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Production of renewable diesel by hydroprocessing of soybean oil: Effect of catalysts

Bambang Veriansyah a, Jae Young Han a,b, Seok Ki Kim a, Seung-Ah Hong a, Young Jun Kim a,c,Jong Sung Lim b, Young-Wong Shu c, Seong-Geun Oh c, Jaehoon Kim a,

a Clean Energy Research Center, National Agenda Research Division, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791,

Republic of Koreab Department of Chemical and Biomolecular Engineering, Sogang University, 1 Sinsu-dong, Mapo-gu, Seoul 121-742, Republic of Koreac Department of Chemical Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791, Republic of Korea

a r t i c l e i n f o

Article history:

Received 8 June 2011

Received in revised form 21 October 2011

Accepted 21 October 2011

Available online 7 November 2011

Keywords:

Hydroprocessing

Renewable diesel

Vegetable oil

Catalysts

a b s t r a c t

The effects of various supported catalysts on the hydroprocessing of soybean oil were studied. Several

parameters were taken into account when evaluating the hydroprocessed products, including the conver-

sion, selectivity (naphtha, kero/jet, and diesel), free-fatty acid content, oxygen removal, and saturation of

double bonds. The hydroprocessing conversion order was found to be sulfided NiMo/cAl2O3 (92.9%) >

4.29 wt.% Pd/c-Al2O3 (91.9%) > sulfided CoMo/c-Al2O3 (78.9%) > 57.6 wt.% Ni/SiO2Al2O3 (60.8%) >

4.95 wt.% Pt/c-Al2O3 (50.8%) > 3.06 wt.% Ru/Al2O3 (39.7%) at a catalyst/oil weight ratio of 0.044. The most

abundant composition in the liquid product was straight chain n-C17 and n-C15 alkanes when the Ni or

Pd catalysts were used. Enhanced isomerization and cracking reaction activity on the CoMo catalyst may

produce lighter andisomerizedhydrocarbons. By combining gas-phase andliquid product analyses, decar-

boxylation was a dominant reaction pathway when the Pd catalyst was used, while hydrodeoxygenation

was favored when the NiMo or CoMo catalyst was used.

Crown Copyright 2011 Published by Elsevier Ltd. All rights reserved.

1. Introduction

The hydroprocessing of natural triglycerides into hydrocarbons

is a promising alternative technology for the production of

renewable diesel with a higher energy density, lower nitrogen

oxide (NOx) emissions, and better oxidation stability when com-

pared to the fatty acid methyl esters (FAMEs) synthesized by

transesterification of triglycerides with methanol [13]. Depend-

ing on the reaction conditions and type of catalyst used, a series

of complex reactions occur during the hydroprocessing. This in-

cludes the saturation of double bonds, breakage of CC bonds,

heteroatom (sulfur, nitrogen, or oxygen) removal, isomerization,

and cyclization [4,5]. The liquid product generally contains

straight chain n-alkanes with C15C18 as major compounds via

three different reaction pathways: decarbonylation, decarboxyl-

ation, and hydrodeoxygenation. The content of iso-alkanes, cyclo-

alkanes, and aromatics is typically not significant at a mild

synthetic condition. These paraffin-rich hydrocarbons are known

to have better fuel properties than the FAMEs produced via

transesterification [3]. The n-alkanes produced by hydroprocess-

ing retain a much higher cetane number (>70) than that of petro-

leum diesel fuel ($45), and the boiling point range is comparable

to typical petroleum based-diesel. In addition, the production of

renewable diesel using hydroprocessing can be employed in the

existing infrastructure of petroleum refineries, which can reduce

the initial capital investment [68].

Thereaction conditionsand types of catalysts have significant ef-

fects on the composition and quality of the liquid product. Gusmao

et al. investigated thehydrocracking of soybean and babassuoils for

the production of hydrocarbons over sulfided NiMo/c-Al2O3 and a

reduced Ni/SiO2 catalyst in a batch reactor at temperatures of

350400 C andhydrogenpressuresof 120 MPa [9]. The mainreac-

tion products were aliphatic hydrocarbons via total decarbonyla-

tion, decarboxylation, or hydrogenation. Da Rocha Filho et al.

investigated the hydrocracking reaction of soybean oil and other

vegetable oils such as maracuja, tucuma, buriti, and babassu oils

over sulfided NiMo/c-Al2O3 in a batch reactor [10]. The reaction

products were n-alkanes (6676 wt.%), cycloalkanes (up to

13 wt.%), and alkyaromatics (up to 4 wt.%) after a 2-h reaction at

360 C and an initial hydrogenpressureof 14 MPa. Huber et al.stud-

ied thehydrotreatingof sunflower oil using a flow-type reactor with

a sulfide NiMo/Al2O3 catalyst at temperatures of 300450 C and a

hydrogen pressure of 5 MPa [4]. Under optimal conditions, the mo-

lar yield of carbonsfrom n-C15 to n-C17 was71%. Simceket al. inves-

tigatedthe hydroprocessing of rapeseedoil using a flowtype reactor

at temperatures of 260340 C and a hydrogen pressure of 7 MPa

using three different types of commercial NiMo/Al2O3 catalysts

[11]. At 340 C and 7 MPa, the liquid product contained more than

70 wt.% of n-C15 and n-C17. Moreover, n-alkanes with a carbon

0016-2361/$ - see front matter Crown Copyright 2011 Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.fuel.2011.10.057

Corresponding author. Tel.: +82 2 958 5874; fax: +82 2 958 5205.

