environmental impacts of amine- based co post...

CSIRO ENERGY TRANSFORMED FLAGSHIP

ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS TEST PROCEDURE FOR POST-COMBUSTION CAPTURE OF AMINES

Phil Jackson, Graeme Puxty, Moetaz Attalla, Paul Feron, Merched Azzi September2013

Prepared for Australian National Low Emissions Coal Research and Development

Final report

Revised January 2014

Citation

Jackson, P., Puxty, G., Attalla, M., Feron, P., Azzi, M. (2013): TEST PROCEDURE FOR POST-COMBUSTION CAPTURE OF AMINES. Prepared for ANLEC R&D. CSIRO, Australia.

Copyright and disclaimer

© 2013 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO.

Important disclaimer

CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures | i

Contents

Acknowledgments ............................................................................................................................................. iii

Summary ............................................................................................................................................................ iv

Part I Methyldiethanolamine (MDEA) Degradation 6

1 Introduction .......................................................................................................................................... 7

2 Task description/Scope of work .......................................................................................................... 10

3 Literature Review of MDEA Degradation Products ............................................................................. 12

4 Degradation Protocol .......................................................................................................................... 16

4.1 Solvent Ageing Apparatus ......................................................................................................... 16

4.2 Sample Analysis Methods ......................................................................................................... 17

5 Experimental Results of Sample Ageing and Sample Analysis ............................................................ 19

5.1 Experimental Conditions ........................................................................................................... 19

5.2 Reaction Mixture Sample Analysis Results ............................................................................... 21

5.3 Volatiles Sample Analysis Results ............................................................................................. 23

6 Discussion and Conclusions ................................................................................................................. 25

7 References ........................................................................................................................................... 27

Part II Piperazine (PZ) and 3-piperidinemethanol (3-PM) Degradation 28

1 Introduction ........................................................................................................................................ 29

2 Degradation Protocol .......................................................................................................................... 30

2.1 Sample analysis methods .......................................................................................................... 30

3 Experimental Results of Sample Ageing and Sample Analysis ............................................................ 31

3.1 Experimental Conditions ........................................................................................................... 31

3.2 Results for Piperazine ............................................................................................................... 33

3.3 Results for 3-piperidinemethanol ............................................................................................. 35

4 Discussion and Conclusions ................................................................................................................. 38

5 References ........................................................................................................................................... 40

Figures Figure 1 Degradation product assignments in Lawal and Idem [5] (left column) and assignments supported by other laboratories and/or the findings presented in this report (right column) ....................... 14

Figure 2 Carousel six-port reactor system used in the solvent degradation (ageing) experiments ................ 16

Figure 3 Primary (> 10 ppm) degradation products detected for MDEA degradation and postulated routes of formation .......................................................................................................................................... 23

Figure 4 Chemical structures of piperazine and 3-piperidinemethanol ........................................................... 29

ii | ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures

Figure 5 Speculative structures of some unexpected piperazine degradation products. M/z 70 = dihydropyrroles; M/z 99 = dihydropyrazin-2-ones; M/z 169 (L to R) = tetrahydropyrazine 1, tetrahydropyrazine 2, oxazolopyrazine 1, imidazolylpiperazinone, oxazolopyrazine 2; M/z 187 = imidazolidinone 1, ethanone 1 ......................................................................................................................... 34

Figure 6 Speculative degradation routes from piperazine to form the two major degradation products detected............................................................................................................................................................ 35

Figure 7 Speculative structures for the degradation products of M/z less than 146 identified for 3-piperidinemethanol. Alternative configurations with rearrangement of groups are possible for some structures, but these are not given in the figure.............................................................................................. 37

Tables Table 1 Degradation markers and the techniques used to detect their presence........................................... 17

Table 2 Experimental conditions ...................................................................................................................... 20

Table 3 Oxide composition of Vales Point black coal flyash obtained using X-ray fluorescence spectroscopy (SGI Australia) ............................................................................................................................. 20

Table 4 Unexpected ions observed in the direct-infusion mass spectrometry (MS) spectrum of degraded N-methyl-diethanolamine (MDEA) solutions. Established degradation products also observed are in italics. Compositions and preliminary identities are based on MS/MS information ....................................... 21

Table 5 Maximum concentration (ppm) of each degradation product detected in each sample ................... 22

Table 6 Degradation products for environmental monitoring (excluding monoethanolamine, MEA). C = known carcinogen; M = major degradation product; N = undergoes nitrosation (secondary amine); P = precursor to nitrosamines or other degradation products that nitrosate ....................................................... 26

Table 7 Degradation markers and the techniques used to detect their presence........................................... 30

Table 8 Oxide composition of Vales Point black coal flyash obtained using X-ray fluorescence spectroscopy (SGI Australia) ............................................................................................................................. 32

Table 9 Synthetic flue gas composition, time of exposure and temperature used in the sample ageing apparatus .......................................................................................................................................................... 32

Table 10 Unexpected ions observed in the direct-infusion mass spectrometry (MS) spectrum of degraded piperazine solutions. Compositions and preliminary identities are based on MS/MS information ....................................................................................................................................................... 33

Table 11 Ions observed in the direct-infusion mass spectrometry (MS) spectrum of degraded 3-piperidinemethanol solutions. Compositions and preliminary identities are based on MS/MS information . 36

Table 12 Degradation products for environmental monitoring. C = known carcinogen; M = major degradation product; N = undergoes nitrosation (secondary amine); P = precursor to nitrosamines or other degradation products that nitrosate ...................................................................................................... 38

ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures | iii

Acknowledgments

The authors wish to acknowledge financial assistance provided through Australian National Low Emissions Coal Research and Development (ANLEC R&D). ANLEC R&D is supported by Australian Coal Association Low Emissions Technology Limited and the Australian Government through the Clean Energy Initiative.

iv | ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures

Summary

Predicting the degradation of amine solvents in amine-based post-combustion CO2 capture (PCC) plants before their deployment is crucial for both economic purposes and environmental benefits. The current project deals with the development of technical procedures that can be used to identify the degradation products of amines with major environmental and health concerns under selected operational conditions. The industry and regulatory agencies can use these procedures as a screening tool to gain the early information they require about anticipated PCC emissions.

In an amine-based PCC process, the combination of high temperatures, oxygen, SOx and NOx in the flue gas and dissolved metals degrade the amine solution. The rate and extent of degradation is controlled by the properties of the amine, concentration of dissolved gases, temperature, and concentration and types of dissolved metals.

The degradation of amines generates a range of different degradation compounds with varying physical and chemical properties. It also reduces the concentration of amine, affects its CO2 capture performance, and increases the cost of the operation.

In an operational amine-based CO2 post combustion capture (PCC) plant it is unlikely to be able to completely eliminate the degradation of amines and the potential formation of secondary products within the process. The management of solvent degradation and the potential release of its degradation products to the environment require a proper understanding of degradation chemistry which is not well understood. To overcome these difficulties, screening and characterisation of solvent degradation has emerged as a critical step in the early stage of solvent selection. During the execution of the current activity, an experimental rig was developed and tested and analytical procedures were implemented to screen the degradation of different solvents.

The procedures followed to select and acquire the test rig have been described in the report along with its

operating protocols and details of its components. The test rig was used to identify the key parameters that

affect the lifetime of the selected solvents.

As the detection and quantification of the selected amines and their degradation products were of major

importance for this research activity, a considerable amount of time was spent to develop techniques and

procedures to be able to perform the analysis needed on different analytical instruments. The approach

followed and the technical actions taken to develop and improve these methods and the technique setups

have also been discussed. The calibration curves are also presented for all analytes tested. It can be

concluded that with the systems and methods developed throughout this project, the screening of

degradation products of solvents used for CO2 capture before being used in an industrial plant can be

successfully undertaken.

During the first stage of this Activity, we have developed and tested a procedure for the degradation of PCC solvents, with the purpose of identifying the chemical compounds that are likely to be formed during the operation of an amine-based PCC plant. The procedure can be executed by any commercial or government laboratory that has access to the appropriate analytical instruments and validated analytical procedures.

The procedure – which is conducted on a small scale within a well-ventilated laboratory – consists of two key steps:

solvent ageing, using a synthetic flue gas partially representative of Australian conditions, with the omission of NOx in Part II to avoid nitrosamine formation

measurement of solvent ageing, using markers that appear during the course of the experiment.

ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures | v

In the first stage, the aqueous 30 wt% solution of monoethanolamine (MEA) considered as the benchmark absorbent for PCC was tested and the degradation products were evaluated. Depending on the chemical and physical properties of the degradation products, plant design and operating conditions, some of the degradation products compounds may be entrained or escape from a MEA-based PCC capture plant.

Degradation compounds present in the samples were identified using liquid chromatography-mass spectrometry and an anion chromatography-electrochemical detector. Amine loss and CO2 loading were determined using titration methods. Metal concentrations were determined using inductively coupled plasma-mass spectrometry.

The MEA results obtained in this study and reported in the first progress report of this activity suggest that selected chemicals should be monitored in any vented gas streams and wastewaters for environmental release. Criteria for the selection include volatility, abundance and toxicity (implicit or explicit).

During the second stage of this study, the developed test procedures were applied to screen the major

degradation products of the following solvents Methyldiethanolamine (MDEA), Piperazine (PZ) and 3-

piperidinemethanol (3-PM).

