renewable fuels via catalytic hydrodeoxygenation

Applied Catalysis A: General 397 (2011) 112

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Applied Catalysis A: General

journa l homepage: www.e lsev ier .com

Review article

Renewable fuels via catalytic hydrodeoxygenatio

T.V. ChouConocoPhillips

a r t i c l

Article history:Received 1 NoReceived in reAccepted 20 FAvailable onlin

Keywords:Bio-fuelsDeoxygenationRenewablesPyrolysis oilsTriglycerides

Contents

1. Introd2. HDO o

2.1. Hydroprocessing in stand-alone mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.1.1. Inuence of process conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.1.2. Inuence of feed and catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2. Hydroprocessing in co-processing mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3. Potential future research areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3. HDO of bio-oil feeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.

3.2.

3.3.4. Life cy5. Concl

Refer

1. Introdu

Renewabthose deriv

CorresponE-mail add

0926-860X/$ doi:10.1016/j.HDO of bio-oils derived from high pressure liquefaction of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.1. Inuence of nature of feed-stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.2. Inuence of catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.3. Inuence of operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7HDO of bio-oils derived from pyrolysis of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.2.1. Stabilization studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2.2. Dual stage studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2.3. Combined dual stage studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Potential future research areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10cle assessment (LCA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

uding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11ences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

ction

le transportation fuels may be generally dened ased from the processing and upgrading of various forms

ding author.ress: [email protected] (T.V. Choudhary).

of biomass and degradable municipal waste feedstocks. Typi-cal products are hydrogen, methane, propane, ethanol, butanol,gasoline and diesel. Another denition used by regulatory and gov-erning bodies around the world describes a renewable fuel as anyfuel derived from renewable sources of biomass designed to reducethe amount of fossil fuel within the transportation fuel pool of aregion [1]. Renewable fuels are often classied into three gener-ations [2]; those produced from (i) the conventional processing

see front matter 2011 Elsevier B.V. All rights reserved.apcata.2011.02.025dhary , C.B. PhillipsCompany, Bartlesville Technology Center, Bartlesville, OK 74004, USA

e i n f o

vember 2010vised form 14 February 2011ebruary 2011e 24 February 2011

a b s t r a c t

There is considerable interest in investigating the deoxygenation process, due to the high oxygen contentof the feed-stocks used for the production of renewable fuels. This review addresses studies related tothe catalytic hydrodeoxygenation of two feed-stocks (a) oils with high content of triglycerides and (b)oils derived fromhigh pressure liquefaction or pyrolysis of biomass. Future research directions that couldpotentially bridge the existing gaps in these areas are provided.

2011 Elsevier B.V. All rights reserved.

uction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1f triglyceride-based feeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3/ locate /apcata

n

2 T.V. Choudhary, C.B. Phillips / Applied Catalysis A: General 397 (2011) 112

of edible feedstocks (e.g., cane-based ethanol via fermentation,biodiesel via esterication); (ii) the advanced processing (e.g., gasi-cation, hydroprocessing, pyrolysis) of non-edible feedstocks (e.g.,waste greases, lignocelluloses, refuse) and (iii) the harvesting andadvanced p

A simplfrom biombroken dowand fats/oilcellulose frafatty acids.ten [6] havefor upgradiprocess owthe entire rtional hydroproduction(HDO) of fa

HDO isproduction(green) dreactions afractions algenation (Hof olens/a

(thiophene

C4H8 +H2 (pyrrole)C4

(furan)C4H4

These hto removethrough a sthe oxygenless attentias petroleuhydroprocetion step s500,000ppmspeciationwof biomassa renewablefacility mayHowever, alignocelluloof phenols,by Bridgwafast pyrolysuble lignin(1015wt%

Estericroutes for pbased feedgrease. In tfatty acidmwith triglycmonly refer

CH2(R1COO

+3RCOOMHere, th

carbon chaTheFAMEm

making it a diesel oxygenate. Additional information on this topiccan be found elsewhere [13].

When the distillate fuel is produced by catalytically removingoxygen (e.g., HDO) completely from the triglyceride (assuming sat-

acyl

1COO

O

resuH3) iablere fr

pariset alnomne oe biog equignicomtry.ent

d feei) suse aent lof theumses. Bthese froepreethoxybeundsaresic Hl, resils auchstersontrn forundsfor dtandundper istockg degike mf a sreprolvetiontudieeir iuchstroitesr intthubtaioffe

ly inrocessing of ultra-high yield biomass (e.g., algae).istic schematic showing renewable fuels productionass is provided in Fig. 1. The biomass itself may ben into three basic categories, carbohydrates, lignin

s. Carbohydrates primarily include cellulose and hemi-ctions. Fats are mainly comprised of triglycerides and

Corma [3], Huber [4], Kamm [5] and Centi and van San-adequately outlined the various bio-rening strategies

ng these fractions into chemicals and fuels using blockdiagrams. The intent of this paper is not to review

esearch area but rather to focus exclusively on conven-processing studies (with real feed-stocks) as related toof renewable fuels from catalytic hydrodeoxygenationts/vegetable oils and biomass derived oils.an example of hydroprocessing application for theof both renewable (green) gasoline and renewableiesel as discussed in detail by Marker et al. [7]. HDOlso occur during the hydroprocessing of petroleumong with hydrodesulfurization (HDS), hydrodenitro-DN), hydrodemetallization (HDM) and the saturation

romatics [8].

)C4H4S + 3H2 C4H8 +H2S HDS (1)C4H10 Saturation (2)

H5N + 3H2 C4H8 +NH3 HDN (3)O + 3H2 C4H8 +H2O HDO (4)

ydroprocessing reactions use high pressure hydrogenS, O and N heteroatoms out of petroleum feedstockseries of hydrogenolysis and hydrogenation steps. Since,in petroleum is typically less than 3000ppmw(Table 1),on has been paid to HDO as compared to HDS as farm upgrading research is concerned. However, in thessing of biomass feedstocks, HDO is a critical reac-ince a neat biomass feedstock may contain up towoxygenwithminimal amounts of sulfur. Theoxygenithin these feedstocksvaries signicantlywith the type

and upgrading methods employed [911]. For instance,HDO feedstockproduced fromagasication-to-liquidscontain a signicant amount of alcohols and ethers.bio-oil HDO feedstock derived from the pyrolysis ofse may contain a relatively disproportionate amountcarboxylic acids and ketones. According to the workter and Peacocke [12], a bio-oil produced from manyis operations yields mostly water (2030wt%), insol-(1520wt%), aldehydes (1020wt%), carboxylic acids) and carbohydrates (510wt%).ation and HDO are considered important commercialroducing distillate range bio-fuels from triglyceride-

-stocks such as vegetable oils, animal fat and ediblehe liquid-phase, commercial esterication reaction, aethyl ester (FAME) biofuel formedby reactingmethanolerides in the presence of caustic or acid catalyst is com-red to as bio-diesel.

