hydrogen production technologies: current state and future

Hindawi Publishing CorporationConference Papers in EnergyVolume 2013 Article ID 690627 9 pageshttpdxdoiorg1011552013690627

Conference PaperHydrogen Production Technologies Current State andFuture Developments

Christos M Kalamaras and Angelos M Efstathiou

Chemistry Department University of Cyprus 1678 Nicosia Cyprus

Correspondence should be addressed to Angelos M Efstathiou efstathucyaccy

Received 9 January 2013 Accepted 31 March 2013

Academic Editors Y Al-Assaf and A Poullikkas

This Conference Paper is based on a presentation given by ChristosM Kalamaras at ldquoPower Options for the EasternMediterraneanRegionrdquo held from 19 November 2012 to 21 November 2012 in Limassol Cyprus

Copyright copy 2013 C M Kalamaras and A M Efstathiou This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Hydrogen (H2) is currently used mainly in the chemical industry for the production of ammonia and methanol Nevertheless in

the near future hydrogen is expected to become a significant fuel that will largely contribute to the quality of atmospheric airHydrogen as a chemical element (H) is the most widespread one on the earth and as molecular dihydrogen (H

2) can be obtained

from a number of sources both renewable and nonrenewable by various processes Hydrogen global production has so far beendominated by fossil fuels with the most significant contemporary technologies being the steam reforming of hydrocarbons (egnatural gas) Pure hydrogen is also produced by electrolysis of water an energy demanding process This work reviews the currenttechnologies used for hydrogen (H

2) production from both fossil and renewable biomass resources including reforming (steam

partial oxidation autothermal plasma and aqueous phase) and pyrolysis In addition othermethods for generating hydrogen (egelectrolysis of water) and purification methods such as desulfurization and water-gas shift reactions are discussed

1 Introduction

Hydrogen is the simplest and most abundant element onearth Hydrogen combines readily with other chemical ele-ments and it is always found as part of another substancesuch as water hydrocarbon or alcohol Hydrogen is alsofound in natural biomass which includes plants and animalsFor this reason it is considered as an energy carrier and notas an energy source

Hydrogen can be produced using diverse domesticresources including nuclear natural gas and coal biomassand other renewable sources The latter include solar windhydroelectric or geothermal energyThis diversity of domes-tic energy sources makes hydrogen a promising energycarrier and important for energy security It is desirable thathydrogen be produced using a variety of resources and pro-cess technologies or pathways The production of hydrogencan be achieved via various process technologies includingthermal (natural gas reforming renewable liquid and biooil

processing biomass and coal gasification) electrolytic (watersplitting using a variety of energy resources) and photolytic(splitting of water using sunlight through biological andelectrochemical materials)

The annual production of hydrogen is estimated to beabout 55 million tons with its consumption increasing byapproximately 6 per year Hydrogen can be produced inmany ways from a broad spectrum of initial raw materi-als Nowadays hydrogen is mainly produced by the steamreforming of natural gas a process which leads to massiveemissions of greenhouse gases [1 2] Close to 50 ofthe global demand for hydrogen is currently generated viasteam reforming of natural gas about 30 from oilnaphthareforming from refinerychemical industrial off-gases 18from coal gasification 39 from water electrolysis and 01from other sources [3] Electrolytic and plasma processesdemonstrate a high efficiency for hydrogen productionbut unfortunately they are considered as energy intensiveprocesses [4]

2 Conference Papers in Energy

The fundamental question lies in the development ofalternative technologies for hydrogen production to thosebased on fossil fuels especially for its utilization as a fuelin the transportation sector This problem can be faced bythe utilization of alternative renewable resources and relatedmethods of production such as the gasification or pyrolysisof biomass electrolytic photolytic and thermal crackingof water However it is not possible to consider only theecological perspective since for example photolytic crackingof water is environmentally friendly but its efficiency forindustrial use is very low It is thus clear that the processes tobe taken into account must consider not only environmentalconcerns but also the most favorable economics

2 Hydrogen from Fossil Fuels

Fossil fuel processing technologies convert hydrogen- con-taining materials derived from fossil fuels such as gasolinehydrocarbons methanol or ethanol into a hydrogen-richgas stream Fuel processing of methane (natural gas) is themost common commercial hydrogen production technologytoday Most fossil fuels contain a certain amount of sulfurthe removal of which is a significant task in the planningof hydrogen-based economy As a result the desulfurizationprocess will also be discussed In addition the very promisingplasma reforming technology recently developed will also bepresented

Hydrogen gas can be produced from hydrocarbon fuelsthrough three basic technologies (i) steam reforming (SR)(ii) partial oxidation (POX) and (iii) autothermal reforming(ATR) These technologies produce a great deal of carbonmonoxide (CO) Thus in a subsequent step one or morechemical reactors are used to largely convert CO into carbondioxide (CO

2) via the water-gas shift (WGS) and preferen-

tial oxidation (PrOx) or methanation reactions which aredescribed later

21 Steam Reforming Steam reforming is currently one ofthe most widespread and at the same time least expensiveprocesses for hydrogen production [5] Its advantage arisesfrom the high efficiency of its operation and the low oper-ational and production costs The most frequently used rawmaterials are natural gas and lighter hydrocarbonsmethanoland other oxygenated hydrocarbons [6] The network ofreforming reactions for hydrocarbons and methanol used asfeedstock is the following [7]

C119898H119899+ 119898H

2O (g) 997888rarr 119898CO + (119898 + 05 119899)H

2 (1)

C119898H119899+ 2119898H

2O (g) 997888rarr 119898CO

2+ (2119898 + 05 119899)H

2 (2)

CO + H2O (g) larrrarr CO

2+H2 (3)

CH3OH +H

2O (g) larrrarr CO

2+ 3H2 (4)

Thewhole process comprises two stages In the first stagethe hydrocarbon raw material is mixed with steam and fedin a tubular catalytic reactor [8] During this process syngas(H2CO gas mixture) is produced with lower content in CO

2

((1) and (2)) The required reaction temperature is achieved

by the addition of oxygen or air for combusting part of theraw material (heating gas) inside the reactor In the secondstage the cooled product gas is fed into the CO catalyticconverter where carbon monoxide is converted to a largeextent by means of steam into carbon dioxide and hydrogen(3) The steam reforming catalytic process requires a rawmaterial free of sulfur-containing compounds in order toavoid deactivation of the catalyst used

The SR process requires modest temperatures for exam-ple 180∘C for methanol and oxygenated hydrocarbons andmore than 500∘C formost conventional hydrocarbons [9 10]The catalysts used can be divided into two types nonpreciousmetal (typically nickel) and precious metals fromGroup VIIIelements (typically platinumor rhodium)Due to severemassand heat transfer limitations conventional steam reformersare limited by the effectiveness factor of pelletized catalystswhich is typically less than 5 [11]Therefore kinetics is rarelythe limiting factor with conventional steam reformer reactors[12] and therefore less expensive nickel catalysts are usedindustrially

An important factor characterizing the SR process is theH C atom ratio in the feedstock material The higher thisratio is the lower carbon dioxide emission is formed Amembrane reactor can replace both reactors in a conventionalSR process for achieving the overall reaction (2) [13] Theheat efficiency of hydrogen production by the SR of methaneprocess on an industrial scale is around 70ndash85 [14] Anumber of other raw materials are also possible to achievethis efficiency in the near future such as solid communalwaste wastes from food industry oils purposefully cultivatedor waste agricultural biomass and fuels of fossil origin suchas coal The disadvantage is the high production of CO

