Treatment of amine wastes generated in industrial processes.
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IOP Conference Series: Materials Science and Engineering
PAPER • OPEN ACCESS
Treatment of amine wastes generated in industrial processes.
To cite this article: S. R. S. Salim 2021 IOP Conf. Ser.: Mater. Sci. Eng. 1092 012051
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iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
Treatment of amine wastes generated in industrial processes.
S. R. S. Salim
Abstract. Amines such as monoethanolamines (MEA), ethanolamines (EA), diethanolamines
(DEA), and N-methyldiethanolamine (MDEA) are widely used in post combustion CO 2 capture
process (CCP) at natural gas conditioning plants to remove acid gas impurities. These amines
have significant impact to the environment and human health. Therefore, amine wastes generated
from CCP must be treated before they are exposed to the environment. This paper reviews some
of the available methods to treat amines such as using physical treatments (filters, increase in
temperature, polymerization), chemical treatments (SOX and NOX in the flue gas, fly ash, acid
solvents), and biological treatments (aerobic degradation and anaerobic degradation by
microbacteria, nitrate respiration).
1. Introduction
The release of green house gases has affected earth climate change as the temperature rises. One of the
most common green house gases is carbon dioxide (CO2). In this modern world, the release of CO2 from
industrial factories is high as there are raising demands in productions sector. Thus, there is a need to
develop cost effective and energy saving CO2 absorption schemes [1].
Amine has been used commercially in many industrial processes mainly for the removal of acid
gas impurities such as hydrogen sulfide (H2S), carbonyl sulfide (COS), carbon disulfide (CS2), and also
carbon dioxide (CO2) in post combustion CO2 capture at natural gas conditioning plants [2]. It has been
established for over 60 years in chemical, oil, and gas industries to remove hydrogen sulphide and CO2
from gas stream. This process is called natural gas sweetening operations [3]. This is an absorption
process where flue gas stream is exposed to an aqueous amine solution to remove CO2 and recycle CO2
in the flue gas stream. This chemical absorption by amines has been used to reduce CO2 release to the
environment. There are several reasons to why amines have been used in the natural gas conditioning
operations. This is because it is easy to use as aqueous amines have high CO2 absorption capability in
the chemical reactions and can obtain high yield of CO2 [4]. For example, Figure 1 showed the reaction
of ethanolamine (EA) with CO2 to form (2-hydroxyethyl) carbamate ion and a protonated amine. In
today’s world, the need of clean and environmentally friendly energy resources has increased the
demand for natural gases. This is why amines have to be used in natural gas conditioning plants in order
to reduce the CO2 release to the environment. .
Figure 1: Reaction of two MEA molecules with CO2 to form the carbamate anion and a protonated
amine [4].
There are a few types of amines used in the process, which can be classified into two categories:
chemical and physical solvents [5]. Amines used in treating low and medium pressured gas streams are
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IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
called chemical solvents such as monoethanolamine (MEA), diethanolamine (DEA), N-
methyldiethanolamine (MDEA), and several other alkanolamines mixtures. The examples of chemical
formulae of different types of amine used in CCP are listed in Table 1. High-pressurised gas streams are
treated with physical solvents such as propylene carbonate. Amines are organic compounds that can be
used in rapid reaction with CO2 selectively and reversibly as they have active N atoms.
Monoethanolamines (MEA) have been used commercially in many post combustion CO2 capture plant
as they have suitable characteristics such as high reactivity, water solubility, and also cost effective [6].
Table 1: Examples of common amines used in CO2 capture process [4].
2. The problems of using amines
The wide usage of amines in post combustion CO2 capture has it significant effect to the environment.
The high reaction rate and its capability of removing traces of CO2 made it the most suitable and cost
effective solvents in CO2 capture processes but at a hefty price. There are non-volatile degradation
products from the process that must be removed from amines solvents before the recycling of solvents
and to be treated as hazardous chemical wastes [7]. This removal process will add extra works and cost
to the CO2 capture process.
