Sicong Tian

Polyethyleneimine–nano silica composites: a low-cost and promising adsorbent for CO2 capture

Adsorbents for CO2 captured with nano silica as support were synthesized by impregnating polyethyleneimine (PEI) into nano silica. For impregnation of PEI into nano silica, the 2–40 nm pore of silica support plays an important role in the synthesis process of adsorbents. The PEI loading content, adsorption temperature and CO2 partial pressure influenced CO2 adsorption capacity and PEI utilization efficiency. At 105 °C and under 1 atm CO2 partial pressure, the adsorbent with 60% PEI loading content obtained a CO2 adsorption capacity of 186 mg g−1 adsorbent and a PEI utilization efficiency of 304 mg g−1 PEI. The CO2 cycling adsorption–desorption was tested under the condition as follows: adsorption at 90 or 105 °C under pure CO2 and desorption at 120 °C under pure N2 showed relatively good adsorption–desorption stability, and no evident deactivation of amines was observed under this condition. However, for adsorption at 90 or 105 °C under pure CO2 and desorption at 135 or 150 °C under pure CO2, evident deactivation of amines occurred, and the formation of linear or cyclic urea is one reason which led to the decrease of CO2 adsorption capacity.

A novel calcium looping absorbent incorporated with polymorphic spacers for hydrogen production and CO2 capture

High temperature looping cycles can be used to produce hydrogen or capture CO2 from power stations, though sintering of absorbents is frequently a problem, reducing reactivity. In this work we develop materials, in which the crystal structure and volume of polymorphic materials change with temperature, as active spacers to reduce sintering.

Effects of ultrasound pre-treatment on the amount of dissolved organic matter extracted from food waste

This paper describes a series of studies on the effects of food waste disintegration using an ultrasonic generator and the production of volatile fatty acids (VFAs) by anaerobic hydrolysis. The results suggest that ultrasound treatment can significantly increase COD [chemical oxygen demand], proteins and reducing sugars, but decrease that of lipids in food waste supernatant. Ultrasound pre-treatment boosted the production of VFAs dramatically during the fermentation of food waste. At an ultrasonic energy density of 480W/L, we treated two kinds of food waste (total solids (TS): 40 and 100g/L, respectively) with ultrasound for 15min. The amount of COD dissolved from the waste increased by 1.6-1.7-fold, proteins increased by 3.8-4.3-fold, and reducing sugars increased by 4.4-3.6-fold, whereas the lipid content decreased from 2 to 0.1g/L. Additionally, a higher VFA yield was observed following ultrasonic pre-treatment.

A novel low temperature vapor phase hydrolysis method for the production of nano-structured silica materials using silicon tetrachloride

Here we report for the first time, a novel method of low temperature vapor phase hydrolysis for the production of nano-structured silica particles. Silica nanoparticles were obtained by the hydrolysis of silicon tetrachloride vapor with water vapor at a low temperature range (150–250 °C). The effects of reaction temperature and residence time on the specific surface area and size distribution were determined to obtain optimal synthesis conditions. Silica nanoparticles with a specific surface area of 418 m2 g−1 and an average size of 141.7 nm were obtained at a temperature of 150 °C and with a residence time of 5 s. The particle morphology, phase composition, chemical composition, thermal analysis, and chemical functional groups present were determined by TEM, XRD, XRF, TGA, and IR methods, respectively. Results indicated that silica synthesized by low temperature vapor phase hydrolysis method is an amorphous mesoporous material, with an approximately spherical shape, a mass friction demission of 2.29, and a high hydroxyl density of 13.03 nm−2. This method provides a simple and environmentally benign way for the mass production of silica nanoparticles, as well as a quick method for the preparation of functional silica materials.

