ORIGINAL PAPER

Producing clean diesel fuel by co-hydrogenation of vegetableoil with gas oil

Csaba Toth • Peter Baladincz •

Sandor Kovacs • Jen}o Hancsok

Received: 15 November 2010 / Accepted: 26 February 2011 / Published online: 16 March 2011

� Springer-Verlag 2011

Abstract The goal of our investigation was the produc-

tion of partially bio-derived fuels in the gas oil boiling

point range. Our aim was the production of diesel fuel

blending components by co-hydrogenation of mixtures of

high-sulphur gas oil (about 1.0%) and vegetable oil raw

materials with different vegetable oil contents (0, 5, 15, 25

and 100%). The experiments were carried out on a NiMo/

Al2O3 catalyst with a targeted composition (T = 300–

380�C, P = 60–80 bar, LHSV = 1.0/h and H2/HC =

600 Nm3/m3). We obtained that both the vegetable oil

conversion reactions and the gas oil quality improvement

reactions took place. Under the favourable operational

conditions (360–380�C, P = 80 bar, LHSV = 1.0/h and

H2/HC = 600 Nm3/m3 and up to 15% vegetable oil con-

tent of the feed), the main properties of the high-yield

([90%) products except for the Cold Filter Plugging Point

(CFPP) value satisfied the requirements of the standard of

diesel fuels (EN 590:2009). The amount of vegetable oil

higher than 15% reduced the desulphurization efficiency,

because of the intake of large quantities of oxygen with the

triglyceride molecules of the vegetable oil. The products—

depending on the vegetable oil content of the feedstocks—

have an increased n- and i-paraffin content, so their com-

bustion properties are very favourable, and the emission of

particles is lower.

Keywords Bio gas oil � Diesel fuel � Co-processing �Co-hydrogenation � Vegetable oil � Hydrodeoxygenation �Hydrodesulphurization � Biodiesel

Introduction

The aspiration for the use of the bio-derived fuels in the

recent decades has come into view in the whole world. The

principal impulsions of the aspiration are the increasing

need for the mobility, the depletion of oil stocks, the

dependence of crude oil and import energy sources and the

need to reduce the environmental pollution. The energy

demand of passenger and freight transport is covered

mostly from fossil fuels today. To partially redeem these

(cover the increase of the usage), furthermore to improve

their quality the favourable solution would be the usage of

biofuels from biomass as a renewable energy source

(Wenzel 2009). Currently, the research and the continu-

ously growing application of the second-generation biofu-

els produced from renewable sources can certainly

contribute to these demands.

The currently utilised first-generation biodiesels (fatty

acid methyl esters) and their production technologies have

a lot of unfavourable properties (e.g. poor heat and oxi-

dation, and thus poor storage stability caused by the high

unsaturated content, corrosion problems caused by the high

water content, sensitivity to hydrolysis, unfavourable cold

properties, less energy content, etc.) (Ng et al. 2010). To

eliminate these unfavourable properties, the researchers of

the world have proposed a number of different processes to

produce biofuels from triglyceride-containing materials

(Hancsok et al. 2007a, b; Kovacs et al. 2010; Kubickova

et al. 2005; Maki-Arvela et al. 2007). One of the examined

different thermal and catalytic possibilities may be the

C. Toth (&) � P. Baladincz � S. Kovacs � J. Hancsok

Department of MOL Hydrocarbon and Coal Processing,

University of Pannonia, Egyetem Street 10,

8200 Veszprem, Hungary

e-mail: tothcs@almos.uni-pannon.hu

URL: www.uni-pannon.hu

123

Clean Techn Environ Policy (2011) 13:581–585

DOI 10.1007/s10098-011-0364-2

positive solution of the co-hydrogenation of vegetable oils

and gas oils together (Corma and Huber 2007; Egeberg

et al. 2010; Huber et al. 2007; Krar et al. 2010; Melis et al.

2009; Mikulec et al. 2009; Walandziewski et al. 2009).

However, some research results suggest that with the

conversation of gas oil with high sulphur content

(0.6–1.2%) and vegetable oil mixtures the catalytic alter-

ation cannot reduce the sulphur content of the products

to or below 10 mg/kg, which is expected in the EU

(Bezergianni et al. 2009; Mikulec et al. 2010). Therefore,

the aim of our experimental activity was to choose a cat-

alyst and specify proper process conditions to produce

products which fulfil the requirements of the European

diesel fuel standard (EN 590:2009).

