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Co-Production of Hydrogen and Copper from Copper Waste using a Thermochemical Cu-Cl Cycle Farrukh Khalid, Ibrahim Dincer, and Marc Rosen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03857 • Publication Date (Web): 12 Jan 2018 Downloaded from http://pubs.acs.org on January 14, 2018

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Energy & Fuels

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Co-Production of Hydrogen and Copper from Copper Waste using a Thermochemical CuCl Cycle

3 4 5 6

Farrukh Khalid, Ibrahim Dincer, Marc A. Rosen Faculty of Engineering and Applied Science, University of Ontario Institute of Technology 2000 Simcoe Street North, Oshawa, Ontario, L1H 7K4, Canada Emails: [email protected], [email protected], [email protected]

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Abstract

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A novel hybrid Cu-Cl thermochemical cycle is developed and assessed for the co-production of

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hydrogen and copper using copper waste. An experiment is also conducted to establish the high

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temperature electrolytic step as a proof of concept. A detailed parametric study is conducted to

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assess the effects of such parameters as process step temperature and energy efficiency of the

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electrical power plant that provides electricity to the cycle on the energy and exergy efficiencies

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of the overall cycle. The values of the energy and exergy efficiencies of the cycle are 31.8% and

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69.7%, respectively. The maximum specific exergy destruction occurs in the electrolytic step.

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The results show that the proposed cycle performs better in terms of energy and exergy

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efficiencies compared to similar four-step Cu-Cl cycles. By using the proposed cycle, a new

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avenue may be open for copper waste to be more advantageously managed, potentially

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enhancing the sustainability of the relevant processes through improved environmental

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protection and resource recovery.

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Keywords: High temperature electrolysis, Thermochemical cycle, Energy, Efficiency,

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Hydrogen, Copper waste, Waste management

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1. Introduction

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Use of energy play an important part in the progress of any country. With increasing populations

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and rising living standards in many countries, demand for energy is growing. The present

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dependence on fossil fuels to meet most of this energy demand and the challenges associated 1 ACS Paragon Plus Environment

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with fossil fuels has led to research around the world to develop environmentally benign energy

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sources, like renewable and nuclear. During the past decade, there has been an increasing interest

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in the development of large-scale non-fossil hydrogen production technologies, particularly

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coupled with renewables and nuclear process heat/waste heat which leads to clean hydrogen

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production with almost negligible life cycle emissions and hence minimized environmental

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impact. In this regard, thermochemical and/or electrochemical processes with renewables or

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nuclear options offer an environmental-friendly option [1-5].

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A number of thermochemical cycles have been investigated [6-8] to produce hydrogen from

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water. However, most of these cycles operate at over 800°C. The relatively lower temperature

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(550°C) requirement and use of inexpensive chemicals make the copper-chlorine (Cu-Cl)

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thermochemical cycle a promising process for hydrogen production. To build large scale

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hydrogen production facilities based on this cycle some challenges need to be resolved. Firstly,

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the difficulty in separation of CuCl and CuCl2 from the spent anolyte in the electrolytic step

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needs to be addressed. Secondly, some copper crossover is observed in the electrolyser

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membrane resulting in degradation of the electrolyser performance. One of the possible ways to

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achieve better kinetics and integration is the introduction of a high temperature electrolysis step

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in the Cu-Cl cycle. Such a high temperature electrolysis step needs to be thoroughly examined in

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terms of feasibility and practical viability.

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Copper is one of the most widely used metals in the world, with applications including energy

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technologies, electronic devices, electricity transport, and coin production. With advances in

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electrical and electronic technology and decreases in prices, the use of such equipment has

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increased [9, 10]. This has led to increases in copper waste, especially in the industrial world

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[11], posing a worldwide challenge for safe disposal [12-13]. There are numerous methods 2 ACS Paragon Plus Environment

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available to recycle copper from copper waste, like pyrometallurgy, hydrometallurgy [14-17].