Synthesis of Highly Efficient CaO-Based, Self-Stabilizing CO2 Sorbents via Structure-Reforming of Steel Slag

Capturing anthropogenic CO2 in a cost-effective and highly efficient manner is one of the most challenging issues faced by scientists today. Herein, we report a novel structure-reforming approach to convert steel slag, a cheap, abundant, and nontoxic calcium-rich industrial waste, as the only feedstock into superior CaO-based, self-stabilizing CO2 sorbents. The CO2 capture capacity of all the steel slag-derived sorbents was improved more than 10-fold compared to the raw slag, with the maximum uptake of CO2 achieving at 0.50 gCO2 gsorbent(-1). Additionally, the initial steel slag-derived sorbent could retain 0.25 gCO2 gsorbent(-1), that is, a decay rate of only 12% over 30 carbonation-calcination cycles, the excellent self-stabilizing property allowed it to significantly outperform conventional CaO, and match with most of the existing synthetic CaO-based sorbents. A synergistic effect that facilitated CO2 capture by CaO-based sorbents was clearly recognized when Mg and Al, the most common elements in steel slag, coexisted with CaO in the forms of MgO and Al2O3, respectively. During the calcium looping process, MgO served as a well spacer to increase the porosity of sorbents together with Al2O3 serving as a durable stabilizer to coresist the sintering of CaCO3 grains at high temperatures.

Pine cone shell-based activated carbon used for CO2 adsorption

In this study, pine cone shell-based activated carbons were used to adsorb CO2. After a carbonization process at 500 °C, the resulting preliminary activated carbons (Non-PAC) were activated under different conditions. The results indicated good CO2 adsorption performance of pine cone shell-based activated carbons. For example, after activation at 650 °C and with a KOH:Non-PAC ratio of 2, the activated carbon (named as PAC-650/2) achieved a high CO2 adsorption capacity of 7.63 mmol g−1 and 2.35 mmol g−1 at 0 °C under 1 and 0.15 bar pressure, respectively. To determine the potential correlation between the amount of CO2 adsorbed and micropore distribution, linear correlations between cumulative pore volume over different ranges and amount of CO2 adsorbed were analyzed. Results showed that pores <0.70 nm played an important role in the CO2 adsorption process at 0 °C and 0.1 bar, and in contrast to previous research, pore volumes <0.80 nm or 0.82 nm did not show good linear correlation with the amount of CO2 adsorbed at 0 °C and 1 bar, and we inferred that this was most likely due to the unique pore structure of pine cone shell-based activated carbons. The highest Brunauer–Emmett–Teller (BET) surface area of 3931 m2 g−1 was obtained after activation at 800 °C and with a KOH:Non-PAC ratio of 2, but the highest BET surface area did not result in the highest CO2 adsorption capacity. This is mainly due to the BET surface area having regions unavailable for CO2 adsorption. X-ray photoelectron spectroscopy (XPS) analysis results for all activated carbons indicated a higher stability of pyridonic-N than pyridinic-N. Furthermore, in order to better understand the interaction between CO2 and pine cone shell-based activated carbons, we analyzed the isosteric heat of adsorption (Qst). Qst was higher than 22 kJ mol−1 for all activated carbons, and the highest initial isosteric heat of adsorption of 32.9 kJ mol−1 was obtained for the carbon activated at 500 °C and a KOH:Non-PAC ratio of 1. The optimal Qst (Qst,opt) under the conditions of a vacuum swing adsorption (at 25 °C, adsorption under 1 bar and desorption under 0.1 bar) process was 30 kJ mol−1.

A green and scalable synthesis of highly stable Ca-based sorbents for CO2 capture

High-temperature sorption of CO2via calcium looping is a promising technology for the implementation of carbon capture and storage (CCS). However, the rapid deactivation of CaO sorbents due to sintering is currently the major drawback of this technology. We, for the first time, report an economical and environmentally benign strategy to reduce sintering by adding fly ash, a waste stream of coal-fired plants, into Ca-based sorbents through a simple dry process. The as-synthesized sorbents were tested using a TGA and showed an extremely high stability under the most severe multi-cycle conditions (calcined at 920 °C in pure CO2). Upon 100 cycles, its CO2 capture capacity was 0.20 g(CO2) g(sorbent)−1, and the average deactivation rate was only 0.18% per cycle. The most possible stabilization mechanism was discussed on the basis of a range of characterizations including N2 physisorption, SEM, TEM (coupled with EDX mapping) and XRD; it was concluded that stable and refractory gehlenite (Ca2Al2SiO7) particles were formed and evenly dispersed around CaO crystal grains during calcination at 950 °C, leading to sintering resistance. This strategy achieved superior enhancement in the cyclic stability of Ca-based sorbents as well as the reuse of industrial solid waste, and is thus a green technology for scaled-up CO2 capture.

