Simulation of Formaldehyde Production ProcessRuhul Amin, Nazibul Islam, Rezwanul Islam, Yusuf Imtiaz, Saeed M., Unaiza M.

Department of Chemical EngineeringBangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh

Abstract

Formaldehyde plays a major role in the synthesis of many important compounds. Worldwide production

of formaldehyde is growing day bay day. There are various industrial processes for the production of

formaldehyde. This article starts with an overview of formaldehyde and the history of formaldehyde

production. Subsequently, production of formaldehyde using silver catalyst is simulated with the help of

Aspen Hysys 7.1. Important parameters such as temperature profile, pressure profile, fluid properties etc

were investigated with this simulation process. The effect of temperature in the reaction was also

examined. The simulation process validated that for maximum conversion to take place, the reaction must

occur in 550C. Finally, 74% formaldehyde was obtained as product.

Key Words: Formaldehyde, Oxidation-dehydrogenation, NRTL, Simulation

1. Introduction

Formaldehyde was discovered in 1859 by a

Russian chemist named Aleksandr Butlerov.

However it was in 1869, that German chemist

August Hofmann developed a practical method

to synthesis formaldehyde from methanol. [1] It is

a colorless gas with a distinctive pungent order.

It is highly flammable with a flashpoint of 500C;

the heat of combustion is 134.1kcal/mol or

4.47kcal/g.[2] Formaldehyde is soluble in a

variety of solvents and is miscible in water. [2, 3]

Formaldehyde is a key chemical component in

many manufacturing processes. It is used as a

building block for the synthesis of more

complex compounds and materials. [4] In

approximate order of decreasing consumption,

products generated from formaldehyde include

urea formaldehyde resin, melamine resin, phenol

formaldehyde resin,poly-oxy-methylene plastics,

1,4-butane-di-ol, and methylene-di-phenyl-di-

iso-cyanate.[5] In biomedical industry,

formaldehyde is used in vaccines, medicines,

plastics and in x-ray machines. The phenolic

molding resins produced from formaldehyde are

used in appliances, electrical control, telephone

and wiring devices. [6] In the automotive and

building industries, formaldehyde-based acetal

resins are used in the electrical system,

transmission, engine block, door panels and

break shoes. [7]

The total annual formaldehyde capacity in 1998

was estimated by 11.3 billion pounds. Since then

and the production capacity around the globe is

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expanding exponentially reaching a world’s

production of 32.5 million metric tons by 2012. [7, 8] There are two main routes for formaldehyde

production: oxidation-dehydrogenation using a

silver catalyst involving both the complete or

incomplete conversion of methanol; and the

direct oxidation of methanol to formaldehyde

using metal oxide catalysts. [9, 10] In the

oxidation-dehydrogenation route, vaporized

methanol with air is passed over a thin bed of

silver-crystal catalyst at about 6500C.

Formaldehyde is formed by the de-

hydrogenation of methanol. [11, 12] The other route

involves the oxidation of methanol over a

catalyst of molybdenum and iron at 3500C. [13]

This article deals with the detailed study of the

simulation of formaldehyde production from

methanol. Simulation has been done with the

help of Aspen Hysys v7.2. Although simulation

does not give the real world performance or the

real life production environment but if the basic

process is known and related data are available,

it is the best way by which an individual can get

ideas of an industrial process without conducting

any experiment.

2. Methodology

The process of producing formaldehyde from

methanol is simulated in Simulation software

Aspen Hyssy 7.1. Aspen Hysys is a simulation-

software which comes along with excellent

reference & tutorial manuals for simulating a

process. Hysys does not wait until entering

every process condition before beginning

calculation. It calculates as much as it can at all

time and results are always available, even

during calculation. Any changes that one makes

to the data are automatically propagated

throughout the program to anywhere that entry

appears and all necessary recalculations are

instantly carried out. It tends to be a lot easier to

catch errors as one gradually converge the

process simulation.

The Fluid package used in this simulation is

NRTL. The non-random two-liquid model is

known as NRTL equation in short[14]. NRTL is

an activity coefficient model that correlates

the activity coefficients of a compound i with

its mole fractions in the liquid phase concerned.