)CH(R2COO)CH2(R3COO) + 3MeOH C3H5(OH)3e (5)

e fatty hydrocarbon tail may vary R =R1, R2 or R3 inin length, as well as, number of unsaturated regions.olecule (RCOOMe) contains twooxygenatoms thereby

urated

CH2(R

+6H2the

uct (R

RenewstructuA comKalnesan eco[17], othat thexistin

A smodelchemisfundamderiveoil, (icellulorepresmanypetroleproces120 ofrhizomoften ras, 2-mmethocompooil andcellulosorbitolipid-oacids salkyl ehave creactiocompousefulunderscompothispafeed-svaryin

Unlistry oof fewies invinteracvious slose thtures sto thealyst sweakestudieseasily oies alsostronggroups and no oxides of carbon production),

)CH(R2COO)CH2(R3COO) + 12H2 C3H8 +3RH3(6)

lting straight-chain, renewable hydrocarbon fuel prod-s referred to as renewable diesel in the marketplace.diesel molecules are indistinguishable in molecularom conventional petroleum-derived diesel molecules.on of the fuel properties was provided in the reports by. [14], Kuronen et al. [15] and Rantanen et al. [16]. Fromics viewpoint according to Holmgren and co-workersf the most important advantages of the HDO route is-based feedstocks can be processed at reneries usingipment and thereby minimizing capital cost.cant amount of work has been dedicated to usingpounds/surrogates for understanding the HDO reactionModel compounds/surrogates are selected based on theal structural classes describing the upgraded biomass-d-stocks namely; (i) lignin precursors to represent biogars and sugar alcohols to represent cellulose/hemi-nd (iii) triglycerides and fatty acid derivatives toipids or fats/oils. A review by Furimsky [18] mentionsoxygen containing model compounds present in both

oils and bio-oils derived from pyrolysis or liquefactionridgwater and co-workers [19] recently identied overe type of compounds in the fast GCMS pyrolysis ofm cassava plants. Liquefaction and pyrolysis oils aresented in the literature by the model compounds suchxyphenol or guaiacol, ethylphenol, diethylsebecate andnzene or anisole. However, one should note that theserepresent only the 25wt% phenolic portion of the bio-

more representative of lignin precursor molecules. ForDO feeds, C5 and C6 sugar alcohols such as, xylitol andpectively have served as model species [4,20]. Fats andre often represented by model triglycerides and fattyas, tristearate and stearic acid, respectively or as fatty(e.g., methyl stearate). Krause and co-workers [2127]

ibuted signicantly to the understanding of the HDOfats and their corresponding derivatives using modelover the last decade. The model feedstock studies are

etermining the relative activities of HDO catalysts anding HDO reaction kinetics. While some relevant modelstudies will be mentioned herein, the main purpose ofto report the recentprogress in thecatalyticHDOof reals (e.g., vegetable oils, pyrolysis oils, etc.) that containrees of oxygen.odel feed-stock studies which focus on the chem-

ingle representative compound or a simple mixtureesentative compounds [28,29], real feed-stocks stud-investigation of bulk effects arising from intertwinings of complex mixtures of molecules [30,31]. From pre-s, it has been established that individual molecules can

dentity and respective inuence within complex mix-as those found in real feed-stocks [32]. This is relatedng adsorption of certain molecules on the active cat-resulting in inhibition of other molecules that exhibiteraction with the catalyst sites [33]. Real feed-stocks offer practically relevant information that cannot bened frommodel compound studies. These types of stud-r information related to various contaminants that mayuence the overall feed-stock processability and impact

T.V. Choudhary, C.B. Phillips / Applied Catalysis A: General 397 (2011) 112 3

omass

the catalysHDO can bhydroprocecessing of bof biomass.lowed by abiomass. Suthis reviewcondensatioing operatio

2. HDO of

One of tmethods fois that the coxygen freetional petro

]. Inble in) dersign

tly inum-alsoy issre qufeeds-procRela

Table 1Atomic compo

Substance

Pine (Hard)Corn stoverRice huskCottonseed hCelluloseHemi-celluloLigninCrude oilLiquefactionPyrolysis bioGasolineDieselEthanolDMEMTBEMethaneFig. 1. Hydrodeoxygenation of the basic building blocks of bi

t stability. Real feedstock studies related to catalytice broadly classied into two main categories; (i) thessing of triglyceride-based feeds and (ii) the hydropro-io-oil feeds derived from the liquefaction or pyrolysisHerein, triglyceride-based feeds are addressed rst fol-discussion on studies related to bio-oils derived fromgar-based feed-stocks have purposely been avoided insince the production of higher hydrocarbons involvesn steps [34,35] outside of the traditional hydroprocess-ns.

[3638guisha(FAMEcontainnicanpetroleFAMEstabilitoil mobasedof (costocks.triglyceride-based feeds

he main advantages of the HDO route relative to otherr making biomass-derived diesel (e.g., FAME synthesis)orresponding renewable-fuel product is a high quality,, hydrocarbon fuel completely fungible with conven-leum-based renery fuel blendstocks and components

2.1. Hydrop

Studiesrelevance inin the food i

sition of various feed stocks and fuels adapted from Ref. [3,18,87].

C (mol%) H (mol%) O (mol%)

32 48 2033 46 2129 48 23

ull 22 48 3029 48 23

se 33 48 1940 46 143846 5472


Fig. 2. Key proable fuels.Adapted from

tion (Eq. (7)

(triolein)C5

Howevefuel producto alkanes [molecule watoms andCO bond hstraight-cha

O

OO

R1

R2

R1 = (C

x1:n

1)

In recenoptimizingthe hydrophave focusehave investproduction

2.1.1. InueSeveral

hydroprocesimplisticaldation of tproduced frreaction nesunower oKaluza [50]vated tempdecomposefollowed byreactions toalcohols arefatty alcoho

(octadecano

(methylocta

C18H3The dec

long-chain

from

monpanie

cacid

ordinn oing u

O

x1:n

1

y-hl gro

O

he aimultaneously even within the same triglyceride moleculeg only one -elimination. However, in the presence ofperty differences between different types of available diesel renew-

[2].

) of vegetable oils [39,40].

7H104O6 +3H2 C57H110O6(tristearate) (7)r, the hydroprocessing studies related to the renewabletion involve complete conversion of the vegetable oils4143]. As shown below, a single mole of a triglycerideith an acyl group (Ri) containing xi number of carbonni CC double bonds can be reduced completely viaydrogenolysis and hydrogenation to produce 3mole ofin parafndiesel, 1mol of propane and6mole ofwater.

O O

R3

O

+ H2(12+3n)R1

HR2

HR3

H

+ OH2CH3

CH3

+ 6

t years, there has been considerable interest inthe production of renewable hydrocarbon fuels viarocessing route. As described below, some studiesd on optimizing the process conditions while othersigated different catalyst options for renewable fuels.

nce of process conditionssequential and concurrent reactions occur during thessing of triglyceride-based feeds. These reactions canbely classied as saturation of olenic bonds [44], degra-riglycerides [45] and hydrogenation of intermediatesomthedegradationof triglycerides [4648]. A completetwork was illustrated by Huber and co-workers usingil [49] and more recently in the work by Kubicka and

Adapted

carbonaccom

(steari

Accpositioproducacids;

R1 = (C

or bthe acy

O

O

R3

O

R2

In toccur sallowinusing rapeseed oil. In the presence of hydrogen at ele-eratures, the fatty acyl chains become saturated and/ord into fatty acids, mono- and diglyceride fractionsdecarboxylation, decarbonylation and hydrogenationproduce renewable diesel. In hydrogenolysis, fattyreduced to diesel and fatty esters [51] are reduced tols directly or via dehydrationhydrogenation steps

l)C18H37OH + H2 C18H38 +H2O (8)

decanoate)C17H33COOCH3 +3H27OH + CH3OH (9)arboxylation and decarbonylation reactions producealkanes and alkenes by releasing carbon dioxide and

hydrogen aquickly satuoff the glyc

Expectein deningtion tempecatalyst atThe long-ching reactionand alkylbeworkers inhydroproceNiMo catalygenated int360 C. FormFig. 3. Effect of reaction temperature on Buriti oil.[53].

oxide, respectively. The release of carbon monoxide isd by the simultaneous rejection of water.

)C17H35COOH C17H36 +CO2 (10)

g to Vonghia et al. [52], triglyceride thermal decom-ccurs through a concerted -elimination pathwaynsaturated glycol di-fatty acid esters (UGDEs) and fatty

O O

O

R1

O

R3OR2

H

H

HH

H

)

O O

R3

H

OO

R1

O

O

R2

H

H

H

H

ydrogen transfer resulting in CC bond cleavagewithinup also producing straight-chain, olen diesel.

