MXPA97005149A - Composition and process for the selective purification of gaseous currents based on aqueous solutions of alcanolami - Google Patents

Abstract

The present invention relates to: A composition composition of mixtures, exclusively, of two alkanolamines, characterized in that the composition ranges of the diethanolamine are: between 5 and 45 percent by weight of diethanolamine and between 5 and 45 percent by weight of methyldiethanolamine , with the proviso that the total of the sum of the percentages by weight of each of the alkanolamines is between 15 and 50 percent by weight and the difference for the total of 00 percent is the weight of the solution either of

Description

COMPOSITION AND PROCESS FOR THE SELECTIVE PURIFICATION OF GASEOUS CURRENTS BASED OF AQUEOUS SOLUTIONS OF ALCANOLAMINES DESCRIPTION TECHNICAL FIELD OF THE INVENTION The present invention relates to a composition and process for the selective purification of gaseous streams based on aqueous solutions of alkanolamines. The composition is constituted by a mixture of two alkanolamines, in aqueous solution whose composition can comprise a wide range of values, either in units of weight percent, volume percent, molar concentration, etc., for selective purification, applied to a process It is a cyclical industrial type that mainly comprises the gas / liquid absorption and the regeneration of the absorber solution by raising the temperature of gaseous streams composed mainly of light hydrocarbons. Particularly, the invention relates to mixtures composed simultaneously of diethanolamine and methyldiethanolamine in water and to a process for the efficient removal of acid gases, such as hydrogen sulfide and carbon dioxide, which occur as contaminants in different gaseous hydrocarbon streams.

BACKGROUND OF THE INVENTION The absorption of gases in liquids can occur naturally, such as the dissolution of environmental oxygen in water, or be caused to be used industrially for the purpose of carrying out chemical transformations of raw materials and intermediate currents and to carry out industrial separation processes . In this latter application it is common practice to selectively separate those undesirable gaseous components from a main gas stream to achieve product quality specifications, to obtain new products or to reduce polluting emissions to the environment.

For example, for more than sixty years it has been common practice to industrially use aqueous solutions of a single alkanolamine, either of the primary type, e.g. monoethanolamine, secondary, e.g. diethanolamine, or tertiary, e.g. triethanolamine, for the removal of hydrogen sulphide and carbon dioxide, also known as acid gases, from gas streams, natural or industrial, rich in light hydrocarbons. The removal of acid gases from a wide variety of gas streams, such as natural gas, refinery gas, synthesis gas, etc., aims to increase the industrial and commercial utility of hydrocarbon streams, reduce polluting emissions environment during the combustion of those, reduce corrosion problems in equipment and pipes caused by the presence of acid gases and additionally take advantage of these gases for application in other industrial processes, such as in the production of sulfur in the case of acid hydrogen sulfide The removal of acid gases from gaseous mixtures of hydrocarbons, when they are contacted with an aqueous solution of an alkanolamine, is mainly carried out by means of a phenomenon of a chemical nature, that is to say, different chemical reactions occur between the acid gases and the gases. two components of the solution. In the industrial processes of absorption of acid gases for the purification of different types of gaseous streams rich in hydrocarbons, it has been traditional to use separately the primary alkanolamine called ethanolamine or monoethanolamine and the secondary alkanolamine called diethanolamine in an aqueous solution. However, it is only recently that the reaction mechanisms have been understood by means of which the absorption of the aforementioned acid gases is carried out and for which it has been concluded that these alkanolamines are not selective by themselves to some of the acid gases that they are absorbed. On the other hand, the products of degradation or decomposition of these alkanolamines produce thermally stable salts that are the source of important operational problems in the industrial process that is currently used, such as foaming in the absorption tower, corrosion and fouling in the different process equipment. Additionally, since the aqueous solutions individually containing any of the two alkanolamines mentioned are highly corrosive, particularly when they react with the acid gases, there are limitations as to the increase in the concentration of the alkanolamine to improve the absorption capacity towards the acid gases.

