Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units

Distributed H2 production from
bioalcohols and biomethane in
conventional steam
reforming units

8

A. Vita, C. Italiano, L. Pino
Institute for Advanced Energy Technologies (ITAE), “Nicola Giordano,” National Research
Consilium (CNR), Messina, Italy

Abbreviations
BOP
BSR
CSD
DDGS
DOE
ESR
FC
FCEV
FP
gge
GHG
GSR
HTS
ICE
ICEV
IEA
LHV
LTS
MMBtu

MSR
NREL
O&M
PSA
RFA
SF
SR
WGS
WWTP

balance of plant
butanol steam reforming
compression, storage, and dispensing
distillers dried grains and solubles
Department of Energy
ethanol steam reforming
fuel cell
fuel cell electric vehicle
fuel processor
gallon of gasoline equivalent
greenhouse gas
glycerol steam reforming
high-temperature shift
internal combustion engines
internal combustion engine vehicles
International Energy Agency
lower heating value (kJ/mol)
low-temperature shift
Million British thermal unit
methane steam reforming

National Renewable Energy Laboratory
operating and maintenance
pressure swing adsorption
Renewable Fuel Association
solid fuel
steam reforming
water-gas shift
wastewater treatment plants

Bioenergy Systems for the Future. />© 2017 Elsevier Ltd. All rights reserved.


280

Bioenergy Systems for the Future

Symbols
ButOH,IN
CH4,IN
EtOH,IN
Glycerol,IN
H2,OUT
LHVFuel
LHVH2
nFuel
nH2
Q
QRecovered
QReformer
S/C

YH2
ηH2
ηth

8.1

number of mol of feed butanol (mol)
number of mol of feed methane (mol)
number of mol of feed ethanol (mol)
number of mol of feed glycerol (mol)
number of mol of produced hydrogen (mol)
fuel lower heating value (kJ/mol)
hydrogen lower heating value (kJ/mol)
fuel molar flow (mol/s)
hydrogen molar flow (mol/s)
energy provided and recovered (kW)
heat recovered from the heat exchange systems (kW)
heat to support the reformer (kW)
steam-to-carbon molar ratio
hydrogen yield (%)
overall efficiency (%)
overall thermal efficiency (%)

Introduction

One of the priorities in research programs energy field is to identify some strategic
technologies that can contribute to the shift toward a low-carbon economy through
the use of renewable energy sources while reducing the CO2 emissions. In this area,
the sustainable hydrogen production technologies and the fuel cell (FC) systems will
play an extremely important role in the portfolio for the future energetic economy

(Andrews and Shabani, 2012; Midilli and Dincer, 2007). This is particularly true
for the transport sector that today is marked by an extreme dependency on oil.
Cost-effective hydrogen needs to be produced with zero or near-zero CO2 emissions.
Currently, the primary route for hydrogen production is the conversion of natural gas
and other light hydrocarbons. Approximately 96% of the produced hydrogen come
from fossil fuels’ conversion, such as natural gas; reforming in large-scale (central)
facilities produces more than 500,000 kgH2 =day (US DRIVE, 2013). This process causes the coproduction of large amounts of carbon dioxide, the main responsible for the
so-called “greenhouse effect.” Therefore, renewable energy sources tuned with suitable technologies for hydrogen production will be necessary during the coming
decade (Balat, 2008). The use of fuels directly derived (without further synthesis steps
that involve hydrogen) from renewable sources (biomass and waste) can give an
important contribution to meet the current and future energy requirements.
In this scenario, biofuels such as biomethane, bioethanol, biobutanol, and glycerol
can be considered very interesting renewable fuels for hydrogen production (Andrews
and Shabani, 2012; Edelmann, 2001) through conventional SR process. The biogas
(biomethane) can be produced from a variety of organic raw materials from various


Distributed H2 production from bioalcohols and biomethane

281

sectors, ranging from zootechnical to agro-industrial. Renewable ethanol and butanol
can be derived from fermentation of sugar-based, corn-based, and cellulose-based
materials. Glycerol can be obtained as a by-product in biodiesel production.
The sustainable utilization of these biofuels, due the local nature of the related feedstocks, will play an important role to increase the distributed hydrogen production, the
most feasible approach for introducing hydrogen as an energy carrier in the near/
midterm (<2020). This approach requires low capital investment, due to the small
hydrogen capacity initially needed, and it does not necessitate infrastructures for
hydrogen transport and delivery. Small-scale (distributed) facilities would produce
from <100 to 1500 kgH2 =day with the production site connected to the fueling stations. Small-scale natural gas reformers are commercially available and this technology that represents the state of the art should be capable of meeting also the hydrogen

production cost targets when fully deployed. Instead, the reforming systems for the
distributed H2 production from gaseous and liquid biofuels are not completely mature
and required research activities especially on reactor design and catalytic materials.
Nevertheless, these systems are expected to move into commercial production in
the midterm (2020) (US DRIVE, 2013). Then, the distributed hydrogen produced
in small-scale reformers can be used for the heat treatment of metals, glass making,
microelectronics fabrication, power generator cooling, hydrogenation of food oils,
and feeding existing and nascent fuel cell systems. However, the greatest potential
growth will be in using hydrogen as a distributed fuel for the transportation sector.
A recent study by Ludwig-B€
olkow-Systemtechnik and Hinicio (2015) identified
the most promising green hydrogen production routes that may help to meet ambitious
energy targets. Between these, a possible pathway considers the reforming of biofuels
for the production of distributed renewable H2 to feed fuel cell electric vehicles
(FCEVs) with small-scale fuel processor (FP). Recently, the interest in hydrogen production from biogas for FCEVs is continuously growing. The National Renewable
Energy Laboratory (NREL) elaborated a market study called “Renewable hydrogen
potential from biogas in the United States” (Saur and Milbrandt, 2014). The report
details the availability of biomethane from wastewater treatment plants (WWTPs),
manure, and industrial/commercial sources, as well as landfills, in the context of
demand from the FCEV market and other users. Besides, a recent study in the bioenergy sector has evidenced the advantages of the alternative fuel utilization to reduce
climate change disorder and to mitigate greenhouse gas (GHG) emission in the environment ( Joselin and Unni Krishnan, 2016).
Thus, decentralized hydrogen production plant using small-scale reformers for biogas or liquid biofuels (bioalcohols) may become part of the future sustainable energy
network. Currently, there are different types of biofuels produced from biomass
resources that can be used for on-site hydrogen production. Particularly, bioalcohols
(ethanol, glycerol, and butanol) and biomethane are the more interesting biofuels due
to their high lower heating value (LHV) per mass and their availability. In addition,
bioalcohols are sulfur- and nitrogen-free oxygenates. The main characteristics of these
biofuels, in term of SR and maximum H2 yield, LHV, and starting source, are reported
in Table 8.1. SR hydrogen yield has been calculated considering the theoretical mol of
hydrogen produced from the fuel steam reforming (SR) reaction to H2 and CO, while

282

Table 8.1

Main properties of biofuels derived from biomass materials for on-site hydrogen production
SR H2 yield
(y/2 + x2z)

Ethanol

C2H6O

4

Glycerol

C3H8O3

4

Butanol

C4H10O

8

Methane

CH4

3

SR
theoretical
H2 yield

LHV
(MJ/kg)

Maximum H2
yield (y/2 + 2x2z)

0.17 kg
H2/kg ethanol

27

6

0.09 kg H2/kg
glycerol
0.22 kg H2/kg
butanol

16

7

34

12

0.38 kg H2/kg
methane

47

4

Source
Sugary, strarchy and
lignocellulosic biomass
(fermentation)
By-product in biodiesel
production
Sugary, strarchy and
lignocellulosic biomass
(fermentation)
Biogas purification

Bioenergy Systems for the Future

Biofuel

Molecular
formula
CxHyOz

Distributed H2 production from bioalcohols and biomethane

283

the maximum hydrogen yield considers the fuel conversion to H2 and CO2 by SR
coupled with water-gas shift (WGS) reactions.

