WO2020082197A1

WO2020082197A1 - Catalyst for treatment of coal-based ethylene glycol tail gas and preparation thereof

Info

Publication number: WO2020082197A1
Application number: PCT/CN2018/111134
Authority: WO
Inventors: Bichao LIANG
Original assignee: Pujing Chemical Industry Co., Ltd
Priority date: 2018-10-22
Filing date: 2018-10-22
Publication date: 2020-04-30
Also published as: RU2709811C1; AU2018446394A1

Abstract

A catalyst for treating a coal-based ethylene glycol tail gas is provided. The catalyst comprises an active component, an auxiliary agent, and a carrier. The active component comprises one or more active component elements selected from the group consisting of Cu, Pd, Pt, an oxide thereof, and a combination thereof. The auxiliary agent comprises one or more auxiliary agent elements selected from the group consisting of sixth periodic transition metals other than Group VIII, rare earth elements, an oxide thereof, and a combination thereof. The carrier is aluminum oxide. Also provided are the preparation and uses of the catalyst.

Description

CATALYST FOR TREATMENT OF COAL-BASED ETHYLENE GLYCOL TAIL GAS AND PREPARATION THEREOF

FIELD OF THE INVENTION

The invention relates to a catalyst for treating a coal-based ethylene glycol tail gas.

BACKGROUND OF THE INVENTION

Ethylene glycol is an important chemical raw material as well as a strategic material for manufacture ofpolyester, which can be used to produce Polyester fiber, beverage bottles, films, explosives and glyoxal. It can be used an antifreeze, plasticizer, hydraulic fluid, and solvent, etc. "Coal-based ethylene glycol" is ethylene glycol produced in a route via an oxalic ester using coal instead of ethylene in petroleum. Experts have pointed out that such a technical production route isin line with the characteristics of the Chinese resources such as lack of oil, scarce of gas, and relatively abundant coal.

At present, the coal-to-ethylene glycol route is mainly used for the oxalic ester method in China. Due to side reactions and the gas impurity brought in by the raw material gas, some inert components in the circulating gas are continuously accumulated so that a part of such gas is discharged as a tail gas from the industrial production equipment. Direct discharge will cause serious environmental pollution due to the large amounts of nitrogen oxides (NO _x) and methyl nitrite (MN) in the tail gas. MN is not only a flammable and explosive gas, but also has strong toxicity. After inhalation, MN can form methemoglobin with red blood cells in the blood so that the red blood cells lose the ability to carry oxygen. The mechanism of its toxicity is similar to that of carbon monoxide, but its toxicity is much greater than carbon monoxide. Therefore, it is necessary to treat the tail gas by lowering theNO _x concentration to meet the environmental standard, and lowering MN concentration by converting MNbefore the discharge.

Although originaldenitration catalysts are currently available on the market, such originaldenitration catalysts are not suitable due to the particularity of the composition of the coal-based ethylene glycol tail gas. First, the NO _x concentration in the tail gas is high, and its concentration is about 3-20%, which is higher than the NO _x concentration in an ordinary tail gas. Second, the composition of a coal-based ethylene glycol tail gas is complicated. In addition to NO _x, it contains a relatively high concentration of MN, carbon monoxide (CO) , methane, methanol vapor, etc. In particular, the MN concentration reaches about 16%. The use of ordinary denitration catalysts in the treatment of a coal-based ethylene glycol tail gas would cause problems such as excessive NO _x emissions, ashort catalyst life, and incomplete conversion of MN. Therefore, there remains a need for a catalyst suitable for treatment of a coal-based ethylene glycol tail gas to meet the emission standards for tail gas discharge, successful production of ethylene glycol and great industrial applications.

SUMMARY OF THE INVENTION

The present invention provides a catalyst and its preparation and uses.

A catalyst for treating a coal-based ethylene glycol tail gas is provided. The catalyst comprises an active component, an auxiliary agent, and a carrier. The active component comprises one or more active component elements selected from the group consisting of Cu, Pd, Pt, an oxide thereof, and a combination thereof. The auxiliary agent comprises one or more auxiliary agent elements selected from the group consisting of sixth periodic transition metals other than Group VIII, rare earth elements, an oxide thereof, and a combination thereof. The carrier is aluminum oxide.

