RU2760125C1 - Method for purifying hydrocarbon gases from n2o - Google Patents

Abstract

FIELD: nitrous oxide purifying.

SUBSTANCE: invention is a method for purifying ethylene/propylene nitrous oxide or pyrolysis feedstock from ethane, propane, butane, WSLH, ethane-propane fraction (EPF) and other hydrocarbon fractions. A method for purifying hydrocarbon gases from N₂O is proposed, in which the stream of the gas to be purified is passed through a container filled with a catalyst, characterized in that the apparatus is filled with a copper-zinc catalyst containing 20 to 80% CuO by weight, and the rest is zinc oxide and alumina in as a binder, and the flow is passed at a temperature of 45 to 110°C, a pressure of 0.1 to 3.0 MPa, a space velocity of 500 to 5000 h^-1, at the same time, before starting the apparatus into operation, the catalyst is reduced with a nitrogen-hydrogen mixture to transfer copper from the oxidized form to the reduced one, and the hydrogenation process is not used in the purification process itself.

EFFECT: creation of a method for purification of hydrocarbon gases from N₂O on zinc-copper catalysts without the use of hydrogen and without loss of target products.

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Description

Technology area

The invention relates to the field of purification of gas mixtures and can be used in the extraction and processing of gas, in gas treatment plants and other industries that require a cleaner gas stream, in particular, the invention is a method of purification of ethylene / propylene nitrous oxide or pyrolysis feedstock from impurities : ethane, propane, butane, NGL, ethane-propane fraction (EPF) and other hydrocarbon fractions.

State of the art

The most common method for producing ethylene and propylene is pyrolysis - thermal cracking of hydrocarbon feedstock diluted with water vapor, which takes place in tube furnaces. The raw material for pyrolysis is natural raw materials - NGL, gasoline, ethane, LPG [Mukhina T.N., Pyrolysis of hydrocarbon raw materials / Mukhina T.N., Barabanov N.L., Babash S.Ye. and others // M .: Chemistry, 1987. - 240 p.]. Depending on the raw materials used, various trace impurities will be formed in commercial products, such as carbon monoxide, carbon dioxide, oxygen, nitrogen oxides, etc.

One of the impurities contained in the pyrolysis feedstock and, accordingly, product streams is nitrous oxide N ₂ O, which has the following negative effects:

• leads to clogging of operational equipment with solid particles, since nitrous oxide is prone to cryoprecipitation in a low-temperature block [Drobyshev A., Features of structural and phase transformations in solid nitrous oxide / Drobyshev A., Aldiyarov A., Korshikov E., Sokolov D., V. Kurnosov, // Low Temperature Physics, 2012, 1340 p.];

• when the temperature rises, it can decompose with a large release of energy and belongs to explosive compounds;

• is a catalytic poison for the polymerization of ethylene and propylene, as it is a strong oxidizing agent.

To avoid the negative effects of nitrous oxide, it is advisable to purify raw materials and / or pyrolysis products. There are known methods for purifying various streams from nitrous oxide, described in various publications.

Impurities of nitrogen oxides in dry catalytic cracking gas are purified by hydrogenation on a NiO catalyst, for example Olemax 100-series, or on a NiO-MoO catalyst PuriStar R8-21 (BASF). Removal of nitrogen oxides on a nickel catalyst Olemax 100-series, after thorough cleaning from hydrogen sulfide impurities, proceeds at a temperature of 190-232 ° C. At the outlet, the concentration of nitrogen oxides is no more than 0.01 ppm by volume. Nickel catalyst PuriStar R8-21 with an active complex based on CuO in an amount of 10-50%, supported on alumina or silicon oxide, is used at a high CO content in the stream. A special feature is that before the main reaction, it is necessary to carry out sulfiding with the formation of Cu ₂ S. Operating conditions are in the range of 150-275 ° C. As a result, nitrogen oxides and oxygen are converted by 99.7% [Churilin A.S., Methods of purification and separation of ethylene from dry gases of catalytic cracking / Churilin A.S., Zelentsova N.I., // Processing 49 - 50 p. ].

