continuous production of amine-derivative silica for carbon capture

8/13/2019 Continuous Production of Amine-derivative silica for Carbon Capture

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The place of useful learning

The University of Strathclyde is a charitable body, registered in Scotland, number SC015263

ContinuousProduction of

Amine

Derivatives ofGreen Silica forCarbon Capture

Abdul Wadood Sharif

Supervisors:Dr. Ashleigh FletcherDr. Siddharth Patwardhan

Sponsored by:The Carnegie Trust

Interns@Strathclyde


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Table of Contents

Acknowledgments 2Abstract 31 Background on Carbon Dioxide 42 Current Technologies 43 Aims and Objectives 54 Theory 55 Analytical Methods for Characterisation 66 Experimental 67 Results & Discussion 88 Conclusion & Recommendations 119 References 1210 Reflective Report 13


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Acknowledgments

I would like to thank my supervisors, Dr. Ashleigh Fletcher and Dr. Siddharth Patwardhan for their help,

advice and encouragement for the duration of the placement.

I would also like to personally thank Dr. Thomas Yip for his assistance, input and demonstrations in the

laboratory.

I would like to express thanks to the University of Strathclyde and the members of chemical and

process engineering department for this invaluable opportunity.


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Abstract

With carbon dioxide emissions and mitigation becoming a pressing legal issue for industry, new

solutions to the otherwise costly, established method currently used must be investigated.

Alternative solutions include zeolites, activated carbons and amine grafted silica. Although promising

these suffer from distinct disadvantages: loss of CO2capacity with presence of moisture, low CO2/N2selectivity and long, toxic, costly production respectively.

A new method for production of amine-functionalised silica has been investigated by the Patwardhan

group at Strathclyde University. This technique is inspired by biological processes and is a green

method: quick reaction completion employs ambient conditions (both temperature and pH) and uses

environmentally-friendly reagents.

The aims of this report were to optimise the batch process of production and then investigate different

methods of continuous production of the amine-silica sorbent using a plug flow reactor with

poly(allylamine hydrochloride) as the amine adsorbent. Following reaction, the products were

centrifuged and washed with deionised water three times and then allowed to dry in an oven overnight.

From the results the yields for both the batch and semi-batch process were found to be the highest.

This was due to the accuracy of the pH achieved (7 0.05) and the extended reaction time during the

first centrifuge. The yield was a little lower for the batch run with excess acid at the end as the excess

acid prevents further aggregation and this indicated that longer times should be given for full

aggregation. The lowest yield was found with flow runs mostly due to the lack of pH measurement due

to the excess acid present.

Intelligent gravimetric analysis results indicated that the presence of amine in the samples were crucial

for CO2uptake.

All samples exhibited peaks at 1055 1035 cm-1and 1545 1520 cm-1from FTIR analysis. The former

represents the presence of Si-O-Si bonds while the latter indicates NH bonds. This implies that there is

both silica and amine present in samples.

Further work includes CHN analysis for nitrogen loading, BET for porosity and surface area analysis

and further IGA for CO2uptake of flow samples.


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1 Background on Carbon Dioxide

Global climate change due to greenhouse gas emissions is one of the key issues faced by industry

today. Although many greenhouse gases exist, such as methane, the most significant is carbon

dioxide, due to its abundance. The most recent estimate for carbon dioxide emission is approximately

530 million metric tons (2010) for the United Kingdom. [1]With the introduction of legislation (Climate

Change Act 2008), the United Kingdoms target for 2050 is to reduce carbon emissions by 80% fromthe 1990 baseline (approximately 600 million metric tons). [2]

2 Current Technologies

2.1 Amine scrubbing

Currently the most established and widely-used method of carbon capture is the process of amine

scrubbing. During this process flue gas, which is generated from combustion of fossil fuels and

contains mainly carbon dioxide, nitrogen and water, is passed up through an absorption column whilst

a liquid amine is pumped to the top of the column and passed down. The amine absorbs the carbondioxide and must then be regenerated for further use.

Figure 1Amine Scrubbing Diagram

Although widely implemented, the process suffers from one main disadvantage. This process is

expensive, costing approximately $50 per ton CO 2 removed or 30% of the power generated by a

power plant.[3]This cost is associated with high energy required for regeneration of the amine at the

reboiler stage and the power for pumping.