2 ca

705 kg CO2kg H

2

22 Partial Oxidation Partial oxidation (POX) and catalyticpartial oxidation (CPOX) of hydrocarbons have been pro-posed in hydrogen production for automobile fuel cells andsome other commercial applications [15 16] The gasifiedraw material can be methane and biogas but primarily heavyoil fractions (eg vacuum remnants heating oil) whosefurther treatment and utilization are difficult [17] POX is anoncatalytic process in which the raw material is gasifiedin the presence of oxygen ((5) and (6)) and possibly steam((7) ATR) at temperatures in the 1300ndash1500∘C range andpressures in the 3ndash8MPa range In comparisonwith the steamreforming (H

2 CO = 3 1) more CO is produced (H

2 CO =

1 1 or 2 1) The process is therefore complemented by theconversion of CO with steam into H

2and CO

2 This reaction

contributes to the maintenance of equilibrium between theindividual reaction products [18]

CH4+O2997888rarr CO + 2H

2 (5)

CH4+ 2O2997888rarr CO

2+ 2H2O (6)

CH4+H2O (g) 997888rarr CO + 3H

2 (7)

The gaseous mixture formed through partial oxidationcontains CO CO

2 H2O H2 CH4 hydrogen sulfide (H

2S)

and carbon oxysulfide (COS) A part of the gas is burned

Conference Papers in Energy 3

to provide enough heat for the endothermic processesThe soot created by the decomposition of acetylene as anintermediate product is an undesired product Its amountdepends on the proportion of H C in the initial raw fuelmaterial There has been therefore like with the SR anendeavor to shift to raw materials containing a higher H Cratio for example to natural gas While the operation ofthe reactor is less expensive in comparison with the steamreforming the subsequent conversion makes this technologymore expensive Since the process does not require the useof a catalyst it is not necessary to remove sulfurous elementsfrom natural gas which lowers the efficiency of the catalystThe sulfurous compounds contained in the gasified rawmaterial are converted into hydrogen sulfide (ca 95) andcarbon oxysulfide (ca 5) [19]

Catalysts can be added to the partial oxidation system(CPOX) in order to lower the operating temperature ca700ndash1000∘C However temperature control is proving hardbecause of coke and hot spot formation due to the exothermicnature of the reactions [10 15 16 20] For natural gasconversion the catalysts are typically based on Ni or RhHowever nickel has a strong tendency to coke and thecost of Rh has increased significantly Krummenacher etal [16] had succeeded in using catalytic partial oxidationfor decane hexadecane and diesel fuel The high operatingtemperatures (gt800∘C) [16] and safety concerns may maketheir use for practical and compact portable devices difficultdue to thermal management [21] Typically the thermalefficiency of POX reactors with methane as fuel lies in therange of 60ndash75 [22]

23 Autothermal Reforming As previouslymentioned in theautothermal reforming (ATR) steam is added in the catalyticpartial oxidation process ATR is a combination of both steamreforming (endothermic) and partial oxidation (exothermic)reactions [23] ATR has the advantages of not requiringexternal heat and being simpler and less expensive than SRof methane

The range of operation of a fuel processor for hydrogenproduction is depicted in Figure 1 The selection of operationconditions of the reformer depends on the specific targetA main target is the high hydrogen yield with low carbonmonoxide content Maximum hydrogen efficiency and lowcarbon monoxide content are possible for steam reformingHowever steam reforming is an endothermic process andtherefore energy demanding This energy has to be trans-ferred into the system from the outside

Another significant advantage of ATR over SR processis that it can be shut down and started very rapidly whileproducing a larger amount of hydrogen than POX alone [23]There are some expectations that this process will becomeattractive for the ldquoGas to Liquidrdquo fuel industry due to favor-able gas composition for the Fischer-Tropsch synthesis ATRrsquosrelative compactness lower capital cost and the potential foreconomies of scale [24] For methane reforming the thermalefficiency is comparable to that of POX (ca 60ndash75) andslightly less than that of steam reforming Gasoline and otherhigher hydrocarbons may be converted into hydrogen on

EndothermicEndothermic

Total oxidation Steam reforming

Partialoxidation

Oxidativesteam reforming

Autothermal reforming

nhydrogen = 0 nhydrogen = maximum

119876heat = minimum

Figure 1 Operating conditions for POX ATR and SR

board for use in automobiles by the autothermal processusing suitable catalysts [25]

24Water-Gas Shift PreferentialOxidation andMethanationThe reforming process produces a product gas mixturewith significant concentrations of carbon monoxide often5 vol or more (ca 10 vol) [10] To increase the amount ofhydrogen the product gas is passed through a water-gas shift(WGS) reactor to decrease the carbon monoxide contentwhile at the same time increasing the hydrogen content (3)Typically a high temperature is desired in order to favor fastkinetics However this results in high equilibrium carbonmonoxide selectivity and decreased hydrogen product yieldTherefore the reduction in the CO content of syngas isachieved in a two-step process that involves a high- and alow-temperature water-gas shift reaction known as ldquoHTSrdquoand ldquoLTSrdquo processes respectively (Figure 2) In the firststep carried out in the 310ndash450∘C range with the use ofFe3O4Cr2O3catalyst the CO concentration is reduced from

10 to 3 vol In the second step carried out in the 180ndash250∘Crange the CO content is further reduced to the low level of500 ppm using CuZnOAl

2O3catalysts [26]

To further reduce the carbon monoxide content in theproduct gas a preferential oxidation (PrOx) reactor or acarbon monoxide selective methanation reactor is used [1027] Sometimes the term selective oxidation is used in placeof preferential oxidation Selective oxidation refers to carbonmonoxide reduction within a fuel cell typically a protonexchange membrane (PEM) fuel cell whereas preferentialoxidation occurs in a reactor external to the fuel cell [27]ThePrOx and methanation reactors have their own advantagesand challenges The preferential oxidation reactor increasesthe systemrsquos complexity because precise concentrations ofair must be added to the system [10 27] However thesereactors are compact and if excessive air is introduced somehydrogen is burned

Methanation reactors are simpler in that no air isrequired However for every CO reacted three H

2molecules

are consumed Also CO2reacts with hydrogen and careful

control of reactorrsquos conditions needs to be maintained inorder to minimize unnecessary consumption of hydrogenCurrently preferential oxidation is the primary technique indevelopment [27] The catalysts are typically noble metalssuch as platinum ruthenium or rhodium supported onAl2O3[10 27] At the same time H

2is purified by alternative


Steam reforming

catalyst Ni

oxidation or

methanationH2O

CH4

+ 700-800∘C

PreferentialWGS reactor

H2O(g)CO119909 + H2

HTS LT

S

Figure 2 A diagram of methane steam reforming with subsequentcarbon monoxide conversion into carbon dioxide and hydrogen

approaches namely pressure-swing adsorption cryogenicdistillation and membrane technologies which can ensurethe necessary purity of hydrogen (ca 98-99) The mostadvantageous gas-purification method is the pressure-swingadsorption for its high efficiency (gt9999) and flexibility

