DE1146475B - Process for the desulphurization of petroleum coke using hot hydrogen-containing gases - Google Patents

Description

Process for the desulfurization of petroleum coke using hot hydrogen-containing Gases The invention relates to a method for the desulfurization of fluidized coke shaped bodies, in the case of the moldings at elevated temperatures and at least normal pressure treated with a hydrogen-containing gas.

Recently, an improved process known as the fluidized bed coking process has been used for the production of fluidized coke and the thermal conversion of heavy hydrocarbon oils developed into lighter fractions.

One factor making the sale of fluidized coke difficult is the small size of the coke particles, which are predominantly, i. H. about 60 to 90 percent by weight of the coke, between 60 and 1000 meshes per square centimeter having sieves. The production of much larger particles is not compatible with satisfactory operation of the fluidized bed. On the other hand, the industry requires coke particles with a diameter of at least about 3 to 25 mm.

Another problem is the high sulfur content of the fluidized coke particles. The fluidized bed coking process is best used to improve the quality of low-value residues formed during the vacuum distillation of petroleum and pitches from asphalt-containing and acidic crude oils. These residues often have a high sulfur content, d. H. of 3 weight percent or more, and the coke products obtained from these high sulfur feeds are also high in sulfur. In general, the coke product obtained from fluidized bed coking contains about twice as much sulfur as the residue feed from which it is obtained. The sulfur content of the coke obtainable from acid residues can be 5 to 8% or more.

The high sulfur content of the coke product is a major problem for its effective use. In many cases where the coke is not used as a fuel or make-up fuel, a low sulfur content of the coke of about 3 weight percent or less is required. Thus, coke with a low sulfur content z. B. in the production of phosphorus, in the production of calcium carbide, for burning lime in the production of soda ash or other alkalis, in various metallurgical processes and in the production of carbon electrodes for various electrochemical purposes, such as. B. the production of aluminum and the like., Is required. The problem of insufficient particle size of the fluidized coke is overcome by compressing the particles. The compacts made from fluidized coke in the required size can be in the form of pellets, extruded pieces, briquettes, and other shapes. All compacts have in common the use of an adhesive, carbonaceous substance as a binding agent.

The tacky carbonaceous substances that can be used include suitable hydrocarbon binders such as e.g. B. asphalt and petroleum residues, aromatic tars, e.g. B. high-temperature tars reduced under vacuum, tars obtained by hot blowing, heavy # residues of coal tar, such as. B. coal tar pitch with a lowest softening point of about 37'C, as well as heavy residues from the coking process, d. H. Material boiling above 565 ° C.

These materials are used in an amount of about 5 to 40 percent by weight, preferably 10 to 30 percent by weight, based on the coke charge. The fluidized coke can be used in the usual particle sizes, although it is preferred to crush a portion of the coke particles.

In general, pellets are made by crushing the fluidized coke so that it passes through a sieve of 1,550 meshes per square centimeter. The binding oil, which must have a correspondingly high softening point, is also comminuted in such a way that it passes through a sieve of 1550 meshes per square centimeter. About 50 parts of uncomminuted coke, 50 parts of a crushed coke and 10 to 20 parts of a crushed binding oil are mixed thoroughly and moistened with 15 to 25 parts of water. The mixture is placed in a rotating drum in which it is shaped into spheres approximately 6.3 to 19 mm in diameter. The coke spheres or pellets are carefully dried at about 105 to 120 ° C and hardened by firing at about 480 ° C or higher temperatures.

The briquettes are produced by mixing the fluidized coke, as it is obtained or partially comminuted, at a temperature of about 95 to 150.degree. C. with about 10 to 20% of an adhesive, carbonaceous substance. The hot mixture is briquetted in a hydraulic press at a pressure of about 350 to 1260 atm, and the shaped bodies are allowed to cool in air.

These form bodies have to decompose the binder as well as to Achieving sufficient strength and cohesion Temperatures above 480'C are cured. To avoid impermissible oxidation the firing is preferably carried out in the absence of air.

The most common methods of removing sulfur from coke Ordinary origin by means of gaseous reagents were generally not very satisfying. If the processes are applied to fluidized coke, they are Results compared to coke produced with "delayed coking" still worse. A treatment gas comes in proportion to the "delayed coke" difficult to get to the sulfur contained in the fluidized coke, since fluidized coke is laminar Structure is made up of about thirty to one hundred layers of coke one on top of the other can exist. It is therefore difficult for a reagent, e.g. B. a treatment gas, further than penetrating into some outer layers. This with the treatment of the eddy coke The difficulties associated with the above may be increased than the normal sulfur content of the high sulfur oil feed Coke obtained increased even further.

