18

catalyst, acidic ion exchange resins NKC-9, is supplied by Hecheng technology Co.,

19

Ltd., Nankai, Tianjin.

20

Experimental setup

21

A series of pilot plant experiments of the synthesis of n-amyl acetate from n-amyl

22

alcohol and acetic acid have been carried out in a pilot-scale reactive distillation 5



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1

column with SCPI as shown in Figure 1. The RD column is made of stainless steel,

2

with an inner diameter of 50 mm and a total height of approximately 6 m. The overall

3

packing height of the pilot-scale column was 4 m, divided into four sections equipped

4

with SCPI and θ-ring packing. Along with the packing sections, 0.5 m θ-ring packing

5

is equipped in the bottom of the first segments the stripping section, and another 0.5

6

m θ-ring packing in the top of the fourth segment as the rectifying section. In the

7

middle, 3 m high SCPI is installed into the column as reaction section，the detailed

8

description of SCPI is shown later.

9

The reboiler with a total liquid hold-up of 7 L is externally heated by a

10

high-temperature circulating oil bath pot. The bottom product was collected from it by

11

a gear pump. The mass flow rate of the bottom product stream was measured using a

12

balance by monitoring the time derivative of the change in mass. At the top of column,

13

a vertical glass-made decanter has been equipped after the total condenser for

14

liquid-liquid separation. The mass flow rate of the distillate was calculated from the

15

time derivative of the change in the distillate mass by using an electric balance.

16

Peristaltic pumps were used to dose the reactants from the feed tanks. The mass flow

17

rate also adjusted with the electric balance by monitoring the time derivative of the

18

change in mass. Both the AmOH and the HAc feed stream pipes were equipped with

19

heat exchangers to preheat them before feeding them into the pilot-scale column.

20

There are four feed locations above the particular packing section on the pilot-scale

21

column for two reactants.

22

In order to maintain a stable operating temperature of the column, the column 6


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1

outside wall is surrounded by insulation jacket with a layer of mineral wool with an

2

electric heating wire. The electric heating wire was controlled with a PI controller set

3

to the mean value of the vapor-phase temperature above the particular packing section.

4

In the underpart and middle part of each column segment, thermocouples are

5

equipped to measure the vapor temperature inside the column and the wall

6

temperature respectively. Besides, temperatures are measured in the reboiler,

7

condenser and reflux flow path. To operate the column at the vacuum during the

8

experimental investigation, the RD column is vacuumed by a vacuum pump

9

continuously. A pressure transducer was installed in front of the total condenser to

10

measure the pressure at the top of the column. The pressure drop along the packed

11

section was monitored using a differential pressure sensor. All of these data is shown

12

on the control panel thus we can view and record it expediently.

13

Catalytic packing SCPI

14

In this work, the novel structured packing SCPI, developed by the National

15

Engineering Research Center for Distillation Technology in China (Li et al., 2008),

16

was selected for the CD experiments. The smallest structural unit of the internal used

17

in our experiment is composed of two segments while their structures are shown in

18

Figure 2.

19

Each segment of SCPI has a height of 50 mm and an external diameter of 50 mm,

20

which is equal to the internal diameter of the pilot-scale column. The SCPI consists of

21

corrugated metal sheets and catalyst containers with avert-overflow baffles. The

22

corrugated metal sheets, serving as the separation section, are the common 1000Y 7



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1

corrugated packing. The main parameters of 1000Y corrugated packing and SCPI

2

segment are shown in Table 1. While the catalyst containers, serving as the reaction

3

zone, are closed boxes filled with catalyst particles with avert-overflow baffles. The

4

acidic ion exchange resins NKC-9 is chosen as the heterogeneous catalyst which is

5

immobilized in the SCPIs after soaking for 24 h with n-amyl alcohol. Wire meshes

6

are installed in the top and bottom surfaces of the closed boxes to fix the 20 ml

7

catalysts particles in each segment. Two segments of SCPI are installed in the column

8

alternately, and 20ml θ-ring packing is loaded between every two segment to promote

9

gas-liquid mass transfer. Figure 3 illustrates the expected gas−liquid flow

10

characteristics within the SCPI. The liquid flows uniformly downward through the

11

corrugated metal sheets and catalyst containers, whereas gas flows upward only

12

through the corrugated sheets, which avoids contact between gas and liquid in the

13

catalyst particles bed.

14

Experimental procedure

15

A start-up procedure for the pilot-scale CD experiments was established as follow.

16

Firstly, 4.7 L of mixed reactants of n-amyl alcohol and acetic acid with the molar ratio

17

of 1:1 was added into the reboiler to start total reflux. After the device debugging and

18

total reflux for a period of time until stable operation, n-amyl alcohol and acetic acid

19

was fed into the column continuously from the top of reaction section by a peristaltic

20

pump. The cooled condensate (30℃) from the condenser was introduced into the

21

decanter and demixed into two phases, the upper organic phase and the lower aqueous

22

phase. Afterwards the organic phase was fed back into the column totally and the 8


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1

aqueous phase was withdrawn continuously. The produced n-amyl acetate was

2

concentrated in the stripping zone and withdrawn through the bottom product stream

3

quantificationally during all four experiments while the produced water was

4

withdrawn from the top at the same time. This start-up procedure was used in this

5

work to reach steady-state conditions. After the start-up phase was completed, the

6

fine-tuning of the operating conditions was performed and the column was operated

7

until the following two criteria were fulfilled: (1) The component balances and the

8

reaction stoichiometry in the column were satisfied. (2) The temperature and pressure

9

deviations at each measurement location along the column were below ±2 K and ±

10

1kPa within 6h, respectively. This took in average 10h of operating time for each

11

experiment to prove the first criterion.

