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The amine-based post-combustion capture method utilizes reactive solvents, amines, to absorb CO2 from industrial flue gas. Despite its proven success, this method faces a significant challenge due to its high energy requirements. Efforts have been made to enhance the process’s efficiency, particularly in reducing its energy demand. One such endeavor involves the development of solvents with tailored properties. Avor et al.’s work in 2022 focused on creating a novel bi-blend solvent, which exhibited a 57% decrease in heat of desorption compared to the standard solvent, 5M MEA.

Another avenue for improving the efficiency of CO2 capture involves introducing a catalyst. Catalysts are known to expedite reactions by lowering their activation energies. Consequently, faster reactions lead to increased cyclic capacity, reduced absorber and stripper sizes, and decreased energy requirements during solvent regeneration.

This study is twofold. Firstly, it aims to evaluate the performance of the novel bi-blend solvent (developed by Avor et al., 2023) with or without catalyst in a bench-scale pilot plant. Various performance factors—such as mass transfer coefficient, heat duty, CO2 loading, cyclic loading, absorption and desorption rates, degradation and ammonia emissions will be examined under different operating conditions.

Secondly, the study involves subjecting the solvent to impurities mimicking industrial flue gas compositions. This aims to determine the degradation rate and identify and quantify emitted products in both catalytic and non-catalytic systems.

Successful outcomes from these investigations will not only endorse the use of the novel amine in catalytic CO2 absorption from power industry flue gas as an environmentally sustainable approach but also establish it as an energy-efficient process ripe for commercialization.

The fundamentals of chemistry can help us to understand why heat stable salts (HSSs) make an amine solution more prone to foaming. Foaming is one of the operational issues that can reduce the ability of an amine to capture the CO2. Foam behaviour of the amine solvent is a manifestation of its surface tension. If we dig deeper into the atomic level, one will find out that the surface tension of the amine is controlled ultimately by the strength of the hydrogen bonding and dipole-dipole forces holding the amine and water molecules together. The principle is that the stronger the forces existing in the solution, the higher its surface tension, and the harder it is for the amine to foam. The strength of the amine-water intermolecular forces changes with HSSs contamination. Once formed from the undesirable degradation of amine, these HSSs instantly tie up the amine molecules which in turn, interrupts the amine-water molecular connectivity.  This weakens the original intermolecular forces that exists within the amine solution. This occurrence definitely lowers the amine surface tension which subsequently makes the amine solution more susceptible to foam.

This phenomenon is represented graphically as shown in the figure below. The top picture depicts the scenario in the absence of HSS. The intermolecular forces existing between amine and water are so strong, resulting in a high surface tension, yielding less foaming of the amine. The bottom picture on the other hand illustrates the presence of HSS created as a result of amine degradation. These salts disrupt and break the intermolecular forces that exist between the amine and water, lowering the resistance of the surface forces. As a result, weak intermolecular forces exist between amine and water at the surface, which consequently lowers the surface tension of the amine solution and leads to high foaming. Based on this understanding, a monitoring system that tracks the concentration of HSS must be put in place so as to know when to remove the HSS as their concentration builds up. Apart from using high pressure drop across the absorber tower as a marker for amine foaming, surface tension can also be considered as one of the parameters that can help track the foaming tendency of the amine solution.

The global concern over climate change has led to the implementation of various measures to reduce greenhouse gas emissions, including carbon capture and storage (CCS) technology. One of the most promising CCS technologies involves the removal of CO2 from flue gas emitted by power plants and industrial processes, and either use or store it. However, the presence of sulfur dioxide (SO2) and nitrogen dioxide (NO2) in flue gas poses challenges to the efficient operation of amine-based CO2 capture systems. SO2 and NO2 in the flue gas does not only contribute to air pollution and acid rain but also, harm the CO2 capturing process by reacting with the amine to form Heat Stable Amine Salts (HSAS). HSAS causes corrosion, promote foaming and ‘handcuff’ the amine solution used for CO2 absorption.

