Amine Absorbent for Selective H2S Removal
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Solution Overview
Problem
Existing absorbents for selectively removing hydrogen sulfide (H2S) over carbon dioxide (CO2) from fluid streams face challenges such as phase separation at regeneration temperatures, high volatility, and decreased selectivity at higher pressures, which affect their efficacy in gas treatment processes.
Innovation Solution
An absorbent comprising an aqueous solution of amines with specific structural features, including secondary amino groups and cyclic structures, which reduces phase separation up to 130°C and maintains selectivity, along with the addition of an acid to enhance regeneration and selectivity, is used to selectively remove H2S over CO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If hydroxyl-substituted amines (alkanolamines) are used to improve solubility and suppress phase separation, then the absorbent maintains single phase at higher temperatures, but selectivity for H2S decreases at higher pressures due to direct physical absorption of CO2 and reaction with hydroxyl groups
Solution Approach 1:
The patent modifies the molecular structure of alkanolamines by replacing terminal hydroxyl groups with ether groups (e.g., -OCH3, -OCH2CH3). This parameter change in chemical structure reduces the reactivity toward CO2 while maintaining phase stability, thereby resolving the contradiction between phase stability and selectivity loss at higher pressures
2Object-generated harmful factors
If severely sterically hindered secondary amines and tertiary amines are used for selective H2S removal, then kinetic selectivity for H2S over CO2 is achieved, but phase separation occurs at regeneration temperatures
Solution Approach 1:
The patent creates composite amine structures combining sterically hindered amine groups (for H2S selectivity) with ether-substituted alkyl chains (for phase stability). This composite molecular design integrates the beneficial properties of both components: the sterically hindered amine provides kinetic selectivity while the ether-substituted structure prevents phase separation at regeneration temperatures
3Ease of operation
If alkanolamines are used to improve aqueous solubility, then circulation through absorber/regeneration towers is facilitated, but CO2 reacts with hydroxyl groups leading to progressive loss in H2S selectivity with increasing pressure
Solution Approach 1:
The patent changes the chemical parameter of the amine structure by substituting terminal hydroxyl groups with ether groups. This modification maintains aqueous solubility and circulation ease while eliminating the harmful reaction between hydroxyl groups and CO2, thereby preventing selectivity loss at higher pressures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The absorbent effectively maintains a single phase up to 130°C, enhances H2S selectivity, and improves regeneration efficiency, allowing for high H2S cleanup at low solvent circulation rates, suitable for various gas treatment applications.
Implementation Method 1
The reaction kinetics allow H2S to react directly, more rapidly, with the amine groups of the sorbent to form a hydrosulfide ion in aqueous solution
Implementation Method 2
When acid gases are dissolved in the absorbent, ions form with the bases
Implementation Method 3
The absorbent can be regenerated by decompression to a lower pressure and/or by stripping, whereby the ionic species react in reverse and the acid gases are released
Implementation Method 4
the acid gases are released and/or stripped out by means of an inert fluid, e.g., steam
Data Source
AI summary
An absorbent for the selective removal of hydrogen sulfide over carbon dioxide from a fluid stream, wherein the absorbent contains an aqueous solution, comprising an amine of formula (I) and/or an amine of formula (II) wherein U—V—W is CH—O—CHR5, N—CO—CHR5 or N—CO—NR5; U′—V′—W is C—O—CR5; R1 is independently C1-C5-alkyl; R2 is selected from hydrogen and C1-C5-alkyl; R3 is independently selected from hydrogen and C1-C5-alkyl; R4 is independently selected from hydrogen and C1-C5-alkyl; R5 is selected from hydrogen, C1-C5-alkyl, (C1-C5-alkoxy)-C1-C5-alkyl, and hydroxy-C1-C5-alkyl; and x is an integer from 1 to 10. The absorbent has a reduced tendency for phase separation at temperatures falling within the usual range of regeneration temperatures for the aqueous amine mixtures and a low volatility in aqueous solvents.