E-mail address: [email protected] (J. Kim).

Fuel 94 (2012) 578585

Contents lists available at SciVerse ScienceDirect

Fuel

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f u e l
http://dx.doi.org/10.1016/j.fuel.2011.10.057mailto:[email protected]://dx.doi.org/10.1016/j.fuel.2011.10.057http://www.sciencedirect.com/science/journal/00162361http://www.elsevier.com/locate/fuelhttp://www.elsevier.com/locate/fuelhttp://www.sciencedirect.com/science/journal/00162361http://dx.doi.org/10.1016/j.fuel.2011.10.057mailto:[email protected]://dx.doi.org/10.1016/j.fuel.2011.10.057

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number lower than 15 (n-C15), iso-alkanes of C16C18, and cycloal-

kanes formed as the minor the liquid product.

The choice of catalyst is crucial to determine the composition

and fuel properties of hydroprocessed triglycerides. The present

study focused on the effects of various supported catalysts on the

hydroprocessing of soybean oil. Various types of catalysts, includ-

ing supported NiMo and CoMo hydrotreating catalysts and noble

metal (i.e., Pt, Pd, Ni and Ru) supported catalysts, were tested in

a batch mode. The hydroprocessing conversion and selectivity to

diesel, jet/kerosene, and naphtha were determined using simulated

distillation. In addition, the composition of the liquid products,

including the n-alkane content, oxygen content, free-fatty acid

content, and double bond content, was determined in detail. Dif-

ferent reaction mechanisms on the various catalysts were also

presented.

2. Experimental methods

2.1. Materials

The soybean oil used was a commercial product manufactured

by CJ Cheiljedang Co. (Seoul, Korea). Table S1 in the Supplementary

data lists the composition of fatty acids in the soybean oil, which

was characterized using gas chromatography (GC) according to

BS EN14103 [12]. The largest fatty acid component of the soybean

oil consisted of the C18 species (C18:0, stearic acid; C18:1, oleic

acid; C18:2, linoleic acid; C18:3, alpha linolenic acid; 80.93 wt.%),

while the second largest fatty acid component was palmitic acid

(C16:0, 10.98 wt.%). Hydrogen (purity of 99.9%), helium (purity of

99.9999%), air, nitrogen (purity of 99.9%), and 14.9 vol.% H2S in

H2 were purchased from the Shinyang Sanso Company (Seoul,

Korea). 66.0 3 wt.% Ni/SiO2Al2O3, 5.0wt.% Pd/c-Al2O3, and

5.0 wt.% Ru/Al2O3 were purchased from Alfa-Aesar (MA, USA).

CoMo/c-Al2O3 with 3.5 wt.%(CoO)/14.0 wt.% (MoO) and 5.0 wt.%

Pt/c-Al2O3 were purchased from Strem Chemical (MA, USA). The

metal loadings were given by the vendors. NiMo/c-Al2O3 was ob-

tained from a petroleum refinery company in Korea.

2.2. Apparatus and procedure

The hydroprocessing experiments were conducted using a

custom-built, high-pressure batch reactor system. Fig. S1 in the

Supplementary data shows a schematic diagram of the apparatus.

The high-pressure reactor was cylindrical in shape, with an inside

diameter of 34.5 mm and an inside height of 117 mm, giving it a

volume of 109 cm3. Extensive stirring of the oil and supported cat-

alysts in the reactor was achieved using a magnetically driven stir-

rer with a DC geared motor. Prior to each experiment, 28.1 g of

soybean oil was introduced into the oil feed tank and then the feed

tank was purged with N2 for at least 30 min to remove any oxygen

that might have been dissolved in the oil and present in the oil feedtank. A known amount of the supported catalyst was charged into

the reactor, and then the reactor was purged with N2 for at least

30 min. When the Pt, Pd, Ru, or Ni catalyst was used, the reactor

was purged with H2 for at least 10 min and then pressurized with

H2 at 2 MPa. The temperature of the reactor was then increased

and kept at 400 C for 1 h to reduce the catalyst. When the CoMo

or NiMo catalyst was used, the reactor was purged with

14.9 vol.% H2S in Ar for at least 10 min and then pressurized with

14.9 vol.% H2S in H2 at 2.9 MPa. The temperature of the reactor

was then increased and kept at 400 C for 1 h to activate the CoMo

or NiMo catalyst via sulfidation. After the temperature of the reac-

tor decreased to$35 C and the pressure decreased to atmospheric

pressure, the soybean oil in the feed tank was transferred to the

reactor. The reactor was then purged again with N2 for at least20 min, followed by purging with H2 for at least 10 min. The reac-

tor was then pressurized with H2 to the pressure desired for the

experiment (9.2 MPa). Once the desired initial H2 pressure was

reached, the mixture in the reactor was stirred using the magnet-

ically driven stirrer, and the temperature of the reactor was in-

creased to the temperature desired for the experiment (400 C)

for an hour. After the reaction temperature reached 400 C, the

reaction was carried out for an hour. The reactor temperature

was then decreased to room temperature. The gas product was col-

lected and analyzed using gas chromatographs (GC). The reactor

was then vented to atmospheric pressure, and the liquid product

was collected and analyzed.