12

During the experiments, the temperature and the pressure of each measuring point

13

as well as the feed amount were recorded, and liquid samples were drawn from the

14

top and bottom of the column every 2h after confirming the steady-state operating

15

point. The samples were cooled down instantaneously and then analyzed by gas

16

chromatography. Three experimental conditions, top pressure, molar feed ratio and

17

the feeding mode, were varied within this investigation. When the feeding mode was

18

“mixed”, the reactants were mixed in advance and fed into the column from the top of

19

reactive section (Feed 1). When the feeding mode was “split”, n-amyl alcohol was fed

20

from the forth segment (Feed 1) while acetic acid was fed from the third segment

21

(Feed 2) as n-amyl alcohol was the heavy boiling feed and acetic acid was the light

22

boiling component. 9



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1

Analytical methods

2

The gas chromatography PE XL supplied by PerkinElmer Inc was applied to

3

analyze the composition of all organic samples offline taken from the bottom using

4

the external standard method. The GC devise was equipped with a flame ionization

5

detector (FID) and an HP-5 capillary column (30 m×0.32 mm×0.25µm). The carrier

6

gas was high purity helium with a gas flow rate of 0.5 ml/min. The split-ratio was

7

180:1 while the gas flow rate of hydrogen and air was 30 ml/min and 300 ml/min

8

respectively. The column temperature was held at 333K for 9 min, afterwards,

9

increased to 388 K at a rate of 12℃/min, and then increased to 513 K at the rate

10

of15℃/min, this temperature was maintained for additional 5 min. The typical

11

retention times were 8.1 min for n-amyl alcohol, 12.9 min for n-amyl acetate, and

12

16.3 min for amyl ether.

13

As the aqueous phase samples taken from the decanter mainly consisted of water

14

and acetic acid, and the FID was only able to analyze the mass fraction of the organic

15

components, moreover, the HP-5 capillary column would be eroded by acetic acid,

16

therefore acid base titration and 0.1M potassium hydroxide solution was used to

17

determine the acid content namely acid value. The acid value is the number that

18

expresses in milligrams the quantity of potassium hydroxide required to neutralize the

19

free acids present in 1 g of the sample.

20

Design of experiments

21

In order to verify the feasibility of amyl acetate synthesis via catalytic distillation

22

with SCPI, a series of RD experiments have been carried out in the pilot-plant column. 10


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1

In this work, four catalytic distillation experiments (numbered as Exp1-Exp4) were

2

successfully performed and the operating parameters such as operating pressure,

3

molar feed ratio of the reactants, the feeding modes are analyzed. In this section the

4

experimental results obtained in the reactive distillation column is discussed. A

5

summary of the process parameters of these experiments is illustrated in Table 2. The

6

feeding mode of Exp4 differed from the other experiments. In Exp4, amyl alcohol

7

was fed to the RD column from the upper reactive zone while acetic acid was fed

8

from the lower part. In this case, the molar feed ratio of 1 was hard to achieve due to

9

the issue of precision, thus the molar feed ratio of 1.1 was chosen.

10

One specific operating condition will be adjust when one experiment goes over to

11

the next experiment, as shown in Table 2, the altered parameters during the four

12

experiments are top pressure, molar feed ratio and feeding mode respectively. The RD

13

column requires undergoing a period of adjustment to reach steady state again after

14

the previous experiment reaching the steady state for a long time and then changing

15

the parameter. The reproducibility, and thus the reliability, of the experimental data

16

have been tested by performing twice experiments under the same operating

17

conditions.

18

Modeling and Simulation

19

To systematically evaluate the effects of important operating parameters on the

20

RD process it is necessary to develop a reliable model for the process simulation. The

21

modeling of reactive distillation processes evolves from the conventional distillation

22

models, and now extensive literature is available on the modeling of RD process.23,24 11



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1

Generally, the traditional stage concept is used to simulate reactive distillation

2

processes, either using the equilibrium stage (EQ) or non-equilibrium stage (NEQ)

3

models. The EQ model assumes that exiting vapor and liquid streams of each stage

4

are in thermodynamic equilibrium. In contrast, the NEQ model takes mass and energy

5

transfer in account in a more detailed way.25

6

In this work, an equilibrium stage model was used to describe the RD process of

7

amyl acetate synthesis. The simulation approach assumed phase equilibrium between

8

the exiting streams of each stage. In the description of the reaction, the reactant

9

conversion was realized with a kinetic model. To take the heterogeneous catalytic

10

reaction into account, the liquid hold-up in each equilibrium stage had to be known.

11

Furthermore, the parameters of reaction and separation (the residence time and

12

separation efficiency) were reasonably set to meet the characteristic of SCPI in order

13

to describe the reactive distillation process with this specific internals reliably. A

14

correlation published by Gao et al.26 was implemented into the simulation model to

15

calculate the liquid hold-up of the used SCPI. The column simulated in this work is

16

assumed to be operated adiabatically and both bulk phases are perfectly mixed. The

17

liquid–liquid phase separator was modeled as an ideal, adiabatic phase separator and

18

all pumps and heat exchangers are assumed to show ideal behavior. The

19

equation-oriented simulation environment Aspen Plus® was used to implement the

20

modeling approaches. In these simulations, to obtain accurate simulated results of

21

composition and temperature profiles, some operational conditions such as pressure,

22

feeding condition, column configuration, as well as the thermodynamic data were 12


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1

previously input.

