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A fossil-fuel based recipe for clean energy

Surendra K Saxena�, Vadym Drozd, Andriy Durygin

CeSMEC (Center for the Study of Matter at Extreme Conditions), College of Engineering and Computing, Florida International University,

Miami, FL 33199, USA

a r t i c l e i n f o

Article history:

Received 15 December 2007

Received in revised form

27 April 2008

Accepted 28 April 2008

Available online 17 June 2008

Keywords:

Hydrogen

Carbon-sequestration

Coal-burning power plant

nt matter & 2008 Internane.2008.04.050

thor.Saxenas@fiu.edu (S.K. Sa

a b s t r a c t

A zero-emission process of hydrogen production from fossil fuel through a system of

reactions involving hydroxide, carbon, CO, CO2 and water is described here. It provides for a

complete sequestration of carbon (CO2 and CO) from coal/natural-gas burning plants. The

CO and or CO2 produced in coal or natural gas burning power plants and the heat may be

used for producing hydrogen. Economically hydrogen production cost is less than the

current price of fossil-fuel produced hydrogen with the added benefit of carbon

sequestration. The reduced cost of the hydrogen may aid in making a hydrogen fueled

automobile economically viable.

& 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights

reserved.

1. Introduction

Steam methane reforming is the most common and the least

expensive method to produce hydrogen at present [1]. Coal

can also be reformed to produce hydrogen, through gasifica-

tion. Hydrogen production by CO2-emitting-free methods are

either more expensive compared to those using fossil fuel or

are in the very early stages of development. Examples are the

methods proposed by Gupta et al. [2], the zero-emission coal

technology (ZEC) by Zlock et al. [3,4], GE’s fuel-flexible

technology [6] and several others [7–9]. Since United States

has vast proven coal reserves, coal based technology of

hydrogen production is very attractive. However, effective

and low cost carbon sequestration technology has yet to be

developed.

Hydrogen is regarded as the energy for future but to

produce and use hydrogen either by direct combustion or in

a fuel cell, we need to use other sources of energy. Thus

hydrogen or use of any material in producing energy cannot

be an environmentally clean and economically viable solution

unless we sequester carbon. We may eventually have the

hydrogen solution for our transportation and other energy

tional Association for Hyxena).

uses. However, such energy will continue to be dependent on

the use of fossil fuel for long time and may not be economic.

To turn things around, we have to use alternate methods of

using coal, producing hydrogen and hydrides. Many hydrides

are currently under consideration for use in on-board

generation of hydrogen and the cost of producing the hydride

is an important consideration.

Coal is used extensively in producing synthetic fuels [1].

Use of coal in gasifiers is well established and hydrogen may

be produced by the reaction: C+2H2O ¼ CO2+2H2. Gasifiers are

operated between 500 and 1200 1C, and use steam, oxygen

and/or air and produce a mixture of CO2, CO, H2, CH4 and

water. The CO produced can be further processed by the shift-

gas reaction to produce H2 with production of CO2: CO+-

H2O ¼ CO2+H2. The following is an extract from a report by

National Academy of Engineering, Board on Energy and

Environmental Systems [5] and shows the importance of the

present study: ‘‘At the present time, global crude hydrogen

production relies almost exclusively on processes that extract

hydrogen from fossil fuel feedstock. It is not current practice

to capture and store the by-product CO2 that results from the

production of hydrogen from these feed stocks. Consequently,

drogen Energy. Published by Elsevier Ltd. All rights reserved.

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more than 100 Mt C/yr are vented to the atmosphere as

part of the global production of roughly 38 Mt of hydrogen

per year.’’

It would then appear that when coal is used in gasifiers or

in direct burning in power- and other manufacturing-plants,

CO2 and CO are prominent among other gases released to

Fig. 1 – (a) Phase equilibrium in the system Ca(OH)2+C+H2O; (b

composition in the system 2NaOH+CO; (d) equilibrium in the sys

more complex gas composition and at higher temperature than

atmosphere. Their emission is not only harming the environ-

ment but as considered here is also a waste of resources. For

industry this has been an economic issue. This study will

provide a clear economic incentive to sequester carbon (CO2

and CO) without significantly affecting our current modes of

operations.