2.3. Catalyst characterization

The surfaceareas, average pore diameters, andpore volumes of the

supportedcatalysts weremeasuredusinga BELSORP-mini II apparatus

(Bel Japan, Inc., Osaka, Japan). The Pt, Pd, or Ru metal loading and CoO,

MoO3, and NiO2 loading on thesupport were measured using A Varian

170 ES (Varian, CA, USA) inductively coupled plasma-emission spec-

trometry(ICP-ES).TheNi metal loading wasmeasuredusinga UNICAM

M seriesatomic absorptionspectrophotometer (AAS, UNICAM,NHand

USA) with anair/acetyleneflame. Themorphologyof each catalyst was

characterized using a Philips Model CM30 transmission electron

microscope (TEM, Eindhoven, Netherland). Thesizeof themetal parti-

cles wasestimatedby analyzing theTEMimages using Canvasby ACD

systems (Miami, Florida). The average diameter of the particles was

definedas thearithmeticaverageof thediametersof thehemispher-

ically shaped particles in the images.

2.4. Product analysis

Two different gas chromatographs were used to evaluate the li-

quid product composition. First, the liquid product was analyzed

using a Perkin-Elmer model Clarus 600 gas chromatograph (GC)

equipped with an on-column injector, flame ionization detector

(FID), and Sim Dis capillary column (polymethylsiloxane, with

the dimensions of 10 m 0.53 mm 1.0lm). The simulated dis-tillation of hydroprocessed products was carried out according to

the ASTM D-7213 procedure under an assumption that the areas

of each distillation fraction were proportional to the amount of

carbon in that fraction. This assumption is valid when the amount

of oxygenated species in the liquid product is low.

In this study, hydrotreating reaction conversion (%), which is

used to evaluate hydroprocessing efficiency, is defined as the per-

centage of the feed fraction with a boiling point higher than 360 C

that has been converted into lighter hydrocarbons with a boiling

point lower than 360 C.

Conversion% Feed

360 Product

360

Feed360

100 1

where Feed360+ and Product360+ are the weight percent values for

the feed and product, respectively, with a boiling point higher than

360 C.

The hydrotreating selectivity of naphtha, kero/jet, or diesel is

defined based on its boiling point range as follows.

Naphtha selectivity% Product

40200 Feed

40200

Feed360

Product360

100 2

Kero=jet selectivity% Product

170270 Feed

170270

Feed360

Product360

100 3

Diesel selectivity% Product

180360 Feed

180360

Feed360

Product360 100 4

B. Veriansyah et al./ Fuel 94 (2012) 578585 579
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where Feed360+ and Product360+ are the weight percent values for

the feed and product, respectively, with a boiling point higher than

360 C, Feed40200 and Product40200 are the weight percent values

for the feed and product, respectively, with a boiling point between

40 and 200 C (naphtha fraction), Feed170270 and Product170270 are

the weight percent values for the feed and product, respectively,

with a boiling point between 170 and 270 C (kero/jet fraction),

and Feed180360 and Product180360 are weight percent values for

the feed and product, respectively, with a boiling point between

180 and 360 C (diesel fraction).

Second, the concentration of n-alkanes in the liquid products

was analyzed using a Hewlett-Packard model 5890 Series II gas

chromatograph (GC) equipped with a flame ionization detector

(FID) and a nonpolar column (HP-1, with the dimensions of

60 m 0.32 mm 0.25 lm). The concentration of n-alkanes

(wt.%) in the liquid product is defined as follows:

Concentration of n alkanes in the liquid productwt%

P20

i8

MnC

Mp 100% 5

whereP20

i8MnC is the total weight of the n-alkanes (from n-C8 to n-

C20) in the liquid product, and Mp is the total weight of the liquid

product. The n-alkanes of n-C5n-C7 could not be analyzed because

of the peak overlapping with the solvent peak.

The free fatty acid (FFA) content in the liquid product was mea-

sured according to the official method of the American Oil Chem-

ists Society (AOCS) (Cd 3a-63) [13]. The water content in the

liquid products was measured using an Orion AF8 Volumetric Karl

Fischer titrator (Thermo Scientific, MA, USA). The carbon, hydro-

gen, nitrogen, and sulfur were analyzed using a Flash 2000 Series

CHNSO Analyzer (Thermo Scientific, MA, USA) equipped with a

flame ionization detector (FID) and a Multiseparation Column

(PTFE, 2 m 6 mm 5 mm). The oxygen was analyzed using a Fi-

sons-EA-1108 (Thermo Scientific, MA, USA) equipped with a flame

ionization detector (FID) and an Oxygen Separation Column (SS,

1 m 6 mm 5 mm).

