CET vol 99


 
 
 
 
 
 
 
 
 
 
                                                                                                                                                                 DOI: 10.3303/CET2399007 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 20 December 2022; Revised: 11 March 2023; Accepted: 17 April 2023 
Please cite this article as: Miskolczi N., Tomasek S., 2023, Catalytic Upgrading of Bio-Oils Obtained from Different Sources, Chemical 
Engineering Transactions, 99, 37-42  DOI:10.3303/CET2399007 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL.  99, 2023 

A publication of 

 

The Italian Association 

of Chemical Engineering 

Online at www.cetjournal.it 

Guest Editors: Sauro Pierucci, Flavio Manenti 

Copyright © 2023, AIDIC Servizi S.r.l. 

ISBN 978-88-95608-98-3; ISSN 2283-9216 

Catalytic Upgrading of Bio-oils Obtained from Different 

Sources 

Nobert Miskolczi*, Szabina Tomasek 

Department of MOL Hydrocarbon and Coal Processing, Research Centre for Biochemical, Environmental and Chemical 

Engineering, University of Pannonia, Egyetem utca 10. Veszprém, Hungary 

miskolczi.norbert@mk.uni-pannon.hu 

This work focusses on the investigation of catalytic quality improvement of pyrolysis products. The yield of gases 

can increase significantly using Ni-Al2O3 and Ni-Al2O3/MoO3/CeO2 catalysts in case of both residential sewage 

sludge and farm waste sewage sludge raw materials (from 10.7-26.8% to 11.0-39.3%). It was found, that in 

addition to the oxygen content of the raw materials, the reaction conditions also greatly influenced the yield and 

properties of aqueous phase. The yield of aqueous phase was 9.7-17.9% without catalyst and that of 11.2-

21.8% with catalyst. The amount of oxygen-containing organic substances in products (e.g. aldehyde, ketone 

and carboxylic acid) decreased significantly after the quality improvement. The efficiency of the catalysts was 

also influenced by the raw materials and temperatures in the 1st reactor. The hydrogen content and hydrocarbon 

distribution of the gas products changed favourably after the catalytic treatment, because less aldehyde, ketone, 

alcohols, carboxylic acids, phenols and its derivate were formed.  

Keywords: waste, catalysts, pyrolysis, utilization, quality improving 

1. Introduction 

The further treatment and disposal of sewage sludge is an important challenge due to its increasing amount 

[Lee et al. 2021]. Currently, agricultural utilization and composting are mostly used for the further treatment of 

sewage sludge [Kiseley et al. 2019, Buta et al. 2021]. However, significant amount of the sewage sludge is still 

landfilled [Buta et al. 2021]. The main problem of the sewage sludge is that they contain significant amount of 

impurities, e.g. bacteria, pathogens, viruses, metals, phosphorus, nitrogen, sulfur, etc. [Buta et al. 2021, Wang 

et al. 2022]. Some of these get into the environment with current applications and contaminate that. Based on 

references, it was demonstrated, that the thermal treatment of sewage sludge looks prospective solution to 

these problems [Fonts et al. 2012, Gao et al. 2020]. The products of thermal processes are gases, bio-oil and 

char. The amount of products and their composition are significantly affected by the reaction parameters 

[Inguanzo et al. 2002]. At higher temperatures, more gas products should be obtained. The composition of bio-

oil is also mostly influenced by the properties of raw materials. In many cases, catalysts are also used to increase 

the amount of more valuable products and to achieve more favorable product properties. Al2O3, synthetic 

zeolites (e.g. HZSM-5, y-zeolite) and other oxides are used as catalysts [Gao et al. 2020, Inguanzo et al. 2002, 

Haghighat et al. 2020]. The combination of zeolites and other inorganic materials with transition metals proved 

to be beneficial for the in-situ bio-oil upgrading. Nickel-based catalysts are mostly used for this purpose. 

However, the advanced catalyst property can be further improved by promoters. Regarding the promoters 

mainly Ce, Cu, Fe, La, Mo or Zn are used to increase the hydrogen yield. Catalysts should be used by mixing 

them with raw material (in-situ quality improvement) or as catalyst to improve the property of pyrolysis product 

(post-situ quality improvement) in a separated reactor [Haghighat et al. 2020, Bai et al. 2022, Chen et al. 2021]. 

