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“Production of 50 ton/day of dichloromethane by HOECHST method”

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ABSTRACT Objective of this project report is to deal with literature survey of a process which is 50 TPD of dichloromethane production rate along with their relevant aspects such as Manufacturing Process, Energy balance, Heat Exchanger design calculations. Di-Chloromethane finds its applications in various field. Keeping these points in mind we urged to work & we are feeling great to present our work on ‘Production of 50 ton/day of dichloromethane by HOECHST method ’ This report is divided in different sections first of all the introduction of the process given which highlights its importance. Next are detailed description of Production of Di-chloromethane and its main methods of production then the selection of process. Afterwards material and energy balance of heat exchanger and its design calculation is presented. Calculations ,discussions and results are the part of the report.

Key words: Heat transfer, Heat exchanger design, Production of Dichloromethane ,Heat exchanger energy balance.

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Introduction Manufacturing Processes Preparation of Dichloromethane: Chloromethane and its derivatives are prepared on the industrial scale by the treatment of Methane and Chlorine, while chlorinated products are obtained as a mixture. Reactions for the chlorination of methane and its derivatives are as follows CH4 + Cl2 → CH3 Cl + HCl + ∆H = −103.5kJ/mol CH3 Cl + Cl2 → CH2 Cl2 + HCl + ∆H = −102.5kJ/mol CH2 Cl2 + Cl2 → CHCl3 + HCl + ∆H = −99.2kJ/mol CHCl3 + Cl2 → CCl4 + HCl + ∆H = −94.8kJ/mol Instead of taking start from methane, most of the industries takes mono-chloromethane as the starting material for producing chlorinated methane’s and production of mono-chloromethanes is also done from CH3OH and HCl. The methanol hydro-chlorination reaction is CH3 OH + HCl → CH3 Cl + H2 O + ∆H = −33kJ/mol

This is the only way, the inevitable build-up of HCl can be considerably compacted and the complete method can be made more economical. Moreover, methanol is easier to transport and store than methane. Also, the availability of methane depends on natural gas resources.

Production Methods: There are two methods for the production of Dichloromethane: •

Methanol Hydrochlorination.

•

HOECHST Method

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Comparative Study of Production Methods: HOECHST method

Hydrochlorination of Methanol

No catalyst is used.

Activated Aluminum Oxide is used as catalyst.

Temperature is 390 °C

Temperature is 280-350°C

1.1 bar

Pressure for this reaction is 3 to 6 bar.

It

produces

all

the

derivatives

of It gives us mono-Chloromethane as target product and

chloromethane.

only one by product dimethyl ether in very small quantity.

It produces hydrochloric acid as a byproduct.

It utilizes hydrochloric acid

Process Selection: The two major processes for the industrial production of Dichloromethanes are through/from reactions of HCl with CH3OH and CH4 with Cl2. The later yields other chlorinated hydrocarbons in substantial amounts. The methanol– hydrogen chloride reaction yields methyl-chloride as the main product with minor amounts of dimethyl-ether by-product. It is commercially carried out in both gas-phase and liquid-phase. Hydrogen chloride is often the defining factor in choosing the best route to produce Methyl Chloride. The chlorination route produces HCl while the Hydrochlorination route utilizes HCl. The separation of unreacted methane and hydrogen chloride by-product in the chlorination process is most easily, and most often, done by absorbing the HCl in water. If there is a sufficiently large use for aqueous HCl, this process is viable to make Methyl Chloride on an industrial scale. Solvay describes a process whereby the methane and hydrogen chloride are separated without the use of water. The methanol hydrochlorination process is a user of either anhydrous HCl or aqueous hydrochloric acid. The liquid-phase process can use either form of hydrogen chloride. If anhydrous HCl is available, the gas-phase hydrochlorination process is viable. Di-methyl ether produced in both hydrochlorination processes can easily be recovered as Methyl Chloride by a catalytic, gasphase process. So we have selected the HOECHST Method Dichloromethanes..