The compositions of the gaseous products were analyzed using

two gas chromatographs (GC). The first GC was a Hewlett-Packard

model 5890 Series II GC with a thermal conductivity detector (TCD)

and the second GC was a Young Lin model ACME 6100 GC with a

pulsed discharge helium ionization detector (PDHID, Vici Valco

Instruments Co. Inc., TX, USA). The detailed description of both

GC methods is described in the previous paper [14].

3. Results and discussion

3.1. Reaction pathway

Fig. 1 shows representative pressure and temperature changes

with reaction time during the soybean oil hydrotreating using

57.6 wt.% Ni/SiO2Al2O3. Triglyceride conversions over hydrotreat-

ing catalysts in the presence of hydrogen have complex reaction

pathways and consist of parallel and/or consecutive reaction steps,

including saturation, cracking, decarboxylation, decarbonylation,

and/or hydrodeoxygenation (see Fig. 2). As shown in Fig. 1, a signif-

icant drop in hydrogen pressure was observed at temperatures in

the range of 100130 C. In this step, the double bonds that were

present in the triglycerides were saturated with hydrogen. The

fatty acids containing double bonds in the chain included palmito-

leic acid (C16:1), oleic acid (C18:1), linoleic acid (C18:2), alpha lin-

olenic acid (C18:3), and eicosenoic acid (C20:1), which were

transformed into palmitic acid (C16:0), stearic acid (C18:0), andarachidic acid (C20:0), respectively.

As the temperature increased, a second drop in hydrogen pres-

sure was observed at temperatures in the range of 270330 C. In

this second step, the hydrogenated triglyceride degraded into vari-

ous intermediates, including monoglycerides, diglycerides, and free

fatty acids, which was followed by the conversion of the intermedi-

ates into deoxygenated products. The formation of n-alkanes from

free fatty acid cantakeplace by one or a combinationof three differ-

ent reaction pathways: decarboxylation, decarbonylation, and/or

hydrodeoxygenation [4]. The decarboxylation pathway converts

the carboxylic acid group in the free fatty acids to straight chain al-

kanes by releasing CO2. It is not necessary to use hydrogen in the

decarboxylation reaction. The decarbonylation pathway produces

alkanes by reacting the carboxylic acid group in the free fatty acids

with hydrogen and forming CO and water. The alkanes produced

by decarboxylation and decarbonylation contain odd numbers of

carbonsin their chains.In thecase of soybeanoil, themost abundant

component is n-C17 and the second most abundant component is n-

C15 if decarboxylation and/or decarbonylation are the dominant

reaction pathways. In contrast, the hydrodeoxygenation pathwayproduces alkanes with even numbers of carbons by converting the

carboxylic acid with hydrogen and releasing water. Thus, the ratio

ofn-alkanes with odd numbers of carbon atoms to n-alkanes with

even numbers of carbon atoms (e.g., n-C17/n-C18) can serve as an

indicator for evaluating the reaction pathways of decarboxylation/

decarbonylation and hydrodeoxygenation. In addition to the major

reactions of decarboxylation, decarbonylation, and hydrodeoxygen-

ation,competitivereactions of isomerization, cyclization, and crack-

ing can result in iso-alkanes, aromatics, and lighter hydrocarbons.

Light gaseous compounds such as carbon dioxide, carbon mon-

oxide, and water generated by the hydroprocessing reaction can

participate in a methanation reaction and watergas-shift reaction.

When the methanation reaction is negligible, the molar ratio of

CO2/CO can serve as an indicator for evaluating the reaction path-ways of decarboxylation and decarbonylation. It should be noted

that the methanation reaction is undesirable because it consumes

expensive hydrogen during hydroprocessing.

Methanation of CO2 : CO2 4H2 $ CH4 2H2O 6

Methanation of CO : CO 3H2 $ CH4 H2O 7

Water-gas shift reaction : H2 CO2 $ CO H2O 8

3.2. Effects of catalysts

A series of experiments was conducted to investigate the effects

of catalysts on the hydroprocessing efficiency and product compo-sition. Six different types of supported catalysts were tested:

Fig. 1. Representative pressure and temperature profile during hydrotreating of

soybean oil using 57.6 wt.% Ni/SiO2Al2O3. The catalyst/oil weight ratio was 0.044.

580 B. Veriansyah et al./ Fuel 94 (2012) 578585

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Ni/SiO2Al2O3, Pd/c-Al2O3, Pt/c-Al2O3, Ru/Al2O3, CoMo/c-Al2O3,

and NiMo/c-Al2O3. Fig. S2 shows TEM images of the metal-sup-

ported catalysts and Table S2 lists the surface areas, pore diame-

ters, pore volumes, metal particle sizes, and metal loadings of the

catalysts, which were characterized using BET, ICP-ES, and TEM

measurements.