During the MDEA degradation campaign, the results showed that the most common degradation product in

MDEA solutions is diethanolamine (DEA). The later can be easily nitrosated to form a secondary

degradation product nitrosodiethanolamine (NDELA). After few weeks of continuous degradation, DEA

concentration in the degraded MDEA solutions reached 2500 ppm and the NDELA concentrations reached

130 ppm. Other major degradation products include the amino acids bicine and N-(2-

hdroxyethyl)sarcosine. These two products are likely to escape as vapour from the plant. The organic acids

are not volatile and would stay in the process. Residues of N-nitrosomorpholine and N-nitrosopiperidine

were aso present in the reaction vessels.

PZ can form a carbamate or dicarbamate, and can also form both mono- and dinitrosamine species during PCC applications if the flue gas contains NOx gas. The results of this degradation run confirm that PZ is one of the more robust amines being considered for PCC applications. Considering the lack of thermal degradation products detected, it is likely that significantly higher temperatures than used here (< 100 °C) are needed to thermally degrade PZ solvents. The degradation products detected and quantified were ethylenediamine, 2-oxopiperazine, HEEDA, N-formyl piperazine, diethylamine and 1,4-dimethylpiperazine. There are no prior reports of the detection of 2-oxopiperazine, although it can be expected to form whenever PZ is exposed to oxygen.

The most abundant and persistent products were 2-oxopiperazine and ethylenediamine. All other products did not exceed 3 ppm concentration during the run, and 2-oxopiperazine and ethylenediamine only exceeded 1 ppm during Stage 3 of the degradation experiment when the largest gas flows were used.

3-PM is a heterocyclic secondary amine, with a hydroxymethyl group located two carbon atoms distant from the nitrogen centre. In contrast to PZ, 3-PM appeared to be seriously degraded after 6–8 weeks simulated flue gas (SFG) exposure. A single degradation product at M/z 239, tR = 18.1–18.2 eventually dominates in this system, however it was not identified. Further work is required to identify this product and draw conclusions about its potential impacts.

6 | ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures

Part I

Methyldiethanol

amine (MDEA) Degradation

ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS - Screening Test Procedures | 7

1 Introduction

Amine scrubbing technology has been widely used over the past several decades for removal of acid gases from gaseous streams in the chemical and oil industries. It is based on the reversible chemical reactions of the acid gas with organic solvents such as amines. Its application to the CO2 removal from the flue gas produced by the combustion of fossil fuels has attracted much attention over the past few years. This technology may be directly retrofitted to a power plant to remove CO2 from flue gas streams of fossil-fuelled power plants.

As a result of rising atmospheric CO2 levels, research into the chemical capture of CO2 – either via aqueous amine solutions, ionic liquids or metal-organic frameworks – has intensified in recent years. At present, the reversible chemisorption route to CO2 capture using organic amines at large-point sources (e.g. coal-fired power stations) appears to be the most promising immediate technology to reduce anthropogenic CO2 emissions. This process is known as post-combustion CO2 capture (PCC).

The chemistry forming the basis of the PCC process occurs between aqueous organic capture amines (known as alkanolamines) and CO2, either at the gas–liquid interface or in the aqueous phase, and can be described by coupled equilibria (see Scheme 1). An alkaline or high-pH environment is necessary for capture to take place. Otherwise, the CO2-reactive part of the alkanolamine molecule (–NH2) protonates to form –NH3

+, rendering it unreactive.

The chemistry of primary and secondary alkanolamines is similar in most regards, and is

dominated by formation of a carbamate capture product: R1R2-N-CO2. To form a carbamate,

the alkanolamine must have one or two hydrogen atoms (one R1 or R2 = H, secondary

alkanolamine; two R1 = R2 = H, primary alkanolamine) bonded to the nitrogen group. The stability of the carbamate that forms is governed by the structure of the alkanolamine at the molecular level. For instance, monoethanolamine (MEA, primary, HO-CH2-CH2-NH2) forms a

stable carbamate (HO-CH2-CH2-NH-CO2), whereas 2-amino-2-methyl-1-propanol (AMP,

primary, CH3-C(CH3)(NH2)-CH2-OH)) forms a very unstable carbamate (CH3-C(CH3)(NH-CO2)-

CH2-OH), which can only be observed using sensitive chemical detection methods such as mass spectrometry.


R1R2R3N + H2O ⇌ R1R2R3NH+ + OH− (1)

OH− + CO2 ⇌ HCO3− (2)

R1R2NH + CO2 + B ⇌ R1R2NCO2− + BH+ (3)

R1R2NCO2− + H2O ⇌ R1R2NH + HCO3

− (4)

Scheme 1 Equilibria describing CO2 capture by alkanolamine molecules at high pH. B = alkanolamine or water acting as a proton acceptor. R1, R2, R3 designate either hydrogen atoms or organic functional groups, e.g. for MEA, R1 = H, R2 = H and R3 = HO-CH2-CH2-, and for diethanolamine (DEA), R1 = R2 = HO-CH2-CH2-, and R3 = H. Only Equilibria 1 and 2 apply for tertiary amines

With increasing temperature or decreasing pH, even stable carbamates hydrolyse to

regenerate the parent alkanolamine and produce CO2 or HCO3. This hydrolysis reaction

appears to be much faster for unstable amines such as AMP. Stable carbamates need more heat to liberate the captured or sequestered CO2, leading to an energy penalty for the cyclic capture process. Amines that react most quickly with CO2 (good kinetics) invariably form stable carbamates that hydrolyse slowly, whereas amines that form unstable carbamates react more slowly with CO2 (bad kinetics), but tend to hydrolyse quickly. Tertiary amines (those with no

hydrogen atoms bonded to the nitrogen atom) can only react to form HCO3 via Equilibria 1

and 2 in Scheme 1.

All the reactions in Scheme 1 are feasible for primary and secondary alkanolamines. Tertiary alkanolamines are usually associated with slow capture kinetics, but favourable regeneration energies. Excellent CO2 capture characteristics are alkanolamine-specific, and include properties such as low volatility, fast kinetics, lower heats of regeneration, high CO2 capture capacity, and robustness at high temperatures in an oxidising environment. Many amines exhibit a desirable mix of these properties, which has lead to an explosion of research interest from industry, academic and government institutes.

Flue gas from pulverised-fuel power stations contains a number of gaseous components and trace metals. The chief components with deleterious impacts on alkanolamines are O2 (usually 5–10%), NOx (up to 700 ppm) and SOx (up to 600 ppm). Other components may be more important in an international context, and will depend on the abundance of trace components in the fuel used, and whether flue gas desulphurisation or de-NOx technologies employed upstream of the PCC plant.

Acidic components in the gas stream also degrade alkanolamines during PCC. There is now renewed interest in the chemistry of the alkanolamine degradation process, and how this affects the capture of CO2 from flue gases. Most work to date has focussed on the effects of heat and oxygen on amine integrity. In broad terms, degradation in the open literature is categorised as either thermal, oxidative or carbamate-induced. This categorisation is usually based on the conditions under which the laboratory degradation experiments were performed, e.g. in the presence/absence of oxygen, or at temperatures characteristic of either absorption or stripping. Occasionally, it is based on the chemical structure of the degradation products. Many degradation products, such as imidazolidinones and oxazolidinones, appear under a range of non-specific conditions.


An aspect of amine degradation that is important in the Australian context is the generation of nitrosamines caused by the interaction between secondary amines and NOx. Nitrosamines are known to be carcinogenic to mammals and so international PCC research, particularly in parts of Europe, is now focussed on assessing the environmental impacts of capture operations using alkanolamines. The chemistry describing nitrosamine formation at low pH can be described as:

NO2(g) → NO2 H2O→ HONO + OH∙ (1)

HONO H+

→ H2ONO+ → H2O + NO

+ (2)

NO+ + R1R2NH → R1R2NNO + H+ (3)

Scheme 2 The formation of aqueous nitrosamines at low pH from secondary amines and NO2

Stable nitrosamines have only been observed in the aqueous phase for secondary amines. The nitrosamines of primary amines are thought to decay according to Scheme 3:

R1HNNO + H+ → R1HNNOH

+ (1)

R1HNNOH+hydrogen shift→ R1NNOH2

+ → R1NN+ + H2O (2)

R1NN+decomp.→ R1

+ + N2 H2O→ R1OH + H

+ (3)

Scheme 3 Nitrosation of primary amines, which leads to decomposition in an aqueous environment. An alcohol and nitrogen are the by-products

This document reports the experimental outcomes obtained after subjecting several common PCC alkanolamines (piperazine, methyldiethanolamine and 3piperidine) to laboratory tests for the purposes of such an assessment.


2 Task Description/Scope of Work

The following project proposal excerpt was submitted to ANLEC as Sub-task 5 of the funded project: “Environmental Impacts of PCC Emissions”. The following text forms the original project proposal:

“It is likely that in the next years there will be a wide range of candidate amines from different vendors, all suitable for application in PCC. Apart from the amine process performance (reactivity towards CO2, energy requirement for regeneration etc.), the environmental performance will also determine whether one particular amine is preferred over another. Therefore screening of the relative suitability of different liquid absorbents for PCC should also include an evaluation using a protocol by which the amines can be assessed for their propensity to produce harmful by-products in a typical PCC process, with the potential to lead to undesirable emissions.

