EP0082536A2 - Process for the continuous pressure-hydrogenation of coal - Google Patents

Abstract

1. Process for the continuous hydrogenation of coal, in which finely ground coal suspended in coal oil is hydrogenated in the presence of a conventional coal hydrogenating catalyst at elevated temperature and elevated pressure in a tubular reactor having a ratio of length to diameter of more than 200 with the introduction of hydrogen at several points along the tubular reactor, the heat of reaction being transferred to an external cooling medium via the wall of the reactor or removed by the introduction of cold oil at several points of the reactor, the mixture leaving the reactor is separated into a liquid fraction and a gas fraction in a hot separator and the product fractions are worked up, characterised by the combination of the following features : a) the grain size of the coal put into the process is maximally 500 mu m, b) the hydrogen is introduced in such a quantity at 2 to 6 points along the reactor that at least 80% by weight of the quantity of hydrogen introduced is dissolved in the suspension under the hydrogenation conditions, c) a tubular reactor with a ratio of length to diameter of 1100 : 1 to 10000 : 1 is used and d) hydrogenation is carried out at a temperature of 480 to 530 degrees C and a pressure of from 700 to 1500 bar.

Description

The invention relates to a process for the continuous pressure hydrogenation of coal in a tubular reactor, wherein coal with a grain size of at most 500 pm, mixed with coal oil and conventional coal hydrogenation catalysts to form a suspension and reacted with hydrogen and the mixture emerging from the reactor is separated into a liquid fraction and a gas fraction in a hot separator and these product fractions are worked up.

The hydrogenation of coal and the further processing of the hydrogenation products into fuels is generally known. (Compare: W. Krönig: "The catalytic pressure hydrogenation of coal, tars and mineral oils" (1950) Springer-Verlag, Berlin). In general, a coal suspension with or without a catalyst is hydrogenated in standing reactors at pressures of 200 to 400 bar, in exceptional cases up to 700 bar. To settle coal particles as well as a To ensure adequate mixing of the relatively viscous coal suspension with the hydrogenation hydrogen, it is necessary to run the reactors with larger amounts of cycle gas. In addition, cold gas must be fed in to remove the heat of reaction. In order to achieve complete coal conversion, it is necessary to connect several reactors in a cascade. The residence time is relatively long and is generally more than 30 minutes. The large amounts of circulating gas represent a significant expenditure of compression energy and investments. The usable volume of the reactors is severely impaired by the large amounts of circulating gas which must be made available for each individual reactor in the cascade, which reduces the otherwise possible space / time Yield results.

Tube reactors for coal hydrogenation are also mentioned in the literature (compare FR-PS 817 488; JP Kokai Tokkyo Koho 79.106 506).

FR-PS 817 488 does not give any more precise information about the conditions under which the reaction should be carried out in a tubular reactor. According to the Japanese patent publication, a tube reactor must be used which has vertically ascending and descending tube segments, the ascending tube segments having a larger diameter than the descending ones. With the pressures used, the gases are predominantly in the gas phase, so that. it is necessary to gasab at the upper pipe bends to provide separators. The actual reactor is surrounded by a second tube, and hydrogen gas and possibly carbon oil or coal suspension are passed through the intermediate space, which can penetrate into the actual reaction tube through numerous holes in the inner tube. For this reason, the temperature profile of the reactor cannot be controlled in narrow ranges which are desired per se. The heat of reaction cannot be removed via the reactor wall, which is why, according to the examples, hydrogenation can only be carried out at relatively low temperatures of 430 to 460 ° C., it still being absolutely necessary to feed cold coal oil or cold coal suspension into the reaction mass. However, it is desirable to use higher temperatures, since the reaction rate increases considerably with increasing temperature.

The present invention is ⁱ the object to perform the pressure hydrogenation of coal in a tubular reactor under conditions such that the reaction time or residence time is as short as possible, the conditions in the reaction mixture in a simple manner and can be reliably monitored or controlled, and the highest possible oil gain is achieved. It has been found that this object can be achieved in a technically relatively simple and easily reproducible manner by using the combination of the measures mentioned below.

• a) die Hydrierung bei einer Temperatur im Bereich von 465 bis 530 °C durchführt,
• b) bei einem Druck von mehr als 700 bar arbeitet,
• c) Wasserstoff an mehreren Stellen längs des Rohrreaktors in einer solchen Menge einführt, daß unter Hydrierbedingungen mindestens 70 Gew.% der eingeführten Wasserstoffmenge in der Suspension gelöst sind,
• d) einen Rohrreaktor mit einem Verhältnis Länge zu Durchmesser von 800 : 1 bis 20.000 : 1 verwendet und
• e) die Reaktionswärme über die Reaktorwand an ein äußeres Kühlmedium abführt.