Catalysts can also reduce the amount of oxygen-containing compounds and polyaromatic hydrocarbons. 

Furthermore, the BET surface of the bio-char can be also effected by promoters of the catalysts. The amount of 

solid pyrolysis residue can also be reduced, if the catalysts are used in the mixed form with the raw material.In 

case of post-situ upgrading, mainly the yields of gases and liquid product is primarily changed. It is also known 

that the liquid products are the mixture of aqueous phase and hydrocarbons (bio-oil).  

37



The hydrocarbon bio-oil is usually consisting of aldehydes, ketones, carboxylic acids, alcohols, phenols, and 

other hydrocarbons. Since oxygen-containing components have unfavorable properties regarding their further 

use, e.g. they have acidic character, or low transportation and storage stability. Therefore, the primary goal of 

both in-situ and post-situ upgrading is to decrease the concentration of oxygen-containing component [Chen et 

al. 2021]. The main aim of this work was the investigation of post-situ upgrading of bio-oils obtained from sewage 

sludge pyrolysis using different catalysts and reaction conditions. 

2. Materials & methods 

2.1 Raw material 

Two different kinds of sewage sludge were used in this work; a residential sewage sludge (RSS) and farm waste 

sewage sludge (FW). The RSS had carbon of 39.1%, hydrogen of 5.9%, nitrogen of 4.8%, sulfur of 0.3%, while 

the FW had carbon of 29.8%, hydrogen of 3.9%, nitrogen of 1.6%, sulfur of 2.7%. 

2.2 Catalyst 

Nickel based catalysts had been used to modify the product yields and composition: Ni-Al2O3 and Ni-

Al2O3/MoO3/CeO2. The nickel was coated on the supporter surface by wet impregnation. In case of Al2O3/MoO3 

supporter, the 70% -Al2O3, 20% MoO3 and 10% CeO2 was used. 

2.3 Equipment 

Raw materials had been pyrolyzed in a two-stage steel pyrolysis reactor; in the 1st reactor zone 400 and 600°C 

were used, while the temperature in the 2nd reactor was 600°C (Figure 1). In each case, 200g of raw material 

was placed in the 1st reactor. To investigate the fast pyrolysis of raw materials, the temperature in the 1st reactor 

was elevated by 100°C/min heating rate, while it was preliminary set in the 2nd reactor. 

 
Figure 1: The pyrolysis process 

Volatiles from the 1st reactor was driven through a 15g fixed bed of catalyst placed in the 2nd reactor, then it was 

cooled by a tubular heat exchanger, then the condensed liquid products (mixtures of aqueous phase and bio-

oil) were separated from the gases and then further analyzed. 

2.4 Product analysis 

DANI gas chromatographs were used to investigate the composition of gases: a GC-FID (Rtx-1 PONA type 100 

m long column with an internal diameter of 0.25 mm and film thickness of 0.5 μm) and GC-TCD (CarboxenTM 

1006 PLOT (30m×0.53mm) column). The chromatograms were evaluated using Clarity software. 

The bio-oils were analyzed by DANI GC-FID (Rtx 1 dimetil-polysiloxan capillary column (30m × 0.53 mm, 

thickens of 0.25 µm)). Samples were dissolved in CS2, and then injected to the instrument. Initial temperature 

of 40 °C for 5 min was used, then the temperature was elevated by 8 °C/min till 340 °C and it was kept at 340 

°C till 20 min. The chromatograms were evaluated using Clarity software.The density, viscosity, acid number of 

bio-oils and the pH of water phase were followed by standardized methods. 