Over the past four years as part of the post combustion CO2 capture solvent development program, a comprehensive amine degradation project has been undertaken at the CSIRO laboratories. Our research and that of others clearly demonstrates that capture solvent parameters, such as solution pH, CO2 loading, and acid gas components, will all impact to some degree in reducing or increasing amine losses through volatility and degradation. A specific test protocol incorporating/addressing these variables should be considered for any amine volatility and environmental impacts study.

It has been established that acid gases will degrade alkanolamines, as well as result in the formation of heat-stable salts. Oxidative degradation will give rise to small but volatile amides, aldehydes and small organic acids (as well as ammonia), whereas thermal degradation will result in polymeric amides and organic ureas (via isocyanates). Hence, it is essential that a test protocol should take these factors and products into consideration. It is for this reason that a test protocol needs to be developed that takes into consideration the different classes of degradation products.

The test protocol that will be developed as part of this project is expected to rely on mass spectrometry as the detection method of choice. The preference for mass spectrometry over other detection methods is the combination of sample detection sensitivity and unambiguous product identification.

The test protocol front-end coupling will be developed around either chromatography based on liquid separation, or separation in the gas phase, depending on the degradation product profile developed as part of the lead up work. Another separation method that will be considered as part of the investigation is the utilisation of thermogravimetric analysis combined with mass spectrometry or a combination thereof.


The experimental timeframe will be an important consideration, and will largely depend on the robustness of the amine or blend. Incremental temperature increases will be crucial to the identification of degradation breakthrough, as will headspace or dissolved gases. It is envisaged that a purpose-built reactor will be coupled to a suitable separation/detection unit, incorporating fine control temperature and control of headspace gas composition. A cold trap may/may not necessarily be employed to concentrate degradation products.”


3 Literature Review of MDEA Degradation Products

Fewer groups have investigated the degradation chemistry of N-methyl-diethanolamine (MDEA) than of MEA. However, the broad consensus is that MDEA – and tertiary amines in general – are more robust than MEA in the presence of acid gases. Due to the paucity of more recent publications, all MDEA degradation studies identified in the literature have been included in the following review.

Chakma and Meisen [1-3] were the first to study the acid-gas induced degradation of MDEA. They aimed to understand the inhibition of (selective) H2S removal from hydrocarbon gas streams. An autoclave was used to degrade 250-ml volumes of MDEA in the presence of a CO2 gas headspace (2.6 MPa) for periods of up to 140 h and temperatures up to 180 °C. Gas chromatography (GC) with electron impact mass spectrometry and GC with chemical ionisation mass spectrometry were used to identify and quantify degradation products. Major products identified include trimethylamine, ethylene glycol, 2-(dimethylamino)ethanol, either N-

ethylpiperazine or N,N-dimethylpiperazine (note: N,N-dimethylpiperazine is cited in the journal articles, whereas ethylpiperazine is cited in the thesis of Chakma), 1,4-(2-hydroxyethyl)piperazine and diethanolamine. Minor degradation products were tetrakis-

N,N,N,N-(2-hydroxyethyl)ethylenediamine, 3-(2-hydroxyethyl)-1,3-oxazolidin-2-one, 1-(2-hydroxyethyl)-4-methylpiperazine and triethanolamine (TEA). The concentrations of triethanolamine and 2-(dimethylamino)ethanol increase initially, and then plateau, suggesting these products are consumed by secondary reactions.

In a follow-up autoclave study, the same authors confirmed trimethylamine as a secondary product of 2-(dimethylamino)ethanol degradation. N-methylethanolamine was not detected as a degradation product in these studies.

Critchfield and Jenkins [4] studied 500 aqueous MDEA process solutions from tail gas treating units. They aimed to dispel the myth (at the time of publication) that MDEA, unlike MEA and diethanolamine (DEA), was resistant to degradation. No details regarding methods of measuring degradation products were given, but we assume that ion chromatography was used to analyse the organic acids. As the work was funded by Huntsman Corporation, a large chemical manufacturer with significant research operations, it can be assumed that state-of-the-art methods such as GC with a nitrogen–phosphorus detector or GC-mass spectrometry (MS) were used to quantify N-containing degradation products. The authors remark that formation of secondary amines reduces MDEA’s specificity towards H2S at the same time as increasing solvent reactivity towards CO2. They also suggest that MDEA should be used in niche applications for H2S removal. Major markers of MDEA degradation identified in the study included the secondary amines diethanolamine and 2-aminomethylethanol, the tertiary amines bicine (bis-N,N-(2-hydroxyethyl)glycine) and N-(2-hydroxyethyl)sarcosine, plus the organic acids formate, acetate, glycolate and oxalate. Bicine and N-(2-hydroxyethyl)sarcosine are designated as undesirable degradation products because of their metal chelating properties (potential corrosion accelerators). The authors attempted to correlate the abundance of heat-stable salts with the extent of MDEA degradation throughout the article. Secondary amines were found to reach concentrations of up to 10% of total amines in heavily degraded samples, and plant upsets caused such extensive degradation that in some instances,


whole solvent inventories had to be replaced after only two months’ operation (usually after tail gas treating unit catalyst failure). Critchfield and Jenkins were unable to measure 2-aminomethylethanol accumulating in fresh MDEA monitored over time, and proposed that it was lost due to its higher volatility.

Lawal and Idem [5] studied the degradation reactions of MEA–MDEA blends at different temperatures, solution-headspace and gas-headspace compositions using a stirred autoclave. GC-MS and a high-performance liquid chromatograph coupled to a refractive index detector (HPLC-RID) were used in an attempt to characterise degradation products. A large number of degradation products are reported, including some products that are consistent with results from other groups, e.g. bicine, formate and 2-methylaminoethanol.

After reviewing the literature and carefully considering the findings from the current study (reported in the following sections), we suggest that Lawal and Idem [5] may have made some errors attempting to identify reaction products using electron ionisation (EI)-mass spectra. For example, the crown ether ‘degradation products’ included in various reaction schemes within the article are more likely to be derived from de-phasing of the carbowax GC column used in the analyses. It is well known that aqueous solutions de-phase GC column stationary phases at typical GC operating temperatures, and that carbowax is derived from polyethylene glycol (this is stated by the authors in the paper). Ethylene glycol has been identified as a degradation product by Chakma and Meisen [1-3], but polymerisation requires an excess of ethylene oxide and a silver catalyst: very atypical conditions for PCC.

Other unusual findings reported by Lawal and Idem [5] include products with unprecedented branching, e.g. 2-propanamine. Other groups (e.g. Chakma and Meisen) have identified trimethylamine as an MDEA degradation product, which is also more likely on the basis of parent chemical structure. Also, within some of the reaction schemes presented by Lawal and Idem, the products of harsh amine oxidation (e.g. formate) appear alongside heptadienols, which are molecules that would only form under milder, reducing conditions. Heptadienols would act as oxygen scavengers and would at least appear as epoxides under these conditions.

Other major products that appear to have been mis-identified include hydrazinocarbonylimidazoles, which are more likely to be the oxidised side-chain derivative of N-(2-hydroxyethyl)imidazole (HEI), i.e. 1H-imidazol-1-ylacetic acid (see Figure 1). HEI has been detected as a major product in a number of MEA degradation studies. It is also likely that HEI itself (M/z 112) has been incorrectly identified as a heptadienol (M/z 112). 2-amino-2-methyl-1,3-propandiol has not been measured in degraded MDEA solutions previously. However, it has the same mass as DEA, which is an abundant degradation product of both MEA and MDEA, and both species have almost identical EI-mass spectra (see NIST webbook: http://webbook.nist.gov/).

Idem et al. [6] also examined MEA–MDEA blends in two pilot-scale operations (Boundary Dam and University of Regina R&D capture plants). With the exception of identifying ethylene glycol as a significant degradation product, the authors’ results differ from the major MDEA degradation products found in other studies. Neither formate nor N-(2-hydroxyethyl)sarcosine were detected, although no attempts were made to quantify organic acids.

http://webbook.nist.gov/


Figure 1 Degradation product assignments in Lawal and Idem [5] (left column) and assignments supported by other laboratories and/or the findings presented in this report (right column)

Lepaumier et al. [8,9] studied the degradation of 50% MDEA solutions in a stirred autoclave (250 rpm) at 140 °C with a headspace of CO2 (2 MPa) and O2 (0.4 MPa, synthetic air). CO2-induced degradation products identified using various hyphenated GC and LC mass

spectrometric methods included N,N-dimethylaminoethanol, ethylene glycol, DEA and TEA.

DEA and N,N-dimethylaminoethanol were again identified as major degradation products in


the oxygen headspace experiments (together with N-methylaminoethanol and bicine), suggesting that categorisation of products as thermal, oxidative or carbamate-induced is an oversimplification. In terms of organic acids (the only degradation products than can be discretely categorised, i.e. oxidative), MDEA oxidation produced formate > glycolate > acetate > oxalate.

Closman and Rochelle [10] studied the effects of oxygen and temperature cycling on the degradation of 7 molal MDEA. An integrated solvent degradation apparatus (laboratory scale PCC plant) was used to expose the solvent to a gas stream (100 cm3/min) of 98% O2/2% CO2 composition in an oxidation column (T = 55 °C) for several minutes. The solvent was then pumped (0.2 L/min) through to a desorption column and heated to 120 °C. Degradation was monitored using a sub-sample of established (incl. DEA, bicine, formate) and unprecedented (formamide) MDEA degradation products. Carbon accounting suggests these products account

for 55% of the total carbon lost, with DEA alone accounting for > 40%. Some engineering thermodynamic information pertaining to 7 molal MDEA was derived by assuming plug-flow reactor behaviour for the solvent. The formation of degradation products was monitored using LC-MS, GC-MS, ion chromatography (IC) and HPLC with electrochemical detection.