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for the production of

Table 3.1. PFD Description: Equipme

Heat

React

Proce

nt

Excha

or

ngers

Code

P-101 P-102

R-101

Abso

Ne

Dryin

Com

Liqu

ss Gas rber

utr

g

press

ifacti ation

Coole

aliz Towe

or

on

Colum Column Column

r

er

r

unit

n-I

-II

-III

C-101 A-

N-

D-

CS-

LU-

D-101

D-102

D-103

101

101

101

101 101

CS-

P-103

102

4

Distill

Distillat Distillat ion

ion

Process Flow Diagram: LU-101

C-101 10

5 3

11

15

Water Water

5 °C Ammonia

20

N-101

A-101

2

D-101

R101

4

25

CHCl3

16

13

g

D-101 14

CH4

22

CH2Cl2

-28 °C

P-102

D-102

P-103

D-103 21

19

350 °C Steam

4a

9

24

CS-102

6

CS-101 1

18

Water

Water

Fan

Cl2

CH3CL

7

23

12

8

NaOH

P-101 Recycle CH4

Dilute Water Brine Spent H2SO4 HCl

Steam

Steam

98% H2SO4

Figure : PFD of process

Process Description: Chlorine and methane streams are mixed well and the mixture of Cl2 and CH4 is introduced into the reactor at 400–500 °C. The products are cooled and introduced into the absorber to remove HCl from the products. In the absorbers used washing solvent is 21% HCl while the carrier gasses are our main products. The solvent takes the HCl and its concentration is increased to 31% which is removed from the downstream of the absorber. The remaining amounts of water and the traces of HCl are removed in the neutralization system. For this purpose, NaOH is used which is recovered from the bottom of the neutralizer. The gaseous products are then compressed, cooled and then condensed to convert the product into the compressed liquefied form. This crude product is introduced into the series of three distillation columns to separate the components into mono, di, tri and tetra chloromethane. The weight percentages of the products obtained are 70 % CH2Cl2, 27% Chloroform and negligible amount of tetra chloromethane. Mono-chloromethane is recycled into the feed stream .

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Steam

CCl4

Equipment’s: Plug Flow Reactor Loop reactor internally is made up of steel and nickel and coaxial inlet and a regular system is responsible for keeping internal gas mixture, to get harmless and problematic free service the loop reactors is used.

Principally, the inlet gases are carried readily to the beginning

temperature so there is no chance of fiery material being formed. Absorber An absorption tower is an industrial tower used to separate out components of a rising gas with the use of a falling liquid to trap the gas. This tackle is used in a diversity of sceneries for cleansing, processing of resources, and other actions. To ensure efficient and smooth operations the absorption tower typically desires to be designed for a precise application. Regular checking and cleaning is required just like other parts of factory to get it functioned properly. In this apparatus gas is fed from bottom. The gas that is entered along with impurities starts to rise up. Aerosolized liquid is squirted into the tower to be in contact with gas that is rising up. The liquid that is dropped from top removes the impurities and takes them to the bottom for gathering. Some towers have numerous points where liquid is fed to remove impurities or exploit the quantity of substantial entombed .

Neutralizer Neutralizer is the equipment that neutralizes the acidic stream by using the basic stream and vice versa to make the pH of the solution equals to 7. In our case, the stream of HCl is neutralized using the NaOH basic stream.

Drying Tower H2O contents from the gas are removed using drying tower. Gas can be dried to a dew point of minus 40 °C. The strength of sulfuric acid used varies from 78% to 98.5%. Drying towers are operated at low temperatures (70 °C) than absorbers. Gases are introduced into the tower at temperatures less than atmospheric. Concentration of acid led to the tower is proportional to the temperature. For highly concentrated acid high ranges of temperature are used. The operating pressure depends upon plant type used .

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Material Balance of overall plant:

Methane=1291.348kg/hr

Mono=710.007kg/hr Di=2068.376kg/hr

Chlorine=7909.038kg/hr

Tri=1680.116kg/hr Water=21533.057kg/hr

PLANT Tetra=249.827kg/hr

H2SO4=30.843kg/hr Dil.HCl=24989.084kg/hr

NaOH=668.369kg/hr

Brine=1233.142kg/hr

Spent acid=75.958kg/hr

Figure : Material Balance Of whole process Table: over all material balance Component

IN (kg/hr)

Component

OUT (kg/hr)

Methane

1291.348

Mono-Chloromethane

710.007

Chlorine

7909.038

Di-Chloromethane

2068.376

Water

21533.057

Tri-Chloromethane

1680.116

Sodium Hydroxide

668.369

Tetra-Chloromethane

249.827

Sulfuric Acid

30.843

Hydrochloric Acid

24989.084

Brine

1233.142

Spent Acid

75.958

Total

31432

Total

31432

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Energy Balance on Heat Exchanger: Calculation of energy balance

