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Licensed Unlicensed Requires Authentication Published by De Gruyter January 29, 2020

Exergoenvironmental Analysis of Tetrahydrofuran/Ethanol Separation through Extractive and Pressure-Swing Distillation

Patrick Vaz Mangili ORCID logo and Diego Martinez Prata

Abstract

Extractive distillation uses a high-boiling point solvent for changing the relative volatility of the azeotropic mixture, whereas pressure-swing distillation is based on the difference of operating pressures for such a purpose. In this paper, said separation technologies were applied to a tetrahydrofuran/ethanol mixture and compared with regard to their thermodynamic and environmental performances. The former was assessed by determining the total exergy destruction rate and rational efficiency of each configuration, while the latter was evaluated by estimating their respective indirect carbon emissions. The results showed that the pressure-swing process has not only the lowest exergy destruction rate (383.1 kW) but also the lowest CO2 emission rate (678.7 kg/h), which is mainly due to its lower thermal energy requirements. A sensitivity analysis was then carried out in order to determine how the carbon emissions respond to both the efficiency and the fuel type of the utility boiler.

Acknowledgements

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors thank Honeywell® for providing the Federal Fluminense University with academic licenses of the UniSim® Design Suite software.

Symbols Used

Symbols

B

Molar exergy flow, kW

Bch

Chemical exergy flow, kW

Bdesired

Desired exergy output rate

Bdest

Exergy destruction rate, kW

Bin

Exergy input rate, kW

Bloss

Exergy loss rate, kW

Bout

Exergy output rate, kW

Bph

Physical exergy flow, kW

BQ

Thermal exergy flow, kW

Bused

Net exergy use rate

BW

Shaft work-related exergy flow, kW

Bwaste

External exergy loss rate, kW

C1

Column 1

C2

Column 2

h

Enthalpy, kW

HX

Cooler

k

Number of electricity-driven machineries

m

Number of heating devices

M*

Molar flow rate, kmol/h

mCO2

Mass flow rate of CO2 emitted, kg/h

ηboiler

Boiler efficiency

Q

Heat transfer rate, kW

Qheat

Thermal energy, kW

s

Entropy, kW/K

Qheat

Thermal energy, kW

T

System temperature, K

To

Reference temperature, K

W*

Power, kW

xEG

Molar composition of ethylene glycol

xEtOH

Molar composition of ethanol

xTHF

Molar composition of THF

Greek symbols

δelec-CO2

Electricity-CO2 emission factor, kg/kWh

δfuel-CO2

Fuel-CO2 emission factor, kg/kWh

ψ

Rational efficiency

Subscripts

δelec-CO2

Electricity-CO2 emission factor, kg/kWh

i, j

Components

k

Machinery

o

Reference conditions

p

Heating device

s

System conditions

Abbreviations

CW

Cooling water

ED

Extractive distillation

HPS

High-pressure steam

ID

Inside diameter

LPG

Liquefied petroleum gas

LPS

Low-pressure steam

MPS

Medium-pressure steam

NG

Natural gas

PSD

Pressure-swing distillation

RR

Reflux ratio

THF

Tetrahydrofuran

UNIQUAC

UNIversal QUAsiChemical

References

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Received: 2019-10-14
Revised: 2019-12-17
Accepted: 2019-12-17
Published Online: 2020-01-29

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