CA1113723A - Process for the removal of acidic gases - Google Patents
Process for the removal of acidic gasesInfo
- Publication number
- CA1113723A CA1113723A CA297,301A CA297301A CA1113723A CA 1113723 A CA1113723 A CA 1113723A CA 297301 A CA297301 A CA 297301A CA 1113723 A CA1113723 A CA 1113723A
- Authority
- CA
- Canada
- Prior art keywords
- absorbent
- contacting
- aqueous
- column
- zone
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1493—Selection of liquid materials for use as absorbents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1456—Removing acid components
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/11—Purification; Separation; Use of additives by absorption, i.e. purification or separation of gaseous hydrocarbons with the aid of liquids
Abstract
ABSTRACT OF THE DISCLOSURE
A process for the removal of acidic gages from a gas-eous mixture containing the game by contacting the said gaseous mixture countercurrently in a contacting zone at a temperature in the range of 15 to 135°C and at a pressure of from 1 to 100 kg/cm2 abs., with an aqueous absorbent comprising an amine with a pkb of 3-14 at 25°C in an amount of 10 to 70% by weight and sulfolane and/or its derivatives in an amount of 25 to 70% by weight, which aqueous absorbent is introduced at the top of the contacting zone, and a fat aqueous absorbent is finally with-drawn from the contacting zone at the bottom thereof for regen-eration by means of heating and/or stripping, in which process at an intermediate point at the lower part of the said contact-ing zone the said aqueous absorbent is withdrawn from said contacting zone as a semi-fat absorbent and is reintroduced into the said lower part of said contacting zone after having been cooled externally, for further contacting with the said aqueous mixture.
A process for the removal of acidic gages from a gas-eous mixture containing the game by contacting the said gaseous mixture countercurrently in a contacting zone at a temperature in the range of 15 to 135°C and at a pressure of from 1 to 100 kg/cm2 abs., with an aqueous absorbent comprising an amine with a pkb of 3-14 at 25°C in an amount of 10 to 70% by weight and sulfolane and/or its derivatives in an amount of 25 to 70% by weight, which aqueous absorbent is introduced at the top of the contacting zone, and a fat aqueous absorbent is finally with-drawn from the contacting zone at the bottom thereof for regen-eration by means of heating and/or stripping, in which process at an intermediate point at the lower part of the said contact-ing zone the said aqueous absorbent is withdrawn from said contacting zone as a semi-fat absorbent and is reintroduced into the said lower part of said contacting zone after having been cooled externally, for further contacting with the said aqueous mixture.
Description
~37Z3 The present invention relates to a process for the removal of acidic gases from a gaseous mixture containing the same.
Processes for the removal of acidic gases, such as H2S
and C02, from gaseous mixtures containing the same are well known in the art. In general, these processes involve scrubbing the gaseous mixture with a liquid absorbent in an absorption zone whereby the acidic gases are removed from the gaseous mixture and a loaded absorbent stream (generally called the fat absorbent) is obtained which is passed to a regeneration zone where the absorbent is heated and/or stripped with solvent vapour, e.g., steam, resulting in the release of the acidic gases. The regenerated absorbent (generally called the lean absorbent) is returned into contact with the feed gas mixture in the absorption zone while the evolved acidic gases are passed to a cooler/
condenser in which the solvent vapours are condensed and separated from the acidic gases.
For a variety of industrial applicationS,it is further necessary or desirable to reduce the sulphur content of a ~ gaseous mixture containing significant quantities of COS
- and/or mercaptans in addition to H2S and C02 to low levels prior to further processing and/or utilization of the gaseous mixture. For example, sour gas available from certain natural gas reservoirs is known to contain up to about 0.1% by volume (1000 ppm) COS and some 0.01% by
Processes for the removal of acidic gases, such as H2S
and C02, from gaseous mixtures containing the same are well known in the art. In general, these processes involve scrubbing the gaseous mixture with a liquid absorbent in an absorption zone whereby the acidic gases are removed from the gaseous mixture and a loaded absorbent stream (generally called the fat absorbent) is obtained which is passed to a regeneration zone where the absorbent is heated and/or stripped with solvent vapour, e.g., steam, resulting in the release of the acidic gases. The regenerated absorbent (generally called the lean absorbent) is returned into contact with the feed gas mixture in the absorption zone while the evolved acidic gases are passed to a cooler/
condenser in which the solvent vapours are condensed and separated from the acidic gases.
For a variety of industrial applicationS,it is further necessary or desirable to reduce the sulphur content of a ~ gaseous mixture containing significant quantities of COS
- and/or mercaptans in addition to H2S and C02 to low levels prior to further processing and/or utilization of the gaseous mixture. For example, sour gas available from certain natural gas reservoirs is known to contain up to about 0.1% by volume (1000 ppm) COS and some 0.01% by
-2--q~
:
volume (100 ppm) mercaptans in addition to substantial quantities of H2S and C02. Since the COS and mercaptans present in the sour gas make-up part of the total sulphur, substantial removal of same, in addition to the H2S
present, is necessary to meet many of the specifications for conventional end uses of such gas, e.g., residential heating and industrial uses. Further, in conventional partial combustion processes utilizing sour liquid hydro-carbon oils or sulphur-containing coals as the primary fuel source, a crude synthesis gas product is obtained which typically contains 100 to 1500 ppm COS in addition to the H2S and C02 partial combustion by-products. In many cases this crude synthesis gas product is subject to further processing, e.g., contact with sulphur-sensitive ~ C0-shift catalysts in hydrogen manufacture, or funnelled to industrial and consumer end-uses, e.g., as energy source in gas turbine generation of electricity or as a town gas for private consumption, which makes it desirable or even essential that the total sulphur content of the combustion gas be reduced to very low levels.
Although the commercially available gas-treating processes are generally satisfactory with respect to the degree of removal of undesirable gas contaminants, there is still room for further improvement of such processes.
A major cost factor for these regenerative processes constitutes the stripping steam requirement for regener-` ~137Z3 ating the fat absorbent which can be very high for many solvents.