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Each process has drawbacks, however. For instance, the energy consumption is very high and the

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temperature requirement is high (more than 1273 K) in pyrometallurgy [18] while the Cu is

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recovered in the form of Cu-based compounds such as Cu2O and CuCl in hydrometallurgy [19-

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21]. Jadhao et al. [22] have been able to extract Cu from printed circuit board using green

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chelation technology. They have claimed that upto 84% of copper can be recovered using

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Ethylenediaminetetraacetic acid (EDTA). Zhang et al. [23] have recovered the copper from the

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waste printed circuit board using a green chemical [BSO3HPy].H2SO4. Hence, efficient recovery

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of copper from copper waste is one of the most challenging issues in the disposal of copper

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waste.

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The main objective of this work is to carry out the electrolytic step at higher temperature for

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better thermal management and integration for a Cu-Cl based hydrogen production. Since all the

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reactions of the Cu-Cl cycle are at a higher temperature except the electrolytic step which is at

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very low temperature, this causes a temperature mismatch between the electrolytic step and the

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other steps. Thus, in the present study, a novel hybrid thermochemical Cu-Cl cycle is newly

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developed for the co-production of hydrogen and copper using copper waste, and assessed in

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terms of energy and exergy efficiencies of the overall cycle. The effects of such parameters as

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process step temperature and energy efficiency of the electrical power plant that provides

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electricity to the cycle on the energy and exergy efficiencies of the overall cycle are evaluated.

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An experiment is also conducted to establish high temperature electrolytic step at a proof of

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concept level.

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2. System Description

3 ACS Paragon Plus Environment

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Fig. 1 shows the proposed novel four step Cu-Cl cycle for co-production of hydrogen and copper

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from copper waste. As shown in that figure, the cycle is comprised of the following four main

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steps:

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Step 1 (Hydrolysis Step)

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Cl() + H O() 2HCl() + O()

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In this step, high temperature steam reacts with chlorine gas to produced hydrogen chloride

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(HCl) gas and oxygen. The hydrogen chloride gas produced in this step is utilised in Step 2.

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Dokiya and Kotera [24] suggest that Step 1 should be carried out at above 900 K. Gupta et al.

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[25] show experimentally that at 900 K an equilibrium conversion of about 90.0% can be

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achieved.

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Step 2 (Hydrogen Production Step)

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2Cu (waste) + 2HCl() 2CuCl() + H()

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This step has been well studied by various researchers [26,27]. The copper waste obtained from

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industry is crushed to a fine powder before being utilised in this step. That powder is heated to

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723 K and allowed to react with heated HCl gas to produce CuCl liquid and hydrogen gas. The

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CuCl liquid obtained from this step is utilised in Step 3.

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Step 3 (Electrolytic Step)

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4CuCl() 2Cu() + 2CuCl()

(1)

(2)

(3)


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In this step, the CuCl liquid obtained from Step 2 is electrolysed to produce CuCl2 liquid and

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copper. This copper is pure, as it is obtained through an electrolytic step. The CuCl2 produced in

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this step is used in Step 4.

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Step 4 (Decomposition Step)

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2CuCl() Cl() + 2CuCl()

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The CuCl2 obtained from Step 3 is heated to 833 K and decomposed into CuCl liquid and

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chlorine gas. The chlorine gas obtained from this step is input to Step 1 while obtained CuCl

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liquid is input to Step 3. Gupta et al. [28] show that, for a temperature above 750 K, CuCl2 solid

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can decompose to CuCl solid and chlorine gas. However, in this case we suggest that this

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reaction be carried out at 833 K (i.e., above the melting point of CuCl, which is 771 K).

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In the proposed cycle, all the products/reactants (except water and copper waste) are recycled

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and thus form a closed cycle. In other words, for the overall cycle, copper waste and water are

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the only material inputs while oxygen, hydrogen and pure copper are the only useful material

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outputs.

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3. Experimental setup and procedure

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The high temperature electrolyser (i.e., the high temperature reactor for Step 3) is shown in Fig.

