Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 The present invention relates to an alkaline
2 promoter system comprising specific mixtures of non-
3 sterically hindered amino compounds and sterically
~ hindered amino acids and their use in acid gas scrubbing
processes, particularly in the "hot pot" type acid gas
6 scrubbing processes.
7 The present invention pertains to an improved
8 process for carrying out what is known as the aqueous
g base scrubbing process or "hot potash" ("hot pot")
process. In this process a relatively small level of an
11 amine is included as an activator for the aqueous base
12 used in the scrubbing solution. This type of process
13 is generally used where bulk removal of an acid gas,
14 such as CO2, is desired. This process also applies
to situations where the CO2 and feed gas pressures
16 are high. In such processes, useful results are achiev-
17 ed using aqueous potassium carbonate solutions and an
18 amine activator. Many industrial processes for removal
19 of acid gases, such as CO2, use regenerable aqueous
alkaline scrubbing solutions, such as a potassium
21 carbonate and an activator comprising an amine, which
22 are continuously circulated between an absorption zone
23 where acid gases are absorbed and a regeneration zone
24 where they are desorbed, usually by pressure reduction
and steam-stripping~ The capital cost of these acid gas
26 scrubbing processes is generally controlled by the size
27 of the absorption and regeneration towers, the size of
28 the reboilers for generating stripping steam, and the
29 size of the condensers which condense spent stripping
steam so that condensate may be returned to the system
31 to maintain proper water balance. The cost of operating
32 such scrubbing plants is generally related to the amount
33 of heat required for the removal of a given amount o
3~ acid gas, e.g., thermal efficiency, sometimes expressed
as cubic feet of acid gas removed per pound of steam
36 consumed. Means for reducing the costs in operating
~1
1 these industrial processes have focused on the use o~
2 absorbing systems or combinations of chemical absorbents
3 which will operate more efficiently and effectively in
4 acid gas scrubbing processes using existing equipmentO
There are a number of patents which describe
6 processes to improve the efficiency of the "hot potash"
7 process. Some of these improvement processes are
8 described below.
g In U.S. Patent No. 2,718,454, there is
described a process for using potash and similar alkali
11 metal salts in conjunction with amines, such as mono-
12 ethanolamine, diethanolamine and triethanolamine to
13 remove acid gases from a gas mixture. The combination
14 of the alkali metal compounds in conjunction with the
designated amine yields higher capacity for acid gases
16 than systems with the amines alone.
17 In U~Sn Patent No. 3,144,301, there is dis-
18 closed the use of potassium carbonate in conjunction
19 with monoethanolamine and diethanolamine to remove C02
from gaseous mixtures.
21 U.S. Patent Nos. 3,563,695; 3,563,696, and
22 3,642,430 to Benson et al. disclose processes for
23 removing C02 and H2S from gaseous mixtures by alkaline
24 scrubbing processes wherein at least two separate
regeneration zones are provided. Alkanolamines and
26 amino acids such as glycine are described as activators,
27 but the use of sterically hindered amino compounds i5
28 not taught or disclosed in these patents.
29 In U.S0 Patent Nos. 3,637,345; 3,763,434, and
3,848,057 processes for the removal of acid gases by
31 means of aqueous carbonate scrubbing solutions activated
1 by an amino compound such as 1,6-hexanediamine, piperi-
2 dine and their derivatives are described.
3 In U.S. Patent No. 3,356,921, there is dis-
4 closed a process for removal of acid gases from fluids
by use o~ a basic salt of an alkali or alkaline earth
6 metal and an amino compound activator, such as 2-methyl-
7 aminoethanol, 2-ethylaminoethanol, morpholine, pyrroli-
8 dine and derivatives thereof.
g Belgian Patent No. 767,105 discloses a process
for removing acid gases from gaseous streams by contact-
11 ing the gaseous streams with a solution comprising
12 potassium carbonate and an amino acid, such as substi-
13 tuted glycines (e.g., N-isopropyl glycine, N-t-butyl-
14 glycine, N-cyclohexylglycine, etc.). The data in Table
IV of the patent indicates that the highly substituted
16 compounds, such as N-t-butylglycine, are inferior to the
17 straight chain compounds, such as N-n-butyl glycine, but
18 N-cyclohexyl glycine, a sterically hindered amine, has a
19 good rate of absorption. Similarly, British Patent No.