3. Results & discussion 

3.1 Product yield 

Figure 2 summarizes the product yields. Based on the results, it is clear that the product yields changed 

significantly using different reaction parameters. In general, more volatiles could be obtained from the RSS raw 

material, than that of from the FW raw material. The amount of char remaining in the 1st reactor was ~60% at 

400°C, while that of was ~47% at 600°C using FW raw material. Regarding the RSS raw material, the char yield 

was ~51% at 400°C and ~31% at 600°C. The liquid product of pyrolysis was the mixture of aqueous phase and 

hydrocarbons. During the pyrolysis, up to ~300°C, primarily the aqueous phase was formed, while more and 

more hydrocarbons produced by the further increase of the temperature.  

38



Based on results, a bit more bio-oil could be obtained from the RSS raw material, than that of from the FW raw 

material. However, the bio-oil/water ratio was higher in case of FW raw material.  

  
Farm waste Residential sewage sludge 

Figure 2: The yields of products 

The amount of gases increased significantly using catalysts. Comparing the two catalysts, the Ni-Al2O3 catalyst 

can increase the yields of gases in higher proportion, than the Ni-Al2O3/MoO3 catalyst. It was explained by the 

higher surface area of the Ni-Al2O3 catalyst. At higher temperature, more gas and liquid products were formed. 

Based on the results, it can also be seen that the catalysts increased the gas yield more significantly in case of 

600°C catalyst temperature, than using 400°C. The reason for this was, that the smaller molecules produced at 

600°C were better suited to the active sites of the catalyst, therefore their chemical bonds can be broken in 

higher degree. It is also important to mentioned, that more water was found in the presence of Ni-Al2O3/ MoO3 

catalyst, which was the consequence of the dehydrogenation reactions of the oxygen-containing components. 

3.2 Gases 

The composition of gases are demonstrated in Figure 3. Based on the data, there were clearly visible differences 

between the gas composition using the FW and RSS raw materials. 

  

  
Farm waste Residential sewage sludge 

Figure 3: The composition of gases 

0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0

0

20

40

60

80

100

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

R
at

io

P
ro

d
u

ct
 y

ie
ld

, %
Char Water Oil
Gases Bio-oil/water Gases/water

400°C 600°C

0.0

0.5

1.0

1.5

2.0

2.5

0

20

40

60

80

100

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

R
at

io

P
ro

d
u

ct
 y

ie
ld

, %

Char Water Oil
Gases Bio-oil/water Gases/water

400°C 600°C

0

20

40

60

80

100

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
o

m
p

o
si

ti
o

n
, %

C2-C6 CH4 CO2 CO2 H2

400°C 600°C

0

20

40

60

80

100

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
o

m
p

o
si

ti
o

n
, %

C2-C6 CH4 CO2 CO2 H2

400°C 600°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0

0.5

1.0

1.5

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
O

/C
O

2

H
yd

ro
ge

n
/C

O

Hydrogen/CO CO/CO2

400°C 600°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0

0.5

1.0

1.5

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
O

/C
O

2

H
yd

ro
ge

n
/C

O

Hydrogen/CO CO/CO2

400°C 600°C

39



Without catalysts, the concentration of CO2 was high; 70.5% (FW) and 66.2% (RSS) in the case of 400°C 1st 

reactor temperature, while it decreased to 47.0% (FW) and 39.0% (RSS) using 600°C catalyst bed temperature. 

Furthermore more hydrogen, CO, methane and C2-C5 hydrocarbons was found at 600°C. The reason for this 

was that the macromolecules from the raw material degraded to greater extent at higher temperature. Regarding 

the effect of the catalysts, it is clear that they increase the amount of hydrogen, CO and methane, while the 

amount of CO2 is reduced. At 400°C catalyst temperature using FW raw material, catalyst had significantly less 

effect to the gas composition, than that of using RSS raw material. More hydrogen and CO were produced using 

Ni-Al2O3/MoO3 catalyst. Especially in case of 600°C 2nd reactor temperature. Regarding the hydrogen/CO ratio, 

higher value was found in the presence of catalysts, regardless of the raw materials and the temperature. This 

was the consequence of the hydrogenation-dehydrogenation property of the transition metals on the catalyst 

surface. Significantly higher values of hydrogen/CO ratio were obtained at higher temperature, than at the 400°C 

in case of thermo-catalytic pyrolysis of FW raw material. A similar increase was also observed in the CO/CO2 

ratio. The reason for this was a decrease in the amount of CO2 rather than an increase in the concentration of 

CO. Both higher hydrogen/CO ratio and CO/CO2 ratio was observed in Ni-Al2O3/MoO3 catalyst. 