The concept of NRTL is based on the hypothesis

of Wilson that the local concentration around a

molecule is different from the bulk

concentration. This difference is due to a

difference between the interaction energy of the

central molecule with the molecules of its own

kind Uii and that with the molecules of the other

kind Uij. The energy difference also introduces a

non-randomness at the local molecular level.

The NRTL model belongs to the so-called local-

composition models. Other models of this type

are the Wilson model, the UNIQUAC model,

and the group contribution model UNIFAC.

These local-composition models are not

thermodynamically consistent due to the

assumption that the local composition around

molecule i is independent of the local

composition around molecule j. This assumption

2

is not true, as was shown by Flemmer in

1976[15, 16].

2.1 Process Description

Formaldehyde results from the exothermic

oxidation and endothermic hydrogenation of

methanol. These two reactions occur

simultaneously in commercial units in a

balanced reaction, called auto thermal because

the oxidative reaction furnishes the heat to cause

the dehydrogenation to take place. About 50 to

60 percent of the formaldehyde is formed by the

exothermic reaction. The oxidation requires

1.6m3 of air per kilogram of methanol reacted, a

ratio that is maintained when passing separate

streams of these two materials forward. Fresh &

recycled methanol are vaporized, superheated

and passed into the methanol-air mixer.

Atmospheric air is purified, compressed and pre-

heated to 540C in a finned heat exchanger. The

products leave the converter at 620oC and at 34

to 69 KPa absolute. The converter is a small

water-jacketed vessel containing the silver-

catalyst. About 65 percent of the methanol is

converted per pass. The reactor effluent contains

about 25% formaldehyde, which is absorbed

with the excess methanol and piped to the make

tank. The latter feeds the methanol column for

separation of recycle methanol overhead, the

bottom stream containing the formaldehyde and

a few percent methanol. The water intake adjusts

the formaldehyde to 37% strength (marketed as

formalin). The yield from the reaction is 85 to

90 percent. The catalyst is easily poisoned so

stainless-steel equipment must be used to protect

the catalyst from metal contamination.

2.2 Simplified Block Diagram

Figure 1: Block diagram of the total process

2.3 Set Stoichiometry and Rate of

Reaction

3

As mentioned earlier, Formaldehyde results

from the exothermic oxidation and endothermic

de-hydrogenation of methanol.

CH3OH + 1/2 O2 CH2O + H2O; H = -156 KJ

CH3OH CH2O + H2; H = +85 KJ

So the stoichimetry for Methanol in the 1st and

2nd reaction would be -1

For Formaldehyde it would be +1 for the both

reactions.

For Oxygen it would be -0.5 in the 1st reaction

And for water and Hydrogen it would be +1 for

the 1st and 2nd reaction respectively.

The rate of reaction for the first reaction will be:

−r m1 [

molegcatalysthr

]= k 1 pm1+k 2 pm

Where,

lnk 1=12.50−8774T

And

lnk 2=−17.29+7439T

The rate of reaction for the second reaction will be:

rm2[

molegcatalysthr

]= K 1√ pm1+K 2√ pm

Where,

lnK 1=16.9−12500T

And

lnK 2=25.0−15724T

For all the equations, T is in Kelvin. [8]

2.4 The Simulation Environment

1. First Methanol and feed air are delivered

to a mixer and later preheated to 55⁰ C

and delivered to the reactor.

2. In the first step of the reaction, methanol

reacts with oxygen to give formaldehyde

and water

3. In the 2nd stage some of the methanol

breaks up to formaldehyde and

hydrogen.

4. The vapor from the reactor outlet is

cooled to 10⁰ C and delivered to a

separator.

5. The Hydrogen is separated from the

mixture.

6. The remaining mixture is heated to 100⁰ C and fed to the distillation column.

7. From the distillation column, we get the

liquid product of 83.2% formaldehyde

and a vapor product of 44.1%

formaldehyde.

8. The vapor product is heated to 35⁰ C

and delivered to a storage tank.

4

2.5 Importance of Temperature in

the Simulation

The heated feed that is delivered to the

first reactor is heated to a temperature of

55° C by delivering the feed to a heater.

