Destructive hydrogenation produced for the purpose of obtaining from hard or heavy liquid fuel light liquid fuels - gasoline and kerosene. By its chemistry, this is a very complex process, in which the splitting (destruction) of high-molecular compounds (coal macromolecules) occurs simultaneously with the formation of simpler saturated and unsaturated hydrocarbons and fragments and the addition of hydrogen to the fragments - at the site of double bonds and to aromatic hydrocarbons. Depolymerization and other processes also occur.
The addition of hydrogen (hydrogenation) is accompanied by a decrease in volume and release of heat. The occurrence of hydrogenation reactions is promoted by an increase in pressure and removal of reaction heat.
Usually the hydrogenation of coals is carried out at a pressure of 2000-7000 ncm2 and a temperature of 380-490 ° C. Catalysts are used to speed up the reaction - oxides and sulfides of iron, tungsten, molybdenum with various activators.
Due to the complexity of the hydrogenation process, the process of obtaining light fuel from coal - gasoline and kerosene - is carried out in two stages - in the liquid and vapor phases. The most suitable for hydrogenation are young black and brown coals containing a significant amount of hydrogen. Coals are considered the best, in which the ratio between carbon and hydrogen is not more than 16-17. Harmful impurities are sulfur, moisture and ash. Permissible moisture content 1-2%, ash 5-6%, sulfur content should be minimal. In order to avoid a high consumption of hydrogen, oxygen-rich fuels (eg wood) are not hydrogenated.
The technology of the hydrogenation process is as follows. Finely ground coal (up to 1 mm) with the desired ash content is mixed with a catalyst, most often iron oxides, dried and carefully ground in a pestle mill with oil, which is obtained by separating hydrogenation products. The content of coal in the paste should be 40-50%. The paste is fed into the hydrogenation unit with a pestle pump at the required pressure; fresh and circulating hydrogen is supplied there by compressors 2 and 3. The mixture is preheated in heat exchanger 4 by heat
Coming from the hydrogenation column, vapors and gases, and then in a tube furnace 5 to 440 ° C and enters the hydrogenation column 6, where the temperature rises to 480 ° due to the heat of reaction. After that, the reaction products are separated in the separator, the upper part of which leaves vapors and gases, and the sludge from the lower part.
The gas-vapor mixture is cooled in the heat exchanger 4 and the water cooler 8 to 50°C and separated 9. After the pressure is removed, the condensate is distilled, obtaining a "broad fraction" (300-350°) and heavy oil. The broad fraction after the extraction of phenols from it enters the second stage of hydrogenation. The sludge separated in the separator 7 is separated by centrifugation into a heavy oil and a solid residue, which is subjected to semi-coking. As a result, a heavy oil and a fraction are formed, which are added to the broad one. Ash residues are used as fuel. Heavy oils are used to make pasta. The gases separated in the separator 9, after the absorption of hydrocarbons in the scrubber 10 by pressurized oils, are returned to the process by means of the circulation pump 3.
Hydrogenation in the second stage is most often carried out in the presence of WSo under a pressure of 3000 nm2 at 360-445°C. Gasoline and kerosene or diesel fuel are isolated from the resulting hydrogenation product. There are no unsaturated hydrocarbons in the fuel obtained by hydrogenation, and sulfur is in the form of hydrogen sulfide, which is easily removed by washing with alkali and then with water. Destructive hydrogenation is carried out in columns made of alloy steels containing chromium, nickel, molybdenum. The wall thickness is up to 200 l and the height is up to 18 m and the diameter is 1 m. In columns for hydrogenation in the vapor phase, the catalyst is placed on mesh shelves.
The yield of gasoline can reach 50-53% per combustible mass of coal.
To obtain valuable chemical compounds from coal, heat treatment processes (semi-coking, coking) or heat treatment in the presence of hydrogen under pressure (hydrogenation) are used.
Thermal decomposition of coal is accompanied by the formation of coke, tar and gases (mainly methane). Coal semi-coking resins mainly contain aromatic compounds. Brown coal semi-coking tars, along with aromatic compounds, also contain a significant amount of saturated cycloalkanes and alkanes. Coke is the target product of semi-coking. During the thermal processing of coal in the presence of hydrogen, it is possible to almost completely convert the organic mass of coal into liquid and gaseous hydrocarbons.