2

Thermodynamic and physical properties

3

The accuracy of simulation results depends heavily on reliable thermodynamic

4

and physical data. Aspen Plus® is used to calculate the thermodynamic and physical

5

properties in this work. To take into account the nonideal liquid phase behavior the

6

NRTL activity coefficient models is applied, and the Hayden O’Connell equation of

7

state27 is used to consider the nonidealties in the gas phase. Table 3 lists the complete

8

set of binary interaction parameters used in calculations.10

9

The boiling points of the pure components and azeotropic mixtures are important

10

properties when using RD columns.28 The boiling points of the pure components at

11

the operating pressure of 20kPa are ranged as follows: water 60.06℃, acetic acid

12

72.12℃, amyl alcohol 95.07℃, amyl acetate 96.78℃. Meanwhile the system is

13

characterized by strong liquid phase non-idealities with several azeotropes presents,

14

furthermore, the azeotropic data is influenced by the pressure. Detailed azeotropic

15

data at different operational pressure can be found in Table 4. As shown in Table 4,

16

the product water can form azeotropes with both amyl alcohol and amyl acetate.

17

Especially, the ternary azeotrope of AmAc-AmOH-H2O was found to be the

18

minimum azeotrope, and the relevant ternary phase diagram at the operational

19

pressure of 20kPa is shown in Figure 4. This ternary azeotrope tends to go to column

20

top and condense into two liquid phases, which leads to difficulties in reaction and

21

separation. Thus it is necessary to install a phase splitter at the top in order to return

22

the organic phase to the RD column otherwise the concentration of reactant and 13



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1

product will both decrease.

2

Reaction kinetics

Page 14 of 52

3

Several studies of the reaction equilibrium and the reaction kinetics of amyl

4

acetate synthesis are available. Lee et al. had studied the kinetic behavior of

5

heterogeneous esterification of acetic acid with amyl alcohol using ion-exchange resin

6

Amberlyst 15 as catalyst.21, 29 Experiments to determine the kinetic behavior of amyl

7

acetate synthesis catalyzed by NKC-9 have been performed by our previous study.22

8

Based on our measurements, the reaction rate can be expressed according to a

9

quasi-homogeneous model.30

10

r = k 1 C HAC C AmOH − k −1 C AmAC C H 2 O

11

where r is the reaction rate per unit catalyst volume [mol/(m3·s)] and C represents the

12

molar density of the corresponding component (mol/m3), k1 [m3/(mol·s)] is the

13

forward reaction rate constant, k-1 [m3/(mol·s)] is the reverse reaction rate constant

14

and K eq = k1 / k −1 ，is the equilibrium constant. In this study, according to Wu,22

k1 = 24100.7924e-50191/RT

15 16

(2)

(3)

with T in kelvin, and

17

K eq =

18

Results and Discussion

19

Research errors and main effects

k1 = 54.27e -8372/RT k −1

(4)

20

In order to ensure the accuracy and stability of the experimental results, it is

21

necessary to maintain the steady state operation of the catalytic distillation column,

14


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1

which is also the difficult point of this experimental research. Many factors can affect

2

the operation stability, for instance, the control error of feed and withdraw amount

3

will influence the substance conservation, control inaccuracy of feed ratio or column

4

pressure will lead to instability of the experimental data. During the experiments,

5

these factors should be control stably as far as possible to reduce research errors.

6

Similarly, there are many factors that may cause errors in the simulation process,

7

resulting in lower accuracy of the simulation results, such as the correct choice of

8

thermodynamic and kinetic data will affect the output results enormously. Thus it

9

requires us to select the most appropriate model and data to reduce the impact of these

10

factors for accurately simulating the experimental process.

11

Experimental results

12

Figure 5 shows the change of temperature, pressure and mass flow rate during all

13

four experiments. All experiments have been running for more than 24 hours,

14

however, the stable steady-state operating point is not all the time reached. In this

15

study, the standard that measures whether the column reaches the steady state

16

operation is strict: only when the whole process has a stable input and output and

17

maintains material balance, meanwhile the variance of pressure, temperature and flow

18

rate is acceptable, we can judge that the column is in the steady state. Then the most

19

stable period in each experiment is selected to discuss, as the shaded areas illustrated

20

in Figure 5. For example, Figure 5 shows that Exp4 was operated continuously more

21

than 80h, but only the experimental data from the 160th hour to 170th hour was used to

22

investigate. The average input and output mass flow rates as well as the experimental 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

results of these four selected period are shown in Table 5.

2

The experimental results indicated that the advantages of SCPI packing were

3

remarkable. The total pressure drop of SCPI in this study remained at 3-4kPa, which

4

was lower than the other catalytic packings. In addition, a high conversion and

5

product quality as well as a large liquid holdup were achieved in the CD column with

6

SCPI, which demonstrated the high catalytic efficiency and separation ability of

7

SCPI.

8

Influence of top pressure

9

Exp1 and Exp2 presents the top pressure’s influence, Exp1 was performed with a

10

top pressure of 30kPa, and other operating conditions could be seen in Table 2. Exp2

11

was performed at the same operating conditions, but with a top pressure of 20kPa.

12

As pressure in the column decreased, the concentration profiles shift slightly.

