sodium hydroxide-assisted desulphurization

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Sodium hydroxide-assisted desulphurization

of petroleum fluid coke

Zacheria M George and Linda G. Schneider

Albert a Research Coun cil , 17315-87 Avenu e, Edmon ton, Alberta, T6G 2C2, Canada

(Received 1 July 1982)

Desulphurization of a fluid coke produced commercially from a conventional petroleum crude oil was

attempted. Direct hydrodesulphurization of the coke at 700°C resulted in ~31 w% sulphur removal;

however, impregnation of the fluid coke with trace amounts of sodium hydroxide and subsequent

hydrodesulphurization resulted in > 80 wp/o sulphur removal primarily as Hz % A significant part of the

alkaline reagent could be recovered by hot water leaching of the desulphurized coke. The calorific value

of the desulphurized coke is slightly lower than that of the starting material. The mechanism appears to

be complex as the change in surface area was negligible upon impregnation and hydrodesulphurization.

Economic evaluation of the desulphurization process, carried out at the Alberta Research Council,

indicates that it has significant economic advantages over fluidized-bed combustion of the coke with

limestone or combustion of the coke with flue gas desulphurization.

(Keywords: desulphurization; fluid; coke; sodium hydroxide)

Although much work has been carried out on methods of

desulphurizing coal and coal chars, few studies are

reported in the literature on the desulphurization of

petroleum cokes. In coal, a significant portion of the

sulphur may be present as inorganic sulphides and

methods such as that of Meyer1 are very efficient for

removal of these sulphur compounds. In petroleum cokes

however, a considerable part of the sulphur may be

present as organic sulphur compounds and these

compounds are not easily desulphurized. Further,

petroleum cokes exhibit significant differences depending

upon the origin of the petroleum, coking process

employed and the amount and type of sulphur

compounds present in the petroleum.

El Kaddah and Ezz’ investigated thermal

desulphurization of petroleum coke containing 8.3 wt%

sulphur and observed 30 wt% sulphur removal in 30 min

at 1600°C. Sef3 studied hydrodesulphurization of

petroleum coke containing 2 wt% sulphur and reported

85 wt% sulphur removal using small particles of coke, a

pressure of 659 Pa, and high space velocities. Mahmoud et

al4

observed a maximum at 600°C for the

hydrodesulphurization of petroleum coke containing 3

wt% sulphur, this maximum being attributed to the onset

of sintering. George5 and Tollefson and Parmar have

studied the hydrodesulphurization of Athabasca oil sands

delayed coke and observed that the level of

desulphurization was not significant under the

experimental conditions and that the reaction was

controlled by pore diffusion. Mason7 has reported the

beneficial effects of preoxidation of coke on the

subsequent hydrodesulphurization;

however, the

optimum conditions of the preoxidation appear to vary

widely. Thakker* showed that impregnation of petroleum

coke with sodium carbonate enhances the level of sulphur

removal during hydrogenation. Ridley’ reported that

001~2361/82/12126%07%3.00

@ 1982 Butterworth & Co (Publishers) Ltd.

1260 FUEL, 1982, Vol 61, December

sodium hydroxide and sodium sulphide when

impregnated on coke particles aided desulphurization.

Lukasiewicz and Johnson” and Sabott” observed that

significant desulphurization of petroleum coke can be

achieved by impregnating the coke with an alkaline

reagent, calcination of the impregnated coke in an inert

atmosphere at elevated temperatures and subsequent hot

water leaching of the coke to remove the metal sulphides.

Parmar and Tollefson6 employed a fluidized-bed reactor

to evaluate several methods to desulphurize delayed coke

produced by Suncor Canada. George, Parmar and

Tollefson” investigated the desulphurization of oil sands

delayed coke involving impregnation with an alkaline

reagent,

and subsequent calcination, and George,

Schneider and

Tollefson’3 have reported the

desulphurization of a high sulphur fluid coke by this

method. These experiments showed that to achieve

significant desulphurization, large (twice stoichiometric

amount to form metal sulphides) quantities of the alkaline

reagents were necessary and posed serious corrosion and

environmental problems.

The objective of this investigation was to develop an

economically attractive process for the desulphurization

of petroleum coke prior to combustion. A sample of

petroleum fluid coke (sulphur content 7.3 f 0.3 wt%) was

obtained from Getty Oil Company, Delaware, USA, and

an attempt to desulphurize this coke was made so that the

sulphur dioxide level produced during combustion may

be tolerated with minimum environmental damage.

