1-s2.0-S0165237000001984-main

7/28/2019 1-s2.0-S0165237000001984-main

1/17

Journal of Analytical and Applied Pyrolysis

60 (2001) 187203

Influence of residence time and catalystregeneration on the pyrolysiszeolite catalysis

of oil shale

Paul T. Williams *, Hafeez M. Chishti 1

Department of Fuel and Energy, The Uni6ersity of Leeds, Leeds LS2 9JT, UK

Received 21 April 2000; accepted 20 October 2000

Abstract

Oil shale from the Kark region of Pakistan has been pyrolysed in a fixed bed batch reactor

and the properties of the derived shale oil determined. The reactor system was then modified

to incorporate a second reactor where the derived vapours from oil shale pyrolysis were

passed directly to the second reactor containing zeolite ZSM-5 catalyst. The influence of the

process parameters of vapour residence time (VRT) over the catalyst and the regeneration of

the catalyst were examined. The yield and composition of the derived gases before and after

catalysis were determined. In addition, the yield and composition of the derived oil in terms

of total nitrogen and sulphur content and the content of aromatic hydrocarbons in the oils

was investigated. The results showed that the yield of oil after catalysis was reduced with a

consequent higher yield of gases and formation of coke on the catalyst. The main gases from

the pyrolysis of oil shales were CO2, CO, H2, CH4, C2H4, C2H6 and C3H6, C3H8 and minor

concentrations of other hydrocarbon gases. The main role of catalysis was to convert the

long chain alkanes and alkenes in the oil to lower molecular weight, short chain, alkyl

substituted and iso species and high concentrations of aromatic hydrocarbons. Total

nitrogen and sulphur contents in the oils were markedly reduced after catalysis. This

reduction was reflected in the reduced concentration of nitrogen and sulphur containing

aromatic hydrocarbons. The influence of longer VRTs was to increase the formation of

aromatic hydrocarbons, reduce the nitrogen, and sulphur compounds in the oils. The

influence of catalyst regeneration, involving five regenerations was not significant on the yield

and composition of the derived catalytically upgraded oils. 2001 Elsevier Science B.V. All

rights reserved.

www.elsevier.com/locate/jaap

* Corresponding author. Tel.: +44 1132 332 504; fax: +44 1132 440 572.

E-mail address: [email protected] (P.T. Williams).1 On leave from the Institute of Geology, Punjab University, Lahore, Pakistan.

0165-2370/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved.

P I I : S 0 1 6 5 - 2 3 7 0 ( 0 0 ) 0 0 1 9 8 - 4

7/28/2019 1-s2.0-S0165237000001984-main

2/17

188 P.T. Williams, H.M. Chishti/J. Anal. Appl. Pyrolysis 60 (2001) 187203

Keywords: Oil shale; Zeolite; Catalysis

1. Introduction

Oil shales represent a long range potential source of liquid hydrocarbons as an

alternative to petroleum. Although there are very large, reserves of oil shale their

widespread development has not yet been realised due in part to the processingcosts of oil shale retorting and the relatively high concentrations of nitrogen and

sulphur in the derived shale oil [1,2]. It is essential to remove nitrogen and sulphur

from the oils if transport grade fuels are to be produced due to the legislative

requirements related to NOx

and SOx

emissions when such derived fuels are

combusted in automotive engines. The process of nitrogen and sulphur removal

from shale oils has almost exclusively concentrated on high pressure catalytic

hydrotreatment since this is the conventional route used to treat heavy crude

petroleum oils and refinery residues in the petroleum industry [36]. Further

refining of the oils in the petroleum industry involves low-pressure zeolite catalytic

cracking to produce refined products [7].

In a recent paper, the authors reported on the coupling of the pyrolysis stage of

processing and the nitrogen and sulphur removal/catalytic upgrading stage ofprocessing [8]. The pyrolysis and on-line zeolite catalysis of oil shale produced an

upgraded, low nitrogen and sulphur oil with a high aromatic content and reduced

heavier end. The influence of catalyst temperature between 400C and 550C on the

yield and composition of the derived oils and gases was reported. In this paper, we

report on the role of vapour residence time (VRT) of pyrolysis vapours over the

catalyst and the influence of the number of catalyst regenerations on the yield and

composition of the derived oils from the same two-stage pyrolysis/catalysis of oil

shales experimental system. Pyrolysis of the oil shales was also undertaken in the

absence of catalysis to compare with the two-stage pyrolysis/catalysis results.

2. Experimental section

The details of the experimental equipment and analytical methodologies have

been described in a previous related paper [8]. Therefore, only a brief outline will be

presented here.