13

However, the temperature decreases significantly because the boiling point of all the

14

components will decrease under lower pressure, leading to a reduction of the reaction

15

rates. For this reason, pressure directly influences the conversion of both acetic acid

16

and amyl alcohol under the same residence time. It can be seen from Table 5 that the

17

conversion of alcohol drops from 94.6% at 30kPa to 92.2% at 20kPa. Because of the

18

reduction of conversion of both reactants, the amyl acetate concentration in the

19

bottom product should normally reduce. However, the experimental data shows an

20

opposite result that the purity of amyl acetate in the bottom product is lower under the

21

pressure of 30kPa. The increase of the column pressure leads to the increase of

22

column temperature and the side reaction rate, which probably explains this 16


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1

phenomenon. The side reaction is significantly suppressed under the condition of low

2

pressure and low temperature, as the experimental result shows, the content of the

3

main by-product, amyl ether, is obviously lower at a lower pressure, which decreases

4

from 3.487% at 30kPato 0.3% at 20kPa. Therefore, the bottom amyl acetate purity is

5

abnormally higher at the operational pressure of 20kPa.

6

Influence of molar feed ratio

7

The influence of varying mole ratio of acetic acid to amyl alcohol is illustrated by

8

Exp.2 and Exp.3. Exp.3 was performed with a molar feed ratio of 2, while the other

9

operating conditions were kept constant to Exp.2.

10

With an increase of molar feed ratio, more acetic acid is introduced into the

11

column, and the mass fraction of amyl alcohol is lowered in the entire column.

12

Majority of acid would rise to the top of column as acetic acid is the light component,

13

thus the column top temperature slightly decreases when the molar feed ratio changes

14

into 2. While in the lower part of the column, the column temperature of Exp.3 is

15

higher than Exp.2, since the excess of acetic acid could form high boiling azeotropes

16

with amyl acetate, which can be seen from Table 4.

17

There is no liquid-liquid phase separation occurs in the decanter during Exp.3,

18

which is one experimental phenomenon differing from Exp.2. This phenomenon is

19

also mainly attributable to the large excess of acid, leading to an increase of mutual

20

solubility with amyl alcohol or water. This means that the unreacted acid and part of

21

the produced water would reflux to the RD column, resulting in a lower amyl acetate

22

purity and higher acetic acid purity in the entire column. The higher ratio of acetic 17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

acid to amyl alcohol leads to increased amyl alcohol conversion and relatively

2

decreased acetic acid conversion. From Table 5, the amyl alcohol conversion

3

increases from 92.2% to 99.8% as the molar feed ratio increases from 1 to 2. However,

4

the redundant acetic acid would lead to the decreased bottom amyl acetate purity. The

5

mass fraction of amyl acetate in the bottom product for Exp.2 is 99.3% and for Exp.3

6

is 97.8%. The acid value of the top samples also increases as the feed ratio increased.

7

Thus the performance of Exp2 was superior to Exp3.

8

Influence of feeding mode

9

The effect of changing the feeding mode on the performance of the catalytic

10

distillation column is shown by Exp.2 and Exp.4. Exp.2 was performed with the

11

feeding mode of “mixed”. In contrast, Exp4 was carried out with the feeding mode of

12

“split”. The other operating conditions of both experiments were unchanged.

13

The change of the feeding mode results in changes in the composition profile

14

over the whole column height. Since amyl alcohol is fed from the upper part while

15

acetic acid is fed from the lower part during Exp.4, thus the amyl alcohol

16

concentration is higher in the upper part of the RD column and the acid concentration

17

is higher in the lower part in contrast to Exp.2. The amount of light and heavy

18

components directly affects the temperature profiles, thus temperature of Exp.4 is

19

higher above the first feed inlet but lower below it. Compared to Exp.2, the purity of

20

bottom product decreased from 99.3% to 94.3% and the acid concentration of bottom

21

product increases significantly, the acid value of bottom samples increased from

22

0.161mgKOH/g in Exp2 to 55.24mgKOH/g in Exp4. The possible reason may be that 18


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1

different feeding modes led to different concentration profiles and temperature

2

profiles and then influenced the reaction rate. The experimental result showed that the

3

feeding mode of “mixed” had an advantage over the “split” feeding mode and the

4

reason need to be further investigated via simulations.

5

Model validation

6

Reliable models are decisive for RD process, and the equilibrium stage model

7

described in section 4 was used to simulate the experiments in the present study. The

8

validation of this model is performed by comparing the experimental results with

9

simulated results in the form of table and graph. The comparison of experimental

10

amyl acetate purity and temperature with simulated results is shown in Table 6, in

11

which T1, T2, T3, T4 represents the temperature of 1st-4th column segment

12

respectively. And Figure 6 compared the simulated and experimental composition and

13

temperature profiles of all four experiments.

14

During the simulation of the RD column, no side reaction was taken into

15

consideration since no kinetics data were available in the literature for describing it. It

16

can be observed from Table 6 and Figure 6 that all experimental data have a

17

satisfactory agreement with simulated results over the entire packing height. On

18

account of the side reaction occurred at 30kPa, the experimental AmAc purity of

19

Exp1 differed from its simulated result obviously. Except for Exp.1, deviations

20

between experimental data and simulation results are within experimental error. The

21

amyl alcohol conversion of Exp 2 is 97.8% in the simulated result while the

22

experimental value is 94.6%, which may be attributed to the fact that the experimental 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

values are subject to measurement errors. These results demonstrate the suitability of

2

the equilibrium-stage model for the describing reactive distillation process.