The effects of the catalysts on the hydrotreating efficiency and

product composition were examined at a catalyst/oil weight ratio

of 0.044 and the results are shown in Figs. 3 and 4 and listed in Ta-

ble 1. The current batch reactor required an hour to reach the

experimentally desired temperature of 400 C (see Fig. 1), after

which the reaction proceeded for another one hour at 400 C. The

distillation profiles of the soybean oil and petroleum diesel areshown in Fig. 3 for comparison purposes. The pure soybean oil

was distilled mainly at 590615 C. Over 85 wt.% of the petroleum

diesel was distilled at the narrow boiling points of 183359 C.

When the soybean oil was hydrotreated using the Pd or NiMo cat-

alyst, the distillation profiles were flat over a wide recovery range

at the narrow boiling points of 290330 C, which fall into the die-

sel fuel boiling point range. The fractions of higher boiling points

from 380 C to 450 C may be partially reacted intermediates be-

tween triglycerides and alkanes. The similarity of the final boiling

points of the hydroprocessed products to that of soybean oil may

be the result of unreacted triglycerides. Another possibility for

the heavy fraction in the liquid product might be related to oligo-

merization or aromaticization of reaction intermediates containing

double bonds in their molecular structures [15]. In contrast,

approximately 80 wt.% of the liquid product using the Ru catalyst

was over the diesel fuel boiling point range. This indicates the pre-

dominate formation of high-molecular-weight species, probably as

a result of the polymerization of the double bonds present in thetriglycerides. The low hydroprocessing activity of the Ru catalyst

Fig. 2. Possible reaction pathways of triglycerides over hydrotreating catalyst.

Fig. 3. Simulated distillation curves of hydrotreated products of various catalysts.The catalyst/oil weight ratio was 0.044.

Fig. 4. (a) Effects of catalysts on conversion and selectivity and (b) effects of

catalysts on the dry gas composition. The catalyst/oil weight ratio was 0.044.


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may have been the result of deactivation by unsaturated deoxy-

genation and cracking species [16].

As shown in Fig. 4, the order of hydroprocessing conversion was

NiMo/c-Al2O3 (92.9%) > Pd/c-Al2O3 (91.9%) > CoMo/c-Al2O3 (78.9%) >

Ni/SiO2-Al2O3 (60.8%) > Pt/c-Al2O3 (50.8%) > Ru/Al2O3 (39.7%). The

conversion and the selectivity estimation using the simulated dis-

tillation are based on the assumption that the amount of oxygen-

ated species in the liquid product is low. As will be discussed in

the later section, the amount of oxygen in the hydroprocessed li-

quid using the Ni, Pt, Ru catalysts was high (oxygen content was

4.79.3 wt.%), so the analysis can have a large error. At room tem-

perature, the product was solid when the Ni, Pt, or Ru catalyst was

used, while the product was a colorless liquid when the Pd catalyst

was used and a yellowish liquid when the NiMo or CoMo catalyst

was used. When the Pd or NiMo catalyst was used, the diesel selec-

tivity was high, in the range of 93.597.8%. Only a small amount of

lighter hydrocarbons (naphtha selectivity of 3.26.5%) was pro-duced, suggesting that the hydrocracking reaction was negligible

at the given reaction condition. Typically naphtha consists of C5

C12 hydrocarbons mixtures. As was the case with the Pd and NiMo

catalysts, diesel production was mostly favored when the Ni or Pt

catalyst was used (diesel selectivity of 95.096.0%). In contrast, a

shift in the distillation curve toward lower boiling points was ob-

served when the CoMo catalyst was used (see Fig 3). The higher

hydrocracking activity with the CoMo catalyst may have resulted

in a much higher naphtha selectivity of 17.7% and a lower diesel

selectivity of 82.3%.

Even though the distillation profiles of the liquid products using

the Pd and NiMo catalysts were very similar, the compositions of

the hydrotreated products were quite different, as shown in Ta-

ble 1. When the Pd catalyst was used, the straight chain n-alkanecontent from n-C8 to n-C20 in the liquid product was 85.7 wt.%.

We were not able to quantify the n-C5 to n-C7 species because

the GC peaks of the n-C5 to n-C7 species overlapped with that of

dichloromethane, which was used as the GC solvent. However, as

can be inferred from the low naphtha selectivity, the content of

the n-C5 to n-C7 species may not have been significant. The two

most predominating n-alkanes were n-C17 (63.66 wt.%) and n-C15(8.49 wt.%) when the Pd catalyst was used. A small amount of

shorter chain hydrocarbons from n-C8 to n-C12 formed by hydro-

cracking of the longer chain n-alkanes. Note that a non-negligible

amount of free-fatty acid was present in the liquid product when

the Pd catalyst was used. When the NiMo catalyst was used, the

n-alkane content from C8 to C20 in the liquid product was much

smaller (66.4 wt.%) compared to that with the Pd catalyst. In addi-tion, the contents of the n-C17 (41.0 wt.%) and n-C15 (4.58 wt.%)

species were also much smaller compared to those with the Pd cat-

alyst. The free-fatty acid content of the liquid produced using the

NiMo catalyst was also smaller (0.06 wt.%) than when using the

Pd catalyst. By taking into account the similar hydrotreating con-

versions of the soybean oil using the Pd and NiMo catalysts, the

much smaller n-alkane content may suggest that the formation

of iso-alkane, cycloalkanes, or aromatic carbon species was en-

hanced by the NiMo catalyst, but no further analysis was per-

formed to identify their compositions. A higher amount of iso-

alkane, cycloalkanes, or aromatic carbon species in the hydropro-

cessed vegetable oil is desirable because it can enhance low tem-

perature flow properties [4,15] .