2.1. Oil shale

The oil shale used was the Kark oil shale of Eocene age from the Kohat basin

area of northern Pakistan and has been described in detail before [9]. The catalyst

was of the high acidity, shape selective, zeolite ZSM-5 type and consisted of 2 mmdiameter spheres. The catalyst pore size was a mean of 5.5 A, and the surface area

was 300 m2g1.

7/28/2019 1-s2.0-S0165237000001984-main

3/17

189P.T. Williams, H.M. Chishti/J. Anal. Appl. Pyrolysis 60 (2001) 187203

2.2. Experimental

The reactor used for pyrolysis was a 200 cm3 fixed bed gas purged type heated by

an electric ring furnace. The weight of oil shale used throughout the experiments

was 50 g and grain size 0.51 mm. The heating programme was a fixed heating rate

of 10C min1 to the final pyrolysis temperature of 520C and held at the final

temperature for 1 h. The liquid oil phase was trapped in a series of cold traps and

the non-condensed gases were sampled and analysed off-line using packed column

gas chromatography. Fig. 1 shows a schematic diagram of the pyrolysis reactor.The two-stage pyrolysis/catalysis reactor incorporated a second batch reactor

containing the zeolite catalyst which was attached directly to the pyrolysis reactor

so that the pyrolysis gases generated were passed directly over the fixed catalyst

bed. For the pyrolysis/catalysis experiments, the oil shale was heated at fixed

pyrolysis conditions of 10Cmin1 to 520C and the catalyst temperature was

450C. The effluent from the reactor was passed to the condensation system

described for the pyrolysis reactor to trap the derived oils and subsequent analysis

of gases. Coke formation on the catalyst was determined by the difference in mass

Fig. 1. Schematic diagram of the pyrolysis reactor.

7/28/2019 1-s2.0-S0165237000001984-main

4/17


Fig. 2. Schematic diagram of the pyrolysiscatalysis reactor.

before and after catalytic regeneration. The VRT of pyrolysis vapours over the

catalyst of 16.6, 10.9, 6.1 and 3.0 s and the number of catalyst regenerations usingfresh catalyst and catalysts after 1, 3 and 5 regenerations were investigated. The

regeneration took the form of heating the used catalyst in a furnace at a tempera-

ture of 550C in the presence of air for a period of 8 h. Fig. 2 shows a schematic

diagram of the pyrolysis/catalysis reactor.

2.3. Analytical procedures

The non-condensable gases from the pyrolysis and pyrolysis/catalysis experiments

were analysed for C4 hydrocarbons, CO2, CO, N2, H2, CH4, and O2 by packed

column gas chromatography. In this work, the gas yield was calculated from thetotal individual gas concentrations rather than by difference.

The derived oils from pyrolysis and pyrolysis/catalysis were analysed for their

7/28/2019 1-s2.0-S0165237000001984-main

5/17


molecular weight distribution using size exclusion chromatography. The total

nitrogen and sulphur content of the oils was carried out using a PerkinElmer

elemental analyser.

It has been shown that the majority of nitrogen and sulphur present in shale oils

is contained in the aromatic fraction of the oils [2,3,10]. Therefore, the aromatic

fraction of the oils was isolated using chemical class fractionation using liquid

column chromatography. Isolation was followed by analysis of the fractions using

capillary gas chromatography with mass spectrometry and also with a variety of

selective detectors. The liquid column chromatography used sequential elution ofthe column with pentane, benzene, ethyl acetate and methanol to produce chemical

class fractionation in terms of increasing polarity, namely, aliphatic, aromatic,

ester and polar fractions.

The pentane fraction was analysed for aliphatic compounds using capillary

column gas chromatography with flame ionisation detection. The benzene fraction

was analysed for aromatic compounds including nitrogen and sulphur containing

species. Aromatic nitrogen compounds were determined using capillary column gas

chromatography with mass spectrometry (g.c./m.s.) and also using gas chromatog-

raphy with alkali salt, nitrogen selective detection. Aromatic sulphur compounds

were identified with the aid of the g.c./m.s., and the characteristic mass numbers of

sulphur containing species and also using capillary column gas chromatographywith flame photometric sulphur selective detection. Aromatic hydrocarbons con-

taining no nitrogen or sulphur were analysed by capillary g.c./m.s. Extensive uses

of retention indices were also used for identification throughout the analytical

work. The ethyl acetate and methanol fractions could not be analysed using the

available instrumentation.