8.2

Biomass feedstocks: routes and technologies for
biofuels generation

In both developing and industrialized countries, the demand for bioenergy increased
significantly in the last decade, with the primary objective to reduce the fossil fuels
dependence and the GHG emissions in view of climate change. In this regard, some
studies of the International Energy Agency (IEA) highlighted a global overview of
biomass use in the industrial and transport sectors. Currently, biomass covers
$10% of the global energy supply (IEA, 2015), as evidenced in Fig. 8.1, while the
Oil: 4202 (31%)

Coal: 3946 (30%)

Other renewables: 161 (1%)
Hydro: 326 (2%)
Nuclear: 676 (5%)
Bioenergy: 1376 (10%)
Gas: 2901 (21%)
2013
Coal: 2495 (16%)

Oil: 3351 (22%)

Gas: 3335 (22%)

Other renewables: 1470 (10%)
Hydro: 558 (4%)
Bioenergy: 2331 (15%)

Nuclear: 1627 (11%)
2040

Fig. 8.1 Various energy sources in relation to the world’s total primary energy demand in 2013
and in a possible new scenario in 2040 (Mtoe).


284

Bioenergy Systems for the Future

share of fossil fuels in the global energy system is still high (% 82%). It is estimated
that new policies and technologies finalized to support the utilization of renewable
sources, including biomass, can contribute to reducing in the near/midterm this consumption to about 60% (Vakkilainen et al., 2013).
The term biomass refers to the biodegradable fraction of products, waste, and
residues from agriculture (including vegetal and animal substances), forestry, and
related industries and the biodegradable fraction of industrial and municipal waste.
The biofuel or biorenewable fuel is assigned to a solid, liquid, or gaseous fuel that
is predominantly derived from biomass. Purification, upgrading, and conversion
technology finalized to the hydrogen production will be described in the following
paragraphs principally for the bioethanol and biomethane production; nevertheless,
information on other alternative promising bioalcohols (n-butanol and glycerol),

directly produced from biomass or as a by-product of the process that involves biomass, will be also reported.
In the current bioenergy scenario, bioethanol and biogas (biomethane) are the most
promising candidates as biofuels for distributed hydrogen production. Apart from biodiesel, bioethanol and biogas are the most abundant bioderived fuels (EurObserv’ER
site web Accessed 19 May 2016) that show good potential for distributed hydrogen
generation. Bioethanol and biomethane can be produced anywhere in the world,
and their transportation infrastructures already exist and are undergoing expansion
to meet the increasing demand finalized to promote an energy scenario based on a
low-carbon economy (Leitner and Lindorfer, 2016; RFA, 2016; REN21, 2015;
European Commission, 2011; RFA, 2006). Other minor renewable bioderived liquid
options to generate H2 include biobutanol and glycerol. The actual scenario for these
biofuels is mostly based on the production as a by-product of other well-developed
processes. Glycerol can be derived as by-product from the production of biodiesel
(Verma and Sharma, 2016), while biobutanol comes from the fermentation of sugary
biomass (Cai et al., 2014).

8.2.1 Bioalcohols: sources, production, and purification
8.2.1.1

Bioethanol

Bioethanol is a promising source for hydrogen production since it can be produced
renewably in large quantities from several biomass sources, such as energy plants,
waste materials from agro-industries, or forestry residue materials (Authayanun
et al., 2015; He et al., 2015). It is obtained as a metabolic product by fermentation
of sugar with yeasts and classified as first and second bioethanol. First bioethanol generation originated from sucrose-containing (e.g., sugar cane, sugar beet, and sweet sorghum) and starchy materials (e.g., maize, wheat, rye, and corn), while second
bioethanol generation is produced from low-cost nonedible lignocellulosic biomass
(i.e., wood, grass, and straw). This classification, based on the generation technologies, is adopted for all biofuels, where third and fourth generations include algae
and vegetable oil-biodiesel, respectively. Bioethanol contains 20 vol% of ethanol with
water as the major component; additional impurities such as diethyl amine, acetic

Distributed H2 production from bioalcohols and biomethane

285

acid, methanol, and propanol are present with concentrations ranging between few
ppm to 1% (Devianto et al., 2011). The Renewable Fuels Association (RFA,
2015), also known as the leading trade association for America’s ethanol industry,
determined 25.7 billion gallons total of bioethanol produced in 2015. The United
States and Brazil are the main bioethanol producers, as shown in Fig. 8.2.
Generally, the process of the bioethanol production includes four steps: pretreatment, hydrolysis, fermentation, and distillation, as synthesized in Fig. 8.3 (Dan
et al., 2015; Hou et al., 2015). The first-generation ethanol plants utilize either sugar
or starch. The pretreatment step consists in the grains milling and subsequent starch
liquefaction. The second step is the hydrolysis or saccharification, which releases glucose monomers into the solution. Then, fermentation with yeast converts the sugar
into ethanol (c.10% w/v) and carbon dioxide. Finally, the fermentation liquid is distilled to separate and purify ethanol and dehydrated to concentrate ethanol (above
99.7% w/v). The bottom distillate is further treated to obtain distillers dried grains
and solubles (DDGS) as animal protein sources. The second-generation ethanol

United States (58%)

Thailand (1%)
Canada (2%)
China (3%)
Rest of the World (3%)
Europe (5%)
Brazil (28%)

Fig. 8.2 World bioethanol production (RFA analysis of public and private estimates).

Water

Grains or
ligno-cellulose

Pretreatment

Yeast

Hydrolysis

CO2

Fermentation

First or second
generation bioethanol

Distillationdehydration

Stillage (to animal
feed and solid fuel)

Fig. 8.3 Process outline for first- and second-generation bioethanol.


286

Bioenergy Systems for the Future

utilizes different types of lignocellulosic materials as substrates that require being broken down to sugar molecules by using a combination of heat and enzymatic treatments. In this case, solid fuel (SF) can be obtained as waste material from the

bottom distillate (Lennartsson et al., 2014).
Bioethanol has attracted much interest because of its advantages, such as safe handling, easy transport, biodegradable nature, high solubility in water, low cost, low
toxicity, sulfur-free composition, and environmental friendliness (Carvalho et al.,
2016; Devianto et al., 2011). Bioethanol can easily react in the presence of water
by SR reaction, thus providing an important route for hydrogen production. In vision
of a low-carbon economy, bioethanol SR is raising particular attention, due to its
potential to be “carbon-neutral” on a life-cycle basis. Indeed, the bioethanol conversion to hydrogen can be considered CO2-neutral since the carbon dioxide produced is
consumed for biomass growth. Moreover, the direct feed of dilute ethanol to the
reformer appears a very interesting solution, preventing the expensive costs for ethanol purification/concentration (Palma et al., 2016). Unfortunately, the presence of
several impurities (heavier alcohol, organic acids, aldehydes, and esters) may affect
both the hydrogen yield and the catalyst stability.