The said steam requirement is greatly dependent on the amount of absorbent circulating, so that reduction of this absorbent circulation would necessarily bring about a reduction in the steam consumption. The amount of absorbent to be used in a particular case is dictated by the partial pressures of the acidic gas components in the gaseous mixture to be treated and the desired degree of gas purification. A reduction in the absorbent circulation would also contribute to further savings from a capital cost point of view in that smaller absorption and regeneration columns are required and in that less absor-bent solvent for filling the columns is necessary.
This invention seeks to provide a process for the -removal of acidic gases as identified to a very high degree while using a reduced absorbent circulation.
Accordingly, the present invention relates to a pro-cess for the removal of àcidic gases from a gaseous mixture containing the same by contacting the said gaseous mixture countercurrently in a contacting zone at a temperature in the range of 15 to 135C and at a pressure of from 1 to 100 kg/cm2 abs., with an aqueous absorbent comprising an amine with a PKb Of 3-14 at 25C in an amount of 10 to 70~ by weight and sulfolane and/or its derivatives in an amount of 25 to 70~ by weight, which aqueous absorbent is introduced at the top of the contacting zone, and a fat aqueous absorbent is finally with-drawn from the contacting zone at the bottom thereof for regeneration by means of heating and/or stripping, in which process at an intermediate point at the lower part of the said contacting zone the said aqueous absorbent is withdrawn from said contacting zone as a semi-fat absorbent and is reintroduced into the said lower part of said contacting zone after having ,~
1~137Z3 been cooled externally, for further contacting with the said aqueous mixture.
The process of the present invention is particularly suitable for treating gaseous mixtures comprising acidic gases at relatively low partial pressures. This may be the case when the mixture to be treated comprises little acidic gas components or when it contains the said gas components at relatively low pressures~ The sum of the partial pressures of hydrogen sulphide and carbon dioxide should preferably be lower than 3.0 bar, and more preferably lower than 2.0 bar at the temperature applied during absorption. The greatest benefit will be derived from the process of the invention when applying it to gaseous mixtures having a hydrogen sul-phide partial pressure in the range of from 0.025 to 0.6 bar at a lean absorbent temperature of 30 to 65C. In applying the process of the invention for the removal of carbon dioxide from gaseous mixtures comprising substantially no hydrogen sulphide (less than 0.1% vol. H2S) the carbon dioxide partial pressures may vary in the range of from 0.1 to 2.0 bar at a lean absorbent temperature as indicated.
. :
ci ~113723 The process of the invention is also very suitable for application in those areas of the world where deep cooling to temperatures below 50C is not well possible because the ambient temperature in these areas during at least part of the year does not drop below the figure indicated.
Even in these instances intermediate cooling to temper-atures of about 65C may considerably add to reducing the absorbent circulation.
The contacting zone used preferably comprises of from 10 to 50 contacting layers, such as valve trays, bubble cap trays, baffles and the like. The aqueous absorbent is suitably withdrawn at an intermediate point above the second contacting layer but below the fifteenth contacting layer of the absorption zone if 20 layers or more are applied or below the tenth contacting layer if less than 20 layers are applied.
The aqueous absorbent used in the present process comprises a "chemical" solvent part, i.e., the weak basic component, and a "physical" solvent part, i.e., sulfolane and/or its derivatives.
The chemical solvent part comprises certain components or mixtures of these components of the class of amines.
; For the process according to the invention these amines should have a weakly basic character. (The basic strength of a compound is conveniently expressed in terms of the negative logarithm of the basic dissociation constant,.
Thus, a strong base has a low pKb, while a weak base has a value approaching the upper limit PKb = 14). Bases suit-able for the process according to the invention have a PKb at 25C in the range of 3 to 14. Alkanolamines are particularly suitable, especially those amines having 1 to 4, and preferably 2 to 3, carbon atoms per alkanol radical. Typical species are, inter alia, monoethanol-amine, diethanolamine, methyldiethanolamine, di-iso-propanolamine, triethanolamine and mixtures thereof.
Especially the dialkanolamines can be used with advantage.
The physical solvent part comprises certain com-ponents or mixtures thereof, selected from the group of cyclotetramethylene sulphones. The derivatives from the basic sulphone cyclotetramethylene sulphone (thiophene tetrahydro-1,1-dioxide) which is also known as sulfolane, should preferably have not more than 4, more preferably not more than 2 alkyl substituents in the tetramethylene sulphone ring. Sulfolane itself is the preferred species of this class of compounds.
It has been found advantageous to use in the process an aqueous absorbent which preferably contains the weak basic component within the range of 20-55%wt. An absorbent containing 30-45%wt of the weak basic component has been found very suitable. The sulfolane or its derivatives are preferably present in the absorbent in an amount of 30 to 55%wt. The balance of the mixed solvent consists essentially of water, generally in the range of 5-35%wt.
_7_ , ~1~3723 The descending aqueous absorbent can be withdrawn from the absorption column by means of a total draw-off tray. Such a tray divides the column in two sections with respect to the flow of absorbent, but has a passage for the rising gas mixture to allow it to pass from the lower section into the upper section. The absorbent col-lected on the draw-off tray is withdrawn from the ab-sorption column and externally cooled by indirect heat exchange to a temperature in the range of from 20 to 70C. More preferably, the withdrawn aqueous absorbent which is semi-fat, is cooled to a temperature which is ~; the same as the temperature of the aqueous absorbent introduced at the top of the absorption column. There-after the cooled, semi-fat absorbent is reintroduced into the column in the lower section, preferably directly under the total draw-off tray. It will be evident by the position of the total draw-off tray that the lower section of the column is shorter than the upper section of the column, which latter section encompasses more absorption trays.
It is also possible to use two absorption columns of different column length and arranged such that the gaseous mixture contacts first in the shorter one of the two columns a cooled semi-fat absorbent introd~ced at the top of this shorter column and then countercurrently contacts a lean absorbent in the taller one of the two columns.
. ' ~
~1137;:3 The fat absorbent leaving the shorter column is regener-ated, cooled and introduced at the top ~ the taller column as the lean absorbent.