It is for the above that in the search and evaluation of new solvents, to be applied industrially in processes of absorption or purification of gas streams, the most important factors to consider are that the solvent has a high absorption capacity towards both acid and low gases. capacity of absorption by the hydrocarbons, simultaneously it is desirable to have selectivity towards one of the acid gases, likewise, that no undesirable products are generated, eg the thermally stable salts or carbamates, to considerably reduce the problems of foaming, corrosion and fouling; so that all this as a whole gives rise to an industrial process of purification of different gaseous streams more efficiently, technically and environmentally, and more economically.

Some of the characteristics mentioned in the previous paragraph are found with the use of aqueous solutions of tertiary alkanolamines, since they have a high absorption capacity towards acid gases, they are selective towards hydrogen sulfide and do not present the reaction that gives rise to the carbamates, thus reducing the foaming, corrosion and fouling in the equipment used in the industrial process for the purification of gaseous streams rich in hydrocarbons. These properties have the overall effect that the amount of aqueous solution of tertiary alkanolamine used in the process is substantially lower than that used in the processes using the aqueous solutions of a primary alkanolamine or a secondary alkanolamine and therefore that the amount of energy used in the process, mainly in the stage of regeneration of the solvent after the absorption of acid gases, is significantly reduced and consequently the operating costs are also lower than in the two cases mentioned.

On the other hand, the simultaneous combination of a secondary alkanolamine with a tertiary alkanolamine in aqueous solution has as additional advantages to that described above the obtaining of a solvent of high absorption capacity and at the same time with high selectivity towards hydrogen sulfide.

The use of a solution consisting of a mixture of secondary alkanolamine and a tertiary alkanolamine has a higher rate of absorption by carbon dioxide, compared to a solvent based on a mixture of two tertiary alkanolamines. Action that is positive when the treated gas is used as a fuel of adequate calorific value.

Then, the composition of the aqueous solution for the removal of acid gases from gas streams rich in hydrocarbons, object of the present invention, is based on the use of mixtures of two alkanolamines, one of them secondary, diethanolamine, and the other of the tertiary type, methyldiethanolamine.

Next, mention will be made of the novel aspects of the industrial use of aqueous solutions, in well-defined composition intervals, of diethanolamine and methyldiethanolamine for the removal of acid gases, by means of the industrial process of the cyclic type known as absorption, of gaseous streams. rich in hydrocarbons that contain them.

Aqueous solutions of diethanolamine and methyldiethanolamine have the characteristic of high absorption capacity towards acid gases; which are present in gaseous streams rich in hydrocarbons.

Aqueous solutions of diethanolamine and methyldiethanolamine have the characteristic, by virtue of the previous paragraph, of requiring substantially lower flows of circulation in the industrial process than the aqueous solutions of a single alkanolamine traditionally used in the industry. This results in a lower consumption of aqueous solution of the two alkanolamines and in the reduction of energy costs by pumping and by steam regeneration of said aqueous solution of alkanolamines.

Aqueous solutions of diethanolamine and methyldiethanolamine have a high selectivity of absorption towards hydrogen sulfide in relation to that corresponding to carbon dioxide.

Aqueous solutions of diethanolamine and methyldiethanolamine can be used to remove acid gases, which are found as contaminants in hydrocarbon-rich streams, in a wide range of partial pressures of said acid gases and total pressure of gaseous streams of gas-contaminated hydrocarbons acids.

Aqueous solutions of diethanolamine and methyldiethanolamine for the removal by absorption of acid gases, can be applied in different types of gaseous streams rich in hydrocarbons, such as natural gas, refinery gas and synthesis gas.

The aqueous solutions of diethanolamine and methyldiethanolamine for the removal by absorption of acid gases, present lower corrosivity than the aqueous solutions of a single alkanolamine traditionally used in the industry.