8.2.1.2

Biobutanol

Biobutanol can be produced by fermentation of sugar beet, sugarcane, corn, wheat,
lignocellulosic biomass, starch-based waste packing peanuts, and agricultural wastes
(Cai et al., 2014; Qureshi et al., 2010). The fermentation process generates acetone,
butanol, and ethanol in roughly 6:3:1 ratio, known as “ABE” (Wang and Cao, 2011).
In comparison with methanol, n-butanol shows higher hydrogen content (13.5 wt% vs
12.5 wt%) and higher energy density (26.9 MJ/L vs 16.0 MJ/L). Furthermore,
n-butanol can be used directly in existing fuel distribution pipelines (Nahar and
Madhani, 2010).

8.2.1.3

Glycerol

Glycerol is obtained as a by-product in biodiesel production (Zamzuri et al., 2016).

Massive amounts of glycerol are being obtained in the manufacture of fatty acids
and mostly in biodiesel production where glycerol represents around 10 wt% of the
plant product. It has low commercial value and high toxicity, due to the presence
of several impurities, such as methanol; water; inorganic salts; free fatty acids;
unreacted mono-, di-, and triglycerides; and methyl esters (Yurdakul et al., 2016).
There are two main options to use biodiesel-derived glycerol: (a) purification to obtain
high-purity glycerol for use in food, cosmetics, and pharmaceutical industries and
(b) upgrading to produce different value-added chemicals and/or energy using different valorization routes such as gasification, steam reforming, and supercritical
reforming. (Remo´n et al., 2016). Due to the low purity and the high cost of refining,
the crude glycerol has good potential for hydrogen production via SR (Senseni et al.,
2016). If the biodiesel production will increase significantly in the future, large
amounts of glycerol will be available for hydrogen production.


Distributed H2 production from bioalcohols and biomethane

8.2.2

287

Biomethane: sources, production, purification and
upgrading

Biogas is produced from the anaerobic digestion of organic material, such as manure,
sewage sludge, organic fraction of household and industrial waste, and energy crops.
All types of biomass can be used as substrates for biogas production as long as they
contain carbohydrates, proteins, fats, cellulose, and hemicelluloses as main components. Only strong lignified organic substances, for example, wood, are not suitable
due to the slow anaerobic decomposition. Biogas is a mixture of methane (35%–
77%) and carbon dioxide (30%–60%) with small amounts of other gases and
by-products, that is, nitrogen (0%–5%), carbon monoxide (<0.6%), hydrogen sulfide

(0.005%–2%), oxygen (0%–3%), and ammonia (<1%). Trace amounts of siloxanes
(0%–0.02%), halogenated hydrocarbons (<0.65%), and other nonmethane organic
compounds as aromatic hydrocarbons, alkanes, alkenes, etc. are also occasionally present. Usually, this mixed gas is saturated with steam and may contain dust particles.
The biogas yield and its content of methane depend directly on the organic composition of the feedstock, as different raw materials have different degradation rates. Fats
provide the highest biogas yield but require a long retention time due to their poor
bioavailability. Carbohydrates and proteins show much faster conversion rates but
lower gas yields. The biogas composition, related to different types of feedstock, is
collected in a large number of studies (Delsinne, 2010; Rasi, 2009; Petersson,
2007; Lampe, 2006; El-Fadel et al., 1997). In Table 8.2, typical biogas compositions
as a function of the main biogas sources are given. These are (i) sewage treatment
plants (primary and secondary sludge resulted from aerobic treatment of wastewater),
(ii) landfills, (iii) agricultural organic streams (manure and slurries from different animals, energy crops, catch crops, grass, and other by-products), (iv) industrial organic
waste streams (from food processes as milk and cheese manufacture, slaughter houses,
and vegetable canning; from beverage industry as by-products from breweries, fruit
processing, distilleries, coffee, and soft drinks; and from industrial products, for example, paper and board, sugar plants, rubber, and pharmaceuticals), and (v) municipal
solid waste (organic fraction of household waste).
Actually, most of the biogas is combusted in internal combustion engines (ICE) to
produce electric power and heat. Moreover, the methane in biogas can be also utilized
as vehicle fuel or as source to produce hydrogen via reforming processes for mediumlong-term application (2020–30) (LBST-Hinicio, 2015). For the upmentioned application, where it is important to have high energy content in the gas stream, the biogas
purification and upgrading into biomethane are required. Several technologies for biogas purification and biogas upgrading are commercially available and others are at the
pilot or demonstration plant level. In those upgrading technologies, in which carbon
dioxide is separated from the biogas, some of the other unwanted compounds are also
separated. However, to prevent corrosion and mechanical wear of the upgrading
equipment, it can be advantageous to clean the biogas before the upgrading (Lo´pez
et al., 2012). The purification step relates to the main impurities that can be found
in biogas, such as sulfur, halogenated hydrocarbons, organic silicon compound (siloxanes), oxygen, nitrogen, ammonia, water, and particulates. The principal technologies


288

Table 8.2

Biogas composition
Municipal
waste

Waste
water

Agricultural animal
waste

Waste from agrofood
industry

CH4 (vol%)
CO2 (vol%)
N2 (vol%)

50–60a
34–38a
0–5a
0–1a

50–70a–d
30–50a,c,d
<1a
<1–2b,<3c
<1b,<0.5a

50–75a,c
26a

O2 (vol%)
H2 (vol%)
CO (vol%)
H2S (ppm)
Aromatic (mg/m3)
Ammonia
Halog. compounds (mg/m3)
Benzene (mg/m3)
Toluene (mg/m3)
Siloxanes (ppmv)
Non-CH4 organics (% dry wt)
Volatile organics (% dry wt)

55–77a–d
30–45a–d
<2b
<1a,d
<1b,<0.5a
63–3000a,c,d

32–1000a,b

280a

a

70–650a

0–200a

50–100a mg/mc
a

100–800

Naskeo Environment site web Accessed 18 May 2016.
Delsinne (2010).
Lampe (2006).
d
Rasi (2009).
e
El-Fadel et al. (1997).
f
Petersson (2007).
b
c

0.1–0.3b
2.8–11.8b
2–15c,d

0.7–1.3b
0.2–0.7b
<0.4d

Landfill
35–70d–f
35–60b–f

5–15b–f
0–3e
0–5e,f
0–3e
10–20.000b,d–f
30–1900e
5 ppm
1–2900e
0.6–2.3b
1.7–5.1b
0.1–3.5c,d
0–0.25c
0–0.1c