The principal attainment of the process of this in-vention is the high degree of removal of acidic gas com-ponents from gaseous mixtures at very low partial pressures of these acidic gas components and at reduced absorbent flows. Because a low temperature has particularly a favour-able effect on the absorption of hydrogen sulphide and/or carbon dioxide, intermediate cooling of the absorbent before its introduction into the lower section results in more favourable absorption equilibria for hydrogen sulphide and/or carbon dioxide in the bottom of the absorption column. When a gaseous mixture enters the lower section of the absorption column countercurrent to a descending stream of cold liquid absorbent, a high degree of ab-sorption is obtained even at the relatively low partial pressures of the acidic gases. This high degree ~ ab-sorption is maintained as the total amount of acidic gas components progressively decreases as the gas mixt-ure proceeds upward in the column, because in proceeding upwards the gaseous mixture is contacted with an absorbent, the temperature whereof is decreasing.
Gaseous mixtures which can advantageously be treated by the process according to the invention, include natural gas, refinery gas or synthesis gas obtained by the partial -_g_ oxidation of heavy oil fractions or coal. The process is particularly attractive for the treatment of gases con-taining high amounts of acidic gases, such as hydrogen sulphide and carbon dioxide at relatively low partial pressures. The gaseous mixtures to be treated in ac-cordance with the process of the present invention may also contain carbonyl sulphide in amounts of from 0 to 1500 ppmv and mercaptans in amounts of from 0 to 500 ppmv.
The process may be adapted to treat such feedstocks which also contain higher molecular weight hydrocarbons.
An important step in the process of the invention comprises intimately contacting the gaseous mixture and the aqueous absorbent at pressures in the order of 1 to 100 kg/cm2 abs. A preferred pressure range is from 5 to 70 kg/cm2 abs. A highly preferred aspect of the operation of the absorption column is to conduct absorption under countercurrent contacting at temperatures in the range of about 15C to about 135C, more preferably of about 30C
to 80C and wherein the temperature of the bottom of the absorption tower is about 5C to 30C higher than the temperature in the top part of the absorption zone.
; Normally, intimate contacting is effected in a vertical column, the sweet dry gas leaving the column near or at the top while the fat absorbent solution leaves at or near the bottom of this column.
.~
The fat absorbent contains dissolved acidic gases, such as hydrogen sulphide and carbon dioxide, carbonyl sulphide and/or mercaptans, together with possible con-taminating proportions of hydrocarbons, originally present in the gaseous mixture. Under the preferred absorption conditions, the proportion of hydrocarbons contaminant to hydrogen sulphide is maintained at a low level.
The fat absorbent is conducted from the bottom portion of the absorption column under high pressure to a regener-ation zone wherein the pressure is reduced to 0.0-4 kg/cm2 gauge for the purpose of removing the acidic gases and other absorbed gaseous contaminants. In this zone, referred to as a gas stripper or stripper column, the solution is heated to a temperature sufficient to volatilize the acidic gases and other absorbed gaseous contaminants, and water therefrom, which leave the stripping column at the top. The fat absorbent may also be sent firstly to a flashing zone wherein a major part of the absorbed acidic gases and other absorbed gaseous contaminants is removed from the absorbent by reducing the pressure to 1.5-8 kg/cm2 abs. Thereafter the absorbent is regenerated as described.
One of the chief advantages of the use of the aqueous absorbent of the present invention is experienced during -the stripping operation.
It has been found that in stripping the fat absorbent ; to remove the acidic gases absorbed the steam requirement ,, 7Z;~
per unit volume of absorbent is more or less constan~.
Thus, by reducing the solvent circulation less steam has to be used. It is possible to employ stripping temperatures between about 100C and 190C at pressures between about 0 and 4 kg/cm2 gauge. The use of these low regeneration temperatures has a distinct advantage in that any thermal degradation of the organic solvent fractions of the ab-sorbent is greatly reduced.
Fig. 1 shows a schematic flow diagram of an embodiment of the process of the invention, in which a gaseous feed stream is countercurrently contacted with a descending ab-sorbent flow. Apart from the heat exchangers and pumps shown any further ancillary equipment has been omitted.
Fig. 2 shows a different embodiment of the process of the invention in which two separate absorption columns are used instead of a single column divided into two separate sections.
In Fig. 1 a gaseous mixture comprising acidic gases is introduced into the lower section of an absorption column 2 via a line 1. The absorption column 2 is provided with trays of which the lowest one is indicated by a and the top one by b. The said column is divided in two sections by means of a total draw-off tray 4 which is provided somewhere between the second and tenth tray. The gaseous mixture is introduced below the first tray (tray a) and the aqueous absorbent is introduced above the top tray (tray b) via a line 9. The gaseous mixture rises in the lower section and passes via the total draw-off tray 4 into the upper section of the column. It is counter-currently contacted by the descending aqueous absorbent.
As result of the released heat of absorption during the absorption of acidic gases the aqueous absorbent is gradually increasing in temperature. The warmed-up ab-sorbent is withdrawn from the column via a line 5 and externally cooled in a heat exchanger 6 and re-introduced into the lower section of the absorption column 2 by means of a pump 7 and a line 8. The gaseous mixture in the lower section is contacted with a cooled and semi-fat aqueous absorbent. As a result of the absorption of the acidic gases the temperature of the absorbent rises again.
The treated gaseous mixture which is now substantially free of acidic gases and/or carbonyl sulphide and/or mer-captans, if present, leaves the column via a line 11. The hot, fat absorbent leaves the column 2 at the bottom thereof via a line 12 and is heat-exchanged with hot, regenerated absorbent in a heat exchanger 10. Thereafter, the fat aqueous absorbent is introduced into a stripper column 13 for regeneration.
The stripper column operates at a reduced pressure with respect to the pressure applied in the absorption column. It is heated by means of a reboiler 18. Hot aqueous absorbent is withdrawn at the bottom of the 11137Z~
stripper column 13 via a line 14 and further heated in the reboiler 18. It is re-introduced into the stripper column via a line 19. The acidic gases stripped from the ab-- sorbent leave the stripper column via a line 20. The lean regenerated absorbent leaves the stripper column 13 via a line 15 and is pumped back to the absorption column 2 by means of a pump 16. The hot lean absorbent is cooled by heat exchange in the heat exchanger 10 as set out above and further cooled in a cooler 17.
The acidic gases obtained in the process of the in-vention can be used for the preparation of elemental sulphur.
This may be done by the well-known modified Claus process.
