DESC:FIELD OF INVENTION

The present disclosure relates to an absorption formulation for the removal of acid gases from gaseous mixtures.

BACKGROUND

Glycol ethers are used for the separation of acid gases, such as CS2, H2S, SO2, COS, VoCs, etc, from gaseous mixtures using the principle of low temperature absorption and high temperature desorption. These glycol ethers are available in the market, for example with the name of GENOSORB. Glycol ethers of different grades undergo oxidation in the presence of air resulting in the formation of peroxides and other degraded compounds. stabilizers are used to arrest such oxidation. Amine based stabilizers like alkanolamines are generally utilized.

Conventional processes utilize absorption formulations comprising polyalkylene glycol alkyl ethers and alkanolamines as stabilizers at milder conditions (at low temperatures). It has been observed that alkanolamine based stabilizers lead to the formation of black carbon containing particle deposits at high temperatures on process equipment’s surfaces such as on heat exchanger plates etc. Due to such black particle deposition, there is a depletion of alkanolamines concentration. This requires frequent replenishment of the stabilizer to maintain the desired concentration.

Additionally, black particle deposition on the process equipment (hot surfaces of heat exchangers) causes scaling and/or choking, resulting in reduction in effective heat transfer area of heat exchangers and thus excessive consumption of steam and energy. The black particle deposition further causes increased pressure drop across the heat exchangers and hence increase in load on circulation pump which limits the absorption solvent circulation flow rate and eventually results in lower process efficiency. Such process equipment requires frequent cleaning to remove scaling/choking which results in loss of absorption solvent (glycol ether) and the cleaning agent associated with it. Also, frequent cleaning damages the gaskets and create isolation valve choking /passing problems which may require plant shut down for replacement.
Therefore, there is a need for an absorption formulation which prevents formation of black deposits on process equipment’s surfaces.

SUMMARY

An absorption formulation for removing acid gases from a gaseous mixture is disclosed. Said formulation comprises:

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)

where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3;
and

- from about 1 to 10% by weight of water.

A process for removing acid gases from a gaseous mixture is also disclosed. Said process comprises:

a. contacting said gaseous mixture with an absorption formulation in an absorption column, the absorption formulation comprising

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)

where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3;
and

- from about 1 to 10% by weight of water;

thereby obtaining a treated gas and an acid gases enriched- absorption formulation;

b. passing said acid gases enriched-absorption formulation to a desorption column comprising a stripping media to cause stripping of the acid gases from said acid gases enriched-absorption formulation, and obtain acid gases enriched-stripping media and regenerated absorption formulation;

c. passing said acid gases enriched-stripping media through a condenser to obtain acid gases therefrom; and

d. returning the regenerated absorption formulation into absorption column.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates a schematic representation of the process in accordance with an embodiment of the present invention.

DETAIL DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed composition, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

In its broadest scope, the present disclosure provides an absorption formulation for removal of acid gases from gaseous mixtures. In particular, the present disclosure relates to an absorption formulation for removal of acid gases from Sulphur-based gaseous mixtures. Said formulation comprises:

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)
where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3; and

- from about 1 to 10% by weight of water.

In accordance with an aspect, the stabilizer disclosed herein does not have an alkanolamine functionality. Such stabilizer prevents the formation of black particle deposits on the process equipment. It has been identified that utilization of conventional absorption formulations results in the formation of black particle deposits due to the presence of glycol ether, amine based stabilizer and sulphur. The stabilizer as per the present disclosure does not participate in side reactions which are responsible for the formation of black particle deposits on the process equipment. Further, such stabilizer is able to withstand high temperatures and can be reused in the process as it does not participate in the side reactions.

Stabilizers are used to avoid auto-oxidation of absorption solvent of different grades in the presence of air. Stabilizers reacts with free radicals present in the absorption solvent and results in depletion of its concentration. In accordance with an aspect, to avoid auto degradation and sustain absorption capacity, stabilizer is used in an amount from about 0.01 to 5% by weight of the absorption solvent. Preferably, stabilizer is used in an amount from about 0.05 to 1% by weight of the absorption solvent. The concentration of the stabilizer in the absorption formulation may be varied depending on the process requirements and operation duration.