Bioenergy Systems for the Future

Components


Distributed H2 production from bioalcohols and biomethane

289

for the abatement of sulfur are adsorption on activated carbon, chemical absorption,
and biological treatment. Siloxanes can be removed by cooling the gas; by adsorption
on activated carbon (spent after use), activated aluminum, or silica gel; or by absorption in liquid mixtures of hydrocarbons. Siloxanes can also be removed while separating hydrogen sulfide. Oxygen and nitrogen can generally be removed in
desulfurization processes or in some of the biogas upgrading processes. Ammonia
is usually separated when the gas is dried or when it is upgraded. Water can be
removed by cooling, compression, absorption, or adsorption methods. Particulates
are separated by mechanical filters. Regarding the separation of CO2, the most widely

used technologies for biogas upgrading are pressure swing adsorption (PSA), water
scrubbing, organic physical scrubbing, and chemical scrubbing (Petersson and
Wellinger, 2009). A comparison between the principal parameters for common
upgrading processes is reported in Table 8.3 (Urban et al., 2008). The choice of
the most suitable technology depends on specific parameters, such as the availability
of cheap heat and the electricity price. It should also be noted that it is often possible to
increase the methane purity and to lower the methane loss but at the expense of a
higher energy consumption.

Table 8.3

Comparison between common upgrading processes
Organic
physical
scrubbing

Parameter

PSA

Water
scrubbing

Chemical
scrubbing

Precleaning neededa
Working pressure
(bar)
Methane loss

Methane content in
upgraded gas
Electricity
consumption (kWh/
Nm3) of raw biogas
(7 bar)
Heat requirement (k)
Controllability
compared
to nominal load
Upgrading costb,c
(€/kWh)

Yes
4–7

No
4–7

No
4–7

<3%/6%–10%
>96%

<1%/<2%
>97%

2%–4%
>96%

Yes
No
pressure
0.1%
>99%

0.25

<0.25

0.24–0.33

<0.15

No
Æ10%–15%

No
50%–15%

328–353
10%–100%

433
50%–100%

% 1.6b

% 1.5–1.7b

% 1.2–1.5c

–

% 1.6–1.7b
% 1.2c

Refers to raw biogas with <500 mg/m3 of H2S. For higher concentrations, precleaning is recommended also for the
other techniques.
Biogas capacity ¼ 500 Nm3/h.
c
Biogas capacity ¼ 2000 Nm3/h.
Modified from Urban, W., Girod, K., Lhomann, H., 2008. Technologien und Kosten der Biogasaufberitung und
Einspeisung in das Erdgasnetz. Ergebnisse der Markterhebung 2007–2008. Copyright Fraunhofer UMSICHT.
a

b


290

Bioenergy Systems for the Future

Actually, the use of biomethane as a transport fuel is increasing. The largest markets are in Europe, where roughly 10% of the biomethane produced is used in the
transport sector (EurObserv’ER site website Accessed 19 May 2016). As example,
in Sweden, the biogas used for the transportation has reached 88,744 toe, in Germany
42,992 toe, and 1462 toe in Finland. In addition, Germany and Italy support a strong
infrastructure for natural-gas-based (methane) vehicles with more than 900 natural gas
refueling stations. The upmentioned initiatives can be considered preparatory for an
alternative and more sustainable utilization of the biomethane finalized to the on-site

hydrogen production to feed FCEVs by filling stations based on reforming process.

8.3

Biofuels reforming for distributed hydrogen
production

8.3.1

Steam reforming technology

The catalytic SR is a well-developed and highly commercialized process for largescale application, through which almost all hydrogen worldwide is produced
(Khothari et al., 2008; Sperling and Cannon, 2004). Industrial (chemical and petrochemical) methane steam reforming (MSR) plants have a size ranging between
5000 and 200,000 Nm3/h, which translates into hourly production rates of
450–18,000 kgH2 =h (US DRIVE, 2013). This production plant may enjoy lower production cost, but the cost related to the hydrogen production is mostly linked to the
distribution cost (40%–75%) from the large central plant to the various users. It
includes compression, transport, and storage costs.
However, the small/medium capacity of hydrogen production plants from biofuels
can allow the development of decentralized infrastructures for on-site hydrogen production. In this scenario, renewable hydrogen may be produced in semicentral facilities, located on the edge of urban areas or industrial sites, reducing the cost and
infrastructure needed for hydrogen delivery. Small-scale facilities would produce
from <100 to 1500 kgH2 =day with the production site at the fueling stations
(US DRIVE, 2013). Medium-scale (also known as semicentral or city gate) facilities
would produce from 1500 to 50,000 kgH2 =day on the outskirts of cities (US DRIVE,
2013). The small-/medium-scale steam reformers can be considered as downscaled
versions of the large-scale SR technology. The reforming process simply consists
in transforming hydrocarbons into hydrogen, but important steps as feedstocks purification and hydrogen upgrading must be included in the global system. Thus, the
overall process for hydrogen production from biofuels takes place in four main stages
(see Fig. 8.4): (i) purification of the biofuel, (ii) reforming of the clean biofuel, (iii) CO
cleanup, and (iv) H2 purification.
The purification section has been discussed before and depends on the type of

biofuels. In the steam reforming (SR) unit, the clean biofuel reacts with steam in
the presence of a catalyst to produce a synthesis gas composed mostly of H2 and
CO, by the following general reaction (Eq. 8.1):
Cx Hy Oz + ðx À zÞH2 O ! xCO + ðy=2 + x À zÞH2

À

°
ΔH298
>0

Á

(8.1)


Distributed H2 production from bioalcohols and biomethane

Flue
gas

H2O
tank

291

H2O recovered
Reformer

Heat

exchanger

LTS

Compressor
Raw
biofuel

Purification
unit

H2O

Heat
exchanger

Burner
HTS
Heat
exchanger

Blower

Off gas
tank

separator
PSA

Hydrogen

Fig. 8.4 General flow diagram (purification unit, steam reformer, CO cleanup, and PSA
sections) for H2 production from biofuels.

The amount of steam varies depending on the biofuel. Indeed, the reforming of bioethanol and other bioderived liquid fuels requires higher steam content compared with
the reforming of biomethane (Contreras et al., 2014). The main disadvantage of SR
process is its endothermicity, which means the need for a significant amount of heat
provided by an external source. The process is markedly favored at high temperature,
low pressure, and excess steam to limit carbon deposition. In the conventional largescale plant, the steam reforming reaction is carried out over a catalyst contained in
parallel vertical tubes placed inside a radiant furnace. The heat is usually supplied
by burning part of the fuel feedstock and transferring the liberated heat to the steam
reforming reaction. Similarly, in a small-/medium-scale system, a part of the biofuel
is burned in a combustor thermally integrated with the reforming reactor. Suitable
operating temperatures range between 973 and 1173 K.
Then, the carbon monoxide contained in the hydrogen-rich syngas exiting the
reformer passes through a WGS reactor that converts the CO into H2 and CO2
(Eq. 8.2) by using the steam available in the syngas or additional steam added to
the system. In practice, based on the CO content in the reformate and on the final utilization of the syngas, this cleanup step can include a high-temperature shift (HTS)
reactor operating between 473 and 673 K and a low-temperature-shift (LTS) reactor
operating between 400 and 450 K:
CO + H2 O $ H2 + CO2