As listed in Table 1, the order of the n-C17/n-C18 ratio was

Ru/Al2O3 (39.6) > Ni/SiO2-Al2O3 (29.3) > Pd/c-Al2O3 (11.9) > NiMo/

c-Al2O3 (2.49) % CoMo/c-Al2O3 (2.16) > Pt/c-Al2O3 (0.92). This

indicates that decarboxylation and/or decarbonylation were the

dominant reaction pathways when the Ru, Ni, or Pd catalyst wasused, while hydrodeoxygenation was more important when the

NiMo, CoMo, or Pt catalystwas used. Bifunctional catalysis, hydroge-

nation on the NiMoor CoMosites, and dehydration on the acid sites

may be responsible for the enhanced hydrodeoxygenation reaction

[4]. Fig. 4b shows the effects of various catalysts onthe dry gas com-

position. When the gas-phase analysis was combined with the li-

quid-phase analysis, the dominating reaction pathway was found

to be decarbonylation with the Pd catalyst because the CO2/CO

molar ratio was very low (0.4). The much higher value of CO2/CO

with the Pt (13.7) or NiMo (15.4) suggests that decarboxylation

Table 1

Effects of catalysts on product composition. All of the experiments were performed at a hydrogen pressure of 9.2 MPa, reaction temperature of 400 C, reaction time of 2 h, and

catalyst/oil weight ratio of 0.044.

Soybean oil Ru Pt Ni Pd CoMo NiMo

Free fatty acid content (wt.%) 0.03 21.68 13.52 7.96 4.04 0.58 0.06

Moisture (wt.%) 0.059 0.072 0.023 0.021

n-alkanes content (wt.%) 39.3 41.0 46.3 85.7 43.3 66.4

n-C8 (wt.%) 0.1 0.27 0.49 0.71 1.83 0.25

n-C9 (wt.%) 0.8 0.35 0.67 0.77 1.47 0.26n-C10 (wt.%) 1.0 0.43 0.80 0.84 1.42 0.22

n-C11 (wt.%) 0.7 0.41 0.88 0.89 1.26 0.21

n-C12 (wt.%) 1.2 0.42 0.92 0.90 1.01 0.21

n-C13 (wt.%) 1.4 0.43 0.96 0.93 0.90 0.21

n-C14 (wt.%) 1.5 0.44 1.01 0.87 0.82 0.18

n-C15 (wt.%) 5.4 2.46 5.00 8.49 5.16 4.58

n-C16 (wt.%) 2.2 2.93 1.47 1.70 2.89 2.37

n-C17 (wt.%) 23.8 15.51 31.69 63.66 17.5 41.0

n-C18 (wt.%) 0.6 16.81 1.08 5.37 8.12 16.5

n-C19 (wt.%) 0.4 0.28 0.33 0.51 0.55 0.33

n-C20 (wt.%) 0.2 0.21 0.97 0.10 0.32 0.14

n-C17/n-C18 39.6 0.92 29.3 11.9 2.16 2.49

Fig. 5. Simulated distillation curves of hydrotreated products of various catalysts.The catalyst/oil weight ratio was 0.088.

582 B. Veriansyah et al./ Fuel 94 (2012) 578585

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waspreferred over decarbonylation. When theNi or Ru catalyst was

used, CH4 was the major gas compound (69.8 mol%, Ni catalyst;

49.9 mol%, Ru catalyst). This was because Ru and Ni are preeminent

methanation catalysts [1719]. A methanation reactionby the con-sumption of COand CO2 in thegas-phasewas responsiblefor thefor-

mation of CH4 (see Eqs. (6)(8)). The methanation reaction was not

very active when the Pd, Pt, NiMo, or CoMo catalyst was used. The

formationof the C2C4 species in thegaseous product indicated that

a cracking reaction took place during the hydroprocessing of the

soybean oil. A larger amount of C2C4 species formed when the Pt

catalyst was used compared to the other catalysts. Propane, one of

the main byproducts formed by hydroprocessing of the vegetable

oil, was produced in a larger quantity with the Pt catalyst

(7.76 mol%) when compared to the other catalysts (Ru, 0.89 mol%;

Ni 0.3 mol%; Pd, 2.23 mol%; CoMo, 2.34 mol%; NiMo, 2.8 mol%).