) equilibrium in the system 2NaOH+C+H2O; (c) equilibrium

tem 4NaOH+C+CO2; and (e) the gas-shift reaction produces a

reactions (2)–(4).

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2. Reactions

We may divide the hydrogen producing reactions in two

categories. The first category reactions are for the gasification

process unrelated to coal-burning power plants. These are:

CaðOHÞ2ðsÞ þ CðsÞ þH2OðgÞ ! CaCO3ðsÞ

þ 2H2ðgÞ; DH ¼ �606 kJð627 �CÞ (1)

2NaOHðsÞ þ CðsÞ þH2OðgÞ ! Na2CO3ðsÞ

þ 2H2ðgÞ; DH ¼ 645:8 kJð600 �CÞ (2)

The use of the following reactions may be considered in

relation to coal-burning power and other industrial plants:

2NaOHðsÞ þ COðgÞ ! Na2CO3ðsÞ

þH2ðgÞ; DH ¼ �119 kJð600 �CÞ (3)

4NaOHðsÞ þ CðsÞ þ CO2ðgÞ ! 2Na2CO3ðsÞ

þ 2H2ðgÞ; DH ¼ �662 kJð600 �CÞ (4)

Sodium in the above reactions may be replaced by potassium.

We performed both thermodynamic equilibrium calcula-

tions using the software FACTSAGE and the databases therein

and conducted several experiments for verification. Reaction

(1) was considered by Saxena [10] and Xu et al. [11]. In the

reaction, the gas is multicomponent and hydrogen yield is

only partial (see Fig. 1a) (Moles H2:H2O:CH4:CO ¼ 1.5:.27:.

113:.044). Reaction (2) was proposed by Saxena [6] and

although endothermic, it produces a much cleaner hydrogen

yield than reaction (1) (Fig. 1b) and over a wider temperature

range. Reactions (3) and (4) are exothermic. Reaction (4) can

be considered as a combination of the Boudouard reaction:

Cþ CO2 ! 2CO (5)

and reaction (3). Reaction (4) may also be considered as a

combination of

2NaOHþ CO2 ! Na2CO3 þH2O (6)

and

2NaOHþ CþH2O! Na2CO3 þ 2H2 (2)

Fig. 2 – Equipment for the study of hydrogen gen

An equilibrium calculation (Fig. 1b) shows that Na2CO3 also

known as soda ash and hydrogen are produced over a wide

temperature range starting from 100 to 800 1C.

Similar compositions result by the use of reactions (3) and

(4) (Fig. 1c and d). We may compare reactions (2)–(4) with the

gas-shift reaction (CO+H2O ¼ CO2+H2), which differs only in

the form of introduction of water. It is quite clear that there is

a significant advantage in using reactions (2)–(4) over the gas-

shift reaction (Fig. 1e). Reaction between sodium hydroxide

and carbon monoxide yielding sodium formate was described

by Berthelot in 1856. When heated above 250 1C, sodium

formate transforms into oxalate with release of hydrogen:

2HCOONa! Na2C2O4 þH2 (7)

In 1918 Boswell and Dickson [12] demonstrated that when

carbon monoxide is heated with excess of sodium hydroxide

at temperatures at which formate is transformed into oxalate,

oxidation almost quantitatively to carbon dioxide occurs with

the evolution an equivalent amount of hydrogen:

COþ 2NaOH! Na2CO3 þH2 (8)

3. Experimental results

Experiments were conducted to verify the theoretical predic-

tions for reactions (2) and (3) using an in-house method

involving measurement of evolving hydrogen (Fig. 2). Anhy-

drous sodium hydroxide, supplied by Alfa Aesar (97%), was

allowed to react with a mixture of carbon and water for

reaction (2) and with CO and N2 (carrier gas) for reaction (3).