Depending on the H2S/C02 ratio in the acidic gases they may be fed directly - preferably after cooling and condensation of the water vapour - into the thermal stage of the sulphur recovery unit or they should be subjected to a further en-richment step prior to their introduction into the said thermal stage.
In Fig. 2 the same reference numerals have been used for identical parts. Instead of a single column 2 two separate columns 2a and 2b are used. The gaseous mixture leaves column 2a - comparable with the lower section of the column 2 in Fig. 1 - via a line 40 at the top and enters column 2b at the bottom thereof. The semi-fat ab-sorbent leaves column 2b at its bottom and is introduced after cooling at the top of column 2a.
The invention will now be illustrated with the fol-lowing Examples.
EXAMPLE I
A natural gas feed stream comprising 3 vol.% H2S and 12 vol.% C02 was fed at a temperature of 40C and a pressure of 12 bar abs. and a flow rate of 100,000 Nm3/h to an absorber/stripper unit as shown in Fig. 1. The aqueous absorbent usedc~prised 45% of di-isopropanolamine, 40%
of sulfolane and 15% by weight of water. It was introduced at the top of the absorber column at a temperature of 41C.
The column was provided with 40 trays, a total draw-off tray being installed between the 3rd and 4th tray. The temperature of the semi-fat absorbent withdrawn from the column was 66C. The absorbent was externally cooled with water and reintroduced at a temperature of 41C directly under the draw-off tray. The temperature of the fat ab-sorbent leaving the column was 57C and passed at indirect heat exchange with the hot, lean absorbent to the regener-- ation column. It was introduced at a temperature of 91C
into the regeneration column operating at a pressure of 2.0 kg/cm2 abs. The regenerated lean absorbent left the regeneration column at a temperature of 137C. After heat exchange with the fat absorbent and cooling with water it was introduced at a temperature of 41C at the top of the absorber column.
7~3 The treated gas mixture leaving at the top of the ab-sorber column comprised less than 4 ppm H2S and 500 ppm C02.
The amount of absorbent flow was 360 m3/h and the amount of steam required for the regeneration 43 tons/h.
Processing of the above feed in a standard gas treat-ing unit not having external cooling facilities as shown in the Figure and having 35 trays, would have required 500 m3/h of absorbent and 57 tons/h of steam to obtain the same degree of purification of the gaseous mixture treated.
EXAMPLE II
In the same manner as described in Example I two further experiments were carried out with feed gases of different compositions and at different flow rates. The reaction conditions and the results obtained have been tabulated in the Table. In this Table also the conditions and results of the experiment of Example I have been in-serted as Experiment No. 1.
1~137Z3 . , .' g g ~
v~ o ~ -I oo o ~
~ ~ t` 00 h t~ _ O O .......
O O O ~
o o ~ ~ co O ~ a~
~ ~1 1~ . . h ~ 00 O O
_ _ _. __ O^ ON ~O O
N V
~ _ o O ~
O 1~ U~ 00O O V) O t~) ^ O N ~) ILl ¦ _ _ ~ ~ ~ . h ., g ~0 0 ~ ' .' U) N ^ t~ N U)O O Q) ~ O . h ~1 .~ oO O O ~ ~ ' :- ~ ' ~ N ^ t~ N117 h .
O ,D ~o\O o\
O V~ .0 V~
t~) ~o ,~ o~d .~ a) ~ ~1 ~ u~U~ N.~ t~4 V~ U~ N . C
(D ~ hUl O N O ~ O N O ~
h h ~~d 0~ ~ ~ X ~ O
a) ~d ~ 41~ td c~
X ~ o . E-l .... 1 -.
;~ ~
, o t~r` 00 O In N O
O L~ 00 O I ~ ~t N ~t ~
.. _ l u~ ~ o ~ ~ n L
00 ~ I
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O Ln O Lr~ U~
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.__ o u) o n _~ ~ ~ ~
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. _ ___ _ . _ ._ '.' ~1 . - .
O L~ OLr~ _I I I d-Ln ~ ~ _l ~ ~ ,:
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:
volume (100 ppm) mercaptans in addition to substantial quantities of H2S and C02. Since the COS and mercaptans present in the sour gas make-up part of the total sulphur, substantial removal of same, in addition to the H2S
present, is necessary to meet many of the specifications for conventional end uses of such gas, e.g., residential heating and industrial uses. Further, in conventional partial combustion processes utilizing sour liquid hydro-carbon oils or sulphur-containing coals as the primary fuel source, a crude synthesis gas product is obtained which typically contains 100 to 1500 ppm COS in addition to the H2S and C02 partial combustion by-products. In many cases this crude synthesis gas product is subject to further processing, e.g., contact with sulphur-sensitive ~ C0-shift catalysts in hydrogen manufacture, or funnelled to industrial and consumer end-uses, e.g., as energy source in gas turbine generation of electricity or as a town gas for private consumption, which makes it desirable or even essential that the total sulphur content of the combustion gas be reduced to very low levels.
Although the commercially available gas-treating processes are generally satisfactory with respect to the degree of removal of undesirable gas contaminants, there is still room for further improvement of such processes.
A major cost factor for these regenerative processes constitutes the stripping steam requirement for regener-` ~137Z3 ating the fat absorbent which can be very high for many solvents.
The said steam requirement is greatly dependent on the amount of absorbent circulating, so that reduction of this absorbent circulation would necessarily bring about a reduction in the steam consumption. The amount of absorbent to be used in a particular case is dictated by the partial pressures of the acidic gas components in the gaseous mixture to be treated and the desired degree of gas purification. A reduction in the absorbent circulation would also contribute to further savings from a capital cost point of view in that smaller absorption and regeneration columns are required and in that less absor-bent solvent for filling the columns is necessary.
This invention seeks to provide a process for the -removal of acidic gases as identified to a very high degree while using a reduced absorbent circulation.