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2.2 Emerging Solutions

Table 1 Comparison of possible solutions for carbon capture

Solution Advantages Disadvantages

Zeolites[4] High Capacity (3-4 mmol/g) Performance suffers with moisture.

Activated

Carbons[5] High Capacity (8.59 mmol/g) Low CO2/N2 Selectivity (bad for flue

gas)

Amine

Grafted

Silica[6][7]

High Capacity (Up to 7.9 mmol/g)

Favourable repeatability cyclic

tests.

Low Regeneration temperatures.

Quick uptake (~10 mins)

Unfavourable reaction conditions:oHarsh pH

oHigh temperatures

oToxic materials

oLong reaction times

oMulti-step Process

Above lists some emerging solutions to the issue of carbon capture, although more exist such as

membranes[REF: Pennline] and metal organic frameworks [REF: mason].

Highlighted is amine-grafted silica, which shows promising capabilities but suffers from complicated,

toxic

3 Aims and Objectives

The main aims of this study were:

1) Study of batch manufacture of bio-inspired silica materials (See section4.1)

2) Optimisation of batch processes for process scale-up

3) Study of flowing manufacture with different arrangements

These objectives were met by a combination of synthetic processes and characterisation of products to

ensure the composition and properties were unaltered by the processing conditions. Characterisation

methods included product yield, FTIR analysis and IGA analysis (See Analytical Methods for

Characterisation).

4 Theory

4.1 Bio-inspired Green Silica

To combat the problems faced by amine-silica production the Patwardhan group have utilised a

biologically inspired procedure.

Using a biologically inspired component (amine), it is possible to imitate nature. Furthermore the

method of production is green: it employs ambient conditions, non-toxic materials and relatively quick

reaction time (5 minutes).

The procedure involves reacting an amine and silica precursor together at neutral pH (pH=7) which can

be achieved via a titration with 1M HCl acid. Aggregation is best promoted at this pH. Further additionof acid to a obtain pH 2 results in a situation akin to freezing of aggregation. This is due to the

interactions between the amine and precursor being less favourable in extreme pH.


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For a material to be a viable candidate for carbon capture, it must be readily scaled up with as few

complications as possible. Production of amine-grafted silica is difficult to scale up due to extreme

conditions, toxic materials, long reaction times and multi-step process. The advantages of the green

process should allow for promising scalability for large production.

4.2 PAH - Poly(allylamine hydrochloride)

The amine used for investigation was poly(allylamine hydrochloride) or PAH with average molecular

weight of 15000 g/mol.

Figure 2 Molecular Structure of PAH

PAH was used as the amine component since previous investigation performed by the group

highlighted PAH as one of the most promising for carbon capture. [8]Additionally, further research into

PAH indicated this amine gave the highest yield in solid produced via batch synthesis. [9]

5 Analytical Methods for Characterisation

5.1 Intelligent Gravimetric Analysis (IGA)

By employing IGA it is possible to investigate the CO2adsorbed on to the material surface in mmol/g.

The intelligent gravimetric analyser is capable of measuring uptake by exposing a known quantity of

sample with CO2and then precisely measuring the weight difference. For the purposes of this study,

the CO2was exposed at 100 mbar, the industrially relevant pressure.

5.2 Fourier Transform Infrared Spectroscopy (FTIR) analysis

FTIR analysis was used to determine whether Silica and Poly (allylamine Hydrochloride) was present

in the samples generated. By obtaining an infrared spectrum of absorbance, peaks can be assigned toa fingerprint region from literature, this in turn indicates which bonds and hence molecules are present.

6 Experimental

6.1 Reagents used

Sodium metasilicate (Na2SiO3.5H2O) and Sodium Hydroxide (NaOH) pellets (99% purity) were

purchased from Fisher Scientific. The amine polymer poly (allylamine hydrochloride) with average

molecular weight 15,000 g/mol and 1M hydrochloric acid were purchased from Sigma Aldrich.

Deionised water was readily available.


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6.2 Experimental procedure

6.2.1 Batch Synthesis

Sodium metasilicate and PAH was weighed out to obtain a 30 mM solution on a 50 ml (0.3182 g) basis

and 1mg/ml (0.05 g) solution respectively. 25ml deionised water was added to the sodium metasilicate

and 22.5 ml deionised water was added to the PAH.