1,305,718 describes the use of beta- and gamma amino
21 acids as promoters for alkaline salts in the "hot pot"
22 acid gas treating process. These amino acids, however,
23 are not suitable because the beta- amino acids undergo
24 deamination when heated in aqueous potassium carbonate
solutions. The gamma amino acids form insoluble lactams
26 under the same conditions.
27 Recently, it was shown in U.S. Patent No.
28 4,112,050 that sterically hindered amines are superior
29 to diethanolamine (DEA) and 1,6-hexanediamine ~IMDA) as
promoters for alkaline salts in the "hot pot" acid gas
31 scrubbing process. U.S. Patent No. 4,094,957 describes
32 an improvement to the '050 patented process whereby
33 amino acids, especially sterically hindered amino acids,
34 serve to prevent phase separation of the aqueous solu-
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1 tion containing sterically hindered amines at high2 temperatures and low fractional conversions during
3 the acid gas scrubbing process. In these patents
4 "sterically hindered amines" are defined as amino
compounds containing at least one secondary amino group
6 attached to either a secondary or tertiary carbon atom
7 or a primary amino group attached to a tertiary carbon
8 atom. At least one nitrogen atom w;ll have a sterically
9 hindered structure.
In some instances, where an existing commer-
11 cial gas treating plant utilizes a non-sterically
12 hindered amine promoter such as diethanolamine or
13 1,6-hexanediamine, there is a need to increase the C02
14 scrubbing capacity due to increased levels of CO2 in
the gas. The need to meet this increased C2 capacity
16 can be accomplished by increasing the size o the plant
17 (e.g., adding treating towers and the like) or by
18 replacing the non-sterically hindered amine with steri-
19 cally hindered amines as proposed in U.S. Patent Nos.
4,094,957 and 4,112,050. In the case of the latter
21 approach, the preexisting scrubbing solution must be
22 removed and replaced with the fresh solution containing
23 potassium carbonate and sterically hindered amine. This
24 change-over procedure requires some "downtime" of the
plant with consequent losses of production. Therefore,
26 increasing the size of the gas treating plant or chang-
27 ing over the scrubbing solution can be costly.
28 It has now been discovered that one may add
29 sterically hindered amino acids to the non-sterically
hindered amino compound-promoted carbonate scrubbing
31 solution and thereby increase the CO2 absorption rate
32 relative to that of the pre-existing non-sterically
33 hindered amino compound-promoted carbonate.
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1 Accordingly, in one embodiment o~ the present
2 invention, there is provided a process for the removal
3 of C2 from a gaseous stream containing C2 which com-
~ prises contacting said gaseous stream as follows:
(1) in an absorption step absorbing said CO2
6 from said gaseous mixture with an aqueous absorbing
7 solution, comprising:
8ta) a basic alkali metal salt or hydrox-
9ide selected from the group consist-
10ing of alkali metal bicarbonates~
11carbonates, hydroxides, borates,
12phosphates and their mixtures, and
13(b) an activator or promoter system for
1~said basic alkali metal salt or
15hydroxide, comprising:
16(i) at least one non-sterically
17hindered amino compound, and
18(ii) at least one sterically hinder-
19ed amino acid, and
20(2) in a desorption and regeneration step,
21 desorbing at least a portion of the absorbed CO2 from
22 said absorbing solution.
23 The mole ratio of the non-sterically hindered
24 amino compound to the sterically hindered amino acid
25 may vary widely, but is preferably 1:3 to 3:1, most
26 preferably 1:1. The sterically hindered amino acid may
27 be added to the scrubbing solution containing the
28 non-sterically hindered amino compound all at once or in
~9 increments during the gas scrubbing operation.
1 As another embodiment of the invention, there
2 is provided an acid gas scrubbing composition, compris-
3 ing:
4 (a) 10 to about 40% by weight of an alkali
metal salt or hydrox;de;
6 (b) 2 to about 20~ by weight of a non-steri-
7 cally hindered amino compound;
8 (c) 2 to about 20% weight of a sterically
g hindered amino acid; and
(d) the balance, water.