3. Results and discussion

3.1. Product yield and gas composition

Table 1 shows the product yield and gas composition from the pyrolysis of oil

shale at 520C and also the pyrolysis of oil shale with zeolite catalytic upgrading in

relation to the pyrolysis VRT over the catalyst. The oil yield in the absence of the

catalyst was 14.6 wt.% representing a significant yield of oil. The main gases

consisted of hydrogen, carbon monoxide, carbon dioxide, methane, ethane, ethene,

propane, propene, with lower concentrations of iso-butane, butane and butene.

Table 1 shows that the influence of the zeolite catalyst was to significantly

reduce the yield of oil, there was a consequent increase in the production of gases

and formation of coke on the catalyst. Water production was slightly decreased inthe presence of the catalyst. The spent shale left after pyrolysis remained fairly

constant, since the pyrolysis was undertaken at identical conditions for the catalyst

7/28/2019 1-s2.0-S0165237000001984-main

6/17


experiments. As the residence time of the pyrolysis gases over the catalyst was

reduced, the influence of the catalyst was thereby reduced, and an increase in the

yield of oil, coupled with a reduction in gas and water yields and coke formation

on the catalyst was apparent. The formation of carbonaceous coke on the catalyst

is an inevitable disadvantage of catalytic upgrading and under the conditions of

fixed bed, catalysis used in this work represents a significant loss of organic

material. The formation of coke is related to the interaction of the catalyst with the

high concentrations of asphaltenes, aromatic compounds and alkenes found in the

shale oil [7].Table 1 shows that there was a marked increase in gases in the presence of the

zeolite catalyst. The gas increase was due mainly to increases in carbon dioxide and

the hydrocarbon gases. Both alkane and alkene gases were increased in the presence

of the catalyst compared to the uncatalysed pyrolysis. As the VRT over the catalyst

Table 1

Influence of VRT on the pyrolysis/catalysis of oil shale (wt.%)

No catalystProduct VRT (s)

10.9 6.1 3.016.6

Oil 6.614.6 6.7 7.75.4

8.710.210.1Gases 12.25.3

3.8Coke 3.7 3.24.6

9.2 8.0Water 7.6 7.6 6.5

71.271.270.1 71.2Spent shale 71.8

99.5 99.3Mass closure 97.3102.0 99.4

Non-hydrocarbon gases

Hydrogen 0.12 0.16 0.16 0.190.08

0.490.340.26Carbon monoxide 0.47 0.65

3.574.02Carbon dioxide 4.112.09 4.74

4.65 4.41Total 2.43 5.20 4.75

Hydrocarbon gases

Methane 0.92 0.75 0.71 0.640.420.680.34 0.55 0.56 0.58Ethane

0.23 1.26Ethene 1.04 0.92 0.89

Propane 1.270.17 1.54 0.621.23

0.06Propene 0.861.191.221.46

0.360.13 0.27Isobutane 0.25 0.09

0.11 0.13Butane 0.050.13 0.17

0.220.03 0.07 0.05 0.02Butene

5.27 5.04 3.76Total 1.48 6.60

Sum of Alkanes (C1C4) 1.992.882.953.671.19

2.322.93 2.160.32Sum of Alkenes (C1C4) 1.73

0.67 1.85Ethene/Ethane 1.90 1.64 1.53

0.35 1.38Propene/Propane 0.970.960.95

0.23 1.29Butene/Butane 0.58 0.38 0.42

0.27 0.79Alkenes/Alkanes 0.860.750.80

7/28/2019 1-s2.0-S0165237000001984-main

7/17


was shortened, the influence of the catalyst was reduced and the production of, in

particular, carbon dioxide and the hydrocarbon gases were reduced. Also shown in

Table 1 are the ratios of the C2C4 alkanes and alkenes. The alkene/alkane ratios

all showed a significant increase after catalysis. Alkene/alkane gas ratios particu-

larly ethene/ethane ratios in the evolved gases from oil shale pyrolysis have been

used to indicate the degree of oil cracking reactions [9,11]. Higher alkene/alkane

ratios indicating a higher degree of cracking. It has also been shown that the oil

vapour cracking reactions, which produce increased ethene/ethane ratios, are linked

to reduce yields of oil [12]. The alkene/alkane ratios of Table 1 show a clearincrease after catalysis showing that indeed cracking reactions are as expected

occurring. The reduced oil yield is also apparent. In addition, the ratios of

ethene/ethane and butene/butane show a clear reduction as the VRT over the

catalyst is reduced reflecting a decreased time for the cracking reactions to occur

and consequently a higher oil yield. There is also a reduced formation of coke on

the catalyst. However, the relationship of the propene/propane ratio and total

C2C4 alkene/alkane ratios does not show such a clear relationship.