It is heated to 55° C because this is the

optimum temperature of reactor inlet.

The final top product from the

distillation column is delivered to a

heater before it is stored in the storage

tank. The outlet from the heater is

heated to a temperature between 35-45°

C. At temperatures below 35° C, the

product forms formaldehyde polymer

which is not desired. Storage at

temperatures between 35-45° C further

inhibits the formation of formaldehyde

polymers[2].

3. Results and Discussions

Final composition of Formaldehyde obtained is

74.8%.

Different parameters of the distillation column are shown in different graphs below-

3.1 Temperature Profile of Distillation

Column

Figure 2: Graphical representation of

Temperature vs Tray position from top

From figure 2 we can see that the condenser

temperature is around -2500C. The

temperature rises rapidly from the condenser

and reaches near 1000C at stage 2 that is first

tray after the condenser. From tray 2, the

temperature rise is linear and is around

1100C in the reboiler.

5

0 2 4 6 8 10 12 14 16

-300-250-200-150-100

-500

50100150

Number of Tray

Tem

pera

ture

3.2 Pressure profile of Distillation column

Figure 3: Graphical representation of

Temperature vs Tray position from top

From this graph we can visualize the pressure

profile of the distillation column. Here we see

that the pressure profile is almost linear. The

linear equation for this curve is,

Y=0.6081X+10.551

With, R2= 0.9946

3.3 Light Liquid Composition

Figure 4: Graphical representation of light liquid (mole fraction) vs Tray position from top

Here, we see that there is a slight rise of mole

fraction of the light liquid from condenser to

tray 1. After that up to tray 7 this value remains

somewhat constant. From tray 7, which is the

feed tray we again see a perfect linear increase

in light liquid mole fraction right up to the

reboiler.

3.4 Flow rate vs. Tray Position

Figure 5: Graphical representation of flow vs

Tray position from top

In the case of molar flow, we see that the

vapor flow starts from zero at tray 1 and

increases rapidly up to tray 3. From tray 3

this increase in flow is much sluggish. For

the liquid however, there are rapid increases

in flow from reboiler to tray 1 and also in

tray 7 which is the feed tray. In between

these rapid increases, the flow is somewhat

constant. Finally there is a drastic drop in

the flow of liquid at the reboiler.

6

-1 1 3 5 7 9 11 1302468

101214161820

Number of Tray

Pres

sure

(psia

)

0 2 4 6 8 10 12 14 161000

10000001000000000

10000000000001000000000000000

1E+0181E+0211E+0241E+0271E+030

Light

liqu

id

Tray Number

0 2 4 6 8 10 12 14 160.00E+00

1.00E+03

2.00E+03

3.00E+03

4.00E+03

5.00E+03

6.00E+03

7.00E+03

8.00E+03

Tray position

Net

mol

ar fl

ow(lb

mol

e/hr

)

Liquid

Vapor

3.5 Light Liquid Composition vs. Tray

Position

Figure 6: Graphical representation of composition (light liquid) vs Tray position from

top

For the light liquid, we see that water

composition is higher than Formaldehyde in the

condenser. But from the condenser a gradual

increase in Formaldehyde composition takes

place right up to the reboiler. Evidently the

water composition decreases from the condenser

to reboiler.

3.6 Heavy Liquid Compositon vs. Tray Position

Figure 7: Graphical representation of composition (vapor) vs Tray Position from top

Here we also see that starting from zero in the

condenser; the composition of formaldehyde

gradually increases. In the case of water, the

composition reaches its maximum at tray 2 and

from there it gradually decreases.

3.7 K-values vs tray position

Figure 8: Graphical representation of k-values

vs Tray position from top

In the case of k-values (Distribution Co-

efficient), we see that the distribution co-

efficient of hydrogen (present in the feed)

7

0 2 4 6 8 10 12 14 160

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Tray Position

Mol

e Fr

actio

n

Formaldehyde(Light)

H2O(Light) 0 2 4 6 8 10 12 14 160

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Mol

e Fr

ac-

tion

Tray Posi-tion

H2O

0 2 4 6 8 10 12 14 161.00E-671.00E-591.00E-511.00E-431.00E-351.00E-271.00E-191.00E-111.00E-031.00E+05

Tray position

K V

alue

Water

Hydrogen

Formaldehyde

remains constant with respect to water and

formaldehyde. The k-values for the letter two

increase dramatically up to tray 2 from where

they decrease a little and remain perfectly

constant.