Of greatest interest are catalysts for the decomposition of nitrogen oxides Cu-ZSM 5 by the decomposition reaction:

A mixture containing N ₂ O, O ₂ , CO, NO was experimentally created and diluted with helium. Cobalt-based ZSM 5 catalysts showed increased thermal stability in tests, while Fe- and Cu-ZSM-5 are deactivated under hydrothermal conditions. However, Cu-ZSM-5 was more active than other catalysts of the group [Kapteijn F., Kinetic Analysis of the Decomposition of Nitrous Oxide over ZSM-5 Catalysts / Kapteijn F., Marban G., Rodriguez-Mirasol J., Moulijn J // Journal Of Catalysis 167, 1997, p. 256-265].

The following examples of developments can be cited as inventions similar to the problem being solved:

There is a method for catalytic purification of waste gases in the production of nitric and sulfuric acids, ammonium and sodium nitrate, given in the application SU 793933 A1, publication date 01/07/1981, which uses a non-platinum catalyst in the presence of ammonia. This method differs in that, in order to increase the degree of purification and reduce the consumption of ammonia, the volume ratio of ammonia to nitrogen oxides in the source gases is maintained equal to 0.7-1.5 and the purification is carried out on an alumina-vanadium-manganese catalyst supported on alumina at 350 ° C .The degree of purification of exhaust gases from nitrogen oxides reaches 98 - 100%. The disadvantage of this method is its impossibility of cleaning from N ₂ O.

The use of various zeolites also helps to get rid of unwanted nitrogen oxide impurities. The known method is described in the application ES 2693283 T3, publication date 10.12.2018, however, this method applies to cleaning air from N₂O, and the object of this invention is to purify ethylene and propylene streams. Low temperature air separation requires preliminary cleaning to remove high boiling components. Water, carbon dioxide and nitrous oxide must be removed. Conditions have been selected to reduce the concentration of water, carbon dioxide and nitrous oxide in the supplied air stream before cryogenic distillation. Passing through the first layer of adsorbent, CO is removed₂and H₂O, through the second - N₂O. Henry's constant for adsorption of N₂O measured at 30 ° C is less than 500 mmol / g / atm. Selectivity for CO₂ with respect to N₂O is not more than 5. The regeneration gas is then passed at a second pressure and a first temperature in the range of 140 to 220 ° C in the opposite direction to the supply direction, then the regeneration gas is passed at a second pressure and a second temperature lower than the first. It was assumed that N₂O can be removed well by CaX, however, CaX proved to be ineffective, so it was replaced with 13X zeolites (NaLSX), having a Si / Al ratio of at least 1.15.

The closest to the proposed invention is the method described by BASF in patent CA 2660334 A1, publication date 02/28/2008 (the closest analogue). This method consists in the removal of oxygen, nitrogen oxides, acetylenes and / or dienes from hydrogen-rich gas mixtures containing olefins obtained by pyrolysis. Removal of impurities is based on the contact in the reaction zone of a gas mixture containing mainly ethylene, propylene (about 60%) and a large excess of hydrogen, with a catalyst containing CuS on a carrier. The initial content of nitrogen oxides in the gas mixture ranged from 1 to 2000 ppm. The temperature in the reaction zone is in the range from 150 to 300 ° C, the pressure is from 5 to 40 bar. As a result of adsorption on this catalyst, 98% of interfering impurities, including catalytic poisons and nitrogen oxides, are removed.

The disadvantages of the proposed method are:

потери целевых продуктов за счет реакции гидрирования;

loss of target products due to the hydrogenation reaction;

необходимость подачи избытка водорода;

the need to supply excess hydrogen;

высокие температуры процесса.

high process temperatures.

List of drawings

Figure 1 shows a diagram of the purification of hydrocarbon gases from N ₂ O.

Disclosure of invention

Thus, the aim of the present invention is to overcome the disadvantages of known technical solutions and create a method for purifying hydrocarbon gases (ethylene, propylene, ethane, propane, NGL and other light hydrocarbon fractions) from N ₂ O on zinc-copper catalysts without using hydrogen and without losing the target products.

