RU2760126C1 - Method for purification of saturated hydrocarbons from impurities - Google Patents

Abstract

FIELD: gas mixtures purification.SUBSTANCE: invention relates to the field of purification of gas mixtures and can be used in the extraction and processing of gas, at gas cleaning facilities and in other industries that require a cleaner gas flow. A method is proposed for purifying gas streams of saturated hydrocarbons from nitrogen oxides, including N2O, in which the stream of the purified gas is passed through a tank filled with a catalyst, before entering the reactor, hydrogen is supplied to the stream to be purified, while the apparatus is filled with a heterogeneous catalyst based on oxide aluminum with supported metals selected from the group: Pt, Pd, Pt/Pd and Ni, containing from 0.1 to 3% of active metal by weight, and the rest is aluminum oxide as a binder, and the flow is passed at a temperature of 150 to 280°C, a pressure of 1.5 to 3 , 0 MPa, space velocity from 500 to 3000 h-1, while before starting the apparatus into operation, the catalyst is reduced with a nitrogen-hydrogen or methane-hydrogen mixture.EFFECT: neutralization of the negative impact of nitrogen oxides on the technological scheme of the pyrolysis unit and further production.3 cl, 1 dwg, 1 tbl, 4 ex

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, at gas treatment facilities, oil and gas chemical plants and in other industries that require a cleaner gas flow, in particular, the invention is a method of purification from impurities of oxides nitrogen (including N2O) of raw material streams of pyrolysis production: ethane, propane, butane, NGL, ethane-propane fraction (EPF), other hydrocarbon fractions, including wet streams.

State of the art

The pyrolysis process, which is steam cracking of hydrocarbon feedstock in tube furnaces, is the most common method for producing olefins (ethylene and propylene) for further petrochemical processes. As a raw material for the process, gasoline, NGL (broad fraction of light hydrocarbons), ethane, LPG (liquefied hydrocarbon gases) can be used [Mukhina T.N., Pyrolysis of hydrocarbons / Mukhina T.N., Barabanov N.L., Babash S. E. and others // M .: Chemistry, 1987. - 240 p.].

Impurities of nitrogen oxides contained in the pyrolysis feedstock are partially converted in the steam cracking process itself, after which, during the gas separation of the pyrolysis gas, they are concentrated in the target streams (ethane-ethylene and propane-propylene fractions).

The greatest negative impact of nitrogenous impurities is possessed by nitrous oxide (N ₂ O), which belongs to explosive compounds and causes blockage of equipment with solid particles, since nitrous oxide is prone to cryoprecipitation in a low-temperature block [A. Drobyshev, Features of structural-phase transformations in solid nitrous oxide / Drobyshev A., Aldiyarov A., Korshikov E., Sokolov D., Kurnosov V., // Physics of low temperatures, 2012, 1340 pp.].

In addition, nitrous oxide enters the ethylene and propylene product streams directed to polymerization units, where it negatively affects the process and is a strong catalytic poison.

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

Thus, the removal of nitrogen oxides, oxygen and acetylenic compounds from catalytic cracking gases is carried out by hydrogenation on a NiO catalyst, for example, Olemax 100-series (SudChemie) or NiO-MoO catalyst PuriStar R8-21 (BASF). At process temperatures of 190-232 ° C, a partial pressure of hydrogen of 10 ⁵ -2⋅10 ⁵ Pa, NO _x is removed to a concentration of less than 0.01 ppm by volume. For gases with a high concentration of CO, it is recommended to use the catalyst R3-81 (BASF) with an active complex based on CuO. After primary reduction and sulfidation, this catalyst provides a _{99.7% NO x} conversion at a process temperature of 150-275 ° C and a pressure of 5⋅10 ⁵ -3.5⋅10 ⁶ Pa. [Churilin AS, Methods of purification and separation of ethylene from dry gases of catalytic cracking / Churilin AS, Zelentsova NI, // Processing 49 - 50 pp.].

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 is applied to the purification of air from N ₂ O, and the purpose of this invention is the purification of ethylene and propylene streams. Low temperature air separation requires preliminary cleaning to remove high boiling components. To remove water, carbon dioxide and nitrous oxide from air was applied load circuit in several layers, in which the first adsorbent layer removes CO ₂ and H ₂ O, the second - N ₂ O. It was assumed that the N ₂ O is removed well zeolite CaX However, CaX proved to be ineffective, so it was replaced by 13X zeolites (NaLSX) with 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. The 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 that contains 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:

- loss of target products due to the hydrogenation reaction;

- the need to supply excess hydrogen;

- high process temperatures.

In order to neutralize the negative impact of nitrogen oxides on the technological scheme of the pyrolysis unit and further production, for example, the production of polyethylene, it is most expedient to remove them by hydrogenation in pyrolysis feed streams.

List of drawings

FIG. 1 shows a diagram of the purification of hydrocarbon gases from nitrogen oxides.

