RU2325949C2 - Catalyst and method of purifying effluent gases - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: principle refers to catalyst and method of complex purification of waste gases of different production, heat and power utilities, automobile transport, which works on natural gas (methane). Described is a method of complex purification of effluent gases from nitrogen oxides, carbon oxide and hydrocarbons and it involves passing the effluent gases at temperatures 455-600°C through a layer of mechanical mixture of nickel chromium oxide industrial catalyst a copper zink nickel industrial catalyst in a volume composition of 1:1 to 20:1 respectively. To the effluent gases, methane up to a volume composition of CH₄/O₂ 0.07-0.15 can be added before passing it through the catalyst layer. Nickel chromium oxide industrial catalyst contains NiO 38-42 %; ZnO 28-32 %; NiO 4-6 % and not less than Al₂O₃ 17 % masses.

EFFECT: increasing of the purifying index of effluent gases.

3 cl, 4 ex

Description

The invention relates to catalysts and methods for the comprehensive purification of gas emissions from various industries, thermal power plants and motor vehicles operating on natural gas (methane). Waste gases from these plants usually contain nitrogen oxides, carbon monoxide and residual amounts of unburned hydrocarbons, which are harmful and polluting the atmosphere. Purification from such impurities is carried out by their catalytic reduction (nitrogen oxides) and oxidation (carbon monoxide and hydrocarbons).

It is known that the most effective in the process of complex purification of exhaust gases from toxic components are catalysts based on platinum group metals [Granger P., Lecomte JJ, Dathy C. et al // J. Catal. 1998, V.175, N2, P. 194.] However, the disadvantages of these catalysts are their scarcity and high cost.

A known catalyst, which is a copper-nickel alloy from the moneli family, consisting of 66% Ni; 31.5% Cu; 0.9% Mn; 1.35% Fe; 0.12% C; 0.005% S; 0.15% Si [US Patent No. 3565574, 1971]. The use of this catalyst allows the purification of exhaust gases from oxides of nitrogen and carbon, as well as hydrocarbons. But the specified catalyst only works efficiently at sufficiently high temperatures (above 400 ° C).

It is also known to use nickel-chromium granular catalyst for the purification of exhaust gases from nitrogen oxides, which showed high catalytic activity at a temperature of 450 ° C and with a ratio of CH ₄ / O _{2 of} 0.5 [Tikhonenko A.D. and other Uzbek chemical journal, 1970, N4, p.6-8.]. The disadvantages of this catalyst include the necessity of introducing an excess of a reducing agent (natural gas or hydrogen) into the gas to be purified and carrying out the process only at high temperature.

In the patent of the Russian Federation No. 2050191, 1995, a catalyst used for cleaning exhaust gases from a mixture of an iron-chromium industrial catalyst of the STK brand and copper-zinc-nickel industrial catalyst NTK-10-1, taken in a volume ratio of 0.5-5.0: 1, is described . The operating temperature for such a catalyst does not exceed 400 ° C, while the temperature of the exhaust gases can be significantly higher (500-550 ° C and even more). In addition, this catalyst was not used for the purification of exhaust gases from carbon monoxide.

The closest to the proposed catalyst in technical essence and the result obtained is the industrial catalyst NTK-1, used to reduce nitrogen oxides in the presence of CO [Nekrich EM and other chemical technology. 1974, N5, p. 38-39]. The composition of the catalyst includes oxides of Zn, Cr and Cu. The catalyst effectively (conversion rate of more than 80%) reduces NO _x at temperatures above 230 ° C. A close to 100% conversion of NOx is observed at temperatures above 275 ° C. The catalyst is also active in the presence of oxygen; however, a significant excess of a reducing agent, carbon monoxide, should be added to the gas mixture.

A disadvantage of the known catalyst is its low activity at low temperatures and non-selectivity in the presence of oxygen.

The aim of the invention is to provide a catalyst for the comprehensive purification of gases from oxides of nitrogen and carbon, which has high activity and selectivity in a wide temperature range.

The present invention allows for the purification of oxygen-containing gases from nitrogen oxides by reducing them with hydrocarbons in one stage on a cheap, affordable catalyst with high efficiency. For this, the gas to be purified along with the reducing agent is passed through the catalyst bed at an elevated temperature. In the cleaning process, a multicomponent oxide catalyst is used, which is a mechanical mixture of industrial nickel chromium oxide and copper-zinc-nickel catalysts taken in a ratio of 1: 1 to 20: 1, respectively.