11 The non-sterically hindered amino compound may
12 be any compound having amino functionality which is
13 water soluble in the presence of the sterically hindered
14 amino acid co-promoter. Typically, the non-sterically
hindered amino compound will comprise those amino
16 compounds heretofore used or described in acid gas
17 treating processes. By the term "non-sterically hin-
18 dered", it is meant those compounds that do not contain
19 at least one secondary amino group attached to either a
secondary or tertiary carbon atom or a primary amino
21 group attached to a tertiary carbon atom. Typically,
22 the nitrogen atoms will not have a sterically hindered
23 structure. For example, such compounds will include
24 diethanolamine, monoethanolamine, triethanolamine,
1,6-hexanediamine, piperidine and their derivatives and
26 the like. Preferably, the non-sterically hindered amino
27 compound will be diethanolamine or 1,6-hexanediamine
28 which are presently used in commercial acid gas treating
29 plants throughout the world.
The sterically hindered amino acids may
31 include any amino acid which is soluble in the alkaline
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1 aqueous solution to be used in thle acid gas treating
2 solution. Preferably, the amino acid will have 4 to 8
3 carbon atoms and contain one amino moiety. By the term
4 "sterically hindered amino acid", it is meant those
S amino acids that do contain at least one secondary amino
6 group attached to either a secondary or tertiary carbon
7 atom or a primary amino group attached to a tertiary
8 carbon atom. At least one of the nitrogen atoms will
9 have a sterically hindered structure. Typical steri-
cally hindered amino acids useful in the practice of
11 the present invention will include N-secondary butyl
12 glycine, pipecolinic acid, N-isopropyl glycine, N-2-amyl-
13 glycine, N-isopropyl alanine, N-sec. butyl alanine,
14 2-amino-2-methyl butyric acid and 2-amino-2-methyl
valeric acid.
16 In general, the aqueous scrubbing solution
17 will comprise an alkaline material comprising a basic
18 alkali metal salt or alkali metal hydroxide selected
19 from Group IA of the Periodic Table of Elements. More
preferably, the aqueous scrubbing solution comprises
21 potassium or sodium borate, carbonate, hydroxide,
22 phosphate or bicarbonate. Most preferably, the alkaline
23 material is potassium carbonate.
24 The alkaline material comprising the basic
alkali metal or salt or alkali metal hydroxide may be
26 present in the scrubbing solution in the range from
27 about 10% to about 40% by weight/ preferably from 20~
28 to about 35% by weight. The alkaline material, the
29 non-sterically hindered amine and the amino acid acti-
vator or promoter system remain in solution throughout
31 the entire cycle of absorption of CO2 from the gas
32 stream and desorption of CO2 from the solution in the
33 regeneration step. Therefore, the amounts and mole
34 ratio of the non-sterically-hindered amines and the
amino acids are maintained such that they remain in
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1 solution as a single phase throughout the absorption and
2 regeneration steps. Typically, these criteria are met
3 by including from about 2 to about 20%, preferably from
4 5 to 15% more preferably, 5 to 1()% by weight of the
non-sterically hindered amino compound and from 2 to
6 about 20% by weight, preferably 5 to about 15% by weight
7 of the sterically hindered amino acid.
8 The scrubbing solution may be premixed and
g placed into use in the absorbing reactors. Alternative-
ly, in an existing acid gas treating plant where the
11 non-sterically hindered amino compound is being used,
12 the sterically hindered amino acid may be added to the
13 scrubbing solution, preferably in increments.
14 The aqueous scrubbing solution may include
a variety of additives typically used in acid gas
16 scrubbing processes, e.g., antifoaming agents, anti-
17 oxidants, corrosion inhibitors and the like. The amount
18 of these additives will typically be in the range that
19 they are effectivel i.e., an effective amount.
Figure 1 graphically illustrates the capacity
21 for potassium carbonate solutions activated by diethano-
22 lamine (DEA) and mixtures of diethanolamine/pipecolinic
23 acid, 1,6-hexanediamine (~MDA) and 1,6-hexane-diamine/
24 N-secondary butyl glycine (SBG) at 80C wherein the
cumulative liters of C02 reabsorbed is a function of
26 time.
27 The term C02 includes C02 alone or in combi-
28 nation with ~l2S, CS2, HCN, COS and the oxides and sulfur
29 derivatives of Cl to C4 hydrocarbons. These acid gases
may be present in trace amounts within a gaseous mixture
31 or in major proportions.