3

Process analysis

4

Due to the limitations in experimental setup of the catalytic distillation column,

5

some of the important design parameters might be difficult to be studied

6

experimentally. Therefore, in this section, the validated model is used to determine

7

the effects of varying process parameter on the AmAc purity of bottom products and

8

rebolier duty by sensitivity analysis. The sensitivity analysis was performed

9

systematically by varying one parameter at a time and investigating the effects on the

10

process outputs to acquire an optimum process for the RDC of amyl acetate synthesis.

11

Within this investigation, the position of feeding, the column pressure, the stages of

12

reactive zone and the molar feed ratio were varied. The changes in operational

13

parameters are shown in Table 7.

14

Position of feeding

15

The RD column for different positions of feeding was studied. The simulation

16

results of Cheng and Yu31 revealed that the feed location of the heavy reactant should

17

not be lower than the light reactant. So the feeding position of HAc was not placed

18

higher than AmOH. In this set of simulations, the operating conditions like column

19

pressure, molar feed ratio, bottom flow rate and the reaction zone from 10th stage to

20

32nd stage were all unchanged. As it makes no sense if the feed inlet was placed

21

beyond the reaction zone, thus the feeding position was moved from top to bottom of

22

the reaction zone in the simulations. Firstly, the acid feeding and alcohol feeding were 20


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1

at the same position and both moved from the 10th theoretical stage to the 32nd. Next,

2

the position of alcohol feeding was fixed and the feed location of HAc was changed

3

from top to bottom of the reactive section.

4

The effects of changing the same feeding position of acid and alcohol on AmAc

5

purity and reboiler duty were shown in Figure 7. There is no significant purity change

6

when the feed location moved down from the top, the purity of AmAc keeps virtually

7

constant in a wide region. As continued to move down to the bottom of reaction zone,

8

the AmAc purity decreased rapidly from 98% to 81%. This result shows that the

9

mixed feeding position has little effect on the purity unless the feed stage is at the

10

lowest part of the reaction zone. Figure 8 illustrated the influence of varying the acid

11

feeding location while fixing the alcohol feeding location in 12th stage. As the acid

12

feeding location moved down, the AmAc purity first increased slightly from 98.5% to

13

99.4%, and then decreased to 89.0% gradually. The reason for this phenomenon

14

mainly attribute to the difference of concentration profiles. The concentration profiles

15

of three different feeding modes are shown in Figure 9. First, the feeding mode of

16

Exp2, both AmOH and HAc are fed from the 12th stage. Second, AmOH is fed from

17

12th stage and HAc is fed from 13th stage. And third, the feeding mode of Exp4, the

18

feeding position of AmOH is the same and the feeding position of HAc is the 20th

19

stage. As illustrated by Figure 9, the second mode resulted in higher reactants

20

concentration and lower products concentration in the reaction zone comparing with

21

the first mode, thus increased the reaction rate and consequently led to higher AmAc

22

purity. And compared to the other two feeding modes, the feeding mode of Exp4 led 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

to much higher HAc purity and lower AmAc purity over the column. This simulated

2

result was consistent with the experimental result discussed before, that the feeding

3

mode of Exp2 is better than the feeding mode of Exp4. The second feeding mode can

4

not only make both reactants fully preheated and reacted, but also prevent acetic acid

5

from entering the reboiler. The change trend of reboiler duty was basically the same

6

in both two cases, seeming like that the energy consumption have little to do with the

7

feeding position, maybe because the vapor flow in the column kept unchanged. Thus

8

in order to obtain a higher AmAc purity, feeding the reactants into the column from a

9

close location is an optimal choice, but the mixed feeding mode can also achieve a

10

promising result in the practical production.

11

Column pressure

12

Different from conventional distillation process, choosing operating pressure in

13

the RD column is restricted by the effects of pressure on the reaction rate and the

14

reaction equilibrium, too low pressure makes against the smooth running of the

15

reaction. In addition, the column pressure is limited by the thermal stability of the

16

catalyst since the resin catalyst would lose its activity at high column temperature.

17

Therefore, in the case of kinetics-controlled reaction of our CD system, the choosing

18

of operating pressure could not also be too high. In this simulation, the column

19

pressure was varied from 15kPa to 30kPa, meanwhile the feeding position, height of

20

the reaction zone, molar feed ratio, as well as the bottom flow rate, were fixed.

21

Figure 10 showed the effects of operating pressure on AmAc purity and reboiler

22

duty. With increasing pressure in the column, the temperature of reaction zone rises 22


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1

and the reaction rate as well as equilibrium constant increases subsequently, resulting

2

in a higher AmOH conversion and AmAc purity. At the same time, the increase in

3

operating pressure decreases the relative volatility, leading to the increase of reboiler

4

duty. Theoretically, a higher column pressure increases the AmAc purity in the

5

bottom product. However, as we discussed above, the experimental result indicated

6

that the byproduct concentration increased visibly as the column pressure and

7

temperature rises. Therefore, considering the reboiler duty, the side reaction andthe

8

suitable temperature of catalyst, the feasible column pressure should be chosen

9

comprehensively.