The reaction between carbon, sodium hydroxide and water

was carried out in a gas-flow system (Fig. 2). Sodium

hydroxide was dissolved using a minimal amount of distilled

water in an alumina boat and then activated carbon was

immersed into this solution. The alumina crucible was put in

a tubular furnace with a quartz tube. Nitrogen gas with a flow

rate of 50 ml/min was used as a carrier to deliver steam to the

reactor.

eration using laser break down spectroscopy.

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Fig. 3 – (a) Experimental data for reaction (2) (2NaOH(s)+C(s)+H2O (g) ¼ Na2CO3(s)+2H2). Temperature was increased at a rate of

4 1C/min; and (b) experimental data for reaction (3) (2NaOH(s)+CO(g) ¼ Na2CO3(s)+H2(g)). Temperature was increased at rate of

4 1C/min. Two different rates of flow of CO were used. Lower hydrogen yield for higher CO flow could be explained if one takes

into account CO disproportionation reaction 2CO-CO2+C, the rate of which depends on the CO partial pressure. Released CO2

will react with sodium hydroxide decreasing amount of the latter available for the reaction with carbon monoxide.

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The reaction between NaOH and CO was studied using the

same experimental setup.

Hydrogen concentration in the effluent gases from the

reactor was determined by laser break-down spectroscopy.

Before analysis the gases were passed through liquid nitrogen

(NaOH/C/H2O reaction) or acetone/dry-ice (NaOH/CO reac-

tion) cooled condenser to remove all hydrogen containing

species except for H2 gas.

The reactions were first explored with temperature increas-

ing at a fixed rate, reaction (2) between 100 and 700 1C (Fig. 3a)

and reaction (3) between 110 and 400 1C (Fig. 3b). Reaction (3)

was studied at two different flow rates of CO (10 and

20 ml/min) (Fig. 3b). Both reactions were complete in less

than 200 min. Results of isothermal kinetic experiments at

several temperatures are shown in Fig. 4a (reaction 2) and b

(reaction 3).

4. Discussion

For existing power stations, where CO2 is produced, we may

choose reaction (4):

4NaOHþ Cþ CO2 ! 2Na2CO3 þ 2H2 (4)

One may compare this reaction with the combination of the

gasifier reaction C+2H2O ¼ CO2 +2H2 and the CO2 absorbing

reaction 2NaOH+CO2 ¼ Na2CO3+H2O to accomplish similar

result. It is shown in Fig. 1b and c that the reaction (4) has

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definite advantage being the carbon-sequester and hydrogen

producing reaction. A comparison of the figures shows that

much higher temperature is required to obtain a significant

amount of hydrogen mixed with CO in Fig. 1e than is required

when using reaction (4) (Fig. 1d). Catalysis of the reactions,

where coal is involved may be needed and has been discussed

00

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in detail in literature [1]. A high production rate would result if

the hydrogen is formed by continuous flow processes. As

envisaged here, the equilibrium calculations are for a closed

system with a complete conversion of fixed ratio of reactants

and production of the carbonate and hydrogen. Catalysis and

partial conversion of the reactants will affect the costs.

Fig. 5 shows the cost analysis. Through reaction (4), we will

sequester 11 kg of CO2 for every 40 kg of sodium hydroxide

producing 1 kg of hydrogen and 53 kg of sodium carbonate. If

we accept the following per kg prices: Sodium hydroxide $0.42

and sodium carbonate 0.36, the material cost of hydrogen

production is $ �2.28 per kg giving us an advantage in offsetting

the energy costs. The new hydrogen DOE cost goal of

$2.00–3.00/gge (delivered, untaxed, 2005$, by 2015) is inde-

pendent of the pathway used to produce and deliver

hydrogen. Better cost calculations are needed to insure the

economic viability of the process. Note that less energy is

required to electrolyze sodium chloride to produce sodium

hydroxide than to produce sodium. It will be necessary to

integrate the production of NaOH at the power plants instead

of purchasing it from an outside manufacturer. In-house

sodium hydroxide manufacture will provide significant ship-

ping cost savings, efficient process integration, and safety.

There are many uses of Na2CO3 and as long as the use does not

release the CO2 to the atmosphere, the carbon sequestration remains

effective.