O

O

R1

H

R3

+O

O

O

O

R1

OH

CH2

O

R2

'

R'3 = (R

3-1:n

3+1)

bsence of hydrogen, both decomposition routes cannd conventional hydroprocessing catalysts, alkenes arerated, thus allowing additional-eliminations to occur

erol back-bone.dly, the reaction temperature plays an important rolethe nal product composition. The inuence of reac-

rature on the yields from Buriti oil over a sulded NiMoa hydrogen pressure of 14MPa is shown in Fig. 3 [53].ain alkane yield was found to decrease with increas-temperature (360430 C), while the gas, cycloalkane

nzenes yields were found to increase. Simacek and co-vestigated the effect of reaction temperature on thessing of rapeseed oil over a commercial hydrotreatingst [54]. The small content of un-reacted feed and oxy-ermediates that was observed at 310 C was absent atation of n-heptadecane and iso-alkanes was found to


increase with increasing temperature, whereas n-octadecane con-tent decreased. These studies indicate that the decarboxylationreaction, which results in formation of an alkane with one lesscarbon atom than the corresponding carboxylic acid, is favored athigher tempand pour pature, as exqualitativehydrogen ptemperaturobserved fobased cataltemperaturspective of

Model cstudies havprocess [57supported Nqualitativeexplained bkinetic expr

r = kKH(1 + KH

where thehydrogen dative amoucatalyst (Karate of reacat 310 C ancatalyst in a[53]. The coest pressureinvestigatednegligible dtration of aincreased frthepressurethe other haSimacek ancessingpreshydrotreatiwith pressuperature indecreased s15MPa, howtivity for n-on the reacthe selectivsure, whileexactly oppeffectswerepoint) propand temperwarded for

The effenized mesoAt 280 C, thfrom 100selectivity(280 C)wapressure thit was aboulower at 0.7from the h

atty a

from

atalyy acire sizactioin leernationof peacidi533

Inuefatty[53

s conhe rropr

on ththemedig. 4,ve ama ae withe veasen incdiestive component as well as the support on the stand-alonerocessingof triglyceride-based feed stocks [6365]. The ef-NiMo/Al2O3, Ni/Al2O3 and Mo/Al2O3 sulded catalysts has

ly been compared in hydrotreating rapeseed oil [63]. At acontent of active sites (3.4 atoms/nm2), the NiMo/Al2O3

und to be much more active than the mono-metallic cat-The selectivity to hydrocarbons (at iso-conversion levels)e bimetallic NiMo catalyst was also signicantly higher asred to the Mo/Al2O3 and Ni/Al2O3 catalysts. The enhancedance of the NiMo catalyst was attributed to the synergy

n NiMo for the bimetallic catalysts. From a reaction net-iewpoint, the Ni/Al2O3 catalyst resulted in products fromcarboxylation pathway whereas the NiMo/Al2O3 catalystinantly formed products by the hydrogenation pathway.

heless, the NiMo/Al2O3 catalyst yielded signicant productsoth pathways. In a separate study, Yakovlev et al. founde bimetallic NiCu catalysts were superior than Ni cata-eratures. The cold ow properties such as cloud pointoint were found to improve with increasing temper-pected from the increase in iso-alkanes content. Thetrend for the temperature effect was similar at bothressures studied (7MPa and 15MPa). Also, a similare effect on the product yields (as described above) wasr different NiMo catalysts [55]. Investigation of CoMo-ysts on different supports showed that an increase ine decreased the selectivity of oxygenated products irre-the support used [56].ompounds as well as vegetable oil hydroprocessinge shown that higher pressures are favorable for the,58]. In the HDO of tricaprylin and caprylic acid overiMo oxide catalysts, Boda et al. [59] discussed how

trends in total hydrogen pressure (1022atm) could bey LangmuirHinshelwoodHougenWatson (LHHW)essions;

2pH2KacidCacid

2pH2 + KacidCacid)2(11)

adsorption and reactions of fatty acids with surfaceetermine the kinetic rates. For the cases where the rel-nt of surface hydrogen is low due to the nature of thecidCacid KH2CH2), the hydrogen pressure will increasetion. Product yields obtained from Buriti oil processedd different hydrogen pressures over a sulded NiMobatch reactor further illustrates the effect of pressure

ncentrationof un-reacted fatty acidwashighat the low-(7MPa) investigated, however, at the highest pressure(14MPa), the amount of un-reacted fatty acids was

ue to complete hydrogenation. Although the concen-lkanes increased signicantly when the pressure wasom7MPa to 10MPa, it remained almost constantwhenwas increased from10MPa to14MPa. Thegasmakeonnd increased almost linearly with increasing pressure.d co-workers also investigated the effect of hydropro-sureon theupgradingof rapeseedoil overacommercialng NiMo catalyst [54]. Interestingly, different trendsre were observed in this study depending on the tem-vestigated. At 310 C, the selectivity for n-heptadecaneignicantly on increasing the pressure from 7MPa toever it was insensitive to pressure at 360 C. The selec-

octadecane also showed a different trends dependingtion temperature. At the lower reaction temperatureity for n-octadecane increased with increasing pres-the pressure effect on n-octadecane selectivity was

osite at the higher reaction temperature. The opposingalso observed from the cold ow (cloud point and pour

erties of the products obtained under different pressureature conditions.Unfortunatelynoexplanationwas for-these unexpected results.ct of pressure has also been investigated over orga-porous alumina (OMA) supported CoMo catalysts [56].e conversion of triglycerides (in rapeseed oil) dropped

% (pressure =7MPa) to 80% (pressure =0.7MPa). Thefor oxygenated products and the nC18/nC17 ratios also found tobevery sensitive topressure. At the lowere selectivity for theoxygenatedproductwas45%whilet 10% at 7MPa. The nC18/nC17 ratio was considerablyMPa, indicating that there was a higher contribution

ydrodecarboxylation reaction at the lower pressure.

Fig. 4. Festers.Adapted

OMA cto fattthe poand retic chathe intboxyla(26%)Lewissites (2

2.1.2.The

in Fig. 4alkaneacids. Toil hydbaseding onoils, soFromFthathato tucuincreastion ofto incrwith a

Stuthe achydropcacy ofrecentsimilarwas foalysts.over thcompaperformbetweework vthe depredomNevertfrom bthat thcid composition of vegetable oils as determined by analysis of methyl

[53].

st supports are synthesized with surfactants similard intermediates (e.g., stearic and lauric acids) [60], soes (24nm) allow space for reasonable diffusion ratesn. A typical oleoyl or stearyl group with a characteris-ngth of roughly 21 A [61] can access the active sites onl surfaces of these materials. The increased hydrodecar-selectivity on OMA may be due to the small populationnta-coordinated aluminum that provides intermediatety [62] between octahedral (6570%) and tetrahedral%).

nce of feed and catalystacid composition of different vegetable oils is shown

]. Hydroprocessing studies have shown that the producttain equivalent or one less carbon than the parent fattyenewable diesel product composition of the vegetableocessing reaction can thereby be roughly estimatede fatty acid composition of the feed. However, depend-chain length and degree of saturation of the vegetableifferenceshavebeenobserved in theproductyields [53].the soybean, buriti andmaracuja oils contain fatty acidslonger chain lengthandaremoreunsaturated comparednd babassu oils. The product gas yields were found toth decrease in chain length and the degree of unsatura-egetable oils. Further, the alkane selectivity was foundwhile the cycloalkane selectivity was found to decreaserease in the degree of saturation.have been undertaken to understand the effect of both


lysts for the upgrading of bio-diesel [66]. Their study indicatedthat the deoxygenation over Ni/CeO2 proceeded via CO bondhydrogenolysis, while decarboxylation was the major route overthe NiCu/CeO2 catalyst. Synergy for bimetallic systems (rheniummodied Pinvolving h

Althougconventionrier, someIn a recentoil deoxyge41 with vaAl into thehydrocarboportswas inCoMo catalsignicantlorganized mtionmechanwas moreto the CoMthe effect o16, DMS-1)[71]. The sein the follo16CoMowere foundthe HMS-su