À °
Á
ΔH298 ¼ À41kJ=mol

(8.2)

Finally, the dry reformate is cooled to ambient temperature and sent to a purification
unit. PSA is the more adequate technology for H2 separation for capacities of

50–1000 Nm3/h (Xia et al., 2016). Two kinds of PSA are recognized: PSA to separate
H2 and/or PSA to separate CO2, followed by a condensation step to remove the
remaining H2O. Both PSA separation techniques are commercial but energy-intensive
technologies; they can provide various degrees of H2 purity (up to >99%) in dependence of the final utilization (Majlan et al., 2009; Ribeiro et al., 2008; Voss, 2005;
Warmuzinski and Tanczyk, 1997). Besides, unwanted gases, mainly CO2, can be


292

Bioenergy Systems for the Future

removed by using absorbing beds, while the not separated H2 residual fraction can be
recycled as fuel for heat generation in the reforming step. Another promising purification technology capable to produce high H2 purity (>99%) involves the Pd-based
membrane for H2 separation. Unfortunately, this process is considered at moment
uneconomic (Adhikari and Fernando, 2006).
Commercial FP units, following the previously described configuration, have been
developed by several suppliers; these systems are generally designed for distributed
H2 production from natural gas and biogas (Specchia, 2014; Phyrenees Association,
2010). Some of the existing suppliers and the principal characteristics of the FP units
are reported in Table 8.4 (, 2016; , 2016;
, 2016; 2016; http://www.
ztekcorporation.com, 2016).
À The
Á performance of a reforming system can be evaluated by its overall efficiency
ηH2 , calculated by the ratio between the LHV of the hydrogen produced to the LHV
of the fuel consumed (Real et al., 2016; Kolb, 2008), as follows:
ηH2 ¼

nH2 Á LHVH2
nFuel Á LHVFuel

(8.3)

where n are the molar flows and LHV are in units of kJ/mol. The LHV of a CxHyOz
fuel is calculated by the following general equation (Kolb, 2008; Ahmed and
Krumpelt, 2001):
LHVkJ=mol ¼

y
2


+ 2x À z 198:8 + 25:4

(8.4)

The numerical values represent the slope (198.8) and the intercept (25.4) derived from
the linear relationship between LHV and maximum hydrogen yield (y/2+2xÀz)
(Hagh, 2004).
The energy conversion efficiency of large-scale MSR plants is about 75%–80%,
although an efficiency of 85% might be achieved by optimization of heat recovery
and utilization and recycling of the off gas coming out from PSA step (Chaubey
et al., 2013).
A more practical performance measure of a reforming system is the overall thermal
efficiency (ηth), which includes all the other additional energy provided and recovered
(Q) from the system (Northrop et al., 2012):
ηth ¼

nH2 Á LHVH2
nFuel Á LHVFuel + Q

(8.5)

where Q ¼ QReformerÀQRecovered; QReformer is the heat needed to support the reformer
(including the heat for the steam generation), while QRecovered is the heat potentially
recovered from the heat exchange systems. The US Department of Energy (DOE)
adopted a similar definition of efficiency, introducing also the electricity energy delivered to the system (Thomas et al., 2009). Actually, the DOE target related to the


List of suppliers of SR units for distributed hydrogen production

Supplier

Feed

H2 quality
Vol. (%)

HyGear B.V.b
(Netherlands)
Helbio S.A.c (Greece)

Natural gas

99.5–99.999

Biogas

99.9–99.999

Natural gas

99.999%

Natural gas

99.99%

Natural gas
Biogas

99.99%

Mitsubishi Kakoki Kaishae
(Japan)
ZTEKf (United States)
Hyradixg (United States)

H2 capacity
(kg/day)

Dimensionsa
L × W × H (m)

Start-up time cold-warm
load variation

10
224
107

3.5 Â 1.2 Â 2.6
9.1 Â 2.5 Â 2.5
6 Â 2.5 Â 2.5

107
431
36
243
107
215

3.4 Â 2.7 Â 3.3
7.5 Â 8.7 Â 3.3
1.8 Â 1.8 Â 1.8
n.a.d
2.3 Â 5.0 Â 2.5
2.3 Â 6.1 Â 2.5

Max 3 h–max 30 min
20%–100%
n.a.d
n.a.d
4 h–n.a
30%–100%
n.a.d
n.a.d
2 h 45 min–1 h 30 min
30%–100%

Distributed H2 production from bioalcohols and biomethane

Table 8.4

a

Total mounting space including Balance of Plant (Bop).
Accessed 5 July 2016.
Accessed 5 July 2016.
d
n.a. ¼ not available.
e
Accessed 5 July 2016.
f
Accessed 5 July 2016.
g
Accessed 5 July 2016.
b
c

293


294

Bioenergy Systems for the Future

energy efficiency of distributed hydrogen production from natural gas (biomethane) is
fixed at 75% and 70%–75% from biomass-derived liquid fuels by 2020 (http://energy.
gov Accessed 7 July 2016).

8.3.2

H2 production cost and principal technical challenges

On-site hydrogen production is an attractive and versatile way to facilitate the transition to a hydrogen-based economy in the near term. The main advantage in the production of local and near-use hydrogen is the overcoming of the problem related to the
lack of dedicated infrastructures. In addition, the production of distributed hydrogen
through biofuel pathway has low-carbon footprint compared to the hydrogen produced from natural gas or other fossil fuels. To do this, several technology challenges,
such as reducing the cost of the feedstock production/purification, increasing the H2
production efficiency, reducing the H2 costs, and developing active and durable catalyst, need to be overcome. The US DOE set numerical targets regarding the hydrogen
production cost, expressed in $/kg or $/gge (a gallon of gasoline equivalent, gge, is
approximately equal to a kilogram of hydrogen on an energy-content basis). These
targets should serve as guidelines in hydrogen production in both research area and
development/demonstration activities (Ruth and Joseck, 2011; Lomax, 2007). The
cost is independent of the technology pathway and takes into consideration a range
of assumptions for FCEVs to be competitive with gasoline internal combustion engine
vehicles (ICEVs). In the early market time frame of 2015 to $2020, the hydrogen cost
targets have been set up at 7 $/kg, untaxed and dispensed at the pump ( Joseck and
Sutherland, 2015). Considering the DOE technical targets for biomass-derived liquid
fuel ( Accessed 7 July 2016), the cost of distributed production
of hydrogen (plant capacity ¼ 1500 kgH2 =day) from bioethanol reforming could be
reduced from 6 $/kg ( 7.7 $/kg, dispensed) to 2.3 $/kg ( 4 $/kg, dispensed) during
the time frame of 2015–20. In Fig. 8.5 is a reported comparison between the scenario
relative to 2015 and 2020 considering the breakdown of the costs for distributed
hydrogen production by bioethanol reforming.
From the analysis of the data in Fig. 8.5, the target cost of 4 $/kg hydrogen
delivered and dispensed could be achieved if the feedstock cost is reduced and the
equipment cost and efficiency targets are met.
Similar considerations can be done for the distributed hydrogen (plant
capacity ¼ 1500 kgH2 =day) produced from biomethane obtained by biogas upgrading.