10

Theoretical stages of reaction zone

11

In order to avoid the residence time limitations or inadequate catalyst capacity, it

12

is reasonable to increase the number of theoretical stages of reaction zone. The

13

increase of reaction zone height could increase the catalyst weight. However the

14

initial equipment investment would increase if the number of theoretical stages of

15

reaction zone increases excessively. Therefore, it is necessary to determine an

16

appropriate height of reaction zone. In this set of simulations, the range of the number

17

of theoretical stages of reaction zone was set reasonably from 10 to 22, while other

18

conditions such as bottom flow rate and column pressure were kept unchanged.

19

The effects of changing the number of theoretical stages of reaction section on

20

the AmAc purity and reboiler duty were shown in Figure 11. As we can observe from

21

it, the AmAc purity increased obviously when the number of theoretical stages of

22

reaction zone was 10 to 18, and then increased slightly when the theoretical stages 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

were more than 18. It shows that 14-18 stages are sufficient to achieve the desired

2

AmAc purity, and further increases in the number ofreactive stages hardly influence

3

the performance of the RD column. Meanwhile the reboiler duty kept basically

4

constant. The improvement of theoretical stages of reactive section provided a

5

sufficient residence time to receive higher conversion and higher purity, but when the

6

residence time is too long, the reverse reaction and the investment will increase. In

7

addition, discussed earlier by Gangadwala et al. 32, providing higher reaction zone

8

height and more catalyst degrades the product purity, thus an optimum number of

9

catalytic stages must be provided in the reactive section.

10

Molar feed ratio of acid to alcohol

11

As the price of n-amyl alcohol was way above the acetic acid, the acetic acid was

12

usually excessive in actual production in order to promote the full conversion of

13

n-amyl alcohol. However, too much acetic acid would in turn result in problems of

14

reaction and separation. In the other hand, the reactants would form a variety of

15

azeotropes with the products amyl acetate and water, which increases the difficulty of

16

separation. Meanwhile the molar feed ratio has a great impact on both reactants

17

conversion and energy consumption, thus more attention should be paid to it. In this

18

simulation, HAc and AmOH were fed into the tower from the same tray of the

19

distillation column, with the molar ratio of HAc to AmOH changed from1.0 to 2.0,

20

and other parameters, like feed and bottom flow rate, height of reaction zone,

21

remained stationary. The impacts were evaluated by comparing the product purity and

22

energy consumption. 24


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1

Figure 12 showed the effects of different molar feed ratios on the bottom AmAc

2

concentration and reboiler duty. The straight rise of reboiler duty was mainly

3

attributed to the increase column top remove rate and the gas flow rate. The AmAc

4

purity of bottom product increased obviously when the molar feed ratio was a bit

5

more than 1 and then decreased rapidly from 99.6% to 96% as the molar feed ratio

6

increased from 1.03 to 2. The reason for this phenomenon was that in any case a small

7

amount of acid would withdraw from the decanter with the aqueous phase. When the

8

feed molar ratio is equal to 1, the loss of acid would result in part of unreacted amyl

9

alcohol entering the column bottom and then reducing the product purity. Both the

10

experimental and simulated results had demonstrated this explanation. The acid

11

values of top aqueous phase samples were around 100mgKOH/g for all experiments,

12

and in all simulations the HAc mass fraction in the aqueous phase was around 10%,

13

means that the loss of acetic acid with the aqueous phase was about 0.03 mol per mol

14

of produced water. Therefore, the reaction would proceed more complete under the

15

condition of a slight excess of acid, which making up for the loss of acid. When the

16

feed ratio kept on increasing from 1.03 to 1.19, the concentration of acetic acid

17

increased greatly, the excess acid would not be completely converted and then reduce

18

the bottom product purity. Considering the product purity and energy consumption,

19

the optimal molar feed ratio of HAc to AmOH should be 1.03 in the present

20

simulations. However, from the practical point of view, no control system can keep

21

this ratio with such accuracy, thus in the practical production the molar feed ratio of

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

HAc to AmOH of 1 is optimum as it can easily be controlled and also achieve a

2

satisfactory performance.

3

Conclusions

4

The synthesis of amyl acetate via reactive distillation has been studied in the

5

present work. A novel independently developed packing, Seepage Catalytic Packing

6

Internal (SCPI), was applied as the structured catalytic packing. A series of catalytic

7

distillation experiments and a process simulation using equilibrium stage model were

8

performed to analyze the influence of operating parameters. A detailed analysis of the

9

experimental and simulated results demonstrates that the synthesis of amyl acetate in

10

a catalytic distillation column with SCPIs is feasible. The EQ model is sufficient to

11

describe the performance of the CD column. The simulation studies indicated that, to

12

achieve high product purity and amyl alcohol conversion in this process, the reactant

13

HAc should be feed into the column close to the AmOH feeding location. Beforehand

14

mixing the reactants proportionally and then feeding into the column from the same

15

position is easier to control and can also achieve a satisfactory performance. The

16

theoretical stages of reaction zone, the molar feed ratio and operational pressure

17

should be set reasonably. The molar feed ratio was chosen to close to unity, acetic

18

acid could be a little excess. Under the suitable operating conditions of operating

19

pressure of 20-22kPa and 16-18 theoretical stages of reaction zone, both the amyl

20

acetate purity and amyl alcohol conversion can be obtained more than 95%. These

21

research achievements of the present paper could be applied to facilitate the industrial

22

application of SCPI and used for the optimum design of amyl acetate synthesis via 26


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1

CD.

2

Acknowledgments

3

The authors are grateful for the financial support from National Natural Science

4

Foundation of China (Nos. 21336007, 21690084), the Key Technology R&D Program

5

of Tianjin (No.15ZCZDGX00330), and International S&T Cooperation Program of

6

China, ISTCP (No. 2015DFR40910).