Whilst investigating methods of desulphurizing this

petroleum coke, it was observed that if the fluid coke were

impregnated with a small amount of base, such as sodium

hydroxide, and then hydrodesulphurized at M700°C

significant sulphur removal could be achieved. This Paper

summerizes results on this method of desulphurizing a

sample of Getty fluid coke.



Desulphurizat ion of petroleum fluid coke: 2. M. George and 1. G. Schneider

Tab/e 1 Analysisof Gettyfluid coke (db)

Carbon

86.9 wt %

Hydrogen

1.8wt%

Sulphur

7.3 f 0.3 wl %

Nitrogen

1.3wt%

Ash

0.1 w-t%

Nickel

1 Ash

30 PPm

Vanadium 225 ppm

Tab/e 2 Sulphur content of fluid cokes examined

Source Sulphur mntent (wt %)

Getty Coke, Delaware, USA

7.3 ?: 0.3

Petrofina, Montreal 6.4 f 0.3

Imperial Oil, Sarnia 3.2 + 0.2

EXPERIMENTAL

Materials

Most of the experiments were carried out using fluid

coke obtained from Getty Oil Company, Delaware, USA.

Analysis of this coke is summarized in

Table 1.

Limited

experiments were performed on samples of fluid coke

obtained from Petrofina, Montreal, and Imperial Oil,

Sarnia, Canada. The sulphur contents of these cokes are

listed in Tabl e 2. The reagents used in this study were all

as-received grade. The surface area of the coke samples

was usually determined by the high speed surface area

analyser (Micromeritics Model 2200) and periodically by

the BET measurements.* The coke sample was activated

in dry helium for 4 h at 100°C before surface area

measurements.

For the sodium hydroxide-assisted desulphurization of

fluid coke the following steps are involved: (1)

impregnation of the coke particles with a suitable alkaline

reagent; (2) hydrodesulphurization; (3) leaching to remove

and

recover the alkaline reagent; (4) sulphur

determination in the coke.

1.

Impregnati on of he coke w it h alk ali ne reagents.

Coke

granules, 40/60 US mesh, were slurried with an aqueous

solution of the alkaline reagent and evaporated to dryness

at x 80°C with stirring. The ratio of the weight of alkaline

reagent to the weight of coke is defined as the weight ratio,

W/R.

Most of the experiments reported here involved

impregnation with 1M NaOH. Impregnation and drying

at higher temperatures or at room temperature resulted in

significantly lower desulphurizations during the

hydrogenation step. A few experiments were also carried

out using KOH and LiOH. Impregnation in an air or

inert atmosphere did not appear to influence the level of

sulphur removal in subsequent hydrogenation.

2. Hydrodesulphurization. A fixed-bed flow reactor

system

Figure I)

was constructed from 316 stainless steel

tubing except for the reactor which was made out of

quartz tubing.? The reactor consisted of a 3.2 cm i.d. x 61

cm long quartz tube and had a quartz fibre plug midway

to support the coke sample. The reagent-loaded coke (5.0

g) was charged into the reactor at room temperature, a

* BET surface

area measured by N, adsorption at 77K was only to

check the surface area measured by the one-point system

7 Initially, a stainless steel reactor was employed; but the reactor was

sulphided and interfered with gc. analysis.

hydrogen flow established, and the furnace switched on.

The reactor was heated by a Lindberg heavy duty furnace

(type 59344) equipped with a controller

_+

5’C). It took

= 30 min for the furnace to reach the desired temperature

Figure 2). The rate of hydrogen flow, 120 ml mine’,. was

measured at the reactor outlet under ambient condltlons.

The product stream was sampled and analysed every 5

min by gas chromatography and the reactor effluent was

scrubbed with NaOH prior to venting.

3.

Leaching.

After hyprodesulphurization the coke was

leached with tap water E 5 g coke/500 ml H,O) at 80°C

for 12 h. The water was then decanted and the sample

Hz He O2 HZS

H20

Flow

m t r

ie

Figure 1

Flow reactor for coke desulphurization. D, Sampling

10-0~; V, 7-port sampling valve; m, metering valve; T, thermomuple;

Tc, thermal mnductivity detector; CON, controller for the furnace;

El, electronic integrator; PS, Power supply for gas chromatograph

8o08533

Time (mln)

f&urel

Coke temperature (0) and H.# mncentration in the

reactor effluent gas; (A) as a function of time after reactor start-up.

