Phase transitional absorption method

The present invention is directed to an improved method and system for separating and purifying gas using gas-liquid absorption. According to this invention, the method is carried out in an absorber, where a liquid absorbent, a gas mixture containing a gas to be absorbed were introduced from an inlet. During absorption, the second liquid phase was separated out from the absorbent. The absorbed gas was accumulated in one of liquid phases. After absorption, two liquid phases were separated. One of the liquids with rich absorbed gas was forward to regenerator. After regeneration, the liquid was cycled back to absorber. The liquid phase with lean absorbed gas was back to absorber directly to complete the cycle.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates to the method for gas separation. In particular, this invention relates to gas separation by phase transitional absorption.

Current technologies for gas absorption are still limited to using one liquid phase as absorbent. The gas in gas mixture is absorbed into absorbent. The absorbent with absorbed gas is regenerated in regeneration column. After regeneration, the absorbent is recycled back to absorber to complete the cycle.

SUMMARY OF INVENTION

The present invention is directed to an improved method and system for separating and purifying gas using gas-liquid absorption.

According to this invention, the method is carried out in an absorber, where a liquid absorbent, a gas mixture containing a gas to be absorbed were introduced from an inlet. During absorption, the absorbed gas was accumulated in one of liquid phases. After absorption, two liquid phases were separated. One of the liquids with rich absorbed gas was forward to regenerator. After regeneration, the liquid was cycled back to absorber. The liquid phase with lean absorbed gas was recycled back to absorber directly to complete the cycle.

In one aspect, the method of the present invention could be used to remove an impurity gas from a gas mixture of interest or to collect a gas of interest from a gas mixture at improved efficiency. In another aspect, the method of the present invention provides significant saving on regeneration energy because solvent phase (gas lean phase) was separated before regeneration, only part of the absorbent (gas rich phase) was forward to regeneration. Yet in another aspect, absorption rate could be increased significantly by selecting proper solvent.

It is apparent that two or three or more compounds may compose the liquid absorbent.

It is be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION

The following description is demonstrative in nature and is not intended to limit the scope of the invention or its application of uses. There are a number of significant design features and improvements incorporated within the invention.

The objective of the current invention for a low-cost viable process to capture and purify a gas based on phase-transitional absorption process.

The difference between traditional absorption with phase transitional absorption was the absorbent. In phase transitional absorption, the liquid absorbent was composed of two or three or more compounds. In the components of absorbent, some of the components called activated agent that reacted with absorbed gas to form a new compound. Some of the components called solvent that play the role of improving the physical and chemical properties of the absorbent. During absorption, the activated agent reacted with absorbed gas to form new compounds. The new compounds were not soluble in solvent and separated out from absorbent to form new liquid phase with rich absorbed gas.

According to the current invention, the method is carried out in an absorber, where a liquid absorbent, a gas mixture containing a gas to be absorbed were introduced from an inlet. During absorption, the absorbed gas was accumulated in one of liquid phases. After absorption, two liquid phases were separated. One of the liquids with rich absorbed gas was forward to regenerator. After regeneration, the liquid was cycled back to absorber. The liquid phase with lean absorbed gas was recycled back to absorber directly to complete the cycle.

In one aspect, the method of the present invention could be used to remove an impurity gas from a gas mixture of interest or to collect a gas of interest from a gas mixture at improved efficiency. In another aspect, the method of the present invention provides significant saving on regeneration energy because solvent phase (gas lean phase) was separated before regeneration, only part of the absorbent (gas rich phase) was forward to regeneration. Yet in another aspect, absorption rate could be increased significantly by selecting proper solvent.

An example for explanation is as follows.

Compound A was an activated agent in liquid. Compound B was a solvent. Compound A dissolved in solvent B. A and B formed solution for CO2absorption. During absorption, compound A reacted with CO2to form A.CO2. A.CO2was not soluble in solvent B. A.CO2formed new phase. After separation of phase A.CO2with solvent B, solvent B was cycled back. A.CO2was forward to regeneration. After regeneration, the compound A was cycled back and mixed again with solvent B for CO2absorption.

Absorption Rate

In the inventor's study, the carbon dioxide absorption rates were measured. The absorbents included water, aqueous solution of ammonium carbonate (150 g/l), aqueous solution of potassium carbonate (150 g/l), aqueous solution of diethanolamine (20% by volume), diethanolamine activated potassium carbonated solution(K2CO3150 g/l+DEA 2% by volume) and the absorbent of phase transitional absorption. The absorbent used in phase transitional absorption was composed of 80% solvent B and 20% activated agent A. All experiments were conducted at the same experimental conditions. The carbon dioxide gas was supplied by cylinder with over 99.99% purity. The CO2absorber was a 3-liter glass container with a cooling and heating coil. 900 ml liquid (absorbent) was filled into absorber. Absorption was operated at 25° C., 1 atm. The liquid was agitated at the speed of 60 rpm. The gas was also agitated at the same speed. The absorption rate of carbon dioxide at time t was determined by the difference of two flow rates, in and out of absorber with two foam film flow meters. The experimental results showed inFIG. 1.

As seen inFIG. 1, the absorption rate by using the technology of phase transitional absorption had amazing results. The absorption rate by phase transitional absorption (80% solvent B and 20% activated agent A) was 3 times faster than DEA (20% by volume) aqueous solution, 3 times faster than ammonium carbonate solution (150 g/L), 7 times faster than K2CO3(150 g/l), 6 times faster than DEA (2% by volume) activated K2CO3(150 g/l).

CO2loading capacity or specific absorption capacity of the solutions for each cycle is related to the energy cost of regeneration. The measured specific absorption capacity in CO2rich phase is 0.144-0.2 g CO2/g solution. This result was far from optimized. This compares favorably to current MEA (monoethanolamine) technology that has demonstrated capacity of 0.036 g CO2/g solution for standard 20% MEA solution. The CO2loading capacity by phase transitional absorption is 4-6 times higher than that by standard 20% MEA solution.

Regeneration

After absorption, two liquid phases appeared. One was the phase of solvent B, another was the phase of A.CO2. The samples were taken from both phases to determine the composition. The analysis was conducted by gas chromatograph. The analytical results showed that 0% of component A in the phase of solvent B, and more than 97% of component A in the phase of A.CO2.

In the current invention, the absorbent was consisted of 80% solvent B and 20% activated agent A. After absorption, A.CO2phase was separated. Only 20% of the absorbent (A.CO2) was forward to regeneration. This is a savings in regeneration energy.

The inventor's study showed that A.CO2started decomposition at about 80° C. However, the decomposition amount of A.CO2is the function of temperature. The total percentage of the carbon dioxide in solution was evolved up to the temperature. Another method to regenerate A.CO2is using steam to strip CO2. This method is similar with the regeneration of CO2from MEA solution.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the point and scope of the appended claims should not be limited to the description of the preferred versions contained herein.