25 Desulfurization As discussed before current hydrogenproduction arises primarily from the processing of naturalgas although with the substantial advances in fuel cells thereis an increased attention to other fuels such as methanolpropane gasoline and logistic fuels such as jet-A dieseland JP8 [28] With the exception of methanol all of thesefuels contain some amount of sulfur with the specific sulfur-containing compounds dependent on the fuel type andsource For this reason desulfurization is considered as a veryimportant step in fuel processing technologies

The desulfurization processes can be classified based onthe nature of the key physicochemical process used for sulfurremoval (Figure 3)Themost developed and commercializedtechnologies are those that catalytically convert organosulfurcompounds with sulfur elimination Such catalytic conver-sion technologies include conventional hydrodesulfurization(HDS) hydrotreating with advanced catalysts andor reactordesigns and a combination of hydrotreating with someadditional chemical processes to maintain fuel specifications[29 30] The main feature of the technologies of the secondtype is the application of physicochemical processes differentin nature from catalytic HDS to separate andor trans-form organosulfur compounds from refinery streams Suchtechnologies include as a key step distillation alkylationoxidation extraction adsorption or combination of these[31]

26 Plasma Reforming In the case of plasma reformingthe network of reforming reactions is the same as that inconventional reforming However energy and free radicalsused for the reforming reaction are provided by plasmatypically generated with electricity or heat [32ndash35] Whenwater or steam is injected with the fuel H∙ OH∙ and O∙radicals in addition to electrons are formed thus creatingconditions for both reductive and oxidative reactions tooccur Plasma reforming technologies have been developed tofacilitate POX ATR and steam reforming with the majorityof the reactors being POX and ATR [35]There are essentiallytwo main categories of plasma reforming namely thermaland nonthermal [35]

Desulfurization

Conventional HDS

HDS by advanced catalysts

HDS by advanced

HDS with fuel

Catalytic distillation

Alkylation

Extraction

Oxidation

Adsorption

Catalytic transformationwith S elimination

Physicochemical separationtransformation of S-compounds

Precipitationspecification recovery

reactor design

Figure 3 Desulfurization technologies classified by the nature ofthe key process to remove sulfur

Plasma devices referred to as plasmatrons can generatevery high temperatures (ca gt2000∘C) with a high degreeof control using electricity [32ndash35] The heat generated isindependent of reaction chemistry and optimal operatingconditions can be maintained over a wide range of feedrates and gas compositions Compactness of the plasmareformer is ensured by high energy density associated withthe plasma itself and by the reduced reaction times resultingin short residence times Hydrogen-rich gas streams canbe efficiently produced in plasma reformers from a varietyof hydrocarbon fuels (eg gasoline diesel oil biomassnatural gas and jet fuel) with conversion efficiencies close to100 [32 36] The plasma reforming technology has poten-tial advantages over conventional technologies of hydrogenmanufacturing [32ndash35] The plasma conditions (eg hightemperatures high degree of dissociation and substantialdegree of ionization) can be used to accelerate thermody-namically favorable chemical reactions without a catalystor provide the energy required for endothermic reformingprocesses to occur Plasma reformers can provide a numberof advantages namely compactness and low weight (due tohigh power density) high conversion efficiencies minimalcost (simple metallic or carbon electrodes and simple powersupplies) fast response time (fraction of a second) operationwith a broad range of fuels including heavy hydrocarbons(crude) and ldquodirtyrdquo hydrocarbons (high sulfur diesel) Thistechnology could be used to manufacture hydrogen for avariety of stationary applications such as distributed andlow-pollution electricity generation for fuel cells [32] Itcould also be used for mobile applications (eg on-boardgeneration of hydrogen for fuel cell powered vehicles) and forrefueling applications (eg stationary sources of hydrogen forvehicles)

The only disadvantages of plasma reforming are thedependence on electricity and the difficulty of high-pressureoperation (required for high-pressure processes such asammonia production) High pressure while achievableincreases electrode erosion due to decreased arcmobility andtherefore it decreases electrode lifetime [33]


3 Hydrogen from Renewable Sources

Hydrogen could be also produced by other methods thanreforming of fossil fuels A brief description of the biomass-based approaches (eg gasification pyrolysis and aqueousphase reforming) along with production of hydrogen fromwater (eg electrolysis photoelectrolysis and thermochemi-cal water splitting) is described later

31 Biomass Gasification In the near term biomass is antici-pated to become the most likely renewable organic substituteto petroleum Biomass is available from a wide range ofsources such as animal wastes municipal solid wastes cropresidues short rotation woody crops agricultural wastessawdust aquatic plants short rotation herbaceous species(eg switch grass) waste paper corn and many others [3738]

Gasification technology commonly used with biomassand coal as fuel feedstock is very mature and commerciallyused in many processes It is a variation of pyrolysis andtherefore is based upon partial oxidation of the feedstockmaterial into a mixture of hydrogen methane higher hydro-carbons carbon monoxide carbon dioxide and nitrogenknown as ldquoproducer gasrdquo [37] The gasification processtypically suffers from low thermal efficiency since moisturecontained in the biomass must also be vaporized It can beperformed with or without a catalyst and in a fixed-bed orfluidized-bed reactor with the latter reactor having typicallybetter performance [38] Addition of steam andor oxygen inthe gasification process results in the production of ldquosyngasrdquowith a H

2CO ratio of 21 the latter used as feedstock to a

Fischer-Tropsch reactor to make higher hydrocarbons (syn-thetic gasoline and diesel) or to a WGS reactor for hydrogenproduction [38] Superheated steam (ca 900∘C) has beenused to reform dry biomass to achieve high hydrogen yieldsHowever gasification process provides significant amounts ofldquotarsrdquo (a complex mixture of higher aromatic hydrocarbons)in the product gas even operated in the 800ndash1000∘C rangeA secondary reactor which utilizes calcined dolomite andornickel catalyst is used to catalytically clean and upgrade theproduct gas [38] Ideally oxygen should be used in thesegasification plants however oxygen separation unit is costprohibitive for small-scale plants This limits the gasifiers tothe use of air resulting in significant dilution of the productas well as the production of NO

119909 Low-cost efficient oxygen

separators are needed for this technology For hydrogenproduction a WGS process can be employed to increase thehydrogen concentration followed by a separation process toproduce pure hydrogen [39] Typically gasification reactorsare built on a large scale and require massive amounts ofmaterial to be continuously fed They can achieve efficienciesin the order of 35ndash50 based on the lower heating value [4]One of the problems of this technology is that a tremendousamount of resourcesmust be used to gather the large amountsof biomass to the central processing plant Currently the highlogistics costs of gasification plants and the removal of ldquotarsrdquoto acceptable levels for pure hydrogen production limit thecommercialization of biomass-based hydrogen production

Future development of smaller efficient distributed gasifi-cation plants may be required for this technology for costeffective hydrogen production

32 Pyrolysis and Copyrolysis Another currently promisingmethod of hydrogen production is pyrolysis or copyrolysisRaw organic material is heated and gasified at a pressure of01ndash05MPa in the 500ndash900∘C range [40ndash43] The processtakes place in the absence of oxygen and air and thereforethe formation of dioxins can be almost ruled out Since nowater or air is present no carbon oxides (eg CO or CO