5.0 g coke sample, 40160 US mesh, 2 h, 700°C, Hz flow = 120 ml

min-I,

W/t? =

0.04

FUEL, 1982, Vol 61, December 1261



Desulphurizat ion of petroleum fluid co ke: Z. M. George and L . G. Schneider

Table3

Summary of preliminary experiments, Getty fluid coke, 7OO”C, 40160 US mesh, 2 h, 5.0 g sample. Gas flow: 120 ml min-’

Desulphurization

Desulphurization Surface area before

Surface area after

NaOH loading

medium

(96)

leaching (m2 g-l)

leaching (m2 9-l)

(Ml kg-‘)

None N2 2 11 11 30.24

W/R = 0.04 N2

29

<O.l

None “2 31 11

W/R = 0.04

‘42

90 <O.l 3 29.08a

W/R = 0.04 H, wet 85 10 3

W/R = 0.04 None None <O.l 5

W/R = Weight ratio,

Wt NaOH(g)

Wt coke(g)

a Leached sample

dried at 100°C in air. Leaching was practised as an

integral part of desulphurization as the NaOH used for

the impregnation of the coke is an expensive component

of desulphurization which could be recovered by leaching

and may be used for reagent make-up for further

impregnation.* Also, the presence of alkaline compounds

in the coke may lead to serious problems in the boiler

tubes during combustion. The rate of leaching was

significant initially but declined with time. Approxi-

mately 50% of the base could be extracted in E 1 h

and =7&75x in 12 h. Because of the small amount of

NaOH used in these experiments to achieve >80%

desulphurization and as a significant portion of the

alkaline reagent may be recovered by leaching and re-

used, the NaOH used appeared to act as a catalyst.

4.

Determinat ion of

sulphur

removal.

Gas

chromatographic

analysis and high temperature

combustion (ASTM D-3177-75) were employed

independently to determine desulphurization via H,S and

the total sulphur removal, respectively.

G.c. analysis

To quantitate sulphur removal from the coke as H,S or other

gaseous sulphur compounds during hydrodesulphurization,

the effluent of the reactor was analysed by g.c. every 5 min. By

switching a six-port sampling valve

Figure Z),

sample of the

effluent gas (2.0 ml) was swept into the analytical column, 8

feet of Poropak Q followed by 2 feet of Poropak T, maintained

at 15O”C,and analysed over a calibrated thermal conductivity

detector. During the initial stages of hydrodesulphurization,

CO, CH,, CO,, H,S and H,O were detected. Only H,S and

H,O remained during the later stages. COS, CS, and SO,

were not detected. Generally, the H,S concentration profile in

the product followed that of H,O. Integration of the H,S area

under the peak (i.e. graph of the partial pressure of H,S

uersus

time,

Figure

2) was used to determine the extent of

desulphurization by H,S.

Hi gh temperat ure sulphur determinat ion

This method is designed specifically for the rapid

determination of sulphur in coal and coke and consists of

burning a sample of coke within a tube furnace at * 1000°C

in a stream of oxygen. Sulphur oxides are absorbed in a

hydrogen peroxide solution, yielding sulphuric acid

(equation 1) which is titrated against standard NaOH to a pH

of 4.5.

SO, + H,O, -+H,SO,

(1)

* Although the composition of the leachate has not been determined, it

is probably a mixture of NaOH, Na,CO, with traces of Na,S.

The method was tested against the Standard Eschka

methodI

and agreement with 4% was obtained. Duplicate

analysis of the desulphurized and leached sample as well as a

single analysis of the starting material, were made for each

experiment.

The percentage desulphurization was

determined by comparing the percentage of sulphur in the

residue with that of the starting sample. Any residual basic

sodium compounds in the coke have been shown to form the

corresponding metal sulphates and these do not decompose

to form SO, during combustion. Unless specifically stated,

high temperature combustion was used for sulphur

determination.

RESULTS

Preliminary experiments

Before investigating the desulphurization of NaOH-

assisted fluid coke in detail, experiments were conducted

to investigate the sulphur removal by volatilization

(calcination to 700°C in flowing nitrogen) and by direct

hydrodesulphurization. Samples impregnated with

NaOH were investigated also under the same conditions

and the results are summarized in

Table 3.

The significant

effect of trace amounts of NaOH on the level of

desulphurization was evident; in particular the effect on

hydrodesulphurization was very pronounced in that,

whereas direct hydrodesulphurization resulted in 30 wt%

sulphur removal, incorporation of x 3 wt% NaOH in the

coke led to 90 wt% sulphur removal under the same

experimental conditions.