Accordingly, the present invention relates to a pro-cess for the removal of àcidic gases from a gaseous mixture containing the same by contacting the said gaseous mixture countercurrently in a contacting zone at a temperature in the range of 15 to 135C and at a pressure of from 1 to 100 kg/cm2 abs., with an aqueous absorbent comprising an amine with a PKb Of 3-14 at 25C in an amount of 10 to 70~ by weight and sulfolane and/or its derivatives in an amount of 25 to 70~ by weight, which aqueous absorbent is introduced at the top of the contacting zone, and a fat aqueous absorbent is finally with-drawn from the contacting zone at the bottom thereof for regeneration by means of heating and/or stripping, in which process at an intermediate point at the lower part of the said contacting zone the said aqueous absorbent is withdrawn from said contacting zone as a semi-fat absorbent and is reintroduced into the said lower part of said contacting zone after having ,~
1~137Z3 been cooled externally, for further contacting with the said aqueous mixture.
The process of the present invention is particularly suitable for treating gaseous mixtures comprising acidic gases at relatively low partial pressures. This may be the case when the mixture to be treated comprises little acidic gas components or when it contains the said gas components at relatively low pressures~ The sum of the partial pressures of hydrogen sulphide and carbon dioxide should preferably be lower than 3.0 bar, and more preferably lower than 2.0 bar at the temperature applied during absorption. The greatest benefit will be derived from the process of the invention when applying it to gaseous mixtures having a hydrogen sul-phide partial pressure in the range of from 0.025 to 0.6 bar at a lean absorbent temperature of 30 to 65C. In applying the process of the invention for the removal of carbon dioxide from gaseous mixtures comprising substantially no hydrogen sulphide (less than 0.1% vol. H2S) the carbon dioxide partial pressures may vary in the range of from 0.1 to 2.0 bar at a lean absorbent temperature as indicated.
. :
ci ~113723 The process of the invention is also very suitable for application in those areas of the world where deep cooling to temperatures below 50C is not well possible because the ambient temperature in these areas during at least part of the year does not drop below the figure indicated.
Even in these instances intermediate cooling to temper-atures of about 65C may considerably add to reducing the absorbent circulation.
The contacting zone used preferably comprises of from 10 to 50 contacting layers, such as valve trays, bubble cap trays, baffles and the like. The aqueous absorbent is suitably withdrawn at an intermediate point above the second contacting layer but below the fifteenth contacting layer of the absorption zone if 20 layers or more are applied or below the tenth contacting layer if less than 20 layers are applied.
The aqueous absorbent used in the present process comprises a "chemical" solvent part, i.e., the weak basic component, and a "physical" solvent part, i.e., sulfolane and/or its derivatives.
The chemical solvent part comprises certain components or mixtures of these components of the class of amines.
; For the process according to the invention these amines should have a weakly basic character. (The basic strength of a compound is conveniently expressed in terms of the negative logarithm of the basic dissociation constant,.
Thus, a strong base has a low pKb, while a weak base has a value approaching the upper limit PKb = 14). Bases suit-able for the process according to the invention have a PKb at 25C in the range of 3 to 14. Alkanolamines are particularly suitable, especially those amines having 1 to 4, and preferably 2 to 3, carbon atoms per alkanol radical. Typical species are, inter alia, monoethanol-amine, diethanolamine, methyldiethanolamine, di-iso-propanolamine, triethanolamine and mixtures thereof.
Especially the dialkanolamines can be used with advantage.
The physical solvent part comprises certain com-ponents or mixtures thereof, selected from the group of cyclotetramethylene sulphones. The derivatives from the basic sulphone cyclotetramethylene sulphone (thiophene tetrahydro-1,1-dioxide) which is also known as sulfolane, should preferably have not more than 4, more preferably not more than 2 alkyl substituents in the tetramethylene sulphone ring. Sulfolane itself is the preferred species of this class of compounds.
It has been found advantageous to use in the process an aqueous absorbent which preferably contains the weak basic component within the range of 20-55%wt. An absorbent containing 30-45%wt of the weak basic component has been found very suitable. The sulfolane or its derivatives are preferably present in the absorbent in an amount of 30 to 55%wt. The balance of the mixed solvent consists essentially of water, generally in the range of 5-35%wt.
_7_ , ~1~3723 The descending aqueous absorbent can be withdrawn from the absorption column by means of a total draw-off tray. Such a tray divides the column in two sections with respect to the flow of absorbent, but has a passage for the rising gas mixture to allow it to pass from the lower section into the upper section. The absorbent col-lected on the draw-off tray is withdrawn from the ab-sorption column and externally cooled by indirect heat exchange to a temperature in the range of from 20 to 70C. More preferably, the withdrawn aqueous absorbent which is semi-fat, is cooled to a temperature which is ~; the same as the temperature of the aqueous absorbent introduced at the top of the absorption column. There-after the cooled, semi-fat absorbent is reintroduced into the column in the lower section, preferably directly under the total draw-off tray. It will be evident by the position of the total draw-off tray that the lower section of the column is shorter than the upper section of the column, which latter section encompasses more absorption trays.
It is also possible to use two absorption columns of different column length and arranged such that the gaseous mixture contacts first in the shorter one of the two columns a cooled semi-fat absorbent introd~ced at the top of this shorter column and then countercurrently contacts a lean absorbent in the taller one of the two columns.
. ' ~
~1137;:3 The fat absorbent leaving the shorter column is regener-ated, cooled and introduced at the top ~ the taller column as the lean absorbent.
The principal attainment of the process of this in-vention is the high degree of removal of acidic gas com-ponents from gaseous mixtures at very low partial pressures of these acidic gas components and at reduced absorbent flows. Because a low temperature has particularly a favour-able effect on the absorption of hydrogen sulphide and/or carbon dioxide, intermediate cooling of the absorbent before its introduction into the lower section results in more favourable absorption equilibria for hydrogen sulphide and/or carbon dioxide in the bottom of the absorption column. When a gaseous mixture enters the lower section of the absorption column countercurrent to a descending stream of cold liquid absorbent, a high degree of ab-sorption is obtained even at the relatively low partial pressures of the acidic gases. This high degree ~ ab-sorption is maintained as the total amount of acidic gas components progressively decreases as the gas mixt-ure proceeds upward in the column, because in proceeding upwards the gaseous mixture is contacted with an absorbent, the temperature whereof is decreasing.
