Production of Formaldehyde

FACULTY OF CHEMICAL & NATURAL RESOURCES ENGINEERING UNIVERSITY MALAYSIA PAHANG

BKF 3553 PROCESS SIMULATION & COMPUTER AIDED DESIGN LECTURER: DR ING- RIZZA BIN OTHMAN

MINI PROJECT

PREPARED BY: CHOO WEI CHUN

KE11037

HOR CHEE HENG

KE11029

TAN YONG CHAI

KA11206

LEE HON KIT

KA11182

LEE JHIN ONN

KA11178

DATE OF SUBMISSION: 27th MAY 2014

Table of Contents 1.0

INTRODUCTION ............................................................................................................3

1.1 Process Description ............................................................................................................3 1.1.1 Background...................................................................................................................3 1.1.2 History of formaldehyde production ............................................................................4 1.1.3 Objectives ......................................................................................................................4 1.1.4 Scope of study ...............................................................................................................5 1.2 PFD (Process Flow Diagram) ............................................................................................5 1.3 Reaction kinetics.................................................................................................................9 1.4 Operating conditions........................................................................................................10 2.0

MODELLING & SIMULATION METHODOLOGY ...............................................11

2.1 Chemical components definition .....................................................................................11 2.2 Thermodynamic properties selection .............................................................................11 2.3 Flowsheet design ...............................................................................................................12 2.4 Plant capacity....................................................................................................................13 2.5 Input parameters setup for each unit operation............................................................14 2.6 Mass balance of major equipments.................................................................................15 3.0

RESULTS & DISCUSSION ..........................................................................................17

4.0 CONCLUSION & RECOMMENDATION .......................................................................19 References ...................................................................................................................................20

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1.0

INTRODUCTION

1.1 Process Description 1.1.1 Background Formaldehyde is also known as Methanal, Methylene oxide or Formalin. It is the first in the series of aliphatic aldehydes, with the structure H2C=O. Formaldehyde is a reactive and versatile chemical intermediate. Pure formaldehyde is a colourless gas with a pungent and suffocating odour at ordinary temperatures. The ignition temperature of formaldehyde gas is 430°C (Gerberich and Seaman, 2004). Mixtures with air are explosive. It is stable at 80 - 100°C when pure, but small amounts of impurities such as water cause rapid polymerisation to poly (oxymethylenes). Formaldehyde liquefies at -19.2°C and solidifies at -118°C, giving a white paste. At temperatures of up to 80°C, the liquid and gas forms of formaldehyde polymerise rapidly. Formaldehyde (CH2O), the target product of this project, acts as a synthesis baseline for many other chemical compounds including phenol formaldehyde, urea formaldehyde and melamine resin that subsequently used as adhesives and binders for particle board and plywood. The most widely produced grade is formalin (37 wt. % formaldehyde in water) aqueous solution. In this project’s study, formaldehyde is to be produced through a catalytic vapor-phase oxidation reaction involving methanol and oxygen according to the following reactions:

The first desired reaction is exothermic while the second is an endothermic reaction. The project’s target is to design a plant with a capacity of 50,000 metric ton formalin/annum with the operating days of 49weeks/343 days in a year. This plant is to include three major units; a reactor, an absorber and a distillation column. Also it includes pumps, compressors and heat exchangers. All are to be designed and operated according to this production capacity. 3

1.1.2 History of formaldehyde production In 1859, Aleksandr Butlerov, a Russian chemist, discovered formaldehyde. After 10 years, another chemist form German who named August Hofmann finally identified formaldehyde. The production of formaldehyde began in the beginnings of the twentieth century. The annual growth rate for formaldehyde production averaged to 11.7% between 1958 and 1968. The production was 54% of capacity in the mid-1970s. Annual growth rate of formaldehyde was 2.7% per year from 1988 to 1997. The production of formaldehyde was ranked 22nd among the top 50 chemicals manufactured in the United States in 1992. The total annual formaldehyde capacity in 1998 was estimated by 11.3 billion pounds and its production capacity is increasing exponentially in the global until it reaches a world’s production of 32.5 million metric tons by 2012. The demand of the formaldehyde becomes high because of its low costs compared to other materials and its receptivity for reaching high purities. It is also the center of many chemical researches and alternatives manufacture methods. Applications of formaldehyde in industries include building block for organic compounds, photographing washing, woodworking, cabinet-making industries, glues, adhesives, paints, explosives, disinfecting agents, tissue preservation and drug testing field.