Table 2 shows the product yield and gas composition for the pyrolysis/catalysis

of oil shale in relation to the number of catalyst regenerations. Also shown are the

results for pyrolysis of oil shale in the absence of the catalyst, discussed earlier, for

comparison. It might be expected that fresh catalyst would be more active thanregenerated catalyst and after each subsequent regeneration the effectiveness of the

catalyst in cracking the oil may be reduced. This is shown by the fresh catalyst

having a higher conversion of the pyrolysis vapours to gases and a higher coke

formation on the catalyst compared to catalyst which had been regenerated a

number of times. This was also reflected in consequent lower oil yields. As before,

the yield of all the gases and particularly carbon dioxide and the alkane and alkene

gases dominate the gas produced after catalysis. The ethene/ethane ratios, which for

the VRT experiments showed a clear link between the degree of catalyst cracking,

in this case showed an increase with the number of catalyst regenerations. Fresh

catalyst would be expected to be the most effective in cracking the oil and therefore

a higher ethene/ethane ratio would be expected compared to a catalyst which had

been regenerated several times. However, the opposite trend is shown in Table 2.

Similarly, the propene/propane ratios also show no clear trend. Overall, the

influence of the number of catalyst regenerations appeared not to be significant for

the range of regenerations investigated. However, the range of 05 regenerations is

very limited and industrial scale catalytic cracking may involve orders of magnitude

higher numbers of regenerations.

3.2. Elemental composition of the oils

Table 3 shows the elemental composition of the uncatalysed pyrolysis oil and the

pyrolysis/catalysis oils in relation to VRT and the number of catalyst regenerations.

Initial nitrogen and sulphur contents in the pyrolysis shale oil were 0.4 and 1.5wt.%, respectively. After catalysis, the oils showed significant reductions in nitrogen

and sulphur levels. There was evidence that with shorter residence times of the

7/28/2019 1-s2.0-S0165237000001984-main

8/17


Table 2

Influence of the number of catalyst regenerations on the pyrolysis/catalysis of oil shale (wt.%)

No catalystProduct Number of regenerations

0 1 3 5

6.7 6.514.6 6.66.1Oil

5.3 13.4 11.7 11.1 11.1Gases

4.9 3.95.0 3.8Coke

7.6 7.6Water 7.69.2 8.6

70.2 70.069.7 70.3Spent shale 70.1

Mass closure 101.8 99.1 99.1 99.599.5

Non-hydrocarbon gases

0.17 0.16Hydrogen 0.160.08 0.21

0.68 0.620.95 0.51Carbon monoxide 0.26

4.75 4.51Carbon dioxide 4.102.09 5.50

5.60 5.28 4.776.672.43Total

Hydrocarbon gases

0.69 0.710.82 0.75Methane 0.42

0.34 1.07 0.88 0.59 0.57Ethane

1.28 1.041.47 1.050.23Ethene

1.22 1.10Propane 1.120.17 1.261.17 1.121.29 1.10Propene 0.06

0.25 0.26 0.26Isobutane 0.13 0.30

0.14 0.130.16 0.110.13Butane

0.08 0.05 0.06Butene 0.03 0.12

5.71 5.00 5.026.48Total 1.48

3.18 2.79 2.81Sum of Alkanes (C1C4) 1.19 3.61

2.53 2.21 2.212.88Sum of Alkenes (C1C4) 0.32

1.45 1.76Ethene/Ethane 1.840.67 1.37

0.96 1.021.02 0.98Propene/Propane 0.35

0.61 0.35Butene/Butane 0.560.23 0.76

0.80 0.79 0.790.80Alkenes/Alkanes 0.27

pyrolysis vapours over the catalyst the catalyst was less effective in removing the

nitrogen and sulphur. However, the number of catalyst regenerations did not

significantly influence the nitrogen and sulphur content of the derived oils.

There are few data in the literature reporting the removal of nitrogen and

sulphur from shale oils using zeolite catalysis. However, zeolite catalytic cracking

of petroleum shows that nitrogen removal from petroleum oils is largely to form

products on the coke and some formation of gaseous nitric oxide [12]. The

removal of sulphur from petroleum oils is mostly through the production ofhydrogen sulphide gas and only a small faction forms products on the coke

[13,14].