Gaseous mixtures which can advantageously be treated by the process according to the invention, include natural gas, refinery gas or synthesis gas obtained by the partial -_g_ oxidation of heavy oil fractions or coal. The process is particularly attractive for the treatment of gases con-taining high amounts of acidic gases, such as hydrogen sulphide and carbon dioxide at relatively low partial pressures. The gaseous mixtures to be treated in ac-cordance with the process of the present invention may also contain carbonyl sulphide in amounts of from 0 to 1500 ppmv and mercaptans in amounts of from 0 to 500 ppmv.
The process may be adapted to treat such feedstocks which also contain higher molecular weight hydrocarbons.
An important step in the process of the invention comprises intimately contacting the gaseous mixture and the aqueous absorbent at pressures in the order of 1 to 100 kg/cm2 abs. A preferred pressure range is from 5 to 70 kg/cm2 abs. A highly preferred aspect of the operation of the absorption column is to conduct absorption under countercurrent contacting at temperatures in the range of about 15C to about 135C, more preferably of about 30C
to 80C and wherein the temperature of the bottom of the absorption tower is about 5C to 30C higher than the temperature in the top part of the absorption zone.
; Normally, intimate contacting is effected in a vertical column, the sweet dry gas leaving the column near or at the top while the fat absorbent solution leaves at or near the bottom of this column.
.~
The fat absorbent contains dissolved acidic gases, such as hydrogen sulphide and carbon dioxide, carbonyl sulphide and/or mercaptans, together with possible con-taminating proportions of hydrocarbons, originally present in the gaseous mixture. Under the preferred absorption conditions, the proportion of hydrocarbons contaminant to hydrogen sulphide is maintained at a low level.
The fat absorbent is conducted from the bottom portion of the absorption column under high pressure to a regener-ation zone wherein the pressure is reduced to 0.0-4 kg/cm2 gauge for the purpose of removing the acidic gases and other absorbed gaseous contaminants. In this zone, referred to as a gas stripper or stripper column, the solution is heated to a temperature sufficient to volatilize the acidic gases and other absorbed gaseous contaminants, and water therefrom, which leave the stripping column at the top. The fat absorbent may also be sent firstly to a flashing zone wherein a major part of the absorbed acidic gases and other absorbed gaseous contaminants is removed from the absorbent by reducing the pressure to 1.5-8 kg/cm2 abs. Thereafter the absorbent is regenerated as described.
One of the chief advantages of the use of the aqueous absorbent of the present invention is experienced during -the stripping operation.
It has been found that in stripping the fat absorbent ; to remove the acidic gases absorbed the steam requirement ,, 7Z;~
per unit volume of absorbent is more or less constan~.
Thus, by reducing the solvent circulation less steam has to be used. It is possible to employ stripping temperatures between about 100C and 190C at pressures between about 0 and 4 kg/cm2 gauge. The use of these low regeneration temperatures has a distinct advantage in that any thermal degradation of the organic solvent fractions of the ab-sorbent is greatly reduced.
Fig. 1 shows a schematic flow diagram of an embodiment of the process of the invention, in which a gaseous feed stream is countercurrently contacted with a descending ab-sorbent flow. Apart from the heat exchangers and pumps shown any further ancillary equipment has been omitted.
Fig. 2 shows a different embodiment of the process of the invention in which two separate absorption columns are used instead of a single column divided into two separate sections.
In Fig. 1 a gaseous mixture comprising acidic gases is introduced into the lower section of an absorption column 2 via a line 1. The absorption column 2 is provided with trays of which the lowest one is indicated by a and the top one by b. The said column is divided in two sections by means of a total draw-off tray 4 which is provided somewhere between the second and tenth tray. The gaseous mixture is introduced below the first tray (tray a) and the aqueous absorbent is introduced above the top tray (tray b) via a line 9. The gaseous mixture rises in the lower section and passes via the total draw-off tray 4 into the upper section of the column. It is counter-currently contacted by the descending aqueous absorbent.
As result of the released heat of absorption during the absorption of acidic gases the aqueous absorbent is gradually increasing in temperature. The warmed-up ab-sorbent is withdrawn from the column via a line 5 and externally cooled in a heat exchanger 6 and re-introduced into the lower section of the absorption column 2 by means of a pump 7 and a line 8. The gaseous mixture in the lower section is contacted with a cooled and semi-fat aqueous absorbent. As a result of the absorption of the acidic gases the temperature of the absorbent rises again.
The treated gaseous mixture which is now substantially free of acidic gases and/or carbonyl sulphide and/or mer-captans, if present, leaves the column via a line 11. The hot, fat absorbent leaves the column 2 at the bottom thereof via a line 12 and is heat-exchanged with hot, regenerated absorbent in a heat exchanger 10. Thereafter, the fat aqueous absorbent is introduced into a stripper column 13 for regeneration.
The stripper column operates at a reduced pressure with respect to the pressure applied in the absorption column. It is heated by means of a reboiler 18. Hot aqueous absorbent is withdrawn at the bottom of the 11137Z~
stripper column 13 via a line 14 and further heated in the reboiler 18. It is re-introduced into the stripper column via a line 19. The acidic gases stripped from the ab-- sorbent leave the stripper column via a line 20. The lean regenerated absorbent leaves the stripper column 13 via a line 15 and is pumped back to the absorption column 2 by means of a pump 16. The hot lean absorbent is cooled by heat exchange in the heat exchanger 10 as set out above and further cooled in a cooler 17.
The acidic gases obtained in the process of the in-vention can be used for the preparation of elemental sulphur.
This may be done by the well-known modified Claus process.
Depending on the H2S/C02 ratio in the acidic gases they may be fed directly - preferably after cooling and condensation of the water vapour - into the thermal stage of the sulphur recovery unit or they should be subjected to a further en-richment step prior to their introduction into the said thermal stage.
In Fig. 2 the same reference numerals have been used for identical parts. Instead of a single column 2 two separate columns 2a and 2b are used. The gaseous mixture leaves column 2a - comparable with the lower section of the column 2 in Fig. 1 - via a line 40 at the top and enters column 2b at the bottom thereof. The semi-fat ab-sorbent leaves column 2b at its bottom and is introduced after cooling at the top of column 2a.
The invention will now be illustrated with the fol-lowing Examples.