2.2. Hydrop

Fromanfeed-stocksa relativelysome studievacuum gastigated co-p

In the stcommerciafound thatmuch fastersion of sunsulfur conveprocessingthe selectivwith increaThe studiesinvestigatedover the su

Additionand co-worinhibit sulfulyst [72]. Hearlier [49]the selectivcontent wagen consumaromatic codecrease inwas attribuaromatic cosion.Due togravity andseed oil conin vegetablof the diese

the feed from 0% to 25% resulted in an increase in the cloud pointproduct from4.4 C to 10.5 C [72]. In a separate study [73], the coldlter plugging point was found to be lower than 10 C for a 10%rapeseed oil content feed, while it was higher than 0 C for the 20%

ed cong wlsonaling]. Lignit itheNiMhe pr, whlthoutly an cogateiffereto gahyd

raturtion

tenti

ougerideationh ation

echated-alkle d

nforter tothe

h cozingnic ps [77ing b) prohav

miniIt wts wt ofal coics

izatiroce

m anssaren cing tighernd wnsumthe

ft andesirtentctedt/H-ZSM-5) has also been observed in a recent studyydrotreating of jatropha oils [65].h much of the research undertaken thus far employedal alumina as the active component support or car-studies have also considered other supports [6569].study, Kubicka and co-workers investigated rapeseednation over Co and Mo suldes supported on MCM-rying Si/Al ratios [70]. Although the incorporation ofMCM-41 framework enhanced the selectivity towardsns, the performance of the catalysts with MCM-41 sup-ferior to a catalyst using conventional alumina support.ysts supported on MCM-41 were also found to havey inferior performance to CoMo catalysts supported on

esoporous alumina (OMA) [56]. From a deoxygena-ismviewpoint theCOhydrogenolysis (HDO)pathway

dominant for the CoMo/OMA catalysts as comparedo/MCM-41 catalyst. Nava et al. recently investigatedf mesoporous silicate supports (SBA-15, HMS, SBA-on the hydroprocessing of an olive oil by-product

lectivity for parafn production was found to decreasewing order: CoMo/SBA-15>CoMo/HMS>CoMo/SBA-

/DMS-1. The SBA-15, SBA-16 andDMS-1 based catalyststobe signicantlymore effective indeoxygenation thanpported catalyst.

rocessing in co-processing mode

economics viewpoint, co-processing triglyceride-basedwith petroleum fractions in existing renery units islow cost method to produce renewable fuels. Whiles have considered co-processing of vegetable oils withoil (VGO) boiling range petroleum, others have inves-rocessing with light gas oil (LGO) fractions.udies involving blends of VGO and sunower oil over al sulded NiMo/Al2O3 catalyst, Corma and co-workersthe kinetics of oxygen removal from sunower oil wasthan that of sulfur removal from VGO [49]. The conver-ower oil at 350 C was 100% while the correspondingrsionwasonly 41%. Similar to stand-alone vegetable oil

studies [54] even in the sunower oil-VGOblend studiesity for decarboxylation products was found to increasesing temperature and increasing sunower oil content.also revealed that sunower oil in the concentration(up to 50%) did not decrease the rate of desulfurization

lded NiMo/Al2O3 catalyst.al agreement was provided in the studies by Knudsenkers that also suggested rapeseed oil (up to 25%) did notr removal from LGO over a sulded NiMo/Al2O3 cata-owever in contrast to the VGO blend work described, the LGO-rapeseed oil studies revealed a decrease inity of decarboxylation products when the rapeseed oils increased from 15 to 25%. Although the total hydro-ption was highest for the 25% rapeseed oil feed, thenversion was the highest for the LGO alone feed. Thearomatic conversion for rapeseed oil containing feedsted to the inhibition of the hydrogenation of mono-ringmpounds by CO formed from the rapeseed oil conver-the increase inparafnic content of theproduct, theAPIcetane of the product increased with increasing rape-tent. In general, it has been observed that an increase

e oil content is detrimental to the cold ow propertiesl product. An increase in the rapeseed oil content in

rapeseAlo

have afunctioupgrad[7476(FCC) utigatedover a[74]. Tto 39.230%. Anicannitrogeinvestiover ddieselon thetempeproduc

2.3. Po

Althtriglycinformresearcconventhe msatura(C15+ ndesirabalso uIn ordricingresearcoptimiparafprocesfollowand (bshouldwhileyields.catalysamounregioneconomisomerhydrop

Frounnecehydrog(breakably hCC bogen coexceedgas shiof theThe exis expentaining feed.ith conventional hydrotreating catalysts, some studiesconsidered the use of hydrocracking catalysts (bi-catalysts containing metals and acidic component) forblends of vegetable oils and petroleum feed-stocksht cycle oil (LCO) from the uidized catalytic cracking

s a very poor quality diesel range material. Yunqi inves-mild hydrocracking of soybean oil in LCO blend (030%)oP-HUSY/Al2O3 catalyst at 370 C and 4MPa pressureoduct cetane number was found to increase from 32.7en the soybean oil content was increased from 0% togh the corresponding sulfur conversion was not sig-ffected by the presence of additional triglycerides, thenversiondropped from86.1% to 83.1%. Bezergianni et al.d the hydroprocessing of sunower oil and VGO blendsnt hydrocracking (differing acidity) catalysts [75]. Thesoline ratio in the product could be manipulated basedrocracking catalyst used. As expected, higher reactiones were found to be favorable for maximizing naphthafrom the sunower oil-VGO blends.

al future research areas

h previous studies on the hydroprocessing of-based feed-stocks have forwarded considerable, from a commercial viewpoint there are still some

reas that would benet from more attention. Theal hydroprocessing of triglycerides, irrespective ofnisms, dominantly results in the formation of linearhydrocarbons. While linear saturated hydrocarbonsanes) are extremely attractive from the viewpoint ofiesel combustion properties such as cetane, they areunately responsible for inferior cold-ow properties.maximize diesel volume without signicantly sac-desirable properties, it would be benecial for themmunity to further increase their research focus oncatalytic isomerization or dewaxing of the long-chainroduct formed from the triglyceride hydroprocessing]. The research in this area could be classied in theroad sections: (a) improved isomerization catalystcess optimization. The desirable dewaxing catalystse sufcient acidity to perform isomerization activitymizing cracking activity for maintaining high distillateould be benecial to have a series of isomerizationhich have a range of activity for providing optimalcold-ow property upgrading (depending on the

ld-ow product property constraints). From a processviewpoint, it would be most benecial to locate theon/dewaxing catalyst in the same reactor after thessing catalyst.economics and environmental viewpoint, minimizing

y hydrogen consumption is important. The amount ofonsumed for triglyceride conversion by the HDO routehe CO linkage with no release of CO/CO2) is consider-than that by the decarboxylation route (breaking of aith release of CO or CO2). However, the total hydro-ed by the decarboxylation route could theoretically

HDO route through secondary reactions such as waterd methanation [72]. Moreover, there is a loss in volumeed product associated with the decarboxylation route.of hydrogen consumption via the different mechanismsto be sensitive to the process conditions and catalysts.


More studies need to beundertaken to develop further insights intominimizing unnecessary hydrogen consumption.

Toensureoptimal co-processingof triglycerideswithpetroleumfractions in existing renery units, it is critical to developan enhanceand converfraction. Sothat thereand dieseltion over tsaturationtriglyceridescarce. Singen duringworldwideto conducterides on tcatalysts.