In general, because of the wide variety in resource quality and accessibility, there is
considerable uncertainty and subjectivity in estimating biomethane extraction costs
from biogas sources. Murray et al. (2014) estimate this cost including recovery,
upgrading, and purification; the production costs of biomethane from WWTPs depend
on the facility size, due to economies of scale, the granularity of unit operations,
and the diminishing returns. Considering plant with a capacity between 10 and
200 million gallons per day (MGD), the cost of biomethane varies between 1.4
and 2.9 $/MMBtu. Hydrogen production cost from biomethane using MSR is estimated equal to 2.94 $/kg (4.73 $/kg, dispensed) for a reforming small-scale plant


Distributed H2 production from bioalcohols and biomethane

295

(a) Feedstock : 5.1 (66%)

(d) O&M: 0.2 (3%)

(c) Capital cost: 0.7 (9%)

(b) CSD: 1.7 (22%)
2015
(a) Feedstock : 1.6 (39%)

(d) O&M: 0.2 (5%)

(b) CSD: 1.7 (43%)

(c) Capital cost: 0.5 (13%)

2020

Fig. 8.5 Breakdown ((a) ¼ feedstock cost; (b) ¼ compression, storage, and dispensing, CSD;
(c) ¼ production unit capital cost; and (d) ¼ operation and maintenance, O&M, cost) of H2 costs
in $/kg for distributed hydrogen production (1500 kgH2 =day) from bioethanol reforming (http://
www.energy.gov Accessed 7 July 2016).

(1500 kgH2 =day) (Milbrandt et al., 2016; Accessed
14 July 2016). The production cost decreases by increasing the plant capacity (0.89 $/kg
for a plant of 50,000kgH2 =day). In Fig. 8.6 is a reported breakdown of the costs for
distributed hydrogen production by biomethane reforming. The feedstock cost (biomethane) is lower compared with the cost of bioethanol (Fig. 8.7, 2015 scenario),
while the other cost contributions are similar. The cost of hydrogen production from


296

Bioenergy Systems for the Future

(a) Feedstock : 2.03 (42%)

(d) O&M: 0.31 (7%)

(b) CSD: 1.79 (38%)

(c) Capital cost: 0.6 (13%)

Fig. 8.6 Breakdown ((a) ¼ feedstock cost; (b) ¼ compression, storage, and dispensing, CSD;
(c) ¼ production unit capital cost; and (d) ¼ operation and maintenance, O&M, cost) of H2 costs
in $/kg for distributed hydrogen production (1500 kgH2 =day) from biomethane and natural gas
reforming ( Accessed 14 July 2016).

CH3CHO
–H2
CH3CH2OH
–H2O
CH2CH2

CH4 + CO
+H2O
CO + H2

+H2O

CO2 + H2

+H2O
coke

Fig. 8.7 Proposed reaction mechanism for ethanol steam reforming.

biomethane strongly depends on the chemical composition of biogas, which mainly
affects the operating and maintenance (O&M) cost, related to purification/upgrading
treatments. In general, the O&M cost should be reduced by developing more flexible
systems. In addition, the composition of biogas can vary during the annual production,
affecting the performance and the stability of the catalytic reformer.
The reliability of balance of plant (BOP) equipment (pumps, compressors, blowers,
sensors, etc.) is often the limiting factor in overall system reliability. Another technical
aspect to address regard the physical footprint of the reforming plant. As reported in
Table 8.4, suppliers have recently improved the compactness and the capacity of
small-scale reformers, but further improvements are needed to reduce costs and to

increase efficiency. Also control and safety issues, including on-off cycling, require
improvement. Effective operation control strategies are fundamental to minimize cost
and emissions, to maximize efficiency, and to enhance safety, but costs still remain
high due to complex system designs and high-cost sensors. In addition, SR and


Distributed H2 production from bioalcohols and biomethane

297

WGS unit operations also generate considerable costs, which can be lowered by developing catalysts capable of increasing the activity performances in term of H2 yield.

8.4

Novel catalytic formulations for steam reforming
process

8.4.1

Bioalcohols

8.4.1.1 Bioethanol
The bioethanol steam reforming (ESR) reactions are listed in Eqs. (8.6), (8.7), in
which ethanol reacts with steam to form CO and H2 (Eq. 8.6), producing 4 mol of
hydrogen for 1 mol of ethanol reacted. The CO then reacts with steam in the WGS
reaction (Eq. 8.2) to form CO2 and additional H2. The overall reaction of hydrogen
production by steam reforming of bioethanol (Eq. 8.7) is obtained by adding
Eqs. (8.2), (8.6), according to which the maximum yield of hydrogen is 6 mol for
1 mol of ethanol reacted (Banach and Machocki, 2015). This involves the total
CO conversion to CO2:

CH3 CH2 OH + H2 O ! 2CO + 4H2

À

CH3 CH2 OH + 3H2 O ! 2CO2 + 6H2

°
ΔH298
¼ À14 kJ=mol

À

Á

°
ΔH298
¼ 174 kJ=mol

(8.6)
Á

(8.7)

This reaction is highly endothermic (ΔH ¼ 174 kJ/mol) and presents significant differences to the steam reforming of biomethane due to the presence of a CdC bond
and oxygen atom in ethanol (Bej et al., 2014). Nevertheless, the reaction mechanism
is complex and is comprised by several secondary reactions (Eqs. (8.8)–(8.20):
Methanation : CO + 3H2 $ CH4 + H2 O

(8.8)

Methane steam reforming : CH4 + H2 O ! CO + 3H2

(8.9)

Acetic acid formation : CH3 CH2 OH + H2 O ! CH3 COOH + 2H2

(8.10)

Decomposition to methane : CH3 CH2 OH ! CH4 + CO + H2

(8.11)

Dehydration to ethylene : CH3 CH2 OH ! CH2 CH2 + H2 O

(8.12)

Ethylene steam reforming : CH2 CH2 + H2 O ! 2CO + 4H2

(8.13)

Dehydrogenation to acetaldehyde : CH3 CH2 OH ! CH3 CHO + H2

(8.14)

Acetaldehyde decomposition : CH3 CHO ! CH4 + CO

(8.15)

Condensation to acetone : 2CH3 CH2 OH ! CH3 COCH3 + CO + 3H2

(8.16)


298

Bioenergy Systems for the Future

The final hydrogen yield/efficiency depends on the operating conditions, mostly
because of the equilibrium of WGS and methanation reactions (Eqs. (8.2), (8.8)).
Moreover, it is strictly connected to the intensity of the secondary reactions
(Eqs. 8.8–8.20), which can produce by-products (e.g., carbon monoxide, methane,
acetaldehyde, acetone, and ethylene), thus reducing H2 yield and causing catalyst
deactivation by coke deposition (Montero et al., 2015). Carbon formation is affected
by the Boudouard reaction (Eq. 8.17), methane cracking (Eq. 8.18), ethylene decomposition (Eq. 8.19), and carbon gasification (Eq. 8.20):
Boudouard reaction : 2CO $ CO2 + C

(8.17)

Methane cracking : CH4 $ C + 2H2

(8.18)