Processes such as Selective Catalytic Reduction (SCR), Selective Non-catalytic Reduction (SNCR), and Flue Gas Desulfurization (FGD) are employed in industries to control SOx and NOx emissions. Nonetheless, with the deployment of these pollutant removal technologies, residual quantities of SO2 and NO2 remain in the flue gas entering the carbon capture system. For this reason, two of the major suppliers of CO2 capture plant, Fluor and Mitsubishi Heavy Industries (MHI), recommend limits for these contaminants in the flue gas entering the amine scrubber in other to minimize the detrimental effect of these impurities. Fluor suggested a SOx and NOx limits of 10 ppmv and 20 ppmv, and Mitsubishi Heavy Industries (MHI) discussed a SOx limit of 1–2 ppmv and a low but undefined NO2 limit (Reddy et al., 2008). As a result, to optimize the performance of amine-based CO2 capture systems, it is essential to develop effective pretreatment methods that enable simultaneous removal of SO2 and NO2 from flue gas before carbon capture with amine solvents.

Integrated wet scrubbing involves the use of tailored scrubbing solutions or suspensions that can effectively absorb both SO2 and NO2 simultaneously. This approach minimizes the need for separate treatment systems and reduces capital and operating costs. Additionally, combined sorbent-based systems utilize advanced sorbent materials capable of selectively capturing both SO2 and NO2 from flue gas. These materials exhibit high sorption capacities, selectivity, and stability, ensuring efficient removal of pollutants without compromising the performance of amine solvents in subsequent CO2 capture steps. Integration of these pretreatment techniques with amine-based CO2 capture systems can enhance overall process efficiency, reduce energy consumption, and minimize environmental impacts.

Our student will investigate the simultaneous NO2 and SO2 removal from flue gas using a novel, low-cost, and formulated green solvent. His study will emphasize the significance of optimizing operational parameters, such as temperature, residence time, and flue gas composition, to achieve efficient simultaneous removal of SO2 and NO2. The study will be conducted on a laboratory batch-scale using a simulated flue gas stream with varying concentrations of NO2 and SO2. Furthermore, empirical data generated from his work will be evaluated to study the performance and kinetics of the formulated solvent for further study.

Today’s post on Back to Basics is a reminder to all researchers on the importance of

TAKING RESPONSIBILITY !!

It is easy to get caught up in producing results to meet deadlines that we miss the impacts our results have on key decisions that shape our world.

So, the next time you take a sample from your reactor, ask yourselves some real questions as shown in the image above.

In this post, we explain why carbamate of sterically hindered AMP is unstable relative to that of MEA. The instability of AMP carbamate leads to an easy break down to release CO2 and amine in the desorption process, thus giving rise to a higher CO2 loading and a lower desorption heat requirement than those of MEA. As shown on the graphical abstract, AMP structurally has 2 methyl groups (-CH3) on the tertiary carbon adjacent to the nitrogen while in contrast to MEA, the same carbon has only 2 hydrogens attached to it. Methyl groups in AMP are known as electron releasing groups so that they are relaying their electron density to the tertiary carbon and then the nitrogen.

This phenomenon causes AMP carbamate to destabilize by being explosed to 1) increased electron density on the N which is highly desirable for a reaction with proton from amine (H+) to trigger the carbamate breakdown process and 2) increased electron repulsion with the delocalized electrons on the carbonyl group whose effect destabilizes the carbamate and makes the break-down process more favorable.

In comparison to MEA, the 2 hydrogens (-H) on the tertiary carbon do not have the same inductive effect as seen from the methyl groups. As a result, the carbamate nitrogen reactivity is not enhanced by any extra electron density as seen in AMP carbamate and so its reaction with proton to break down it. The instability effect triggered by electron repulsion with the carbonyl group also is not there. The stability of MEA carbamate is therefore attributed to a combination of these 2 factors which then makes the compound break down process harder to occur compared to that of AMP. The CO2 loading and heat requirement as a result are higher than the case of AMP.

This post, we explain how the concentration of an unknown amine is determined using the internal standard curve method which is known to help reduce run to run/day to day inconsistency, thus improving the analysis accuracy.

From the graphical abstract;

Step 1 is used to prepare standard samples containing different concentrations of the amine of interest whose solutions are spiked with the same concentration of an internal standard compound. Selection of the internal standard must be done carefully so that the chosen standard has no or little interference to the amine in the sample. This means the standard should be structurally similar to that of the amine to ensure the compatibility and inertness when present in the sample. The standard must also chromatographically separate completely from the amine peak and all other species that are also present in the sample. This is essential for the accurate determination of the internal standard and amine responses used to generate the calibration curve.

Step 2 involves a use of a chromatographic instrument such as Gas Chromatograph (GC) or Liquid Chromatograph (LC) to analyze all the standard samples made from Step 1. The instrument separates the internal standard and the amine whose responses are displayed as peaks in the chromatogram. Since, the peak size measured as peak area/height, is directly proportional to the compound concentration. The internal standard peak area remains the same in all samples while that of amine increases with an increase of the amine concentration.