Reversibi l i ty of NaOH impregnati on

25 g

of the coke was impregnated with NaOH to a

weight ratio of 0.040 in a Teflon beaker. The reversibility

of the impregnation was examined by serial hot water

extraction of the base from a weighed sample of the

impregnated coke. Determination of the sodium in the

leachate by atomic absorption indicated that S&85% of

the base could be leached out. The remainder was

irreversibly adsorbed, probably within the coke matrix. A

similar experiment carried out on NaOH-impregnated

coke which had been hydrodesulphurized showed that

only x 70 wt% of the base could be recovered.

Loss

of base

could have resulted from chemical reaction with the coke

and with the quartz reactor, which was extensively

corroded.

Sodium balance

0.3 wt% sodium was determined in the desulphurized

and leached coke indicating that

x80

wt’? of the




Desulphurization of petroleum fluid c oke: 2. M. George and L. G. Schneider

I

I

I

1

500 600 700 800 900

Coke tempemture (“C)

Figure3 Effect of coke temperature on desulphurization.

W/R = 0.040 NaOH. Conditions as in Figure 2

I

I I I I

1

I

004

I

I

008 0.12

(N&i-l/coke) mtlo

I

0.16 0.20

Figure 4

Effect of NaOH/coke ratio on desulphurization. Condi-

tions as in F&we 2

impregnated NaOH was removed during the process.

Whereas coke containing higher loadings of NaOH fused

during laboratory combustion, coke containing 0.3 wt%

sodium did not cause problems during laboratory

combustion at 1000°C.

Effect

of

process variables in the hydrodesulphuri zati on of

NaOH impregnated coke

Temperature. Results summarized in Figure 3 for a

weight ratio of 0.040 in the temperature range 55&85o”C

for 2 h show a maximum desulphurization at ~700°C.

The decrease in the extent of sulphur removal at > 700°C

may be associated with the collapse of the coke structure

or loss of NaOH by volatilization. To test this latter

possibility, the NaOH impregnated coke was heated to

and maintained at 700°C in a flow of helium (150 ml

min-‘) for 4 h. The effluent of the reactor, collected in

distilled water and analysed for sodium, indicated

negligible loss of sodium suggesting that the maximum

observed in the desulphurization may be due to factors

other

than

volatilization of NaOH. In these

desulphurization experiments, weight loss amounted to

z 15% of the initial charge of the coke. The sulphur

content of the coke was determined by the high

temperature combustion method.

Weight r ati o.

Coke samples with NaOH weight ratios

of 0.010, 0.020, 0.040, 0.100 and 0.200 were

hydrodesulphurized at 700°C and the results, summarized

in Figure 4, show that as the weight ratio (NaOH) is

increased, desulphurization increases quite rapidly and

reaches a constant level at E 85% at a weight ratio of 0.040.

32% desulphurization at 0 weight ratio refers to direct

hydrodesulphurization.

lime on stream. Data for these experiments presented in

Figure 5 demonstrate that sulphur removal increases with

time up to 2 h and reaches a constant level at ~85%

desulphurization. Consequently, desulphurization

experiments were set for 2 h.

Part i al pressure of hydrogen. Desulphurization was

investigated at different partial pressures of hydrogen at

700°C by keeping the total flow rate constant and diluting

helium with hydrogen. Results shown in Figure 6 indicate

a strong dependence on the partial pressure of hydrogen.

29% desulphurization at zero partial pressure of hydrogen

refers to desulphurization in helium under the same

experimental conditions.

Eflect of Na+, K+ and Li ’ on desulphurizat ion.

A few

experiments indicated that the effectiveness of the

I

I

I I

I

I

80-

1

I I I I

1

0 2 4 6 8

Time on streum (h)

F ure5

Effect of time on hydrodesulphurization

I-

O-

O

‘O-

O-

0

I I I

26.7 53.3 78.0

pH, (kPa)

Fgure 6 Effect of partial pressure of hydrogen




Desulphurizat ion of petroleum fluid co ke: 2. M. George and L. G. Schneider

401

I I

I

I

0.04 006

0.08 0.10

Weight mtlo NaOH

Figure 7 Effect of NaOH/coke ratio on desulphurization via H2.S

(A) and total desulphurization (0). Conditionsas in Figure 2

reagents in hydrodesulphurization (700°C 4 h, a

hydrogen flow of 150 ml min- ‘) decreases in the order

NaOH > LiOH > KOH. With a metal/sulphur molar

ratio of 0.50, the respective desulphurizations were 88%

(MaOH), 61% (LiOH), and 53% (KOH).