The catalyst may comprise the active component at 0.01-5.0 wt. The active component may be prepared from an active component precursor selected from the group consisting of a sulfate, a nitrate and a chloride.

The catalyst may comprise the auxiliary agent at 0.1-2.0 wt%. The auxiliary agent may be prepared from a precursor selected from the group consisting of a sulfate, a nitrate and a chloride. The sixth periodic transition metals other than Group VIII may be selected from the group consisting of La, Pr, Sm, Eu, Hf, Ta, W, Re and a combination thereof.

The catalyst may have a molar ratio of one or more active component elements to the one or more auxiliary agent elements at 0.005-500.

A process for preparing the catalyst of the invention is also provided. The process comprises impregnating the carrier in an impregnation solution, which comprises the active component and the auxiliary agent, to form a mixture, and calcining the mixture. As a result, the catalyst is prepared. The mixture may be calcined at 200-1000℃. The impregnation solution may have a pH of 0-7. The process may further comprise drying the mixture before calcining.

A catalyst prepared according to the process of the present invention is provided.

A method for treating a coal-based ethylene glycol tail gas is further provided. The method comprises exposing a coal-based ethylene glycol tail gas to an effective amount of the catalyst of this invention. The tail gas comprises nitrogen oxides and methyl nitrite. Theexposure may be performed in the presence of a reducing gas. The reducing gas may be selected from the group consisting of carbon monoxide, hydrogen and a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows NO _x concentrations in a coal-based ethylene glycol treated with a catalyst having active component loading at (A) 0.05 wt%, (B) 0.1 wt%or (C) 0.5 wt%over time.

FIG. 2 shows MN concentrations in a coal-based ethylene glycol tail gas treated with a catalyst having active component loading at (A) 0.05 wt%, (B) 0.1 wt%or (C) 0.5 wt%over time.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a catalyst for treating a coal-based ethylene glycol tail gas and its preparation and uses. The catalyst comprises an active component, an auxiliary agent and a carrier. The inventors have unexpected discovered synergy between the active component and the auxiliary agent and synergy among the active component, the auxiliary agent and the carrier, which synergies promote catalytic activity and stability of the catalyst. When used in the treatment of a coal-based ethylene glycol tail gas, the catalyst of this invention can reduce the high concentration of NO _x in the tail gas to a level below 100mg/L, which meets environmental emission standards. It can also reduce the high concentration of methyl nitrite in the tail gas to a level below 10 mg/L. Further, the catalyst can remain highly active with a long catalyst life suitable for long-term use.

A catalyst for treating a coal-based ethylene glycol tail gas is provided. The catalyst comprises an active component, an auxiliary agent and a carrier. In one embodiment, the catalyst consists of the active component, the auxiliary agent and the carrier.

The term “tail gas” used herein refers to a gas discharged into the atmosphere from a chemical process that generates the gas. A coal-based ethylene glycol tail gas is the tail gas that is generated from the production of ethylene glycol using coal and is discharged into the atmosphere. The coal-based ethylene glycol tail gas maycomprise nitrogen oxides (NO _x) and methyl nitrite (MN) .

The term “feed gas” used herein refers to a gas that is introduced into a chemical process. The feed gas may react with other substances in the chemical process. The feed gas used in the production of ethylene glycol using coal may comprise nitrogen monoxide (NO) , carbon monoxide (CO) , methyl nitrite (MN) and nitrogen (N ₂) .

The term “loading” used herein refers to the amount of one substance in a catalyst. An active component loading [活性组分负载量] refers to the relative weight percentage (wt%) of an active component in a catalyst. An auxiliary agent loading refers to the relative weight percentage (wt%) of an auxiliary agent in a catalyst.