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1 The contacting of the absorbent mixture and
2 the acid gas may take place in any suitable contacting
3 tower. In such processes, the gaseous mixture from
4 which the acid gases are to be removed may be brought
in~o intimate contact with the absorbing solution using
6 conventional means, such as a tower packed with, for
7 example, metal or ceramic rings or with bubble cap or
8 sieve plates, or a bubble column reactor.
g In a preferred mode of practicing the inven-
tion, the absorption step is conducted by feeding the
11 gaseous mixture into the base of the tower while fresh
12 absorbing solution is fed into the top. The gaseous
13 mixture freed largely from acid gases emerges from the
14 top. Preferably, the temperature of the absorbing
solution during the absorption step is in the range from
16 about 25 to about 200C, and more preferably from 35
17 to about 150C. Pressures may vary widely; acceptable
18 pressures are between 5 (3.5) and 2000 psia (1906 kg/
19 cm2), preferably 100 (70.3) to 1500 psia (1054.5 kg/
cm2), and most preferably 200 (140.6) to 1000 psia
21 (703 kg/cm2) in the absorber. In the desorber, the
22 pressures will range from about 0 (0) to 1000 psig (703
23 kg/cm2). The partial pressure of the acid gas, e.g.,
24 CO2 in the feed rnixture will preferably be in the
range from about 0.1 (0.0703) to about 500 psia (351.5
26 kg/cm2), and more preferably in the range from about 1
27 (0.703~ to about 400 psia (281.2 kg/cm2). The contact-
23 ing takes place under conditions such that the acid gas,
29 e.g., CO2, is absorbed by the solution. Generally,
the countercurrent contacting to remove the acid gas
31 will last for a period of from 0.1 to 60 minutes,
32 preferably 1 to 5 minutes. During absorption, the
33 solution is maintained in a single phase. The amino
34 acid aids in reducing foam in the contacting vessels.
The aqueous absorption solution comprising the
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1 alkaline material, the activator system comprising the
2 non-sterically hindered amino compound and the steri-
3 cally hindered acid which is saturated or partially
4 saturated with gases, such as CO2 ancl H2S may be regen-
erated so that it may be recycled back to the absorber.
6 The regeneration should also take place in a single
7 liquid phase. Therefore, the presence of the highly
8 water soluble amino acid provides an advantage in this
g part of the overall acid gas scrubbing process. The
regeneration or desorption is accomplished by conven-
11 tional means, such as pressure reduction, which causes
12 the acid gases to flash off or by passing the solution
13 into a tower of similar construction to that used in the
14 absorption step, at or near the top of the tower, and
passing an inert gas such as air or nitrogen or prefer-
16 ably steam up the tower. The stripping steam may be
17 generated by boiling the solution. The te~perature of
18 the solution during the regeneration step may be the
19 same as used in the absorption step, i.e., 25 to about
200C, and preferably 35 to about 150C. The absorbing
21 solution, after being cleansed of at least a portion of
22 the acid bodies, may be recycled back to the absorbing
23 tower. Makeup absorbent may be added as needed. Single
24 phase is maintained during desorption by controlling the
acid gas, e.g., CO2, level so that it does not fall
26 into the region where two liquid phases form. This, of
27 course, following the practice of the present invention
28 is facilitated by the use of the highly water soluble
29 amino acid in the mixture.
As a typical example, during desorption, the
31 acid gas, e.g., CO2-rich solution from the high pressure
32 absorber is sent first to a flash chamber where steam
33 and some CO2 are flashed from solution at low pressure.
3~ The amount of CO2 flashed off will, in general, be about
35 to 40% of the net CO2 recovered in the flash and
36 stripper. This is increased somewhat, e.g., to 40 to
1 50~, with the high desorption rate promoter system owing
2 to a closer approach to equilibrium in the flash. Solu
3 tion from the flash drum is then steam stripped in the
4 packed or plate tower, stripping steam having been
generated in the reboiler in the base of the stripper.