Inlet Temp 25°C Outlet Temp 300°C Recycle methane Temp -24°C Tin = 1.375+273.16=274.535K Tout = 300+273.16=573 °K AvgT= 423.685 CP of methane = 5.34+.0115(T avg) =5.34+0.0115(423.685) =10.214 Cal/mol°K = 10.214 X 4.18 J/m = 42.694KJ/kmole 8

Methane Q=mcp∆T Heat Capacity of Methane at Tavg (423.685 K) = 42.694kJ/kmol.hr

(Perry’s Chem. Eng.

Handbook) Qcold = 80.7077x42.694x(573-274.375) = 1028985.062 kj/hr. Qcold = 1028985.062 kj/hr. Enthalpy of Steam at T (638 K) & P (19832.6 kPa) = 2428kJ/kg m=Q/H m= 1028985.062 /2428 m=423.79 kg/hr. Qhot=mh Qhot = 423.79x2428 Qhot = 1028985.062 kj/hr. To react Methane and Chlorine to produce Chloromethanes. Following reactions are taking place in the reactor at the temperature of 280-350 °C.

CH4 + Cl2 → CH3 Cl + HCl + ∆H = −103.5 𝑘𝐽/𝑚𝑜𝑙 CH3 Cl + Cl2 → CH2 Cl2 + HCl + ∆H = −102.5 𝑘𝐽/𝑚𝑜𝑙 CH2 Cl2 + Cl2 → CHCl3 + HCl + ∆H = −99.2 𝑘𝐽/𝑚𝑜𝑙 CHCl3 + Cl2 → CCl4 + HCl + ∆H = −94.8 𝑘𝐽/𝑚𝑜𝑙

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Table cp of components Components

Cp at 460.5K(Kj/Kmol.K)

CH4

44.687

Cl2

35.819

CH3Cl

52.578

CH2Cl2

63.831

CHCl3

78.6318

CCl4

95.5734

HCl

29.61

Equipment Design: Design of Heat exchanger:

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Introduction: A heat exchanger is a device that is used to transfer thermal energy (enthalpy) between two or more fluids, between a solid surface and a fluid, or between solid particulates and a fluid, at different temperatures and in thermal contact. Objective in the process: Objective in the process is to lower the temperature of process gas coming from high temperature reactor, also preheating boiler feed water to 70 0C.

Classification of Heat Exchangers: Heat exchangers are classified according to •

Transfer process

•

Number of fluids

•

Degree of surface contact

•

Design features

•

Flow arrangements

•

Heat transfer mechanisms

Classification According to Construction: • Tubular heat exchanger ( double pipe, shell and tube, coil type) •

Plate heat exchanger (gasket, spiral, plate coil)

•

Extended surface exchanger (tube fin, plate fin)

•

Regenerators (fixed matrix, rotary)

Classification According to Transfer Process: • Indirect contact (double pipe, shell and tube, coil type) •

Direct contact (cooling tower)

Classification According to Flow Arrangement: • Parallel flow •

Counter flow

•

Cross flow

The choice of particular flow arrangement is dependent upon the required exchanger effectiveness, fluid flow paths, packaging envelope, allowable thermal stress, temperature levels etc.

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Classification According to Phase Of Fluid: These classifications are made according to the phase of fluid i-e gas-gas •

Liquid-liquid

•

Gas-liquid

Selection Criteria of Heat Exchanger: •

Material of construction

•

Operating pressure and temperature

•

Flow rates

•

Flow arrangements

•

Performance parameters---- thermal effectiveness and pressure drop

•

Fouling tendencies

•

Types and phase of fluids

•

Maintenance inspection and cleaning

•

Environmental Health & Safety Consideration & Regulations

•

Availability

•

Cost

Shell and Tube Heat Exchanger: Shell and Tube heat exchangers are most commonly used in heating or cooling process fluids and gases. Typically found in applications where a need to heat or cool large volumes exist; however small volume applications are also very common. Shell and tube exchangers come in many variations to meet process requirements in almost every industry or application. They deliver reliable heat transfer performance by utilizing a high turbulence and counter flow, making one or more passes. While one (1), two (2) and four (4) pass models are standard, multi-pass custom models of any size are available. Types of Shell and Tube Heat Exchanger: •