Thus, coal hydrogenation can be used to obtain not only motor and aviation fuels, but also the main petrochemical raw materials.
Hydrogenation liquefaction of coal is a complex process, including, on the one hand, the downsizing of the structure of the organic mass of coal with the breaking of the least strong valence bonds under the influence of temperature, and on the other hand, the hydrogenation of broken and unsaturated bonds. The use of hydrogen is necessary both to increase the H:C ratio in products due to direct hydrogenation and to stabilize the degradation products of eliminated macromolecules.
The implementation of the process of coal hydrogenation under relatively low pressure - up to 10 MPa - is possible with the use of a hydrogen donor-paste former of oil or coal origin and the use of efficient catalysts.
One of the main problems in coal liquefaction is the optimization of the process of hydrogen transfer from donor-paste formers to coal matter. There is an optimal degree of hydrogen saturation of donor molecules. The paste-forming agent should contain 1-2% more hydrogen than in coal liquefaction products. The introduction of substituents of various types into the structure of donors affects both the thermodynamic and kinetic characteristics. The transfer of hydrogen from donors to carriers - molecules of aromatic compounds - proceeds stepwise according to the free radical mechanism.
At low pressure (up to 10 MPa), the use of donors allows coal to add no more than 1.5% hydrogen, and for deep liquefaction of coal (90% or more), it is necessary to add up to 3% hydrogen, which can be done by introducing it from the gas phase.
The molybdenum catalyst used in combination with iron and other elements significantly intensifies the process, increases the depth of coal liquefaction and reduces the molecular weight of the products.
The main primary products of coal hydrogenation are hydrogenated product and sludge containing ~15% solid products (ash, unconverted coal, catalyst). Gaseous hydrogenation products containing C1-C4 hydrocarbons, ammonia, hydrogen sulfide, carbon oxides mixed with hydrogen are sent for purification by short cycle adsorption, and gas with 80-85% hydrogen content is returned to the process.
During the condensation of the hydrogenate, water is separated, which contains dissolved ammonia, hydrogen sulfide and phenols (a mixture of mono- and polyhydric).
Below is a schematic diagram of the chemical processing of coal (Scheme 2.3).
The water condensate contains 12-14 g/l of phenols of the following composition (in % (wt.):
To obtain phenols, aromatic hydrocarbons and olefins, a scheme for the chemical processing of coal liquefaction products has been developed, which includes: distillation to separate the fraction from bp. up to 513 K; isolation and processing of crude phenols; hydrotreating of the dephenolized wide fraction with bp. up to 698 K; distillation of the hydrotreated product into fractions with bp. up to 333, 333-453, 453-573 and 573-673 K; hydrocracking of medium fractions in order to increase the yield of gasoline fractions; catalytic reforming of fractions with bp. up to 453 K; extraction of aromatic hydrocarbons; pyrolysis of raffinate gasoline.
During the processing of brown coal from the Borodino deposit of the Kansko-Achinsk coal basin in terms of dry weight of coal, the following compounds can be obtained (in wt %)):
In addition, 14.9% of C1-C2 hydrocarbon gases can be isolated; 13.4% - liquefied hydrocarbon gases C 3 -C 4 , as well as 0.7% ammonia and 1.6% hydrogen sulfide.
The invention relates to chemical technology, namely the liquefaction of coal and can be used to produce synthetic motor fuels. The method of coal hydrogenation includes the preparation of a coal-oil paste containing coal, a paste-forming agent based on products of thermal modification of a high-boiling fraction of coal hydrogenate in a water vapor environment on iron oxides at a temperature of 450-500 ° C and an iron-containing catalyst subjected to mechanochemical treatment and dispersed using ultrasound in the fraction of products hydrogenation of coal, boiling off at a temperature of 180-300°C and taken in an amount of 5-20% by weight of the above paste-forming agent, followed by its introduction into the paste-forming agent. Next, the coal-oil paste is heated at elevated pressure in a hydrogen medium, followed by separation of the target products. The technical result of the invention is to improve the quality of distillate fractions of liquid products of coal hydrogenation by reducing the sulfur content without reducing their yield. 1 tab.
