EP0027962B1 - Process for the production of liquid hydrocarbons from coal - Google Patents

Description

It is known to convert ground coal by means of splitting pressure hydrogenation in the bottom phase, optionally with the addition of catalysts, into distillable products and to further hydrogenate these in the gas phase over fixed catalysts.

The ground coal is generally rubbed with a mixture of medium and heavy oil. Catalysts are added to the ground coal if such substances are not already sufficiently present in the coal. The coal pulp thus obtained is then pressurized together with hydrogen and / or cycle gas, heated and passed through one or more reaction spaces in which the so-called bottom phase hydrogenation (1st hydrogenation stage) takes place. The products leaving the bottom phase hydrogenation are passed into a hot separator which is kept slightly below the reaction temperature, where a separation into a bottom product (sludge) on the one hand and gaseous and vaporous products on the other hand takes place. The sludge contains the heaviest oil components, asphalt, unreacted coal particles and possibly other solids. The sludge can be thickened (topped), for example in a flash evaporation with subsequent vacuum stage, for. B. to a solids content (insoluble in benzene) of about 40 to 60%. The resulting distillate oil can be used to grind the coal. The topped sludge can be gasified by partial oxidation in the presence of steam at 1100 to 1500 ° C to a mixture of carbon oxides and hydrogen, which can be worked up for hydrogen.

The gaseous and vaporous products leaving the hot separator are cooled in heat exchangers against incoming coal pulp and then in a final cooling to near room temperature and fed to a stripper, where the separation into liquid and gaseous products takes place and the gaseous products are recycled as recycle gas. The liquid products are depressurized to atmospheric pressure and, after the aqueous phase has been separated off, subjected to distillation at atmospheric pressure, gasoline, medium oil and heavy oil being obtained. A portion of the heavy oil and the middle oil are generally used to grind the coal. The remaining parts and the gasoline, which together make up the oil, are generally further hydrogenated in the gas phase on fixed catalysts.

De-A-2 651 253 describes a coal hydrogenation in which a fraction boiling at about 280 to 420 ° C. is separated from the gaseous hydrogenation products and at least partially mixed with the coal pulp to be hydrogenated. A discharge of hydrogenation products in the boiling range from 280 to 420 ° C is not intended. This procedure means that there is no oil gain in the boiling range 280 to 420 ° C. Rather, these parts are repeatedly fed to the carbohydrate section until they have been split to form hydrogenated products.

A process has now been found for the production of liquid hydrocarbons from coal by splitting pressure hydrogenation, in which ground coal, optionally together with catalysts, is rubbed with a mixture of medium oil and heavy oil obtained in the process and the coal pulp thus obtained is mixed with hydrogen The pressure is heated and passed through one or more reaction spaces, the reaction products are led into a hot separator which is kept slightly below the reaction temperature, the bottom product from the hot separator is separated into a distillate oil for grinding the coal and a residue which is converted to synthesis gas, and which is at the top of the The heat separating gases and vapors, if necessary, are passed through a second heat separator and then cooled in series-connected heat exchangers, which is characterized in that the condensates accumulating between and behind the heat exchangers are collected in wipers, namely a heavy oil condensate, which boils essentially above 325 ° C, a medium oil condensate, which boils essentially between 180 and 325 ° C and a gasoline condensate, which boils essentially in the range between 30 and 180 ° C, from these capacitors a portion for the grinding oil and subtracts a portion as an oil gain and feeds both portions without intermediate distillation for grinding coal or hydrogenation in the gas phase or mixed phase.

In this process, the coal pulp can be produced, for example, by grinding practically asphalt-free medium and heavy oils in the process in a coal: oil ratio of 1: 1 to 1: 3. Suitable catalysts are, for example, mixtures containing iron compounds, such as Bayer mass or lux mass (the latter also in used form), iron ores or iron salts. Bayer mass or lux mass are the residues resulting from the digestion of bauxite with sodium hydroxide solution or soda, for example 48.6% Fe203.20% AbOa, 9.2% Si02.6.0% Ti02.0.2% MnO2.1, 20/0 CaO, 0.5% MgO, 6.2% Na ₂ 0, 0.2% K ₂ 0 and 13 to 15% H ₂ 0 (see Ullmann, Encyclopedia of Technical Chemistry, Volume 10, page 499 (1958)). Ferrosulfate, for example, can be used as the iron salt, which can be impregnated onto the coal in aqueous solution. The catalysts can be added, for example, in amounts of 0.5 to 5.0% by weight, based on the water-free and ash-free coal (pure coal). If the coal already contains such catalyst components, the addition of catalysts to the coal slurry can also be omitted.