6 Pressure in the flash drum and stripper is usually 16
7 (11.2) to about 100 psia (70.3 kg/cm2), preferably 16
8 (11.2) to about 30 psia (21.09 kg/cm2), and the temper-
9 ature is in the range from about 25 to about 200C,
preferably 35 to about 150C, and more preferably 100
11 to about 140C. Stripper and flash temperatures will,
12 of course, depend on stripper pressure, thus at about 16
13 (11.2) to 25 psia (17.6 kg/cm2) stripper pressures,
14 the temperature will be about 100 to about 140C
during desorption. Single phase is maintained during
16 desorption by regulating the amount of acid gas, e.g.,
17 CO2, recovered.
18 In the most preferred embodiment oE the
19 present invention, the acid gas, e.g., CO2 is removed
from a gaseous stream by means of a process which
21 comprises, in sequential steps, (1) contacting the
22 gaseous stream with a solution comprising 10 to about 40
23 weight percent, preferably 20 to about 30 weight percent
24 of potassium carbonate, an activator or promoter system
comprising 2 to about 20 weight percent, preferably 5 to
26 about 15 weight percent, more preferably 5 to about 10
27 weight percent of at least one non-sterically hindered
28 amino compound as herein defined, 2 to about 20 weight
29 percent, and preferably 5 to about 15 weight percent of
the sterically hindered amino acid as herein defined,
31 the balance of said solution being comprised of water,
32 said contacting being conducted at conditions whereby
33 the acid gas is absorbed in said solution, and prefer-
34 ably at a temperature ranging from 25 to about 200C,
more preferably from 35 to about 150C and a pressure
36 ranging from 100 (70) to about 1500 psig (1054.5 kg/cm2),
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1 and (2) regenerating said solution at conditions whereby
2 said acid gas is desorbed from said solution. By
3 practicing the present invention, one can operate the
4 process above described at conditions whereby the
working capacity, which is the difference in moles of
6 acid gas absorbed in the solution at the termination of
7 steps (1) and (2) based on the moles of potassium
8 carbonate originally present, is greater than that
9 obtained under the same operating conditions for remov-
ing acid gases from gaseous streams, wherein said same
11 operating conditions do not include the mixture of the
12 non-sterical]y hindered amino compound and the ster-
13 ically hindered amino acid co-promoter system. In other
14 words, working capacity is defined as follows:
15 CO2 in solution C2 in solution
16 at completion of less at completion of
17 absorption desorption
18 Which is:
19 Moles of CO2 Absorbed Moles Residual CO2 Absorbed
less
21 Initial Moles K2CO3 Initial Moles K2CO3
22 It should be noted that throughout the speci-
23 fication wherein working capacity is referred to, the
24 term may be defined as the difference between CO2 load-
ing in solution at absorption conditions (step 1) and
26 the CO2 loading in solution at regeneration conditions
27 (step 2) each divided by the initial moles of potassium
28 carbonate. The working capacity is equivalent to the
29 thermodynamic cyclic capacity, that is the loading
is measured at equilibrium conditions. This working
31 capacity may be obtained from the vapor-liquid equilib-
32 rium isotherm, that is, from the relation between
33 the CO2 pressure in the gas and the acid gas, e.g., CO2
34 loading in the solution at equilibrium at a given tem-
perature. To calculate thermodynamic cyclic capacity,
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1 the following parameters must usually be specified: (1)
2 acid yas, e.g., CO2 absorption pressure, (2) acid gas,
3 e.g., CO2 regeneration pressure~ (3) temperature of
4 absorption~ (4) temperature of regeneration, (5) solu-
tion composition, that is weight percent of the non-
6 sterically hindered amino compound, weight percent
7 of the sterically hindered amino acid and weight percent
8 of the alkaline salt or hydroxide, for example potassium
g carbonate, and (6) gas composition. The skilled artisan
may conveniently demonstrate the improved process which
11 results by use of the non-sterically hindered amino-
12 compound and the sterically hindered amino acid mixture
13 by a comparison directly with a process wherein the14 mixture is not included in the aqueous scrubbing
solution. For example, it will be found when comparing
16 two similar acid gas scrubbing processes (that is
17 similar gas composition, similar scrubbing solution
18 composition, similar pressure and temperature condi-
19 tions) that when the sterically hindered amino acid is
utilized in the mixture the difference between the
21 amount of acid gas, eOg., CO2 absorbed at the end of
22 step 1 (absorption step) defined above and step 2
23 (desorption step) defined above is significantly greater
24 This significantly increased working capacity is observ-
ed even though the scrubbing solution that is being
26 compared comprises an equimolar amount of a prior art
27 amine promoter, such as diethanolamine, 1,6-hexane-
28 diamine, ~alone) etc. It has been found that the use of
29 the admixture of the non-sterically hindered amino
compound and the sterically hindered amino acid of the
31 invention provides a working capacity which is greater
32 than the workiny capacity of a scrubbing solution which
33 does not utilize this new activator or promoter system.