3. HDO of

Conversstudied viaand (b) pyrbio-oil prodtype of biomcatalytic HDsure liquefasections bel

3.1. HDO ofbiomass

3.1.1. InueResearch

compared tfraction obtwas produccessing studcatalyst bedthe light oilating condivelocity) ana signicanilar to thatconsume lecompared t

In a sepacessability oto operatio[80]. GCMcompositioring phenolconcentratiInterestingltheir ability1 was a supwell as prodpoor HDOoil 2 due tobe the maimechanism

3.1.2. InueConvent

rior HDO pe

such as copperchromite and supported Ni catalyst [79]. While thecopperchromite catalyst suffered from lowactivity, theNi catalystproduced more undesirable gaseous products, consumed consid-erably more hydrogen and was less stable. Also, the sulded form

oMoformt is u, it m) duing oo dre fa

ts shen t

diesrotress [8withloweowede volts wore vts wrrow

Inueert eting

al sodiong fromtracrotreticwideangeversd-sththaensimospoking

easeystemt andsioninc

en clightreatito thedmg th

he hyhydr

DO of

-oil psupprocing oare cd understanding of the effect of triglycerides (feedsion products) on the processing of the petroleumme of the studies described earlier have revealedis no inhibition effect for the HDS reaction (VGO) over a NiMo catalyst [49,72]. However, inhibi-he NiMo catalysts has been observed for aromatic[72] and nitrogen removal [74]. Studies related toco-processing over CoMo catalysts are relatively

ce CoMo catalysts inherently consume less hydro-LGO hydrotreating, a large number of ULSD units

use CoMo catalysts. It would therefore be benecialfocused studies to understand the effect of triglyc-he processing of the petroleum fractions over CoMo

bio-oil feeds

ion of biomass to bio-oil feedstocks has been mainlytwo routes: (a) highpressure hydrothermal liquefactionolysis. The differences in physical properties betweenuced by both processes can vary signicantly due to theass feed, conditions and reactor design (Table 2). TheO studies of the bio-oils obtained from the high pres-ction and pyrolysis processes are discussed in separateow.

bio-oils derived from high pressure liquefaction of

nce of nature of feed-stockers at Pacic Northwest National Laboratory (PNNL)he processability of a bio-oil with that of a lighter oilained from the (same) bio-oil [78,79]. The bio-oil (TR7)ed from high pressure liquefaction of wood. Hydropro-ies were conducted using a continuous ow xed bedsystem using an up-ow conguration. Compared tofraction, the complete oil required more severe oper-tions such as a higher residence time (lower spaced operating pressure. Also, the complete oil consumedtly larger amount of hydrogen. This observation is sim-for petroleum feed-stocks wherein lighter fractions

ss hydrogen and are easier to hydrotreat (HDS, HDN)o a crude oil.rate study the same research group compared the pro-f two bio-oils, which exhibited different properties duenal differences employed by the liquefaction processS characterization studies revealed the difference in then of the two bio-oils. While cyclic ketones and singleics were predominantly observed in bio-oil 1, a largeron of multi-ring phenolics was observed in bio-oil 2.y the two bio-oils also showed signicant differences into beupgraded via thehydroprocessing process. Bio-oilerior feed-stock in terms of ease of oxygen removal asuction of a desirable lighter hydrocarbon product. The

performance was exacerbated even further with Bio-a signicant alkali content, which was considered to

n reason for catalyst deactivation via a pore plugging.

nce of catalystionalhydrotreatingcatalystswere found tohaveasupe-rformance as compared to other catalysts investigated

of the Coxidiccatalysbio-oilof H2Sscreenwere nthe samcatalyshydrogties.

Stuof hydbiomaalystsmuchlyst shits porcatalystheir pcatalysthe na

3.1.3.Gev

pretrearesiduextractvaryinvent exfor hyda magnover aature rthe conthe feeof napmore sand atture, crange.

Incralyst scontenconvertion tohydrogof thehydrotnentsproposavoidin(over tin the

3.2. H

Bioto havefactionupgradsis oilshydrotreating catalyst considerably outperformed theof the same catalyst. This implies that if a hydrotreatingtilized for completing the HDO of liquefaction derivedust remain in a sulded form (using appropriate sourcering the bio-oil upgrading process. A study involvingf different hydrotreating catalysts revealed that thereamatic differences between the performances withinmily of catalysts [80]. In general, all the hydrotreatingowed a similar trend for residual oxygen content ando carbon ratio with varying liquid hourly space veloci-

have also been undertaken to investigate the effectating catalyst pore size on the upgrading of liqueed1]. Three catalysts were used in this study; two cat-large average pore diameters and one catalyst with

r pore diameter. Although the smaller pore size cata-the best HDO performance, it was unable to maintain

ume during the course of the run (6h). Since the twoith larger pore diameters were better able to maintainolumes, itwas speculated that the higher pore diameterould show a better long term performance compared topore catalyst due to higher stability.

nce of operating conditionst al. investigated solvent extraction as a process forbio-oils (separating light oil from heavier fraction andium salts) before hydroprocessing (HDO) [82,83]. The

yields were found to be very sensitive to the solvent3 to 74vol% pentane to acetone, respectively. The sol-

ted bio-oil was subsequently investigated as feed-stockeating studies over a sulded CoMo/Al2O3 catalyst inally stirred autoclave system. Studies were undertakenrange of operating pressure (515MPa) and a temper-of 300390 C. The hydrotreating process resulted in

ion of some heavier oxygen-containing components ofocks into lighter hydrocarbon components. The yieldswere small without a catalyst and were found to be

tive to temperature than pressure. While the naphthaheric gas oil yields increased gradually with tempera-was found to be minimal in the medium temperature

d gasoline yields can be obtained by using a dual cat-: hydrotreating catalyst for decreasing the oxygena cracking component for enhancingheavy component

. Baker et al. proposed a two step process modica-rease the aromatic gasoline yields while minimizingonsumption [84]. Their process involved separationer components from the products obtained after theng step and thereby only feeding the heavier compo-e hydrocracking section. According to the authors theodicationmaximizedaromatic gasolineproductionbye unnecessary saturation/loss of aromatic compoundsdrocracking catalyst) of the gasoline fraction produced

otreating step.

bio-oils derived from pyrolysis of biomass

roduction from the pyrolysis of biomass is considerederior economics than that from the high pressure lique-ess [85]. Consequently more studies have targeted thef pyrolysis bio-oils. The properties of different pyroly-ompared with high pressure liquefaction oils in Table 2


Table 2Comparison of properties of pyrolysis oils with high pressure liquefaction oils [86].

Pyrolysis oils High pressure liquefaction oils

Georgia tech Waterloo SERI Laval VTT peat TR7 TR12

Carbon (wt%) 39.5 45.3 48.6 49.9 51.0 74.8 72.6Hydrogen (wt%) 7.5 7.5 7.2 7.0 7.8 8.0 8.0Oxygen (wt%) 52.6 46.9 44.2 43.0 40.3 16.6 16.3Moisture (wt%) 29.0 24.5 NA 18.4 NA 3.5 5.0Density@55 C (g/ml) 1.23 1.20 1.23 1.23 1.15 1.10 1.09Viscosity@65 C cps 10 59 NA NA NA 3000 17,000

[86]. The pyrolysis oils have considerably higher oxygen contentthan the high pressure liquefaction oils [80]. Correspondingly thepyrolysis oils, due to their more polar nature, contain signicantamounts of dissolved water (%). Although the pyrolysis oils have ahigher density, they have a much lower viscosity due to the highwater content and low molecular weight organics, such as formicacid and acetic acid [87]. A comparison of properties between realpyrolysis oils and model compounds is shown for reference inTable 3.

As a result of the high oxygen content, and presence of somehighly reactive species (e.g., guaiacol, alkoxyphenols), the pyrol-ysis oils areoils have ahydrotreatilization stepoils [86]. Fowork has bewith low tewith low tearate stepstemperaturfrom rst st

3.2.1. StabiEarly stu

ysis oils atreactor sys[86]. Basedture step fopyrolysis oitemperaturtion activitya continuouwood derivreactor plugsimilar ope

Table 3Comparisonoffrom bio-oil.