The term “active component” used herein refers to a substance in the catalyst that promotes reduction of nitrogen oxides (NO _x) and methyl nitrite (MN) in a coal-based ethylene glycol tail gas.The active component comprises one or more active component elements. Each active component element is selected from the group consisting of Cu, Pd and Pt. The active component may comprise an oxide of an active component element, for example, Cu, Pd and Pt, or a combination thereof. The active component loadingmay be about 0.01-5.0 wt%, preferably about 0.03-1.5 wt%, more preferably about 0.05-0.1 wt%.

The term “active component precursor” used herein refers to a substance that provides the active component in the catalyst. The active component precursor may be a sulfate, a nitrate or a chloride.

The term “auxiliary agent” used herein refers to a substance in a catalyst that promotes the interaction between an active component and a carrier in the catalyst, or that interacts synergistically with an active component.The auxiliary agent comprisesone or more auxiliary agent elements. Each auxiliary agent element is selected from the group consisting of sixth periodic transition metals other than Group VIII, rare earth elementsand an oxide thereof. Each sixth periodic transition metal other than Group VIII may be selected from the group consisting of La, Pr, Sm, Eu, Hf, Ta, W and Re. The auxiliary agent element may be selected from the group consisting of La, Pr, Sm, Eu, Hf, Ta, W and Re.The auxiliary agent loading may be about 0.1-2.0 wt%, preferably about 0.02-1 wt%, more preferably about 0.05-0.1%.

The term “auxiliary agent precursor” used herein refers to a substance that provides the auxiliary agent in the catalyst. The auxiliary agent element may be sulfate, a nitrate or a chloride.

The catalyst may have a molar ratio of the active component element(s) to the auxiliary agent element(s) in the range of about 0.005-500, preferably about 0.1-50, more preferably about 0.5-2.

The term “carrier” used herein refers to a substance in the catalyst that provides support for an active component and an auxiliary agent. The carrier is aluminum oxide.

The term “catalyst life” used herein refers to the period of time during which a catalyst remains highly active, for example, at least about 80%, 90%, 95%, 99%or 100%active, in promoting reduction of NO _x concentration and/or MN concentration in a coal-based ethylene glycol tail gas.

For each catalyst of the present invention, aprocess for preparing the catalyst is provided. The process may comprise loading an active component onto a carrier by dissolution and impregnation.

In the process of dissolution, an impregnation solution may be prepared by dissolving an active component and/or an auxiliary agent in water, an organic solvent or an acidic solution. An impregnation solution comprising an active component may be prepared by dissolving the active component in water, an organic solvent or an acidic solution. An impregnation solution comprising an auxiliary agent may be prepared by dissolving the auxiliary agent in water, an organic solvent or an acidic solution. An impregnation solution comprising an active component and an auxiliary agent may be prepared by dissolving the active component and the auxiliary agent in water, an organic solvent or an acidic solution, either simultaneously or in sequence. The impregnation solution comprising an active component and an auxiliary agent may have a molar ratio of the active component element (s) to the auxiliary agent element (s) in the range of about 0.005-500, preferably about 0.1-50, more preferably about 0.5-2, for example, about 1: 1. The impregnation solution comprising an active component and an auxiliary agent may be adjusted by, for example, nitric acid, to a pH of about 0-7, preferably 2-3.

In the process of impregnation, an active component and an auxiliary agent may be loaded onto a carrier, either simultaneously or in sequence, by impregnating the carrier with an impregnating solution comprising the active ingredient and/or the auxiliary agent. The impregnation may be equal volume impregnationor excess impregnation. The term “equal volume impregnation” used herein refers to an impregnation method in which an impregnating solution is used to impregnate a carrier in an amount equal to the absorption capacity of the carrier. Theterm “excess impregnation” used herein refers to an impregnation method in which an impregnating solution is used to impregnate a carrier in an amount greater than the absorption capacity of the carrier. Equal volume impregnation is preferred because it make it easy to control the loading of the active component and/or the auxiliary agent.

After impregnation of the carrier with the active component and the auxiliary agent, the impregnated carrier may be dried and then calcined, or directly calcined to obtain a catalyst. It is preferred to calcine after drying. Thecalcination temperature may be about 200-1000 ℃, preferably about 400-600 ℃.