1.1.3 Objectives 1. To study an integrated design of a plant for formaldehyde production with specified capacity in a point of view in chemical engineering. 2. To investigate the entire process unit design of the plant such as process flow diagrams and operation parameters.

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1.1.4 Scope of study 1.

To apply knowledge of mass and heat transfer, fluid dynamics, unit operations,

reaction kinetics and process control in the project. 2. To perform mass and energy balances, Hysys simulation of the Process Flow

Diagrams, design of the reactor, design of heat exchangers, design of the absorber and distillation column and energy optimization in the project.

1.2 PFD (Process Flow Diagram)

Figure 1.2.1: Formalin process flow diagram (Turton et al., 2009)

Figure 1.2.1 is a process of producing formalin (37 wt% formaldehyde in water) from methanol using the silver catalyst process.

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Air (0.21% Oxygen; 0.79% Nitrogen; 25 °C; 1 atm) is compressed and mixed the methanol (30 °C; 1.2 bar) which has been preheated, fresh and recycled to provide reactor feed. The feed mixture contains around 39 mol% methanol in air, which is more than upper flammability limit for methanol. (For methanol, UFL= 36 mol%; LFL= 6 mol%). In the PFR reactor, there are two reactions happen:

The reactor (length 0.347m and diameter 0.050799m) is using the silver catalyst (Bed voidage 0.5 and particle density 1500 kg/cum), in the form of wire gauze, suspended above a heat exchanger tube bank. It is a must to the remove the heat produced in the adiabatic reactor section due to the net reaction is highly exothermic, thus the close proximity of the heat exchanger tubes. Inside the heat exchanger, there is a pool of water on the shell side. The set point on a level controller is adjusted when it detects the temperature of the effluent is very high. The level controller will send signal to the boiler so that to increase the feed water rate entering from the reboiler to the heat exchanger to increase the water vaporization rate to remove more heat. In general, the liquid-level controller on the boiler feed water is adjusted to keep the tube bundle fully immersed. The reactor effluent enters an absorber in which most of the methanol and formaldehyde are absorbed into water, with most of the remaining light gas purged into the off-gas stream. The formaldehyde, the methanol, and water enter a distillation column, in which the overhead product, methanol is recycled; the bottom product, formaldehyde/ water mixture that contains <1 wt% methanol as an inhibitor. Due to there are some batch downstream process, this mixture send to a storage tank after cooling. A suitable amount of water is added inside the storage tank when the downstream process draws from the storage tank because the composition in the storage tank exceeds 37 wt% formaldehyde. The storage tank contents must be maintained between 35°C and 45°C to prevent unfavourable conditions like polymerization and

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formic acid formation from happening. Figure 1.2.2 shows the block flow diagram of formalin production.

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Figure 1.2.2: Formalin block flow diagram 8

1.3 Reaction kinetics Kinetic information for the methanol oxidation reaction:

The rate expression is:

Where p is a partial pressure in atm, and m refers to methanol. The rate expression is only valid when oxygen is present in excess. The constants are defined as:

Where T is in Kelvin, the rate data as follows for the side reaction:

The rate expression is:

Standard enthalpies of reaction (298 K, 1 atm) for the two reactions are given as:

