Kaimin Li

Volatile fatty acids production from food waste: effects of pH, temperature, and organic loading rate.

The effects of pH, temperature, and organic loading rate (OLR) on the acidogenesis of food waste have been determined. The present study investigated their effects on soluble chemical oxygen demand (SCOD), volatile fatty acids (VFAs), volatile solids (VS), and ammonia nitrogen (NH4(+)-N). Both the concentration and yield of VFAs were highest at pH 6.0, acetate and butyrate accounted for 77% of total VFAs. VFAs concentration and the VFA/SCOD ratio were highest, and VS levels were lowest, at 45 °C, but the differences compared to the values at 35 °C were slight. The concentrations of VFAs, SCOD, and NH4(+)-N increased as OLR increased, whereas the yield of VFAs decreased from 0.504 at 5 g/Ld to 0.306 at 16 g/Ld. Acetate and butyrate accounted for 60% of total VFAs. The percentage of acetate and valerate increased as OLR increased, whereas a high OLR produced a lower percentage of propionate and butyrate.

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 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.

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.

Highly efficient CO2 capture with simultaneous iron and CaO recycling for the iron and steel industry

An efficient CO2 capture process has been developed by integrating calcium looping (CaL) and waste recycling technologies into iron and steel production. A key advantage of such a process is that CO2 capture is accompanied by simultaneous iron and CaO recycling from waste steel slag. High-purity CaO-based CO2 sorbents, with CaO content as high as 90 wt%, were prepared easily via acid extraction of steel slag using acetic acid. The steel slag-derived CO2 sorbents exhibited better CO2 reactivity and slower (linear) deactivation than commercial CaO during calcium looping cycles. Importantly, the recycling efficiency of iron from steel slag with an acid extraction is improved significantly due to a simultaneous increase in the recovery of iron-rich materials and the iron content of the materials recovered. High-quality iron ore with iron content of 55.1–70.6% has been recovered from waste slag in this study. Although costing nearly six times as much as naturally derived CaO in the purchase of feedstock, the final cost of the steel slag-derived, CaO-based sorbent developed is compensated by the byproducts recovered, i.e., high-purity CaO, high-quality iron ore, and acetone. This could reduce the cost of the steel slag-derived CO2 sorbent to 57.7 € t−1, appreciably lower than that of the naturally derived CaO. The proposed integrated CO2 capture process using steel slag-derived, CaO-based CO2 sorbents developed appears to be cost-effective and promising for CO2 abatement from the iron and steel industry.

Biogas dry reforming for syngas production: catalytic performance of nickel supported on waste-derived SiO2

SiO2 synthesized from photovoltaic waste by a vapor-phase hydrolysis method was applied as a support for a nickel catalyst in a biogas dry reforming process for the first time. The catalytic performance was compared with those of commercial precipitated SiO2 and ordered mesoporous SiO2. Nickel supported on waste-derived SiO2 exhibited high CH4 conversion (92.3%) and high CO2 conversion (95.8%) at 800 °C, and there was no deactivation after a 40 h-on-stream test. Catalyst characterization results revealed that the SBET values and pore properties of catalysts affected the catalytic performance. A higher pore volume/SBET ratio led to a smaller crystal metal size and higher metal dispersion, thus the catalyst was less prone to deactivation. This discovery will help improve catalyst design. The use of nickel supported on waste-derived SiO2, which is competitive with commercial and mesoporous catalysts, shows the use of photovoltaic waste as a high value-added product; it can also deliver a cheap and environmentally benign support for catalysts in the biogas dry reforming process.

Effect of initial total solids concentration on volatile fatty acid production from food waste during anaerobic acidification

The effect of initial total solids (TS) concentration on volatile fatty acid (VFAs) production from food waste under mesophilic conditions (35 °C) was determined. VFAs concentration and composition, biogas production, soluble chemical oxygen demand concentration, TS and volatile solids (VS) reduction, and ammonia nitrogen release were investigated. The VFAs concentrations were 26.10, 39.68, 59.58, and 62.64 g COD/L at TS contents of 40, 70, 100, and 130 g/L, respectively. While the VFAs’ yields ranged from 0.467 to 0.799 g COD/g VSfed, decreased as initial TS increased. The percentage of propionate was not affected by TS concentration, accounting for 30.19–34.86% of the total VFAs, while a higher percentage of butyrate and lower percentage of acetate was achieved at a higher TS concentration. Biogas included mainly hydrogen and carbon dioxide and the maximum hydrogen yield of 148.9 ml/g VSfed was obtained at 130 g TS/L. concentration, TS and VS reductions increased as initial TS increased. Considering the above variables, we conclude that initial TS of 100 g/L shall be the most appropriate to VFAs production.