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1. It consists of a heating mantle (having two heating tapes of 630 W each) comprised of a glass

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vessel (in order to sustain high temperature), graphite rods (diameter 1/4"), an electricity supply,

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a potentiostat (Gamry Instruments Reference 3000), CuCl powder (CAS-7758-89-6, provided by

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Spectrum chemicals) an oxygen analyser (HHAQ-104, provided by OMEGA), two temperature

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controllers, an argon flowmeter, a condenser, a scrubber, and a crucible. One of the temperature

(4)


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controllers provided by Glas-col (having a J-type thermocouple) is used to monitor the

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temperature of the heating mantle while the other temperature controller provided by Omron

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(having a K-type thermocouple) is used to measure the inside temperature of the reactor. The

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condenser (made of quartz glass) is utilised to condense some of the CuCl vapor exiting the

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reactor (as it can be harmful). The purpose of the scrubber (made of quartz glass and having a

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mixture of 4.5 L of water and 390 g sodium hydrogen carbonate (NAHCO3)) is to neutralize the

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gases from the condenser before exhausting them to the fume hood. Fig. 2 shows the designed

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experimental setup inside a fume hood.

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Before starting the experiment, argon is fed to the reactor for purging the air completely.

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Throughout the experiment the flow rate of argon is set to 100 mL/min. The CuCl powder in the

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crucible is heated to 773 K. Once the required temperature is achieved, a voltage is applied to the

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graphite electrodes using the potentiostat. The product (a dark brown solid) is collected after the

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test and crushed to fine powder. The fine powder is examined using X-ray powder diffraction

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(XRD) (Rigaku Corporation, Japan).

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4. Analysis

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In this section, a complete thermodynamic analysis of the proposed Cu-Cl cycle is presented

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using energy and exergy analyses [29,30]. Engineering equation solver (EES) software is used to

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calculate the thermophysical properties of each chemical substance in the cycle. The following

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assumptions, which are reasonable for the cycle, are invoked in the analysis:

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1. All chemical reactions are taken to go to completion, according to their stoichiometry.

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2. The changes in kinetic and potential energies and exergies are negligible.


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Energy & Fuels

3. The quantities like specific enthalpy and specific exergy are evaluated per mole of hydrogen produced.

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4. All reactants and products are assumed to be at a pressure of 1 atm.

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5. The ambient temperature and pressure are 299 K and 100 kPa, respectively.

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6. The energy efficiency of the electrical power plant supplying electricity to Step 3 is taken to be 40.0% [31].

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The specific exergy of a chemical material flow can be expressed as follows:

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=

139

where

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In order to assess the performance of each step, its exergy efficiency is used, defined as follows:

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%&',)*&" = 1 − &'

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Relevant energy and exergy efficiencies are used to evaluate the performance of the overall

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cycle. The energy efficiency of the overall cycle is calculated as

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%&4,56 = ∑ =>= ;

145

where @AB8; is the lower heating value of hydrogen, q is the total specific heat required per mol

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of hydrogen to drive all the steps of the cycle and C&= is the thermal equivalent of electric energy

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required by the electrolytic step (Step 3), which can be written as

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C&= =

"#

$#

+

"#

(5)

is the specific physical exergy and

$#

is the specific chemical exergy.

&'-,./01

(6)

23,./01

789:

(7)

0?

D23,0E0F

(8)

G03,11


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where HI4,&J&$ is the amount of electricity required per mol of hydrogen in the Step 3, and %&4,""

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is the energy efficiency of the electrical power plant supplying electricity to Step 3.

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The exergy efficiency of the overall cycle can be expressed as

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%&',56 = ∑ &'' K >D;

153

where

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exergy input to the cycle, which can be expressed as

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∑

&'':

(9)

23,0E0F

L

8;

is the specific chemical exergy of the hydrogen product, and ∑

N

N

N

= ((C ) M1 − O Q + (C ) M1 − O Q + (CR ) M1 − O Q NP

N;

NS

L

is the thermal

(10)

156 157 158

5. Results and Discussion

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Fig. 4 shows the I-V curve of the proposed high temperature electrolytic step (Step 3). It can

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been seen that a current of 100 mA can be achieved when the applied voltage is 2.0 V. With

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increasing voltage, the current increases.