Step 3 uses the amine and the internal standard peak area ratios and their corresponding concentration ratios to generate the calibration curve. The curve also provides the equation that mathematically expresses the relationship of the peak area and concentration ratios useful for the concentration determination of any unknown amines. This area ratios are used to compensate for the above-mentioned run to run/day to day inconsistency that occurs due to drifts of the instrument run conditions.

In Step 4, the unknown amine is prepared similarly to those of the standard samples with the identical concentration of internal standard being added. The unknown sample is subsequently analyzed to obtain the peak area ratio of the amine and the internal standard. The exact concentration of the unknown amine is finally obtained by calculation using the calibration curve equation generated from step 3.

In order to attain net zero carbon emissions by 2050 and meet a 45% of biofuel production from waste resources target by 2030, there is the need to explore catalysts for increasing biofuel yield. This work will explore the use of environmentally benign materials for biodiesel production.

Through photosynthesis, plants use water and CO2 in the atmosphere produce oxygen and glucose which is converted to alcohol (ethanol) on fermentation. Some plants can synthesize oils. This process helps in reducing the carbon content in the atmosphere as afforestation is being encouraged for this purpose. However, the use of fossil-based fuels releases enormous amounts of CO2 into the atmosphere. This release effect cannot be curbed by plant photosynthesis only.  Bio-based fuels have relatively lower carbon content and hence release relatively minimal amounts of CO2 during energy production. Recycling of CO2 produced from biofuels (biodiesel) into plants via photosynthesis, to produce oxygen as a by-product, yields a net zero carbon emission into the atmosphere. Waste cooking oil (WCO) from restaurants and ethanol will be used as the main raw materials for the biodiesel production via transesterification reaction.

Heterogeneous catalysts have attracted great attention in recent times for use in biodiesel production. The need for the development of heterogeneous catalysts has risen because homogeneous catalysts used for biodiesel production pose some drawbacks, such as wastewater generation and loss of biodiesel as a result of washing. Various environmentally benign catalysts are being developed to increase biodiesel yields and quality. Cheap yet efficient catalysts, including fish scales, cow bones, and eggshells, are being investigated in this research due to their high CaO content, which has higher basicity, is non-corrosive, easier to handle than homogenous catalysts, and is safe to the ecosystem which makes it an interesting choice for a catalyst. The main purpose of this research work is to modify fish scales, cow bones, and eggshells as environmentally benign catalysts to have a large surface area and high basicity to enhance the production of biodiesel from waste cooking oil feedstock. The catalyst production procedure will also be varied in terms of catalyst mix ratio, catalyst mix procedure and catalyst impregnation species. The best performing catalyst will be characterized by BET, XRD, XRF, SEM, TGA and CO2-TPD techniques. The transesterification reaction parameters will be specified for the best performing catalyst blend [catalyst dose, reaction temperature, stirring rate and reaction time, WCO to ethanol ratio] to determine the optimum conditions. GC-MS will be used to quantify the purity (FAME composition) of the produced biodiesel.

If we want to know the concentration of our sample solution, how can we do it?

In analytical chemistry, a calibration curve, also known as a standard curve, is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. If the concentration of the sample responds to the instrumental signal, the concentration of your samples can be quantified. It can be said that the calibration curve provides data on an empirical relationship.

Here is the simple way to determine the sample concentration using the external calibration curve.

First, you must know what your sample is to prepare the standard solution.

Step 1: Prepare different concentrations of standard solutions.

Step 2: measure or analyze all standard samples and unknown samples by corresponding instrument (ie. UV/VIS spectrometer, Gas or liquid chromatography, etc.)

Step 3: Plot the graph between instrumental responses as the y-axis (i.e. peak area, peak height, intensity, etc.) and the concentrations of the standard solution as the x-axis, then create the equation of the line. If the calibration obtained is a straight line, the equation will be y = mx + c (m = slope of the graph and c = interception). In addition, the precision of the  curve is reflected by the R-square (expected R2 is 1.000) of the equation.

Step 4: Calculate the concentration of the unknown using the calibration curve equation. Put the response of the unknown as the “y” value and solve the equation to get the “x” value that represents the concentration of the unknown one.

The accuracy of the results will depend on the accuracy of the instrument and the precision of the prepared standard solution.