The adhesive, carbonaceous ones used as binders Substances can also contain considerable sulfur, e.g. B. 3%, thereby reducing the sulfur content in the finished molded articles even further is made more difficult.

The invention provides a method of thermosetting and desulfurization consisting of fluidized coke and an adhesive carbonaceous material Moldings. The procedure consists in making the mold bodies at elevated temperatures and at least normal pressure is brought into contact with a hydrogen-containing gas.

The fact that the shape body according to the inventive method can be desulfurized is surprising considering that the Problem of coke desulphurization through the use of a sulfur-containing binder has been made more difficult. For this reason it is particularly surprising that the with the results achieved with the method according to the invention with regard to the reduction the sulfur content in the moldings is at least as good and usually even better are considered to be the results obtained by looking at the fluidized coke treated similar procedures alone.

The hydrogen treatment is carried out at a temperature of 650 to 870.degree. C., preferably 705 to 815.degree. The treatment time is about 1 to 10 hours, preferably 2 to 3 hours. The amount of hydrogen used is about 100 to 5000 V / V coke moldings per hour, the partial pressure of the hydrogen in the treatment gas in a process carried out under normal pressure is about 550 to 7000 mm of mercury, while the residual pressure is inert gases, such as. B. nitrogen, methane, etc., is omitted. The partial pressure of the hydrogen is correspondingly higher at elevated pressures, which can be up to 14 atmospheres and more.

The hydrogen-containing gas can be obtained from the gas generated in the coker after removing most of the hydrocarbons formed in the coking process be won. Other sources are pure hydrogen or that in a hydroforming plant formed exhaust gas. The hydrogen-containing gas is preferably used before it is used Treated in the usual way to make hydrogen sulphide and other sulphurous Remove connections.

The moldings can be placed in a moving layer in a vertical shaft furnace be heated. However, other treatment methods can also be used. The risk of deformation after initial heating to a temperature of about 480 ° C, at which the binding oil cokes, does not exist. The initial heating can be made in a flat layer over a grate or by placing in an out hot fluidized coke existing layer can be carried out.

It is particularly preferred to treat the fluidized coke particles prior to shaping for subsequent hydrogen desulfurization either at 315 to 540 ° C with an oxygen-containing gas or at 650 to 980 ° C with steam.

The pretreatment with the oxygen-containing gas is carried out at temperatures of 315 to 54-0'C, preferably 345 to 455'C. This oxidative treatment at low temperatures is preferably carried out with coke particles in the form of a dense fluidized bed. While it is possible to achieve the desired result of the oxidation at low temperatures by treating a resting bed or a moving layer of coke with an oxygen-containing gas, with this type of process the temperature control is caused by the problem of heat dissipation from the solid coke layer (except for very small plants ) extremely difficult. In contrast to this, the oxidation temperature in a fluidized bed can be very easily regulated when coke is oxidized by treatment with an oxygen-containing gas. The temperature can be controlled by means of a snake body inserted into the fluidized bed. The oxygen-containing gas can be air or air enriched with oxygen at normal pressure or overpressure. The time of the oxygen treatment can vary largely between 15 minutes and 50 hours, depending on the temperature, oxygen concentration and pressure. If the pre-oxidation is carried out at higher temperatures within the suggested range, between about 425 and 540 ° C, it is preferred to use low-oxygen air, e.g. B. with nitrogen, exhaust gas and the like. Diluted air is used. Air enriched with oxygen can be used in the lower temperature ranges. If desired, some of the gases withdrawn during the oxidation can be returned to the oxidation zone. The best control means for these areas is to reduce the yield of the oxidized coke. The conditions are set so that the maximum loss of yield is 20 percent by weight, preferably 10 percent by weight, or, conversely, a minimum yield of 80 percent, preferably 90 percent by weight, is achieved. The oxidation carried out at low temperatures is a reaction which cannot be influenced catalytically and in which the use of a catalyst is not necessary.

The treatment with steam is carried out at a temperature of 650 to 980.degree. C., preferably 760 to 870.degree . The treatment time, which depends on the temperature, is between 1 and 10, preferably between 2 and 3 hours. The steam treatment is usually carried out at normal pressure, although pressures from 0.5 to 3 atmospheres can be used. The extent of the steam treatment depends on the temperature and is determined by the amount of coke removed. The - amount of removed coke can be up to 60 percent by weight, but is preferably less than. 40 percent by weight based on the original charge. Removal of 15 to 35 weight percent coke is often sufficient. Fluidized bed treatment is generally preferred, but other types of treatment can be used.

The extent of the desulfurization of the formal bodies depends primarily on the temperature, the time and the pressure prevailing during the treatment such as also of those used in the previous oxidation or steam treatment Conditions.