7

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Amyl Acetate Process: Coupled Reactor/Column and Reactive Distillation. Ind.

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34 (7), 960-963. 30


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1 2

(30) Xu, Z.; Chuang, K. Kinetics of Acetic Acid Esterification over Ion Exchange Catalysts. Can. J. Chem. Eng. 1996, 74 (4), 493-500.

3

(31) Cheng, Y. C.; Yu, C. C. Effects of Feed Tray Locations to the Design of Reactive

4

Distillation and Its Implication to Control. Chem. Eng. Sci. 2005, 60 (17),

5

4661-4677.

6

(32) Gangadwala, J.; Kienle, A.; Stein, E.; Mahajani, S. Production of Butyl Acetate

7

by Catalytic Distillation: Process Design Studies. Ind. Eng. Chem. Res. 2004, 43

8

(1), 136-143.

9 10 11 12 13 14 15 16 17 18 19 20 21 22 31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Figures Captions

2

Figure 1. Scheme of the pilot-scale RD column used for experimental

3

investigation of amyl acetate synthesis from acetic acid and amyl alcohol.

4

Figure 2. The structures of two segments of SCPI.

5

Figure 3. Schematic diagram of gas−liquid flow paths within the SCPI

6

Figure 4. Ternary phase diagram for the subsystem consisting of amyl

7

alcohol, amyl acetate and water at the pressure of 20kPa.

8

Figure 5. Experimental data of Exp.1-4.

9

Figure 6. Comparison of the experimental and simulated results of all

10

four experiments.

11

Figure 7. Effects of feeding position of acid and alcohol on AmAc purity

12

and reboiler duty.

13

Figure 8. Effects of acid feeding position on AmAc purity and reboiler

14

duty.

15

Figure 9. Concentration profiles of different feeding modes.

16

Figure 10. Effects of operating pressure on AmAc purity and reboiler

17

duty.

18

Figure 11. Effects of reaction zone theoretical stages on AmAc purity and

19

reboiler duty.

20

Figure 12. Effects of molar feed ratio on AmAc purity and reboiler duty.

21

32


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1 2

Figure 1. Scheme of the pilot-scale RD column used for experimental

3

investigation of amyl acetate synthesis from acetic acid and amyl

4

alcohol. (1)condenser; (2)reflux ratio controller; (3)decanter;

5

(4)reactants storage tank; (5)reboiler; (6)buffer tank; (7)vacuum

6

pump; (Feed 1,2) two different feed inlets.

7 8 9 10 11

33



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2

(a)

(b)

3

Figure 2. The structures of two segments of SCPI. (a) SCPI filled

4

with catalyst and corrugated metal sheets; (b) complete SCPI with

5

wire meshes installed in the top of catalyst container.

6 7 8 9 10 11 12 13 14 15 16 17 18 19

34


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1 2

Figure 3. Schematic diagram of gas−liquid flow paths within the

3

SCPI: (1) corrugated metal sheets; (2) gas flow; (3) θ-ring packing; (4)

4

liquid flow; (5) liquid layer; (6) catalyst particles.

5 6 7 8 9 10 11 12 13 14 15 16

35


0 .1 0 .1 5

5 0 .8 0 .8

0 .2

0 .9 0 .7

0 .3

0 .2 5

5 0 .7 93.75 C

0 .6

0 .4

0 .3 5

5 0 .6

0 .6

0 .5 5

H2 O 0 .5 0 .4 5

0 .4 OH .45 AM .5 0 0 5 0 .5 0 .3

0 .7

0 .6 5

5 0 .3

0 .7 5

5 0 .2 0 .2

0 .8

57.78 C

0 .1

0 .9

0 .8 5

5 0 .1

0 .9 5

5 0 .0

1

Page 36 of 52

5 0 .9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

0 .0 5


0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 56.41 C 56.42 C AMAC

2

Figure 4. Ternary phase diagram for the subsystem consisting of

3

amyl alcohol, amyl acetate and water at the pressure of 20kPa.

4 5 6 7 8 9 10 11 12 13 14

36


Page 37 of 52

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2

(a)

3 4

(b)

5 6

(c)

7

Figure 5. Experimental data of Exp.1-4. (a):temperature;(b):column

8

pressure; (c): feed and withdraw rates.

37



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

2

3

4 5

Figure 6. Comparison of the experimental and simulated results of all four

6

experiments. Symbols represent the experimentally obtained results and lines

7

represent the simulated results: (left) mass compositions of liquid phase; (right)

8

temperature profile of vapor phase. 38


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Page 39 of 52

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1 2 3

Figure 7. Effects of feeding position of acid and alcohol on AmAc purity and reboiler duty.

4 5 6 7 8 9 10 11 12 13 14

39



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3

Figure 8. Effects of acid feeding position on AmAc purity and reboiler duty.

4 5 6 7 8 9 10 11 12 13 14

40


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1 2

(a)

(b)

3 4

(c)

5

Figure 9. Concentration profiles of different feeding modes. (a)

6

AmOH (12)-HAc (12); (b) AmOH (12)-HAc (13); (c) AmOH

7

(12)-HAc (20).

8 9 10 11 12

41



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2

Figure 10. Effects of operating pressure on AmAc purity and reboiler

3

duty.

4 5 6 7 8 9 10 11 12 13 14

42


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1 2 3

Figure 11. Effects of reaction zone theoretical stages on AmAc purity and reboiler duty.