The aqueous solutions of diethanolamine and methyldiethanolamine for the removal by absorption of acid gases, cause less fouling than the aqueous solutions of a single alkanolamine traditionally used in the industry.

The aqueous solutions of diethanolamine and methyldiethanolamine for the removal by absorption of acid gases originate lower degradation products, carbamates, than the aqueous solutions of a single primary or secondary alkanolamine traditionally used in the industry.

The published patent application No. 9304934 of August 13, 1993, of Dow Chemical, entitled "Improved solvent composition for removing acid gases, describes the use of a mixture of methyldiethanolamine and N, N'-bis (dimethyl) - N-hydroxyethyl-ethylenediamine.

The certificate of invention 6342 of Shell I.R. describes the use of a dialkyl-mono-alkanolamine for the removal of acid gases from gas mixtures.

Patent 163137 of Shell I.R. describes a process for separating acid gases from a gaseous mixture containing methane using a physical and a chemical absorbent.

The U.S. patent No. 5, 100,643, from the University of Texas describes a process for separating acidic components from gas streams.

The U.S. patents 4,775,519 to Texaco Inc., 4,714,480 to Shell Oil Co .; 4,702,898 from Union Carbide Corp .; 4,696,803 to Texaco, Inc .; 4,540,552 of Union Carbide Corp .; 4,460,385 to Exxon; 4,359,450 from Shell Oil Co .; 4,160,810; 4,093,701 to Union Carbide Corp .; 4,079.1 1 7 of Union Carbide Corp .; 4,412,977 of Shell Oil Co. and 5,246,619 of Dow Chemical Co., refer to the removal of acid gases from gaseous streams containing them.

The novelty of the present composition for selectively purifying gaseous streams consists in using an aqueous mixture of a secondary amine and a tertiary amine, taking advantage of the qualities of these two types of amines, unlike all the cited documents.

Similarly, the process for selectively purifying gaseous streams using a composition based on an aqueous mixture of a secondary amine and a tertiary amine, presents novel features that distinguish it from the state of the art.

DETAILED DESCRIPTION OF THE INVENTION The composition of aqueous solutions of diethanolamine and methyldiethanolamine, object of the present invention, for the removal by absorption of acid gases, is used industrially in a cyclic process, see figure 1, which consists of a contact section or absorbent tower where said solutions are put intimately in contact, countercurrently, with the gaseous mixture rich in hydrocarbons containing the acid gases and another section, regeneration of the solution rich in acid gases by desorbing them by means of steam at high temperature, or tower desorbedora. Once part of the aqueous solution of mixtures of diethanolamine and methyldiethanolamine has been regenerated, it is recycled to the absorber tower, after an exchange of heat with part of the solution rich in acid gases coming from the lower section of the absorbing tower. The purified or sweetened stream (elimination of acid gases) of hydrocarbons leaves the top or dome of the absorber tower and acid gases are obtained in the upper section or dome of the desorbing tower for later use in other industrial processes.

The aqueous solutions of diethanolamine and methyldiethanolamine for the removal by absorption of acid gases, contain determined quantities of the two alkanolamines in a wide range of composition, which obviously includes a wide range of proportions of one with respect to the other, in any unit of composition, with which it is possible to treat industrially different gaseous streams rich in hydrocarbons with different contents of acid gases.

The removal of acid gases from gas streams rich in hydrocarbons, in accordance with the present invention, is carried out with aqueous solutions of mixtures, of determined composition, of two alkanolamines, one classified as a secondary type, the diethanolamine, and the other of tertiary type, metildietanolamine.

More particularly, the composition of the aqueous solution of diethanolamine and methyldiethanolamine which is used for the removal of acid gases contained in gas streams rich in hydrocarbons can be established according to the specific needs of each case. That is, the composition or proportions of the alkanolamines can vary in very wide ranges and the exact composition is established at will according to the requirements for the treatment of some particular type of gaseous current, natural or industrial, rich in hydrocarbons and more particularly according to the content of the acid gases both in the feed stream to the absorber tower and in the sweetened stream of hydrocarbons.