3.3 Bio-oil 

Bio-oils were black colour liquids with high density and viscosity. They were the mixtures of mainly 

hydrocarbons, aldehyde, ketone, carboxylic acids, alcohols and phenolic compounds. The composition of bio-

oils are shown in Figure 4. 

  
Farm waste Residential sewage sludge 

Figure 4: The composition of bio-oil 

The composition of bio-oils show many differences depending on the reaction conditions. In case of farm waste 

raw material, the bio-oil contained significant amount of aldehyde, ketone and phenolic compounds, while the 

main components were the carboxylic acids in case of RSS raw material. Regarding the effect of temperature, 

it is clear, that a bit more oxygen free hydrocarbons and other undefined compounds were found at 600°C 1st 

reactor temperature. This was the consequence of more significant scission of chemical bonds containing 

oxygen. Catalysts can significantly reduce the concentration of oxygen containing compounds, therefore less 

aldehyde, ketone, carboxylic acid and phenolic compounds were found. 

The chemical cause for this phenomenon is to be found in deoxygenation reactions. Compounds containing -

OH, -CHO, -C=O or -COOH groups could be transformed by the escape of water to the compounds without 

oxygen by the use of transition metal-containing catalysts. This is also indicated by the fact that the water content 

of the products usually increased by 2-5% in the presence of catalysts. The amount of oxygen-free components 

was higher by the use of catalysts, than without them. In case of 600°C catalyst temperature, higher increase 

can be observed, than using 400°C. In particular, the amount of oxygen-free compounds increased with the use 

of Ni-Al2O3/MoO3/CeO2 catalyst. 

In case of FW raw material, the Ni-Al2O3/MoO3/CeO2 catalyst showed significantly higher activity in reducing the 

amount of phenolic compounds and alcohols, than Ni-Al2O3. It is worth to mention, that the Ni-Al2O3 catalyst 

reduced the amount of aldehydes and ketones in more degree, although there was no significant difference 

between the two catalysts in this respect. It can be also said about both catalysts, that they showed high activity 

in reducing the amount of oxygen-containing groups primarily at 600°C. This was particularly noticeable with 

the FW raw material. In the case of the RSS raw material, the composition of the bio-oil changed only slightly at 

catalyst temperature of 400˘C. However at 600°C, the amount of carboxylic acids decreased significantly. In 

case of Ni-Al2O3/MoO3/CeO2 catalyst, significantly less phenolic compounds were formed. 

0

20

40

60

80

100

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
o

m
p

o
si

ti
o

n
, %

Hydrocarbon (oxygen free) Aldehyde, ketone

Carboxilic acids Phenol and derivates

Alcohols Other

400°C 600°C

0

20

40

60

80

100

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
o

-c
at

al
ys

t

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
o

m
p

o
si

ti
o

n
, %

Hydrocarbon (oxygen free) Aldehyde, ketone

Carboxilic acids Phenol and derivates

Alcohols Other

400°C 600°C

40



The acid number, viscosity and density are important for the long term utilization of bio-oils. Especially the 

corrosion properties, the transportation and storage stability can be deteriorated in case of high values of acid 

numbers. Table 1 shows the acid number, viscosity and density of bio-oils and the pH values of aqueous phase. 

Based on the results it is clear, that the bio-oils had relatively high acid numbers, which can be decreased by 

catalysts. Especially the Ni-Al2O3/MoO3/CeO2 catalyst had favourable property for acid number decreasing. 

Comparing the two raw material, RSS derived bio-oils has higher acid number, than farm waste derived. This 

was the consequence of the high carboxylic acid content of RSS derived bio-oils. Regarding the density and 

viscosity, the CeO2 had unfavourable property, because higher density and viscosity can be measured in this 

presence. Presumably, the active centres of catalysts was partially blocked by CeO2, which resulted less activity 

in C-C scission. 