Disclosure of invention

The aim of the present invention is to overcome the disadvantages known from the prior art technical solutions and to develop a method for purification of feed streams of saturated hydrocarbons, for example, pyrolysis feedstock, from impurities of nitrogen oxides (including N ₂ O).

This goal is achieved by the fact that for the purification of saturated hydrocarbon feedstock, in particular, pyrolysis feedstock, the gas stream is passed through a vertical apparatus filled with a fixed bed of a heterogeneous catalyst. Before entering the reactor, hydrogen is fed into the stream to be cleaned. When the flow passes through the catalyst bed, it is purified from impurities of nitrogen oxides as a result of the ongoing hydrogenation reactions (nitrogen oxides are reduced to molecular nitrogen or ammonia):

N ₂ O + H ₂ → N ₂ + H ₂ O

N ₂ O + 2.5 H ₂ → NH ₃ + H ₂ O

NO _x + x H ₂ → ½ N ₂ + xH ₂ O

NO _x + (x + 3/2 _{) H 2} → NH _{3 + xH 2} O

The process of purification from impurities of nitrogen oxides by hydrogenation proceeds at temperatures of 150-280 ° C, pressure from 1.5 to 3.0 MPa, space velocity from 500 to 3000 h ^-1 . Palladium (Pd), platinum (Pt) or mixed palladium-platinum systems (Pt / Pd) on an alumina-based support, or nickel hydrogenation catalysts (Ni) can be used as process catalysts. The catalyst contains from 0.1 to 3% of active metal by weight, and the rest is alumina as a binder. In this case, before starting the apparatus into operation, the catalyst is reduced with a nitrogen-hydrogen or methane-hydrogen mixture.

At the same time, an additional advantage of the proposed method is that it can also be used for cleaning wet gas streams (with an H2O content of up to 0.5% by volume), i.e. no pre-drying of the stream is required, which also makes it possible to simplify the method of cleaning gas streams, and also allows to reduce energy and financial costs.

The proposed method and its advantages will be described in more detail below.

Known technologies propose methods for purifying streams from a catalytic cracking unit, which contain olefins up to 30% and hydrogen up to 20%. Further, these streams can be involved in the pyrolysis unit, but not in the pyrolysis stage, but in the gas separation stage (after pyrolysis). We offer purification of the pyrolysis feedstock flow - ethane, propane, NGL and other fractions that contain only paraffins. The essence of the cleaning process is very similar. In the proposed process, hydrogenation is also carried out, only in the case of known methods for the purification of unsaturated streams, the main purpose of purification is selective hydrogenation, i.e. impurities should be hydrogenated and olefins should be minimally hydrogenated. In our technology, the issue of selective hydrogenation is not raised, impurities are hydrogenated, while paraffins cannot be hydrogenated, since they are saturated. Thus, the loss of the target products is eliminated and the process scheme is simplified: for example, in the selective hydrogenation of streams from the cracking cattle, it is necessary to dose sulfur in order to control the catalyst activity; in our case, no additional manipulations are required.

The composition of the purified stream with respect to hydrocarbons does not change, nitrogen oxides are converted into elemental nitrogen and partially into ammonia, according to the above reactions, then this stream, which does not contain impurities of nitrogen oxides, is already used for pyrolysis.

In this case, the resulting reaction products go further with the gas flow to pyrolysis and then to the gas separation scheme of the installation, given their low concentrations (ppm), they do not affect the scheme: nitrogen enters into methane during separation and then into fuel, ammonia is absorbed by water at the stage of water washing and is displayed along with the drains. In such quantities, they do not change the quality of the streams.

Thus, we are talking about a new method of purification of just streams of saturated hydrocarbons - pyrolysis feedstock in particular. The advantages of the proposed method include a low demand for hydrogen (only for the reaction with nitrogen oxides) and the absence of the problem of hydrogenation of olefins due to parallel reactions of hydrogenation of ethylene and propylene, since there are no olefins in this stream.

As process catalysts, palladium, platinum or mixed palladium-platinum systems on a support based on alumina, or nickel hydrogenation catalysts can be used. The catalyst is loaded into the hydrogenation reactor for the entire service life and is not regenerated during operation; the primary activation of the catalyst is performed with a nitrogen-hydrogen or methane-hydrogen mixture. The advantage of these catalysts is that they provide 100% purification at relatively low hydrogenation temperatures. The catalyst is not consumed, being a heterogeneous catalyst, the metals are supported on a carrier - alumina. The mechanism of action of the catalyst is assumed to be standard: adsorption of hydrogen and nitrogen oxides on the surface, reaction, desorption of products.

The range of the quantitative content of active metal is 0.1 to 3 wt. % is due to the following: the amount of metal in the catalyst should be large, since the more metal, the greater the activity of the catalyst with respect to the removed impurities, while for the manufacture of the catalyst you need a binder - aluminum oxide. If the metal is less than 0.1 wt. %, the cleaning efficiency sharply decreases, and if more than 3 wt. %, then the economic costs increase sharply due to the high cost of materials. In this case, the cleaning efficiency does not noticeably increase and 3 wt. % is quite enough to completely remove harmful impurities.

