Energy Balances for mini dp

6.0

ENERGY BALANCE

6.1

General Manual for Energy Balance

Heat of formation : Δ𝐻f = Σ 𝑣𝑖 Δ𝐻P − Σ 𝑣𝑖 Δ𝐻R Heat of reaction : Δ𝐻𝑅

=[Σ

] T

The first law of thermodynamics says that energy be neither created nor destroyed. The following is a systematic energy balance performed for each unit of the process. The datum temperature for calculation is taken as 25 OC. The pressure is taken to be 1 atm throughout the process. The physical properties such as density, specific heat, heat of reaction, and heat of formation were assumed as constant over the temperature range.

Component

)

Ethylene

52.30

0.05450

Chlorine

0

0.03394

Ferric chloride

-399.40

0.03832

Vinyl chloride

-94.12 (solid)

0.05363

Hydrogen

0

0.02884

Hydrogen chloride

-92.30

0.02910

Dichloroethane

-169.70

0.12900

Acetic acid

-867.10

0.12310

Oxygen

0

0.91776

Table 1 : Heat Capacity and Enthalpy Data

6.2

Energy Balance Calculations

Nomenclature used 

– Enthalpy heat reaction of reactant



– Enthalpy heat of formation



– Enthalpy heat reaction of product – Specific heat capacity

Cp



– Enthalpy heat reaction



)

6.2.1

Energy balance for direct chlorination

6.2.1.1

Mixer

Stream involved: 

Stream 1



Stream 2



Stream 3

Enthalpy of formation of reaction at 25°C @ 298K: →

+

Δ𝐻𝑜𝑓 = Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑃 − Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑅 = (-169.7– 52.3- 0) =(

⁄

)

Enthalpy of reactants: Reactants are added at 25°C.

=[

+

] T

=[ 0.05450 𝑥 1 + 0.03394 𝑥 1 ](393-298) = 8.4018 ⁄

Enthalpy of products:

Products leave at 25° C.

=

T =[0.129 x 1 ](393-298)

= 12.255 ⁄

Enthalpy of reaction:

⁄

The negative sign in the above calculation

Enters at 25 C and leaves at 120 C.

6.2.1.2

Energy balances at Reactor

Stream involved: 

Stream 1



Stream 2



Stream 6

indicates that the reaction is exothermic.

Main Reaction:

Table 3 : Direct chlorination reactor parameter Reactor temperature (°C)

180

Reactor pressure (kpa)

350

Reactor volume (

90

Tube diameter (in)

2

Tube length (ft)

112

Residence time (hr)

0.018

Direct chlorination :

+

→

(1)

Ethylene and chlorine combine in a homogeneous catalytic reaction to form EDC. Normally, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor. Due to high selectivity, ferric chloride is the common catalyst of choice for chlorination of ethylene. The catalytic reaction utilizes an electrophilic addition mechanism. The catalyst polarizes chlorine (Eqn. 2) and then the polarized chlorine molecule acts as an electrophilic reagent to add Cl- to the double bond of ethylene.

+

↔ +

(2) →

+

(3)

For oxychlorination

(4)

EDC pyrolysis 2

(5)

Overall reaction 2

(6)

Enthalpy of formation of reaction at 180°C @ 453K: →

+

Δ𝐻𝑜𝑓 = Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑃 − Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑅 = (-169.7– 52.3- 0) =(

⁄

)

Enthalpy of reactants:

Reactants are added in reactor.

Stream 1 Δ𝐻R1

=[

] T

=[ 0.05450 𝑥 1](453-323) = 7.085 ⁄

Stream 2 Δ𝐻R2

=[

] T

=[ 0.03394 𝑥 1 ]( 453-323) = 4.4122 ⁄

= 7.085 + 4.4122 = 11.4872 ⁄

Enthalpy of products:

Products leave at 180° C.

=

T =[(0.1231 x

= 10.1232 ⁄

Enthalpy of reaction:

⁄

The negative sign in the above calculation

6.2.2

indicates that the reaction is exothermic.

Energy balances at oxychlorination

Table 3 : Oxychlorination reactor parameter Reactor temperature (°C)

120

Reactor pressure (psig)

15

Reactor volume (

461

Tube diameter (in)

2

Tube length (ft)

1320

Residence time (hr)

0.05

Since the value of oxygen is small thus, it assume to be neglected. O2 at T 305

= 0.9964 (

Enthalpy of formation :

)

Δ𝐻𝑜𝑓 = Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑃 − Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑅 = [0 + (-169.7) – ( ⁄

=( 6.2.2.1

+ 2( -92.30) + (52.3) )]

)

Energy balances in mixer

Stream involved: 

Stream 1



Stream 2



Stream 3

Enthalpy of formation of reaction at 25°C @ 298K: →

+

Δ𝐻𝑜𝑓 = Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑃 − Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑅 = (-169.7– 52.3- 0) ⁄

=(

)

Enthalpy of reactants: Reactants are added at 25°C.

⁄

= ⁄

Enthalpy of products:

Products leave at 25° C.

= [

+

] T

=[ 0.05450 𝑥 0.4413 + 0.03394 𝑥 0.5587 ](393-298) = 4.0862 ⁄

Enthalpy of reaction:

⁄

The negative sign in the above calculation

indicates that the reaction is exothermic.

Enters at 25 C and leaves at 120 C.

6.2.2.2

Energy balances at heat exchanger

Stream involved: 

Stream 3



Stream 5

Enthalpy of formation of reaction at heat exchanger :

+

→

Since it is heat exchanger, thus there is no formation occur. There is just flow of component inside the heat exchanger to increase temperature to 180 .

Enthalpy of formation:

Enthalpy of products:

=

T =[ = 4.0862 ⁄

Enthalpy of reactant:

⁄

= ⁄ Enthalpy of reaction:

⁄

6.3

Energy balances at the separator

Stream involved : 

Stream 6



Stream 7



Stream 8

+

→

Separator is to separate the components into two streams; one for HCl recycle (stream 6) and one for vinyl chloride(stream 8).

Enthalpy of formation of reaction at 50°C @ 323 K:

Δ𝐻𝑜𝑓 = Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑃 − Σ 𝑣𝑖 Δ𝐻𝑜𝑓𝑅 = (-92.12 +(-94.12) – 52.3- 0) ⁄

=(

)

Enthalpy of reactants: Reactants are added at 50°C. Stream 6

⁄

= ⁄

Enthalpy of products:

Products leave at 50° C.

= [

T

=[ 0.05363 x 1 ](393-298) = 5.09485 ⁄

Enthalpy of reaction:

⁄