7/28/2019 1-s2.0-S0165237000001984-main

9/17


Table 3

Elemental composition of pyrolysis and pyrolysis/catalysis oils in relation to VRT and number of

catalyst regenerations

Element (wt.%)Process conditions

Nitrogen SulphurCarbon Hydrogen

Pyrolysis

0.4 1.510.1520C 79.2

Pyrolysis/Catalysis

VRT

0.1 0.79.116.6 s 88.5

10.9 s 0.287.9 0.79.3

0.2 0.89.684.36.1 s

9.882.7 0.2 0.93.0 s

Regenerations

0.1 0.69.20 89.3

0.11 0.788.6 9.2

0.1 0.79.33 87.9

5 0.287.9 0.79.3

Fig. 3. Molecular weight range of the oils derived from the pyrolysis and pyrolysis/catalysis of oil shale

in relation to VRT.

7/28/2019 1-s2.0-S0165237000001984-main

10/17


Fig. 4. Molecular weight range of the oils derived from the pyrolysis and pyrolysis/catalysis of oil shale

in relation to the number of catalyst regenerations.

3.3. Molecular weight range of the oils

Fig. 3 shows the molecular weight range of the uncatalysed pyrolysis oil and the

pyrolysis/catalysis oils in relation to the residence time of the pyrolysis vapours over

the catalyst. Only the uncatalysed oil and 16.6 s and 3.0 s VRT results are shown

for clarity. Fig. 4 shows the molecular weight range of the uncatalysed oil and the

pyrolysis/catalysis oils in relation to the number of catalyst regenerations. Only the

uncatalysed oil and 0 and 5 number of catalyst regeneration results are shown for

clarity. The molecular weight range of the uncatalysed shale oil ranged from a

nominal 60 to over 2300 Da with a peak at :600 Da. After catalysis, there was a

significant decrease in the molecular weight range of the derived oils. The influence

of VRT showed a further reduction in the molecular weight range in relation tolonger residence times of the vapours over the catalyst. Extended reaction times

producing more catalytic cracking with a consequent lowering of the molecular

weight of the oils, such that at 16.6 s residence time, the molecular weight range of

the pyrolysis/catalysis oil was from a nominal 60 to :800 Da and with a peak at

about 200 Da. The influence of the number of catalyst regenerations was not

however, significant. Although there was a clear reduction in molecular weight

distribution after catalysis, the oils generated from the 05 number of regenerations

were almost identical.

3.4. Detailed composition of the oils

Table 4 shows the chemical class fractionation of the oil derived from the

uncatalysed pyrolysis of oil shale and the pyrolysis/catalysis of oil shale in relation

7/28/2019 1-s2.0-S0165237000001984-main

11/17


to the residence time of the pyrolysis vapours over the catalyst and the number of

catalyst regenerations. The pentane, benzene, ethyl acetate and methanol fractions

representing, aliphatic, aromatic, ester and polar material respectively. The un-

catalysed shale oil contained high concentrations of the more polar material.

However, after catalysis the polar material fraction was markedly reduced with a

consequent increase in the aliphatic and aromatic material of the pentane and

benzene fractions. The influence of VRT was that, as the residence time of the

pyrolysis vapours over the catalyst was reduced, there was less time for reaction

and consequently a progressive increase in more polar material and reducedproduction of aliphatic and aromatic material. The number of catalyst regenera-

tions had a marginal effect on the chemical class fractionation of the pyrolysis/

catalysis oils.

Detailed analysis of the pentane fraction of the uncatalysed pyrolysis oil showed

that the aliphatic material consisted of mostly n-alkanes and 1-alkenes together

with lower concentrations of branched chain compounds ranging from carbon

number C10 to C35. After catalysis the pentane fraction had a much reduced carbon

number distribution, the majority of the aliphatic material having a carbon number

less than C15. In addition, the n-alkane and 1-alkene material had largely been

converted to short chain, alkyl substituted and iso-aliphatic material. There has

been a large volume of literature related to the petroleum industry regarding thecracking of pure n-alkanes and 1-alkenes and mixtures of these straight chain

hydrocarbons over zeolite catalysts [1520]. The cracking of these compounds

produces a marked reduction in the carbon number range of the products and

increased formation of aromatic material.