3.8 Transports Properties of the

Distillation Column

0 2 4 6 8 10 12 14 160

20

40

60

80

100

120

Colu

mn

Prop

ertie

s

Tray Po-sition

Surface Tension

Molecular weight

Heat capacity

Figure 9: Graphical representation of column

properties vs tray position from top

If we analyze the properties of the light liquid in

the distillation column, we find that the surface

tension decreases dramatically from condenser

to tray 2 and from there, this decrease in surface

tension is gradual.

The molecular weight increases linearly with the

equation:

Y=0.2622X+23.182

And, R2=0.9981

The heat capacity increases with the linear

equation:

Y=0.0643X+3.698

And, R2=0.8865

3.9 Effect of Temperature on Feed

Figure 10: Graphical representation of heated

flow vs temperature of heated feed

In case of the heated feed, the heat flow keeps

increasing with the increase of temperature of

the heated feed. After 45° C the heat flow does

not increase too much with the change in

temperature and becomes constant. So the

heated feed is heated to a temperature of 55° C.

4. Conclusion

The simulation developed by AspenHYSYS is

useful to understand the detailed environment of

the production process of formaldehyde. The

tray-by-tray characteristics of the distillation

column can be visualized using simulation.

8

20 25 30 35 40 45 50 55 60

-1.40E+08

-1.35E+08

-1.30E+08

-1.25E+08

-1.20E+08

-1.15E+08

Temperature of heated feed (°C)

Heat

flow

(kJ/

h)

Similarly the products of the reactors can be

anticipated. Thus using this simulation, one can

easily calculate the material and energy feed

required for the production of any specific

amount of product. This in turn will help to

calculate the cost required to operate a

formaldehyde production plant.

References

1. CECIL H. , Frank B., JOHN W., PETER P. Formaldehyde Fixation The Journal of Histochemistry and Cytochemistry 1985. 33(8): p. 845-853.

2. Inc. S.A., Formaldehyde, Material Safety Data Sheet version 1.10. 2007: Missouri, USA.

3. NCDOL, A Guide to Formaldehyde. North Carolina Dept. of Labor: 1101 Mail Service Center Raleigh, NC 27699-1101.

4. Robert C., CRC Handbook of Chemistry and Physics 62 ed. 1981.

5. Jacqueline I., Seidel A., Encyclopedia of Chemical Technology. 1997, John Wiley and Sons.

6. Natz B., FORMALDEHYDE: FACTS AND BACKGROUND INFORMATION. 2007: Arlington.

7. Bizzari S.N., Formaldehyde. Chemical Industries Newletter 2007.

8. Sanhoob M A., Sulami A., Shehri F., Rasheedi S., Production of Formaldehyde from Methanol Integrated Final Report. 2012, KFUPM.

9. Austin T.G., Shreve's Chemical Process Industries. 5th ed. Chemical Engineering Seris. 1984, United States: McGraw-Hill Book Company.

10. Perry R.H., Green D.W., Perry’s chemical engineers’ Handbook. 7th ed. 1997: McGraw-Hill.

11. Dryden.C.E., Outlines of Chemical Technology for 21st Century. 1997, New York press.

12. Ketta Mc., Encyclopedia of Chemical Technology,. 1997.

13. Mccabe W. L., Smith J.C., Harriot P., Unit Operations in Chemical Engineering. 6th ed. 2001: McGraw Hill.

14. Renon H. Prausnitz J. M., Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures. AIChE Journal, 1968. 14(1): p. 135-144.

15. Flemmer, Collection of Czechoslovak Chemical Communications. 1976. p. 3347.

16. McDermott C.M., Fluid Phase Equilibrium 1ed. Vol. 33. 1977.

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