34 Besides increasing working capacity and rates
of absorption and desorption, the use of the admixture
36 of the non-sterically hindered amino compound and
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1 sterically hindered amino acid leads to lower steam
2 consumption during desorption.
3 Steam requirements are the major part of the
4 energy cost of operating an acid gas, e.g., CO2 scrub-
bing unit. Substantial reduction in energy, i.e.,
6 operating costs will be obtained by the use of the
7 process wherein the mixture is utilized. Additional
8 savings from new plant investment reduction and debottle-
g necking of existing plants may also be obtained by the
use of the mixture of the invention. The removal of
11 acid gases such as CO2 from gas mixtures is of major
12 industrial importance, particularly the systems which
13 utilize potassium carbonate activated by the unique
14 activator or co-promoter system of the present invention.
The absorbing solution of the present inven-
16 tion, as described above, will be comprised of a ma~or
17 proportion of alkaline materials, e.g., alkali metal
18 salts or hydroxides and a minor proportion of the
19 activator system. The remainder of the solution will be
comprised of water and/or other commonly used additives,
21 such as anti-foaming agents, antioxidant~, corrosion
22 inhibitors, etc. Examples of such additives include
23 arsenious anhydride, selenious and tellurous acid,
24 protides, vanadium oxides, e.gD, V2O3, chromates, e.g.,
K2Cr2O7, etc.
26 Many of the sterically hindered amino acids
27 useful in the practice of the present invention are
28 either available commercially or may be prepared by
29 various known procedures.
Preferred sterically hindered amino acids
31 include N-secondary butyl glycine (CAS Registry Number
32 58695-42-4), N-2-amyl glycine, N-isopropyl glycine,
33 pipecolinic acid, N-isopropyl glycine, N-2-amyl-glycine,
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1 N-isopropyl alanine, N-sec. butyl alanine, 2-amino-2-
2 methyl butyric acid and 2-amino-2-methyl valeric acidO
3 A preferred method for preparing the preferred
4 sterically hindered amino acids comprises first reacting
glycine or alanine under reductive conditions with a
6 ketone in the presence of a hydrogenation catalyst.
7 This reaction produces the sterically hindered monosub-
8 stituted amino acid.
9 Preferred non-sterically hindered amino
compounds include: diethanolamine, monoethanolamine,
11 triethanolamine, 1,6-hexanediamine, piperidine, etc.
12 The invention is illustrated further by the
13 following examples which, however, are not to be taken
14 as limiting in any respect. All parts and percentages,
unless expressly stated to be otherwise, are by weicJht.
16 "Hot Pot" Acid Gas Treating Process
17 Example 1 ~Comparison)
18 The reaction apparatus consists of an absorber
19 and a desorber. The absorber is a vessel having a capac-
ity of 2.5 liters and a diameter of 10 cm., equipped
21 with a heating jacket and a stirrer. A pump removes
22 liquid from the bottom of the reactor and feeds it back
23 to above the liquid level through a stainless-steel
24 sparger. Nitrogen and CO2 can be fed to the bottom of
the cell through a sparger.
26 The desorber is a l-liter reactor, equipped
27 with teflon blade stirrer, gas sparger, reflux condenser
28 and thermometer.
29 The reaction apparatus is the same as shown
in Figure 1 of U.S. Patent 4,112,050.
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1 The following reagents are put into a 2-liter
2 Erlenmeyer:
3 37.8g of diethanolamine
4 187.5g of K2CO3
525g of water
6 When all the solid has dissolved, the mixture
7 is put into the absorber and brought to 80C. The
8 apparatus is closed and evacuated until the liquid
g begins to boil. At this point C02 is admitted. In
total 29 liters oE C02 is absorbed.
11 The rich solution is transferred to the
12 desorber and boiled for one hour, during which time 21
13 liters of C02 is desorbed.
14 The regenerated solution so obtained is
transferred back to the absorber and cooled to 80C.
16 The apparatus is closed and evacuated until the liquid
17 begins to boil. At this point C02 is admitted. 20.5
18 liters of CO2 is re-absorbed, of which 6 liters are
19 re-absorbed in the first minute.