The increase of industrial wastewater production and its release to the environment leads to the
rise of xenobiotic compound in the aquatic environment. Most of the amines solvents used in the process
are recycled to the top of the absorber [8]. A certain amount of the recycled amines are periodically
distilled to remove the impurities and insoluble materials. During these processes, there are a few
problems occured. Accidental spill to the environment is one of the major problems. The amines used
in natural gas capture plants are highly soluble in water [9]. The reclaimer waste will contain water,
amine, ammonia, other degradation products, heat-stable salts, flue gas impurities, and also corrosion
products.
The amines solvents loss due to degradation also occurs during the process in natural gas
sweetening [10]. This will add to the cost of operation, as amines solvents must be top up frequently.
Amine gases that are released to the air could be dissolved in the rain droplets and ended up in water
supplies such as rivers and lakes. High concentration of amines disposed to the environment could leads
to disruption of aquatic life and bioconcentration potential [3]. The reaction of amines with CO2 in flue
gas treatment may also leads to emission of compounds such as ammonia as the main degradation
products of amines [11]. High concentrations of ammonia released to the environment are fairly toxic
and could cause skin burns and irritations to human.
Corrosion of metals especially in the natural gas plants is one of the problems occured when using
alkanolamines [12]. Foaming also occured during the interaction between natural gas and amines that
leads to accumulation of organic acids. The leachate from this process will accidentally released to the
2iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
environment through water table and air thus affect the aquatic life as well as increase in the maintenance
costs.
Amines also have high vapour pressure. This characteristic results in significant vapourization
and solvent loss in the condition with high temperature [7]. This will increase the cost of post combustion
CO2 capture as the need to continuously adding alkanolamines solvent to the process.
3. Treatment options
There are a few criteria in determining good amines treatment methods. The decomposition of amines
into ammonia (NH3) is one of the ways to reduce nitrogen oxides (NOx) emission in the reclaimer plants
to the environment [6]. Amine decomposition is important to reduce their effect to the environment. The
end product to be released to the environment must have the least effect on human health, as well as the
environment. This process can be achieved by physical treatment, chemical treatment and biological
treatment. Summary of these treatments are illustrated in Table 2.
3.1. Physical treatments of amines
There are a few methods to treat amine using physical treatment. Methods such as gravitational breaking
(floatation), ultra-filtration membrane separation, and micro-filtration have been used in the reduction
of ethanolamine in oily wastewater. Thermal methods such as heating and evaporation were also used
in the physical treatments of amines including air stripping [13]. These processes were done to separate
amines waste from oily wastewater.
The increase of temperature up to 160°C reduces the concentration of MEA by 95% in a high
pressured vessel during CO2 removal process [14]. The reduction of MEA concentration was determined
and their capacity to remove CO2 is measured after the concentration reduced.
According to Davis and Rochelle [7], the increase of temperature and loading also increases the
degradation of MEA in the presence of CO2. Thus, the higher the concentration of CO2, the more amines
degraded during thermal degradation [15].
As amines and other degradation product may be emitted through gas phase emission and mist
(aerosol production) during gas conditioning processes, these mist particles must also be contained
before accidentally being released to the open air. Conventionally, water wash sections and demisters
were built together in the plant. Research has been done to control amine mist emission is by using filter
consists of wetted rotating brush and candle filter [16].
Physical treatments of amines have a few disadvantages. The removal of amines wastes by high
temperature is regarded as non-economical [8]. This is because of the high water content that requires
high-energy usage for its evaporation. The trend of degradation reduced after a few weeks of exposure
to the high temperature [17]. This is because of the reduction of other byproducts that are crucial for
amines wastes degradation during the high temperature treatment. As filters are being used for the
treatment process, it must be maintained regularly for the amines to be treated properly. Some filters
must be built in the CCP to ensure the effectiveness of amine treatment process.
3.2. Chemical treatments of amines
The chemical treatment usually involves in the changing of pH of the solvents [13]. Further amine
biodegradation is related greatly to the pH values. There are acid-base reactions where acids and acid
gases reacts irreversibly with amines to form anions that are heat-resistant [4]. This includes SOX and
NOX in the flue gas, mineral acids in feed coal, and also carboxylic acids generated by oxidative
degradation [18]. Amines reactions with NOX can produce nitrates and nitrites. Nitrogen-fixing bacteria
can easily fix these two compounds. Some nitrosamine formation must be expected from any amine
degradation reaction with NOX [19].