For example, hard coal or brown coal of various mining areas are suitable as coal for the process according to the invention. Lignite is preferably used together with a catalytic converter gate used.

The coal pulp is pressurized together with hydrogen, which generally consists of fresh hydrogen and cycle gas. For example, pressures in the range of 100 to 400 bar are suitable. For example, coal pulp and hydrogen can be heated to 380 to 420 ° C. The reaction space or the reaction spaces for the hydrogenation in the bottom phase can, for example, be kept at 420 to 490 ° C.

The reaction products from the bottom phase hydrogenation are fed to a hot separator which is kept at a temperature slightly below the temperature of the bottom phase hydrogenation, for example 10 to 50 ° C. below the temperature of the bottom phase hydrogenation. The sludge separated in the hot separator can be processed further using known methods. For example, a distillate can be obtained from it by flash evaporation with a downstream vacuum stage, which distillate can be used to grind the coal and a topped sludge that is suitable for hydrogen production.

The first hot separator described above can optionally be followed by a second hot separator, which can be operated, for example, 10 to 30 ° C lower than the first hot separator. In the second hot separator, entrained small amounts of solids and asphaltene can be separated. The substances separated in the second hot separator are generally added to the sludge from the first hot separator.

The gases and vapors present after the hot separator (s) are cooled in series-connected heat exchangers. It is an essential feature of the method according to the invention that the condensates accumulating between and behind the heat exchangers are collected in wipers and 3 or more heat exchangers are used for this.

The heat exchangers can be operated, for example, in such a way that heat exchange takes place in the first heat exchangers or the first heat exchanger between the gases and vapors from the hot separator (s) on the one hand and the coal slurry used in the first hydrogenation stage and / or the recycle gas on the other hand. The last or the last heat exchanger is preferably operated with water or air as the coolant. Preferably, two heat exchangers are used for the heat exchange between the outgoing gases and vapors and the incoming feedstocks coal pulp and cycle gas and in the further cooling path one or more air and / or water coolers. The condensates are separated off between or after individual or all heat exchangers, for example in wipers.

The heat exchangers are operated and the condensates are separated off in such a way that three different condensates are collected, namely a heavy oil condensate which boils essentially above 325 ° C, a medium oil condensate which boils essentially between 180 and 325 ° C and a Gasoline condensate, which boils essentially between 30 and 180 ° C. Of course, it is also possible to separate the three aforementioned condensates in several subsets, for example two heavy oil condensates, two medium oil condensates and / or two gasoline condensates. The above-mentioned boiling ranges for individual condensates refer to normal pressure and are approximate values, from which larger deviations are also possible.

The gaseous fractions which remain after the separation of the condensates and contain substantial amounts of hydrogen are preferably recycled as recycle gas before the bottom phase hydrogenation. Water occurs almost exclusively in the gasoline condensate, separates there as the lower insoluble phase and can be drawn off separately from the hydrocarbon phase. If appropriate, the aqueous phase can also be separated off in a downstream settling tank. The boiling limits of the condensates can be regulated in various ways. For example, the boiling limits of the condensates can be influenced by the design of the heat exchanger. Furthermore, the separated high-boiling and still hot condensates or parts thereof, for example the heavy oil condensate, can be cooled by heat exchange for hydrogen and the hydrogen thus heated can be fed to the coal pulp in quantities which are tailored to the requirements, for example before the first heat exchanger or the first heat exchanger happens. The portion of the heavy oil condensate which is recycled to the coal is preferably used for heating the circulating gas. The selectivity between the individual condensates can be increased if the condensates are separated in separators and then individually cooled against recycle gas in reflux coolers. If the heat exchange between the heavy oil condensate or parts thereof and the cycle gas the heavy oil condensate or parts thereof for further use, e.g. B. has not cooled sufficiently as grinding oil for the coal, the heavy oil condensate or parts thereof can be cooled further, for example by air cooling.