In accordance with an embodiment, the stabilizer is selected from a group consisting of alkylated hydroxyl toluenes, alkylated p-cresols and alkylated hydroxyl anisoles and is preferably tertiary butylated hydroxyl toluene. Such stabilizers may be produced by any known process. Alternatively, said stabilizers may be obtained from commercial sources.

Methods for preparing alkyl ethers of polyethylene glycol suitable for use in accordance with the present invention are known to those skilled in art. Alternatively, said compounds are available from commercial sources. Appropriate absorption solvent for the particular process conditions, feed gaseous mixture components, and the like, can be determined by those skilled in the art.

In accordance with an aspect, a process for removing acid gases from a gaseous mixture is also disclosed. Said process comprises:

a. contacting said gaseous mixture with an absorption formulation in an absorption column, the absorption formulation comprising

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)
where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3; and

- from about 1 to 10% by weight of water;

thereby obtaining a treated gas and an acid gases enriched- absorption formulation;

b. passing said acid gases enriched-absorption formulation to a desorption column comprising a stripping media to cause stripping of the acid gases from said acid gases enriched-absorption formulation, and obtain acid gases enriched-stripping media and regenerated absorption formulation;

c. passing said acid gases enriched-stripping media through a condenser to obtain acid gases therefrom; and

d. returning the regenerated absorption formulation into absorption column.

In accordance with an embodiment, the ratio of absorption formulation and gaseous mixture may be varied in accordance with the desired results. Further, appropriate absorption solvent for the particular process conditions, feed gaseous mixture components, and the like, can be determined by those skilled in the art.

In accordance with an embodiment, the stripping media in the desorption column is selected from a group consisting of hot air, nitrogen and steam. In accordance with a preferred embodiment, steam at higher temperature is used as stripping media. In accordance with an alternate embodiment, if water is infinitely soluble with the absorption formulation, hot air or hot nitrogen are used as stripping media. In accordance with a related embodiment, the ratio of the acid gases enriched-absorption formulation and the stripping may be varied in accordance with the content of acid gases in the enriched-absorption formulation and can be determined by those skilled in the art.

In accordance with an embodiment, the absorption formulation fed to the absorption column i.e. lean absorption formulation is at a temperature ranging between 10 to 350C, and preferably at 250C. In accordance with a related embodiment, after absorbing acid gases in the absorption column, the acid gases enriched-absorption formulation is passed to the desorption column at an elevated temperature ranging between 110 to 1450C, and preferably at 1250C to strip the absorbed acid gas from absorption formulation. In accordance with an embodiment, intermediate heat exchangers (HE) are used to interchange heat between lean absorption formulation and the acid gases enriched-absorption formulation. A process in accordance with an embodiment of the present invention has been schematically represented in Figure 1. As shown in Figure 1, in cooler (14), chilled water at 5oC is used to cool the lean absorption formulation to about 25oC. Meanwhile, the acid gases enriched-absorption formulation is heated using steam in Heater (18) to 125oC before supplying to desorption column (12) to interchange heat between lean absorption formulation and the acid gases enriched-absorption formulation. A heat exchanger (16) has also been used to interchange heat between lean absorption formulation and the acid gases enriched-absorption formulation. Herein, a product gas stream which is at least partially depleted in the acid gases (Lean Flash gas) relative to the feed gaseous stream is discharged from absorption column (10).

The acid gases comprise one or more of CS2, H2S, SO2, COS and other Volatile Organic Compounds (VoCs). Essentially, any feed gaseous mixture containing said acid gases, also referred to as Flash gas, can be used in the process of the present invention. For example, the feed gaseous mixture may be produced during various industrial processes, such as during manufacturing of viscose fibers; from chemical plants, petroleum refineries, coal gasification plants and the like.

SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW

An absorption formulation for removing acid gases from a gaseous mixture, said formulation comprising:

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)
where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3; and

- from about 1 to 10% by weight of water.

Such an absorption formulation, wherein the stabilizer is selected from a group consisting of alkylated hydroxyl toluenes, alkylated p-cresols and alkylated hydroxyl anisoles.

Such an absorption formulation, wherein the stabilizer is tertiary butylated hydroxyl toluene.