Carbamate polymerization of amines can occur under low oxygen level, high CO2 loading, and
in high temperature conditions in the boiler of stripper column [4]. Carbamate polymerization can be
3iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
observed in stripping column where there are possibilities of thermal degradation can happen at
temperature above 205°C. Thermal degradation of alkanolamines can also takes place in reaction with
CO2 through a cyclization reaction of carbamate to 2-oxazolidone shown in Figure 2 [20].
Figure 2: The degradation of MEA carbamate to 2-oxazolidone mechanism and transition state
[20].
The usage of fly ash can improve amines degradation. Fly ash contains varying amount of
transition metal ions known to catalyze solvent degradations [21]. Oxidative degradation using fly ash
can be done with two mechanisms; electron abstraction and hydrogen abstraction. During both
mechanisms, the presence of redox reactive metal ions in fly ash such as Fe2O3 and CaO could generate
high numbers of free radicals. Thus accelerating the rate of amine degradation.
Oxidative degradation of amines falls under chemical treatments of amines. Amines degradation
occurs in the presence of O2. Reaction between MEA and carboxylic acids play roles in solvent
degradation. This is proven when N-(2-hydroxyethyl)formamide (HEF) and N-(2-
hydroxyethyl)acetamide (HEA) formation were observed during MEA oxidative degradation using
carboxylic acids [22]. This type of amines degradation can also be done in closed-batch system with a
wet gas blend of CO2 and O2 air [23]. The examples of oxidative degradation of ethanolamines are
shown in Figure 3.
Oxidative degradation of amines are more complex than thermal degradation [17]. This is because
both ionic reactions and radical reactions can take place at the same time. However, by using batch
reactors, degradation of amines can be accelerated [24]. This can be done by alternately exposing amines
to oxidative and thermal degradation in a single system.
4iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
Figure 3: Oxidative degradation pathways for MEA [20].
Chemical treatments of amines also have a few disadvantages. Degradation products such as
methylated amines are more volatile compared to the parent amine [25]. During chemical treatments of
amines, byproducts such as organic acids, aldehyde, and various cyclic compounds were produced [21].
These byproducts need to be collected and treated accordingly.
3.3. Biological treatments of amines
Amines are organic subtances that consist of high amount of carbon and nitrogen. Biological treatment
could be the most suitable method to reduce the amount of amines released to the environment.
Biological treatments of amines consist of two types: Aerobic degradation and anaerobic degradation.
Biological treatment could transform amines wastes into recoverable products without harming the
environment. Aerobic degradation is much more preferable as compared to anaerobic. This is because
it is easier to control aerobic conditions such as to provide sufficient O2 to the reactor.
Ethanolamine in soil is biodegraded and converted to ammonium and acetaldehyde through
hydrolisis process [26]. This biodegradation process occured in aerobic conditions where ammonium is
oxidized to nitrite and nitrate as shown in Figure 4. Ethanol and acetic acid are degraded from
acetaldehyde that is produced from the ethanolamine hydrolisis reaction. Acetic acid and ethanol
produced from this reaction are then used in denitrification process and both compounds can be easily
degraded and used by bacteria.
5iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
Figure 4 Biodegradation of monoethanolamine into ammonium and acetaldehyde [26].
Aerobic degradation using microorganisms require constant supply of oxygen to degrade amines
wastes. Escherichia coli (E.coli) K12 strains culture have been used effectively to transform amines
wastes into biomass, acetyldehyde, and acetic acid [27]. The increase of E.coli K12 growth in amines
wastes solution indicated that the presence of additional nitrogen sources helps in the bioremediation of
amines wastes [27].
The biological removal of nitrogen from amines wastes through nitrification process increases the
rate of amines wastes biodegradation [11]. The main degradation product of amines is ammonia. Aerobic
nitrification process includes the oxidization of ammonia to NO2- and NO3- by nitrite-oxidizing bacteria
and ammonia-oxidizing bacteria. MEA biodegradation process started in anoxic environment of the
denitrification reactor after the nitrification process [11]. This is where nitrous oxides produced during
nitrification process are reduced to nitrogen by electron donated by organic carbon sources. This process
reduces the amount of nitrous oxides released to the environment.