Since the hydroprocessing conversion with the Pt catalyst is lower

than the NiMo, Pd, CoMo, and Ni catalysts, the larger amount of

C2C4 species (including propane) indicates that a more active

hydrocracking reaction occurred with the Pt catalyst. However, the

useof Pt catalyst resultedin lower naphtha selectivity (which is also

the result of hydrocracking reaction) when compared to the CoMo

catalyst, as discussed previously. It is notclearwhat is causingdiffer-

ent hydrocracking activity to produce C2C4 species and naphtha

fraction when the Pd and CoMo catalysts were used. This may arise

from different reaction pathways and different catalytic adsorption

sites of each catalyst. The CoMocatalyst seems to have more proper

active sites to convert vegetable oil to the naphtha fraction.

The effect of the amount of catalyst was examined by increasing

thecatalyst/oil weightratio to 0.088. Theresults areshownin Figs. 5

and 6 and Table 2. The order of hydroprocessing conversion was Ni/

SiO2Al2O3 (95.9%) > NiMo/c-Al2O3 (91.9%) > Pd/c-Al2O3 (90.9%) >

CoMo/c-Al2O3 (79.9%). We did not test the Pt and the Ru catalysts

because of their low hydroprocessing activities. The free fatty acid

content was very low (0.050.55 wt.%), which indicated that the

hydroprocessed products could be regarded as hydrocarbon mix-

tures. Themost significant changein conversionwas observed when

theNi catalystwas used: theconversion increased significantly from

60.8% to 95.9% andthe freefattyacidcontent decreased significantly

from 7.96 wt.% to 0.55 wt.% as the Ni catalyst/oil weight ratio in-

creased from 0.044 to 0.088. Compared to the Ni catalyst/oil weight

ratio of 0.044, the distillation profile was much flatter over a wide

recovery rangeat thenarrowboilingpoints of 270330 C, whichfall

into the diesel fuel boiling point range (see Fig. 5). In contrast, mar-

ginal changes in hydroprocessing conversion were observed when

the Pd, NiMo, or CoMocatalyst was used. An increase in the amount

of catalyst did not lead to the conversion of species with boiling

points higher than 360 C. The n-alkane content in the liquid prod-

ucts increased slightly. When thePd catalystwas used, thefreefatty

acidcontentsweremuch lower compared to those of liquid products

with the catalyst/oil ratio of 0.044, indicating better conversion ofthe carboxylic acid groups.

A comparison of the naphtha, kero/jet, and diesel selectivity

resulting from hydroprocessed soybean oil is shown in Fig. 6a for

the different catalysts tested. The order of diesel selectivity was

Ni/SiO2Al2O3 (98.9%) > Pd/c-Al2O3 (95.6%)%NiMo/c-Al2O3 (95.6%) >

CoMo/c-Al2O3 (88.7%). This indicates that the hydrocracking reac-

tion was more favored when the CoMo catalyst was used. As listed

in Table 2, thecomposition of thehydroprocessed soybeanoil varied

widelywith thedifferentcatalysts.WhentheNi,Pd, or NiMo catalyst

Fig. 6. (a) Effects of catalysts on conversion and selectivity and (a) Effects of

catalysts on the dry gas composition. The catalyst/oil weight ratio was 0.088.

Table 2

Effects of catalysts on product composition. All of the experiments were performed at a hydrogen pressure of 9.2 MPa, reaction temperature of 400 C, reaction time of 2 h, and

catalyst/oil weight ratio of 0.088.

Soybean oil Ni Pd CoMo NiMo

Free fatty acid content (wt.%) 0.03 0.55 0.32 0.45 0.05

Moisture (wt.%) 0.059 0.026 0.065 0.019 0.023

n-alkane content (wt.%) 82.9 87.9 52.3 82.1

n-C8 (wt.%) 0.49 0.66 1.61 0.67

n-C9 (wt.%) 0.59 0.71 1.44 0.69

n-C10 (wt.%) 0.61 0.80 1.38 0.71

n-C11 (wt.%) 0.77 0.90 1.22 0.68

n-C12 (wt.%) 1.01 0.86 1.02 0.65

n-C13 (wt.%) 1.44 1.02 0.89 0.64

n-C14 (wt.%) 2.10 0.92 0.80 0.60

n-C15 (wt.%) 9.20 10.44 6.03 6.43

n-C16 (wt.%) 5.07 2.43 3.11 3.39

n-C17 (wt.%) 57.84 59.77 23.84 46.68

n-C18 (wt.%) 2.66 8.76 9.95 20.29

n-C19 (wt.%) 1.00 0.65 0.65 0.44

n-C20 (wt.%) 0.14 0.04 0.40 0.15

n-C17/n-C18 21.74 6.82 2.34 2.30


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wasused, then-alkanecontent from n-C8 to n-C20 in theliquid prod-

uct was high (82.187.9 wt.%), while the n-alkane content was low

(52.3 wt.%) when the CoMo catalyst was used. This indicates that

the formation of iso-alkanes, cyclic hydrocarbons, or aromatics

wasmorefavoredwith theCoMocatalyst. Thehigher naphtha selec-

tivitywith theCoMocatalyst suggests that thecracking reaction was

more favored compared to the Ni, Pd, and NiMo catalysts.

