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Electrochemical energy storage in beneficial liquid organic hydrogen carriers

IP.com Disclosure Number: IPCOM000249922D
Publication Date: 2017-May-02
Document File: 7 page(s) / 767K

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Pieter van Helden: AUTHOR

Abstract

The concept presented here is related to electrochemical energy storage and describes the outlines of a system that stores energy in an organic liquid carrier of hydrogen (LOHC). Here we describe the overall concept and methods, and suggested apparatus to store and recover electrical energy in a specific class of hydrocarbon molecules which beneficial properties. The system utilizes a Proton Exchange Membrane (PEM) cell for the electrochemical reactions. The examples we give here relate to the use of two molecules (including their isomers, mixes thereof and similar products). These molecules can store energy through the process of electrochemical hydrogenation to form a saturated compound and the release of the energy through electrochemical dehydrogenation reactions. The two examples noted below are the heat transfer oils benzyl-toluene and dibenzyl-toluene [1], along with their partially or completely hydrogenated derivative compounds. These two molecules are also commercially known under the heat transfer fluid brand names of Marlotherm LH (MLH) and Marlotherm SH (MSH), respectively [2] (see Figure 1). These compounds have recently found commercial application as LOHCs

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Electrochemical energy storage in beneficial liquid organic hydrogen carriers

DATE : 6 April 2017

AUTHOR: Pieter van Helden

AFFILIATION: Sasol Group Technology

ADDRESS: 1 Klasie Havenga Road, Sasolburg, 1947, South Africa

E-MAIL: pieter.vanhelden@sasol.com

Copyright Sasol 2017 Page 2 of 7

1 Introduction

The concept presented here is related to electrochemical energy storage and describes the outlines

of a system that stores energy in an organic liquid carrier of hydrogen (LOHC). Here we describe the

overall concept and methods, and suggested apparatus to store and recover electrical energy in a

specific class of hydrocarbon molecules which beneficial properties. The system utilizes a Proton

Exchange Membrane (PEM) cell for the electrochemical reactions. The examples we give here relate

to the use of two molecules (including their isomers, mixes thereof and similar products). These

molecules can store energy through the process of electrochemical hydrogenation to form a saturated

compound and the release of the energy through electrochemical dehydrogenation reactions. The two

examples noted below are the heat transfer oils benzyl-toluene and dibenzyl-toluene [1], along with

their partially or completely hydrogenated derivative compounds. These two molecules are also

commercially known under the heat transfer fluid brand names of Marlotherm LH (MLH) and

Marlotherm SH (MSH), respectively [2] (see Figure 1). These compounds have recently found

commercial application as LOHCs [3].

2 Direct energy storage in Marlotherm

2.1 Beneficial properties

The Marlotherm molecules have great physical properties (see MSH in Table 1 below) and are liquids

that are intrinsically very safe to use. Taking the energy density of typical LOHC in Table 1 we can

see that this gives the possibility for large scale energy storage, i.e. to store 100MWh would take

about 56 000L which is not an exceedingly large volume to manage or store. It could also be used for

mobility as current electric vehicles driving at 20kWh/100km will have a range of 531km with a 60 litre

on-board storage tank. It is therefore suitable for small or large scale energy storage or transfer.

Furthermore, the other properties noted in Table 1 will make this very safe as a consumer product. If

Renewable Energy sources are used for energy production, it will also be a non CO2 emitting system.

(a)

(b)

Figure 1 (a) Representation of (a) dibenzyl-toluene (MSH) and

(b) benzyl-toluene (MLH)

Copyright Sasol 2017 Page 3 of 7

Table 1 Properties of various energy carrier/storage mediums

(adapted from HySA Infrastructure LOHC presentation and ref. [4])

Technology Energy

density

(kWh/L)

Energy

density

(kWh/kg)

System

energy

density

(kWh/kg)

Flammable Toxic Environmentally

friendly

CO 2

emitter*

200 barg 0.48 33 1.5 YES NO YES NO

350 barg 0.78 33 1.6 YES NO YES NO

700 barg 1.31 33 1.8 YES NO YES NO

MH 0.8 0.4 <0.4 YES - YES NO

LH 2

(Cryo) 2.2 33 2 YES NO YES NO

Diesel 9.7 11.6 2.5 YES YES NO YES

Methanol 4.43 5.6 -...