EXAMPLE I
A natural gas feed stream comprising 3 vol.% H2S and 12 vol.% C02 was fed at a temperature of 40C and a pressure of 12 bar abs. and a flow rate of 100,000 Nm3/h to an absorber/stripper unit as shown in Fig. 1. The aqueous absorbent usedc~prised 45% of di-isopropanolamine, 40%
of sulfolane and 15% by weight of water. It was introduced at the top of the absorber column at a temperature of 41C.
The column was provided with 40 trays, a total draw-off tray being installed between the 3rd and 4th tray. The temperature of the semi-fat absorbent withdrawn from the column was 66C. The absorbent was externally cooled with water and reintroduced at a temperature of 41C directly under the draw-off tray. The temperature of the fat ab-sorbent leaving the column was 57C and passed at indirect heat exchange with the hot, lean absorbent to the regener-- ation column. It was introduced at a temperature of 91C
into the regeneration column operating at a pressure of 2.0 kg/cm2 abs. The regenerated lean absorbent left the regeneration column at a temperature of 137C. After heat exchange with the fat absorbent and cooling with water it was introduced at a temperature of 41C at the top of the absorber column.
7~3 The treated gas mixture leaving at the top of the ab-sorber column comprised less than 4 ppm H2S and 500 ppm C02.
The amount of absorbent flow was 360 m3/h and the amount of steam required for the regeneration 43 tons/h.
Processing of the above feed in a standard gas treat-ing unit not having external cooling facilities as shown in the Figure and having 35 trays, would have required 500 m3/h of absorbent and 57 tons/h of steam to obtain the same degree of purification of the gaseous mixture treated.
EXAMPLE II
In the same manner as described in Example I two further experiments were carried out with feed gases of different compositions and at different flow rates. The reaction conditions and the results obtained have been tabulated in the Table. In this Table also the conditions and results of the experiment of Example I have been in-serted as Experiment No. 1.
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v~ o ~ -I oo o ~
~ ~ t` 00 h t~ _ O O .......
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_ _ _. __ O^ ON ~O O
N V
~ _ o O ~
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, . . . .
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, . . . .
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Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the removal of acidic gases from a gas-eous mixture containing the same by contacting the said gaseous mixture countercurrently in a contacting zone at a temperature in the range of 15 to 135°C and at a pressure of from 1 to 100 kg/cm2 abs., with an aqueous absorbent comprising an amine with a pkb of 3-14 at 25°C in an amount of 10 to 70% by weight and sulfolane and/or its derivatives in an amount of 25 to 70% by weight, which aqueous absorbent is introduced at the top of the contacting zone, and a fat aqueous absorbent is finally with-drawn from the contacting zone at the bottom thereof for regen-eration by means of heating and/or stripping, in which process at an intermediate point at the lower part of the said contact-ing zone the said aqueous absorbent is withdrawn from said contacting zone as a semi-fat absorbent and is reintroduced into the said lower part of said contacting zone after having been cooled externally, for further contacting with the said aqueous mixture.
2. A process as claimed in claim 1, in which the contact-ing zone comprises of from 10 to 50 contacting layers and where-in the aqueous absorbent is withdrawn at an intermediate point above the second contacting layer.
3. A process as claimed in claim 2, in which the contact-ing zone comprises 20 or more contacting layers and wherein the aqueous absorbent is withdrawn at an intermediate point below the fifteenth contacting layer.
4. A process as claimed in claim 2, in which the contact-ing zone comprises less than 20 trays and wherein the aqueous absorbent is withdrawn at an intermediate point below the tenth contacting layer.
5. A process as claimed in claim l,in which the withdrawn aqueous solvent is externally cooled to a temperature in the range of from 20 to 70°C.
6. A process as claimed in claim 1, in which the with-drawn solvent is externally cooled to a temperature which is the same or substantially the same as the temperature of the aqueous absorbent introduced at the top of the absorption column.
7. A process as claimed in claim 1, in which the absorp-tion zone is divided in an upper section and a lower section with respect to the flow of the said absorbent by a total draw-off layer for the absorbent.
8. A process as claimed in claim 1, in which the absorp-tion zone comprises two absorption columns of different column length and arranged such that the gaseous mixture contacts first in the shorter one of the two columns a cooled, semi-fat absor-bent introduced at the top of this shorter column and then countercurrently contacts a lean absorbent in the taller one of the two columns, the fat absorbent leaving the shorter column being regenerated, cooled, and introduced at the top of the taller column as the lean absorbent.
9. A process as claimed in claim 7, in which the cooled, semi-fat absorbent is introduced in the lower section directly below the said total draw-off layer.
10. A process as claimed in claim 1, in which the gaseous mixture comprises hydrogen sulphide and carbon dioxide at such partial pressures that the sum thereof is lower than 3.0 bar at the temperature applied during absorption.
11. A process as claimed in claim l, in which the gaseous mixture comprises hydrogen sulphide at a partial pressure in the range of from 0.025 to 0.6 bar at a lean absorbent temper-ature of 30 to 65°C.
12. A process as claimed in claim 1, in which the gaseous mixture is substantially free of hydrogen sulphide and comprises carbon dioxide at a partial pressure in the range of from 0.1 to 2.0 bar at a lean absorbent temperature of 30 to 65°
13. A process as claimed in claim 1, in which the amine is di-isopropanolamine or methyl diethanolamine.
14. A process as claimed in claim 1, in which the fat aqueous absorbent is regenerated at a temperature in the range of from 100 to 190°C and at a pressure in the range of from 0.0 to 4 kg/cm gauge.