Nickel-chromium oxide catalyst (OST 6-03-314-75) was used as a pre-contact in hydrogenation columns. It contains NiO (≥48 wt.%) And Cr ₂ O ₃ (≥27 wt.%). The copper-zinc-nickel oxide catalyst NTK-10-1 was used in the production of butyl alcohols. Its composition includes CuO (38-42 wt.%), ZnO (28-32 wt.%) NiO (4-6 wt.%) And Al ₂ О ₃ (≥17 wt.%).

In accordance with the invention, off-gases at a temperature of 350-600 ° C. are passed through a bed of a mechanical mixture of a nickel-chromoxide industrial catalyst and a copper-zinc-nickel oxide industrial catalyst, taken in a weight ratio of 1: 1 to 20: 1, respectively. When the content of CO and hydrocarbons in the exhaust gases is not sufficient to reduce nitrogen oxides, fuel gas, methane, is added to the exhaust gases before passing through the catalyst bed to a volume ratio of CH ₄ / O _{2 of} 0.07-0.15.

According to the proposed method, on the specified catalyst in a one-step purification process, it is possible to achieve a 90% conversion of nitrogen oxides when they are contained in the gas to be purified in an amount of 0.025-0.14 vol.% In the presence of significant amounts of oxygen (up to 10 vol.%) In the temperature range 400-550 ° C. The optimal ratio is CH ₄ / O ₂ 0.07-0.15.

The proposed catalyst has high activity and selectivity.

The invention is illustrated by the following examples:

Example 1. Nickel-chromium oxide catalysts (hereinafter referred to as Ni-Cr) and NTK-10-1 were taken in a ratio of 10: 1 (10 cm ³ Ni-Cr and 1 cm ³ NTK-10-1) and mixed in a container of the appropriate volume until the granules were uniformly distributed . The resulting mechanical mixture was placed in a catalytic reactor. The gas composition at the inlet of the reactor corresponded to the composition of the exhaust gases of the gas piston unit for power plants (in vol.%: О ₂ - 8.10; N ₂ - 91.57; СН ₄ - 0.25; СО - 0.05; NO _x - 0.03.).

At a volumetric gas flow rate of 10 thousand hours ^-1, a temperature of 550 ° C and a ratio of CH _4/02 = 0,03, NOx conversion was 85%, and CO - practically 100%.

Example 2. Used a catalyst from a mixture of Ni-Cr and NTK-10-1, taken in the ratio 1: 1. The composition of the gas at the entrance to the catalytic reactor, vol.%: O ₂ - 8.00; N ₂ - 91.25; CH ₄ - 0.67; СО - 0.05; NO _x - 0.03 (with additional methane). The volumetric gas flow rate of 12.5 thousand hours ^-1 , temperature 540 ° C, CH ₄ / O ₂ 0,08. The conversion of NO _x was 87%, СО - almost 100%.

Example 3. Used a catalyst with a ratio of Ni-Cr and NTK-10-1, equal to 2: 1. The composition of the gas at the entrance to the catalytic reactor, vol.%: O ₂ - 7.95; N ₂ - 91.17; CH ₄ - 0.73; СО - 0.05; NO _x - 0.03 (with additional methane). The volumetric rate of the gas stream is 14 thousand hours ^-1 , temperature 525 ° C, CH ₄ / O ₂ 0,09. The conversion of NO _x is 85%, CO is almost 100%.

Example 4. Used a catalyst with a ratio of Ni-Cr and NTK-10-1, equal to 2: 1. The composition of the gas at the inlet to the catalytic reactor, vol.%: O ₂ - 7.90; N ₂ - 91.17; CH ₄ - 0.85; СО - 0.05; NO _x - 0.03 (with additional methane). The volumetric gas flow rate of 18 thousand hours ^-1 temperature 550 ° C, CH ₄ / O ₂ 0,11. The conversion of NO _x is 90%, CO is almost 100%.

Claims (3)

1. The method of complex purification of exhaust gases from nitrogen oxides, carbon monoxide and hydrocarbons, comprising passing the exhaust gases at a temperature of 455-600 ° C through a layer of a mechanical mixture of a nickel-chromoxide industrial catalyst and a copper-zinc-nickel oxide industrial catalyst, taken in a volume ratio of 1: 1 to 20: 1, respectively. 2. The method according to claim 1, characterized in that the nickel-chromium oxide industrial catalyst contains NiO in an amount of not less than 48 wt.% And Cr ₂ O ₃ in an amount of not less than 27 wt.%, And the copper-zinc-nickel oxide industrial catalyst contains CuO 38-42 wt.%; ZnO 28-32 wt.%; NiO 4-6 wt.% And Al ₂ About ₃ not less than 17 wt.%. 3. The method according to claim 1, characterized in that methane is added to the exhaust gases before passing through the catalyst bed to a volume ratio of CH ₄ / O _{2 of} 0.07-0.15.