Sequestration of Flue Gas CO2 by Direct Gas–Solid Carbonation of Air Pollution Control System Residues

Direct gas-solid carbonation reactions of residues from an air pollution control system (APCr) were conducted using different combinations of simulated flue gas to study the impact on CO₂ sequestration. X-ray diffraction analysis of APCr determined the existence of CaClOH, whose maximum theoretical CO₂ sequestration potential of 58.13 g CO₂/kg APCr was calculated by the reference intensity ratio method. The reaction mechanism obeyed a model of a fast kinetics-controlled process followed by a slow product layer diffusion-controlled process. Temperature is the key factor in direct gas-solid carbonation and had a notable influence on both the carbonation conversion and the CO₂ sequestration rate. The optimal CO₂ sequestrating temperature of 395 °C was easily obtained for APCr using a continuous heating experiment. CO₂ content in the flue gas had a definite influence on the CO₂ sequestration rate of the kinetics-controlled process, but almost no influence on the final carbonation conversion. Typical concentrations of SO₂ in the flue gas could not only accelerate the carbonation reaction rate of the product layer diffusion-controlled process, but also could improve the final carbonation conversion. Maximum carbonation conversions of between 68.6% and 77.1% were achieved in a typical flue gas. Features of rapid CO₂ sequestration rate, strong impurities resistance, and high capture conversion for direct gas-solid carbonation were proved in this study, which presents a theoretical foundation for the applied use of this encouraging technology on carbon capture and storage.

Performance of steel slag in carbonation–calcination looping for CO2 capture from industrial flue gas

We investigate the performance of steel slag during the carbonation–calcination looping as a potential CO2 adsorbent. The existence of portlandite in the steel slag provided a maximum theoretical CO2 capture capacity of 112.7 mgCO2 gslag−1, and the maximum carbonation conversion of 39.8% was achieved in simulated flue gases with only 5 min duration of carbonation. Sintering of the steel slag particles during both the carbonation and calcination processes, especially the destruction of the 3 nm pores, is the main cause for the deactivation of steel slag. Carbonation–calcination looping of steel slag can significantly improve its total CO2 capture capacity compared to the conventional technical route of direct carbonation sequestration, thus providing an alternative and more feasible option for the use of alkaline industrial wastes to capture CO2 from industrial sources, such as the iron and steel production facilities.

Direct Gas–Solid Carbonation Kinetics of Steel Slag and the Contribution to In situ Sequestration of Flue Gas CO2 in Steel‐Making Plants

Direct gas-solid carbonation of steel slag under various operational conditions was investigated to determine the sequestration of the flue gas CO2 . X-ray diffraction analysis of steel slag revealed the existence of portlandite, which provided a maximum theoretical CO2 sequestration potential of 159.4 kg CO 2 tslag (-1) as calculated by the reference intensity ratio method. The carbonation reaction occurred through a fast kinetically controlled stage with an activation energy of 21.29 kJ mol(-1) , followed by 10(3) orders of magnitude slower diffusion-controlled stage with an activation energy of 49.54 kJ mol(-1) , which could be represented by a first-order reaction kinetic equation and the Ginstling equation, respectively. Temperature, CO2 concentration, and the presence of SO2 impacted on the carbonation conversion of steel slag through their direct and definite influence on the rate constants. Temperature was the most important factor influencing the direct gas-solid carbonation of steel slag in terms of both the carbonation conversion and reaction rate. CO2 concentration had a definite influence on the carbonation rate during the kinetically controlled stage, and the presence of SO2 at typical flue gas concentrations enhanced the direct gas-solid carbonation of steel slag. Carbonation conversions between 49.5 % and 55.5 % were achieved in a typical flue gas at 600 °C, with the maximum CO2 sequestration amount generating 88.5 kg CO 2 tslag (-1) . Direct gas-solid carbonation of steel slag showed a rapid CO2 sequestration rate, high CO2 sequestration amounts, low raw-material costs, and a large potential for waste heat utilization, which is promising for in situ carbon capture and sequestration in the steel industry.