The shaped bodies subjected to the treatment according to the invention can also be fired in the customary manner, provided that a further increase in density and a further reduction in the content of volatile constituents, the specific resistance and the sulfur content is desired. The firing is usually carried out at temperatures above 1 100'C in the presence of nitrogen, steam or a limited amount of air.

The advantages of this invention are further illustrated by the following examples. Example 1 Fluidized coke particles containing 7% sulfur were heated to 128 ° C. and mixed with a binding agent consisting of pitch, also heated to 128 ° C. The quantitative ratio of coke to binder was 9: 1. The pitch binder used in this experiment was obtained from an aromatic tar (tar from the steam cracking of gas oil) by hot blowing for 5 hours at 260.degree. C. with a yield of about 72 percent by weight . The coke and the binding agent consisting of pitch were mixed hot and then pressed at a pressure of 1050 atm to give briquettes about 25 mm in diameter and 25 mm in length. The press temperature is not critical but will depend on the available pressure and the requirements of the press. The somewhat fragile briquettes were heated to 540 to 650 ° C. for about 30 minutes under a layer of coke in order to decompose the binder and harden the briquettes. The briquettes obtained were dense, tough and hard. They were then treated with H2 for 4 hours at normal pressure, 760.degree. C. and a gas velocity of 0.034 m / s. The sulfur content was reduced to 3.63 percent by weight, while that of fluidized coke, which was desulfurized in the same manner, was reduced to only about 5.1 percent by weight. This shows that the process according to the invention achieves a substantial reduction in the sulfur content, even at normal pressure without any pretreatment, which is greater than that achieved with the treatment of fluidized coke particles alone. A more complete desulfurization can be achieved through an even more intensive treatment or through the aforementioned pretreatments. Example 2 Fluidized coke, which had been pre-oxidized at 345'C, was mixed with a pitch which had been produced from an aromatic tar, as described in Example 1 , by hot-blowing in the ratio of 9 parts of coke to 1 part of pitch at 11 5 ' C thoroughly mixed until a uniform mass was formed, and then briquetted in a laboratory press at a pressure of 1050 atm. The briquettes were hardened for 90 minutes under a layer of fluidized coke at 650.degree. The 25-25 mm large cylindrical briquettes were hard, dense and resistant. They were desulphurized by hydrogen treatment at 760 ° C. and normal pressure and the results were compared with those of a similar experiment in which the coke had not been briquetted. The following data were obtained: Coke form Briquettes 1 fluidized coke Heating-up time, hours ......... 0.7 0.7 Duration of treatment at high temperature, hours 4 4 Temperature, 'C ............ 760 760 Hydrogen velocity, m / s ..................... 0.037 0.12 Coke yield, Weight percent .......... 91.4 82.9 Sulfur content of the feed coke, Weight percent .......... 6.7 6.7 Sulfur content of the product, Weight percent .......... 2.8 2.7 This example shows that the same great reduction in the sulfur content was achieved in the compacts as in the fluidized coke particles. However, the same result was obtained in the first case with a higher coke yield and a far lower amount of hydrotreating gas. Example 3 A fluidized coke obtained from Hawkins residues and containing 7% sulfur was mixed at about 150 ° C. with the circulating residues of a coking plant in a ratio of 9 percent by weight coke to 1 percent by weight residue. After thorough mixing, the product was allowed to cool to room temperature, then it was at room temperature with 1225 at 25 - pressed 25 mm briquettes. In order to decompose the binder, the formal bodies were heated to 650.degree. C. in a nitrogen atmosphere under a coke oven for 2 hours. The briquettes obtained were dense, tough and hard. The briquettes were desulfurized by hydrogen treatment in a static layer process at normal pressure. The results are shown in comparison with those of the test of Example 1, in which the non-briquetted coke was treated with hydrogen in a fluidized bed: Coke form Briquettes swirl coke Heating time, hours ......... 0.25 0.8 Duration of treatment at high temperature, hours 4 4 Temperature, 'C ............ 760 760 Hydrogen velocity, m / s ..................... 0.15 0.12 Coke yield, Weight percent .......... 90 92 Sulfur content of the product, Weight percent .......... 