The composition ranges in which the aqueous solution of diethanolamine and methyldiethanolamine can be used industrially in the best manner are: between 5 and 45 percent by weight of diethanolamine and between 5 and 45 percent by weight of methyldiethanolamine, with the proviso that the total of the sum of the percentages by weight of each of the alkanolamines is between 1 5 and 50 percent by weight and the difference for the total of 100 percent by weight is water.

The process for the selective removal of the acid gases contained in gas streams rich in hydrocarbons of the present invention, is carried out with an aqueous solution of alkanolamines in a cyclic form, first comprising a step of contact or countercurrent absorption; then continues the process of purification or sweetening of gaseous streams rich in light hydrocarbons by subjecting the aqueous solution of alkanolamines containing the acid gases, to regeneration or desorption of said gases, in a step after the absorption, in a regenerative column by means of of the application of water vapor at elevated temperature, higher than 100 ° C, then in another stage, recirculate the aqueous solution to the absorber tower and repeat the cycle.

In the process of purification or sweetening of gaseous streams rich in light hydrocarbons using aqueous solutions of mixtures of two alkanolamines, object of the present invention, the temperature conditions in the absorption and regeneration stages are not generally critical, except that they must be those that allow the optimum absorption of acid gases from the hydrocarbon-rich stream and then its proper desorption from aqueous alkanolamines.

In the process of purification or sweetening of gaseous streams rich in light hydrocarbons, the aqueous solutions of mixtures of two alkanolamines, object of the present invention, have the great advantage that they absorb very low amounts of hydrocarbons, which are the main components of the hydrocarbons. Different natural and industrial gaseous streams that can be purified in the present process, so there is no waste of the main product.

To demonstrate the effectiveness of the aqueous solutions of mixtures of known composition of diethanolamine and methyldiethanolamine, object of the present invention, experimental determinations of the solubility or absorption of acid gases were carried out to clearly establish the absorption capacity and selectivity. These experiments used a device designed and built specifically for this purpose.

EXAMPLES EXAMPLE 1 First, Figure 2 shows the absorption capacity (solubility), a 40 ° C, of some of the aqueous solutions of diethanolamine and methyldiethanolamine, object of this invention, towards hydrogen sulfide. The concentrations of the aqueous solutions is as follows: The results of Figure 2, together with the information in the previous table, show that the higher the total alkanolamine content, i.e. percent by weight of diethanolamine + percent by weight of methyldiethanolamine, the greater is its absorption capacity towards hydrogen sulfide. Another very important aspect in relation to the absorption capacity is that the alkanolamin mixtures included in the present patent description have a greater capacity towards hydrogen sulfide when the concentration of methyldiethanolamine is higher than that corresponding to diethanolamine. All this clearly indicates that the solutions included here can be used in a very wide range of total alkanolamine composition and consequently in a very wide range of proportions or relations between the composition of one alkanolamine with respect to the other and be very efficient in the absorption of acid gases.

EXAMPLE 2 Figures 3 and 4 show the absorption capacity of hydrogen sulphide and carbon dioxide, respectively, of some of the aqueous solutions object of this invention, as well as their comparison with the diethanolamine solution at 20% weight, used in the industrial process called Girbotol. It is clearly evident the greater absorption capacity, towards the two acid gases considered, of any of the aqueous solutions of alkanolamines, object of this invention, than that shown by the aqueous solution of diethanolamine. It can be seen from the graphs of results that the partial pressure range of acid gases is very wide, which means that hydrocarbon streams with different contents of acid gases can be treated. EXAMPLE 3 Figure 5 illustrates the specific case for the treatment of a refinery gas, in which the composition of acid gases and the conditions of the gas stream cause the partial pressure of hydrogen sulfide to be 1.0 kg / cm2; in this case, the difference in cyclic thermodynamic capacity of absorption of hydrogen sulfide in one of the aqueous solutions of diethanolamine and methyldiethanolamine, object of the present invention, is 50% greater than that corresponding to the solution used in the Girbotol process (aqueous solution of diethanolamine at 20% weight). This evidently indicates that the aqueous solutions of diethanolamine and methyldiethanolamine, together with the absorption-regeneration process, object of the present invention, are superior to the aqueous solutions of diethanolamine and the Girbotol process.