Example 2 (Comparative)
21 The procedure described above in Example 1 is
22 repeated except that the solution charged into the
23 2-liter Erlenmeyer is as follows:
24 41.4g of 1,6-hexanediamine (HMDA)
187.59 of K2CO3
26 520g of water
27 A total of 30O7 liters of C02 is absorbed.
28 The rich solution transferred to the desorber and boiled
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1 for one hour. The regenerated solution so obtained is
2 transferred back to the absorber and cooled to 80C.
3 The apparatus is closed and evacuated until the liquid
4 begins to boil. At this point C02 is admitted and
21.2 liters of CO2 is re-absorbed, of which 6 liters
6 is re~absorbed in the first Minute.
7 Example 3
8 The procedure of Example 1 is repeated for
9 several acid gas scrubbing solutions containing a
mixture of the non-sterically hindered amino compound,
11 e.g. diethanolamine (DEA) or 1,6-hexanediamine (HMDA)
12 and the sterically hindered amino acid co-promoter of
13 the present invention. The results of these tests along
14 with the results of comparative Examples 1 and 2 are
shown in Tables I and II.
1 ~ ~9~
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1 TABLE I
2 EXPERIMENTS IN 25 WT% K2CO3
Liters C2
4 Amine TotalReabsorbed in
5 Activator(s) Liters CO2 Reabsorbed 1st Mir.ute
-
6 .357 moles DEAl) 20.5 6
7 21.5 6
21.6 6
9 .357 moles HMDA2) 21.2 6
10 .714 moles DEA 22.5 8
11 22.7 8
12 .357 moles DEA +
13 .357 moles SBG3) 28.2 13
14 27.6 12
15 .357 moles HMDA +
16 .357 moles PA4) 25.2 8
17 .357 moles HMDA +
18 .357 moles SBG 25.9 10
19 l)DEA is diethanolamine
2)HMDA is 1,6-hexanediamine
21 3)SBG is N-sec. butyl glycine
4)PA is pipecolinic acid
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1 TABLE II
EXPERIMENTS IN 30 WT% K2C03
3 Amine
4 Activator(s~Liters C02 Reabsorbed 1st Minute
-
5 .357 moles DEAl) 24.2 7
6 24.2 5
7 .714 moles DEA 25.4 8
8 .357 moles DEA +
9 .178 moles SBG3) 29.4 11
2807 11
11 .357 moles HMDA2) +
12 .178 moles PA4) 27.2 9
26.6 9
13 1)DEA is diethanolamine
14 2)HMD~ is 1,6-hexanediamine
3)SBG is N-sec. butyl glycine
4)PA is pipecolinic acid
17 It can be seen from the data in Tables I and
18 II that the addition of the sterically hindered amino
19 acid improves the capacity and rate of reabsorption of
the C02 compared to the scrubbing solution containing
21 the non-sterically hindered amino compound without the
22 sterically hindered amino acid. These results are
23 illustrated in Figure 1 in the case of the DEA, DEA~
24 pipecolinic acid, HMDA-pipecolinic acid and ~MDA-N-
secondary butyl glycine promoted solutions ~herein the
26 cumulative liters of C02 reabsorbed at 80C as a
27 function of time are plotted graphically. Here it is
2~ clear that the sterically hindered amino acids, particu-
29 larly N-secondary butyl glycine enhance the reabsorption
f C02.
sc~
- 20 -
1 Example 4
2 (a) Aging Studies in CO2 ',crubbing Apparatus
3 The following experiments are carried out
4 to ascertain the stability of the amino acids under
accelerated-simulated acid gas treating conditions.
6 The following reagents are charged into a
7 stainless-steel bomb:
8 121 g of N-sec. butyl glycine
9 433 g of KHC03
540 g of H2O
11 The bomb is put into an oven and heated at
12 120C for 1000 hours. Then the content is dischar~ed
13 into a 2 liter flask and refluxed for several hours.
14 750 g is taken and subjected to an absorption-
desorption-reabsorption cycle as described in Example 1.
16 27.9 liters of CO2 is absorbed into the regenerated
17 solution, 10 liters being absorbed in the first minute.
18 Comparison of this result with that obtained
19 with the fresh solution of N-secondary butyl glycine
and potassium carbonate shows that the aging process
21 does not lead to a significant loss of activity.