The invention relates to chemical technology, namely to the liquefaction of coal, and can be used to obtain distillate fractions of liquid coal products with a low sulfur content, which are components of synthetic motor fuels.
Coal hydrogenation is carried out at an elevated temperature under hydrogen pressure in the presence of catalysts in a paste-forming medium with hydrogen-donor properties. A number of methods are known for the hydrogenation of coal using powdered iron ore or iron-containing waste from ore processing activated with sulfur additives or sulfur-containing compounds as catalysts. The conversion of coal increases with the joint processing of catalysts and sulfur in energy-intensive activator mills.
The disadvantage of the above methods is the high sulfur content in the resulting distillate fractions.
Closest to the proposed invention is a method of coal hydrogenation, including the preparation of coal-oil paste from coal, a paste-forming agent and an iron-containing catalyst subjected to mechanochemical treatment together with sulfur, heating the paste at elevated pressure in a hydrogen environment, followed by isolation of target products. A high-boiling fraction of coal hydrogenate is used as a paste-forming agent after its thermal cracking in an environment of water vapor on iron oxides at a temperature of 450-500°C, followed by mixing the paste-forming agent with a catalyst before preparing coal-oil paste.
disadvantage this method is the low quality of the target products due to the high sulfur content in the distillate fractions. The products obtained in the process of hydrogenation cannot be used as components of motor fuels without additional hydrotreatment. In addition, the disadvantages of the method include the duration and insufficient degree of dispersion of the catalyst in a viscous paste-forming agent by mechanical stirring.
The objective of the invention is to improve the quality of distillate fractions of liquid products of coal hydrogenation by reducing the sulfur content without reducing their yield.
The task is achieved by the fact that in the method of coal hydrogenation, including the preparation of coal-oil paste from coal, a paste-forming agent based on the products of thermal modification of the high-boiling fraction of coal hydrogenate in water vapor on iron oxides at a temperature of 450-500 ° C and an iron-containing catalyst subjected to mechanochemical processing, heating the paste at elevated pressure in a hydrogen medium, followed by isolation of the target products, according to the invention, the catalyst subjected to mechanochemical treatment is dispersed using ultrasound in the fraction of hydrogenation products boiling at a temperature of 180-300 ° C and taken in an amount of 5-20% by weight of the paste-forming agent followed by introduction into the paste former.
A comparative analysis with the prototype shows that the distinguishing features are:
The use of a mixture of 95-80 wt.% of the products of thermal modification of the high-boiling fraction of coal hydrogenate in an environment of water vapor on iron oxides at a temperature of 450-500 ° C and 5-20 wt.% of the fraction of coal hydrogenation products boiling in the range of 180-300 °C.
It is known that the mechanical processing of ore materials in energy-intensive activator mills is accompanied not only by a decrease in the particles of the crushed material, but also by their intense aggregation with the formation of agglomerates having a complex structure. When such materials are added to the oil-coal paste with intensive stirring, the destruction of agglomerates does not occur, which significantly reduces the efficiency of using such catalytic systems. The destruction of agglomerates can be achieved by sonication under certain conditions in water and in a number of organic solvents. Preliminary studies have shown that the effective dispersion of iron ore catalysts by this method in the products of thermal modification of the high-boiling fraction of coal hydrogenate in water vapor on iron oxides, used in the prototype as a paste-forming agent, cannot be achieved due to the high viscosity of the latter. We have found that the dispersion of the catalyst using ultrasound is carried out in the environment of hydrogenation products boiling in the range of 180-300°C, followed by adding the resulting mixture in the required amount to the paste former.
The essence of the invention is illustrated by specific examples.
Example 1. The hydrogenation of coal is carried out in a laboratory rotary autoclave with a capacity of 0.25 liters. As a paste-forming agent, a fraction boiling over above 400°C is used, the products of thermal modification at 470°C of the residues of distillation of coal hydrogenate in water vapor in the presence of iron oxides.