Sargent and Howard [11] detail the effects of oxygen-induced degradation of MDEA in their Wilcox gas-treating facility at Lavaca County, Texas. Aside from plant corrosion being an indicator of oxygen contamination in their gas stream (chiefly in the amine pump body), elevated levels of acetate, oxalate and formate were measured. The presence of DEA, TEA and 2-methylaminoethanol also hinted at solvent oxidation. GC-MS was used to quantify levels of bicine, which is known to accelerate plant corrosion, to 600 ppm by weight in the solvent. Ion-exchange reclamation and oxygen scavengers were used to slow, but not eliminate, bicine build-up in the solvent.


4 Degradation Protocol

The protocol to investigate amine degradation encompasses two aspects. The first is the degradation of fresh solvent samples by exposure to simulated flue gas conditions and in the presence of contaminants for a prolonged period. The second is the analysis of both the solvent and any gaseous products produced during the ageing process for the type and quantity of degradation products formed.

4.1 Solvent Ageing Apparatus

A commercial six-port carousel reactor (Radleys Pty Ltd, UK) has been procured for the purposes of the laboratory investigation of flue-gas induced solvent degradation. A photograph of the apparatus is presented in Figure 2 below.

Figure 2 Carousel six-port reactor system used in the solvent degradation (ageing) experiments

In brief, the synthetic flue gas composition is controlled using calibrated mass-flow controllers (Bronkhorst). The synthetic flue gas passes through the reactor head-space cooling disk and is distributed to each of the reactors. The gas flow to any particular reaction solution is controlled using Teflon gas distribution valves at the top of the reactor vessels. The gas contacts the magnetically stirred (700 rpm) reaction samples in the headspace of the reaction flasks. All reaction solutions are maintained at the same pre-defined temperature by a proportional-integral-derivative (PID) controller, which provides feedback control to the hotplate power supply via a thermocouple in contact with the aluminium heat-distribution plate. This plate sits on the top of the heating element, and distributes heat evenly to each reaction flask/mixture. Off-gas exits the reaction flasks via chilled condensers (attached to one

stirred reaction flaskhotplate and stirring

control

syn-flue gas in

gas distribution valves

reactor cooling

disk

off gas to impingers


of two reaction flask side-arms) and proceeds to flow through dedicated impingers, which consist of Dreschel bottles containing 0.1 M H3PO4 to absorb volatile components remaining in the gas. Samples from each reaction flask are taken through a second flask side-arm with a screw cap and Teflon septum. Impinger samples were sent to Asure Quality Pty Ltd, New Zealand, for volatiles analysis. The selected laboratory was chosen because of his proven expertise in analysing these volatiles compounds.

4.2 Sample Analysis Methods

Four principal analytical techniques were used to assess solvent degradation during the course of the project: (i) ion chromatography-multiple reaction monitoring mass spectrometry (IC-MRM-MS), (ii) IC, (iii) GC-MS and (iv) chemiluminescence analysis.

IC-MRM, IC and chemiluminescence methods were developed in-house as part of a broader PCC program examining amine solvent degradation. The experimental conditions for IC-MRM-MS are given in Appendix A. The GC-MS analysis of volatile organic amines and nitrosamines in impinger samples was performed by an external contractor (Asure Quality Pty Ltd). A breakdown of the techniques used to analyse various degradation markers appears in Table 1. Due to co-elution and cross-talk issues, N-methylaminoethanol could not be quantified. Also, the sensitivity of IC-MRM-MS towards N-methylmorpholine is compromised because of co-elution with the MDEA matrix.

Table 1 Degradation markers and the techniques used to detect their presence

Degradation product Method of analysis

Non-volatile aminesa IC

Amides IC-MRM-MS

Polymersa and amino acidsb e.g. bicine, HES IC-MRM-MS

Ureas IC-MRM-MS

Non-volatile nitrosamines e.g. NDELA IC-MRM, chemiluminescence

Volatile nitrosamines (e.g. N-nitrosodimethylamine, nitrosomorpholine)

chemiluminescence – by difference and GC-MS

Volatile amines (e.g. methylamine, dimethylamine) GC-MS

Carboxylates IC

Inorganic ions (NO3, NO2

) and ammonia IC

aN-methylaminoethanol could not be quantified; however, this is an established MDEA degradation product. Other degradation products that could not be quantified which have been reported as significant include ethylene glycol and dimethylpiperazine. bSarcosine quantified using IC.GC = gas chromatography; HES = N-(2-hydroxyethyl)sarcosine; IC = ion chromatography; MRM = multiple reaction monitoring; MS = mass spectrometry; NDELA = N-nitrosodiethanolamine


During the course of these experiments, all efforts have been made to ensure the efficient capture/trapping of volatile materials; however, reproducibility issues with certain volatile analytes may not be preventable.


5 Experimental Results of Sample Ageing and Sample Analysis

5.1 Experimental Conditions

Reagents used in MDEA ageing study, manufacturer and purity (if stated) are listed below:

N-methyldiethanolamine, 99+%, Aldrich

Iron oxalate dihydrate, FeC2O4.2H2O, 98%, Fluka Analytical

Sodium metavanadate, NaVO3, anhydrous, 99.9% metals basis, Aldrich

N-nitrosodiethanolamine, 98%, Sigma Aldrich

Sodium nitrite, NaNO2, 99.99%, Sigma Aldrich

Sarcosine, Diethanolamine, 99%, Sigma-Aldrich

Bis-N,N- (2-hydroxyethyl)piperazine, 99%, Aldrich

Tetrakis-N,N,N,N- (2-hydroxyethyl)ethylenediamine, technical grade, Aldrich

N-(2-hydroxyethyl)piperazine, 98%, Aldrich

1-ethylpiperazine, 98%, Aldrich

Bicine, > 99%, Sigma

N-(2-hydroxyethyl)sarcosine, purity not stated, Matrix Scientific (USA)

N,N-dimethylaminoethanol, 99.5+%, Aldrich

Triethanolamine, > 97%, Fluka

N-methylmorpholine, > 99.5%, Aldrich

Charcoal-filtered water (R > 18 M)

CO2 (g), food grade, BOC gases

O2 (g), food grade, BOC gases

N2 (g), dried, from cryogenic boil-off.

Details of the solvent ageing conditions are given below:

Solution 1: 25 wt% MDEA

Solution 2: 25 wt% MDEA + 80 mg flyash

Solution 3: 25 wt% MDEA (0.1 CO2 loading) + 15 mg NaVO3

Solution 4: 25 wt% MDEA (0.4 CO2 loading)

Solution 5: 100 wt% MDEA

Solution 6: 25 wt% MDEA + 15 mg FeC2O4.2H2O.

Each solution (~ 150 g) occupied one carousel port in the ageing apparatus.

The following experimental conditions given in Table 2 were maintained while carrying out these experiments.


Table 2 Experimental conditions

The flyash composition is given in Table 3.

Table 3 Oxide composition of Vales Point black coal flyash obtained using X-ray fluorescence spectroscopy (SGI Australia)

Component B1992 Run of station

Al2O3 25.32

BaO 0.07

CaO 3.08

Fe2O3 3.23

K2O 1.18

MgO 0.71

MnO 0.06

Na2O 0.58

P2O5 0.30

SO3 0.15

SiO2 61.83

SrO 0.11

TiO2 0.97

V2O5 0.04

ZnO 0.01

ZrO2 0.04

Total 97.67

Solution temperatures 58.8 1 °C

Stirring rate 700 rpm

Solution mass 150 g

Gas flow to each solution 1.98 L/min

Total flow 11.9 L/min

N2 9 L/min

CO2 1.8 L/min

O2 0.5 L/min

1 % NO in N2 0.6 L/min (~ 500 ppm)

Solvent make-up Charcoal-filtered water (R > 18 M)

Impinger solutions/impinger make-up 0.1 M H3PO4


5.2 Reaction Mixture Sample Analysis Results

IC and IC-MRM-MS were used to detect the presence of degradation in the reaction mixture samples. The species found and their maximum concentrations are given in Appendix B.

5.2.1 IDENTIFICATION OF ADDITIONAL SPECIES

Direct infusion MS was used to identify the presence of other potentially significant species in samples collected on 8/5/2012. These unexpected degradation products given in Table 4 may not have been reported in the open literature. Some peaks due to established degradation products (e.g. bicine, HES) are also listed in italic typeface for comparison.

Note: Chemical structures listed in the following tables are based on observed masses from direct infusion experiments and MS/MS fragmentograms, and are preliminary in nature. Literature findings have also been taken into account during structure/composition assignments. Mass measurement using the instrumentation available is not accurate enough to allow for discrimination between CO/C2H4/N2. Standard MS rules for structure assignments have been applied throughout. Quantification of these unexpected degradation products cannot be performed within the reporting timeframe.

