PROCESS FOR PRODUCING ENVIRONMENTALLY IMPROVED COKE BINDER

PROCEDE DE FABRICATION D'UN LIANT A COKE A NOCIVITE ENVIRONNEMENTALE REDUITE

English Abstract

-1-
A pitch material is obtained which is environmentally
acceptable and which is useful as a coke binder. It is
produced by upgrading a petroleum or bitumen derived pitch
having a boiling point above 524°C obtained as a residue
in the hydrocracking of hydrocarbon oils. The upgrading
consists of heating the petroleum or bitumen derived pitch
in a closed vessel at an elevated pressure and a
temperature of about 350-450°C. The product has a very
low polycyclic aromatic hydrocarbon content as compared
with coal tar pitch.

Claims

-1-
Claims:
1. A process for producing an environmentally acceptable
hydrocarbon pitch suitable for binder applications, which
comprises heat treating a petroleum pitch having a boiling
point above 524°C obtained as a residue in the hydrocracking
of hydrocarbon oils, said heat treatment being carried out in
a closed vessel at a pressure of at least 1.72 MPa and a
temperature in the range of 350-450°C, whereby aliphatic side
chains and other non-aromatic components are cracked, but
without the formation of mesophase.
2. A process according to claim 1 wherein the petroleum
pitch is obtained from the hydrocracking of regular crude
oils.
3. A process according to claim 1 wherein the petroleum
pitch is obtained from the hydrocracking of heavy hydrocarbon
oils.
4. A process according to claim 1 wherein the petroleum
pitch is obtained from the hydrocracking of heavy bituminous
oils extracted from tar sands.

Description

200~8Z8
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Process for Producing Environmentally Improved Coke Binder
Background of the Invention
This invention relates to petroleum pitch obtained as
a residue in the hydrocracking of hydrocarbon oils, and
particularly to such pitch material in which environ-
mentally harmful materials are present only in insigni-
ficant trace amounts.
Coal tar pitch is used extensively as a binder for
production of carbon artifacts such as electrodes,
crucibles, blocks and other graphitic materials. Such
coal-based pitch, however, contains high concentrations of
various polycyclic aromatic hydrocarbons (PAH) which are
known to be highly carcinogenic. In order to meet health
and safety standards, an alternative to coal tar pitch is
required. Petroleum based pitches are known to contain
much smaller concentrations of polycyclic aromatic
hydrocarbons than coal tar pitch, typically 1-2 weight
percent of that in coal tar. In order to make a good
binder, the pitch must meet certain specifications
including a high aromatic content. This is usually
measured by the carbon/hydrogen atomic ratio ~C/H).
Petroleum pitches usually possess a C/H of about 0.65 to
0.75 which increases to about 0.8 to 0.9 after passing
through an upgrading process. Typical coal-based pitch
binders possess a C/H of up to 1.8. Moreover, certain
applications, such as the production of electrodes,
requires an upper limit on the softening point of pitch.
Thus, in order to produce pitch suitable for binder
applications, a method is required which can increase the
aromaticity of the petroleum pitch while keeping the
softening temperature within specifications.
All heavy oil and bitumen upgrading plants generate
considerable quantities of residue pitch which has not
normally been converted to distillate products. Economic
and environmentally accepted ways of disposing of this
pitch are highly desirable.

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Summary of the Invention
According to the present invention, it has been
discovered that a hydrocarbon pitch obtained as a residue
in the hydrocracking of petroleum crude can be subjected
to a thermal cracking process within a defined temperature
range and elevated pressure such that an environmentally
acceptable pitch is produced.
The pitches that are used in the present invention are
residues of hydrocracking which usually boil above 524~C
and they ma~ come from the hydrocracking of regular crude
oils or from the hydrocracking of heavy hydrocarbon oils,
including heavy bituminous oils extracted from tar sands.
While the pitches which can be used may be derived from
processes providing a wide range of pitch conversion, they
are usually derived from processes having a pitch
conversion of at least 403 such as that described in
Canadian Patent No. 1,151,579 issued August 9, 1983.
Petroleum pitches which meet other binder specifica-
tions are, according to the present invention, treated in
a closed vessel at temperatures in the range of 350-450~C
for various periods of time determined by the pitch
properties and desired specifications of the treated
product. Typical treatment times are in the order of 1 to
2 hours. During the heat treatment, the system is
preferably maintained at an elevated pressure, e.g. a
pressure of at least 1.72 MPa (250 psi). Thç pressure can
be varied depending on the feedstock and the desired pitch
properties. The process can be operated in a batch or
continuous mode and the product is an upgraded pitch
suitable for binder applications.
The heat treatment according to the present invention
tends to crack aliphatic side chains and other non-aromatic
components but does not proceed as far as production of
mesophase. The pressure maintains a certain concentration
of lighter fractions and solution in the pitch which helps
to effectively control undesirable reactions, such as