Fixed tube

•

U tube

•

Floating head

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Advantages of Shell and Tube Heat Exchanger: •

It is used for high heat transfer duties

•

It occupies less space

•

Its compactness is more

•

Its maintenance is easy

•

It can be fabricated with any type of material depend upon fluid properties

•

Can be used in a system with higher operating pressure and temperature

•

These exchangers are ideal for application of higher flow rates

•

Configuration give large surface area in small volume

•

Cleaning and repair is easy

Thus, according to above advantages the shell and tube heat exchanger is suitable for our process requirement.

Design Steps of Heat Exchanger: The main steps of design the heat exchanger are summarized as follows: 1. Selection of heat exchanger 2. Perform energy balance and find out the heat duty (Q) of the exchanger. 3. Obtain the required properties of hot and cold fluids. 4. Calculate the LMTD and True temperature 5. Assume(Uo) overall heat transfer coefficient and calculate provisional area 6. Configuration selection of tube and shell side. 7. Calculate flow area, mass velocity, Renoyld number 8. Calculate hi and ho 9. Calculate Uo to verify the assumption. 10. Calculate the pressure drop.

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Calculations: Heat duty: Q= mCpΔT Where; m= mass flow rate Cp= Heat capacity ∆T = Temp. Difference Q= 15880 KW Mass flow rate of water: m= Q/CpΔT = 84.4 kg/s Cp of water= 4.18 kj/kg.k ΔT= 45 0C

Hot Stream (gases)

Cold Stream (water)

Viscosity = µ=0.018 mNs/m2

Viscosity=µ=0.8 mNs/m2

Thermal conductivity=k=0.10 W/m0C

Thermal conductivity=k=0.59 W/m0

Density of gases=ρ=2.02 kg/m3

Density of water= ρ =995 kg/m3

Heat capacity= Cp = 3.02 kJ/kg.K

Heat capacity= Cp= 4.18 kJ/kg.K

Log Mean Temperature Difference: LMTD =

∆t1−∆t2 ln( ∆t1/∆t2)

Δt1 = T1-t2,

= 216.5 0C Δt2 = T2-t1

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True Temperature: ΔTm = LMTD ×FT = 205.6 0C FT = 0.95 from graph 1-2 shell and tube exchanger using R and S by D.Q Kern T1−T2

R=

= 1.66

t1−t2 t2−t1

S=

T1−t1

= 0.16

Assume U= 3400 W/m2 Provisional Area: Q

A= UΔTm = 22.7m2 Tube configuration: From table 10. Heat exchanger and condenser tube data BWG = 16 Outer diameter of tube = 0.0254m = 25.4mm Inner diameter of tube = 0.022m = 22mm Length = 4.83m Passes = n= 2 Area of one tube = Π×do×L= 0.385 m2 No of tubes=Nt= Provisinol Area / Area of one tube = 60

Bundle & Shell Diameter: Bundle diameter= Db = (O.D)tube (Nt/k1)1/n1 K1 = 0.249 n1 = 2.207

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Nt = 60 Db = 305 mm Using split ring floating head type, Bundle Diameter clearance= C = 55 mm

(fig. 12.10 from R.KSinnot)

Shell Diameter = Ds= Db+C= 360 mm Tube side coefficient (water) : Mean water temperature = 47.5 0C Tube cross sectional area = Π/4 (di)2 = 380mm2 Tube per pass= 30 Total flow area= At = 30×380×10-6 Mass velocity = Gt= mt/At = 7405 kg/s. m2 Density of water = ρ = 995 kg/m3 Water linear velocity = ut= 7405/995= 7.44m/sec Coefficients for water: Tube side film coefficient = hi =

4200(1.35+0.02t)ut0.8 di0.2

= 7257 W/m2.0C

Shell Side Coefficient: Choose, Baffle spacing =Lb = Ds/5 = 72mm Tube pitch = Pt= 1.25×O.D = 31.75mm Flow area = As =

(pt−do) Pt×Lb×Ds

= 0.1923 m2

Mass velocity = Gs = ms/As = 377 kg/s. m2 1.1

Equivalent diameter = De= do (Pt 2 − 0.917do2 )= 18.2mm Reynold number = Re =

De∗Gs µ

= 39316.4672

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jH factor=120 Prandtl number = Pr =