Table 4

Chemical class fractionation of pyrolysis and pyrolysis/catalysis oils in relation to VRT and number of

catalyst regenerations

Process conditions Chemical class fraction (wt.%)

BenzenePentane MethanolEthyl acetate

Pyrolysis

8.8520C 19.1 28.7 34.7

Pyrolysis/Catalysis

VRT

26.4 42.616.6 s 13.8 1.2

2.115.941.410.9 s 24.8

23.5 34.66.1 s 21.7 3.4

33.4 24.2 4.13.0 s 21.2

Regenerations

0 25.9 43.0 13.2 1.7

2.013.841.81 25.0

24.8 41.53 15.7 1.924.85 41.2 15.9 2.1

7/28/2019 1-s2.0-S0165237000001984-main

12/17


Table 5

Influence of VRT on the nitrogen containing aromatic hydrocarbons in the oils from the pyrolysis and

pyrolysis/catalysis of oil shale (ppm)

No catalystProduct VRT (s)

10.9 6.1 3.016.6

50 50125 55Pyridines 35

Quinolines 370 460 500 7551115

Indoles 100260 105 16090

80 90 15065Carbazole 220

Total 6901720 745 1120560

Table 5 shows the nitrogen containing aromatic hydrocarbons present in the

benzene fraction of the uncatalysed shale oil and the pyrolysis/catalysis shale oils in

relation to VRT. Table 6 shows the influence of the number of catalyst regenera-

tions on the nitrogen containing aromatic compounds found in the benzene fractionof the oils. The nitrogen containing compounds in the oils were dominated by

pyridines, quinolines, indoles and carbazoles. After catalysis there was a signi ficant

reduction in the nitrogen containing species, which was reflected in the reduction in

total nitrogen in the oils after catalysis, shown in Table 3. With shorter residence

times of the pyrolysis vapours over the catalyst, the effectiveness of the catalyst in

removing nitrogen compounds was seen with a progressive increase in their

concentration in the oils. However, the influence of the number of catalyst

regenerations was less significant. Although there was a noticeable increase in the

concentration of the nitrogen compounds as the number of regenerations was

Table 6

Influence of number of catalyst regenerations on the nitrogen containing aromatic hydrocarbons in the

oils from the pyrolysis and pyrolysis/catalysis of oil shale (ppm)


0 1 3 5

30125Pyridines 504035

410395Quinolines 3001115 360

90 90Indoles 260 70 80

60 70Carbazole 70220 50

4501720 535 595 620Total

7/28/2019 1-s2.0-S0165237000001984-main

13/17


Table 7

Influence of VRT on the sulphur containing aromatic hydrocarbons in the oils from the pyrolysis and

pyrolysis/catalysis of oil shale (ppm)

Product No catalyst VRT (s)

10.9 6.1 3.016.6

25 4065 55Benzothiophene 20

Cn-Benzothiophenes 65 110 160 215245

30110 65 70 90Dibenzothiophene

255 380 505215Cn-Dibenzothiophenes 595

Total 4551015 650 865330

increased, thereby reducing the effectiveness of the catalyst in nitrogen compound

removal. The total nitrogen content of the uncatalysed oil shown in Table 3

represented 4000 ppm, whilst those presented in Table 5 and Table 6 totalled much

lower. However, the benzene fraction contained some higher molecular weight

unidentified material and in addition, the ethyl acetate and methanol fractions are

also likely to contain more polar nitrogen containing material.

The benzene fractions of the oils were also analysed for sulphur containing

aromatic hydrocarbons. Table 7 and Table 8 show the in fluence of VRT over the

catalyst and the number of catalyst regenerations on these compounds in the

uncatalysed oil compared to the pyrolysis/catalysis oils. The majority of sulphur

containing aromatic hydrocarbons is benzothiophene and dibenzothiophene and

their alkylated derivatives. The role of the catalyst was to reduce the concentration

of these compounds in the derived oils by significant levels. As the VRT over the

Table 8

Influence of number of catalyst regenerations on the sulphur containing aromatic hydrocarbons in the

oils from the pyrolysis and pyrolysis/catalysis of oil shale (ppm)


0 1 3 5

2065Benzothiophene 302525

9095Cn-Benzothiophenes 100245 120

65 65Dibenzothiophene 110 55 60

230 240Cn-Dibenzothiophenes 250595 210

3851015 335 425 435Total

7/28/2019 1-s2.0-S0165237000001984-main

14/17


Table 9

Influence of VRT on the aromatic hydrocarbons in the oils from the pyrolysis and pyrolysis /catalysis

of oil shale (mg g1)

Product VRT (s)No catalyst

10.9 6.1 3.016.6

37.82 23.6033.58 15.891.331-Ring aromatic

73.90 57.622-Ring aromatic 52.0232.55 79.46

4.94 3.905.43 3.893-Ring aromatic 2.81

1.73 2.28 2.07 1.64 1.904-Ring aromatic

118.73 86.7638.42 73.70120.75Total

catalyst was shortened, the catalyst was less effective in removing the sulphur

containing compounds. The influence of the number of catalyst regenerations was

relatively less significant, in some cases only reflecting a marginal influence on the

extent of sulphur compound removal. As was the case for the nitrogen hydrocar-

bons, the ethyl acetate and methanol fractions are likely to also contain sulphur

species of higher polarity and molecular weight.Table 9 shows the 14 ring aromatic hydrocarbons (non-hetero-atomic) present

in the benzene fraction of the uncatalysed shale oil and the pyrolysis /catalysis shale

oils in relation to VRT. Table 10 shows the influence of the number of catalyst

regenerations on the 14 ring aromatic compounds found in the benzene fraction

of the oils.