The preparation of a catalyst for the process of coal hydrogenation is carried out as follows: the flotation concentrate of the tailings of the electromagnetic separation of iron ores is preliminarily subjected to mechanochemical treatment in a mill-activator of a centrifugal planetary type (AGO-2). Next, 8.8 g of ore catalyst, 110 g of steel balls with a diameter of 8 mm are loaded into the activator drum with a capacity of 0.15 liters, 40 ml of distilled water and 0.16 g of sodium hydroxide (0.1 M solution) are added, after which it is closed and processing is carried out for 30 minutes at a drum rotation speed of 1820 rpm. Under these conditions, the centrifugal acceleration developed by the grinding media is 600 m×s -2 .
An aliquot is taken from the resulting pulp at the rate of 0.30 g of ore material, added to 0.30 g of a fraction of coal hydrogenation products boiling in the range of 180-300 ° C (2.5% by mass of the paste-forming agent), and sonicated using a dispersant UZD1-0.063/22 for 3 min. In the resulting mixture, after dispersion, intensive formation of a precipitate was noted. The resulting catalyst pulp is added to 11.7 g of a fraction boiling above 400°C of the products of thermal modification of the residues of distillation of coal hydrogenate in a vapor medium at 470°C in the presence of iron oxides, and intensively stirred for 15 minutes. The ratio of the fraction of products of thermal modification of the residues of distillation of coal hydrogenate in water vapor in the presence of iron oxides (component 1) and products of coal hydrogenation boiling in the range of 180-300°C (component 2) in the paste-forming agent is 97.5 wt.% and 2, 5 wt.%, respectively.
Coal is added to the prepared mixture of paste-forming agent and catalyst (coal:paste-forming ratio = 1:1). The autoclave is closed, hydrogen is supplied to a pressure of 5.0 MPa. With continuous rotation, the autoclave is heated, upon reaching 430°C, maintained at this temperature for 60 minutes. Then the autoclave is cooled, the products boiling away under conditions equivalent to the boiling point range under normal conditions above 180°C are distilled off directly from the autoclave under vacuum. The products are separated into aqueous and hydrocarbon fractions (hereinafter referred to as the fraction with a boiling point above 180°C) by decantation. Then the contents of the autoclave are extracted with toluene, a fraction is distilled off from the extract, which boils away in the range of 180-300°C. The sulfur content in the obtained fractions is determined by the standard method using the analyzer "Flash EA-1112, Thermo Quest". The results obtained are shown in the table.
Example 2. Similar to example 1, except that after mechanochemical activation of the catalyst, an aliquot of 0.30 g of ore material is taken from the obtained pulp, added to 0.60 g of the fraction of coal hydrogenation products, boiling in the range of 180-300 ° C (5.0% by weight of the paste-forming agent) and sonicated using a dispersant UZD1-0.063/22 for 3 minutes. After dispersion, a homogeneous mixture is formed, the formation of a precipitate is not observed for more than 1 hour after dispersion.
The resulting catalyst slurry is added to 11.4 g of a fraction boiling above 400°C of the products of thermal modification of the residues of distillation of coal hydrogenate in water vapor at 470°C in the presence of iron oxides and intensively stirred for 15 minutes. The ratio of the fraction of products of thermal modification of the residues of distillation of coal hydrogenate in water vapor in the presence of iron oxides (component 1) and products of coal hydrogenation, boiling away in the range of 180-300°C (component 2) in the paste-forming agent is 95 wt.% and 5 wt.% , respectively.
Example 3. Analogously to example 1, except that after mechanochemical activation of the catalyst, an aliquot of 0.30 g of ore material is taken from the obtained pulp, added to 1.2 g of the fraction of coal hydrogenation products, evaporating in the range of 180-300 ° C (10.0% by weight of the paste-forming agent), and sonicated using a dispersant UZD1-0.063/22 for 3 minutes. After dispersion, a homogeneous mixture is formed, the formation of a precipitate is not observed for more than 1 hour after the completion of the dispersion.