This goal is achieved by the fact that to purify hydrocarbon gases from N ₂ O, the stream is passed through a vessel filled with a copper-zinc catalyst containing from 20% to 80% CuO by weight (the rest is zinc oxide and aluminum oxide as a binder) at a temperature from 45 to 110 ° C, pressure from 0.1 to 3.0 MPa, space velocity from 500 to 5000 h ^-1 . In this case, before starting the apparatus into operation, the catalyst is reduced with a nitrogen-hydrogen mixture to transfer copper from an oxidized form to a reduced one. Removal of nitrous oxide occurs due to the reaction of decomposition of nitrous oxide into oxygen and nitrogen with an instantaneous reaction of oxygen with reduced copper, which can be represented by the resulting reaction:

The proposed catalyst, in fact, works as a chemisorbent.

At the same time, in other processes, removal occurs due to hydrogenation on a catalyst:

Thus, for the implementation of the proposed process does not require the supply of hydrogen, respectively, the hydrogenation of olefins does not occur, thereby eliminating the loss of target products and, accordingly, increases the yield of products obtained, facilitates the instrumentation of the process.

The stream is purified using at least two parallel connected devices (one in operation / the second in reserve or on regeneration) (Fig. 1). The catalyst is regenerated with a nitrogen-hydrogen mixture.

The range of the quantitative content of copper oxide 20-80 wt.% Is due to the following: the amount of copper oxide in the catalyst should be as large as possible, since the more copper oxide, the greater the catalyst capacity for the removed impurity, while for the manufacture of the catalyst, a binder is needed - aluminum oxide, zinc oxide. If copper oxide is less than 20%, the purification efficiency is sharply reduced, and if it is more than 80%, then it becomes difficult from a technological point of view to manufacture the catalyst, since the amount of binder is insufficient.

As for the temperature range from 45 to 110 ° C, at which the purification takes place, then at a temperature of less than 45 ° C, the reaction does not take place, and an increase in the temperature above 110 ° C is not advisable, since the activity of the catalyst no longer increases, but the energy consumption for reactor operation. At the same time, by increasing the temperature in the specified range, it is possible to increase the activity of the catalyst and its capacity, i.e. prolong the cycle of operation, as well as vary the activity of the catalyst depending on the content of nitrogen oxide in the gas mixture and the required degree of purification.

As for the reduced pressure range of 0.1 to 3.0 MPa, it is due to the creation of optimal conditions for the reaction inside the reactor without a significant increase in the temperature inside the reactor and loss of the catalyst reactivity, as well as without the risk of equipment failure.

With regard to the specified interval of the space velocity of 500-5000 h ^-1 , it is impractical to reduce the value below the specified minimum value, since this increases the volume of the catalyst, and with an increase in the value above, the probability of breakthrough increases maximally, i.e. passing the volume of the purified gas through the catalyst bed without trapping contaminants.

The time for passing the gas mixture is selected depending on the contamination of the gas and the required degree of purification and can range from several hours to hundreds of hours.

The reactor is a container apparatus with a fixed bed of a heterogeneous catalyst (tablets, balls, extrudates), consisting of at least two parallel connected apparatuses. The gas mixture is purified in one apparatus by passing the gas flow through the catalyst bed. In another apparatus, the spent catalyst is regenerated in parallel. After the regeneration, the gas stream is redirected to the apparatus with the regenerated catalyst, while in the other apparatus, respectively, the catalyst is regenerated. The number of apparatuses can be large, so gas purification can take place, for example, in two apparatuses, and catalyst regeneration can also take place in two apparatuses. It is also possible to use one apparatus, in which gas purification and catalyst regeneration are sequentially carried out, however, this implementation is accompanied by a significant downtime of equipment.

The catalyst is regenerated by passing and contacting the oxidized catalyst with a nitrogen-hydrogen mixture to transfer copper from the oxidized form to the reduced one. The nitrogen-hydrogen mixture has no decomposition products, it is used to reduce copper oxide to copper, while water is released. This happens during the regeneration of the catalyst (no cleaning is in progress). The regeneration gas (nitrogen-hydrogen mixture) after regeneration is essentially converted to nitrogen and discharged into the atmosphere (this is a standard procedure, it is known in the industry), as is the nitrogen formed in the reaction of copper with nitrogen oxide (N ₂ O).

There is no loss of by-products during the purification of gas mixtures due to the fact that the hydrogenation process is not used (no hydrogen is supplied during purification). In this case, if hydrogen were supplied, then the reactions of hydrogenation of ethylene to ethane or propylene to propane would take place, due to this, the target products - olefins - would be lost.

The proposed method was experimentally tested. The test results are shown below.