Ethylene decomposition : CH2 CH2 ! 2C + 2H2

(8.19)

Carbon gasification : C + H2 O ! CO + H2

(8.20)

0.8
0.7

H2

CH4

0.6

Products composition (dry-basis)

Products composition (dry-basis)

Several reaction mechanisms have been proposed for ethanol steam reforming,
depending on the catalyst and operating conditions (Hou et al., 2015; Contreras
et al. 2014; Vizcaı´no et al., 2007; Vaidya and Rodrigues, 2006). For example, in
the scheme reported in Fig. 8.7, ethanol is dehydrated to ethylene and dehydrogenated
to acetaldehyde, which subsequently decomposes to CH4 and CO. Coke is generated
from ethylene decomposition and CO disproportion, while the formation of H2 and
CO2 is due to SR and WGS reactions. Complete ethanol conversion is essential for
the process to be economic, and the catalyst has an important role in getting this goal
because it increases the rate of reaction in such a way that the system tends toward
thermodynamic equilibrium (Contreras et al., 2014).
The equilibrium composition, calculated at fixed steam/EtOH molar ratio equal to
one, varying temperature (570–1170 K) and pressure (1–10 bar), is reported in
Fig. 8.8. The calculation has been done by using a commercial steady-state simulation
package named Aspen Plus, based on the minimization of Gibbs free energy of each of
the existing species. Values are expressed as molar fraction on dry basis for a system

0.5

0.4
0.3

CO
CO2

0.2
0.1
0.0
570

(A)

670

770

870

970

Temperature (K)

1070

0.8
0.7

CH4

0.6

H2

0.5
0.4

CO

CO2

0.3
0.2
0.1
0.0

1170

570

(B)

670

770

870

970

1070

1170

Temperature (K)

Fig. 8.8 Evolution of product distribution with temperature from ethanol steam reforming at
steam/EtOH ¼ 1/1 (molar ratio) and atmospheric pressure (A) or at a pressure of 10 bar (B).


Distributed H2 production from bioalcohols and biomethane

299

composed of CH3CH2OH, H2O, H2, CO, CO2, CH4, and by-products. Ethanol was
found absent from products distribution in every case. Hydrogen concentration
increases by increasing temperature. Analogously, CO concentration increases, while
CO2 and CH4 concentrations decrease with temperature. Moreover, other by-products
(e.g., ethylene, acetaldehyde, and acetone) were found absent from product distribution (maximum molar fraction 10À6). It can be noticed that H2 concentration decreases
by increasing pressure mainly due to lower methane conversion.
The hydrogen yield was calculated based on the theoretical stoichiometric maximum of ethanol conversion (SR and WGS) to H2 and CO2 (H2/EtOH ¼ 6 mol/mol),
toward the equation H2,OUT/(6ÁEtOH,IN). Fig. 8.9 shows the H2 yield calculated varying temperature (570–1170 K) and steam-to-carbon molar ratio (steam/EtOH from 1
to 5). H2 yield increases noticeably with temperature until a maximum is reached (in
the 870–1170 K range, depending on the steam/EtOH molar ratio) by promoting
effectively both SR and WGS reactions. The maximum H2 yield is reached at lower
temperature as the steam/EtOH ratio is increased.
There are numerous papers in literature regarding catalysts for ESR, some of which
are reported in Table 8.5. Among the studied active phases, both noble metal-based
catalysts (e.g., Ru, Rh, Pd, Pt, and Ir) and nonnoble metal-based catalysts (Ni and Co)
are found to be promising candidates for ESR reactions. Moreover, the behavior of

active phases over different supports (e.g., Al2O3, SiO2, TiO2, CeO2, and Nb2O5) has
been investigated. As reported by Contreras et al. (2014), catalysts with the best
performance are characterized by (i) the best active metals and (ii) the best support with
special surface characteristics. Moreover, the preparation method and the operative conditions can help to increase hydrogen selectivity, reducing the formation of coke
and by-products. Among all noble metals, Rh catalysts are more active and selective
to H2 production, favoring the CdC bond cleavage. Ruthenium shows performance
similar to rhodium but rapidly deactivates by coke deposition (Coronel et al., 2014).
100
Steam/EtOH = 5
80

YH2 (%)

Steam/EtOH = 3
60
Steam/EtOH = 1
40
20
0
570

670

770

870

970

1070

1170

Temperature (K)

Fig. 8.9 Evolution of hydrogen yield with temperature from ethanol steam reforming at
atmospheric pressure under different steam/EtOH molar ratios.


Table 8.5

Catalysts for ethanol steam reforming
Chemichal
physical
properties

Operative conditions

Catalyst

S/C

T (K)

GHSV (h21)

BET
(m2/g)

Particle

size
(nm)

Catalytic results
ΧEthanol
(%)

H2 content (%)

By-products

Carbon
deposition
(mgC/gcat)

1 wt%
1.5
973
150,000 Nml gÀ1 hÀ1
130
n.a.
100
72
C2
n.a.
Rh/Al2O3
Rh catalysts is very active and selective to hydrogen production. The reaction proceeds through formation of both acetate as well as formate species
both of which decompose at much higher temperatures causing carbon deposition on the catalyst surface. The decrease of coke on the catalysts is related
with the presence of basic sites on the support. The sequence of activity of Rh supported catalysts is: CeO2-ZrO2 > CeO2-Al2O3 > CeO2 > Al2O3
(Aupr^etre et al., 2002)

1.5
773
26,000
171
1.9
100
72
Traces of C2 6.1
1 wt% Rh/
CeO2Al2O3
The presence of CeO2 disfavors the dehydration reaction observed in base Al2O3, lowering the selectivity to ethylene and increasing catalyst stability.
Due to the high oxygen storage capacity and mobility, CeO2 promoter contribute to coke gasification allowing to recover the acid metallic sites covered
by carbon deposit (Osorio-Vargas et al., 2015a)
1.5
773
26,000
99
1.5
100
70
–
1.1
1 wt% Rh/
La2O3Al2O3
La2O3 promoter suppresses the formation of carbon, due to the presence of La2O2CO3 specie that can reacts with carbon-metal species formed in its
vicinity to produce CO. Thus, La2O3 acts as an intermediate, promoting the reaction between the carbon species and CO2 (Osorio-Vargas et al., 2015a)
1.5
973
150,000 Nml gÀ1 hÀ1
130

n.a.
100
46
1 wt% Pt/
Al2O3
Pt is an efficient catalyst in WGS reaction but it has only limited activity in ESR (Aupr^etre et al., 2002)
0.6 wt%
Rh/La2O3SiO2

1.5

773

200,000 Nml gÀ1 hÀ1

88

1.4

100

56

C2

n.a.