From the heavy oil and medium oil condensates obtained as described above, the envisaged amounts of grinding oil are generally taken. The remaining portions of the heavy oil and medium oil condensate are available together with the gasoline condensate as an oil gain for further processing. The oil gain can be fed to the hydrogenation in the gas phase or mixed phase without significant pressure relief and temperature reduction. In general, the combined oil gain as a whole will be used in the further hydrogenation. If these are to be operated under aromatizing hydrogenation conditions, it is advantageous to refine the gasoline condensate separately to hydrate.

In special cases, it may be advantageous to depressurize individual condensates, in particular the gasoline condensate, to normal pressure and thus to degas them.

The hydrogenation in the gas phase or mixed phase (second hydrogenation stage) is preferably carried out on fixed-bed catalysts. This hydrogenation can be carried out, for example, at 100 to 400 bar and as a refining hydrogenation at 340 to 420 ° C. or as a splitting hydrogenation at 420 to 480 ° C.

Examples of suitable catalysts for the second hydrogenation stage are oxides, sulfides or phosphates of the metals of VI. or VIII. group of the periodic system, such as tungsten or molybdenum, optionally in a mixture with oxides or sulfides of the iron group, expediently applied to supports such as aluminum oxide and its spinels, natural or synthetic bleaching earth, in particular zeolites. Platinum and rhenium are also suitable as hydrogenation catalysts. Highly active catalysts are preferably used in this hydrogenation, for example nickel / tungsten sulfide on supports. In order to maintain the high activity of such catalysts over longer periods of time, a certain H ₂ S partial pressure is necessary during this hydrogenation. The products used in the hydrogenation should therefore have a sulfur content of the order of about 0.1 to 1%. Such a sulfur content can optionally also be maintained by adding sulfur or sulfur compounds.

The reaction products from this hydrogenation can be worked up in a customary manner, in particular by decomposing them into the desired fractions by distillation at atmospheric pressure. The products consist of hydrogen-rich hydrocarbons free of secondary components such as oxygen, nitrogen or sulfur compounds. They can be used as finished products, but are also fully suitable for further processing in the processes customary in the petroleum industry, such as catalytic cracking and reforming, hydrocracking, thermal and pyrolytic cracking.

The advantages of the process according to the invention are, in particular, that after the first hydrogenation stage, the distillation of the condensed gases and vapors, which is carried out at normal pressure according to the prior art, is avoided. In addition, pumping to reaction pressure for those fractions from the first hydrogenation stage which are used in the second hydrogenation stage can be dispensed with. By introducing the heavy oil and medium oil condensates still hot into the hydrogenation with a fixed catalyst, substantial energy savings occur when heating up to the reaction temperature. It should also be mentioned that after the bottom phase hydrogenation with separate accumulation of the gasoline condensate, the removal of the aqueous phase is much easier because of the greater density differences than in the one-stage condensation of the condensable products from the gases and vapors of the hot separator.

When using lignite, products can be obtained after the gas phase hydrogenation which are practically free of nitrogen, oxygen and sulfur and in which the gasoline fraction over 13.4, the middle oil fraction over 12.6 and the heavy oil fraction over 11.8% by weight hydrogen contain. Such products are particularly suitable for pyrolytic cracking for the production of chemical raw materials, primarily olefins and aromatics.