20028~8
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coking. By suitable adjustment of process conditions and
reactor configuration, the softening point can be adjusted
for a given C/H ratio in order to meet the desired
specifications. This can be achieved by releasing set
amounts of cracking volatile components, mostly light
alkanes and olefins, from the reactor during heat
treatment.
Descziption of the Preferred Embodiments
Certain preferred features of the present invention
will be better understood from consideration of the
experimental data in the following examples.
Example 1
A pitch residue was obtained from a process of
hydrocracking heavy hydrocarbon oils using a process of
the type described in Ranganathan et al U.S. Patent
4,435,280 issued March 6, 1984. It was obtained from the
CANMET reactor at the Petro Canada refinery in Montreal.
The pitch obtained had the following composition:
Carbon, wt% 87.4
~ydrogen, wt~ 8.2
Sulphur, wt% 2.5
Nitrogen, wt% 0.96
Toluene insol. wt% 7.09
Ash, wt% 0.1
C/H 0.90
253 g of the above pitch residue was loaded into a
1 liter stirred autoclave, heated up to a temperature of
420 ~C over a period of 2 hours and held at this tempera-
ture for 1.5 hours. The pressure was monitored ana when
it had reached 1.72 MPa (250 psi) the gases were released
to maintain a pressure of 1.72 0.07 MPa. The
autoclave was then cooled and the pitch removed. The C/H
atomic ratio had increased to 1.12 and the softening point
was 121~C.

;~0028Z8
The product obtained was analyzed for content of
polycyclic aromatic hydrocarbon and the results obtained
are shown in Table 1 below, together a polycyclic aromatic
hydrocarbon analysis for a typical coal tar pitch, all
amounts being in mg/kg.
Table 1
Thermally Cracked Coal Tar Pitch
Petroleum Pitch
Fluoranthene 18 13800
Pyrene 74 12600
Benzo(b)naphtho(2,1-d)-
thiophene 117 960
Benzo(ghi)fluoranthene
+ BcPh 23 1100
15 Cyclopenta(cd)pyrene 5 270
Benz(a)anthracene 99 8300
Chrysene + Triphenylene 90 8700
Benzofluoranthene (b+j+k)138 18800
Benzo(e)pyrene 163 9090
Benzo(a)pyrene 197 14600
Indeno(1,2,3-cd)pyrene 84 10000
Dibenz(a,h)anthracene 56 1840
Benzo(ghi)perylene 645 10500
Anthanthrene 78 6400
Coronene 560 2620
It can be seen that the product of this invention
contains very small concentrations of the undesirable
polynuclear hydrocarbons as compared with the coal tar pitch.

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Example 2
The procedure of Example 1 was repeated with the
hydrocracking in the autoclave being conducted at 425~C for
2 hours. This produced volatile gases during the final
S stages of thermal cracking having the following composition
(Vol.%):
C-5 unsaturated 3.6
Propane 6.8
Butane 5.1
Iso-butane 1.5
n-Pentane 4.0
Hydrogen 9.4
Ethane 15.1
Methane 36.5
lS Hydrogen sulphide 3.1
The gas analysis shows the elimination of only aliphatic
components from the feedstock causing the C/H ratio to
increase from 0.84 to 1.06. A solid state C nmr
confirms that the aromaticity increases from 60% in the
original pitch to 80~ in the cracked pitch. There is, at
the same time, only a marginal increase in the carcinogenic
PAH content which remains very low.
Example 3
Green anodes were prepared by mixing calcined petroleum
pitch with (1) coal tar pitch, ~2) residue from the
hydrocracking of heavy hydrocarbon oils and (3) residue from
the hydrocracking of heavy hydrocarbon oils which has been
further subjected to heat treatment at 110~C under
pressure. These anodes were tested for weight loss after
heating at ~20~C for 24 hours followed by heating at 450~C
for 1 hour. The results obtained were as follows:
Weight Loss (%)
Calcined Coke + CANMET resid original 17.1
Calcined Coke + CANMET thermally cracked resid 12.7
Calcined Coke + Coal tar pitch 7.5
The weight loss of the anodes made with the thermally
cracked pitch has been reduced to 12.7% from 17.1%.