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1.4 Operating conditions The process that will be applied in this project is the production of formaldehyde through the vapor phase oxidation reaction between methanol and air (Oxygen). In this process, a reactor, an absorber and a distiller are required for the production of formaldehyde. First and foremost, two streams; first stream is a mixture of fresh methanol (25°C, 1atm) and second stream is recycled methanol (68.3°C and 1.2atm) pumped to 3atm and vaporized to 150°C are received by a reactor. The reactor is designed for 87.4% methanol conversion. Secondly, the absorber receives the outlet stream of methanol from the reactor at 343°C and a fresh stream of water (30°C, 138KPa). Absorption of 99% is expected where the liquid outlet is heated to 102°C. Next, the mixed liquid from the absorber is received by the distillation column and further separated the overhead stream (68.3°C, 1.2atm) then recycles it back to methanol fresh feed mixing point. The bottom formaldehyde stream is pumped and mixed with demonized water forming (37 wt. % formaldehyde) formalin stream that is sent for storage.

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2.0

MODELLING & SIMULATION METHODOLOGY

2.1 Chemical components definition

Figure 2.1: Chemical components involve in formalin production.

2.2 Thermodynamic properties selection

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Figure 2.2: Properties method selection in Aspen Plus V8.0.

The NRTL model can describe Vapor-Liquid Equilibrium and Liquid-Liquid Equilibrium of strongly non-ideal solutions. The NRTL model can handle any combination of polar and non-polar compounds, up to very strong non-ideality. Parameters should be fitted in the temperature, pressure, and composition range of operation. No component should be close to its critical temperature. The vapor phase EOS name for NRTL-HOC property method is Non-Random Two-Liquid on Hayden-O’ Connell. Do not use the Hayden-O'Connell-based property methods at pressures exceeding 10 to 15 atm. (Renon & Prausnitz, 1968)

2.3 Flowsheet design

Figure 2.3: Flowsheet design using Aspen Plus V8.0. 12

2.4 Plant capacity Formalin Production statistics: Optimum Operating hour given: / 343 days Production Rate Given: (50,000 metric tonnes/yr)

Production rate per year =

Since CH2O and H2O has the same no. of mole of CH2(OH)2 produced, therefore, no. of mole of CH2O and H2O feed is

.

Table 2.4: Calculation of Molar and Mass Feed rate. Species

Mole (kmol/yr)

Mass (MT/yr)

Formaldehyde

1041666.67

31280.00

Water

1041666.67

18720.00

Formalin

1041666.67

50,000.00

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2.5 Input parameters setup for each unit operation Table 2.5: Input parameters setup for each unit operation Equipment Mixer 1

Pump Heater 1

Compressor

Heater 2

Mixer 2 PFR

Chiller Absorption Tower

Distillation Column

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Description Mixing of pure methanol and recycled methanol. Inlet and outlet temperature 30oC and pressure 1.5 bar. Inlet and outlet flow rate 76.92 kmol/hr. Outlet pressure of methanol at 3 bar. To heat the reactant from 30 oC to 150 oC To decrease pressure from 3 bar to 2.65 bar. Vapour-liquid valid phase. Compress air. Inlet temperature and pressure are 25 oC and 1 atm. Outlet temperature and pressure are 174 oC and 3 bar. Inlet and outlet flow rate 145.94 mol/hr Oxygen mole fraction: 0.21 Nitrogen mole fraction: 0.79 To heat the reactant from 174 oC to 200 oC To decrease pressure from 3 bar to 2.65 abr. Vapour-liquid valid phase. To mix methanol and air. Outlet temperature is 175 oC after mixing. Operation set at 200 oC Reactor length 0.347m and diameter 0.050799m Catalyst present in the reactor Bed voidage is 0.5 Particle density is 1500 kg/cum Decrease temperature to 100 oC and pressure to 1.5 bar. Vapour-liquid valid phase. Rate-based calculation type 30 number of stages Condenser pressure 1.5 bar Feed streams above stage 1 (intermediate product) Feed streams on stage 30 (water) Equilibrium calculation type 31 number of stages Total condenser Reflux ratio of 37.34 Bottom rate is 1 kmol/hr Condenser pressure 1.5 bar Feed stream at 18th stages