Table 4 Unexpected ions observed in the direct-infusion mass spectrometry (MS) spectrum of degraded N-methyl-diethanolamine (MDEA) solutions. Established degradation products also observed are in italics. Compositions and preliminary identities are based on MS/MS information

M/z Chemical formula Chemical name

75.9 C3H9NO N-methylethanolamine

119.9 C5H13NO2 N-methyldiethanolamine

133.9 C6H16NO2 N-(2-hydroxyethyl)sarcosine

135.9 C5H13NO3 bis-(2-hydroxyethyl)hydroxymethylamine

142.0 C5H13NO2Na Na+-MDEA

147.9 C5H9NO4 N-methyliminodiacetic acid

163.9 C6H13NO4 bicine

177.0 C7H16N2O3 2-[bis(2-hydroxyethyl)amino]-N-methylacetamide

193.0 C8H20N2O3 N,N,N-tris(2-hydroxyethyl)ethylenediamine

207.0 C9H22N2O3

N,N,N-tris(2-hydroxyethyl)-N-

methylethylenediamine or N,N,N-tris(2-

hydroxyethyl)-N-methylurea or 2-[bis(2-hydroxyethyl)amino]-N-(2-hydroxyethyl)acetamide

221.0 C10H24N2O3

2-[bis(2-hydroxyethyl)amino]-N-(2-hydroxyethyl)-

N-methylacetamide or N,N,N-tris(2-hydroxyethyl)-

N-ethylethylenediamine or N,N,N-tris(2-

hydroxyethyl)-N-ethylurea

247.0 C9H24N2O4Na DEA-Na+-MDEA


5.2.2 RESULTS AND DISCUSSION

The products found based on identification and quantification using expected degradation products did not vary significantly across the sample conditions. The maximum concentration of each degradation product detected in each sample is given in Table . DEA was present at the highest concentration in all samples ranging from 1844 to 2504 ppm in both aqueous and pure MDEA. In the aqueous samples, the average concentration of each degradation product had the following trend, with the ranges given in brackets: DEA (1844–2455 ppm) > Bicine (619–980 ppm) > N-(2-hydroxyethyl)sarcosine (HES, 158–264 ppm) > N,N-dimethylaminoethanol

(DMMEA, 97–286 ppm) ≈ N-nitrosodiethanolamine (NDELA, 129–172 ppm) > NMM (14–

43 ppm) > TEA (10–18 ppm). The 50% uncertainty associated with the values means that the error encompasses the observed range for all degradation products except DMMEA and NMM, with no trends apparent. The other degradation products (1-ethylpiperazine, NetPz; 1-(2-hydroxyethyl)piperazine, HEP; 1,4-bis(2-hydroxyethyl)piperazine, BHEP; N,N,N’,N’-tetrakis(2-hydroxyethyl)ethylenediamine, THEED; and 3-(2-hydroxyethyl)oxazolidin-2-one, HEOD) were not detected or detected at levels below 10 ppm in aqueous solution. The large error associated with detection at such low levels makes quantification difficult. However, THEED and HEOD were consistently observed in the 1–3 ppm range. Pure MDEA resulted in higher concentrations of all the degradation products. This suggests that water is not required for their formation.

In terms of timing, DMMEA consistently appeared after 3–4 weeks’ exposure to the simulated flue gas. NDELA was detected after two weeks’ exposure, and HEOD after 2–3 weeks’ exposure. All other detected degradation products were present after one week.

Table 5 Maximum concentration (ppm) of each degradation product detected in each sample

Chemical Name 25%

MDEA

25% MDEA + 80mg Fly

Ash

25% MDEA + 0.1 ld + 15mg NaVO3

25% MDEA +

0.4 ld

25% MDEA +

15mg FeC2O4

100% MDEA

N,N-dimethylaminoethanol (DMMEA) 97 286 128 122 206 1710

1-ethylpiperazine (NEtPz) - 0.6 2 2 - -

diethanolaimine (DEA) 2015 2455 2205 1844 1988 2507

N-methylmorpholine (NMM) 33 28 21 14 43 214

triethanolamine (TEA) 16 18 17 10 18 49

1-(2-hydroxyethyl)piperazine (HEP) - - - - - 20

Bicine 704 980 982 619 975 1496

1,4-bis(2-hydroxyethyl)piperazine (BHEP) - - 0.2 - 1 -

N,N,N,N-tetrakis(2-hydroxyethyl)ethylenediamine (THEED) 3 2 3 3 2 6

3-(2-hydroxyethyl)oxazolidin-2-one (HEOD) 2 3 2 1 2 45

N-(2-hydroxyethyl)sarcosine (HES) 158 271 181 138 264 590

N-nitrosodiethanolamine (NDELA) 164 172 163 129 136 555


If all the degradation products that have formed at > 10 ppm are considered, a rational route of formation can be postulated for each based on common chemical transformations. This is summarised in Figure 3. Demethylation of MDEA results in DEA; being a secondary amine, DEA will undergo nitration in the presence of dissolved NO2. Dehydroxylation and hydroxylation of MDEA will form DMMEA and TEA, respectively. The demethylation and dehydroxylation reactions are likely to be a result of thermal degradation. Oxidation of TEA produces bicine, while oxidation of MDEA produces HEA. Finally, ring closure via loss of water to form a six-membered ring results in NMM, which is also most probably a thermal degradation product. If the species identified but not quantified (as described in Section 6.2.7) are also considered, it is likely that the same types of reactions have resulted in the formation of these species.

Figure 3 Primary (> 10 ppm) degradation products detected for MDEA degradation and postulated routes of formation

5.3 Volatiles Sample Analysis Results

Impinger samples were analysed for volatile nitrosamines/alkylamines by AsureQuality laboratories, Wellington, New Zealand. This data is reproduced in its entirety – without modification – according to specified reporting requirements.


The samples were analysed using headspace GC-MS. Results are reported to two significant figures in milligrams per litre (mg/L), equivalent to ppm. Detection limits are reported to one significant figure. Results are given below.

5.3.1 VOLATILE AMINES

Within the detection limits of the analysis given below, none of the volatile amines listed were detected in the impinger samples.

Analyte Limit (mg/L)

methylamine 20

dimethylamine 5

ethylamine 5

diethylamine 0.5

5.3.2 VOLATILE NITROSAMINES

Volatile nitrosamines were determined using an in-house isotope dilution high-resolution GC-MS-MS method developed at AsureQuality. Results are reported in Appendix C.

The highest detected concentrations were for N-nitrosodimethylamine (NMDA, 668 ppb) and N-nitrosopiperidine (NPIP, 608 ppb). NMDA is the dehydroxylated form of NDELA, while NPIP may form from NMM, although its formation is not straightforward.


6 Discussion and Conclusions

MDEA is structurally similar to MEA, but it is a tertiary amine that possesses a second hydroxyethyl group and a methyl group attached to the nitrogen atom. Unlike MEA, no hydrogen atoms are attached directly to the central nitrogen atom, but the nitrogen can still accept a proton. The maximum carbon chain length in the molecule is 2, so aldehydes up to C2 should be monitored during degradation studies. The organic acids (carboxylates) can be ignored for stack sampling studies, because of their lack of volatility.

By far the most important degradation product in MDEA solutions is DEA; this study demonstrates that DEA nitrosates to form a secondary degradation product, NDELA, which is a known carcinogen. After a few weeks, DEA concentration in degraded MDEA solutions ranges from 1850 to 2500 ppm (0.18–0.25% MDEA solution), and NDELA concentrations have risen to

130 ppm. (For pure MDEA reaction mixture, a maximum value of 555 ppm is reported. This may be higher than the true value, due to sampling errors.) Note that NDELA presence is reported in ppb in the MEA test results, whereas levels are three orders of magnitude higher in the degraded MDEA solutions (values in hundreds of ppm).

Other major degradation products include the amino acids bicine and N-(2-hydroxyethyl)sarcosine. These products will be present in their deprotonated forms, and are unlikely to escape as a vapour from PCC stacks, unless entrained in droplets. Although not included in this study, it is recommended that N-methylaminoethanol (a secondary amine) be monitored as it is a major product according to other studies, and it could potentially nitrosate.

The following heterocycles were monitored during this study: N-methylmorpholine, N-

ethylpiperazine, N-(2-hydroxyethyl)piperazine and N,N-bis(2-hydroxyethyl)piperazine. Two of these amines have secondary nitrogen centres (N-ethylpiperazine and N-(2-hydroxyethyl)piperazine), and so could possibly undergo nitrosation.

With the exception of the tertiary amine N-methylmorpholine (for the reasons outlined in Section 5.2), the IC-MRM-MS method has excellent sensitivity for all these heterocycles: typically sub-50 ppb in the diluted samples. We can be confident that none of these amines presented as significant degradation products under the conditions of the study.

N-methylmorpholine is the product of either base or acid-catalysed cyclisation of MDEA. Therefore, temperatures in excess of 100 °C may be needed to observe larger quantities of this product. As N-methylmorpholine could potentially undergo demethylation to produce morpholine, it is included as a product to monitor in stack emission studies, as has 1-(2-hydroxyethyl)piperazine (secondary nitrogen centre).

N,N-dimethylpiperazine has also been reported as a degradation product in other studies. Because this study has established that demethylation conditions are favourable in degraded MDEA solutions, it is recommended that N-methylpiperazine and trimethylamine be monitored in stack emission studies. Note that N-nitrosomorpholine could form in a similar fashion to N-methylmorpholine.