According to Lai & Shieh [28], monoethanolamines can be degraded via nitrate respiration under
anoxic condition. This can be done using bacterial biofilms obtained from a reactor which treats a
mixture of MEA. Anaerobic degradation of amines produces CO2 and methane [10]. Anaerobic reactor
must be built for zero O2 presence at all times which can be hard to controlled.
Amines can also be treated in slurry system using suspension of microbacteria in a bioreactor
[29]. Slurry bioreactor system is used for soil polluted by amines under controlled environment.
Reactions in slurry bioreactors increase the mass transfer rates and also increase the contact between
microorganisms and amines.
There were also researches that had been done on anaerobic-aerobic combined system for amines
degradation [30]. Anaerobic degradation process causes amines discoloration by reductive degradation.
Aerobic degradation that occured after introduction of O2 breaks down amines waste into
environmentally friendly elements such as nitrogen and hydrogen. This showed by using both anaerobic
and aerobic degradation systems, the treatment of amines wastes could be achieved.
There are a few disadvantages using biological treatment to treat amines wastes. First, it is hard
to find bacteria that can reduce amines wastes at optimal rates. A group of microbacteria must be used
to achieve this. Second, it is important to consider the end product that does not have any significant
effect when released to the environment. This includes the removal of contaminated media to a specific
treatment area such as designated land treatment area or by composting [31]. Third, it is costly to keep
a reactor O2 free during anaerobic degradation [10].
6iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
Table 2: Summary of amines treatment options.
Treatment Options Methods References
Physical treatment Heating and evaporation including air [13]
stripping.
Carbamate polymerization of amine. [4]
Thermal degradation of alkanolamines with [20]
CO2 through a cyclization reaction of
carbamate to 2-oxazolidone.
Increased temperature reduces the [14]
concentration of MEA in a high-pressured [32]
vessel. [15]
Filter consists of wetted rotating brush and [16]
candle filter to control amines mist emission.
Chemical treatment The changing of pH of the solvents. [13]
Acid-base reactions. [4]
SOX and NOX in the flue gas, mineral acids in [18]
feed coal, and also carboxylic acids generated
by oxidative degradation.
The usage of fly ash as metal ions source. [21]
MEA oxidative degradation using carboxylic [22]
acids.
Closed-batch system with a wet gas blend of [23]
CO2 and O2 air.
Ionic reactions and radical reactions can take [17]
place at the same time
Alternately exposing amines to oxidative and [24]
thermal degradation in a single system.
Biological treatment EA is biodegraded and converted to [26]
ammonium and acetaldehyde through
hydrolisis (aerobic conditions).
Aerobic degradation using microorganisms [27]
(E.coli).
Nitrification process. [11]
Anoxic environment of the denitrification [11]
reactor.
Nitrate respiration under anoxic condition [28]
using bacterial biofilm.
Anaerobic degradation of amines produces [10]
CO2 and methane.
Treatment in slurry system using suspension of [29]
microbacteria in a bioreactor.
Anaerobic-aerobic combined system in [30]
breaking down amines wastes.
7iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
4. Conclusions and recommendations
The goal of amines treatment is to reduce their impact to the environment. While physical and chemical
degradation of amines are simpler to be applied such as increasing the temperature, building filters into
the treatment plants, and adding more chemicals to degrade amines wastes, these methods can be cost
ineffective.
From the review presented, the best amines treatment is by using biological methods. This is
because by using biological methods (aerobic and anaerobic degradation), amines waste can be reduced
to their simplest forms and also the most economically feasible technology to degrade industrial organic
compound. Since amines have carbon and nitrogen, many types of bacteria use these elements as source
of living. This shows that more research needs to be done in this field to obtain more information on the
removal of amines waste from the environment. Research such as using different types of bacteria,
upgrading on-site removal systems, and using blends of amines and other chemicals can be done to add
more information on this field. The research on what type of bacteria that is less harmful to the
environment during the removal of amines can also be done.
The usage of other materials and techniques in CO2 capture plants such as solid sorbents can
also reduce the usage of amines. Such an understanding is essential as amines bioremediation processes
are further optimized.
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8iCITES 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
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IOP Conf. Series: Materials Science and Engineering 1092 (2021) 012051 doi:10.1088/1757-899X/1092/1/012051
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