2) are

formed eliminating the need for secondary reactors (WGSPrOx etc) Consequently this process offers significantemissions reduction However if air or water is present (thematerials have not been dried) significantCO

119909emissionswill

be produced Among the advantages of this process are fuelflexibility relative simplicity and compactness clean carbonbyproduct and reduction in CO

119909emissions [40ndash43] The

reaction can be generally described by the following equation[41]

C119899H119898+ heat 997888rarr 119899C + 05119898H

2 (8)

Based on the temperature range pyrolysis processes aredivided into low (up to 500∘C) medium (500ndash800∘C) andhigh temperatures (over 800∘C) Fast pyrolysis is one of thelatest processes for the transformation of organic materialinto products with higher energy content The products offast pyrolysis appear in the entire phases formed (solid liquidand gaseous) One of the challenges with this approach is thepotential for fouling by the carbon formed but proponentsclaim that this can beminimized by appropriate design Sinceit has the potential for lower CO and CO

2emissions and

it can be operated in such a way as to recover a significantamount of solid carbon which is easily sequestered [41 44]pyrolysis may play a significant role in the future

The application of the copyrolysis of amixture of coalwithorganic wastes has recently received an interest in industriallyadvanced countries as it should limit and lighten the burdenof wastes in waste disposal (waste and pure plastics rubbercellulose paper textiles and wood) [45 46] Pyrolysis andcopyrolysis are well-developed processes and could be usedin commercial scale

33 Aqueous Phase Reforming Aqueous phase reforming(APR) is a technology under development to processoxygenated hydrocarbons or carbohydrates of renewablebiomass resources to produce hydrogen [47 48] as depictedin Figure 4 The APR reactions take place at substantiallylower temperatures (220ndash270∘C) than conventional alkanesteam reforming (ca 600∘C) The low temperatures at whichaqueous-phase reforming reactions occur minimize unde-sirable decomposition reactions typically encountered whencarbohydrates are heated to elevated temperatures [49 50]Also the water-gas shift reaction (WGS) is favorable at thesame temperatures as in APR reactions thus making itpossible to generate H

2and CO

2in a single reactor with

low amounts of CO In contrast typical steam reformingprocesses require multistage or multiple reactors to achieve


ΗΟCH

ΗCH

ΗΟCH

CO

ΗCH Alkene reforming at high T

followed by WGS at low T

and WGS at low T

H2

H2

H2O

H2O

CO2

Δ119866∘lt 0 at low

temperature

Δ119866∘lt 0 at high

temperature

Δ119866∘darr as 119879 darr

Oxygenate reforming (C O = 1 1)

Figure 4 Reaction pathways for the production of H2by reactions

of oxygenated hydrocarbons with water during APR

low levels of CO in the product gas Another advantage ofthe APR process is that it eliminates the need to vaporizewater which represents a major energy saving compared toconventional vapor-phase steam reforming processes Mostof the research to date has been focused on supported GroupVIII catalysts with Pt-containing solids having the highestcatalytic activity Even though they have lower activity nickel-based catalysts have been evaluated due to nickelrsquos low cost[47]The advocates of this technology claim that this technol-ogy is more amiable to efficiently and selectively convertingbiomass feedstock to hydrogen Aqueous feed concentra-tions of 10ndash60wt were reported for glucose and glycols[51] Catalyst selection is important to avoid methanationwhich is thermodynamically favorable along with Fischer-Tropsch products such as propane butane and hexane [4852] Recently Rozmiarek [53] reported an aqueous phasereformer-based process that achieved an efficiency largerthan 55 with a feed composed of 60wt glucose in waterHowever the catalyst was not stable during long-term testing(200 days on stream) [53] Finally due tomoderate space timeyields these reactors tend to be somewhat large Improvingcatalyst activity and durability is an area where significantprogress can be made

34 Electrolysis A promising method for the production ofhydrogen in the future could be water electrolysis Currentlyapproximately only 4 of hydrogen worldwide is producedby this process [2] The electrolysis of water or its breakinginto hydrogen and oxygen is a well-known method whichbegan to be used commercially already in 1890

Electrolysis is a process in which a direct current passingthrough two electrodes in a water solution results in thebreaking of the chemical bonds present in water moleculeinto hydrogen and oxygen

Cathode 2H2O (l) + 2eminus 997888rarr H

2(g) + 2OHminus (aq) (9)

Anode 4OHminus (aq) 997888rarr O2(g) + 2H

2O (l) + 4eminus (10)

Overall 2H2O 997888rarr 2H

2+O2 (11)

The electrolysis process takes place at room temperatureA commonly used electrolyte in water electrolysis is sulfuricacid and the electrodes are of platinum (Pt) which doesnot react with sulfuric acid The process is ecologically cleanbecause no greenhouse gases are formed and the oxygenproduced has further industrial applications However incomparison with the foregoing methods described electrol-ysis is a highly energy-demanding technology

The energetic efficiency of the electrolysis of water(chemical energy acquired per electrical energy supplied) inpractice reaches 50ndash70 [54] It is essentially the conversionof electrical energy to chemical energy in the form ofhydrogen with oxygen as a useful byproduct The mostcommon electrolysis technology is alkaline-based but protonexchange membrane (PEM) and solid oxide electrolysis cells(SOEC) have been developed [55 56] SOEC electrolyzers arethe most electrically efficient but the least developed SOECtechnology has challenges with corrosion seals thermalcycling and chrome migration PEM electrolyzers are moreefficient than alkaline and do not have corrosion problemsand seals issues as SOEC however they cost more thanalkaline systems Alkaline systems are the most developedand the lowest in capital cost They have the lowest efficiencyso they have the highest electrical energy cost

35 Photoelectrolysis Photoelectrolysis is one of the renew-able ways of hydrogen production exhibiting promisingefficiency and costs although it is still in the phase of exper-imental development [57] Currently it is the least expensiveand the most effective method of hydrogen production fromrenewable resourcesThe photoelectrode is a semiconductingdevice absorbing solar energy and simultaneously creatingthe necessary voltage for the direct decomposition of watermolecule into oxygen and hydrogen Photoelectrolysis uti-lizes a photoelectrochemical (PEC) light collection system fordriving the electrolysis of water If the semiconductor pho-toelectrode is submerged in an aqueous electrolyte exposedto solar radiation it will generate enough electrical energyto support the generated reactions of hydrogen and oxygenWhen generating hydrogen electrons are released into theelectrolyte whereas the generation of oxygen requires freeelectronsThe reaction depends on the type of semiconductormaterial and on the solar intensity which produces a currentdensity of 10ndash30mAcm2 At these current densities thevoltage necessary for electrolysis is approximately 135V

The photoelectrode is comprised of photovoltaic (semi-conductor) catalytic and protective layers which can bemodeled as independent components [58] Each layer influ-ences the overall efficiency of the photoelectrochemicalsystemThe photovoltaic layer is produced from light absorb-ing semiconductor materials The light absorption of thesemiconductor material is directly proportional to the per-formance of the photoelectrode Semiconductors with widebands provide the necessary potential for the splitting ofwater [54]

The catalytic layers of the photoelectrochemical cell alsoinfluence the performance of the electrolysis and requiresuitable catalysts for water splitting The encased layer is


another important component of the photoelectrode whichprevents the semiconductor from corroding inside the aque-ous electrolyteThis layer must be highly transparent in orderto be able to provide the maximum solar energy so that itcould reach the photovoltaic semiconducting layer

