Process intensification for post combustion CO₂ capture with chemical absorption: a critical review

The concentration of CO₂ in the atmosphere is increasing rapidly. CO₂ emissions may have an impact on global climate change. Effective CO₂ emission abatement strategies such as carbon capture and storage (CCS) are required to combat this trend. Compared with pre-combustion carbon capture and oxy-fuel carbon capture approaches, post-combustion CO₂ capture (PCC) using solvent process is one of the most mature carbon capture technologies. There are two main barriers for the PCC process using solvent to be commercially deployed: (a) high capital cost; (b) high thermal efficiency penalty due to solvent regeneration. Applying process intensification (PI) technology into PCC with solvent process has the potential to significantly reduce capital costs compared with conventional technology using packed columns. This paper intends to evaluate different PI technologies for their suitability in PCC process. The study shows that rotating packed bed (RPB) absorber/stripper has attracted much interest due to its high mass transfer capability. Currently experimental studies on CO₂ capture using RPB are based on standalone absorber or stripper. Therefore a schematic process flow diagram of intensified PCC process is proposed so as to motivate other researches for possible optimal design, operation and control. To intensify heat transfer in reboiler, spinning disc technology is recommended. To replace cross heat exchanger in conventional PCC (with packed column) process, printed circuit heat exchanger will be preferred. Solvent selection for conventional PCC process has been studied extensively. However, it needs more studies for solvent selection in intensified PCC process. The authors also predicted research challenges in intensified PCC process and potential new breakthrough from different aspects

Assessment of the Suitability of the One-Step Hydrothermal Method for Preparation of Non-Covalently/Covalently-Bonded TiO2/Graphene-Based Hybrids

A hybrid nanocomposites containing nanocrystalline TiO2 and graphene-related materials (graphene oxide or reduced graphene oxide) were successfully prepared by mechanical mixing and the hydrothermal method in the high-pressure atmosphere. The presented X-ray photoelectron spectroscopy (XPS) study and quantitative elemental analysis confirm similar content of carbon in graphene oxide GO (52 wt% and 46 wt%, respectively) and reduced graphene oxide rGO (92 wt% and 98 wt%, respectively). No chemical interactions between TiO2 and GO/rGO was found. TiO2 nanoparticles were loaded on GO or rGO flakes. However, Fourier transform infrared-diffuse reflection spectroscopy (FTIR/DRS) allowed finding peaks characteristic of GO and rGO. XPS study shows that since the concentration of TiO2 in the samples was no less than 95 wt%, it was assumed that the interactions between TiO2 and graphene should not influence the lower layers of titanium atoms in the TiO2 and they occurred as Ti4+ ions. Hydrothermal treatment at 200 °C did not cause the reduction of GO to rGO in TiO2-GO nanocomposites. In general, the one-step hydrothermal method must be considered to be inefficient for preparation of chemically-bonded composites synthesized from commercially available TiO2 and unfunctionalized graphene sheets obtained from graphite powder

Preliminary Findings on CO₂ Capture over APTES-Modified TiO₂

In this work, the impact of TiO2 properties on the CO2 adsorption properties of titanium dioxide modified with 3-aminopropyltriethoxysilane (APTES) was presented. The APTES-modified TiO2 materials were obtained by solvothermal process and thermal modification in the argon atmosphere. The prepared adsorbents were characterized by various techniques such as X-ray diffraction (XRD), Fourier transform infrared (DRIFT), thermogravimetric analysis and BET specific surface area measurement. CO2adsorption properties were measured at different temperatures (0, 30, 40, 50 and 60 °C). Additionally, the carbon dioxide cyclic adsorption-desorption measurements were also investigated. The results revealed that modifying TiO2 with APTES is an efficient method of preparing CO2 sorbents. It was found that the CO2 adsorption capacity for the samples after modification with APTES was higher than the sorption capacity for unmodified sorbents. The highest sorption capacity reached TiO2-4 h-120 °C-100 mM-500 °C sample. It was also found that the CO2 adsorption capacity shows excellent cyclic stability and regenerability after 21 adsorption-desorption cycles

The Effect of the Modification of Carbon Spheres with ZnCl2 on the Adsorption Properties towards CO2