2.9 5.1 As in the previous examples, the advantage in the desulphurization of briquettes compared to the desulphurization of small coke particles which have been treated in a fluidized bed is also shown here. Example 4 The same briquettes as in Example 3 were treated with hydrogen in the same way but for 6 hours. The sulfur content of the briquettes was further reduced to 1.9%. Example 5 Coke made from Hawkins residues which had been oxidized in about 93% yield at 345 ° C. was mixed at about 150 ° C. with circulating residues from a fluidized bed coking plant in a ratio of 9: 1 . The mixture was stirred at 120 to 150'C and at a pressure of about 1225 at about 25 - 25 mm pressed briquettes. The moldings were dense, tough and hard. The briquettes were treated with hydrogen at normal pressure in a static shift. The results, compared to the data from Example 2, relating to non-briquetted coke treated with hydrogen in a fluidized bed, are as follows: Coke form Briquettes swirl coke Heating-up time, hours ......... 0.25 0.7 Duration of treatment at high temperature, hours 4 4 Temperature, 'C ............ 760 760 Hydrogen rate. m / s ..................... 0.15 0.12 Coke yield, Weight percent .......... 86 82.9 Sulfur content in the feed coke, Weight percent .......... 6.5 6.7 Sulfur content in the product coke, weight percent .... 1.5 2.7 At a comparable gas velocity, hydrogen treatment of the briquettes consisting of oxidized coke achieved better desulphurization than the coke particles not pressed in a fluidized bed. Example 2 showed equally good desulfurization at a much lower gas velocity. Example 6 Pellets with a diameter of 12.5 nm were prepared by comminuting half of a coke obtained from Hawkins residues, the particles of which could fall through sieves with 190 to 1550 meshes per square centimeter, to the size of the sieve containing 1550 meshes per square centimeter so that a mat 'erial was obtained with a particle size distribution corresponding to seven 190-16400 stitches per square centimeter. This material was mixed with an oxidized asphalt melting between 82 and 93 ° C, which had been comminuted by grinding while cooling with dry ice. The threaded 'chtsverhältnis of coke to asphalt was 9: 1. The mixture was moistened with about 25 weight percent water and molded in a rotary drum to beads. The spheres were dried under a layer of coke at about HO'C and then fired in a nitrogen atmosphere under a layer of coke for 2 hours at 650 ° C. The dried and fired pellets were hard and firm. Some of these pellets were treated with hydrogen in a resting layer at normal pressure. In comparison with those of the experiment of Example 1, in which the non-pressed coke was treated with hydrogen in a fluidized bed, the results are shown as follows: Coke form 12.5mm # vortex coke Kügellfl, Heating time, hours ......... 0.25 0.8 Duration of treatment at high temperature, hours 4 4 Temperature, 'C ............ 760 760 Hydrogen velocity, m / s ..................... 0.15 0.12 (Continuation) Coke mold 12.5mm Globules of fluidized coke Coke yield, Weight percent ........... 82 92.2 Sulfur content in the loading, Weight percent .......... 7 7 Sulfur content in the product, Weight percent .......... 1, 4 5.1 The desulfurization of the pellets consisting of untreated coke is far greater than that of the fluidized coke particles. In fact, these untreated coke pellets reacted as well as some of the oxidized coke shaped bodies, which, as the previous examples show, are much more amenable to desulfurization by treatment with hydrogen than the oxidized or untreated coke particles Fluidized bed. Example 7 Pellets with a diameter of about 12.5 mm were produced in a manner similar to Example 6, but with a different binder. A mixture, the same parts of a coke obtained from Hawkins residues, the particles of which could fall through sieves with 190 to 1550 meshes per square centimeter, and another part of this coke, the particle size corresponding to a sieve with 1550 meshes per square centimeter and still contained smaller size was comminuted, was mixed at room temperature with pulverized coking residues which had been distilled at 565 ° C. to remove the gas oil. The weight ratio of coke to binder was 9: 1. The binder was solid at room temperature and was satisfactorily comminuted without further cooling. The entire mixture was wetted with about 25% water and formed into spheres in a rotating drum. The spheres obtained, which were solid and hard, were treated with hydrogen for 6 hours at normal pressure, a temperature of about 760.degree. C. and a gas velocity of about 0.075 m / s. At this relatively low gas velocity, the sulfur content of the product was 1.401o, a result which agrees perfectly with the results obtained in Example 6 , in which a slightly higher gas velocity was used with a shorter treatment time. The results obtained in Examples 6, 7 and 8 show significant desulfurization of the beaded, untreated coke.

Claims (1)

PATENT claims process for the desulfurization of petroleum coke by means of hot hydrogen-containing gases, characterized in that molded bodies are produced from petroleum coke obtained by fluidized bed coking with a carbon-containing binder, which after hardening at temperatures above 480'C with the hydrogen-containing gas at temperatures from 650 to 870'C and a duration of 1 to 10 hours. Considered publications: German Patent Specifications No. 900 326, 531965; USA. Patent No. 1 941,462th; "Chemisches Zentralblatt", 1953, p. 8257, Referat W. C. Schafer.