Property

Density (kg/HHV (MJ/kgKV (cSt)@50Water (%)C (wt%)H (wt%)N (wt%)O (wt%)S (wt%)Cl (ppm)Ash (ppm)pH

Guaiacol (C7H

Table 4Comparison of feed and product properties after low temperature hydrotreating ofwood-derived pyrolysis oil [89].

Property Ensyn pyrolysis oil

Feed Product

Acetone insolubles 2.98 0.21pH 3.17 6.5Moisture (%) 24.8 3.6Density (g/cm3)@20 C 1.21 1.07HHV (MJ/kg m.f.) 19.4 30.2H/C ratio 0.117 0.111

to thconpyro

ed frti etderivs od dio avmalrolepres

raturtabilolun

y, theed oed. Tin Tacon

d.eadreduced NiMo based catalyst for mild upgrading of pine

age upgrading of pyrolysis oil over CoMo/Al2O3 [86].

Pyrolysis oils

Laval SERI VTI peat

sing conditionsperature-inlet (C) 258 259 302perature-outlet (C) 400 376 391sure (psig) 2020 1980 2000V (h1) 0.13 0.10 0.19ct yieldssignicantly more difcult to upgrade. The pyrolysishigh propensity for coke formation even under mildng conditions. An additional low-temperature, stabi-is therefore recommended before upgrading pyrolysis

r the purpose of this review, the pyrolysis oil upgradingen classied as follows: (a) stabilization studies dealingmperature hydrotreating (b) dual stage studies dealingmperature and high temperature hydrotreating in sep-(c) combined dual stage studies that couple the lowe and high temperature steps in one system (productage not collected).

lization studiesdiesbyElliott et al. revealed thathydrotreatingofpyrol-temperatures above 350 C resulted in plugging of thetem and catalyst encapsulation by coke-like materialon these studies the authors proposed a low tempera-r stabilization (to prevent rapid coke formation) of thels. Subsequently the authors demonstrated that the lowe stabilization step required a catalyst with hydrogena-, such as Pd, Pt, Ru or Ni [88]. Experiments conducted insowreactorwith inert alumina at260 Cusinghard-ed pyrolysis oil showed very rapid coking followed byging. In contrast a stable operationwas observed underrating conditions with a sulded CoMo catalyst. Com-

properties between real and correspondingmodelHDO feedsderived

Real Model

Fast-py Guaiacol Acetic acid Phenol

L) 1.111.30 1.11 1.05 1.07) 1619 32.9 C 1080 1.2

1530 0 0 0

paredoxygenbilizedobtain

Conwood-tinuouwas fefeed) tisotherture ppartialtempeation sdown vactivitstabilizobtainertiesoxygenthe fee

Instgated

Table 5Single st

ProcesTemTemPresLHS

Produ

3249 68 40 776.98.6 6 7 6

00.4 0 0 04460 36 53 16

0.010.05 0 0 0375 0 0 0

100200 0 0 02.03.7 2.4 (1M)

8O2), acetic acid (C2H4O2), phenol (C6H6O).

Total oil (LAqueous pC5-225 CCarbon coCarbon in

Product proOxygen (wH/C ratio (Specic gre feed the stabilized pyrolysis oil product had a lowertent and higher viscosity [86]. The properties of the sta-lysis oil were found to be closer to that of the bio-oil

om the high pressure liquefaction process.al. investigated the low temperature hydrotreating ofed pyrolysis oil using a sulded NiMo catalyst in a con-w reactor system [89] (Table 4). The hydrogen streamrectly into the reactor (no premixing with the liquidoid plugging of feed lines. Instead of operating underconditions the reactor was operated using a tempera-(140 C at the inlet and 280 C at the outlet) and H2sure of 15MPa. The authors believed that the specice prole was important from the viewpoint of oper-ity. The reactor was operated for 120h and was shuttarily. While there was some initial decrease in catalystcatalyst remained fairly stable after 60h on stream. A

il yield of 72wt%with respect to the dry feed bio-oilwashe product properties are compared to the feed prop-ble 5. The upgrading resulted in a 60% reduction intent and corresponding hydrogen uptake of 264 L/kg of

of using a sulded NiMo catalyst, Xu et al. investi-/L feed oil) 0.42 0.37 0.44hase (L/L feed oil) 0.57 0.51 0.34frac. (L/L feed oil) 0.37 0.27 0.36nversion to gas (wt%) 35.5 25.0 30.0aqueous phase (wt%) 1.0 0.6 1.0pertiest%) 0.8 1.3 1.5mol/mol) 1.7 1.68 1.8avity (kg/L) 0.83 0.85 0.86


sawdust-derived pyrolysis oil [90]. The hydrotreating reaction wasinvestigated in a batch reactor system under the following pro-cess conditions: temperature =273 C, pressure =3MPa, reactiontime=2h. During the upgrading process the pH value of the bio-oilincreased fracids. The6.93wt%. Agupgraded bwhich was

Althoughfocus of mosome studialysts [92hydrotreatifollowingpsure =131derived fromcess conditproduct yiewood oil w0.640.81goils were fophase withwithmore hattributed tuct oil lesspreviously.course of thwas that evact as veryet al. [97] alderived) ovtion procee340 C, 30Mphases werproduct andresidue decrange. Calc6wt% undeactivity. Thperature anbased on ox

3.2.2. DualWhile th

focused onrst and thimportant fstage upgraobtained afstage. Reseacessing ofreactor oveI) step waswhereas sigature =353process conas fed) fromtions (stagecombined yfound to beconversionabout 8.8w

Gagnonstabilizationstage [98].

focused efforts to optimize therst stagewith the second stage. Therst stage studies spanned a temperature (80140 C) and pressurerange (410MPa), whereas the second stage studies were under-taken at 350 C and 17MPa. The dual stage studies showed that

timaeres attns unationmatiing ts furd pocataute

raturt fortedsis os sugo upgzatioas coempoundion,undeindi

condgatee ryieldy i

baseogenre cog fro1.12wpothanherntlyinedge. D0.78phassed tcon

ce vesed tic inund tdrocprodrack

C, 10t anyieldtinglsimil

Combm antudihe highom 2.16 to 2.84 indicating some conversion of organicH content of the bio-oil increased from 6.61wt% toing studies (storage at 5 C for 8months) of the rawand

io-oils indicated a phase separation for the raw bio-oils,not observed for the upgraded bio-oil.

conventional hydrotreating catalysts have been thest stabilization studies on bio-oil upgrading [78,91],

es have also considered the use of noble metal cat-96]. Elliott et al. investigated the low temperatureng of pyrolysis oils over Ru-based catalysts under therocess conditions [96]: temperature =180240 C;pres-5MPa; LHSV=0.220.67h1. The pyrolysis oils were

whitewood and bagasse (sugarcane). Under the pro-ions investigated a deoxygenation of 3170% and ald of 0.540.79g/g feed (dry) was reported for white-hile a deoxygenation of 3246% and product yield of/g feed (dry) was reported for bagasse oil. The productrmed in two separate phases consisting of an aqueousmore hydrophilic components and a dense tar phaseydrophobic components. The twophase formationwaso specic chemical transformations thatmade theprod-hydrophilic and not from polymerization as suggestedA large loss in catalyst activity was observed during thee experiments. An important conclusion of the studyen low levels of contaminants (sulfur and iron) couldstrong poisons for the Ru catalyst. de Miguel Mercaderso investigated the HDO of pyrolysis oil (forest-residueer Ru-based catalysts in a batch reactor. A typical reac-ded for 4h at a temperature range between 230 andPa and 5wt% catalyst. Above 300 C, three distinct

e observed; a heavy bottom oil/catalyst layer, a top-oilan aqueous layer. The amount of top-oil micro-carbon

reased from 4.7wt% to 2.2wt% over the temperatureulated oxygen content in the top-oil also reduced byr the same conditions suggesting an increase in HDOe overall dry product yields were insensitive to tem-d remained relatively constant at 50%. HDO conversionygen removal occurred between 57 and 67%.