36ThermochemicalWater Splitting Thermochemical cycleshave been developed already since the 1970s and 1980s whenthey had to contribute to the search for new sources ofproduction of alternative fuels during the petroleum crisis Inthermochemical water splitting also called thermolysis heatalone is used to decompose water to hydrogen and oxygen[59] It is believed that overall efficiencies close to 50 can beachieved using these processes [60]

The single-step thermal dissociation of water is describedas follows

H2O + heat 997888rarr H

2+ 05O

2 (12)

One drawback of this process comes from the need of aneffective technique to separate H

2and O

2to avoid ending up

with an explosive mixture Semipermeable membranes basedon ZrO

2and other high-temperature materials can be used

for this purpose Separation can also be achieved after theproduct gas mixture is quenched to lower temperatures Pal-ladium membranes can then be used for effective hydrogenseparation

It is well known that water will decompose at 2500∘Cbut materials stable at this temperature and also sustainableheat sources are not easily available Therefore chemicalreagents have been proposed to lower the temperaturewhereasmore than 300 water-splitting cycles were referencedin the literature [61] All of the processes have significantlyreduced the operating temperature to lower than 2500∘Cbut typically require higher pressures However it is believedthat scaling-up the processes may lead to improved thermalefficiency overcoming one of the main challenges faced bythis technology In addition a better understanding of therelationship between capital cost thermodynamic losses andprocess thermal efficiency may lead to reduced hydrogenproduction costs [60]

4 Economic Aspects on Hydrogen Production

At present the most widely used and cheapest methodfor hydrogen production is the steam reforming of methane(natural gas) This method includes about half of the worldhydrogen production and hydrogen price is about 7 USDGJA comparable price for hydrogen is provided by partial oxida-tion of hydrocarbons However greenhouse gases generatedby thermochemical processes must be captured and storedand thus an increase in the hydrogen price by 25ndash30 mustbe considered [62]

The further used thermochemical processes include gasi-fication and pyrolysis of biomass The price of hydrogenthus obtained is about three times greater than the priceof hydrogen obtained by the SR process Therefore theseprocesses are generally not considered as cost competitive ofsteam reforming The price of hydrogen from gasification of

Table 1 Hydrogen production technologies summary

Technology Feedstock Efficiency MaturitySteam reforming Hydrocarbons 70ndash85 Commercial

Partial oxidation Hydrocarbons 60ndash75 CommercialAutothermalreforming Hydrocarbons 60ndash75 Near term

Plasmareforming Hydrocarbons 9ndash85lowast Long term

Biomassgasification Biomass 35ndash50 Commercial

Aqueous phasereforming Carbohydrates 35ndash55 Med term

Electrolysis H2O + electricity 50ndash70 CommercialPhotolysis H2O + sunlight 05lowast Long termThermochemicalwater splitting H2O + heat NA Long term

lowastHydrogen purification is not included

biomass ranges from 10ndash14 USDGJ and that from pyrolysis89ndash155 USDGJ It depends on the equipment availabilityand cost of feedstock [1]

Electrolysis of water is one of the simplest technologiesfor producing hydrogen without byproducts Electrolyticprocesses can be classified as highly effective On the otherhand the input electricity cost is relatively high and plays akey role in the price of hydrogen obtained

By the year 2030 the dominant methods for hydrogenproduction will be steam reforming of natural gas and cat-alyzed biomass gasification In a relatively small extent bothcoal gasification and electrolysis will be usedThe use of solarenergy in a given context is questionable but also possibleProbably the role of solar energy will increase by 2050 [1]

5 Conclusions

There is a tremendous amount of research being pursuedtowards the development of hydrogen (H

2) generation tech-

nologies Currently the most developed and used technologyis the reforming of hydrocarbons In order to decrease thedependence on fossil fuels significant developments in otherH2generation technologies from renewable resources such

as biomass and water are considered Table 1 summarizes thetechnologies along with their feedstock used and efficienciesobtained It is important to note that H

2can be produced

from awide variety of feedstock available almost everywhereThere are many processes under development with minimalenvironmental impact Development of these technologiesmay decrease the worldrsquos dependence on fuels that come pri-marily from unstable regions The ldquoin-houserdquo H

2production

may increase both national energy and economic securityThe ability of H

2to be produced from a wide variety of

feedstock and using a wide variety of processes may makeevery region of the world able to produce much of its ownenergy It is clear that as the technologies develop andmatureH2may prove to be the most ubiquitous fuel available


Nomenclature

APR Aqueous phase reformingATR Autothermal reformingCPOX Catalytic partial oxidationHDS HydrodesulfurizationPEC PhotoelectrochemicalPEM Proton exchange membranePOX Partial oxidationPrOx Preferential oxidationSOEC Solid oxide electrolysis cellSR Steam reformingWGS Water-gas shift

Acknowledgments

The authors gratefully acknowledge the Research Committeeof the University of Cyprus and the Cyprus Research Pro-motion Foundation for their financial support in developingfundamental research on catalytic hydrogen production tech-nologies

References

[1] M Balat and M Balat ldquoPolitical economic and environmentalimpacts of biomass-based hydrogenrdquo International Journal ofHydrogen Energy vol 34 no 9 pp 3589ndash3603 2009

[2] A Konieczny K Mondal T Wiltowski and P Dydo ldquoCatalystdevelopment for thermocatalytic decomposition of methane tohydrogenrdquo International Journal of Hydrogen Energy vol 33 no1 pp 264ndash272 2008

[3] N Z Muradov and T N Veziroglu ldquoFrom hydrocarbon tohydrogen-carbon to hydrogen economyrdquo International Journalof Hydrogen Energy vol 30 no 3 pp 225ndash237 2005

[4] J D Holladay J Hu D L King and Y Wang ldquoAn overviewof hydrogen production technologiesrdquo Catalysis Today vol 139no 4 pp 244ndash260 2009

[5] J M Ogden M M Steinbugler and T G Kreutz ldquoComparisonof hydrogen methanol and gasoline as fuels for fuel cellvehicles implications for vehicle design and infrastructuredevelopmentrdquo Journal of Power Sources vol 79 no 2 pp 143ndash168 1999

[6] M Onozaki K Watanabe T Hashimoto H Saegusa and YKatayama ldquoHydrogen production by the partial oxidation andsteam reforming of tar from hot coke oven gasrdquo Fuel vol 85 no2 pp 143ndash149 2006

[7] J R Rostrup-Nielsen ldquoConversion of hydrocarbons and alco-hols for fuel cellsrdquo Physical Chemistry Chemical Physics vol 3no 3 pp 283ndash288 2001

[8] H Song L Zhang R B Watson D Braden and U S OzkanldquoInvestigation of bio-ethanol steam reforming over cobalt-based catalystsrdquo Catalysis Today vol 129 no 3-4 pp 346ndash3542007

[9] R Farrauto S Hwang L Shore et al ldquoNew material needs forhydrocarbon fuel processing generating hydrogen for the PEMfuel cellrdquo Annual Review of Materials Research vol 33 pp 1ndash272003

[10] C Song ldquoFuel processing for low-temperature and high-temperature fuel cells challenges and opportunities for sustain-able development in the 21st centuryrdquo Catalysis Today vol 77no 1-2 pp 17ndash49 2002