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2.6 Mass balance of major equipments Reactor

n8 = 319.67 kmol/hr xCH3OH = 0.240622 xO2 = 0.096041 xH2O = 0.302024 xN2 = 0.3613067

n9 = 356.46 kmol/hr xCH3OH = 0.0825945 xO2 = 0.0561529 xCH2O = 0.1331915 xH2O = 0.3308004 xH2 = 0.0732467 xN2 = 0.3240139

Assumption: •

Adiabatic

•

No pressure drop

Absorber n11 = 143 kmol/hr xH2O = 1



n13 = 171.67 kmol/hr xCH3OH = 0.117542 xO2 = 0.0002 xCH2O = 0.14636 xH2O = 0.73508 xH2 = 0 xN2 = 0.0008

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Distillation column

n13 = 171.67 kmol/hr xCH3OH = 0.117542 xO2 = 0.0002 xCH2O = 0.14636 xH2O = 0.73508 xH2 = 0 xN2 = 0.0008

n13 = 96.811 kmol/hr xCH3OH = 0 xO2 = 0.00056 xCH2O = 0 xH2O = 0.997285 xH2 = 0.00002 xN2 = 0.00214

n13 = 149 kmol/hr xCH3OH = 0.135425 xO2 = 0 xCH2O = 0.01765 xH2O = 0.8469 xH2 = 0 xN2 = 0

Assumption: •

Light key component is methanol

•

Heavy key component is water

•

Non-heavy key is formaldehyde

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3.0

RESULTS & DISCUSSION Table 3.1: Stream results. 1 MIX1 LIQUID

Substream: MIXED Mole Flow kmol/hr METHANOL OXYGEN FORMA-01 WATER HYDROGEN NITROGEN Mole Frac METHANOL OXYGEN FORMA-01 WATER HYDROGEN NITROGEN Mass Flow kg/hr METHANOL OXYGEN FORMA-01 WATER HYDROGEN NITROGEN Mass Frac METHANOL OXYGEN FORMA-01 WATER HYDROGEN NITROGEN Total Flow kmol/hr Total Flow kg/hr Total Flow l/min Temperature C Pressure bar Vapor Frac Liquid Frac Solid Frac

2 PUMP1 MIX1 LIQUID

3 HEATER1 PUMP1 LIQUID

4 MIX2 HEATER1 VAPOR

5 COM1 VAPOR

6 CHILLER1 COM1 VAPOR

7 MIX2 CHILLER1 VAPOR

8 PFR1 MIX2 VAPOR

9 CHILLER2 PFR1 VAPOR

10 ASB1 CHILLER2 VAPOR

11

12

ASB1 LIQUID

ASB1 VAPOR

13 DIST1 ASB1 LIQUID

14 MIX1 DIST1 LIQUID

15 DIST1 LIQUID

76.9200 0.0000 0.0000 0.0000 0.0000 0.0000

76.9200 0.0542 0.0000 96.5484 0.0019 0.2068

76.9200 0.0542 0.0000 96.5484 0.0019 0.2068

76.9200 0.0542 0.0000 96.5484 0.0019 0.2068

0.0000 30.6474 0.0000 0.0000 0.0000 115.2926

0.0000 30.6474 0.0000 0.0000 0.0000 115.2926

0.0000 30.6474 0.0000 0.0000 0.0000 115.2926

76.9200 30.7016 0.0000 96.5484 0.0019 115.4994

29.4420 20.0165 47.4780 117.9185 26.1098 115.4994

29.4420 20.0165 47.4780 117.9185 26.1098 115.4994

0.0000 0.0000 0.0000 143.0000 0.0000 0.0000

9.2637 19.9816 22.3521 134.7275 26.1084 115.3617

20.1783 0.0350 25.1260 126.1910 0.0015 0.1376

0.0000 0.0542 0.0000 96.5484 0.0019 0.2068

20.1783 0.0000 2.6307 126.1910 0.0000 0.0000

1.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.4428 0.0003 0.0000 0.5557 0.0000 0.0012