In one embodiment, the impregnation solutionis prepared by dissolving platinum nitrate and tantalic chloridewater at a desirable molar ratio, for example, 1: 1 and adjusted to a pH of 1.5-2.5, for example, a pH of 2, with nitric acid. The aluminum oxide was impregnated in the impregnation solution such that the surface of the aluminum oxide was evenly covered by the impregnation solution before the impregnated aluminum oxide is dried, for example, at 120 ℃ for 5 hours, and then calcined, for example, at 500 ℃ for 3 hours. As a result, the catalyst is obtained.

A method for treating a coal-based ethylene glycol tail gas. The treatment method comprises exposing a coal-based ethylene glycol tail gas to a catalyst of this invention under a reducing condition. The concentrations of nitrogen oxides (NO _x) and methyl nitrite (MN) in the tail gas are reduced after the treatment.

To achieve a reducing condition, a reducing gas may be used. The reducing gas may comprise carbon monoxide (CO) , hydrogen (H ₂) , or a combination thereof. The CO gas may come from the untreated tail gas or be brought in externally. An effective amount of the reducing gas may be introduced to the treatment reaction tomaximize conversion of NO _x and lowering the NO _xconcentration to a level below 100mg/Lin the treated tail gas, and to maximize conversion of MN and lowering the MN concentration to a level below 10 mg/L in the treated tail gas.

Nitrogen oxides (NO _x) may include various substances such as nitrous oxide (N ₂O) , nitrogen monoxide (NO) , nitrogen dioxide (NO ₂) , dinitrogen trioxide(N ₂O ₃) , dinitrogen tetroxide (N ₂O ₄) and nitrogen pentoxide (N ₂O ₅) and the like.

The treatment method may be carried out in a fixed bed reactor (固定床反应器) at a temperature of about 50-400 ℃, preferably about 100-350 ℃,more preferably about 150-300 ℃, and under a pressure of about 0-10 barG, preferably about 0-3 barG.

The treatment may be performed in the presence of a reducing gas. The reducing gas may be CO, H ₂ or a combination thereof. The reducing gas may have a space velocity of about 100-10000 h ^-1, preferably about 300-3000 h ^-1, more preferably 500-1500 h ^-1.

After treatment according to this invention, the treated tail gas may comprisethe NO _xat a concentration below 100 mg/L and the MN at a concentration below 10 mg/L.

The catalyst of the present invention has a long catalyst life. During the treatment of a coal-based ethylene glycol tail gas, the catalyst may remain highly active for a long period. For example, the catalyst may remain at least about 80%, 90%, 95%, 99%or 100%active for a predetermined period, for example, for about 500, 10,000, 15,000, 20,000, 25,000 or 30,000 hours. The catalyst may have a catalyst life of at least about 500, 10,000, 15,000, 20,000, 25,000 or 30,000 hours.

The term “about” as used herein when referring to a measurable value such as an amount, a percentage, and the like, is meant to encompass variations of ±20%or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1%from the specified value, as such variations are appropriate.

Example 1. Effects of active component loading

In preparation of a catalyst, Pt, Ta and aluminum oxidewere used as an active component, an auxiliary agent, and a carrier, respectively, with a molar ratio of the active component to the auxiliary agent at 1: 1 and a total active Pt loading at 0.1 wt%. Animpregnationsolution was prepared with platinum nitrate and tantalum chloridea molar ratio of 1: 1 and adjusted to have a pH of 2 with nitric acid. The aluminum oxide was impregnated in the impregnation solution such that the surface of the aluminum oxide was covered evenly by the mixture solution before being dried at 120 ℃ for 5 hoursand then calcined at 500 ℃ for 3 hours. As a result, the catalyst was obtained.

Different catalysts were prepared for treating a coal-based ethylene glycol tail gas and evaluated for the effects of the active component loading on the concentrations of nitrogen oxides (NO _x) and methyl nitrite (MN) in the treated tail gas. The evaluation was carried out in a treatment reactor for no less than 240 hours.