A process for removing acid gases from a gaseous mixture, the process comprising:

a. contacting said gaseous mixture with an absorption formulation in an absorption column, the absorption formulation comprising

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)
where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3; and

- from about 1 to 10% by weight of water;

thereby obtaining a treated gas and an acid gases enriched- absorption formulation;

b. passing said acid gases enriched-absorption formulation to a desorption column comprising a stripping media to cause stripping of the acid gases from said acid gases enriched-absorption formulation, and obtain acid gases enriched-stripping media and regenerated absorption formulation;

c. passing said acid gases enriched-stripping media through a condenser to obtain acid gases therefrom; and

d. returning the regenerated absorption formulation into absorption column.

Such process, wherein the stripping media is selected from a group consisting of hot air, nitrogen and steam.

Such process, wherein the stabilizer is selected from a group consisting of alkylated hydroxyl toluenes, alkylated p-cresols, alkylated hydroxyl anisoles.

Such process, wherein the stabilizer is tertiary butylated hydroxyl toluene.

Such process, wherein the absorption formulation is fed to the absorption column at a temperature ranging between 10 to 350C.

Such process, wherein the acid gases enriched-absorption formulation is passed to the desorption column at an elevated temperature ranging between 110 to 1450C.

Such process, wherein the acid gases comprises one or more of CS2, H2S, SO2, COS and other Volatile Organic Compounds (VoCs).

EXAMPLES

The following examples are provided to explain and illustrate the invention and do not in any way limit the scope of the invention as described and claimed.

Comparative example 1

Diaryl-p-phenylene diamine (Wingstay – 100) was used as a stabilizer in the process for CS2 recovery using Polyethylene-glycol-dibutylether (PGDBE) (Genosorb – 1843; molar mass >270) as an absorption solvent. Absorption of H2S and or CS2 in PGDBE occurs at low temperatures (~25 – 30oC) in absorption column and desorption of CS2 from PGDBE occurs at higher temperatures (~120-140 oC) in desorption column using steam as stripping media.

Absorbed H2S in PGDBE oxidizes at higher temperatures and forms polysulfides and elemental Sulphur in the form of S8 molecules which accumulates in the PGDBE. Sulphur contaminated PGDBE along with Wingstay-100 results in black depositions at higher temperatures. This conclusion was reached by preparing the following solutions and exposing to thermal environment in air for 6 hours at varying levels of stabilizer and Sulphur, as illustrated in below Table 1.

Absorbent Temperature (oC) Stabilizer(Wingstay100)
Content (wt %) Sulphur content
(wt %) % wt black depositions
PGDBE 200 0.5 0.05 0.32
PGDBE 200 0.5 0.225 0.42
PGDBE 200 0.5 0.6 0.53
PGDBE 200 0.5 1 0.52
PGDBE 200 0.21 0.3 0.307
PGDBE 200 0.05 0.3 0.361
PGDBE 175 0.5 0.05 0.29
PGDBE 140 0.05 0.05 0.18
PGDBE 200 0 0.5 No black deposition occurred
PGDBE 200 0.5 0 No black deposition occurred

Table 1

Another experiment was carried out at conditions similar to the above experiments. In this experiment, Wingstay – 100 was replaced with inventive stabilizer (Alkylated Hydroxyl Toluene (AHT)) added to PGDBE (Genosorb – 1843) along with Sulphur and subjecting the solutions to thermal exposures at 200oC for around 15 hr. The experimental results are summarized below:

Absorbent Temperature (oC) Stabilizer (AHT) Content (wt%) Sulphur content
(wt %) % wt black depositions
PGDBE 200 0.01 0 No black deposition occurred
PGDBE 200 0.01 0.3 No black deposition occurred
PGDBE 200 0.01 0.5 No black deposition occurred
PGDBE 200 0.5 0 No black deposition occurred
PGDBE 200 0.5 0.3 No black deposition occurred
PGDBE 200 0.5 0.5 No black deposition occurred

Table 2

From the above table, it can be observed that the presence of AHT in PGDBE limits the degradation of PGDBE and the formation of the black deposition in the presence of Sulphur.