stage studiese earlier section dealt with work that was primarily

the stabilization stage, herein studies dealing with bothe second stage will be considered. Such studies arerom a process optimization viewpoint as the secondding is strongly inuenced by the quality of the productter the stabilization (low temperature hydrotreating)rchers at PNNL investigated the dual stage hydropro-

hardwood-derived pyrolysis oil in a continuous owr a sulded CoMo catalyst [86]. The stabilization (stageundertaken at 274 C and a space velocity of 0.62h1,nicantly more severe operating conditions (temper-

C and LHSV=0.11h1) were used for stage II. Stage Iditions resulted in a decrease in oxygen content (feed52.6wt% to 32.7wt%. Under the high severity condi-

II) the oxygen content dropped further to 2.3wt%. Theield (stage I + stage II) for gasoline and oil products was0.31 and 0.43 L/L feed, respectively and the combinedof carbon to gas (C1C4) was 17%. On a combined basist% carbon was present in the aqueous phase.and Kaliaguine investigated a Ru-based catalyst for the

stage and a NiOWO3/Al2O3 catalyst for the secondThe studies were carried out in a batch reactor with

the opalyst wauthorreactioinformby estifollowauthortion anthe Ru

Visptempecatalysconducpyrolyauthorprior toptimistepwand a twere fformatof thestudiesIn a seinvestiafter thAlkanethis stu

Pd-I hydries werangin0.18 toity) viehigherthe higfrequemaintaing sta0.45 toheavydecreaoxygenin spadecreabiphaswas fooil. Hyphasehydrocat 405withouthe oilInteresa very

3.2.3.Fro

stage sfrom tstage (l rst stage operating conditions for the Ru-based cat-a temperature of 80 C and a pressure of 4MPa. Theributed this to a better control of the polymerizationder the less severe rst stage operating conditions. Therelated to the extent of polymerization was obtained

ng the average molecular weight of the liquid sampleshe reaction. Based on the molecular weight data, thether concluded that along with aldehyde hydrogena-lymerization, hydrogenolysis reactions also occur overlyst.and Huber also studied Ru-based catalysts for the lowe hydrogenation step, however they used a Pt-basedproducingalkanes in the secondstage [99]. Studieswereonly on the aqueous phase of the oak wood-derivedil, which was obtained by extraction with water. Thegest that separation of the pyrolysis oil into two phasesrading allows for better control on catalyst design andn. The low temperature aqueous phase hydrogenationnducted in a Parr batch reactor at a pressure of 6.89MPaerature range of 25175 C. Although low temperaturesto be favorable for minimizing undesirable methane

the higher temperatures favored faster hydrogenationsired components (e.g., sugars and levoglucosan). Thecated the need for time and temperature optimization.step a bifunctional (4wt% Pt/SiO2Al2O3) catalyst was

d for production of alkanes from the product formedst stage (temperature =260 C and pressure =5.17MPa).ds up to 48% of the theoretical yields were obtained inn absence of externally added hydrogen.d catalyst was investigated by Elliott et al. for stageation of the different pyrolysis oils [100]. The stud-nducted in a continuous ow reactor at temperaturesm 310 C to 375 C and space velocities ranging fromh1. From a long term durability (e.g., stability, activ-int, the temperatures investigated in this study werethe optimal temperatures reported previously. Due to

temperatures used in this study, reactor plugging wasobserved. However, adequately stable operations wereto obtain sufcient product for the next hydrocrack-epending on the feed-stock the oil yields varied fromg/g dry feed. Higher oil yields were obtained from thee and whole pyrolysis oil. An increase in temperaturehe oil yields and increased the gas yields, whereas theversion passed though a maximum at 340 C. Increaselocity did not affect the oil yields but signicantlyhe oxygen conversion. The rst stage products werenature and the carbon content of the aqueous fractiono correlate well with the oxygen content of the productracking studies (stage II) were performed with the oilucts obtained from stage I using a sulded conventionaling catalyst. The hydrocracking studies were conductedMPaand0.2 LHSVandstableoperationswereobserved

y reactor plugging. Depending on the pyrolysis oil useds ranged from0.61 to 0.82g/g/dry feed (shown in Fig. 5).y, elemental analysis showedthat thenalproductshadar composition irrespective of the source of bio-mass.

ined dual stage studiesefciency viewpoint it is better to perform the dual

es in a combined reactor system wherein the productrst stage (low severity) is directly fed into the secondseverity). Moreover it is difcult to pump the inter-


0.8

0.9

vy

oil

t pyroAdapted from

mediate prostage. In ordinvestigatedcontinuous250280 C(370400 Cthan 2wt%0.27 to 0.37ity were foucompared tto gas was hmuch lowerto the fact tgas in the cstage studieprocessed tused non-isdual stage h(at lower t(at higher tsis oil provi14MPa anduct oil was lof the aqueseparate dusame catalywas found t

Combineinvestigatedtinuous owa space veloond stage twas obtaineing deoxyg29%. Use ofsupportedreactions wof efuentwas foundfrom eucaly

sed uenatThiss hadsis oe oxto fanic aThusl in th

tenti

ce thereer, tportarea.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Corn stover lightMixed woodphase

Corn stover heaphase

Pyrolysis

Oil

yiel

d (g

/g) d

ry b

asis

Fig. 5. Product oil yields from differen[100].

duct (on account of its high viscosity) into the seconder to simplify the overall process, researchers at PNNLthe pyrolysis oil hydroprocessing in a non-isothermal

ow reactor such that reactor inlet was maintained atwhile the reactor outlet was maintained at a higher) temperature [86]. The nal oxygen content was lessand the yield of gasoline range material ranged fromL/L feed oil (Table 5). The product oil yields and qual-nd to be similar to the separate dual stage. However, aso the separate dual stage studies, the carbon conversionigher, while the carbon lost in the aqueous phase wasin the combineddual stageprocess. Thiswas attributedhat the organics in the aqueous phase are converted toombined stage studies. However, during the separates, the aqueous phase was removed after stage I and nothrough stage II. Recently Elliott and co-workers [100]othermal processing conditions to study the combinedydroprocessing over a Pd-based hydrotreating catalyst

procesdeoxygsis oil.authorpyrolythat th10wt%of orgastage.critica

3.3. Po

Sinable thHowevit is imin thisemperature) and conventional hydrocracking catalystemperature). Studies over mixed wood derived pyroly-ded a product oil yield of 0.5 g/g dry feed at a pressure ofspace velocity of 0.15. The oxygen content of the prod-ess than 1wt% and correspondingly the carbon contentous fraction was less than 0.5wt%. In agreement withal stage (hydrotreating/hydrocracking) studies over thests [100], the chemical composition of the nal producto be independent of the source biomass.d dual stage low severity hydrotreating has also beenfor upgrading pyrolysis oils. The study involved a con-system with two reactors connected in series. Using

city of 0.28h1, rst stage temperature of 148 C, sec-emperature of 355 C, a product yield of 0.53g/g feedd over a sulded NiMo catalyst [101]. The correspond-enation was 95.8% and carbon conversion to gas wasa weak hydrogenation catalyst in the rst stage (spinelCoMo) resulted in exothermic pyrolysis condensationhich in turn caused rapid coke build up and plugginglines. Upgrading of pyrolysis oil obtained from poplarto be signicantly more efcient than that obtainedptus. Even though eucalyptus-derived pyrolysis oil was

mation abosystematicbio-oil qualalyst. Identactivity andbeen identiaddressed tconventionerably loweobservedwcommerciaare optimiznicantly dbe worthwspecicallyapplicationhave the at

a) High actipoint ofm

b) Ability tocoke formPoplar (hot-Corn stover 2filtered)

lysis oils.