Experimental

The aim of our experimental work was to test a selected

catalyst which is suitable—under appropriate process

conditions—to produce product mixtures with a high yield

([90%), and with maximum 10 mg/kg sulphur content

from mixtures of high-sulphur (1.0%) heavy gas oil from

Russian crude oil and Hungarian vegetable oil (sunflower

oil) as raw materials. In the co-hydrogenation experiments,

we applied mixtures of raw materials with different vege-

table oil contents (0, 5, 15, 25 and 100%) (Table 1). To the

pure vegetable oil feedstocks, dimethyl disulphide was

added to increase their sulphur content to 1000 mg/kg. This

ensures the maintenance of the sulphide state of catalyst.

An industrial ‘‘in situ’’ (pre)sulphided Ni(2.7%)Mo(14.3%)/

Al2O3–P(1.7%) desulphurization catalyst was used as a

catalyst, which was selected on the basis of the results of the

pre-experiments with a number of catalyst compositions,

which were carried out by our research group. The BET-

surface of the catalyst was 163.7 m2/g. From the running

down of the adsorption–desorption isotherms, we deter-

mined the mesopore-volume distribution and the incidence

based on the BJH theory. The calculated surface was

211.1 m2/g based on the BJH theory. As this value is greater

than the BET-surface, we concluded that the pores are not

circle symmetrical, or the mouth has a smaller diameter than

the inside diameter of the pore (pear-shape). The pore vol-

ume was 0.3554 cm3/g based on the BJH theory, the volume

of the micropores was 0.0068 cm3/g and the surface of pores

was 18.1 m2/g. The average diameter of the pores was

8.5 nm.

In case of all feedstocks the same process parameter

combinations were used (T = 300–380�C, P = 60–80 bar,

LHSV = 1.0/h and H2/HC = 600 Nm3/m3). The 60–80 bar

pressure and space velocity of 1.0/h values were selected

on the basis of the results of the preliminary experiments.

In the case of lower pressure and higher space velocity, we

could not produce less than 10 mg/kg sulphur containing

product mixture. We investigated the effect of the process

parameters and the vegetable oil content of the feedstocks

on the yield, the physical-, chemical- and application

properties of the main product in continuous mode in

laboratory pilot equipment and on steady-activity catalysts.

The properties of the feedstocks and the products were

specified according to the specifications of the EN

590:2009 ‘‘Automotive fuels-Diesel’’ standard.

Results and discussions

The product mixtures obtained during the heterogeneous

catalytic conversion of the different feedstocks were sep-

arated to gas phase, aqueous phase and organic phase. The

gas phase separated in the separator of the experimental

equipment contained—beside the hydrogen—carbon-

monoxide and carbon-dioxide forming in the deoxygen-

ation reactions (hydrodeoxygenation, decarbonylation and

decarboxylation), propane forming from the triglyceride

molecule, hydrogen-sulphide and ammonia forming in the

heteroatom removing reactions from the gas oil part of the

feedstock, and in addition it contained light hydrocarbon

by-products (C1–C4) forming in the cracking reactions (as a

valuable by-product). The aqueous phase contained water

(forming in the reduction of triglycerides), hydrocarbons

and different oxygen containing compounds. After the

splitting of the aqueous phase, we separated the main

product fraction (gas oil boiling point range fraction—

mainly C11–C22 hydrocarbons till the boiling point of

360�C) and the residue from the organic phase via vacuum

distillation. Components below the boiling point of 180�C

(gasoline) were absent in the products; therefore, the light

hydrocarbons did not have to be separated from those

because their flash points in all cases were greater than

55�C required by the standard. The incidentally obtained

residual fraction contained the unconverted triglycerides,

the formed or rather not converted di- and mono-glyce-

rides, and hydrocarbons with higher carbon numbers

originating from the feedstock or being intermediates, and

also carboxylic acids and esters.

The yield of the gas phase product increased with the

increasing temperature and pressure in case of all the

feedstocks. In this article (in order to avoid wordiness),

we present the yields and the properties of the products

obtained at the most preferential pressure (80 bar) as a

function of the temperature. At higher temperatures, the

triglycerides were increasingly converted, and the unde-

sired (productive of non gas oil products) hydrocracking

reactions came to the front, too. The yield of the aqueous

part of the fluid phase product mixture changed as a

maximum curve, because at low temperatures the

582 C. Toth et al.

123

conversion of the triglycerides is not complete yet, and at

360–380�C temperature where the conversion is almost

complete, the rate of water forming reactions decreases.

The yield of the organic liquid phase decreased with the

increasing temperature because of the high yield (up to

about 20%) of the by-products (CO, CO2, H2O and C3H8)

with the increasing temperature and on the other hand

because of the hydrocracking of the hydrocarbon chains

(Fig. 1). In case of pure gas oil feedstock, the yield of the

organic liquid product mixture was above 98% in all cases,

whilst its value in case of pure vegetable oil was about

82–90% in every case. The liquid organic product mixture

was separated into two fractions: gas oil boiling point range

main fraction and residual fraction. The decreasing of the

residual fraction demonstrates the increase of the conver-

sion with the increasing temperature of the catalytic con-

version (Fig. 2). In case of pure vegetable oil, the yield of

the residual fraction was approximately 10% at 300�C, and

with the increasing temperature, at 360�C it decreased to

0% whilst in case of mixture feedstocks the conversion of

the triglycerides was already complete at 340�C.