The resulting catalyst slurry is added to 10.8 g of a fraction boiling above 400°C of the products of thermal modification of the residues of distillation of coal hydrogenate in vapor at 470°C in the presence of iron oxides and intensively stirred for 15 minutes. The ratio of the fraction of products of thermal modification of the residues of distillation of coal hydrogenate in a vapor medium in the presence of iron oxides (component 1) and coal hydrogenation products boiling away in the range of 180-300 ° C (component 2) in the paste-forming agent is 90 wt.% and 10 wt.%, respectively.
Example 4. Analogously to example 1, except that after mechanochemical activation of the catalyst, an aliquot of 0.30 g of ore material is taken from the obtained pulp, added to 2.4 g of the fraction of coal hydrogenation products, evaporating in the range of 180-300 ° C (20% by weight of the paste-forming agent), and sonicated using a dispersant UZD1-0.063/22 for 3 minutes. After dispersion, a homogeneous mixture is formed, the formation of a precipitate is not observed for more than 1 hour.
The resulting catalyst pulp is added to 9.6 g of a fraction boiling above 400°C of the products of thermal modification of the residues of distillation of coal hydrogenate in a vapor medium at 470°C in the presence of iron oxides and intensively stirred for 15 minutes. The ratio of the fraction of products of thermal modification of the residues of distillation of coal hydrogenate in a vapor medium in the presence of iron oxides (component 1) and products of coal hydrogenation boiling away in the range of 180-300°C (component 2) in a paste-forming agent is 80 wt.% and 20 wt.% , respectively.
Example 5. Similar to example 1, except that after mechanochemical activation of the catalyst, an aliquot of 0.30 g of ore material is taken from the resulting pulp, added to 3 g of the fraction of coal hydrogenation products, boiling in the range of 180-300 ° C (25 0% to the mass of the paste-forming agent), and sonicated using a dispersant UZD1-0.063/22 for 3 minutes. After dispersion, a homogeneous mixture is formed, the formation of a precipitate is not observed for more than 1 hour.
The resulting catalyst slurry is added to 9 g of a fraction boiling above 400°C of the products of thermal modification of the residues of distillation of coal hydrogenate in vapor at 470°C in the presence of iron oxides, and intensively stirred for 15 minutes. The ratio of the fraction of products of thermal modification of the residues of distillation of coal hydrogenate in a vapor environment in the presence of iron oxides (component 1) and products of coal hydrogenation boiling away in the range of 180-300°C (component 2) in a paste-forming agent is 75 wt.% and 25 wt.% , respectively.
The results obtained show a decrease in the degree of conversion and the yield of distillate fractions.
Example 6. (Implementation of the prototype method).
Hydrogenation of coal is carried out in a laboratory rotating autoclave with a capacity of 0.25 liters. As a paste-forming agent, a fraction is used that boils over above 400°C the products of thermal cracking in an environment of water vapor of the residues of the distillation of coal hydrogenate. Steam cracking is carried out at 470°C, a pressure of 3 atm in the absence of hydrogen in the presence of iron oxides.
The preparation of a catalyst for the process of coal hydrogenation is carried out as follows: the flotation concentrate of the tailings of the electromagnetic separation of iron ores is preliminarily subjected to mechanochemical treatment together with elemental sulfur in a mill-activator of a centrifugal planetary type (AGO-2), at the rate of 0.30 g of catalyst (2.5 wt.% to the weight of dry coal) and 0.24 g of sulfur (2.0 wt.% to the weight of dry coal). Further, 8.8 g of ore catalyst, 7.0 g of elemental sulfur and 110 g of steel balls with a diameter of 8 mm are loaded into the activator drum with a capacity of 0.15 liters until the drum is completely filled with 80 ml of distilled water and 0.32 g of sodium hydroxide (0 ,1 M solution), after which it is closed and processed for 30 minutes at a drum rotation speed of 1820 rpm. Under these conditions, the centrifugal acceleration developed by the grinding media is 600 m×s -2 . The resulting pulp of the catalyst is introduced into the paste with vigorous stirring for 1 hour.