[11] A M Adris B B Pruden C J Lim and J R Grace ldquoOnthe reported attempts to radically improve the performanceof the steam methane reforming reactorrdquo Canadian Journal ofChemical Engineering vol 74 no 2 pp 177ndash186 1996

[12] J Rostrup-Nielsen ldquoHydrogen generation by catalysisrdquo inEncyclopedia of Catalysis I T Horvath Ed Wiley Interscience2003

[13] Y Shirasaki T Tsuneki Y Ota et al ldquoDevelopment of mem-brane reformer system for highly efficient hydrogen productionfrom natural gasrdquo International Journal of Hydrogen Energy vol34 no 10 pp 4482ndash4487 2009

[14] B Sorensen Hydrogen and Fuel Cells Academic Press 2011[15] K L Hohn and L D Schmidt ldquoPartial oxidation of methane to

syngas at high space velocities over Rh-coated spheresrdquo AppliedCatalysis A vol 211 no 1 pp 53ndash68 2001

[16] J J Krummenacher K N West and L D Schmidt ldquoCatalyticpartial oxidation of higher hydrocarbons at millisecond contacttimes decane hexadecane and diesel fuelrdquo Journal of Catalysisvol 215 no 2 pp 332ndash343 2003

[17] A Holmen ldquoDirect conversion of methane to fuels and chemi-calsrdquo Catalysis Today vol 142 no 1-2 pp 2ndash8 2009

[18] K Aasberg-Petersen J H Bak Hansen T S Christensen et alldquoTechnologies for large-scale gas conversionrdquo Applied CatalysisA vol 221 no 1-2 pp 379ndash387 2001

[19] A E Lutz R W Bradshaw L Bromberg and A RabinovichldquoThermodynamic analysis of hydrogen production by partialoxidation reformingrdquo International Journal of Hydrogen Energyvol 29 no 8 pp 809ndash816 2004

[20] L Pino V Recupero S Beninati A K Shukla M S Hegdeand P Bera ldquoCatalytic partial-oxidation of methane on a ceria-supported platinum catalyst for application in fuel cell electricvehiclesrdquo Applied Catalysis A vol 225 no 1-2 pp 63ndash75 2002

[21] J D Holladay Y Wang and E Jones ldquoReview of developmentsin portable hydrogen production using microreactor technol-ogyrdquo Chemical Reviews vol 104 no 10 pp 4767ndash4790 2004

[22] T A Semelsberger L F Brown R L Borup and M AInbody ldquoEquilibrium products from autothermal processes forgenerating hydrogen-rich fuel-cell feedsrdquo International Journalof Hydrogen Energy vol 29 no 10 pp 1047ndash1064 2004

[23] F Joensen and J R Rostrup-Nielsen ldquoConversion of hydrocar-bons and alcohols for fuel cellsrdquo Journal of Power Sources vol105 no 2 pp 195ndash201 2002

[24] D J Wilhelm D R Simbeck A D Karp and R L DickensonldquoSyngas production for gas-to-liquids applications technolo-gies issues and outlookrdquo Fuel Processing Technology vol 71 no1ndash3 pp 139ndash148 2001

[25] S Ayabe H Omoto T Utaka et al ldquoCatalytic autothermalreforming of methane and propane over supported metalcatalystsrdquo Applied Catalysis A vol 241 no 1-2 pp 261ndash2692003

[26] C Rhodes B P Williams F King and G J HutchingsldquoPromotion of Fe

3O4Cr2O3high temperature water gas shift

catalystrdquo Catalysis Communications vol 3 no 8 pp 381ndash3842002

[27] P Pietrogrande and M Bezzeccheri ldquoFuel processingrdquo in FuelCell Systems L J M J Blomen and M N Mugerwa Eds pp121ndash156 Plenum Press New York NY USA 1993

[28] M W Twigg Catalyst Handbook Wolfe Publishing LondonUK 1989

[29] I V Babich and J A Moulijn ldquoScience and technology of novelprocesses for deep desulfurization of oil refinery streams areviewrdquo Fuel vol 82 no 6 pp 607ndash631 2003


[30] C Song ldquoAn overview of new approaches to deep desulfuriza-tion for ultra-clean gasoline diesel fuel and jet fuelrdquo CatalysisToday vol 86 no 1ndash4 pp 211ndash263 2003

[31] A J Hernandez-Maldonado and R T Yang ldquoDesulfurization ofliquid fuels by adsorption via p complexation with Cu(I)-Y andAg-Y zeolitesrdquo Industrial amp Engineering Chemistry Researchvol 42 no 1 pp 123ndash129 2002

[32] L Bromberg D R Cohn and A Rabinovich ldquoPlasmareformer-fuel cell system for decentralized power applicationsrdquoInternational Journal of Hydrogen Energy vol 22 no 1 pp 83ndash94 1997

[33] L Bromberg D R Cohn A Rabinovich and N AlexeevldquoPlasma catalytic reforming of methanerdquo International Journalof Hydrogen Energy vol 24 no 12 pp 1131ndash1137 1999

[34] THammer T Kappes andM Baldauf ldquoPlasma catalytic hybridprocesses gas discharge initiation and plasma activation ofcatalytic processesrdquo Catalysis Today vol 89 no 1-2 pp 5ndash142004

[35] T Paulmier and L Fulcheri ldquoUse of non-thermal plasma forhydrocarbon reformingrdquo Chemical Engineering Journal vol106 no 1 pp 59ndash71 2005

[36] L Bromberg D R Cohn A Rabinovich C OrsquoBrien and SHochgreb ldquoPlasma reforming of methanerdquo Energy and Fuelsvol 12 no 1 pp 11ndash18 1998

[37] M F Demirbas ldquoHydrogen from various biomass species viapyrolysis and steam gasification processesrdquo Energy Sources Avol 28 no 3 pp 245ndash252 2006

[38] M Asadullah S I Ito K Kunimori M Yamada and KTomishige ldquoEnergy efficient production of hydrogen and syn-gas from biomass development of low-temperature catalyticprocess for cellulose gasificationrdquo Environmental Science andTechnology vol 36 no 20 pp 4476ndash4481 2002

[39] GWeber Q Fu and HWu ldquoEnergy efficiency of an integratedprocess based on gasification for hydrogen production frombiomassrdquo Developments in Chemical Engineering and MineralProcessing vol 14 no 1-2 pp 33ndash49 2006

[40] M Ni D Y C Leung M K H Leung and K SumathyldquoAn overview of hydrogen production from biomassrdquo FuelProcessing Technology vol 87 no 5 pp 461ndash472 2006

[41] N Muradov ldquoEmission-free fuel reformers for mobile andportable fuel cell applicationsrdquo Journal of Power Sources vol 118no 1-2 pp 320ndash324 2003

[42] A Demirbas and G Arin ldquoHydrogen from biomass via pyrol-ysis relationships between yield of hydrogen and temperaturerdquoEnergy Sources vol 26 no 11 pp 1061ndash1069 2004

[43] A Demirbas ldquoRecovery of chemicals and gasoline-range fuelsfrom plastic wastes via pyrolysisrdquo Energy Sources vol 27 no 14pp 1313ndash1319 2005