15. A process as claimed in claim 1, in which the gaseous mixture is contacted with the aqueous absorbent at a pressure of from 5 to 70 kg/cm2 abs.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB16630/77A GB1589231A (en) | 1977-04-21 | 1977-04-21 | Process for the removal of acidic gases |
| GB16630/77 | 1977-04-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1113723A true CA1113723A (en) | 1981-12-08 |
Family
ID=10080798
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,301A Expired CA1113723A (en) | 1977-04-21 | 1978-02-20 | Process for the removal of acidic gases |
Country Status (12)
| Country | Link |
|---|---|
| JP (1) | JPS53131972A (en) |
| AR (1) | AR210448A1 (en) |
| AU (1) | AU516485B2 (en) |
| BR (1) | BR7704428A (en) |
| CA (1) | CA1113723A (en) |
| DE (1) | DE2817084A1 (en) |
| FR (1) | FR2387678A1 (en) |
| GB (1) | GB1589231A (en) |
| GR (1) | GR64822B (en) |
| NL (1) | NL7804154A (en) |
| TR (1) | TR21114A (en) |
| ZA (1) | ZA782241B (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1128293A (en) * | 1978-04-07 | 1982-07-27 | Roelof Cornelisse | Removal of acid gases from a gas mixture |
| US4397660A (en) * | 1981-06-15 | 1983-08-09 | Shell Oil Company | Process for the removal of H2 S and CO2 from a gas mixture |
| CA1205276A (en) * | 1981-06-15 | 1986-06-03 | Malcolm W. Mcewan | Process for the removal of co.sub.2 and, if present h.sub.2s from a gas mixture |
| AU3097484A (en) * | 1983-07-26 | 1985-01-31 | Bechtel International Corporation | Desulfurization of fuel gas |
| IT1191805B (en) * | 1986-06-11 | 1988-03-23 | Snam Progetti | PROCESS FOR SELECTIVE REMOVAL OF SULPHIDIC ACID |
| FR2771022B1 (en) * | 1997-11-19 | 1999-12-17 | Inst Francais Du Petrole | PROCESS FOR DEACIDIFYING A GAS WITH A HIGH ACID GAS CONTENT |
| EP1474218B1 (en) | 2002-01-14 | 2008-12-10 | Shell Internationale Researchmaatschappij B.V. | Process for removing carbon dioxide from gas mixtures |
| EP1879987A1 (en) * | 2005-05-13 | 2008-01-23 | Shell Internationale Research Maatschappij B.V. | Removal of carbon dioxide from a gas stream |
| US20070221065A1 (en) * | 2006-03-23 | 2007-09-27 | Adisorn Aroonwilas | Heat recovery gas absorption process |
| AU2009262906A1 (en) * | 2008-06-26 | 2009-12-30 | Uop Llc | Carbon dioxide absorber partial pumparound for cooling semi-lean physical solvent |
| FR2936165B1 (en) * | 2008-09-23 | 2011-04-08 | Inst Francais Du Petrole | METHOD FOR DEACIDIFYING GAS BY ABSORBENT SOLUTION WITH CONTROL OF HALF |
| PL2382028T3 (en) | 2009-01-28 | 2018-10-31 | Siemens Aktiengesellschaft | Method for separating carbon dioxide from an exhaust gas of a fossil fired power plant |
| PL2665543T3 (en) * | 2011-01-18 | 2018-03-30 | Commonwealth Scientific And Industrial Research Organisation | Process for capturing acid gases |
| DE102011107814A1 (en) * | 2011-07-01 | 2013-01-03 | Linde Aktiengesellschaft | Process and apparatus for recovering gas products |
| DE102012202703A1 (en) | 2012-02-22 | 2013-08-22 | Siemens Aktiengesellschaft | Improving the enthalpieschen process efficiency of a CO2 capture device in a power plant |
| CA2953219A1 (en) * | 2014-06-06 | 2015-12-10 | Virginia Tech Intellectual Properties, Inc. | Energy-efficient extraction of acid gas from flue gases |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1157455A (en) * | 1956-08-23 | 1958-05-29 | Azote & Prod Chim | Improvement in gas purification processes using regenerable ammoniacal solutions and preparation of very high carbon dioxide |
| NL243608A (en) * | 1958-09-22 | |||
| BE611855A (en) * | 1960-12-23 | |||
| DE1501720B1 (en) * | 1965-11-15 | 1970-07-09 | Linde Ag | Process for separating CO2 and H2S from gas mixtures |
| DE1903693A1 (en) * | 1969-01-25 | 1970-08-20 | Uhde Gmbh Friedrich | Removal of h2s and heavy hydrocarbons from - high-pressure natural gas |
| DE2605287C2 (en) * | 1975-03-27 | 1986-11-06 | Koppers Co., Inc., Pittsburgh, Pa. | Process for removing acidic components from gases |
| NL183225C (en) * | 1975-06-13 | 1988-09-01 | Shell Int Research | METHOD FOR REMOVING ACID GASES FROM A GAS OR LIQUID MIXTURE USING AN AQUEOUS AMINE SOLUTION |
-
1977
- 1977-04-21 GB GB16630/77A patent/GB1589231A/en not_active Expired
- 1977-05-30 AR AR267840A patent/AR210448A1/en active
- 1977-07-06 BR BR7704428A patent/BR7704428A/en unknown
-
1978
- 1978-02-20 CA CA297,301A patent/CA1113723A/en not_active Expired
- 1978-04-19 FR FR7811541A patent/FR2387678A1/en active Granted
- 1978-04-19 TR TR21114A patent/TR21114A/en unknown
- 1978-04-19 NL NL7804154A patent/NL7804154A/en active Search and Examination
- 1978-04-19 DE DE19782817084 patent/DE2817084A1/en active Granted
- 1978-04-19 GR GR56021A patent/GR64822B/en unknown
- 1978-04-19 AU AU35252/78A patent/AU516485B2/en not_active Expired
- 1978-04-19 ZA ZA00782241A patent/ZA782241B/en unknown
- 1978-04-19 JP JP4545478A patent/JPS53131972A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| AR210448A1 (en) | 1977-07-29 |
| FR2387678A1 (en) | 1978-11-17 |
| JPS53131972A (en) | 1978-11-17 |
| TR21114A (en) | 1983-09-30 |
| AU3525278A (en) | 1979-10-25 |
| GR64822B (en) | 1980-06-03 |
| DE2817084C2 (en) | 1992-02-20 |
| GB1589231A (en) | 1981-05-07 |
| NL7804154A (en) | 1978-10-24 |
| JPS6139093B2 (en) | 1986-09-02 |
| FR2387678B1 (en) | 1982-12-31 |
| ZA782241B (en) | 1979-04-25 |
| DE2817084A1 (en) | 1978-11-02 |
| BR7704428A (en) | 1978-11-14 |
| AU516485B2 (en) | 1981-06-04 |
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