The following equipment and process conditions were used in the evaluation: a fixed bed reactor having an inner diameter of 28 mm, a height of 2, 500mm, an internal catalyst volume of 300ml, acatalyst size of 3-5mm and catalyst loading in a constant temperature zone in the middle of the reactor; a normal pressure at 101.25kPa; a gas space velocity of 4000 h ^-1; a reaction temperature of 150 ℃; and a feed gas. The impact of the active component loading on the concentrations of NO _x and MN in the tail gas was evaluated. The composition of the feed gas or the tail gas was analyzed by gas chromatography. Table 1 shows the composition of the feed gas. Table 2 shows the active component loading, the molar ratio of the active component element to the auxiliary agent element, and the concentrations of NO _x and MN in the treated tail gas.

Table 1. Composition of feed gas

Component	NO	CO	MN	N ₂
Content (%)	12.0	20.0	6.0	62.0

Table 2. Effect of active component loading

As shown in Table 2, as the active component loading increased, the NO _x concentrationin the tail gas gradually decreased. When the active component loading was 0.01-5.0 wt%, the NO _x concentration in the treated tail gas was maintained below 100 mg/L. The preferred active component loading was 0.05-0.1%.

Example 2. Effect of active component composition

Different catalysts were prepared for treating a coal-based ethylene glycol tail gas and evaluated for the effects of the composition of their active components on the concentrations of NO _xand MN in the treated tail gas. The preparation and the evaluation of the catalysts were the same as those in Example 1 except the loading and the composition of the activity components. Table 3 shows the active component loading, the molar ratio of the ingredients of the active component, the concentrations of NO _x and MN in the treated tail gas.

Table 3. Effect of active component composition

As shown in Table 3, the bimetallic Catalysts 4 and 6 and the trimetallic Catalyst 6 showed excellent catalytic properties, especially the bimetallic or trimetallic catalysts containing element Cu.

Example 3. Effects of auxiliary agent loading and active component/auxiliary agent molar ratio

Different catalysts were prepared for treating a coal-based ethylene glycol tail gas and evaluated for the effects of the auxiliary agent loading and the molar ratios of the active component to the auxiliary agent on the concentrations of NO _x andMNs in the treated tail gas. The preparation and the evaluation of the catalysts were the same as those in Example 1 except the composition of the activity component and the auxiliary agent loading. Table 4 shows the active component loading, the auxiliary agent loading, the molar ratio of the active component elementto the auxiliary agent element, and the concentrations of NO _x and MN in the treated tail gas.

Table 4. Effect of auxiliary agent loading and ratio of active component to auxiliary agent

*Note: No auxiliary agent in Catalyst 1.

As shown in Table 4, addition of an auxiliary agent promotes conversion of NO _x and MN.The preferred auxiliary agent loading was 0.05-0.1 wt%of the total weight of the catalyst. The preferred active component element/auxiliary agent element molar ratio was 0.5-2.

Example 4. Effect of calcination temperature

Different catalysts were prepared for treating a coal-based ethylene glycol tail gas and evaluated for the effects of the calcination temperature used to prepare the catalysts on the concentrations of NO _x andMN in the treated tail gas. The preparation and the evaluation of the catalysts were the same as those in Example 1 except the calcination temperature and the active component loading at 0.1 wt%. Table 5 shows the calcination temperature and the concentrations of NO _x and MN in the treated tail gas.

Table 5. Effect of calcination temperature

No.	Calcination Temperature (℃)	NO _x (mg/L)	MN (mg/L)
1	150	577	1325
2	200	89	84
3	300	66	35
4	400	57	8
5	500	53	6
6	600	70	9
7	800	76	37
8	1000	98	95
9	1200	533	9567

As shown in Table 5, as calcination temperature increased, the concentrations of NO _x and MN dropped first and then went up. The preferred calcination temperature is 400-600℃.

Example 5. Effect of impregnation solution pH

Different catalysts were prepared for treating a coal-based ethylene glycol tail gas and evaluated for the effects of the pH of the impregnation solution used to prepare the catalysts on the concentrations of NO _x andMN in the treated tail gas. The preparation and the evaluation of the catalysts were the same as those in Example 1 except the pH of the impregnation solution. Table 6 shows the impregnation solution pH and the concentrations of NO _x and MN in the tail gas. The preferred pH is 2-3.