We may also consider the following reaction to use sodium

carbonate gainfully:

Na2CO3ðsÞ þ 2CðgraphiteÞ ! 2NaðgÞ þ 3COðgÞ (8)

This reaction is endothermic with DH of 1160 kJ/mol and is

largely complete around 1127 1C. Since we rely on coal to

provide the heat, the energy cost is not an issue. If we use this

reaction to reduce the amount of sodium carbonate produced

in reactions (2)–(4), we will further decrease the cost of

hydrogen.

US tops in CO2-emissions per capita; in 2003, 121.3 metric

tons of CO2 were released in the atmosphere. In 2004 the total

carbon release in North America was 1.82 billion tons. World-

wide industrial nations were responsible for 3790 million

metric tons of CO2 (Kyoto-related fossil-fuel totals). It is

clearly not practical to consider that we can sequester all this

carbon with reactions (2–4) which would require production

of NaOH on a massive scale which would cause further

Fig. 4 – (a) Hydrogen generation in 2NaOH+C+H2O-Na2CO3

+ 2H2 reaction studied at different temperatures. N2 carrier

gas flow rate 50 mL/min; (b) hydrogen generation in 2NaOH

(s)+CO(g) ¼ Na2CO3 (s)+H2(g) reaction studied at different

temperatures. N2 carrier gas flow rate 50 mL/min; and (c)

hydrogen flow rates in the CO+2NaOH reaction measured at

different temperatures and CO flow rate of 20 mL/min and

N2 flow rate of 50 mL/min. Hydrogen flow rate vs. time

dependence at 300 1C is characterized by quite long (about

3 h) initialization period. However, after 3 h the reaction

accelerated. It may be due to the formation on the initial

stages of the reaction of some intermediates, which

themselves or together with sodium hydroxide melt below

300 1C. The presence of a liquid phase promotes the

reaction.

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Fig. 5 – Hydrogen production and carbon sequestration. The analysis depends on the current price structure of sodium

products. We may also use the other two reactions (2) and (3).

I N T E R N AT I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 3 6 2 5 – 3 6 3 13630

emission of CO2 if fossil fuel is used in the production.

However, in all situations where industry is producing carbon

gases and heat anyway, the production of hydrogen according

to the reactions presented here, would lead to reduction of

carbon in the atmosphere. Most benefit will be obtained if

non-fossil sources of energy (hydro-electricity, nuclear-en-

ergy, solar and wind) are used for NaOH production.

More than 100 Mt C/yr are vented to the atmosphere as part

of the global production of roughly 38 Mt of hydrogen per year.

Through reaction (4), we will sequester 3 Mt carbon (11 Mt of

CO2) for every 40 Mt of sodium hydroxide producing 1 Mt of

hydrogen and 53 Mt of sodium carbonate. The US production

of NaOH is currently 16 Mt per year. NaOH of 1300 Mt will be

needed to sequester all the carbon which is currently emitted

in hydrogen production. In this process 33 Mt of H2 will result.

Sodium hydroxide is produced (along with chlorine and

hydrogen) via the chloralkali process. This involves the

electrolysis of an aqueous solution of sodium chloride. The

sodium hydroxide builds up at the cathode, where water is

reduced to hydrogen gas and hydroxide ion. The total H2

produced in these reactions (reactions 2–4 and electrolysis) if

used in automobiles and other energy devices will have a very

large effect on CO2-emission.

The present work provides a system of reactions to produce

hydrogen from sodium hydroxide and CO or CO2 and carbon.

The carbon gases are produced in industrial plants burning

coal and thus are available at no cost. These gases can also be

obtained at relatively high temperature; the reaction of CO or

CO2 with sodium hydroxide is exothermic and hence no

additional heating would be required. The CO or CO2 would

react to form sodium carbonate and hydrogen and thus

carbon will be sequestered. The hydrogen produced cheaply

with no carbon release in the atmosphere may be used to

synthesize hydrides at low cost.

Acknowledgments

The authors’ work is supported through a grant from National

Science Foundation (DMR-0231291 to K. Rajan, Iowa State

University) and a grant from Air Force (212600548) US Patent

files (PCT/US08/55586).

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