Zinc chloride and potassium oxalate are often applied as activating agents for carbon materials. In this work, we present the preparation of ZnO/carbon spheres composites using resorcinol-formaldehyde resin as a carbon source in a solvothermal reactor heated with microwaves. Zinc chloride as a zinc oxide source and potassium oxalate as an activating agent were applied. The effect of their addition and preparation conditions on the adsorption properties towards carbon dioxide at 0 °C and 25 °C were investigated. Additionally, for all tested sorbents, the CO2 sorption tests at 40 °C, carried out utilizing a thermobalance, confirmed the trend of sorption capacity measured at 0 and 25 °C. Furthermore, the sample activated using potassium oxalate and modified using zinc chloride (a carbon-to-zinc ratio equal to 10:1) displayed not only a high CO2 adsorption capacity (2.69 mmol CO2/g at 40 °C) but also exhibited a stable performance during the consecutive multicycle adsorption–desorption process

The influence of the addition of carbon spheres on photoactivity of TiO2 and ZnO in CO2 reduction process

The development of an effective photocatalyst for CO2 reduction is currently being addressed by many scientists. This study concerns the influence of the addition of carbon spheres (CS) on photoactivity of TiO2 and ZnO. The photocatalysts were tested in a liquid phase system in an alkaline environment. The suspensions of the tested materials were irradiated with UV–Vis light for 6 h. Then, the amount of the obtained products in the gas phase was analysed by gas chromatography. The identified products of CO2 photoreduction were hydrogen, carbon monoxide, and methane. Based on the results, it was found that CS/TiO2 and CS/ZnO showed similar activity in carbon dioxide reduction processes, however, more product amounts were obtained in experiments with the use of CS/TiO2 materials. The addition of carbon spheres to titanium dioxide improved its activity in carbon monoxide production. The maximum photoactivity of CS/TiO2 was observed for the addition of 0.1 g of CS. On the other hand, in the case of CS/ZnO materials, carbon spheres did not positively affect their performance. Nevertheless, their activity increased with the CS amount

Impact on CO2 Uptake of MWCNT after Acid Treatment Study

Greenhouse effect is responsible for keeping average temperature of Earth’s atmosphere at level of about 288 K. Its intensification leads to warming of our planet and may contribute to adverse changes in the environment. The most important pollution intensifying greenhouse effect is anthropogenic carbon dioxide. This particular gas absorbs secondary infrared radiation, which in the end leads to an increase of average temperature of Earth’s atmosphere. Main source of CO2 is burning of fossil fuels, like oil, natural gas, and coal. Therefore, to reduce its emission, a special CO2 capture and storage technology is required. Carbonaceous materials are promising materials for CO2 sorbents. Thus multiwalled carbon nanotubes, due to the lack of impurities like ash in activated carbons, were chosen as a model material for investigation of acid treatment impact on CO2 uptake. Remarkable 43% enhancement of CO2 sorption capacity was achieved at 273 K and relative pressure of 0.95. Samples were also thoroughly characterized in terms of texture (specific surface area measurement, transmission electron microscope) and chemical composition (X-ray photoelectron spectroscopy)

CO₂ Sorbents Based on Spherical Carbon and Photoactive Metal Oxides: Insight into Adsorption Capacity, Selectivity and Regenerability

This work aimed to obtain hybrid composites based on photoactive metal oxide and carbon having adsorption properties. The materials, composed of titanium dioxide or zinc oxide and spherical carbon, were obtained from resorcinol-formaldehyde resin, treated in a solvothermal reactor heated with microwaves and then subjected to carbonization, were received. The functional groups of pure carbon spheres (unsaturated stretching C=C, stretching C−OH and C−H bending vibrations), CS/ZnO and CS/TiO2 samples were determined by FT-IR analysis. The characteristic bands for ZnO and TiO2 were observed below 1000 cm−1. The thermal oxidative properties are similar for TiO2- and ZnO-modified carbon spheres. We have observed that the increased carbon sphere content in nanocomposites results in starting the decomposition process at a lower temperature, therefore, nanocomposites have a broader combustion temperature range. The effect of the oxides’ addition to carbon spheres on their adsorption properties was evaluated in detail by examining CO2 adsorption from the gas phase. The selectivity of CO2 over N2 at a temperature of 25 °C and pressure of 1 bar (a novelty in testing CS-based sorbents) calculated for 3.00 CS/TiO2 and 4.00 CS/ZnO was 15.09 and 16.95, respectively. These nanocomposites exhibit excellent cyclic stability checked over 10 consecutive adsorption–desorption cycles