example 1

106.5 t of dried Rhenish lignite, corresponding to 100.0 t of pure coal (free of water and ash), are mixed with 3 t of Bavarian mass with the composition 48.6% Fe ₂ O ₃ , 20% Al ₂ O ₃ , 9.2% SiO ₂ , 6.0% TiO ₂ , 0.2% MnO ₂ , 1.2% CaO, 0.5% MgO, 6.2% Na ₂ O, 0.2% K ₂ O and 13-15% H ₂ O and with 150 t of oil from the first hydrogenation stage, consisting of 20 t of vacuum distillate (from the sludge distillation), 45.1 t of medium oil condensate and 84 t of heavy oil condensate, to give a coal pulp. The coal pulp is brought to the operating pressure of 300 bar and, together with fresh hydrogen and cycle gas, heated to 430 ° C. via a heat exchanger and a preheater and introduced into the hydrogenation reactor, where the hydrogenation takes place at 470 ° C. with a hydrogen absorption of 4.5 t. The reaction products pass from the reactor into a hot separator kept at 435 ° C, where the separation takes place in a bottom phase product (sludge), which is converted into vacuum distillate and topped sludge by flash evaporation, and the gases and vapors withdrawing from the upper part, the give off part of their latent heat in two heat exchangers connected in series to the incoming mixture of coal paste, cycle gas and fresh hydrogen. In the first heat exchanger, the gases and vapors are cooled to 350 ° C, with 96.2 t of heavy oil condensing, which are taken up in a first stripper. The second heat exchanger cools to 225 ° C, with 72.3 t of medium oil condensing, which is taken up in a second wiper. In the final cooling, the temperature is reduced to 40 ° C., 7.5 t of gasoline condensing, which are taken up in a third wiper. In addition, 10 t of gaseous hydrocarbons C ₁ to C _{4 are produced} . 84 t are removed from the heavy oil condensate and after cooling expanded to normal pressure in a heat exchanger against circulating gas and subsequent air cooling and used as part of the grinding oil. 45.1 t of the middle oil condensate used as a grinding oil component after cooling and relaxation. The three wipers are used to extract oil: 12.2 t heavy oil, 27.2 t medium oil and 7.5 t gasoline and without pressure relief and temperature reduction to the second hydrogenation stage with a fixed catalyst. The hydrogenation of the combined oil gain (46.9 t) in the second hydrogenation stage takes place in the hydrogen cycle gas at 420 ° C. and 290 bar over nickel / tungsten sulfide on aluminum oxide with a hydrogen uptake of 1.6 t. After cooling to 400 C and separating the cycle gas in a further scraper, the following are obtained: 12.1 t of gasoline, 21.7 t of medium oil and 10.7 t of heavy oil.

Example 2

The 12.1 t of gasoline, 21.7 t of medium oil and 10.7 t of heavy oil obtained according to Example 1 are separately subjected to pyrolysis (steam cracking), in separate cracking furnaces and condensation. The pyrolysis conditions are as follows:

The yields obtained from pyrolysis (steam cracking) are as follows (for the entire use of 44.5 t):

The ratio of the olefins to the aromatics can be shifted in favor of the aromatics if the gasoline fraction from the hydrogenation is previously catalytically reformed, the aromatics are obtained from the reformate by extraction and the raffinate is introduced into the pyrolysis. It is advisable to split the hydrocarbons ethane, propane and n-butane from both hydrogenation stages into olefins in a known manner by steam cracking.

Claims (5)

1. A process for the production of liquid hydrocarbons from coal by hydrocracking under pressure, in which ground coal, with or without catalysts, is slurried with a mixture of middle oil and heavy oil obtained in the process and the coal slurry thus obtained is heated under pressure, together with hydrogen, and passed through one or more reaction chambers, the reaction products are fed to a hot separator kept somewhat below the reaction temperature, the bottoms product from the hot separator is separated into a distillate oil for slurrying the coal and a residue, which is converted into synthesis gas, and the gases and vapours taken off at the top of the hot separator are passed over a second hot separator, if necessary, and then cooled in heat exchangers connected in series, wherein three or more heat exchangers are used, and the condensates obtained between and after the heat exchangers, namely a heavy oil condensate essentially boiling above 325° C, a middle oil condensate essentially boiling between 180 and 325° C and a gasoline condensate essentially boiling in the range between 30 and 180°C, are collected in separators and from these condensates, one portion is removed as slurrying oil and one portion is removed as oil gain, and the two portions are passed respectively to the slurrying of coal and the hydrogenation in the gas phase or mixed phase, without intermediate distillation.

2. A process as claimed in claim 1, wherein the hot heavy oil condensate is cooled by heat exchange against hydrogen and the hydrogen thus heated is supplied to the coal slurry.

3. A process as claimed in claims 1 and 2, wherein the oil gain taken off is supplied to the hydrogenation in the gas phase or mixed phase, without substantially letting down the pressure or reducing the temperature.

4. A process as claimed in claims 1 to 3, wherein the hydrogenation in the gas phase or mixed phase is carried out over fixed-bed catalysts.

5. A process as claimed in claim 4, wherein the catalyst is a highly active hydrogenation catalyst, the activity of which is maintained, if necessary, by adding sulphur or sulphur compounds.