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The XRD pattern of the obtained product (dark brown powder) is shown in Fig. 5, which depicts

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the peak for a product called as melanothallite (Cu2OCl2). Melanothallite is formed from the

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reaction between CuCl2 and CuO at a temperature of 773 K, suggesting that Step 3 is possible if

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it is ensured that there is no oxygen present throughout the experiment. This experimental result

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as a proof of concept suggests that Step 3 is possible if the presence of oxygen is avoided. A

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SEM image of the obtained product is required to obtain further details, but is not obtained here

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as it is beyond the scope of this study. 8 ACS Paragon Plus Environment

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Energy & Fuels

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The results of the energy and exergy analyses are presented in Table 1. It can be noted from that

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table that the energy and exergy efficiencies of the proposed cycle are 31.8% and 69.7%,

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respectively. Ozbilen et al. [32] found the energy efficiency of a similar four step Cu-Cl cycle,

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for hydrogen production only, to be 35.7% for a heat-to-work conversion efficiency (i.e., an

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energy efficiency of the electrical power plant) of 50%, while in the present case an energy

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efficiency for the overall cycle of 38.2% is achieved when a heat-to-work conversion efficiency

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of 50% is considered. This result suggests that the proposed cycle has a higher energy efficiency,

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although this observation is limited by the fact the processes have some differences.

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Fig. 6 shows the specific exergy destruction of the various steps of the proposed cycle. The

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maximum specific exergy destruction occurs in the electrolytic step (Step 3), mainly because

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electricity (a high quality energy form) is utilised. Thus effort is merited to reduce the specific

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exergy destruction in this electrolytic step in a cost effective manner. A significant amount of

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specific exergy destruction is observed in Step 2 while the specific exergy destructions in Step 1

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and 4 are found to be negligible.

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The effect of the operating temperature of Step 1 on the energy and exergy efficiencies of the

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overall cycle are shown in Fig. 7. As the temperature increases from 903 K to 953 K, there is no

185

effect on the energy efficiency of the overall cycle while the exergy efficiency decreases from

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69.7% to 69.5%. This result suggests that the reaction needs to be carried out at a temperature of

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around 900 K to achieve a higher exergy efficiency.

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Fig. 8 shows the variation of specific exergy destruction and the exergy efficiency of Step 1 with

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the temperature of Step 1. It can be seen that, with increasing temperature, the exergy efficiency

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of the step decreases while the specific exergy destruction increases. To achieve a higher exergy

191

efficiency for this step, the step operating temperature should be at around 900 K. 9 ACS Paragon Plus Environment

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Fig. 9 shows the effect of the operating temperature of Step 2 on the energy and exergy

193

efficiencies of the overall cycle. No significant effect is observed on the overall energy and

194

exergy efficiencies from changing the operating temperature of Step 2. Similar trends for the

195

exergy efficiency of Step 2 and the specific exergy destruction of Step 2 are observed (see Fig.

196

10).

197

It can be observed from Fig. 11 that, as the Step 3 temperature increases, the energy and exergy

198

efficiencies of the overall cycle decrease from 69.7% to 68.7% and 31.8% to 31.3%,

199

respectively. The reason for this trend is that, with increasing temperature, the Gibbs free energy

200

change of this step increases, suggesting that this step needs to be carried out at a lower

201

temperature, i.e., around 773 K.

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Fig. 12 shows the effect of varying the operating temperature of Step 3 on its exergy efficiency

203

and specific exergy destruction. As the temperature rises, the exergy efficiency of the step

204

decreases while the specific exergy destruction increases.

205

Fig. 13 shows the effect of varying the operating temperature of Step 4 on the energy and exergy

206

efficiencies of the overall cycle. No significant effect of step temperature is observed on either of

207

the efficiencies of the overall cycle.

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It can be observed from Fig. 14 that, with increasing step temperature, the exergy efficiency

209

decreases notably, from 99.4% to 94.0%, while the specific exergy destruction rises sharply from

210

1.18 kJ/mol to 12.2 kJ/mol. Note from this figure that it is not possible to carry out this reaction

211

below 833 K as the specific exergy destruction becomes negative for lower temperature values.

212

This result highlights the importance of applying exergy analysis to chemical reactions as energy

213

analysis does not provide such insights.


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Energy & Fuels

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The variations of the energy and exergy efficiencies of the overall cycle with the energy

215

efficiency of the power plant is shown in Fig. 15. As the energy efficiency of the power plant

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increases, the energy efficiency of the overall cycle increase significantly, suggesting that this

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type of cycle may be beneficial if coupled to a power plant having high efficiencies, such as

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High Temperature Nuclear Reactor based power plants.