Effect of NaOH loadi ng on desulphur izat ion vi a H,S.

Samples of coke were loaded with NaOH in the weight

ratio range 0.02-0.07. Aliquots of these samples were

hydrodesulphurized at 700°C for 2 hat 120 ml min-’ and

the extent of desulphurization via H,S (g.c.) and the

residual sulphur in the desulphurized coke were

determined by the high temperature combustion method.

Data summarized in Figure 7demonstrate that the level of

desulphurization increases up to a

W/R

of 0.04 after which

the total desulphurization as determined by the high

temperature combustion method remains constant, but

the level of desulphurization via H,S decreases. Up to a

weight ratio of 0.04, the extent of desulphurization was

primarily via H,S, as these desulphurized (not leached)

samples failed to show the presence of Na,S by X-ray

diffraction analysis or H,S production on heating the

samples with HCl. However, with samples containing

higher weight ratios of NaOH, significant quantities of

H,S could be detected during leaching of the

desulphurized sample which probably resulted from the

hydrolysis of Na,S:

Na,S + 2H,0+2NaOH + H,S

(2)

X-ray diffraction of this sample confirmed the presence of

Na,S, with d-spacings indicated at 0.380,0.232,0.198 and

0.164 nm.

Surface area

The starting material had a surface area of 11 O+ 2 m*

g

-l, which did not change during heating in nitrogen or

hydrogen.

Impregnation of the coke with NaOH resulted in

significant loss of surface area; this is not surprising as the

pores within the coke granules are probably filled with

adsorbed NaOH. Even after desulphurization at 700°C

where 90 wt% sulphur removal was achieved

Tabl e 3),

the

surface area was negligible. Hot water leaching of this

sample (x4.5 g sample, 500 ml tap water, 80°C overnight)

restored the surface area partially. Hydrodesul-

phurization

of the impregnated sample in wet

hydrogen resulted in 85 wt% sulphur removal, but the

original surface area was retained. These results,

summarized in

Tabl e 3,

suggest that there is no simple

relation between the surface area and the level of

desulphurization.

Diffusional l imi t at ions

Generally desulphurization of coke increases with the

rate of hydrogen flow and then reaches a constant level.

This has been attributed to the presence of a film of

products surrounding the coke granules, and the rate of

desulphurization depends upon the thickness or

concentration of this layer. As the hydrogen flow rate is

increased, the thickness of this layer is decreased, enabling

rapid diffusion of products (H,S) out of the coke granules

thereby increasing the extent of desulphurization.

Desulphurization experiments carried out at 550°C and

700°C at different rates of hydrogen flow, shown in Figure

8, show that, whereas little boundary layer diffusion

control exists at 55o”C, a diffusional barrier is apparent at

700°C where a high level of desulphurization was

attained. Experiments in which the coke particle size was

varied but the NaOH weight ratio maintained at 0.04

indicate that pore diffusion is not significant

Figure

9).

Although not shown in Figure 9, a similar trend

was observed at 700°C with a hydrogen flow rate of

120 ml min- ‘. This is one of the advantages of NaOH-

impregnation of

the

fluid

coke

prior to

hydrodesulphurization. In contrast, direct hydro-

desulphurization of a delayed coke produced by

I

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I

I

I

,L *i

Fgure 8 Effect of hydrogen flow rate on hydrodesulphuristion

at 700°C (0) and 550°C (A)

I I I

1

0.10

030

050

070

0.9

Average coke partlcle diameter mm)

.

Figure9 Effect of coke particle size on hydrodesulphurization.

650°C. 2 h. H2 flow = 40 ml min-t




Desulphurization of petroleum fluid co ke: Z. M. George and L . G. Schneider

Suncor appeared to be controlled by pore diffusion but level of sulphur removal achieved when the coke is

not film diffusion.5s6

impregnated with NaOH.

Scanning electron micrographs

No

significant difference could be detected between the

fluid coke sample as-received and after direct

hydrodesulphurization. However, hydrogenation of the

impregnated samples showed deep cracks and these

persisted during hot-water leaching. It is probably the

combination

of NaOH-impregnation

and high-

temperature hydrogenation that is responsible for these

cracks and these do not appear to have contributed to the

total surface area of the coke

Table 3).

Effect of wet hydrogen on desulphur izat ion

As the partial pressure of H,S closely followed that of

product water, and

wet hydrogen enhanced

desulphurization of oil sands fluid coke,15 the effect of wet

hydrogen on Getty Coke desulphurization was studied.