(fig 28 D.Q kern) cp∗µ k

= 0.54 1

k

µ

0.14

Shell side film coefficient = ho = (d) jH ∗ Re ∗ (Pr )3 (µw)

= 6434 W/m2.0C

Overall coefficient: Uo =

1

1

+ = 3400 W/m2.0C hi ho

Same as assumed value of “U” Pressure Drop Calculations: Shell side: At Re=39316, f=0.0016

(Fig. 29 D.Q Kern)

N+1= L/B.S = 6.19 S= 1.65 ΔPs= [f*Gs2*Ds*(N+1)/5.22*10^10*De*S* )=5.3 psi Tube side: At Re=865541.9, f=0.0009

(Fig 26 D.Q Kern)

S=1 ΔPt =1/2[(f*Gt2*L*n)/(5.22*10^10*Di*S)] = 3.89 psi ΔPr=4*n/S(V2/2g)=0.717 At Gt=753854, V2/2g=0.07

(Fig 27. D.Q Kern)

(ΔP)T= ΔPt + ΔPr=3.89+ 0.717 = 4.60 psi

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Specification Sheet: Heat Transfer Area (A)

22.7 m2

Total number of tubes (Nt)

60

Diameter of shell

360 mm

(Ds)

Overall heat transfer coefficient (U)

3400 W/m2.0C

Total pressure Drop (shell side)

5.3 psi

Total pressure Drop (tube side)

4.6 psi

No. of baffles

5

Results & Discussion: 50 TPD of dichloromethane production process is designed along with their relevant aspects such as Manufacturing Process, Energy balance, Heat Exchanger design calculations. The process is designed on the aspen Hysys and results obtained are very good and So we have selected the HOECHST Method for the production of Dichloromethanes. In this process the reaction temp is about 300-400 0C where the conversion take place in the plug flow reactor. Heat duty of heat exchanger is Q= 15880 KW where the Mass flow rate of water is 84.4 kg/s.The inlet and outlet temperature are Inlet Temp 25°C , Outlet Temp 300°C and Recycle methane Temp -24°C and CP of methane = 5.34+.0115(T avg) = 42.694KJ/kmole Qcold = 80.7077x42.694x(573-274.375) ; Qcold = 1028985.062 kj/hr. While , m=423.79 kg/hr. So , Qhot = 1028985.062 kj/hr. The Provisional Area is calculation shows that the area is 22.7m2 . o Heat Transfer Area (A)

22.7 m2

o Total number of tubes (Nt)

60

o Diameter of shell

360 mm

(Ds)

o Overall heat transfer coefficient (U)

18

3400 W/m2.0C

o Total pressure Drop (shell side)

5.3 psi

o Total pressure Drop (tube side)

4.6 psi

o No. of baffles

5

The results obtained are quiet similar to the results found in simulation and the balance around heat exchanger is calculated and tabulated.

Conclusion: It is concluded that the production of dichloromethane is suitable by the Hoechst method and after the process selected the process flow diagram is discussed with the process description and the energy balance and design calculation of heat exchanger was done which concluded that Qcold and Qhot is equal and its value comes out is 1028985.062 kj/hr. During the design calculations we calculated the Heat Transfer Area (A), Total number of tubes (Nt), Diameter of shell (Ds), Overall heat transfer coefficient (U) , Total pressure Drop (shell side), Total pressure Drop (tube side) and No. of baffles. Overall heat transfer coefficient (U) of heat exchanger is 3400 W/m2.0C.

References: F. Flow, H. Transfer, and M. Transfer, “Coulson & Richardson ’ s.” W. L. McCabe, J. C. Smith, and P. Harriott, “Unit Operations of Chemical Engineering.” p. 1130, 1993. H. Silla, Design and Economics. 2003. C. L. Reese et al., McGraw-Hill Chemical Engineering Series Editorial Advisory Board Building the Literature of a Profession. 1925. T. Information, “METHYL CHLORIDE HANDBOOK,” 2014. M. A. R. Ossberg, H. Aktiengesellschaft, and F. Main, “1. Introduction,” 1840.

Introductory chemical engineering Thermodynamics 2nd edition by J. Richard Elliot Plant design and economics for chemical engineers 5th edition. Heat transfer by DQ. kern

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