EXAMPLE 4 Figure 6 shows the comparison of the cyclic thermodynamic capacity of absorption of carbon dioxide in one of the aqueous solutions of diethanolamine and methyldiethanolamine, object of the present invention, and in aqueous solution of diethanolamine at 20% weight, used in the industrial process called Girbotol. At a partial pressure value of this acid gas, corresponding to a bitter refinery gas, the ratio of cyclic carbon dioxide absorption capacities of the solution object of this patent and of the aqueous 20% diethanolamine solution is much more lower than that corresponding to the cyclic capacity of hydrogen sulfide in the same solutions (figure 5). This difference in the aforementioned relationships is an indicator of the high selectivity towards hydrogen sulfide presented by the aqueous solutions of diethanolamine and methyldiethanolamine, object of this invention, as part of the industrial process proposed in this patent, for the purification of different types of streams. soft drinks rich in hydrocarbons.

The information presented in examples 3 and 4 also clearly shows that the process under which it is proposed to use aqueous solutions of mixtures of diethanolamine and methyldiethanolamine, based on the elimination of acid gases from the hydrocarbon stream in an absorbent towers from which the sweet hydrocarbon stream is obtained through the dome and the aqueous solution of diethanolamine and methyldiethanolamine to subsequently desorb the acid gases in a tower desorbedora or regenerative of the aqueous solution to obtain in the dome acid gases and in the background the aqueous solution free of acid gases to be recirculated back to the tower of absorption, is highly efficient and cheaper than the traditionally used currently in the refining industry EXAMPLE 5 The greater absorption capacity of the aqueous solutions of alkanolamines mixtures, object of this invention, towards acid gases, mainly towards hydrogen sulfide, all evidenced in the previous examples; has as a positive consequence a lower requirement of the amount of absorbent solution circulating in the industrial process, also subject of the present invention, to purify a given amount of gas rich in light hydrocarbons, in comparison with the amount of aqueous solution of diethanolamine that It is used industrially.

On the other hand, since the aqueous solutions of mixtures of alkanolamines, object of this invention, contain a substantially smaller amount of water than the solutions traditionally used industrially, the energy requirement for the regeneration, in the regenerative tower of the industrial process, the solution rich in acid gases is substantially lower compared to that used in the processes with aqueous solution of diethanolamine as absorbent.

Since the costs of a process are of great importance to be able to make decisions regarding its industrial application, results of the economic evaluation for the two aspects discussed in the previous paragraphs are presented in table 1. It is evident the economic benefit that would be achieved with the industrial application of any of the aqueous solutions of alkanolamines mixtures, object of this invention, together with the process that is suggested, also object of the present invention, for the purification of different types of hydrocarbon-rich streams. The comparison shows that the mixtures of the aqueous solutions of alkanolamines and the proposed process, object of this invention, are economically more profitable than the process with aqueous solution of diethanolamine that is currently used in the industry.