4 5 6 7 8 9 10 11 12 13 14

43



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3

Figure 12. Effects of molar feed ratio on AmAc purity and reboiler duty.

4 5 6 7 8 9 10 11 12 13 14

44


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1

Table 1. Main Geometric Parameters of 1000Y corrugated packing

2

and SCPI Parameter

Value

Peak height (mm)

3.1

Specific surface area(m2/m3)

1000

Number of theoretical plates (1/m)

12-14

Void fraction of packing

0.75

Height (mm)

50

External diameter (mm)

50

Catalyst content (ml)

20

1000Y corrugated packing

SCPI segment

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

45



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 52

1

Table 2. Operating conditions of the performed catalytic distillation

2

experiments Experiment number

1

2

3

4

Top pressure (kPa)

30

20

20

20

mixed

mixed

mixed

split

1:1

1:1

2:1

1.1:1

0.76

0.76

0.76

0.77

Feeding mode Molar feed ratio (HAc/AmOH) (mol/mol) Total feed rate (kg/h) 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

46


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Table 3. NRTL Binary Interaction Parameters

1

Comp. i

HAc(1)

HAc(1)

HAc(1)

AmOH(2) AmOH(2)

Comp. j

AmOH(2)

AmAc(3)

H2O(4)

AmAc(3)

H2O(4)

H2O(4)

bij(K)

-316.8

-37.943

-110.57

-144.8

100.1

254.47

bji(K)

178.3

214.55

424.018

320.6521

1447.5

2221.5

cij

0.1695

0.2000

0.2987

0.3009

0.2980

0.2000

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

47


AmAc(3)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 48 of 52

Table 4. Azeotropic data at different pressure

1

Mass fraction (g/g)

Tempera Pressure

20kPa

30kPa

Type of azeotrope ture (℃)

HAc

AmOH

AmAc

Water

homogeneous

96.49

0.1505

0.8495

-

-

homogeneous

94.29

0.0536

0.2842

0.6622

-

homogeneous

93.75

-

0.4306

0.5694

-

heterogeneous

57.78

-

0.3709

-

0.6291

heterogeneous

56.42

-

-

0.5735

0.4265

heterogeneous

56.41

0.0189

0.5519

0.4292

homogeneous

106.23

0.1614

0.8386

-

-

homogeneous

104.62

0.0709

0.3384

0.5907

-

homogeneous

103.81

-

0.5355

0.4645

-

heterogeneous

66.45

-

0.3940

-

0.6060

heterogeneous

65.14

-

-

0.5801

0.4199

heterogeneous

65.12

0.0375

0.5381

0.4244

2 3 4 5 6 7 8 9 10 11 12 13 14

48


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1

Table 5. The average mass flow rates and the experimental results of four steady period

2

Exp1

Exp2

Exp3

Exp4 AmOH:

Feed rate (kg/h)

0.769

0.757

0.725

0.444 HAc: 0.337

Bottom remove rate (kg/h)

0.588

0.584

0.416

0.569

Top remove rate (kg/h)

0.154

0.148

0.296

0.196

1.374

0.161

17.22

55.24

Acetate purity of bottom sample (wt%)

93.6

99.3

97.8

94.3

Amyl alcohol conversion

0.946

0.922

0.998

0.977

LL-phase separation

yes

yes

no

yes

Acid value of bottom sample (mgKOH/g)

Composition at

HAc

5.4

6.8

69.3

0.4

top aqueous

AmOH

trace

trace

0.2

0.5

withdraw stream

AmAc

0.3

0.4

8.6

trace

(wt%)

H2O

94.3

92.8

21.9

99.1

3 4 5 6 7 8 9 10 11

49



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 50 of 52

1

Table 6. Comparison of experimental AmAc purity and temperature

2

with simulated results Exp 1

Exp 2

Exp 3

Exp 4

Parameters Exp

Sim

Exp

Sim

Exp

Sim

Exp

Sim

T4(℃)

74.5

77.5

60.6

68.5

59.9

64.9

56.5

71.8

T3 (℃)

80.6

81.9

71.3

72.5

75.5

80.8

71.6

78.6

T2 (℃)

104.1 109.1 100.1

98.4

101.6

97.9

88.5

88.0

T1 (℃)

108.9 109.8 101.7

99.3

106.6

99.2

89.1

94.4

Bottom flow rate 0.640 0.663 0.610 0.663 0.440 0.460 0.650 0.680 (kg/h) Acid value of bottom 1.374 0.016 0.161 0.030 17.22 23.33 55.24

42.0

sample(mgKOH/g) Bottom AmAc 0.936 0.991 0.993 0.985 0.978 0.976 0.943 0.955 purity(wt) 3 4 5 6 7 8 9 10 11 12 13 14 15

50


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1

Table 7. The changing of operational parameters and design parameters for all sensitivity studies

2

Fixed parameter Changed Position of

Column

feeding

pressure (kPa)

parameter

Theoretical

Molar feed

stages of the

ratio

reaction zone

(HAc:AmOH)

Position of 10-32

20

22

1

12

15-30

22

1

12

20

10-22

1

12

20

22

1-2

feeding Column pressure (kPa) Theoretical stages of the reaction zone Molar feed ratio (HAc:AmOH) 3 4 5 6 7

**************

51



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1

For Table of Contents Only

2

52


Page 52 of 52

Synthesis of n-Amyl Acetate in a Pilot Plant Catalytic Distillation

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