The invention accordingly relates to a process for the continuous pressure hydrogenation of coal in a tubular reactor, wherein coal with a grain size of a maximum of 500 pm, mixed with coal oil and conventional carbohydrate catalysts to form a suspension, reacted with hydrogen, the mixture emerging from the reactor is separated into a liquid fraction and a gas fraction in a hot separator, and these product fractions are worked up, which is characterized by this , that he

• a) the hydrogenation is carried out at a temperature in the range from 465 to 530 ° C.,
• b) works at a pressure of more than 700 bar,
• c) introducing hydrogen in several places along the tube reactor in such an amount that at least 70% by weight of the amount of hydrogen introduced is dissolved in the suspension under hydrogenation conditions,
• d) a tubular reactor with a length to diameter ratio of 800: 1 to 20,000: 1 is used and
• e) dissipates the heat of reaction via the reactor wall to an external cooling medium.

The process according to the invention makes it possible to hydrogenate coal of the most varied degrees of carburization, from lignite to high-carbon coal. The latter cannot be hydrogenated by the known processes.

The coal is finely ground wet or dry under inert gas, the degree of granulation being determined, on the one hand, by the comminution energy to be used and, on the other hand, by the greater reactivity of the smallest possible particles. In view of the greater reactivity, a grain size of at most 300 pm, in particular at most 100 pm, is preferred. Conventional carbohydrate catalysts, generally iron-based, are added to the ground coal and this mixture is processed with coal oil into a pumpable suspension. According to the prior art, medium and heavy oil obtained from the hydrogenation process are used as coal oil. However, the at least partial use of other oils is also conceivable. The ratio of solid to liquid is determined by the fact that the mixture must be pumpable under the given conditions. The highest possible coal content is desirable. A coal content of 35 to 60% by weight, based on the mixture of coal and oil, is expedient, as in the prior art.

The catalysts used in this field according to the prior art are used as catalysts (see Ullmanns Encyklopadie der Technische Chemie, Third Edition, (1958) Volume 10, pages 498 to 500).

The suspension is brought to reaction pressure with suitable pumps at temperatures between 50 and 150 ° C. and heated to the reaction temperature in the preheater. According to the method of the invention, the preheater can be a tube of the same or similar diameter as is used for the hydrogenation. The suspension is heated in a manner known per se.

According to a preferred embodiment, which is particularly advantageous in the hydrogenation of hard coal, the suspension can be preheated to 300 to 400 ° C. at a pressure of at most 25 bar, preferably at most 20 bar compress to hydrogenation pressure and then bring to the actual hydrogenation temperature. The hydrogenation pressure and hydrogenation temperature are understood to mean the ranges mentioned above. Since the suspension of hard coal in oil has a maximum viscosity at approx. 300 ° C, this procedure has the advantage that the suspension can be preheated to temperatures above the maximum viscosity under low pressure in large-volume containers, which leads to the risk of blockage of the otherwise used Small cross-section preheater tubes can be avoided.

An essential feature of the process of the invention is that the hydrogen is introduced at several points along the tubular reactor in such an amount that under hydrogenation conditions at least 70% by weight, preferably at least 80% by weight, and particularly preferably at least 90% by weight are dissolved in the suspension. In principle, it is desirable to dissolve as much hydrogen as possible in the suspension, ie as much as possible of the total hydrogen fed in. At the start of the hydrogenation reaction, as much hydrogen as possible is fed in, but the conditions defined above must be met. Hydrogen is consumed during the hydrogenation reaction. At several points along the tube reactor, hydrogen is replenished according to consumption, but the amount fed in may only be so large that the conditions mentioned above remain fulfilled. The higher the hydrogenation pressure, the more hydrogen can be fed in at the beginning of the hydrogenation reaction and also along the tubular reactor. So it is at high hydrogenation pressures fewer make-up points for the hydrogen are necessary and practical than at low pressures. At pressures in the range of more than 700 bar and up to approximately 1200 bar, approximately 10, preferably a maximum of 8, and particularly preferably a maximum of 6, feed points are sufficient. At higher pressures, fewer feed points can be provided accordingly. B. at pressures in the range of approximately 1,500 _bar ar a maximum of 4 or even a maximum of 2 feed points are sufficient.

As already stated above, the hydrogenation is carried out at a pressure of more than 700 bar. The upper limit for the pressure is determined by the resilience of the material of the tubular reactor and the accessories as well as by the economy (compression costs etc.). It is therefore usually around a maximum of 1,600 bar. The hydrogenation pressure is preferably above 750 bar, particularly preferably above 800 bar and in particular above 900 bar. The upper limit is preferably 1,500 bar.