Table 1: The main properties of bio-oil and aqueous phase (FW raw material) 

1st reactor 400°C 600°C 

2nd reactor No-catalyst Ni-Al2O3 Ni-Al2O3/MoO3/CeO2 No-catalyst Ni-Al2O3 Ni-Al2O3/MoO3/CeO2 

Density, g/cm3 0.989 0.971 0.975 0.947 0.914 0.915 

Viscosity, mPas 71.9 62.8 63.1 53.6 27.6 35.3 

Acid number, mg KOH/g 21.6 17.5 16.1 18.8 12.7 11.9 

pH (aqueous phase) 8.7 8.9 9.1 9.0 9.1 9.2 

Table 1: The main properties of bio-oil and aqueous phase (RSS raw material) 

1st reactor 400°C 600°C 

2nd reactor No-catalyst Ni-Al2O3 Ni-Al2O3/MoO3/CeO2 No-catalyst Ni-Al2O3 Ni-Al2O3/MoO3/CeO2 

Density, g/cm3 0.975 0.959 0.953 0.930 0.902 0.906 

Viscosity, mPas 59.3 50.1 55.6 46.2 25.0 26.8 

Acid number, mg KOH/g 39.2 29.3 25.1 27.3 21.9 20.2 

pH (aqueous phase) 8.9 9.1 9.3 9.1 9.3 9.5 

 

The pH values of aqueous phase also refer to the acidity properties. The pH values were in the range of 8.7-

9.5. It means, that the aqueous products had a bit alkaline characteristic. It was caused by the decomposition 

of nitrogen-containing compounds, which resulted ammonia and organic amines. Furthermore, alkali metals and 

alkali earth metal salts in the raw materials can transform to their hydroxyl derivatives with alkali character. The 

RSS raw material derived aqueous phase had a bit higher pH, while the presence of catalyst can also increase 

the pH values. Presumably the higher pH values refers to more ammonia and organic amines in water. This 

was the consequence of the more significant degradation of nitrogen containing compounds. 

3.4 Catalysts 

The catalyst activity is key parameter for pyrolysis reactions. However, the catalysts activity can be changed 

during their application. In general, coke depositions should be also formed during the pyrolysis reactions, which 

can block the catalysts active sites, result reduced catalyst activity. The carbon deposition on the surface of 

used catalysts is summarized in Figure 5. 

 
Figure 5: The carbon deposition on the used catalyst surface 

It is clear, that coke was deposited on the catalyst surface. Comparing the two raw materials, the pyrolysis of 

farm waste resulted more coke on catalyst surface, than residential sewage sludge. On the other hand, more 

0

2

4

6

8

10

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

N
i-

A
l2

O
3

N
i-

A
l2

O
3

/
M

o
O

3
/C

eO
2

C
ar

b
o

n
 d

e
p

o
si

ti
o

n
, %

400°C 600°C

FW RSS

41



coke was found on Ni-Al2O3 catalyst, which was the consequence of its higher activity in decomposition 

reactions. Regarding the temperature, less carbon deposition was formed at higher temperature, which was the 

consequence of the Bodouard reaction. 

4. Conclusions 

In this work, the thermo-catalytic pyrolysis of different sewage sludge and post situ product upgrading were 

investigated in a two stages laboratory scale batch reactor using Ni-Al2O3 and Ni-Al2O3/MoO3/CeO2 catalysts. It 

was found, that more volatiles were obtained at 600°C catalyst temperature and in the presence of catalysts. 

Due to the higher surface area of catalyst, the application of Ni-Al2O3 occurred more gases than Ni-

Al2O3/MoO3/CeO2 catalyst. The catalyst activity was more significant at 600°C, however, it was affected by the 

raw materials. Less difference in catalyst activity was demonstrated in case of FW raw material, than RSS 

regarding gases. In general, the residential sewage sludge resulted more volatiles, than that of farm waste. 