As for the temperature range of 150-280 ° C used for hydrogenation, at which the purification takes place, at a temperature of less than 150 ° C, the reaction slows down, and an increase in temperature above 280 ° C is not advisable, since the activity of the catalyst no longer increases, but energy costs increase for the operation of the reactor. 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 oxides in the gas mixture and the required degree of purification.

Regarding the reduced pressure range of 1.5 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 catalyst reactivity, as well as without the risk of equipment failure.

As for the specified interval of the space velocity from 500 to 3000 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 gas to be cleaned through the catalyst bed without removing impurities.

The reactor is a container apparatus with a fixed bed of a heterogeneous catalyst (tablets, beads, extrudates) (see Fig. 1). The gas mixture is purified in the apparatus by passing the gas flow through the catalyst bed.

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 2-4 mm balls. The apparatus used for all tests was the same; its design did not change.

Example 1.

A stream of ethane-propane fraction at a temperature of 180 ° C and a pressure of 2.5 MPa was passed through a catalyst bed containing 0.3% Pd on alumina ^{at a space velocity of 2000 h -1} for 21 hours. The concentration of N ₂ O at the inlet was 50 ppm, and at the outlet - 0.1 ppm. The concentration of NO, NO ₂ at the inlet was 50 ppm, at the outlet less than 0.1 ppm.

Example 2.

A stream of ethane-propane fraction at a temperature of 230 ° C and a pressure of 2.1 MPa was passed through a catalyst bed containing 0.5% Pt on alumina ^{at a space velocity of 1000 h -1} for 21 hours. The concentration of N ₂ O at the inlet was 50 ppm, and at the outlet - 0.1 ppm. The concentration of NO, NO ₂ at the inlet was 50 ppm, at the outlet less than 0.1 ppm.

Example 3.

A stream of ethane-propane fraction at a temperature of 280 ° C and a pressure of 1.9 MPa was passed through a layer of Ni catalyst containing 1.0% Ni on alumina ^{at a space velocity of 1000 h -1} for 20 hours. The concentration of N ₂ O at the inlet was 50 ppm, and at the outlet - 0.1 ppm. The concentration of NO, NO ₂ at the inlet was 50 ppm, at the outlet less than 0.1 ppm.

Example 4.

A stream of ethane-propane fraction at a temperature of 240 ° C and a pressure of 2.1 MPa was passed through a catalyst bed containing 0.25% Pt and 0.25% Pd on alumina ^{at a space velocity of 1000 h -1} for 20 hours. The concentration of N ₂ O at the inlet was 50 ppm, and at the outlet - 0.1 ppm. The concentration of NO, NO ₂ at the inlet was 50 ppm, at the outlet less than 0.1 ppm.

Below in table 1 for clarity, the results of gas purification according to examples 1-4 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). For each experiment, a model mixture was used containing 70% ethane and 30% propane, the rest being nitrogen oxides.

Table 1. Examples of cleaning hydrocarbon gases from N ₂ O, NO and NO ₂ .

No. Initial concentration of N ₂ O, ppm vol. Initial concentration ∑NOx, ppm vol. Metal content in the catalyst Volumetric velocity, h-1 Temperature, ° С Pressure, MPa g Hydrogen: ∑NOx ratio, mol: mol Concentration of N ₂ O after purification, ppm Concentration of ∑NOx after purification, ppm vol. 1 50 50 0.3% Pd 2000 180 2.5 10: 1 0.1 Less than 0.1 2 50 50 0.5% Pt 1000 230 2.1 10: 1 0.1 Less than 0.1 3 50 50 1.0% Ni 1000 280 1.9 10: 1 0.1 Less than 0.1 4 50 50 0.25% Pt and 0.25% Pd 1000 240 2.1 10: 1 0.1 Less than 0.1

The presented examples clearly show the effectiveness of the proposed method when cleaning gas streams of saturated hydrocarbons from nitrogen oxides, namely, from N ₂ O, NO and NO ₂ .

Claims (3)

1. A method of purification of gas streams of saturated hydrocarbons from nitrogen oxides, including N ₂ O, in which the stream of the gas to be purified is passed through a vessel filled with catalyst, while before entering the reactor, hydrogen is supplied to the stream to be purified, characterized in that the apparatus is filled with a heterogeneous catalyst based on alumina with supported metals selected from the group: Pt, Pd, Pt / Pd and Ni, containing from 0.1 to 3% of active metal by weight, and the rest is alumina as a binder, and the flow is passed at a temperature from 150 to 280 ° C, a pressure from 1.5 to 3.0 MPa, a space velocity from 500 to 3000 h ^-1 , while before starting the apparatus into operation, the catalyst is reduced with a nitrogen-hydrogen or methane-hydrogen mixture. 2. The method according to claim 1, characterized in that the gas stream of saturated hydrocarbons, the pyrolysis feedstock, is purified without hydrogenation of olefins. 3. The method according to p. 1 or 2, characterized in that the purification is carried out, including a wet gas stream with a H ₂ O content of up to 0.5% vol.

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