The 1-ring compounds present were mainly benzene, toluene and alkylated

benzenes, the 2-ring compounds were mainly naphthalene and its alkylated deriva-

tives, 3-ring compounds included, phenanthrene, anthracene and their alklylated

compounds and 4-ring compounds included pyrene and chrysene. The uncatalysed

oil contained significant quantities of 2-ring hydrocarbons and lower concentrations

of 1-, 3- and 4-ring compounds. However, after catalysis there was a marked

increase in the 1-ring and 2-ring hydrocarbons present in the oils. The 3- and 4-ring

Table 10

Influence of number of catalyst regenerations on the aromatic hydrocarbons in the oils from the

pyrolysis and pyrolysis/catalysis of oil shale (mg g1)


0 1 3 5

1.33 34.821-Ring aromatic 32.56 31.27 30.08

32.55 72.932-Ring aromatic 75.4079.5085.33

2.81 5.783-Ring aromatic 5.38 5.20 4.94

2.072.182.262.434-Ring aromatic 1.73

110.02114.05119.70128.3638.42Total

7/28/2019 1-s2.0-S0165237000001984-main

15/17


hydrocarbons showed a smaller increase. The influence of VRT showed that

longer residence times of pyrolysis vapours over the catalyst produce increased

formation of 1- and 2-ring hydrocarbons. Ono et al. [17] and Sirokman et al.

[18] have shown a similar relationship between residence time and aromatic

production for hexane and pentane over ZSM-5 zeolite catalyst respectively.

Table 10 shows that the influence of the number of catalyst regenerations on the

production of 1- and 2-ring hydrocarbons in the derived pyrolysis/catalysis oils

was small but significant. The increased number of regenerations reducing the

effectiveness of the catalyst.It is clear that zeolite catalysis produces a very aromatic oil, high in 1- and

2-ring hydrocarbons. Thus indicating that the oils had undergone significant

formation of aromatic compounds consistent with catalytic aromatisation reac-

tions of alkanes and alkenes on zeolite catalysts. The clear reduction in the more

polar ethyl acetate and methanol fractions shown in Table 4 indicate that the

catalyst is also effective in cracking these more polar compounds resulting in

possibly aromatic hydrocarbon formation.

In a previous paper by the authors [8] the influence of catalyst temperature on

the pyrolysis/catalysis of oil shale was investigated, using the same experimental

system reported here. In that work, nitrogen and sulphur removal from the shale

oil were similar to that reported here, with increasing catalyst temperature be-tween 400C and 550C producing increased effectiveness of removal. Similar

increases in the 1- and 2-ring aromatic compounds were observed. Consequently,

it may be concluded that of the process parameters investigated for the pyroly-

sis/catalysis of oil shale to produce an upgraded oil, the important parameters

with respect to nitrogen and sulphur removal and aromatic production are the

VRT over the catalyst and the catalyst temperature. However, over the limited

range of 05 regenerations, the effectiveness of the catalyst was not significantly

affected.

In addition to the catalytic reactions of the shale oil, the potential of mere

thermal cracking of the oil vapours should also be considered. Thermal cracking

would produce increased gas and reduced oil production; a shift to lower molec-

ular weight ranges for the oil and increased alkene/alkane ratios as was found

here in the presence of the zeolite catalyst. However, whilst it is inevitable that

thermal cracking reactions are occurring as the oil vapours pass through the hot

bed of catalyst, there is also clear evidence for catalytic reactions occurring. For

example, there is a marked decrease in oil yield and consequent increase in gas

yield at a much higher level than would be expected with mere thermal cracking.

Also, the nitrogen and sulphur contents are markedly reduced in the catalysed

oil, if thermal cracking reactions were dominant, it would be expected that the

heterocyclic compounds would be selectively concentrated in the oil and would

show an increase rather than a decrease. Further, zeolite catalysts are known to

promote the formation of single ring and two ring aromatic compounds due to

their selective size and shape pore structure. The dramatic increase in single ringand two ring aromatic compounds shown in Table 9 and Table 10 confirm that

catalytic reactions of the oil with the zeolite catalyst are indeed occurring.