TABLE 1 ECONOMIC COMPARISON OF A DIETANOLAMINE AQUEOUS SOLUTION AND METHYLENEETHANOLAMINE, OBJECT OF THIS INVENTION (IMP) VS AQUEOUS SOLUTION OF DIETANOLAMINE AT 20% WEIGHT. FLOW OF RICH GAS IN HYDROCARBONS = 796 300 M3N / D, CONTENT OF ACID GAS IN GAS RICH IN HYDROCARBONS: SULF HYDRIC ACID = 1 8.3% MOLAR, CARBON BIOXIDE = 0.5% MOLAR

Claims (14)

NOVELTY OF THE INVENTION

1. - The industrial use of aqueous solutions of mixtures of known composition of two alkanolamines for the removal of acid gases from gaseous streams rich in hydrocarbons containing them.

2. - The industrial use of aqueous solutions of mixtures of known composition of two alkanolamines, according to clause 1, characterized in that one of the alkanolamines is of the secondary type and the other is of the tertiary type.

3. - The industrial use of aqueous solutions of mixtures of known composition of two alkanolamines, in accordance with clauses 1 and 2, characterized in that the secondary alkanolamine is diethanolamine and the tertiary is methyldiethanolamine.

4. - A composition of aqueous solutions of mixtures of two alkanolamines, characterized in that the composition ranges of the diethanolamine and methyldiethanolamine are: between 5 and 45 percent by weight of diethanolamine and between 5 and 45 percent by weight of methyldiethanolamine, with the proviso that the total sum of the percentages by weight of each of the alkanolamines is between 15 and 50 weight percent and the difference for the total of 100 weight percent of the solution is water.

5. - A process for the selective purification of gaseous streams based on aqueous solutions of alkanolamines, characterized in that it comprises the steps of contacting the gaseous stream with the aqueous solution of alkanolamines, such as diethanolamine and methyldiethyleneamine, preferably by countercurrent absorption, for obtain a stream of purified gas and an aqueous solution of alkanolamines containing the absorbed acid gases, subject the aqueous alkanolamin solution containing the acid gases, to regeneration or desorption of these gases, applying steam at an elevated temperature higher than 100 ° C, and then recirculate the recovered aqueous solution to the initial contact zone of acid gases with the aqueous solution of alkanolamines.

6. - The process according to clauses 5, characterized in that the acid gases that are removed can be contained in gaseous streams rich in natural and industrial hydrocarbons.

7. - The process in accordance with clauses 5 and 6, characterized in that the simultaneous removal of acid gases, such as carbon dioxide and hydrogen sulfide, is carried out.

8. - The process according to clauses 5 to 7, characterized in that the selective removal of hydrogen sulfide is carried out with respect to the removal of carbon dioxide.

9. - The process according to clauses 5 to 8, characterized in that the removal of acid gases is carried out from natural and industrial streams, rich in hydrocarbons, in a very wide range of partial pressure, i.e. composition of each of said acid gases.

10. - The process in accordance with clauses 5 to 9, characterized in that the removal of acid gases from natural and industrial streams, rich in hydrocarbons, is carried out over a wide range of temperatures and pressures of the different gaseous and liquid streams involved, but preferably in those values that guarantee the efficient absorption of the acid gases in the absorber tower and the regeneration of the aqueous solution in the regeneration tower.

1 1.- The process according to clauses 5 to 10, characterized in that the solubility or absorption of the light hydrocarbons is minimal and consequently no waste of hydrocarbons of high industrial and commercial value is carried out.

12. - The process according to clauses 5 to 11, characterized in that the problems found in other processes that use a single alkanolamine, such as foaming, fouling and corrosion, are significantly reduced.

13. - The process according to clauses 5 to 12, characterized in that a lower flow of aqueous solutions of the two alkanolamines is required than in the processes using aqueous solutions of a single alkanolamine.

14. - The process according to clauses 5 to 13, characterized in that it requires a smaller amount of energy to carry out the regeneration of the aqueous solutions of two alkanolamines than the processes in which aqueous solutions of a single alkanolamine are used.

In testimony of which I sign the present in Mexico, Federal District on May Day

of 1997.

MEXICAN INSTITUTE OF OIL

LIC. ENRIQUE MARTÍNEZ-CAÑEDO Representative