C2

0.4

Rhodium deactivates by coke formation, due to the presence of metal particles covered by carbon deposit uniformly distributed on the deactivated
catalyst. The catalytic activity depends on metal particle size. By the addition of a low amount of cerium to the catalyst, it was possible to inhibit Rh
oxidation and to increase the metallic dispersion due to the interaction of the promoting oxide with the active phase; however, it did not improve the
stability under reaction conditions (Coronel et al. 2014)
1.5
923
72,000 Nml gÀ1 hÀ1
77
6
70
45
n.a.
5
2 wt%
Ir/CeO2
Catalytic activity and selectivity are due to various factors, depending on the time on stream and the operating conditions. Moderate deactivation is
observed during the initial period on stream (about 2 h) due to a loss of ceria surface. Upon longer testing periods (from 2 to 60 h), a slow and continuous
sintering of the Ir particles and the ceria crystallites leads to an irreversible deactivation essentially due to the degradation of the metal/ceria interface
(Wang et al., 2012)
1.5
973
360,000 Nml gÀ1 hÀ1
n.a.
<2
100
6 molH2 =molEthanol n.a.
20 wt%
2.5 wt%

Ru/Al2O3
The good catalytic performance is due to the extremely small sizes of the supported metallic nanoparticles. Catalysts deactivates by coking phenomena,
probably related to the sintering of active phase (Koh et al., 2008)
1.5
1010
10,600
232
12
98
87
C2
2 wt%
5 wt%
Ni/Al2O3
NI catalyst is active and selective to hydrogen production. The Lewis acid sites of Al2O3 produced ethylene leading to coke formation (Wu et al., 2015)
1.5
773
26,000
99
13
98
76
C2
4.2
10 wt%
Ni/La2O3CeO2Al2O3
The low capacity to break the CdC bond of Ni/Al2O3 catalyst can be explained by an early deactivation of the catalyst from the beginning of the
reaction due to the formation of ethylene by ethanol dehydration and its subsequent polymerization reactions that block the catalyst metal sites
responsible from CdC breaking reaction. The addition of La2O3 and CeO2 to Ni/Al2O3 catalyst induced several changes in the acid-base properties of
the support, which disfavours ethanol dehydration route (Osorio-Vargas et al., 2015b)

1 wt% Ni/
Mg(Al)O

2

723

3600 Nml gÀ1 hÀ1

226

n.a.

80

48

Traces of C2

n.a.
Continued


Table 8.5

Continued

Operative conditions

Catalyst

S/C

T (K)

GHSV (h21)

Chemichal
physical
properties

BET
(m2/g)

Particle
size
(nm)

Catalytic results
ΧEthanol
(%)

H2 content (%)

By-products

Carbon
deposition
(mgC/gcat)

The conversion order Ni > Co is due to the favored CdC bond rupture. Basic MgO inhibits ethanol dehydration to ethylene and greatly reduces coke
formation (Contreras et al., 2014)
873
n.a.
53
24
90
4 molH2 =molEthanol C2
70
20 wt% Co/ 1.5
CeO2Al2O3
Products selectivity is related to the surface area and the crystallite size. Al2O3 support is characterized by high specific surface area and low cost. CeO2
leads to a low formation of CO, owing to the higher mobility of oxygen in the solid solution but it shows small surface area. The combination of CeO2
with Al2O3 leads to the development of support material that possesses interesting mixtures of the properties of these two supports (Maia et al., 2014)
6.5
873
9.2 Kgcat h/Kg molethanol 15
48 (Ni)
86
73
n.a.
25
1 wt%
crude
Rh-30 wt%
ethanol
Ni/CeO2ZrO2
The promoter effect of Rh on ethanol conversion can be related to its ability for breaking the CdC bonds. Reducible CeO2-ZrO2 mixed oxide possesses
potential applications as catalyst support due to their high oxygen storage-release capacity and thermal and mechanical stability (Mondal et al., 2015)
1.5

573
18,000 Nml gÀ1 hÀ1
36
12 (Ni)
69
43
C2
0.1
1 wt%
Pt-10 wt%
Ni/CeO2
Ni/CeO2 catalyst significantly deactivates due to the formation of nickel carbide phase as well as the build up of adsorbed acetates on the support. Pt
addition improves catalyst activity and stability by minimizing the formation of nickel carbide and by promoting the decomposition of acetate species to
hydrogen (Moraes et al., 2015)


Distributed H2 production from bioalcohols and biomethane

303

Platinum is less active, but it catalyzes also the WGS reaction, which is important for
CO removal. Its activity is significantly affected by the size of the metal crystallites
(Kourtelesis et al., 2015; Aupr^etre et al., 2002). Regarding the support, a stronger
metal interaction with weaker surface acidity leads to low-carbon deposition and
high hydrogen production, determining the following order of activity: Rh/CeO2Al2O3 > Rh/CeO2 > Rh/Al2O3. CeO2 disfavors the dehydration reaction, responsible
for ethylene production and consequent carbon deposition. Moreover, it contributes
to coke gasification, recovering the metallic sites blocked by coke. These properties
are closely related to the high oxygen storage capacity (OSC) and oxygen mobility
(OM), allowing the rapid reduction/oxidation capability due to the release and uptake
of oxygen owing to the reversible reaction (Sharma et al., 2016; Osorio-Vargas et al.,

2015a). Other authors determine the following order of activity: Rh/Y2O3 > Rh/
CeO2 > Rh/La2O3 > Rh/Al2O3.
Although noble metal-based catalysts exhibit outstanding activity and stability for
ESR, their utilization at large scales is limited by their high costs (Contreras et al.,
2014). Nonnoble metal-based catalysts, especially Ni-based catalysts, are widely
employed in the reforming process due to their low costs, wide availability, and excellent capability for CdC and CdH bond rupture. However, Ni-based catalysts generally
suffer rapid deactivation caused by sintering of active nickel species and coke deposition (Li et al., 2015). Enormous efforts have been made to increase the resistance to
carbon formation and sintering of the Ni catalysts, for example, via regulating surface
composition, tuning particle sizes and shapes, enhancing metal-support interaction, and
fabricating the hierarchical structure of the catalysts (Zhang et al., 2014). Particularly,
the support provides surface area and promotes OH group migration toward the metal in
the presence of water. Al2O3 support produces ethylene on the acid sites leading to coke
formation. The addition of basic MgO and ZnO inhibits ethanol dehydration to ethylene
and carbon formation. Reducible oxides, such as CeO2, ZrO2, and CeO2-ZrO2 mixed
oxides, possess potential applications as catalyst support due to their high oxygen
storage-release capacity and thermal and mechanical stability. La2O3 promotes dehydrogenation hindering carbon formation (Ohno et al., 2016; Osorio-Vargas et al.,
2015a,b; Contreras et al., 2014). Furthermore, the activity and stability of supported
monometallic catalysts can be improved by adding another metal to overcome the deactivation phenomena (Mondal et al., 2015; Moraes et al., 2015).

8.4.1.2 Biobutanol
n-Butanol is a linear chain compound with four carbons and one terminal OH group.
n-Butanol has high H2 content (13.51 wt%), lower vapor pressure, tolerance to water
contamination, low corrosivity, high energy density, low hygroscopicity, and ease in
handling and distribution to existing fuel pipelines (Horng et al., 2016). n-Butanol
steam reforming (BSR) produces 8 mol of hydrogen from 1 mol of butanol reacted,
according to the following reaction:
C4 H9 OH + 3H2 O ! 4CO + 8H2

À

°
ΔH298
¼ 558:3 kJ=mol

Á

(8.21)