Constant partial pressure of water in hydrogen was

achieved by bubbling the hydrogen through a water

saturator maintained at constant temperature. Although

a systematic investigation was not undertaken, the

experiments indicated that for this fluid coke, the level of

desulphurization was not affected by water vapour in the

hydrogen.

It is likely that the organic sulphur compounds are

distributed uniformly within the coke granule. Hydrogen

can diffuse in and react with the sulphur compounds to

form H,S; however for H,S to diffuse out appears to be

difficult as the pores appear to be blocked. It is possible

that during impregnation and drying, which may be

considered as an activation process for this reaction, the

(C-S) bonds are weakened and these reactive sulphur

compounds may diffuse towards the surface of the

granules where they react readily with hydrogen to form

H,S. As H,S is now formed on the external surface of the

granules, the rate may be limited by film and not by pore

diffusion as observed,

Figures 8

and 9. The following

tentative mechanism may explain desulphurization of the

coke. It is probable that sulphur compounds in the coke

may be present as organic sulphides of the type

R-S-R,

where R could be an aromatic or aliphatic group:

R-S-R + HO-Na+ ZR-S-Na+ + ROH

(4)

R-S-Na+ + ROHgRONa+ + RSH

(5)

ROH+H RH+H,O

(6)

Effect of Na ,CO,

As Na,CO, can be mixed mechanically with coke,

thereby eliminating the impregnation step, and it is much

simpler to handle than NaOH, experiments were carried

out to determine the efficacy of Na,CO, compared to

NaOH. The results indicated that to achieve 80%

desulphurization, a weight ratio of 0.08 was required for

Na,CO, compared to 0.04 with NaOH.

To learn more about the mechanism of

desulphurization, particularly the role of sulphones, the

NaOH-impregnated coke was heated to 700° in a

stream of helium and the effluent of the reactor was

continuously monitored. SO, was not detected indicating

that for this coke desulphurization may not proceed

through a sulphone intermediate.

R-S-H + H, ZRH + H,S

(7)

R-0-Na+ + H,O ZROH + NaOH

(8)

Is possible that the NaOH generated

in-s i tu

(equation 8)

could aid in enhanced desulphurization.

Although the scanning electron micrograph indicates

cracks on the desulphurized coke granules, surface area

determinations do not support the hypothesis that during

hydrogenation of NaOH-impregnated coke, the pores

are opened up leading to enhanced desulphurization.

Further, as shown in Tabl e 3, no simple relation exists

between the desulphurization and surface area.

Possible explanations for the maximum observed at

x 7OO”C,

Figure 3,

are sintering, depletion of NaOH, and

the formation of stable (C-S) compounds by the reverse

reaction

Appli cati on of thi s method for desulphurizati on of other

fluid cokes

H,S+Cz(C-S)+H,

(9)

Detailed experimentation was not attempted; however,

at an NaOH weight ratio of 0.04 and

hydrodesulphurization at 700°C (5.0 g coke and a

hydrogen flow rate of 120 ml min-I), >80 wt% of the

sulphur was removed from the Imperial Oil and Petrolina

cokes.

The calorific value of the desulphurized Getty coke was

29.08 kJ kg- ‘, slightly lower than the starting sample and

the sulphur content of the product coke was 1.0 fO.l wt%

compared to 7.3 +0.3 wt% in the starting material. The

sulphur content of the product coke is within the limits

allowed by the Environmental Protection Agency of the

USA and would probably meet the specifications of the

Canadian and Alberta Governments.

As surface area does not appear to be related to the level of

desulphurization, and there is very little loss of the reagent

by volatilization, the decrease in desulphurization level at

temperatures > 700°C must be related to the formation of

new stable (C-S) sulphur compounds by the reverse

reaction.

The process described in this Paper is covered by

Canadian patent 1,090,464 granted to Z. M. George.

ACKNOWLEDGEMENTS

Valuable discussions with Prof E. Tollefson of the

University of Calgary are gratefully acknowledged. This

manuscript is ‘Alberta Research Council Contribution

No. 157’.

DISCUSSION

REFERENCES

The significant aspect of NaOH-assisted (catalysed)

hydrodesulphurization of this fluid coke is the very high

1 Meyer, R. A.

Hydrocarbon Process.

June 1975, p. 75

2 El Kaddah. N. and E.z.z. S. Y. Fuel 1973. 52. 128

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sodium hydroxide-assisted desulphurization

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