Coal is added to the prepared mixture of paste-forming agent and catalyst (coal:paste-forming ratio = 1:1). The autoclave is closed, hydrogen is supplied to a pressure of 5.0 MPa. With continuous rotation, the autoclave is heated, upon reaching 430°C, maintained at this temperature for 60 minutes. Then the autoclave is cooled, the products boiling away under conditions equivalent to the boiling point range under normal conditions below 180°C are distilled off directly from the autoclave under vacuum. The products are separated into an aqueous fraction and a hydrocarbon fraction (hereinafter referred to as the fraction with a boiling point below 180°C) by decantation. Then the contents of the autoclave are extracted with toluene, a fraction is distilled off from the extract, which boils away in the range of 180-300°C. The sulfur content in the obtained fractions is determined by the standard method using the analyzer "Flash EA-1112, Thermo Quest". The results obtained are shown in the table.
Thus, in the proposed invention, the dispersion of the catalyst using ultrasound in the fraction of coal hydrogenation products, boiling in the range of 180-300°C and taken in an amount of 5-20% by weight of the paste-forming agent, allows you to drastically reduce the sulfur content in distillate products, to obtain comparable with the prototype indicators for the degree of conversion of coal and the yield of distillate fractions.
| Table | ||||||
| Indicators of the hydrogenation process | ||||||
| № | The content of the fraction 180-300°C in the paste, wt.% | The degree of conversion of coal, wt.% | Faction N.K. - 180°C | Fraction 180°С-300°С | ||
| Yield, % of coal weight | S content, wt.% | * Yield, % of the mass of coal | S content, wt.% | |||
| 1 | 2,5 | 87 | 6,1 | 0,1 | 29,0 | 0,2 |
| 2 | 5,0 | 93 | 7,6 | 0,1 | 33,5 | 0,1 |
| 3 | 10,0 | 93 | 7,7 | 0,1 | 36,1 | 0,1 |
| 4 | 20,0 | 91 | 7,7 | 0,1 | 35,3 | 0,1 |
| 5 | 25,0 | 89 | 7,6 | 0,1 | 32,2 | 0,1 |
| 6 | 0 | 94 | 5,6 | 0,4 | 39,0 | 0,6 |
| * - The yield of the fraction boiling in the range of 180-300°C was calculated by the formula: 100% × (the amount of the obtained fraction 180-300°C - the amount of the fraction 180-300°C added to the paste former) / organic mass of the loaded coal. |
A method for coal hydrogenation, including the preparation of a coal-oil paste containing coal, a paste-forming agent based on products of thermal modification of a high-boiling fraction of coal hydrogenate in an environment of water vapor on iron oxides at a temperature of 450-500 ° C and an iron-containing catalyst subjected to mechanochemical treatment, heating the paste at elevated pressure in hydrogen medium with subsequent isolation of the target products, characterized in that the catalyst subjected to mechanochemical treatment is dispersed using ultrasound in the fraction of coal hydrogenation products, boiling off at a temperature of 180-300 ° C and taken in an amount of 5-20% by weight of the above paste-forming agent, with subsequent introduction into the paste former.
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The invention relates to chemical technology, namely the liquefaction of coal and can be used to produce synthetic motor fuels
COAL HYDROGENATION - the conversion of high-molecular substances of the organic mass of coal (OMU) under hydrogen pressure into liquid and gaseous products at 400-500 ° C in the presence of various substances - organic solvents, catalysts, etc. The scientific foundations of this process were developed at the beginning of the 20th century. V. N. Ipatiev, N. D. Zelinsky, F. Bergius, F. Fischer and others. in some countries, in particular in Germany and the UK, were built industrial enterprises for the production of gasoline, diesel fuel from coal and coal tars, lubricating oils, paraffins, phenols, etc. In the 1940s the production of liquid products from coal exceeded 4 million tons/year. In the 1950s hydrogenation of coal was mastered on a semi-industrial scale in the USSR.
In the 1950s rich oil fields have been discovered in the USSR, the Middle East, and other parts of the world. The production of synthetic liquid fuels from coal has practically ceased. its cost was 5-7 times higher than the cost of motor fuel obtained from oil. In the 70s. the price of oil has risen sharply. In addition, it became obvious that with the current scale of oil consumption (~ 3 billion tons/year), its reserves suitable for extraction by economical methods will be depleted in the middle of the 21st century. The problem of involving solid fuels, mainly coal, in processing to obtain liquid oil substitute products has become relevant again.