The study of volatile indicates much higher levels of NDMA being emitted and trapped by impingers (ranging from 85 to 558 ppb). Significant residues are also present in the primary reaction vessels (24–668 ppb). The United States Environmental Protection Agency’s (EPA's)


Integrated Risk Information System (IRIS) database lists the concentration of NDMA in drinking water needed for a one-in-one-million lifetime cancer risk to be 0.7 ng/L (or < 1 ppt). Significant residues of N-nitrosomorpholine and N-nitrosopiperidine were also present in the reaction vessels (43 ppb > NPIP > 608 ppb; 38 ppb > NMOR > 187 ppb). NDMA levels in the impingers are almost as high as the levels in the reaction vessels themselves, whereas NPIP and NMOR levels in impingers are much lower, with detection of these analytes in the impingers being the exception, rather than the rule.

The only analyte in the EPA 521 method not detected in the reaction mixture/impinger solution analyses was N-nitroso-di-n-propylamine. Aside from the volatile nitrosamines already discussed, the other EPA 521 analytes were present in much lower concentrations (< 30 ppb) than NDMA, NPIP and NMOR. The full suite of molecules that it is recommended to monitor are presented in Table 6.

Table 6 Degradation products for environmental monitoring (excluding monoethanolamine, MEA). C = known carcinogen; M = major degradation product; N = undergoes nitrosation (secondary amine); P = precursor to nitrosamines or other degradation products that nitrosate

Chemical Formula CAS Number Properties

Diethanolamine C4H11NO2 111-42-2 M,N,P

N-nitrosodimethylamine C2H6N2O 62-75-9 C

Formaldehyde CH2O 50-00-0 C

Acetaldehyde C2H4O 75-07-0 C

N-nitrosomorpholine C4H8N2O2 59-89-2 C

N-nitrosopiperidine C5H10N2O 100-75-4 C

N-nitrosodiethanolamine C4H10N2O3 1116-54-7 M,C,P

Morpholine C4H9NO 110-91-8 N

N-methylethanolamine C3H9NO 109-83-1 M,N,P

N,N-dimethylethanolamine C4H11NO 108-01-0 M,P

Trimethylamine C3H9N 75-50-3 M,P

N-methylmorpholine C5H11NO 109-02-4 N,P

N-methylpiperazine C5H12N2 109-01-3 N,P

N-ethylpiperazine C6H14N2 5308-25-8 N,P

N-(2-hydroxyethyl)piperazine C6H14N2O 103-76-4 N,P

ENVIRONMENTAL IMPACTS OF AMINE-BASED CO2 POST-COMBUSTION CAPTURE (PCC) PROCESS | 27

7 References

1. Chakma, A.; Meisen, A. Identification of Methyl Diethanolamine Degradation Products by Gas Chromatography and Gas Chromatography-Mass Spectrometry. J. Chromatog. 1998, 457, 287–297.

2. Chakma, A.; Meisen, A. Methyl-diethanolamine Degradation — Mechanism and Kinetics. Can. J. Chem. Eng. 1997, 75, 861–871.

3. Chakma, A. PhD Thesis. University of British Columbia, Vancouver, Ca., June 1987.

4. Critchfield, J.E.; Jenkins, J.L. Evidence of MDEA Degradation in a Tail Gas Treating Plants. Petrol. Tech. Quart. 1999, Spring, 87–95.

5. Lawal, A.O.; Idem, R.O. Effects of Operating Variables on the Product Distribution and Reaction Pathways in the Oxidative Degradation of CO2-Loaded Aqueous MEA-MDEA Blends during CO2 Absorption from Flue Gas Streams. Ind. Eng. Chem. Res. 2005, 44, 986–1003.

6. Idem, R.; Wilson, M.; Tontiwachwuthikul, P.; Chakma, A.; Veawab, A.; Aroonwilas, A.; Gelowitz, D. Pilot Plant Studies of the CO2 Capture Performance of Aqueous MEA and Mixed MEA/MDEA Solvents at the University of Regina CO2 Capture Technology Development Plant and the Boundary Dam CO2 Capture Demonstration Plant. Ind. Eng. Chem. Res. 2006, 45, 2414–2420.

7. Bedell, S.A.; Worley, C.M.; Darst, K.; Simmons, K. Thermal and Oxidative Disproportionation in Amine Degradation — O2 Stoichiometry and Mechanistic Implications. Int. J. Greenhouse Gas Contr. 2011, 5, 401–404.

8. Lepaumier, H.; Picq, D.; Carrette, P.-L. New Amines for CO2 Capture. I. Mechanisms of Amine Degradation in the Presence of CO2. Ind. Eng. Chem. Res. 2009, 48, 9061–9067.

9. Lepaumier, H.; Picq, D.; Carrette, P.-L. New Amines for CO2 Capture. II. Oxidative Degradation Mechanism. Ind. Eng. Chem. Res. 2009, 48, 9068–9075.

10. Closman, F.; Rochelle, G.T. Degradation of Aqueous Methyldiethanolamine by Temperature and Oxygen Cycling. Energy Procedia 2011, 4, 23–28.

11. Sargent, A.; Howard, M. Texas Plant Faces Ongoing Battle with Oxygen Contamination. Oil and Gas J. 2001, July 23, 52–58.

28 | Report Title

Part II Piperazine (PZ) and 3-

piperidinemethanol

(3-PM) Degradation


1 Introduction

The same solvent ageing apparatus and sample analysis described in Part I of this study was also used for two cyclic secondary amines: piperazine (PZ), and 3-piperidinemethanol (3-PM). Due to the propensity of secondary amines to form potentially carcinogenic nitrosamines, the synthetic flue gas used did not contain NO2. This was due to a lack of suitable equipment to safely manage the formation of significant amounts of nitrosamine.

PZ is a heterocyclic diamine. Its structure is shown in Figure 4. PZ has limited solubility in aqueous solution (up to approximately 15 wt%), but has found use as a CO2 absorption rate promoter, due to its fast reaction to form a carbamate. As PZ is a diamine, it may also form a dicarbamate species, but typically this is seen only at low concentrations. PZ is typically added as a rate promoter to solvents such as 2-amino-2-methyl-propanol (AMP) and N-methyl-diethanolamine (MDEA), which have good, albeit slow, CO2-absorbing capacity. The resulting formulation retains good absorption capacity, but has an improved rate of absorption. Such formulations have found commercial application, such as BASF’s MDEA® technology. Concentrated PZ solutions, in which the concentration of PZ is increased through pre-loading with CO2 followed by further addition of PZ, are also undergoing laboratory and pilot-plant testing as potential new solvents (e.g. see ANLEC R&D project number 4-1110-0097). PZ has not been investigated as thoroughly as MDEA in terms of degradation. However, some literature is available on PZ degradation, allowing quantification of a number of degradation products.

3-PM is a promising capture solvent identified by CSIRO and intended for use in CO2 capture plants attached to coal and gas power stations. Its structure is shown in Figure 4. It does not satisfy the criteria described by Chakraborty et al. [1] for classification as a sterically hindered amine: four methyl or bulkier groups, two each at C2 and C6, would be needed. However, the proximity of the single hydroxymethyl group (-CH2OH) to the secondary amine centre may lead to some intra-molecular hydrogen bonding. We propose that this molecular feature reduces the availability of the nitrogen lone pair for carbamate formation. 3-PM is intended to be used as part of an amine solvent mixture, and exhibits similar behaviour to a sterically hindered amine, showing good rates of CO2 absorption and absorption capacity. No information is available in the literature concerning the degradation chemistry of 3-PM in the context of post-combustion CO2 capture (PCC). For this reason, quantitation for 3-PM degradation products is not feasible, because no degradation reports have been published, and the identity of the degradation products needs to be determined from first principles.

Figure 4 Chemical structures of piperazine and 3-piperidinemethanol

30 | Report Title

2 Degradation Protocol

The solvent ageing apparatus as described in Section 4.1 of Part I was also used to age PZ and 3-PM samples. Three of the six ports in the carousel of the ageing apparatus contained PZ samples, and three ports contained 3-PM samples. The synthetic flue gas used did not contain NO2, to avoid the possible formation of significant amounts of carcinogenic degradation products.

2.1 Sample analysis methods

Two principal analytical techniques were used to assess solvent degradation during the course of the piperazine degradation study: ion chromatography-multiple reaction monitoring mass spectrometry (IC-MRM-MS) and IC. All methods used were developed in-house as part of a broader PCC program examining amine solvent degradation. The degradation markers and the analysis techniques used for PZ samples are given in Table .

No information is available regarding the degradation of 3-PM under PCC conditions. For this reason, only preliminary degradation products can be reported. Solutions of PZ at 7.5 wt% were degraded, because of PZ’s low aqueous solubility (15 wt% maximum at room temperature, no loading or pH adjustment) and its tendency to ion-pair in atmospheric pressure ion sources.

Table 7 Degradation markers and the techniques used to detect their presence

ANALYSIS STRATEGY FOR 3-PM

Samples of 3-PM were exposed to the same flow of synthetic flue gas as PZ. On 9/4/2013, a sample from Solution 6 (+15 mg FeC2O4.2H2O, see below) was taken for direct-infusion MS. The sample containing Fe2+ was selected as ‘representative’, because previous experiments (with monoethanolamine (MEA) and MDEA) demonstrate that iron accelerates solvent degradation, and the degradation product distribution produced by iron does not differ greatly from either the ‘flyash’ or ‘loaded sample’ product distribution.