As a matter of course, the yield of the main product in

case of pure gas oil feedstock was the same as the yield of

the organic product mixture, and it decreased with the

increasing temperature of the catalytic conversion. In case

of vegetable oil feedstock this yield increased with

increasing temperature because of the triglyceride

conversion. In case of mixture feedstocks, the yield of the

main product was between the two mentioned rates of the

yield in function of the temperature (Fig. 3).

The sulphur content of the main products decreased by

increasing the temperature (Fig. 4). At 300�C—with the

reduction in the sulphur content of the feedstocks because

of the dilution effect of the vegetable oil—in case of

mixture feedstocks the product from 25% sunflower oil

containing feedstock had the lowest sulphur content, which

was expected, because this material had the lowest sulphur

content, as the vegetable oil is considered practically

Table 1 Properties of the feedstocks

Properties Test method Gas oil

(GO)

95% GO ?

5% SO

85% GO ?

15% SO

75% GO ?

25% SO

Sunflower

oil (SO)

F1 F2 F3 F4 F5

Density (15.6�C), g/cm3 EN ISO 12185:1996 0.8513 0.8553 0.8615 0.8695 0.9226

Viscosity (40�C), mm2/s EN ISO 3104:1996 5.36 6.68 9.18 11.81 31.11

Acid numb., mg KOH/g EN 14104:2003 0.03 0.03 0.04 0.04 0.08

Iodine numb., g I2/100 g EN 14111:2003 0.5 4 17 36 122

Aromatic content, % EN 12916:2006 37.60 35.79 31.91 28.23 0.00

CFPP, �C EN 116:1997 4 5 6 9 20

Sulphur content, mg/kg EN ISO 20846:2004 10370 9860 8815 7770 1000

Nitrogen content, mg/kg ASTM-D 6366-99 228 216 194 172 7

Oxygen content, % CHNS/O analyzer 16 mg/kg 0.57 1.72 2.87 11.50

Flash point, �C EN ISO 2719:2002 79 80 80 81 [300

Distillation characteristics EN ISO 3405:2000

IBP 213 212 214 213 a

10 v/v% 279 285 288 292 a

50 v/v% 324 329 335 340 a

90 v/v% 355 363 a a a

FBP 368 a a a a

Cetane number IQT analyzer 49 48 47 45 36

CFPP cold filter plugging pointa Cannot be measured because of the thermal decomposition of sunflower oil

75

80

85

90

95

100

280 300 320 340 360 380 400

Temperature, °C

Yie

ld o

f or

gani

c liq

uid

phas

e, %

0% 5% 15% 25% 100%

Sunflower oil content of feedstock

Fig. 1 The change of the yield of the organic liquid phase as a

function of temperature and vegetable oil content of the feedstocks.

(P = 80 bar, LHSV = 1.0/h and H2/HC = 600 Nm3/m3)

Producing clean diesel fuel by co-hydrogenation 583

123

sulphur-free. At 360–380�C, the products from 5% (F2)

and 15% (F3) vegetable oil containing feedstocks had

almost the same sulphur content as the products from pure

gas oil (F1) feedstock. The products from 25% vegetable

oil containing (F4) feedstock had higher sulphur content

than the previous ones, because the high oxygen content

(approx. 2.8%) of the feedstocks caused by the triglycer-

ides inhibited the desulphurization reactions, because the

deoxygenation reactions take place on the same (catalytic)

active sites. So the desulphurization efficiency was smaller

despite the fact that the raw material mixture had less

sulphur content. At 380�C from the F1, F2, F3 feedstocks,

less than 10 mg/kg sulphur containing products were made.

The aromatic content of the main product changed as a

minimum curve in function of the temperature, its

favourable range was 340–360�C (Fig. 5). By increasing

the vegetable oil content of the feedstocks the aromatic

content of the products decreased, partly because of the

aromatic hydrogenation reactions, and partly because the

feedstocks had inherently less aromatic content. This turn

was caused by the mixing of sunflower oil. The lowest total

aromatic content achieved was 18%. It is well known that

the lower aromatic content of the diesel fuels results in

better combustion properties, resulting significantly

reduced pollutant emissions (particulate emissions). The

0

1

2

3

4

5

6

7

8

9

10

280 300 320 340 360 380 400Temperature, °C

Yie

ld o

f re

sidu

e, %

0% 5% 15%25% 100%

Sunflower oil content of feedstock

Fig. 2 The change of the yield of the residue as a function of

temperature and vegetable oil content of the feedstocks. (P = 80 bar,

LHSV = 1.0/h and H2/HC = 600 Nm3/m3)