0.4428 0.0003 0.0000 0.5557 0.0000 0.0012

0.4428 0.0003 0.0000 0.5557 0.0000 0.0012

0.0000 0.2100 0.0000 0.0000 0.0000 0.7900

0.0000 0.2100 0.0000 0.0000 0.0000 0.7900

0.0000 0.2100 0.0000 0.0000 0.0000 0.7900

0.2406 0.0960 0.0000 0.3020 0.0000 0.3613

0.0826 0.0562 0.1332 0.3308 0.0732 0.3240

0.0826 0.0562 0.1332 0.3308 0.0732 0.3240

0.0000 0.0000 0.0000 1.0000 0.0000 0.0000

0.0283 0.0610 0.0682 0.4110 0.0796 0.3519

0.1175 0.0002 0.1464 0.7351 0.0000 0.0008

0.0000 0.0006 0.0000 0.9973 0.0000 0.0021

0.1354 0.0000 0.0177 0.8469 0.0000 0.0000

2464.6830 0.0000 0.0000 0.0000 0.0000 0.0000

2464.6830 1.7334 0.0000 1739.3460 0.0039 5.7923

2464.6830 1.7334 0.0000 1739.3460 0.0039 5.7923

2464.6830 1.7334 0.0000 1739.3460 0.0039 5.7923

0.0000 980.6800 0.0000 0.0000 0.0000 3229.7470

0.0000 980.6800 0.0000 0.0000 0.0000 3229.7470

0.0000 980.6800 0.0000 0.0000 0.0000 3229.7470

2464.6830 982.4134 0.0000 1739.3460 0.0039 3235.5390

943.3853 640.5046 1425.5880 2124.3350 52.6343 3235.5390

943.3853 640.5046 1425.5880 2124.3350 52.6343 3235.5390

0.0000 0.0000 0.0000 2576.1850 0.0000 0.0000

296.8288 639.3862 671.1491 2427.1530 52.6314 3231.6840

646.5566 1.1184 754.4387 2273.3660 0.0030 3.8556

0.0000 646.5565 1.7334 0.0000 0.0000 78.9901 1739.3460 2273.3660 0.0039 0.0000 5.7923 0.0000

1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 76.9200 2464.6830 52.1992 30.0000 1.2000 0.0000 1.0000 0.0000

0.5852 0.0004 0.0000 0.4130 0.0000 0.0014 173.7313 4211.5590 82.3914 30.6548 1.2000 0.0000 1.0000 0.0000

0.5852 0.5852 0.0000 0.0000 0.0004 0.0004 0.2329 0.2329 0.0000 0.0000 0.0000 0.0000 0.4130 0.4130 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0014 0.0014 0.7671 0.7671 173.7313 173.7313 145.9400 145.9400 4211.5590 4211.5590 4210.4270 4210.4270 82.4082 37588.4600 59481.0300 30178.8500 30.8119 150.0000 25.0000 174.2000 3.0000 2.6500 1.0133 3.0000 0.0000 1.0000 1.0000 1.0000 1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

0.0000 0.2329 0.0000 0.0000 0.0000 0.7671 145.9400 4210.4270 36135.6900 200.0000 2.6500 1.0000 0.0000 0.0000

0.0000 0.0406 0.0000 0.0874 0.0000 0.0917 1.0000 0.3316 0.0000 0.0072 0.0000 0.4416 143.0000 327.7949 2576.1850 7318.8320 43.4087 108331.0000 30.0000 87.0727 1.5000 1.5000 0.0000 1.0000 1.0000 0.0000 0.0000 0.0000