For the hydrogenation of coal, unoxidized brown and slightly metamorphosed coals are used. The content of the mineral part in them should not exceed 5-6%, the ratio C: H - 16, the yield of volatile substances should be more than 35%, the content of petrographic components of the vitrinite and liptinite groups should be more than 80%. High-ash coals must first be enriched.
OMU with a C content of 70-85%, usually used for hydrogenation, is a self-associated multimer consisting of spatially structured blocks (oligomers). Blocks include macromolecules of carbon, hydrogen and heteroatoms (O, N, S), which causes an uneven distribution of electron density, therefore, donor-acceptor interaction takes place in the blocks, incl. hydrogen bonds are formed. The breaking energy of such bonds does not exceed 30 kJ/mol. There are blocks with a molecular weight of 200-300, 300-700 and 700-4000, soluble in heptane (oils), benzene (asphaltenes) and pyridine (asphaltols), respectively. Inside the blocks, the macromolecules are connected by methylene, as well as O-, N-, and S-containing bridges. The breaking energy of these bonds is 10-15 times greater than the breaking energy of the blocks. When coal is hydrogenated, the blocks are first separated. The subsequent destruction of the blocks requires an elevated temperature, the presence of active H2. To obtain liquid products from coal, it is necessary, along with degradation, to carry out hydrogenation of the formed low molecular weight unsaturated compounds.
principled technology system coal hydrogenation is shown in the figure:
Figure: Schematic diagram of coal hydrogenation.
Initial operations-preparation of coal.
To increase the specific surface area, coal is crushed to particles smaller than 0.1 mm, often combined with drying. top scores are achieved by vibration grinding and grinding in a disintegrator. In this case, the specific surface area increases by 20-30 times, the volume of transitional pores by 5-10 times. Mechanochemical activation of the surface occurs, as a result of which the reactivity of coal increases (especially when crushed in a mixture with a solvent-paste former and a catalyst). Drying plays an important role. Moisture fills the pores, preventing the penetration of reagents to the coal, is released during the process in the reaction zone, reducing the partial pressure of H2, and also increases the amount Wastewater. Coals are dried to a residual moisture content of 1.5% using tubular steam dryers, vortex chambers, dryer pipes, in which hot flue gases with a minimum O2 content (0.1-0.2%) serve as a heat carrier so that the coal does not undergo oxidation . To avoid a decrease in reactivity, the coal is not heated above 150-200 °C.
To increase the degree of conversion of WMD into liquid products, a catalyst is applied to coal (from solutions of salts, in the form of a powder, emulsion or suspension) in an amount of 1-5% by weight of coal. The more active the catalyst, the lower the pressure for coal hydrogenation. Mo, W, Sn compounds have the maximum catalytic activity, using which the hydrogenation of coal can be carried out at a relatively low pressure - 10-14 MPa. However, their use is limited due to the difficulty of regeneration from a mixture with the rest of the unconverted coal. Therefore, in many processes, cheap, albeit low-active, catalysts are used (for example, red mud waste after separation of Al2O3 from bauxites), compensating for their insufficient activity by increasing the hydrogen pressure to 30–70 MPa.
The efficiency of coal hydrogenation is largely determined by the chemical composition and properties of the paste-forming solvent, in a mixture with which (50-60% of the paste-forming agent) the coal is processed. The paste former must contain high-boiling fractions of the coal hydrogenation product (boiling point > 325 °C) with a minimum content of asphaltenes to keep the coal in the liquid phase. In most variants of coal hydrogenation, substances with hydrogen-donating properties are added to the paste-forming agent to stabilize the blocks formed from the coal multimer at a relatively low temperature (200–350 °C), when molecular hydrogen is inactive. Blocks easily split off hydrogen from donors and due to this they do not "stick together".