80

82

84

86

88

90

92

94

96

98

100

280 300 320 340 360 380 400

Temperature, °C

Yie

ld o

f m

ain

prod

uct,

%

0% 5% 15% 25% 100%

Sunflower oil content of feedstock

Fig. 3 The change of the yield of the main product as a function of

temperature and vegetable oil content of the feedstocks. (P = 80 bar,

LHSV = 1.0/h and H2/HC = 600 Nm3/m3)

0

200

400

600

800

1000

Temperature, °C

Sulp

hur

cont

ent,

mg/

kg

0 %

5 %

15 %

25 %

Sunflower oil content of feedstock,

280 300 320 340 360 380 400

Fig. 4 The change of the sulphur content of the products as a

function of temperature and vegetable oil content of the feedstocks.

(P = 80 bar, LHSV = 1.0/h and H2/HC = 600 Nm3/m3)

15

17

19

21

23

25

27

29

31

Temperature, °C

Aro

mat

ic c

onte

nt, %

0%

5%

15%

25%

Sunflower oil content of feedstock,

280 300 320 340 360 380 400

Fig. 5 The change of the aromatic content of the products as a

function of temperature and vegetable oil content of the feedstocks.

(P = 80 bar, LHSV = 1.0/h and H2/HC = 600 Nm3/m3)

0

5

10

15

20

25

30

Sunflower oil content of feedstocks, %

CFP

P, °

C

300°C 320°C

340°C 360°C380°C

0 20 40 60 80 100

Fig. 6 The change of the Cold Filter Plugging Point (CFPP) value

of the products as a function of temperature and vegetable oil

content of the feedstocks. (P = 80 bar, LHSV = 1.0/h and H2/HC =

600 Nm3/m3)

584 C. Toth et al.

123

cold flow properties of the products increased (became

worse) by increasing the vegetable oil content of the

feedstocks, because of the produced large quantities of

n-paraffins, and other derivatives of higher straight chain

hydrocarbons till 360�C boiling point (Fig. 6). However, at

360–380�C reaction temperature from the F4 feedstock

products were made which had almost the same CFPP

value (3�C) as the products produced from pure gas oil.

The CFPP value of the main products can be decreased by

additivation or by further isomerisation step (Hancsok et al.

2007c; Kasza et al. 2010).

Conclusions

On the basis of the results gained from the catalytic

co-hydrogenation of different percentages of (0–100%)

sunflower oil containing gas oil on a targeted composition

NiMo/Al2O3 catalyst we obtained that both the vegetable

oil conversion reactions (olefinic double saturation, deox-

ygenation) and the gas oil quality improvement reactions

(heteroatom removal, aromatic content reduction) took

place. Under the favourable operational conditions (360–

380�C, P = 80 bar, LHSV = 1.0/h and H2/HC = 600

Nm3/m3 and up to 15% vegetable oil content of the feed),

the main properties (total aromatic content: 20–23%, sul-

phur content: \10 mg/kg) of the high-yield ([95%) prod-

ucts satisfied the requirements of standard EN 590:2009 for

diesel fuels except for the cold flow properties; however,

this can be provided for economically by low-level addi-

tivation, or by further isomerization step. The amount of

vegetable oil higher than 15% reduced the desulphurization

efficiency, whereas the removal of heteroatoms took place

on the same active sites of the catalyst. So the deoxygen-

ation reactions forced back the desulphurization reactions

because of the intake of large quantities of oxygen with the

triglyceride molecule of the vegetable oil.

Based on the results, we concluded that an existing

hydrogenation plant (with a suitable pressure reactor) with

a slight alteration may be suitable for the co-processing of

vegetable oil and gas oil mixtures. In a single step, the

quality improvement of gas oil (sulphur, nitrogen, aromatic

content reduction) and the vegetable oil conversion to n-

and i-paraffins can be achieved. The products—depending

on the vegetable oil content of the feedstock—have an

augmented n- and i-paraffin content, and thus the com-

bustion properties are better and the particulate content of

exhaust gas is reduced. With this process gas oils which

cannot be converted to products with adequate cetane

number can be processed because the paraffins produced

from the triglycerides caused a significant increase in the

cetane number.

Acknowledgments TAMOP-4.2.1/B-09/1/KONV-2010-0003: Mobil-

ity and Environment: Researches in the fields of motor vehicle industry,

energetics and environment in the Middle- and West-Transdanubian

Regions of Hungary. The Project is supported by the European Union and

co-financed by the European Regional Development Fund.

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