The temperature in the method according to the invention, as mentioned above, is in the range from 465 to 530 ° C. and thus considerably higher than in comparable methods of the prior art. It is preferred to work at higher temperatures, even if hydrogenation is carried out at higher pressures, since the selectivity of the hydrogenation at high temperature is only steered in the desired direction, ie in the direction of high oil and gasoline selectivity, by using high pressures. The hydrogenation is preferably carried out at a temperature of above 480 ° C., particularly preferably above 490 ° C. The upper temperature limit depends on the strength of the Material. It is therefore preferably around 530 ° C., particularly preferably around 510 ° C. The use of high pressures is particularly advantageous because the reaction rate and thus the space / time yield increases considerably with increasing reaction temperature.

The process according to the invention is carried out in a tubular reactor with a length to diameter ratio of 800: 1 to 20,000: 1. The lower limit for this ratio is expediently about 1,000: 1 and preferably about 1,100: 1. The upper limit is expediently 15,000: 1 and particularly preferably 10,000: 1. The advantage of such a tubular reactor is u. a. in the large ratio of the area of the reactor wall to the reactor volume, which ensures particularly favorable heat dissipation. In addition, there is the possibility of adapting the production capacity to the respective requirements by changing the pump output and the total reactor length. The absolute dimensions of the reactor naturally depend on the desired throughput and the load capacity of the material.

The hydrogenation reaction is highly exothermic. In order to remove the heat, large amounts of cold cycle gas must therefore be introduced into the reactor in the prior art processes. In conventional autoclave reactors, practically no heat can be dissipated through the reactor wall. In contrast, the tubular reactor used according to the invention offers the advantage of a large ratio of wall area to reactor content. In general, it is therefore possible to transfer the total heat of reaction through the reactor wall dissipate to an external cooling medium and, if necessary, recover it. In addition, it is possible to feed coal oil, which has a temperature which is below the hydrogenation temperature, at one or more points along the tube reactor. In this way, a reaction temperature that is particularly uniform over the entire reactor volume can be controlled in a very simple manner. A temperature gradient between the reactor wall and the center of the reactor, as is observed in the conventional autoclave reactors, does not occur. A uniform reaction temperature requires a higher selectivity. At the same maximum temperature, the average temperature along the tube reactor is higher than in the autoclave. This leads to a higher hydrogenation rate and a greater oil recovery.

The process according to the invention enables the hydrogenation to be carried out in a very short time. This is naturally technically advantageous. Under the conditions of the invention, the hydrogenation can be carried out for a period of at most 30 minutes, preferably at most 20 minutes, particularly preferably at most 15 minutes and even for less than 10 minutes. Under these conditions, a significantly higher space / time yield is achieved than with the prior art processes. In addition, the selectivity is positively influenced by a shorter residence time, i.e. H. higher oil yield with reduced gas and asphaltene formation. In the same sense, this has an extremely narrow residence time range when compared to conventional autoclaves when using a tubular reactor.

The total amount of hydrogen to be fed corresponds to the amount required for the reaction, i. H. up to about 10% by weight of hydrogen, based on the carbon contained in the coal. It is therefore not necessary to circulate a large excess of hydrogen, which on the one hand saves reactor volume and on the other hand saves compression and heating energy.

The mixture emerging from the reactor is separated into a liquid fraction and a gas fraction in a hot separator, and these product fractions are worked up in a manner known per se. With regard to this workup, reference is made to the prior art.

According to a particularly preferred embodiment of the process according to the invention, however, it is possible to depressurize the reaction mixture leaving the tubular reactor before it enters the hot separator. It is advisable to relax to a pressure of more than 6 bar, since relaxing to even lower pressures can lead to coking.

An important criterion for the pressure in the hot separator is the temperature of the hot separator, which is limited by the subsequent flash vacuum distillation of the bottom product. Because of this limit temperature above 300 ° C., the pressure in the hot separator should be at least over 6 bar, preferably over 20 bar, particularly preferably over 50 bar, but a maximum of 50 percent of the hydrogenation pressure. The advantage of this method of operation is that the expansion valves can be operated trouble-free and one over the prior art improved simple product separation of hydrogenation residue and valuable products can be achieved. In addition, the hot separator can be manufactured much cheaper due to the low pressure rating.

example 1

203 kg / h coal suspension; Consisting of 100 kg / h of dried hard coal, 100 kg / h of coal oil and 3 kg / h of iron oxide catalyst (so-called Lux or Bayer mass) are fed to a preheater under a pressure of 710 bar. In _V ER- coal suspension are introduced 2.2 kg / h of hydrogen corresponding to about 35 wt.% Of the quantity required for hydrogenation of coal course of the preheating. At the present hydrogen partial pressure of about 700 bar and at a temperature above 400 ° C, about 80% of the amount of hydrogen introduced is dissolved in the coal suspension.

In the preheater, the coal suspension is heated to 490 ° C and then enters a tubular reactor with a length / diameter ratio of L / d = 4,300: 1.

Due to the high initial hydrogen consumption, a large part of the dissolved hydrogen is used up very quickly, so that the gaseous hydrogen also dissolves in the hydrogenation medium after a short residence time.