[44] F G Zhagfarov N A GrigorrsquoEva and A L Lapidus ldquoNewcatalysts of hydrocarbon pyrolysisrdquo Chemistry and Technologyof Fuels and Oils vol 41 no 2 pp 141ndash145 2005

[45] R Sakurovs ldquoInteractions between coking coals and plasticsduring co-pyrolysisrdquo Fuel vol 82 no 15ndash17 pp 1911ndash1916 2003

[46] A Orinak L Halas I Amar J T Andersson andM AdamovaldquoCo-pyrolysis of polymethyl methacrylate with brown coal andeffect on monomer productionrdquo Fuel vol 85 no 1 pp 12ndash182006

[47] R R Davda J W Shabaker G W Huber R D Cortright andJ A Dumesic ldquoAqueous-phase reforming of ethylene glycol onsilica-supportedmetal catalystsrdquoApplied Catalysis B vol 43 no1 pp 13ndash26 2003

[48] GW Huber and J A Dumesic ldquoAn overview of aqueous-phasecatalytic processes for production of hydrogen and alkanes in abiorefineryrdquo Catalysis Today vol 111 no 1-2 pp 119ndash132 2006

[49] G Eggleston and J R Vercellotti ldquoDegradation of sucroseglucose and fructose in concentrated aqueous solutions underconstant pH conditions at elevated temperaturerdquo Journal ofCarbohydrate Chemistry vol 19 no 9 pp 1305ndash1318 2000

[50] B M Kabyemela T Adschiri R M Malaluan and K AraildquoGlucose and fructose decomposition in subcritical and super-critical water detailed reaction pathway mechanisms andkineticsrdquo Industrial and Engineering Chemistry Research vol 38no 8 pp 2888ndash2895 1999

[51] R D Cortright and L Bednarova ldquoHydrogen Generation fromBiomass-Derived Carbohydrates via Aqueous Phase Reforming(APR) Processrdquo in US Department of Energy Hydrogen Pro-gram FY2007 Anual Progress Report J Milliken Ed pp 56ndash59Department of Energy Washington DC USA 2007

[52] R R Davda J W Shabaker G W Huber R D Cortrightand J A Dumesic ldquoA review of catalytic issues and processconditions for renewable hydrogen and alkanes by aqueous-phase reforming of oxygenated hydrocarbons over supportedmetal catalystsrdquo Applied Catalysis B vol 56 no 1-2 pp 171ndash1862005

[53] B Rozmiarek ldquoHydrogen generation from biomass-derivedcarbohydrates via aqueous phase reforming processrdquo inAnnualMerit Review Proceedings J Milliken Ed pp 1ndash6 Departmentof Energy Washington DC USA 2008

[54] J Turner G Sverdrup M K Mann et al ldquoRenewable hydrogenproductionrdquo International Journal of Energy Research vol 32no 5 pp 379ndash407 2008

[55] S A Grigoriev V I Porembsky and V N Fateev ldquoPurehydrogen production by PEM electrolysis for hydrogen energyrdquoInternational Journal of Hydrogen Energy vol 31 no 2 pp 171ndash175 2006

[56] J Pettersson B Ramsey and D Harrison ldquoA review of the latestdevelopments in electrodes for unitised regenerative polymerelectrolyte fuel cellsrdquo Journal of Power Sources vol 157 no 1 pp28ndash34 2006

[57] C N Hamelinck and A P C Faaij ldquoFuture prospects forproduction of methanol and hydrogen from biomassrdquo Journalof Power Sources vol 111 no 1 pp 1ndash22 2002

[58] S E Lindquist and C Fell ldquoFuels-hydrogen productionphotoelectrolysisrdquo in Encyclopedia of Electrochemical PowerSources G Jurgen Ed pp 369ndash383 Elsevier Amsterdam TheNetherlands 2009

[59] A Steinfeld ldquoSolar thermochemical production of hydrogenmdashareviewrdquo Solar Energy vol 78 no 5 pp 603ndash615 2005

[60] J E Funk ldquoThermochemical hydrogen production past andpresentrdquo International Journal of Hydrogen Energy vol 26 no3 pp 185ndash190 2001

[61] M A Lewis M Serban and J K Basco ldquoHydrogen productionat lt550∘C using a low temperature thermochemical cyclerdquo inProceedings of the Atoms for Prosperity Updating EisenhowerrsquosGlobal Vision for Nuclear Energy (Global rsquo03) pp 1492ndash1498Chicago Ill USA November 2003

[62] H Balat and E Kirtay ldquoHydrogen from biomassmdashpresent sce-nario and future prospectsrdquo International Journal of HydrogenEnergy vol 35 no 14 pp 7416ndash7426 2010

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2013

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2013

Journal of


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ISRN Chemical Engineering



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Volume 2013

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Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

International Journal ofPhotoenergy

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Nuclear EnergyInternational Journal of


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High Energy PhysicsAdvances in


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Volume 2013Number 1

Science and Technology of

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Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal

ISRN High Energy Physics


CombustionJournal of




StructuresJournal of

International Journal of

RotatingMachinery


Industrial EngineeringJournal of


TribologyAdvances in


EnergyJournal of







Nuclear InstallationsScience and Technology of





Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

FuelsJournal of








Advances in

Journal ofPetroleum Engineering


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of


Renewable Energy




The fundamental question lies in the development ofalternative technologies for hydrogen production to thosebased on fossil fuels especially for its utilization as a fuelin the transportation sector This problem can be faced bythe utilization of alternative renewable resources and relatedmethods of production such as the gasification or pyrolysisof biomass electrolytic photolytic and thermal crackingof water However it is not possible to consider only theecological perspective since for example photolytic crackingof water is environmentally friendly but its efficiency forindustrial use is very low It is thus clear that the processes tobe taken into account must consider not only environmentalconcerns but also the most favorable economics

2 Hydrogen from Fossil Fuels

Fossil fuel processing technologies convert hydrogen- con-taining materials derived from fossil fuels such as gasolinehydrocarbons methanol or ethanol into a hydrogen-richgas stream Fuel processing of methane (natural gas) is themost common commercial hydrogen production technologytoday Most fossil fuels contain a certain amount of sulfurthe removal of which is a significant task in the planningof hydrogen-based economy As a result the desulfurizationprocess will also be discussed In addition the very promisingplasma reforming technology recently developed will also bepresented

Hydrogen gas can be produced from hydrocarbon fuelsthrough three basic technologies (i) steam reforming (SR)(ii) partial oxidation (POX) and (iii) autothermal reforming(ATR) These technologies produce a great deal of carbonmonoxide (CO) Thus in a subsequent step one or morechemical reactors are used to largely convert CO into carbondioxide (CO

2) via the water-gas shift (WGS) and preferen-

tial oxidation (PrOx) or methanation reactions which aredescribed later

21 Steam Reforming Steam reforming is currently one ofthe most widespread and at the same time least expensiveprocesses for hydrogen production [5] Its advantage arisesfrom the high efficiency of its operation and the low oper-ational and production costs The most frequently used rawmaterials are natural gas and lighter hydrocarbonsmethanoland other oxygenated hydrocarbons [6] The network ofreforming reactions for hydrocarbons and methanol used asfeedstock is the following [7]

C119898H119899+ 119898H

2O (g) 997888rarr 119898CO + (119898 + 05 119899)H

2 (1)