Catalysts can decreased the formation of CO2, and increase the concentration of hydrogen, CO and 

hydrocarbons in gases. The MoO3 and CeO2 in catalyst supporter seems favourable for more hydrogen and CO 

production. Bio-oils consisted of oxygen-containing hydrocarbons and oxygen free hydrocarbons. They were 

viscous, black colour liquid with high density. Comparing the two raw material, the RSS derived bio-oils had 

significantly more carboxylic acids, than FW derived. The main effect of the catalyst was the supporting of 

deoxygenation reactions, which resulted less oxygen-containing hydrocarbons in bio-oil and more CO2 and 

aqueous phase. Especially, the Ni-Al2O3/MoO3/CeO2 catalyst showed high activity in these reactions at 600°C 

using RSS raw material. The bio-oil density and viscosity were in the range of 0.902-0.989g/cm3 and 25.0-

71.9mPas, respectively. They acid number were between 11.9 and 39.2mgKOH/g. The Ni-Al2O3 catalyst can 

reduced the density and viscosity of bio-oil more significantly, however, the Ni-Al2O3/MoO3/CeO2 catalyst 

resulted products with less acidity. The aqueous phase had light alkali characteristic, which a bit was the 

dependence of raw materials and catalyst.  

Acknowledgments 

This project (2019-2.1.13-TÉT_IN-2020-00071) was financed by the Ministry of Innovation and Technology from 

the National Research Development and Innovation Fund, within the 2019-2.1.13-TÉT_IN program. 

References 

Bai J., Lv Q., Fu X., Chen J., Wang H., Lin S., Zhou X., 2022, Catalytic reforming of sewage sludge pyrolysis 

products over the self-derived char, Journal of Analytical and Applied Pyrolysis 168, 105759. 

Buta M., Hubeny J., Zieliński W., Harnisz M., Korzeniewska E., 2021, Sewage sludge in agriculture - the effects 

of selected chemical pollutants and emerging genetic resistance determinants on the quality of soil and 

crops - a review, Ecotoxicology and Environmental Safety, 214, 112070. 

Chen R., Sheng Q., Dai X., Dong B., 2021, Upgrading of sewage sludge by low temperature pyrolysis: Biochar 

fuel properties and combustion behaviour, Fuel 300, 121007. 

Fonts I, Gea G., Azuara M., Ábrego J., Arauzo J., 2012, Sewage sludge pyrolysis for liquid production: A review, 

Renewable and Sustainable Energy Reviews 16, 2781-2805. 

Gao N., Kamran K., Quan C., Williams P.T., 2020, Thermochemical conversion of sewage sludge: A critical 

review, Progress in Energy and Combustion Science 79, 100843. 

Haghighat M., Majidian N., Hallajisani A., Samipourgiri M., 2020, Production of bio-oil from sewage sludge: A 

review on the thermal and catalytic conversion by pyrolysis, Sustainable Energy Technologies and 

Assessments 42, 100870. 

Inguanzo M., Domıńguez A., Menéndez J.A., Blanco C.G., Pis J.J., 2002, On the pyrolysis of sewage sludge: 

the influence of pyrolysis conditions on solid, liquid and gas fractions, Journal of Analytical and Applied 

Pyrolysis, 63, 209-222. 

Kiselev A., Magaril E., Magaril R., Panepinto D., Ravina M., Zanetti M.C., 2019, Towards Circular Economy: 

Evaluation of Sewage Sludge Biogass Solutions, Resources 8, 91. 

Lee S., Kim Y-M, Siddiqui M.Z., Park Y-K, 2021, Different pyrolysis kinetics and product distribution of municipal 

and livestock manure sewage sludge, Environmental Pollution 285, 117197. 

Wang K., Zheng Y., Zhu X., Brewer C.E., Brown R.C., 2017, Ex-situ catalytic pyrolysis of wastewater sewage 

sludge – A micro-pyrolysis study, Bioresource Technology 232, 229-234. 

Wang M., Pan X., Xia Y., Zhu A., Wu Y., Fu C., Zhang P., Zhao J., Li J., Fu J., 2022, Effect of dewatering 

conditioners on pollutants with nitrogen, sulfur, and chlorine releasing characteristics during sewage sludge 

pyrolysis, Fuel, 307, 121834. 

42


	187miskolczi.pdf
	Catalytic Upgrading of Bio-oils Obtained from Different Sources