Implementation of the invention

The method was tested in an apparatus with a fixed bed of a heterogeneous catalyst in the form of pellets, consisting of two sealed reactors connected in parallel. The apparatus used for all tests was the same; its design did not change. All tests were carried out without the use of hydrogen for gas cleaning.

Example 1.

Ethylene at a temperature of 45 ° C and a pressure of 0.1 MPa g. passed through a catalyst bed containing at least 34 wt.% CuO (the rest is zinc oxide and aluminum oxide as a binder), with a space velocity of not more than 2740 h ^-1 for 55 hours. In this case, the concentration of N ₂ O at the inlet was 10 ppm vol., At the outlet - no more than 5 ppb vol.

Example 2.

Ethylene at a temperature of 110 ° C and a pressure of 3.0 MPa g. passed through a catalyst bed containing at least 55% of the mass. CuO (the rest is zinc oxide and aluminum oxide as a binder), with a space velocity of not more than 2740 h ^-1 for 67 hours. In this case, the concentration of N ₂ O at the inlet was 10 ppm vol., At the outlet - no more than 5 ppb vol.

Example 3.

Ethane-propane fraction at a temperature of 45 ° C and a pressure of 0.1 MPa g. passed through a catalyst bed containing at least 34 wt% CuO (the rest is zinc oxide and aluminum oxide as a binder) ^{at a space velocity of not more than 2740 h -1} for 51 hours. In this case, the concentration of N ² O at the inlet was 25 ppm vol., At the outlet - no more than 5 ppb vol.

Example 4.

Ethane-propane fraction at a temperature of 110 ° C and a pressure of 3.0 MPa g. passed through a catalyst bed containing at least 55% of the mass. CuO (the rest is zinc oxide and aluminum oxide as a binder), with a space velocity of not more than 4460 h ^-1 for 47 hours. In this case, the concentration of N ₂ O at the inlet was 25 ppm vol., At the outlet - no more than 5 ppb vol.

Example 5.

Ethane-propane fraction at a temperature of 110 ° C and a pressure of 3.0 MPa g. passed through a catalyst bed containing at least 55% of the mass. CuO (the rest is zinc oxide and aluminum oxide as a binder), with a volumetric velocity of not more than 2740 h ^-1 for 131 hours. In this case, the concentration of N ₂ O at the inlet was 25 ppm vol., At the outlet - no more than 5 ppb vol.

Below in table 1 for clarity, the results of gas purification according to examples 1-5 according to the claimed method are summarized, showing the effectiveness of the proposed method and the achievement of the technical result. For each example, the weight of the tested catalyst sample was 0.145 kg (volume 120 ml).

Table 1. Examples of cleaning hydrocarbon gases from N ₂ O No. Initial concentration of N ₂ O, ppm vol. Gas composition, except for N ₂ O CuO content,% wt. Volumetric velocity, h-1 Temperature, ° С Pressure, MPa g Duration, h Concentration of N ₂ O after purification, ppb vol. 1 ten 100% ethylene 34 2740 45 0.1 55 Less than 5 2 ten 100% ethylene 55 2740 110 3.0 67 Less than 5 3 25 Ethane-propane fraction 34 2740 45 0.1 51 Less than 5 4 25 Ethane-propane fraction 55 4460 110 3.0 47 Less than 5 5 25 Ethane-propane fraction 55 2740 110 3.0 131 Less than 5 * no losses of the gas to be cleaned during the implementation of the proposed method occurred

Claims (2)

1. A method for purifying hydrocarbon gases from N ₂ O, in which the stream of gas to be purified is passed through a vessel filled with a catalyst, characterized in that the apparatus is filled with a copper-zinc catalyst containing from 20 to 80% CuO by weight, and the rest is zinc oxide and aluminum oxide as a binder, and the flow is passed at a temperature of 45 to 110 ° C, a pressure of 0.1 to 3.0 MPa, a space velocity of 500 to 5000 h ^-1 , while the catalyst is reduced to nitrogen before the apparatus is put into operation - a hydrogen mixture to convert copper from an oxidized form to a reduced one, and the hydrogenation process is not used in the purification process itself. 2. A method according to claim 1, characterized in that the stream is purified using at least two parallel connected apparatuses, one of which is in operation, and the second is in reserve or for catalyst regeneration.

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