C119898H119899+ 2119898H

2O (g) 997888rarr 119898CO

2+ (2119898 + 05 119899)H

2 (2)

CO + H2O (g) larrrarr CO

2+H2 (3)

CH3OH +H

2O (g) larrrarr CO

2+ 3H2 (4)

Thewhole process comprises two stages In the first stagethe hydrocarbon raw material is mixed with steam and fedin a tubular catalytic reactor [8] During this process syngas(H2CO gas mixture) is produced with lower content in CO

2

((1) and (2)) The required reaction temperature is achieved

by the addition of oxygen or air for combusting part of theraw material (heating gas) inside the reactor In the secondstage the cooled product gas is fed into the CO catalyticconverter where carbon monoxide is converted to a largeextent by means of steam into carbon dioxide and hydrogen(3) The steam reforming catalytic process requires a rawmaterial free of sulfur-containing compounds in order toavoid deactivation of the catalyst used

The SR process requires modest temperatures for exam-ple 180∘C for methanol and oxygenated hydrocarbons andmore than 500∘C formost conventional hydrocarbons [9 10]The catalysts used can be divided into two types nonpreciousmetal (typically nickel) and precious metals fromGroup VIIIelements (typically platinumor rhodium)Due to severemassand heat transfer limitations conventional steam reformersare limited by the effectiveness factor of pelletized catalystswhich is typically less than 5 [11]Therefore kinetics is rarelythe limiting factor with conventional steam reformer reactors[12] and therefore less expensive nickel catalysts are usedindustrially

An important factor characterizing the SR process is theH C atom ratio in the feedstock material The higher thisratio is the lower carbon dioxide emission is formed Amembrane reactor can replace both reactors in a conventionalSR process for achieving the overall reaction (2) [13] Theheat efficiency of hydrogen production by the SR of methaneprocess on an industrial scale is around 70ndash85 [14] Anumber of other raw materials are also possible to achievethis efficiency in the near future such as solid communalwaste wastes from food industry oils purposefully cultivatedor waste agricultural biomass and fuels of fossil origin suchas coal The disadvantage is the high production of CO

2 ca

705 kg CO2kg H

2

22 Partial Oxidation Partial oxidation (POX) and catalyticpartial oxidation (CPOX) of hydrocarbons have been pro-posed in hydrogen production for automobile fuel cells andsome other commercial applications [15 16] The gasifiedraw material can be methane and biogas but primarily heavyoil fractions (eg vacuum remnants heating oil) whosefurther treatment and utilization are difficult [17] POX is anoncatalytic process in which the raw material is gasifiedin the presence of oxygen ((5) and (6)) and possibly steam((7) ATR) at temperatures in the 1300ndash1500∘C range andpressures in the 3ndash8MPa range In comparisonwith the steamreforming (H

2 CO = 3 1) more CO is produced (H

2 CO =

1 1 or 2 1) The process is therefore complemented by theconversion of CO with steam into H

2and CO

2 This reaction

contributes to the maintenance of equilibrium between theindividual reaction products [18]

CH4+O2997888rarr CO + 2H

2 (5)

CH4+ 2O2997888rarr CO

2+ 2H2O (6)

CH4+H2O (g) 997888rarr CO + 3H

2 (7)

The gaseous mixture formed through partial oxidationcontains CO CO

2 H2O H2 CH4 hydrogen sulfide (H

2S)

and carbon oxysulfide (COS) A part of the gas is burned









Partialoxidation









2O3catalysts [26]



2molecules





Steam reforming

catalyst Ni

oxidation or

methanationH2O

CH4

+ 700-800∘C


H2O(g)CO119909 + H2

HTS LT

S






Desulfurization

Conventional HDS


HDS by advanced

HDS with fuel


Alkylation

Extraction

Oxidation

Adsorption




reactor design















2) are


119909emissionswill




C119899H119898+ heat 997888rarr 119899C + 05119898H

2 (8)


2emissions and




2and CO




ΗΟCH

ΗCH

ΗΟCH

CO



and WGS at low T

H2

H2

H2O

H2O

CO2


temperature


temperature











2O (l) + 4eminus (10)


2+O2 (11)











2+ 05O

2 (12)


2and O

2to avoid ending up



















5 Conclusions


2) generation tech-



2can be produced


2production





Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy











Partialoxidation









2O3catalysts [26]



2molecules





Steam reforming

catalyst Ni

oxidation or

methanationH2O

CH4

+ 700-800∘C


H2O(g)CO119909 + H2

HTS LT

S






Desulfurization

Conventional HDS


HDS by advanced

HDS with fuel


Alkylation

Extraction

Oxidation

Adsorption




reactor design















2) are


119909emissionswill




C119899H119898+ heat 997888rarr 119899C + 05119898H

2 (8)


2emissions and




2and CO




ΗΟCH

ΗCH

ΗΟCH

CO



and WGS at low T

H2

H2

H2O

H2O

CO2


temperature


temperature











2O (l) + 4eminus (10)


2+O2 (11)











2+ 05O

2 (12)


2and O

2to avoid ending up



















5 Conclusions


2) generation tech-



2can be produced


2production





Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy




Steam reforming

catalyst Ni

oxidation or

methanationH2O

CH4

+ 700-800∘C


H2O(g)CO119909 + H2

HTS LT

S






Desulfurization

Conventional HDS


HDS by advanced

HDS with fuel


Alkylation

Extraction

Oxidation

Adsorption




reactor design















2) are


119909emissionswill




C119899H119898+ heat 997888rarr 119899C + 05119898H

2 (8)


2emissions and




2and CO




ΗΟCH

ΗCH

ΗΟCH

CO



and WGS at low T

H2

H2

H2O

H2O

CO2


temperature


temperature











2O (l) + 4eminus (10)


2+O2 (11)











2+ 05O

2 (12)


2and O

2to avoid ending up



















5 Conclusions


2) generation tech-



2can be produced


2production





Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy














2) are


119909emissionswill




C119899H119898+ heat 997888rarr 119899C + 05119898H

2 (8)


2emissions and




2and CO




ΗΟCH

ΗCH

ΗΟCH

CO



and WGS at low T

H2

H2

H2O

H2O

CO2


temperature


temperature











2O (l) + 4eminus (10)


2+O2 (11)











2+ 05O

2 (12)


2and O

2to avoid ending up



















5 Conclusions


2) generation tech-



2can be produced


2production





Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy




ΗΟCH

ΗCH

ΗΟCH

CO



and WGS at low T

H2

H2

H2O

H2O

CO2


temperature


temperature











2O (l) + 4eminus (10)


2+O2 (11)











2+ 05O

2 (12)


2and O

2to avoid ending up



















5 Conclusions


2) generation tech-



2can be produced


2production





Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy








2+ 05O

2 (12)


2and O

2to avoid ending up



















5 Conclusions


2) generation tech-



2can be produced


2production





Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy




Nomenclature


Acknowledgments


References





































































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy








































EnergyJournal of


Journal of


Renewable Energy






Volume 2013

Advances in



ISRN Biotechnology








FuelsJournal of








Advances in


Volume 2013Number 1













RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy







RotatingMachinery






EnergyJournal of













Advances in

FuelsJournal of








Advances in




Journal of


Renewable Energy



hydrogen production technologies: current state and future

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