The hydrogenation rate, which at the same time represents a measure of the hydrogen consumption, can be determined on the basis of the temperature profile.

After about 10% of the reactor length in the flow direction, a further 1.6 kg / h of hydrogen are fed into the hydrogenation medium, corresponding to about 25% of the total amount required for hydrogenating the coal.

In the present example, the temperature of the tubular reactor in the range from 490 to 500 ° C is carried out from the outside with flue gas.

At four further points in the flow direction along the reactor, 1.0 kg / h of hydrogen are fed in, corresponding to about 15% of the total amount required for the hydrogenation.

This means that a total of around 120% of the required hydrogen is used.

In the last part of the tubular reactor, the hydrogenation mixture is cooled to 450 ° C. and fed to the hot separator.

In the present example, the pure coal throughput is 1.77 kg / 1 h and the oil gain is 1.25 kg / 1 h. 97% by weight of the coal used is converted. The products consist of 68% by weight of gasoline and medium oil fractions, about 20% by weight of gaseous hydrocarbons, 7.5% by weight of asphaltene and heavy distillate oils and 4.5% by weight of residues.

Example 2

203 kg / h of coal suspension, consisting of 100 kg / h of dried hard coal, 100 kg / h of coal oil and 3 kg / h of catalyst as in Example 1, are fed to a preheater under a pressure of 1,200 bar.

In the course of the preheating, 2.8 kg / h of hydrogen are introduced into the coal suspension, corresponding to approximately 45% by weight of the total amount required for hydrogenating the coal.

At the present hydrogen partial pressure of approximately 1,180 bar and a temperature above 400 ° C, the hydrogen introduced is dissolved in the coal suspension.

In the preheater, the coal suspension is heated to 510 ° C and then enters a tubular reactor with a length / diameter ratio of L / d = 1,900: 1.

The temperature control of the tubular reactor in the range from 510 to 520 ° C takes place in the present example with flue gas and by feeding in coal oil three times for the respective cooling from 520 to 510 ° C.

The rate of hydrogenation, which at the same time represents a measure of the hydrogen consumption, can be determined on the basis of the temperature run.

After about 15% of the reactor length, a further 2.2 kg / h of hydrogen are fed into the hydrogenation medium, corresponding to about 35% of the total amount required for hydrogenating the coal.

At two further points in the flow direction along the reactor, 1.4 kg / h of hydrogen are fed in, corresponding to about 22% of the total amount required for the hydrogenation.

This means that a total of around 120% of the required hydrogen is used.

In the last part of the tubular reactor, the hydrogenation mixture is cooled to 450 ° C. and fed to the hot separator.

In the present example, the pure coal throughput is 4.00 kg / 1 h and the oil gain is 3.11 kg / 1 h. 97% by weight of the coal used is converted. The products consist of 75% by weight of gasoline and medium oil fractions, approximately 15% by weight of gaseous hydrocarbons, 6% by weight of asphaltene and distillate heavy oils and 4% by weight of residues.

Claims (6)

1. A process for the continuous pressure hydrogenation of coal in a tubular reactor, coal with a grain size of at most 500 pm, mixed with coal oil and conventional coal hydrogenation catalysts to form a suspension and reacted with hydrogen and the mixture emerging from the reactor in a hot separator is separated into a liquid fraction and a gas fraction and the product fractions are worked up, characterized in that a) the hydrogenation is carried out at a temperature in the range from 465 to 530 ° C., b) works at a pressure of more than 700 bar, c) introducing hydrogen in several places along the tube reactor in such an amount that at least 70% by weight of the amount of hydrogen introduced is dissolved in the suspension under hydrogenation conditions, d) a tubular reactor with a length to diameter ratio of 800: 1 to 20,000: 1 is used and e) dissipates the heat of reaction via the reactor wall to an external cooling medium. 2. The method according to claim 1, characterized in that one carries out the hydrogenation for a period of at most 30 minutes, preferably at most 20 minutes, particularly preferably at most 15 minutes. 3. The method according to Anspruc_h 1 or 2, characterized in that such an amount of hydrogen is fed in that under hydrogenation conditions at least 80% by weight thereof, preferably at least 90% by weight thereof, are dissolved in the suspension. 4. The method according to one or more of claims 1 to 3, characterized in that the suspension at a pressure of at most 25 bar, preferably at most 20 bar, at 300 to 400 ° C. preheats and then compresses the suspension to hydrogenation pressure and brings it to the hydrogenation temperature. 5. The method according to one or more of claims 1 to 4, characterized in that coal oil, which has a temperature which is below the hydrogenation temperature, is fed in at one or more points along the tube reactor. 6. The method according to any one of claims 1 to 5, characterized in that the reaction mixture leaving the tubular reactor is released before entering the hot separator.