7/28/2019 1-s2.0-S0165237000001984-main

16/17


4. Conclusions

Pyrolysis/catalysis of oil shales using a zeolite catalyst has shown that the process

is effective in removing nitrogen and sulphur compounds from shale oils. The

quality of the oil is improved by reducing the higher molecular weight material,

reducing the alkene content and increasing the aromatic content of the oils. The gas

yield consisting mainly of carbon dioxide and alkane and alkene gases was

significantly increased after catalysis compared to the uncatalysed pyrolysis. How-

ever, a disadvantage of the pyrolysis/catalysis process is the significant formation ofcoke on the catalyst and the reduced yield of oil compared to pyrolysis with no

catalysis. The reductions in total nitrogen and sulphur contents in the oils were

reflected in the reduced concentration of nitrogen and sulphur containing aromatic

hydrocarbons. The influence of longer VRTs was to increase the formation of

aromatic hydrocarbons and reduce the nitrogen and sulphur compounds. The

influence of catalyst regeneration, involving five regenerations was not significant

on the yield and composition of the derived catalytically upgraded oils.

Acknowledgements

The authors would like to acknowledge the support of the University of Leeds

technical staff, Peter Thompson, Chris Brear, Ed Woodhouse and Rod Holt. The

award of a Pakistan Government Scholarship to H. Chisti is also gratefully

acknowledged.

References

[1] P.L. Russell, Oil Shales of the World, Their Origin, Occurrence and Exploitation, Pergamon Press,

Oxford, 1990.

[2] A. Benyamna, C. Bennouna, C. Moreau, P. Geneste, Fuel 70 (1991) 845.

[3] L.F. Thompson, S.A. Holmes, Fuel 64 (1985) 9.[4] M.V. Landau, M. Herskowitz, D. Givoni, S. Laichter, D. Yitzhaki, Fuel 75 (1996) 858.

[5] H.M. Chishti, P.T. Williams, Fuel 78 (1999) 1805.

[6] D.K. Lee, W.L. Yoon, S.I. Woo, Fuel 75 (1996) 1186.

[7] P.B. Venuto, E.T. Habib, Fluid Catalytic Cracking with Zeolite Catalysts, Marcel Dekker, New

York, 1979.

[8] P.T. Williams, H.M. Chishti, J. Anal. Appl. Pyrolysis 55 (2000) 217.

[9] P.T. Williams, N. Ahmad, Fuel 78 (1999) 653662.

[10] J.T. Andersson, B. Schmid, J. Chromatogr. (A) 693 (1995) 325.

[11] A.K. Burnham, J.R. Taylor, Lawrence Livermore Laboratory Report UCID-18284. Lawrence

Livermore National Laboratory, Livermore, CA, 1979.

[12] A.W. Peters, G.D. Weatherbee, X. Zhao, Fuel Reformulation 5 (1995) 45.

[13] R. Sadeghbeigi, Fluid Catalytic Cracking Handbook, Gulf Publishing, Houston, 1995.

[14] R.F. Wormsbecher, G.D. Weatherby, G. Kim, T.J. Dougan, Emerging technology for reduction of

sulphur in FCC fuels. NPRA, AM-93-55, 1993.[15] Y. Ono, Catal. Rev. Sci. Eng. 34 (1992) 179.

[16] J. Abbot, B.W. Wojciechowski, J. Catalysis 107 (1987) 451.

[17] Y. Ono, H. Kitagawa, Y. Sendoda, J. Jpn. Petrol. Inst. 30 (1987) 77.

[18] G. Sirokman, Y. Sendoda, Y. Ono, Zeolites 6 (1986) 299.

[19] B.W. Wojciechowski, A. Corma, Catalytic Cracking; Catalysts, Chemistry and Kinetics, Marcel

Dekker, New York, 1986.

[20] S. Bhatia, Zeolite Catalysis; Principles and Applications, CRC Press, Boca Raton, 1990.

.

7/28/2019 1-s2.0-S0165237000001984-main

17/17


[17] Y. Ono, H. Kitagawa, Y. Sendoda, J. Jpn. Petrol. Inst. 30 (1987) 77.

[18] G. Sirokman, Y. Sendoda, Y. Ono, Zeolites 6 (1986) 299.

[19] B.W. Wojciechowski, A. Corma, Catalytic Cracking; Catalysts, Chemistry and Kinetics, Marcel

Dekker, New York, 1986.

[20] S. Bhatia, Zeolite Catalysis; Principles and Applications, CRC Press, Boca Raton, 1990.

.

1-s2.0-S0165237000001984-main

Documents

Transcript of 1-s2.0-S0165237000001984-main