Comparative example 2

In this example, the disclosed process was replicated into a large scale industrial process. As explained in Figure 1, the process consists of one absorption column and one desorption column. Holdup PGDBE in the process is 55 ton. PGDBE of 180 m3/h absorbs CS2 in absorption column from gaseous mixtue of 40000 m3/h having CS2 and H2S concentration of ~11 g/m3 and ~2 g/m3, respectively.

It has been observed that, for operation of 6 months, elemental Sulphur concentration in the process becomes ~ 1 wt%, Wingstay-100 concentration depletes from 0.5% to ~ 0.01%. Further, major scaling was observed on hot surface of process heat exchangers (PHE’s) and heater. This led to rise in pressure drop across the heater by ~ 0.7 bar. For operating in the allowable pressure drop range PGDBE circulation rate drops by 40% which results in lower production and process efficiency.

In the same process, 0.5% of AHT was added to monitor formation of black depositions in the system. It has been observed that black deposition was not formed after addition of this stabilizer to the process.

INDUSTRIAL APPLICABILITY

The absorption formulation comprises a non-amine based stabilizer that does not participate in the side reactions, thereby saving the loss of stabilizer from the process. Such formulation also prevents degradation of absorption solvent. Further, the disclosed formulation facilitates absence or reduction in scaling/choking in the process equipment which in turn improves overall process efficiency.

The disclosed process is easy and inexpensive to perform. Said process may be used for any feed gaseous mixture containing one or more of CS2, H2S, SO2, COS and other Volatile Organic Compounds (VoCs). ,CLAIMS:
1. An absorption formulation for removing acid gases from a gaseous mixture, said formulation comprising:

- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)
where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3; and

- from about 1 to 10% by weight of water.

2. An absorption formulation as claimed in claim 1, wherein the stabilizer is selected from a group consisting of alkylated hydroxyl toluenes, alkylated p-cresols and alkylated hydroxyl anisoles.

3. An absorption formulation as claimed in claim 1 or 2, wherein the stabilizer is tertiary butylated hydroxyl toluene.

4. A process for removing acid gases from a gaseous mixture, the process comprising:

a. contacting said gaseous mixture with an absorption formulation in an absorption column, the absorption formulation comprising
- from about 85 to 99% by weight of an absorption solvent, the absorption solvent being a polyalkylene glycol alkyl ether having formula I:

R1—O—(R2—O)x—R3 (Formula I)

where
R1 is C1-C4-alkyl,
R2 is ethylene or 2-methylethylene,
R3 is hydrogen or C1-C4-alkyl,
and
X is an integer from 1 to 10;

- from about 0.01 to 5% by weight of the absorption solvent of a stabilizer, the stabilizer having formula II:
(Formula II)

where
R4 and R5 are an organic group having 3 to 8 carbon atoms and are identical or different from each other,
R6 is -CH3 or -OCH3; and

- from about 1 to 10% by weight of water;

thereby obtaining a treated gas and an acid gases enriched- absorption formulation;

b. passing said acid gases enriched-absorption formulation to a desorption column comprising a stripping media to cause stripping of the acid gases from said acid gases enriched-absorption formulation, and obtain acid gases enriched-stripping media and regenerated absorption formulation;

c. passing said acid gases enriched-stripping media through a condenser to obtain acid gases therefrom; and

d. returning the regenerated absorption formulation into absorption column.

5. A process as claimed in claim 4, wherein the stripping media is selected from a group consisting of hot air, nitrogen and steam.

6. A process as claimed in claim 4, wherein the stabilizer is selected from a group consisting of alkylated hydroxyl toluenes, alkylated p-cresols, alkylated hydroxyl anisoles.

7. A process as claimed in claim 4, wherein the stabilizer is tertiary butylated hydroxyl toluene.

8. A process as claimed in claim 4, wherein the absorption formulation is fed to the absorption column at a temperature ranging between 10 to 350C.

9. A process as claimed in claim 4, wherein the acid gases enriched-absorption formulation is passed to the desorption column at an elevated temperature ranging between 110 to 1450C.

10. A process as claimed in claim 4, wherein the acid gases comprises one or more of CS2, H2S, SO2, COS and other Volatile Organic Compounds (VoCs).