Products were identified from the infusion spectrum, and the corresponding transitions were monitored for the remainder of the experiment. Infusion samples were also collected at subsequent dates to check the evolution of degradation products previously identified. A few degradation standards were purchased and their mass spectrometry (MS/MS) behaviour and retention times compared with degradation products from the experimental run.

Degradation product Method of analysis

PZ, ammonia, carboxylate ions and NO3, NO2

Ion chromatography (IC)

Amides, polymeric products, ureas and some amines IC-multiple reaction monitoring


3 Experimental Results of Sample Ageing and Sample Analysis

3.1 Experimental Conditions

Reagents used in PZ ageing study, manufacturer and purity (if stated) are listed below:

Piperazine, 99%, Sigma

2-(2-aminoethyl)aminoethanol (HEEDA), 99%, Aldrich

Dimethylamine (hydrochloride salt), 99%, Aldrich

Diethylamine , 99.5%, Sigma

Ethylenediamine, 99.5%, Fluka

1,4-dimethylpiperazine, 98%, Aldrich

N-formylpiperazine, > 90%, Aldrich

N-(2-aminoethyl)piperazine, 99%, Aldrich

N-(2-hydroxyethyl)piperazine, 98%, Aldrich

N,N′-bis(2-hydroxyethyl)piperazine, 99%, Aldrich

2-oxopiperazine, 97%, Aldrich.

Reagents used in 3-PM ageing study, manufacturer and purity (if stated) are listed below:

3-piperidinemethanol, 96%, Aldrich.

Common reagents to both studies, manufacturer and purity (if stated) are listed below:

Iron oxalate dihydrate, 98%, Fluka Analytical

Sodium nitrite, 99.99%, Sigma Aldrich

Ammonia, 28% in H2O, Sigma Aldrich

Acetic anhydride, > 99%, Fluka

Potassium nitrate, purity not stated, Merck

Cupric sulphate, 99.0%, Univar

Oxalic acid, 99.999%, Aldrich

Sodium acetate, reagent grade, Sigma

Propionic acid, ≥ 99.5% Sigma Aldrich

Glycolic acid, 99%, Sigma-Aldrich

Formic acid, ~ 98%, Fluka

Methanol, ~ 99.9%, Fluka Analytical

Sodium bicarbonate, 99.5%, Sigma Aldrich

Charcoal-filtered water (R > 18 M)

CO2 (g), food grade, BOC gases

O2 (g), food grade, BOC gases

N2 (g), dried, from cryogenic boil-off.

32 | Report Title

Details of the solvent ageing conditions are given below:

Solution 1: 7.5 wt% PZ + 15 mg FeC2O4.2H2O

Solution 2: 7.5 wt% PZ + 80 mg flyash

Solution 3: 7.5 wt% PZ + 0.2 CO2 loading (2.198 g NaHCO3)

Solution 4: 20 wt% 3-PM + 0.2 CO2 loading (4.383 g NaHCO3)

Solution 5: 20 wt% 3-PM + 80 mg flyash

Solution 6: 20 wt% 3-PM + 15 mg FeC2O4.2H2O

Each solution (~ 150 g) occupied one carousel port.

Table 8 Oxide composition of Vales Point black coal flyash obtained using X-ray fluorescence spectroscopy (SGI Australia)

Table 9 Synthetic flue gas composition, time of exposure and temperature used in the sample ageing apparatus

Composition (L/min) Time (hrs) Temperature (°C)

Stage 1 Absorption 0.033 O2, 0.11 CO2, 0.61 N2 128 40

Desorption 0 O2, 0.099 CO2, 0.53 N2 179 90

Stage 2 Absorption 0.033 O2, 0.10 CO2, 0.53 N2 153 60

Desorption 0.010 O2, 0.17 CO2, 0.89 N2 261 90

Stage 3 (piperazine only)

Absorption 0.067 O2, 0.20 CO2, 1.1 N2 119 60

Desorption 0.067 O2, 0.20 CO2, 1.1 N2 53.5 90

Component B1992 Run of station

Al2O3 25.32

BaO 0.07

CaO 3.08

Fe2O3 3.23

K2O 1.18

MgO 0.71

MnO 0.06

Na2O 0.58

P2O5 0.30

SO3 0.15

SiO2 61.83

SrO 0.11

TiO2 0.97

V2O5 0.04

ZnO 0.01

ZrO2 0.04

Total 97.67


3.2 Results for Piperazine

Unlike MDEA and MEA studied earlier, piperazine does not contain a hydroxyl group but consists of a six-membered ring containing two opposing nitrogen atoms. It is resistant to oxidative degradation and less volatile than MEA and non-corrosive to stainless steel. It is anticipated that the major degradation products to be different from the other studied compounds. The compounds analysed for using IC-MRM-MS were:

Ethylenediamine

Diethylamine

2-oxopiperazine

N-(2-hydroxyethyl)ethylenediamine

1,4-dimethylpiperazine

N-formylpiperazine

N-(2-aminoethyl)piperazine

N-(2-hydroxyethyl)piperazine

N,N′-bis(2-hydroxyethyl)piperazine

The analysis results are presented in Appendix D.

3.2.1 IDENTIFICATION OF ADDITIONAL SPECIES

These samples were collected on 8/5/2013. Direct-infusion MS was used to identify the presence of other potentially significant species in the degraded PZ solvents. The compounds and their preliminary identification are given in Table , and speculative structures for some compounds are given in Figure 5. These unexpected degradation products may not have been reported in the open literature.

Note: Chemical structures listed in the following tables are based on observed masses from direct infusion experiments and MS/MS fragmentograms and are preliminary in nature. Literature findings have also been taken into account during structure/composition assignments. Mass measurement using the instrumentation available is not accurate enough to allow for discrimination between CO/C2H4/N2. Standard MS rules for structure assignments have been applied throughout. Quantification of these unexpected degradation products cannot be performed within the reporting timeframe.

Table 10 Unexpected ions observed in the direct-infusion mass spectrometry (MS) spectrum of degraded piperazine solutions. Compositions and preliminary identities are based on MS/MS information

M/z Chemical formula

Chemical name

70 C4H7N a,b-dihydro-cH-pyrrole1

99 C4H6N2O 3,4-dihydropyrazin-2(1H)-one OR 5,6-dihydropyrazin-2(1H)-one

116 C6H13NO 3-piperidinemethanol (contaminant)

129 Na3CO3 Cluster from addition of sodium bicarbonate

169 C7H12N4O 1,2,3,4,4a,5a,6,9a-octahydroimidazo[2',1':2,3][1,3]oxazolo[4,5-b]pyrazine OR 3-(2,3-dihydro-1H-imidazol-1-yl)piperazin-2-one

171 C4H8N2 Protonated cluster: piperazine plus 1,2,3,4-tetrahydropyrazine OR 1,2,3,6-tetrahydropyrazine

173 Protonated dimer of piperazine

187 C8H18N4O 2-[(2-aminoethyl)amino]-1-(piperazin-1-yl)ethanone

199 C8H14N4O2 N-(2-aminoethyl)-2-(3,4-dihydropyrazin-1(2H)-yl)-2-oxoacetamide OR

34 | Report Title

N-(2-aminoethyl)-2-(2-oxo-3,4-dihydropyrazin-1(2H)-yl)acetamide

227 C8H10N4O4

N-[2-(2,3-dioxo-3,4-dihydropyrazin-1(2H)-yl)ethyl]ethanediamide OR N-[3,4-dihydropyrazin-1(2H)-yl(oxo)acetyl]ethanediamide OR N-(2-aminoethyl)-2-(2,3-dioxo-3,4-dihydropyrazin-1(2H)-yl)-2-oxoacetamide

M/z > 227 (see Figure H3)

Adducts of Na3CO3

+ (due to added NaHCO3, which is used to simulate loading)

1 Possible MS artefact. a,b = 3,4; 2,5; 2,3; c = 2 or 1; 2 ethylpiperazin-2-one and hexahydro-5H-[1,3]oxazolo[3,2-a]pyrazine = tautomers

Figure 5 Speculative structures of some unexpected piperazine degradation products. M/z 70 = dihydropyrroles; M/z 99 = dihydropyrazin-2-ones; M/z 169 (L to R) = tetrahydropyrazine 1, tetrahydropyrazine 2, oxazolopyrazine 1, imidazolylpiperazinone, oxazolopyrazine 2; M/z 187 = imidazolidinone 1, ethanone 1

N N

HNH

M/z 70

ONH

N

ONH

N

ONH

NH

ON

NH

M/z 99

M/z 187

O

NH

NH2

N

NH

O

O

NH

NH2 N

NH

M/z 169

O

NH

NH

NNH

O

NH

NH

NNH

O

NH

NH

N

NH

O

NH

NH

N

NH

NH

NH

N NH


3.2.2 RESULTS AND DISCUSSION

Of the quantified degradation products, only two main products were found for PZ: ethylenediamine and 2-oxopiperazine. Ethylenediamine is likely to form via a combination of ring opening and dealkylation, and represents a form of thermal degradation. 2-oxopiperazine is a result of oxidation. All other degradation markers were not detected or only detected at concentrations below 3 ppm. Speculative routes of formation are given in Figure 6. Based on the speculative structures of the additional species identified using direct-infusion MS, they appear to be additional oxidation products, some dimerisation products or combinations of oxidation products and ethylenediamine.