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6. Conclusions

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A novel hybrid Cu-Cl cycle for the co-production of hydrogen and copper using copper waste is

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proposed and assessed thermodynamically. A preliminary experimental investigation is made to

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establish the feasibility of the high temperature electrolytic step, as this step in aqueous state is

223

well studied in literature. However, to the authors’ knowledge in molten state this step is not yet

224

well understood. The energy and exergy efficiencies of the overall cycle are found to be 31.8%

225

and 69.7%, respectively. The results suggest that using high temperature electrolysis in the Cu-Cl

226

cycle may be beneficial as it provides a higher energy efficiency than some similar cycles

227

reported in the literature. The other benefit of the proposed cycle is that pure copper can be

228

obtained and copper waste can be more advantageously managed, potentially enhancing the

229

sustainability of the relevant through improved environment protection and resource recovery.

230

Nomenclature

231

ex

specific exergy (kJ/mol)

232

h

specific enthalpy (kJ/mol)

233

I

current (A)

234

LHV

lower heating value (kJ/mol)

235

V

voltage (V)

236

P

pressure (kPa) 11 ACS Paragon Plus Environment

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237

q

specific heat (kJ/mol)

238

T

temperature (K)

239

w

specific work (kJ/mol)

240

Greek Letters

241

η

242

Subscripts

243

ch

chemical

244

d

destruction

245

elec

electrical

246

en

energy

247

eq

equivalent

248

ex

exergy

249

max

maximum

250

ov

overall

251

ph

physical

252

pp

power plant

253

s

source

254

0

ambient

255

1,2…

step number

256

References

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efficiency


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307 308

[24] M. Dokiya, Y. Kotera, Hybrid cycle with electrolysis using Cu-Cl system, International Journal of Hydrogen Energy 1 (1976) 117-121.

309 310 311 312 313

[25] A.K Gupta, R.Z. Parker, R.J. Hanrahan, Gas phase formation of hydrogen chloride by thermal chlorine steam reaction. International Journal of Hydrogen Energy 16 (1991) 677-682. [26] C. Zamfirescu, G.F. Naterer, I. Dincer, Kinetics study of the copper/hydrochloric acid reaction for thermochemical hydrogen production, International Journal of Hydrogen Energy 35 (2010) 4853-4860.

314 315 316

[27] M. Serban, M.A. Lewis, J.K Basco, Kinetic study of the hydrogen and oxygen production reactions in the copper–chloride thermochemical cycle, AIChE Spring National Meeting, New Orleans LA, April 25–29, 2004.

317 318 319

[28] A.K Gupta, C.F. Sona, R.Z. Parker, E.J. Bair, R.J. Hanrahan, Closed-cycle HCl/H2/Cl2 energy storage and power generation using a Cu/CuCl catalyst, International Journal of Hydrogen Energy 22 (1997) 591-599.

320 321

[29] F. Khalid, I. Dincer, M.A. Rosen, Energy and exergy analyses of of a solar-biomass integrated cycle for mulitgeneration, Solar Energy 112 (2015) 290-299.

322

[30] M.T Balta, I. Dincer, A. Hepbasli, Enegry and exergy analyses of a new four-step copper

323

cycle for geothermal-based hydrogen production, Energy 35 (2010) 3263-3272.

324 325 326

[31] M.F. Orhan, I. Dincer, M.A Rosen, Efficiency comparison of various design schemes for copper-chlorine (Cu-Cl) hydrogen production processes using Aspen Plus software, Energy Conversion and Management 63 (2012) 70-86.

327 328

[32] A. Ozbilen, I. Dincer, M.A. Rosen, Development of new heat exchanger network designs for a four-step Cu-Cl cycle for hydrogen production, Energy 77 (2014) 338-351.

329


Page 15 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

330 331 332 333

Fig. 1 Schematic of proposed hybrid Cu-Cl cycle for co-production of copper and hydrogen utilising copper waste.


Energy & Fuels

Thermo couple Glass cover Potentiostat Flow Heating mantle

-

+

Graphite rod

Argon

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 25

Crucible Molten CuCl

334 335

Fig. 2 Schematic of experimental set up used for examining the electrolytic step (Step 3).

