CA2002828C - Process for producing environmentally improved coke binder - Google Patents

Abstract

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.

Description

200~8Z8 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.

200;~82a 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 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.

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%.

Claims (4)

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.