nder more severe conditions, the product yields andion was lower compared to the poplar-derived pyroly-was a surprising result as previous studies by the samenot indicated major differences based on the source of

ils. Another important conclusion from this study wasygen content of product oil had to be dropped belowcilitate easy separation ofwater indicating thepresencecids and highly polar intermediate species after the rst, it is evident that hydrogenation over hydrogenolysis ise rst stage.

al future research areas

e bio-oils for the upgrading studies are not easily avail-are several constraints for undertaking these studies.o make adequate progress towards commercializationant that a number of additional studies are undertakenPrevious studies have provided some interesting infor-

ut the upgrading of these bio-oils. However, a morestudy is desirable in the following areas (a) effect ofity (b) effect of process parameters and (c) optimal cat-ication of an optimal catalyst system with adequatestability is critical. Although poor catalyst stability has

ed as a major problem, very few studies have actuallyhe problem. Due to the poor quality of the bio-oils theal hydrotreating catalysts are expected tohave a consid-r catalyst life in bio-oil upgrading operations than thatithpetroleumfeed-stocks.While thecurrentgenerationl catalysts are excellent hydroprocessing catalysts theyed for petroleum feedstocks. Since the bio-oils have sig-ifferent properties than petroleum feed-stocks, itwouldhile to dedicate efforts towards developing catalystsfor upgrading bio-oils. From a wide spread commercials viewpoint an ideal bio-oil upgrading catalyst shouldtributes described below.

vity for deoxygenation: this is important from the view-inimizing the reactor size and obtaining desired yields.withstand large quantities of coke and/or minimizeation: bio-oils have a much higher propensity to form


coke than typical petroleum fractions. In order to elongate thetime between regeneration cycles and to achieve stable opera-tions, the catalyst should be able to hold large quantities of cokeand/or minimize coke formation.

c) High tolepresencegenationupgradinof water,for water[104], itthat canthe oilw

d) Ability tothis will s

e) High tolesition relregeneraversible.of increas

f) Availabilcially prabe requirthat are s

The abovals and appsuperior bioare expectelyst approacto develop aDevelopmeing: (i) analof oxygenatstudies thaing of interbio-oils (asalyst systemthe catalystunlikely thators used init is also wonology to o

4. Life cycl

The LCArenewabletion and thuan essentialthe EnergyCalifornia LUnionsRenaddressed ties deal wit[109] haveprocesses fliquefactionthe assumpused [107].dening systories, andindicate thacompared turated lipid

[105]. For cellulose liquefaction processes atmospheric fast pyroly-sis can provide process energy efciencies of around 5060%,whilepressurized liquefaction processes can be 5055% efcient [109].

clud

ile soHDOh ar

on anduciis annalvelologyer h

he biexityive rr techl impto tee, loginggh thels, oancentinuresea

nces

ergyates, PN.Nai. Corm. Hube. Kammd Pro

. CentiergyMarkNemeEFG36.G. Lel.C. Elliusta,.V. BriL. ThigI, IGT,.V. Br73.

C. Me826Kalne. Kuro31.RantaHolmgrbonFurim

. Pattiy

.R. Dav(200

.I. Sen711

.I. Sen

.I. Sen007) 1.I. Sen.I. Sen-R. Vi43.-R. Vil.J. Girrance to water: previous studies have indicated thatof water can have a detrimental effect on the deoxy-catalyst performance [102,103]. Since the bio-oil

g catalyst is expected to be exposed to large amountsit is important for the catalyst to exhibit high tolerance. Based on the work done by Resasco and co-workersmay also be worthwhile to consider catalyst systemsstabilize water-oil emulsions and catalyze reactions atater interface.regenerate using a simple process (e.g., hot air burn):implify the process and minimize capital expenditure.rance to poisons: the activity lost due to coke depo-ated deactivation can be regained during hot air burntion;however activity loss frompoisons is typically irre-High tolerance for poisons is critical from the viewpointing the overall life of the catalyst load.

ity should not be an issue: if this process is commer-cticed on a wide-scale, a huge amount of catalyst willed. This will preclude the use of materials/componentscarce.

e list can be used to narrow down the possible materi-roaches that could be potentially considered to develop

oil upgrading catalysts. Catalyst development effortsd to be beneted by using a rationalized design of cata-h. However in order to use this approach it is importantrealistic understanding of the bio-oil catalyst systems.

nt of a realistic understanding will require the follow-ytical advances for rapid and quantitative identicationed compounds in complex mixtures and (ii) systematict are designed to obtain comprehensive understand-action between representative molecules present inindividual compounds and mixtures) and different cat-s (active metals, supports etc.) and (iii) understandingdeactivation mechanisms for bio-oils. Since it seemst it would be possible to use the relatively simple reac-conventional hydroprocessing of petroleum fractions,rthwhile to identify/develop appropriate reactor tech-ptimize the reaction-regeneration process.

e assessment (LCA)

on an energy and Green House Gases (GHGs) basis forfuels is required to ascertain the degree of GHG reduc-s its categorization as a renewable fuel. The LCA is alsopart of renewable fuel and low carbon regulations like

Independence and Security Act of 2007 (EISA 2007), theow Carbon Fuels Standard (CA LCFS), and the EuropeanewableEnergyDirective (RED).Anumberofpapershavehe LCA of renewable fuels for HDO, most of these stud-h production of renewable diesel [105108]. Elliot et al.discussed the process efciency for two liquefactionor cellulosic biomass: atmospheric fast pyrolysis, andin pressurized solvents. The LCA results are sensitive to

tions made in the models and the allocation techniquesThus there is a need to develop LCA standards for clearlytem boundaries, setting up feedstock life cycle inven-allocation methods. The renewable diesel LCA studiest GHG reductions of around 5090% can be realizedo petroleum diesel [105,108]. Tallow being a more sat-feedstock can produce a GHG reduction of about 88%

5. Con

Whviousresearcmizatifor proeridesadditioand detechnothe othity of tcomplextensreactomercialimitedtructurchallenAlthouable fuimportwill cofuture

Refere

[1] EnSt

[2] S.[3] A[4] G[5] B

an[6] G

En[7] T.

L.D

[8] R[9] D

ta[10] A[11] P.

V[12] A

1[13] L.

24[14] T.[15] M

40[16] L.[17] J.

ca[18] E.[19] A[20] R

56[21] O

10[22] O[23] O

(2[24] O[25] O[26] T.

33[27] T.[28] Ming remarks

me interesting information has been forwarded by pre-studies, several gaps remain in this very importantea. These gaps can be divided into two types (opti-d technology gaps) depending on the feed-stock usedng renewable fuels. The gap in case of HDO of triglyc-

optimization gap and can be eliminated via someresearch on dewaxing catalysts, process optimizationping a better understanding of inhibition effects. Thegap in case of HDO of biomass derived bio-oils, onand, is exceedingly challenging due to the poor qual-o-oils (high oxygen content, impurity levels, molecularand coking propensity). From a technical viewpoint

esearch on nature of feeds, catalyst systems as well asnology is needed in this area. The challenge of com-lementation of renewable fuels production is not justchnical issues. The non-technical issues (such as infras-gistics and economics) are expected to be at-least asas the technical aspects of renewable fuel production.ere are several uncertainties associated with renew-ne thing is certain the economic and environmentalcoupled with the enormous challenges of this topic,e to maintain this as one of the most vibrant areas ofrch.

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Renewable fuels via catalytic hydrodeoxygenationIntroductionHDO of triglyceride-based feedsHydroprocessing in stand-alone modeInfluence of process conditionsInfluence of feed and catalyst

Hydroprocessing in co-processing modePotential future research areas

HDO of bio-oil feedsHDO of bio-oils derived from high pressure liquefaction of biomassInfluence of nature of feed-stockInfluence of catalystInfluence of operating conditions

HDO of bio-oils derived from pyrolysis of biomassStabilization studiesDual stage studiesCombined dual stage studies

Potential future research areas

Life cycle assessment (LCA)Concluding remarksReferences

renewable fuels via catalytic hydrodeoxygenation

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