Figure 6 Speculative degradation routes from piperazine to form the two major degradation products detected

3.3 Results for 3-piperidinemethanol

No previous studies have analysed the degradation of 3-PM exposed to flue gas. Therefore, it was impossible to carry out calibration and quantification for known degradation products. Because this is the first study of its type, direct-infusion MS was used to complete an initial investigation of the degradation products formed. Quantification of the amounts formed requires additional work.

Postulated chemical formulae for the degradation products detected are given in Table . The chemical structures of those products that can be determined with most certainty (M/z of up to 146) are given in Figure 7. Alternative configurations of the functional groups for some structures are also possible where the M/z value does not define a unique structure. Similarly to PZ, we see ring opening and oxidation. Dehydroxylation of the alcohol side-chain also occurs. The concentration of each degradation product cannot be ascertained at this stage.

36 | Report Title

Table 11 Ions observed in the direct-infusion mass spectrometry (MS) spectrum of degraded 3-piperidinemethanol solutions. Compositions and preliminary identities are based on MS/MS information

M/z Chemical formula Chemical name

98a C6H11N Methyltetrahydropyridine/methyldidehydropiperidine

128a C6H9NO2 (hydroxymethyl)didehydropiperidinone OR hydroxymethylidenepiperidinone OR didehydropiperidinecarboxylic acid

130 C6H11NO2 3-piperidinecarboxylic acid

144a C6H9NO3 Oxopiperidinecarboxylic acid

146 C6H11NO3 2-(aminomethyl)-5-oxopentanoic acid OR 5-amino-2-formylpentanoic acid

188 C8H13NO4

6-(hydroxymethyl)hexahydro-4H-[1,3]dioxino[4,5-b]pyridin-2-one OR 5-hydroxyhexahydro-5H-[1,4]dioxepino[5,6-b]pyridin-3(2H)-one OR 2-hydroxyoctahydro-5H-[1,4]dioxepino[5,6-b]pyridin-5-one OR oxo(piperidin-3-ylmethoxy)acetic acid OR [(2-oxopiperidin-3-yl)methoxy]acetic acid

213 C12H24N2O OR C11H20N2O2

(3'-methyl-1,2'-bipiperidin-3-yl)methanol OR (3'-methyl-1,3'-bipiperidin-3-yl)methanol OR 3-[(piperidin-2-yloxy)methyl]piperidin-2-one OR 5-[(piperidin-2-yloxy)methyl]piperidin-2-one OR 2-(piperidin-3-ylmethoxy)piperidin-3-one

239 C13H22N2O2 5-amino-2-methyl-1-(2,3,5,6-tetrahydrofuro[2,3-b]pyridin-7(4H)-yl)pentan-1-one OR 5-amino-4-methyl-1-(2,3,5,6-tetrahydrofuro[2,3-b]pyridin-7(4H)-yl)pentan-1-one

a Generalised structure name (substitutions/additions/double bond positions variable within structure)


Figure 7 Speculative structures for the degradation products of M/z less than 146 identified for 3-piperidinemethanol. Alternative configurations with rearrangement of groups are possible for some structures, but these are not given in the figure

38 | Report Title

4 Discussion and Conclusions

Piperazine

PZ is a heterocyclic diamine possessing two secondary nitrogen centres. It can form a carbamate or dicarbamate, and can also form both mono- and dinitrosamine species during PCC applications if the flue gas contains NOx gas. In principle, it can capture CO2 via the carbamate route, but only consume one mole of amine per mole of CO2, due to the ability of the second amine group to accept a proton. The results of this degradation run confirm that PZ is one of the more robust amines being considered for PCC applications in the absence of NOX. It is likely that higher temperatures than those used here (these experiments were limited to < 100 °C) are needed to induce significant thermal degradation. The degradation products detected and quantified were ethylenediamine, 2-oxopiperazine, HEEDA, N-formyl piperazine, diethylamine and 1,4-dimethylpiperazine. There are no prior reports of the detection of 2-oxopiperazine, although it can be expected to form whenever PZ is exposed to oxygen.

The most abundant and persistent products were 2-oxopiperazine and ethylenediamine. All other products did not exceed 3 ppm concentration during the run, and 2-oxopiperazine and ethylenediamine only exceeded 1 ppm during Stage 3 of the degradation experiment when the largest gas flows were used. Due to poor sensitivity for dimethylamine, efforts to detect and quantify this analyte were discontinued after the first few samples were taken (it was not present in any sample), The focus was then switched to quantifying and characterising any novel degradation products.

Samples taken on the 8/5/2013 were analysed for possible unreported organic degradation products by direct-infusion MS. Speculative structures from some peaks in the direct-infusion spectra are presented in Figure 5. The products identified are mostly additional oxidation products, some dimerisation products or combinations of oxidation products and ethylenediamine. No specific conclusions can be drawn, because the amounts formed are unknown.

N-nitrosopiperazines (both mono- and di-) are likely products when NOx is a component of the flue gas however no NOx was used in this study due to the reasons outlines in the experimental section. N-nitrosodiethylamine may also be expected to form. It would be prudent to measure levels of N-nitrosodimethylamine, because the interactions of amines with NOx gas are not well characterised at this stage (Jackson and Attalla, 2013), although indications are that NOx will increase decomposition chemistry. Based on all the available information, the degradation products that we recommend to monitor are presented in Table 12.

Table 12 Degradation products for environmental monitoring. C = known carcinogen; M = major degradation product; N = undergoes nitrosation (secondary amine); P = precursor to nitrosamines or other degradation products that nitrosate



N-nitrosodiethylamine C4H10N2O 55-18-5 C

N-nitrosopiperazine C4H9N3O 5632-47-3 C,P

N,N′-dinitrosopiperazine C4H8N4O2 140-79-4 C

Diethylamine C4H11N 109-89-7 N,P

Formaldehyde CH2O 50-00-0 C

Acetaldehyde C2H4O 75-07-0 C

Dimethylamine C2H7N 124-40-3 N,P


2-oxopiperazine C4H8N2O 5625-67-2 M,N

Ethylenediamine C2H8N2 107-15-3 M

3-Piperidinemethanol

3-PM is a heterocyclic secondary amine, with a hydroxymethyl group located two carbon atoms distant from the nitrogen centre. It has been postulated that the hydroxymethyl group can interact with the secondary amine centre and retard carbamate and/or nitrosamine formation. Otherwise, its chemistry should be similar to any other heterocyclic secondary amine. It is not as volatile as PZ.

In contrast to PZ, 3-PM appeared to be seriously degraded after 6–8 weeks simulated flue gas (SFG) exposure. Considering that the SFG did not contain NOx, this amine will have a very short life in a full-scale PCC plant scrubbing any flue gas. In the case of the degradation product at M/z 239, tR = 18.1–18.2, it eventually dominates the degradation soup. While in previous studies degradation product abundance has reached maximum values of a few hundred parts per million (or a few mg/ml in the case of MDEA degrading to DEA), M/z 239 appears to be present in even higher concentrations. Its abundance dramatically rises when oxygen is a component of the SFG at both low and high temperatures (60 °C and 90 °C, see Stage 2 experimental conditions). M/z 146 also appears to increase as the sample is exposed to oxygen at higher temperatures. 3-piperidinecarboxylic acid was positively identified in the degradation soup using a known standard.

It is recommended that the analytes in Table 13 be monitored in the event this amine is used at the pilot or full plant scale. The list is based on structural considerations and the likely formation of nitrosamines if the solvent is exposed to SFG containing NOx. It would also be prudent to monitor formaldehyde, acetaldehyde, propionaldehyde and butyraldehyde because of the importance of these analytes as carcinogens. M/z 213 is cited because it is one of the first degradation markers to appear in the mixture; M/z 239 is cited for reasons previously discussed. Methanol may also form if plant corrosion produces aqueous transition metal ions.

Table 13 Degradation products for environmental monitoring. C = known or probable carcinogen; M = major degradation product; N = undergoes nitrosation (secondary amine); P = precursor to nitrosamines or other degradation products which nitrosate; T = toxic



N-nitrosomethylethylamine 10595-95-6 C

N-nitrosomethylpropylamine 924-46-9 C

N-nitrosopiperidine 100-75-4 C

2-[butyl(nitroso)amino]ethanol C6H14N2O2 – C

4-[(2-hydroxyethyl)(nitroso)amino]butan-1-ol C6H14N2O3 – C

1-nitroso-3-hydroxymethylpiperidine C6H12N2O2 – C

ammonia NH3 7664-41-7 M,T

methanol CH4O 67-56-1 T

formaldehyde CH2O 50-00-0 C

acetaldehyde C2H4O 75-07-0 C

M/z 213 Unknown – M

M/z 239 Unknown – M

40 | Report Title

5 References

1. A.K. Chakraborty, K. B. Bischoff, G. Astarita, and J. R. Damewood, Jr. J. Am. Chem. Soc. 1988, 110, 6947–6954.


CONTACT US

t 1300 363 400 +61 2 94905307 e [email protected] w www.csiro.au

YOUR CSIRO

Australia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills for building prosperity, growth, health and sustainability. It serves governments, industries, business and communities across the nation.

FOR FURTHER INFORMATION

CSIRO Energy Technology Merched Azzi t +61 2 94905307 e [email protected] w www.csiro.au/cET

environmental impacts of amine- based co post...

Documents