The solutions were mixed separately then added together and after 1 minute the pH was recorded

every 30 seconds until 5 minutes had elapsed. As this time elapsed the remaining 2.5ml was added in

the form of 1M HCl acid in aliquots, this volume was determined previously to ensure an end pH of 7

was achieved (See section7.1). The solution was transferred to a vial for centrifugation at 8000rpm for

15 minutes followed by washing with deionised water. This was repeated twice more and finally the

remaining solid was oven dried at 85C overnight.

6.2.2 Semi-Batch Synthesis (FL)

Figure 3 System Diagram with flows of amine (blue), silica (yellow) and product (green)

All masses weighed and volumetric additions for the batch synthesis were multiplied by four so as to

obtain a total output of 200 ml. Sodium Hydroxide pellets were weighed out to obtain a 2M solution on

a 50ml basis (4g).

The vessels were connected to two peristaltic pumps running at 2ml/min each to emulate a plug flowreactor (PFR). The solutions were mixed together in 3mm i.d. silicone tubing which ensured a 5 minute

residence time was maintained. The solution was collected in a vessel until 50ml was collected. The

output from reactor was immediately transferred to another vessel and the same time was allowed to

pass. This process was repeated twice more.

After each 50ml solution had been collected the process of centrifugation as done in the batch process

was immediately initiated followed by drying in oven at 85C overnight.

Following the complete run (after 4x50ml volume collected), 50ml deionised water was added to the

NaOH pellets and allowed to dissolve. The tubing was then purged with this NaOH solution, followed

by 1 litre of deionised water for cleansing purposes.


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6.2.3 Flow Synthesis (FLA)

Similar to the fed batch synthesis however 1.3ml HCl acid was added to each collection vessel prior to

solution collection.

7 Results & Discussion

7.1 Evaluation of Volumetric HCl Requirement

Table 2 HCl added and pH for batch runs (50ml basis)

Sample Reference HCl Acid Added (ml) pH

PAH-7 2.49 6.99

PAH-10 2.50 6.96

PAH-14 2.50 7.02

PAH-15 2.50 7.05PAH-17 2.50 6.97

Average: 2.50

Note: The PAH-7 run was considered an outlier once flow synthesis was attempted.

From the above table it can be observed that the HCl added showed excellent repeatability. Although

the pH varied slightly, the range was considered acceptable (pH 7 0.05). The small variation resulted

in errors associated with initial weighing.

7.2 Yields

Table 3 Number of samples, average mass and yi eld for PAH-Silica

Synthesis Method No. of Samples

Generated

Average Mass

(mg)

Yield (%)

Batch 4 76 6 63 5

Batch w/ Excess Acid 4 56 3 46 1Semi-batch 16 69 2 57 2

Flow 16 21 1 17 1

Considering the higher yields, the highest on average was observed for batch runs, this is expected as

these runs had greatest adaptability of acid added and assurance that a pH as close to 7 as possible

was realised. Furthermore the aggregation of solid occurred continued during the first centrifugation.

The semi-batch process also resulted in a high yield due to the monitoring of pH during reaction and

repeated runs allowed for pH near 7 to be attained. Furthermore the extended run time resulted ingreater residence time.


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The batch excess acid resulted in a lower average yield than that of both methods that did not involve

excess acid additions described above. This was most likely due to incomplete aggregation of solid.

The flow run resulted in a considerably low yield. Similar to the batch excess acid run, aggregation was

most likely incomplete at the time the solution came in contact with the excess acid. There was also no

assurance of good mixing in the plug flow reactor at such low speeds.

7.3 IGA Results

Figure 4 CO2 Capacity for batch, semi-batch, calcined batch and bare silica

Both batch and semi-batch samples resulted in a considerably high uptake.

A calcined batch sample (had amine was removed via heating in the presence of air) and MCM-41, or

bare silica, were both run with IGA. From the results it can be observed that the amine has a very

crucial role to play in the adsorption of CO2.


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7.4 Results: FT-IR analysis

Figure 5 FTIR Spectrum for (a) PAH-Silica, (b) PAH and (c) Sodium metasilicate precursor

FromFigure 3a) peaks at 1055-1035 indicate Si-O-Si bonds and hence silica. The peak between 1545

1520 represents N-H bonds and this indicates that amine is present in generated samples.Figure 3b&Figure 3cthe aligned peaks are further proof of silica and amine presence.

1055-1035

1545-1520

a)

b)

c)


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8 Conclusion & Recommendations

The batch system required a consistent volume of acid for titration (2.5ml) with slight variations in end

pH, most likely due to errors in initial weighing.