The carbon, oxygen, hydrogen, and sulfur contents in the soy-

bean oil and liquid products were measured using the elemental

analyzer, and the results are listed in Table 3. It is obvious thatthere was an increase in carbon and hydrogen content, and a

decrease in oxygen content in the hydroprocessed products from the

soybean oil. When the catalyst/oil weight ratio of 0.044 was tested,

the order of oxygen removal was NiMo/c-Al2O3 (93.6%)% CoMo/c-

Al2O3 (92.7%) > Pd/c-Al2O3 (90.0%) > Ni/SiO2-Al2O3 (57.3%) > Pt/c-

Al2O3 (56.4%) > Ru/Al2O3 (15.5%). The CoMo and NiMo catalysts were

very effectiveat deoxygenating thesoybean oil.Even though theCoMo

andNiMo catalysts weresulfidedpriorto hydrotreating,the sulfurcon-

tent intheliquid productswasbelowthedetection limit.Whenthecat-

alyst/oil weight ratio wasincreasedto 0.088,theoxygen removal order

was NiMo/c-Al2O3 (99.1%)% CoMo/c-Al2O3 (99.1%) > Ni/SiO2Al2O3(95.5%) > Pd/c-Al2O3 (90.9%). The most significant increase in oxygen

removal was observed when the Ni catalyst was used. In contrast,

the oxygen removal with the Pd catalyst increased marginally with

an increase in the catalyst/oil weight ratio.

The effects of the catalysts on the hydroprocessed product com-

position are given by a van Krevelen diagram, as shown in Fig. 7. As

expected, the soybean oil had a higher oxygen content and lower

hydrogen content than all of the hydroprocessed products. For

the liquid product obtained at the lowest conversion with the Ru

catalyst, the oxygen to carbon (O/C) molar ratio was reduced by

1.2 times, while at the highest conversion with the NiMo catalyst,

the O/C ratio decreased more than 17.0 times at a catalyst/oil

weight ratio of 0.044. When the catalyst/oil ratio was increased

to 0.088, the O/C ratio was reduced by $120 times with the CoMo

and NiMo catalysts. As discussed previously, the saturation of the

double bonds that are present in the triglycerides is another impor-

tant reaction in the hydroprocessing process. The catalyst effect on

the saturation extent can be observed via the hydrogen to carbon

(H/C) molar ratio in the van Krevelen diagram. When the cata-

lyst/oil ratio was 0.044, the metal-supported catalysts exhibited

higher H/C values than those of the CoMo and NiMo catalysts. This

indicates that a better hydrogenation reaction occurred on the me-

tal catalysts. However, at the higher catalyst/oil ratio of 0.088, the

H/C ratios of the CoMo and NiMo catalysts were higher than that of

the Pd catalyst. The Ni catalyst showed the highest H/C value of 2.2.

Because of their preeminent oxygen removal and saturation capa-

bilities, along with high conversion and low cost, the CoMo, NiMo,and Ni catalysts are promising catalysts for producing renewable

diesel from natural triglycerides.

4. Conclusions

The effects of various catalysts on the hydroprocessing of soybean

oil to produce a paraffin-rich mixture of hydrocarbons were examined

usinga batch reactor system. Theorderof thehydroprocessing conver-

sion was found to be NiMo (92.9%) > Pd (91.9%) > CoMo (78.9%) > Ni

(60.8%) > Pt (50.8%) > Ru (39.7%) at the catalyst/oil weight ratio of

0.044, and Ni (95.9%) > NiMo (91.9%) > Pd (90.9%) > CoMo (79.9%) at

the catalyst/oil weight ratio of 0.088. The composition of the liquid

products was strongly influenced by the type of catalyst. The

straight-chain n-alkane content was more than 80 wt.% with the Pd

or Ni catalyst, while it was less than 55 wt.% when the CoMo catalyst

was used. The low amountofn-alkane content andthe highernaphtha

selectivity of the CoMo catalyst suggested that isomerization and the

cracking reaction were more enhanced. The higher conversion and

higheroxygen removal capabilities, alongwith thelow cost, associated

with the Ni, NiMo, and CoMo catalysts make them suitable for use in

the hydroprocessing of natural triglycerides.

Acknowledgment

This project was supported by the Korea Ministry of the Envi-

ronment as a Converging technology project. Additional support

from the Korea Institute of Science and Technology was alsoappreciated.

Table 3

Effects of catalysts on carbon, oxygen, hydrogen, and sulfur contents.

Soybean oil Ru Pt Ni Pd CoMo NiMo

Catalyst/oil weight ratio = 0.044

C (wt.%) 77.6 77.8 81.3 80.4 84.1 83.0 84.6

O (wt.%) 11.0 9.3 4.8 4.7 1.1 0.8 0.7

H (wt.%) 11.9 13.7 14.5 14.4 15.0 14.3 14.4

S (wt.%)

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Appendix A. Supplementary data

Supplementary data associated with this article can be found, in

the online version, at doi:10.1016/j.fuel.2011.10.057.

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