336 337

Fig. 3 Actual experimental set up for examining the electrolytic step (Step 3).


Page 17 of 25

0.4

0.3

Current (A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.2

0.1

0 -0.5

338 339

0

0.5

1

1.5

2

2.5

Voltage (V) Fig. 4 I-V curve for proposed high temperature electrolytic step (Step 3).

340 341

Fig. 5 XRD pattern of the obtained product.


Energy & Fuels

Exergy Destruction (kJ/mol)

180

Exergy Efficiency

0.9312

0.994 1

159.5

0.9

160 140

0.8

0.6894

0.7

120

0.6

90.21

100

0.5 80

0.3664

0.4

60

0.3

40 20

Exergy Efficiency

Exergy Destruction

0.2

11.13

0.1

1.176

0

0 Step 1

Step 2

Step 3

Step 4

342

Steps

343

Fig. 6 Specific exergy destruction and exergy efficency of the various steps of proposed Cu-Cl

344

cycle.

0.8

0.7

Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 25

0.6 η en,ovc η ex,ovc

0.5

0.4

0.3 903 345 346

913

923

933

943

953

Tstep1 (K) Fig. 7 Effect of operating temperature of Step 1 on the energy and exergy efficiencies of the overall cycle.

347


16

0.935

0.93

15

0.925 14 exd,step1 η ex,step1

0.92

13 0.915 12

11 903

Exergy Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Specific Exergy Destruction (kJ/mol)

Page 19 of 25

0.91

913

923

933

943

0.905 953

348

Tstep1 (K)

349

Fig. 8 Effect of operating temperature of Step 1 on the specific exergy destruction and exergy efficiency

350

of Step 1.


Energy & Fuels

0.8

0.7

Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 25


0.5

0.4

0.3 723 351 352

733

743

753

763

773

Tstep2 (K) Fig. 9 Effect of operating temperature of Step 2 on the energy and exergy efficiencies of the overall cycle.


91.6

0.705

exd,step2 η ex,step2

91.2 0.7 91 0.695 90.8 0.69 90.6

Exergy Efficiency

91.4

0.71

0.685

90.4 90.2 723

733

743

753

763

0.68 773

353

Tstep2 (K)

354


355

of Step 2.

0.8

0.7

Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels


Page 21 of 25


0.5

0.4

0.3 773 356

778

783

788

793

798

803

Tstep3 (K) 21 ACS Paragon Plus Environment

Energy & Fuels

357 Fig. 11 Effect of operating temperature of Step 3 on the energy and exergy efficiencies of the overall

359

cycle.

165

0.368

164

0.366

163

0.364


162

0.362

161

0.36

160

0.358

159 773

778

783

788

793

798

Exergy Efficiency

358


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 25

0.356 803

360

Tstep3 (K)

361


362

of Step 3.

363


Page 23 of 25

0.8


Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.6

0.5

0.4

0.3 833 364

843

853

863

873

Tstep4 (K)

365

Fig. 13 Effect of operating temperature of Step 4 on the energy and exergy efficiencies of the overall

366

cycle.

367


368

Page 24 of 25

14

1

12 10 0.98 8


6 0.96 4

Exergy Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Energy & Fuels

2 0 833

843

853

863

0.94 873

Tstep4 (K)

369


370

of Step 4.


Page 25 of 25

371

0.8

0.7

0.6

Efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

η en,ovc η ex,ovc

0.5

0.4

0.3

0.2 0.3

0.325

0.35

375

0.4

0.425

0.45

η en,pp

372 373 374

0.375

Fig. 15 Variation of the energy and exergy efficiencies of the overall cycle with the energy efficiency of the power plant. Table 1 Values of parameters calculated and used in the present study. Parameter

Value

Energy efficiency of overall cycle (%)

31.8

Exergy efficiency of overall cycle (%)

69.7

Theoretical specific amount of electricity required 251.7 (kJ/mol) Exergy efficiency of Step 1 (%)

93.1

Exergy efficiency of Step 2 (%)

68.9


36.6


99.4

Total specific heat required by cycle (kJ/mol)

123.5

Maximum temperature in cycle (K)

903

376


Co-Production of Hydrogen and Copper from ... - ACS Publications

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