High average yields were observed for semi-batch (57%) and low average yield were obtained with the

flow system (17%). The former was possible because of pH monitoring and extended residence timesand the latter suffered without these advantages.

IGA results indicated that the amine played a crucial role in adsorption of CO 2.

FTIR confirmed the presence of silica and amines in all samples generated.

Improvements to be made are higher flow rates and inclusion of a static mixer to ensure good mixing

within PFR for flow system.

Further work that can be carried out is CHN-analysis for amine loading, BET for porosity and surface

area and further IGA studies.


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9 References

[1] S. Choudrie, N. Passant, J. MacCarthy, UK Greenhouse Gas Inventory: National Statistics UserGuide (Ed.: D. O. E. a. C. Change), Oxfordshire, 2012.[2] Climate Change Act (2008), (Ed.: U. Government), The Stationary Office Limited, 2008.[3] M. Ramezan, Carbon Dioxide Capture from Existing Coal-fired Power Plants, NETL, 2006.

[4] L. Wang, Z. Liu, P. Li, J. G. Yu, A. E. Rodrigues, Chemical Engineering Journal 2012, 197, 151-161.[5] M. Radosz, X. D. Hu, K. Krutkramelis, Y. Q. Shen, Industrial & Engineering ChemistryResearch 2008, 47(10), 3783-3794.[6] G. G. Qi, Y. B. Wang, L. Estevez, X. N. Duan, N. Anako, A. H. A. Park, W. Li, C. W. Jones, E.P. Giannelis, Energy & Environmental Science 2011, 4(2), 444-452.[7] W. J. Choi, J. B. Seo, S. Y. Jang, J. H. Jung, K. J. Oh, Journal of Environmental Sciences-China 2009, 21(7), 907-913.[8] D. Prentice, A study of amine activated silica adsorption capabilities & the parameters ofevaporation, University of Strathclyde, Glasgow, 2011.[9] C. Scott, Developing Novel Adsorbents for Carbon Capture Technologies, University ofStrathclyde, Glasgow, 2012.


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10 Reflective Report

10.1 PresentationsEvery fortnight the group was required to present at progress meeting to their supervisor (since I had

two supervisors this resulted in a progress meeting each week). During these meetings we were

required not only present our progress but also critically analyse others work and our own. It was alsoan opportunity to raise questions to others and offer help in some areas. This was particularly useful for

my project as there were several people working on similar projects and others findings were often

useful for my own work and vice-versa. During my placement I was able to improve on presentation

skills and also ask relevant questions pertaining to the subject matter.

10.2 ConferencesThroughout my placement, my supervisors would invite myself and others from their group to

conferences. Through these conferences we were able to observe current research developments and

efforts by companies in particular fields. By attending these conferences, the group was given the

chance to see others work and showcase our own. Furthermore these conferences gave theopportunity for myself to network and discuss my project to others. This improved communication skills

as when an individual was unfamiliar with the background and area of my research I had to show

versatility in my explanation for them to understand what I was doing.

10.3 Self-teachingInitially, I was very unfamiliar with many aspects of my project: alternative solutions, theory behind

analytical methods, previous work etc. Although some guidance was given with regards to these, often

I had to find published papers for myself via Web of Knowledge for educating myself with regards to

these topics. For previous work done by the group I was given these papers to read through and learn

what were the limitations and techniques often used to characterise the samples. This method oflearning was very satisfying and having relevant papers I was able to prepare for the technical report at

an early stage.

10.4 Innovative thinkingMany problems were faced for the duration of my placement, some of which have still not been

overcome at the time of writing. One particular example is of the systematic failure of an expensive

piece of equipment, known as FlowSyn. This was the continuous flow reactor which was anticipated to

be used for all flow synthesis of material. By meeting with my supervisor and discussing the issue we

came to the conclusion that we could use a set of pumps and tubing to obtain a make-shift reactor

that could be used instead. These situations I consider one of the most crucial invaluable practicalexperiences I obtained. It allowed me to develop my problem solving skills unlike any coursework had

done thus far.

10.5 Overall ExperienceI found the placement to be highly enjoyable both from an educational and practical experience. My

assumptions on what research life would pertain to were quickly proven wrong. I found the social

aspect to be pleasant and helpful with group lunches and departmental barbeques organised. Although

I hope to experience an industrial placement first, I would be interested in continuing research by

pursuing a PhD.

continuous production of amine-derivative silica for carbon capture

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