22 If the aging experiment is carried out after
23 replacing N-sec. butyl glycine with the equivalent
24 amount of N-cyclohexyl glycine, 145 g, and reducing the
water to 516 g in order to have the same total weight,
26 a considerable amount of solid, identified as 1,4-bis-
27 cyclohexyl-2,5-diketopiperazine is formed. An attempt
L~
- 21 -
1 to carry out an absorption-desorption cycle causes
2 plugging of the unit.
3 (b) Aging Under CO2 and H2S
-
4 The following reagents are charged into a
stainless-steel bomb:
6 121 g of N-sec. butyl glycine
7 24 g of K2S
8 390 g of KHCO3
9 5~4 g of water
The bomb is put into an oven and heated at
11 120C for 1000 hours. Then the content is discharged
12 into a 2 liter flask and refluxed for several hours.
13 765 g is taken and subjected to an absorption-
14 desorption-reabsorption cycle as described in Example lo
28.9 liters of CO2 is absorbed into the regenerated
16 solution, 10 1 being absorbed in the first minute.
17 Comparison of this result with that obtained
18 with the fresh solution of N-secondary butyl glycine and
19 potassium ca~bonate shows that the aging process leads
to only a slight loss of activity.
21 If the aging experiment is carried out after
22 replacing N-secondary butyl glycine with the equivalent
23 amount of N-cyclohexyl glycine, 145 g, and reducing the
24 ~ater to 516 g in order to have the same total ~eight,
2S a considerable amount of solid, identified as 1,4-bis-
26 cyclohexyl-2,5-diketopiperazine is formed. An attempt
27 to carry out an absorption-desorption cycle causes
28 plugging of the unit.
1 The excellent stability under the aging
2 conditions shown above for the N-secondary butyl glycine
3 coupled with its good performance as a promoter demon-
4 strates the desirability of using it in combination with
S non-sterically hindered amines.
6 Examp~e 5
7 This example is given in order to show that
8 beta-amino acids are not stable under alkaline condi-
9 tionsO The following solution is prepared in a 2-liter
Erlenmeyer:
11 CH3 CH3
12 49.7 g of ~ N-CH2CH2CH2NH-CHCH2COOH
13 CH3
14 ~H3 CH3
64.0 g of ~ -CH2CH2CH2NH-CHCH2COOH
16 411 g H2O
17 225 g K2CO3
1~ When everything is dissolved, the solution
19 is put into the absorber described in Example 1. An
absorption-desorption-reabsorption cycle as described
21 in Example 1 gives 32.2 liters of CO2 reabsorbed, of
22 which 11 liters are absorbed in the first minute.
23 The aged solution is prepared in the following
24 way. The following reagents are charged into a stain-
less-steel bomb:
26 CH3~ ICH3
27 66.3 g of ~ N-CH2CH2CH2NH-CHCH2COOH
28 CH3
s~
- 23 -
1 ÇH3 CH3
2 85.3 g of ~ -CH2CH2CH2NH-CHCH2CO0H
3 391.5 g of KHCO3
4 23.9 g f K2S
503 g of H2O
6 The bomb is put into an oven at 120C and left
7 there for 1000 hrs~ After that~ the bomb content is put
8 into a 2-liter flask and boiled at reflux for some
9 hours. 750 g of the solution so obtained is used to
carry out a standard absorption-desorption-reabsorption
11 test. Only 25 liters of CO2 is reabsorbed, of which 6
12 liters are reabsorbed in the first minute.
13 13C-NMR analysis of the aged solution shows
14 the presence of 32 peaks, whereas the fresh solution
only has 18. The aged solution shows the presence of
16 olefin bonds, which indicates that aging has led to
17 decomposition of the diamino acids into diamines and
18 crotonic acid~
19 The results shown above with respect to the
beta-diamino acids agree with those obtained by Corbett,
21 McKay and Taylor, J. Chem_Soc. 5041 (1961) on beta-
22 mono-amino acids.
23 The excellent stability under the aging
24 conditions shown above for N-secondary butyl glycine
compared with other amino acids coupled with its good
26 performance as a co-promoter for the non-sterically
27 hindered amino compounds demonstrates the desirability
28 of using this admixture as a co-promoter system, par~
29 ticularly in de-bottlenecking existing acid gas treating
processes which employ non-sterically hindered amino
31 compounds.