Table 6. Effect of impregnation solution pH

Example 6. Catalyst life

Different catalysts were prepared for treating a coal-based ethylene glycol tail gas and evaluated for their catalyticactivitiesover time and their effects on the concentrations of NO _x and MN in the treated tail gas. The preparation and the evaluation of the catalysts were the same as those in Example 1 except the active component loading. FIG. 1 shows the concentration of NO _x in the tail gastreated with a catalyst having active component loading at (A) 0.05 wt%, (B) 0.1 wt%or (C) 0.5 wt%. FIG. 2 shows the concentration of MN in the tail gastreated with a catalyst having active component loading at (A) 0.05 wt%, (B) 0.1 wt%or (C) 0.5 wt%. The catalysts showed extremely good stability and had a catalyst life greater than 25,000 hours.

Example 7. Comparison with commercially available catalyst

A catalyst prepared according to this invention was compared with a commercially available denitration catalyst. The preparation and the evaluation of the catalyst were the same as those in Example 1. The commercially available denitration catalyst (A) adopts V ₂O ₅-WO ₃ (MoO ₃) /TiO ₂series, that is, the catalyst prepared by using V ₂O ₅ as the main active component and TiO ₂ as the carrier, and WO ₃ and MoO ₃ as the ingredients of the auxiliary agent for antioxidation and antitoxicity. A comparative catalyst (B) was prepared as described in Example 1 except with 0.1 wt%Pt. The comparison results are shown in Table 6.

Table 7. Comparison with commercially available denitration catalyst

As shown in Table 6, the catalyst prepared according to this invention showed far superior activity and stability to the commercially available V ₂O ₅-WO ₃ (MoO ₃) /TiO ₂series denitration catalyst in treating a coal-based ethylene glycol tail gas.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims without departing from the invention.

Claims

A catalyst for treating a tail gas of a coal-based ethylene glycol tail gas, comprising:

(a) an active component comprising one or more active component elements selected from the group consisting of Cu, Pd, Pt, an oxide thereof, and a combination thereof;

(b) an auxiliary agent comprising one or more auxiliary agent elements selected from the group consisting of sixth periodic transition metals other than Group VIII, rare earth elements, an oxide thereof, and a combination thereof; and

(c) a carrier that is aluminum oxide.
The catalyst of claim 1, wherein the catalyst has an active component loading of 0.01-5.0 wt%.
The catalyst of claim 1, wherein the active component is prepared from an active component precursor selected from the group consisting of a sulfate, a nitrate and a chloride.
The catalyst of claim 1, wherein the catalyst has an auxiliary agent loading of 0.1-2.0 wt%.
The catalyst of claim 1, wherein the auxiliary agent is prepared from a precursor selected from the group consisting of a sulfate, a nitrate and a chloride.
The catalyst of claim 1, wherein the sixth periodic transition metals other than Group VIII areselected from the group consisting of La, Pr, Sm, Eu, Hf, Ta, W, Re and a combination thereof.
The catalyst of claim 1, wherein the molar ratio of the one or more active component elements to the one or more auxiliary agent elements is 0.005-500.
A process for preparing the catalyst of claim 1, comprising:

(a) impregnating the carrier in animpregnation solution comprising the active component and the auxiliary agent, whereby a mixture is formed;

(b) calcining the mixture, whereby the catalyst is prepared.
The process of claim 8, wherein the mixture is calcined at 200-1000 ℃.
The process of claim 8, wherein the impregnation solution has a pH of 0-7.
The process of claim 8, further comprising drying the mixture before calcining.
A catalyst prepared according to the process of any one of claims 8-11.
A method for treating a coal-based ethylene glycol tail gas, comprising exposing a coal-based ethylene glycol tail gas to an effective amount of the catalyst of claim 1, wherein the tail gas comprises nitrogen oxides and methyl nitrite.
The method of claim 13, wherein the exposure is performed in the presence of a reducing gas selected from the group consisting of carbon monoxide, hydrogen and a combination thereof.