The hydrogen-donor component of the paste-forming agent is obtained by hydrogenation of the coal hydrogenation fraction with a boiling point of 300-400°C. In this case, bi-, tri- and tetracyclic aromatic hydrocarbons are partially hydrogenated with the formation of hydroaromatic derivatives, which are capable of donating hydrogen with more high speeds than naphthenic hydrocarbons. The amount of the donor in the paste former can be 20-50% (the composition of the paste former is optimized depending on the type of raw material and hydrogenation conditions). High-boiling fractions of oil products are also used as a donor.
The degree of conversion of WMD increases with the introduction of organic additives-compounds capable of interacting with coal and its degradation products (y-picoline, quinoline, anthracene, etc.) into the paste-forming agent. The additives also temporarily stabilize the reactive radicals formed during the primary degradation of coal, and so on. prevent the formation of condensation by-products.
The resulting coal-oil paste mixed with circulating hydrogen-containing gas (80-85% H2 at the inlet, 75-80% at the outlet) is heated in a heat exchange system and a tube furnace and then sent to the reactor for hydrogenation. 1.5-5.5 thousand m3 of gas is injected per 1 ton of paste. Part of the gas is fed into the reactor cold to cool the reaction mixture and maintain a constant temperature, since the hydrogenation of coal releases 1.2-1.6 MJ per 1 kg of coal. With an increase in temperature, the rate of destruction of OMF increases, but the rate of hydrogenation simultaneously decreases.
Hydrogenation is carried out in three or four successively arranged cylindrical hollow reactors. The duration of coal hydrogenation, as a rule, is determined by the volumetric rate of supply of coal-oil paste to the reaction system. This speed depends on the type of coal, paste former, catalyst, process temperature and pressure. The optimal space velocity is selected empirically and is usually 0.8-1.4 tons per 1 m3 of reaction volume per hour (processes with higher space velocity are being developed).
The reaction products are separated in the separator into a gas-vapor mixture and a heavy residue - sludge. Liquid products (oil, water) and gas are separated from the first stream, which, after separation of saturated hydrocarbons (C1-C4), NH3, H2S, CO2 and CO, H2O, is enriched with 95-97% H2 and returned to the process. Sludge is divided into liquid products and solid residue. Liquid products after separation of water are subjected to distillation into a fraction with a boiling point up to 325-400 ° C and the residue, which is returned to the process for preparing a paste.
Due to the complex structure of WMD, the different reactivity of its fragments, the final liquid products contain many components, mainly mono- and bicyclic aromatic and heterocyclic compounds with impurities of paraffinic and naphthenic hydrocarbons, as well as phenols, pyridine bases, and other substances that can be isolated .
, lubricating oils, paraffins, phenols, etc. In the 40s. the production of liquid products from coal exceeded 4 million tons / year. In the 50s. hydrogenation of coal was mastered in the industrial. scale in the USSR.
In the 50s. rich oil deposits have been discovered in the USSR, the Middle East, and other regions of the world. The production of synthetic liquid fuels from coal has practically ceased. its cost was 5-7 times higher than the cost of motor fuel obtained from oil. In the 70s. the price of oil has risen sharply. In addition, it became obvious that with the current scale of oil consumption (~ 3 billion tons / year), its reserves, suitable for extraction by economical methods, will be depleted in the beginning. 21st century The Problem of Involving Solid Fuels, ch. arr. coal, in processing to obtain liquid oil substitute products has become relevant again.
The degree of conversion of WMD increases with the introduction of org. additives-compounds capable of interacting. with coal and its degradation products (y-picoline, quinoline, anthracene, etc.). Additives also temporarily stabilize reactive radicals formed during the primary destruction of coal, etc. arr. prevent the formation of condensation by-products.
Hydrogenation is carried out in three or four successively arranged cylindrical. hollow reactors. The duration of coal hydrogenation, as a rule, is determined by the volumetric rate of supply of coal-oil paste to the reaction. system. This speed depends on the type of coal, paste-forming agent, catalyst, t-ry and process pressure. The optimal volumetric velocity is selected empirically and is usually 0.8-1.4 tons per 1m 3 reaction. volume per hour (processes with a higher volumetric rate are being developed).
The reaction products are separated in the separator into a gas-vapor mixture and a heavy residue - sludge. Liquid products are separated from the first stream (
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