0.1757 0.0003 0.2050 0.6179 0.0000 0.0010 171.6693 3679.3380 75.3443 87.3135 1.5000 0.0000 1.0000 0.0000

0.0000 0.2156 0.0010 0.0000 0.0000 0.0263 0.9957 0.7581 0.0000 0.0000 0.0033 0.0000 96.8113 149.0000 1746.8760 2998.9130 34.2124 59.1553 -43.3864 103.9483 1.5000 1.5000 0.0000 0.0000 1.0000 1.0000 0.0000 0.0000

0.2926 0.1120 0.1120 0.1166 0.0761 0.0761 0.0000 0.1693 0.1693 0.2065 0.2522 0.2522 0.0000 0.0062 0.0062 0.3842 0.3842 0.3842 319.6713 356.4642 356.4642 8421.9860 8421.9860 8421.9860 72856.2000 87930.6300 122158.0000 165.2305 200.0000 100.0000 2.6500 2.6500 1.5000 1.0000 1.0000 1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

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Discussion We unable to solve the material for block DIST1 which is a rigorous distillation column calculation. This is because the method used unable to model the behaviour of formaldehyde that is provided by our reference. In Turton, formaldehyde is assume to “follow” the water but our simulation method assume formaldehyde has very weak solubility in water and very volatile. KValue for formaldehyde/water/methanol system is provided in the Turton’s reference, however aspen does not feature that allow the use of this data. Furthermore, distillate of this block supposedly to contain mostly methanol is recycled back which further complicate the calculation. The complexities lead to the program unable to solve the calculation under a maximum 200 iteration. From Turton reference, formaldehyde is able to be nearly fully absorbed by water with 99% recovery at stream 13. However in our simulation, 47.07% of the formaldehyde is wasted at stream 12 which is an off-gas stream. This suggests that the NRTL-HOC thermodynamic method model the formaldehyde properties as more volatile and less soluble in water than it should in experiment. We have tried more other thermodynamic properties such as NRTL-NTH, UNIFAC, UNIQUAC but the result remains roughly the same. Therefore, we recommend that aspen tech should add a feature whereby user is able to key in experimental K-value data and the program is able to use the data to model the separation process.

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4.0 CONCLUSION & RECOMMENDATION Conclusion We use ASPEN plus V8.0 to plan our operation. We specify the reaction kinetics and NRTLHOC as our thermodynamic property method. The raw material we used is methanol and air and the product is 37 %wt formaldehyde in water also known as formalin. The unit operator that we used is mixer, compressor, heater, chiller, PFR reactor, absorber and distillation column. Finally, we obtained the production of 50,000MT/yr of formalin. Recommendation To improve the energy efficiency of the plant, the hot stream of the reactor outlet can be used to preheat the inlet of the reactor since the reaction is exothermic which require cooling and the reactant require preheating. Basically design heat exchanger network to save on energy cost. Furthermore, this process can be further optimize by perform economic analysis to find the process condition where less operating cost is needed. According to the Ott et al.,(2005), UNIFAC method is used to produce formalin. The reason we not use this method is because we are lacking the binary parameter for formalin-methanol system.

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References Gerberich, H.R., and G.C. Seaman (2004). “Formaldehyde,” Kirk-Othmer Encyclopedia of Chemical Technology, on-line version (New York: John Wiley & Sons). H. Renon and J.M. Prausnitz, (1968). "Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures," AIChE J., Vol. 14, No. 1, pp. 135 – 144. Ott, M., Schoenmakers, H. and Hasse, H. (2005). Distillation of formaldehyde containing mixtures: laboratory experiments, equilibrium stage modeling and simulation. Chemical Engineering and Processing: Process Intensification, 44(6), pp. 687--694. Turton, R., Bailie, R., Whiting, W. and Shaeiwitz, J. (2009). Analysis, synthesis, and design of chemical processes. 3rd ed. Upper Saddle River, N.J.: Prentice Hall PTR.

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Production of Formaldehyde

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