Lipase-Catalyzed Interesterification of Schizochytrium sp. Oil and Medium-Chain Triacylglycerols for Preparation of DHA-Rich Medium and Long-Chain Structured Lipids

DHA-rich medium and long-chain structured lipids (MLSL) were successfully synthesized by lipase-catalyzed interesterification of microbial oil from Schizochytrium sp. with medium-chain triacylglycerols (MCT) containing 99% of caprylic acid. Parameters that affected the reaction process were investigated and the conditions were selected as follows: lipase from Aspergillus oryzae, NS40086; reaction time, 8 hours; substrate molar ratio (MCT/microbial oil), 1:1; lipase load, 8 wt%; reaction temperature, 60 °C. Under these conditions, the proportions of MCT, MLSL, and long-chain triacylglycerols (TAG) in the final products were 12.5%, 62.8%, and 24.6%, respectively. The final product was then subjected to UPLC-MS/MS. Eighty-three types of TAG were identified, in which 54 types contained MCFA and MLSL species with relatively high contents were 22:6–8:0–8:0 (6.8%), 8:0–8:0–16:0 (7.5%), and 16:0–16:0–8:0 (7.5%). This product rich in MLSL with DHA and MCFA in the same TAG molecule is beneficial for fat digestion and absorption in infant and thus can increase the bioavailability of DHA at the molecular level.     

The effect of anionic surfactant (SDS) on pore-fracture evolution of acidified coal and its significance for coalbed methane extraction

Adding the compound solution included hydrochloric acid and hydrofluoric acid into coal seam, the pore structure of coal can be destroyed by acidizing treatment, and the permeability of coal seam can be improved. In order to increase the acidification damage effect, in this paper, the effects of anion surfactant named Sodium Dodecyl Sulfate (SDS) on the pressure relief and enlarge permeability effect of compound solution acidified coal were studied from four aspects: mechanical characteristics, porosity and pore distribution of coal samples, retention effect of fracturing fluid and microscopic morphology of coal sample surface. The results show that the SDS promotes the pressure relief effect of acidified coal body and reduces the strength of the treated coal sample. At the same time, the SDS increases the reaction area of acid fracturing fluid and impurity minerals in the fractures of coal sample, enhancing the acidification effect of HCL and HF on coal sample and increasing the porosity of coal. In the aspect of pore distribution, through the acidification synergism of SDS, the macropores and fractures of coal samples increase obviously. With the addition of SDS, the reversible work required for HCL and HF compound solution to break away from coal molecules is reduced by 18.45?J, which can significantly reduce the water blocking effect caused by the fracturing fluid retention, and improve the efficiency of coalbed methane extraction. After the compound solution erodes the coal sample, the microscopic morphology of coal sample surface has changed greatly, and the destruction degree of acidizing erosion is the highest after SDS synergism. The results of this paper are great significance for studying the mechanism of pressure relief and enlarge permeability effect of acidified coal.     

Water photolysis by carbon nitride

Polymeric carbon nitride has been used with a certain success to produce hydrogen by photocatalysis exploiting its properties of wide-band gap semiconductor with band gap between 2.6 and 3.0 eV, which is suitable to split water into H₂ and O₂ (ΔE = 1.23 eV). Indeed, the conduction band (CB) edge is higher than the H₂/H⁺ potential as well as the H₂O/O₂ potential is higher than the valence band (VB) edge. In addition, carbon nitride contains many active and coordination centers. This makes carbon nitride a very versatile material. However, the direct recombination of the pair electron and hole (exciton) removes energy to the redox reaction. This review is indeed focused on exciton recombination and localization, and on the efficiency of carbon nitride photosystems. Semiconductors and metals has been used to modify the properties of carbon nitride such as engineering the band gap, separating the exciton charges in order to increase hydrogen production. The hydrogen production of these systems coupling two photosystems, involving the Z-scheme, and co-catalysts is much higher than those based on pure polymeric carbon nitride or only on one co-catalyst.     

Characterization of carbonation behavior of fly ash blended cement materials by the electrochemical impedance spectroscopy method

The carbonation behavior of fly ash blended cement materials is studied by the electrochemical impedance spectroscopy (EIS) method, and a novel equivalent circuit model R_s(Q₁(R_ct1W₁)) (Q₂(R_ct2W₂)) is proposed to investigate the influence of fly ash on the carbonation process in the cementitious materials. The experimental results demonstrate that the diameter of the impedance arc in high frequency region increases as carbonation progresses. Increasing the amount of fly ash incorporated in the cement paste is also found to enlarge the high frequency arc. The carbonation process can be quantified by the parameter R_ct2 extracted from the equivalent circuit model R_s(Q₁(R_ct1W₁)) (Q₂(R_ct2W₂)). It is found that the R_ct2 value increases with increase in fly ash content. A linear relationship between the R_ct2 value and the carbonation time is also observed. As a consequence, prediction of the carbonation depth of fly ash bended cement materials can be achieved through knowledge of the R_ct2 value.     

Experimental behaviour of RACFST stub columns after exposed to high temperatures

The experimental studies on the behaviour of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposed to high temperatures are reported in this paper. Forty specimens, including 32 RACFST stub columns and 8 normal concrete-filled steel tube (CFST) stub columns as reference, were tested, and the failure pattern, load versus strain relation and ultimate strength of the specimens were presented and analysed. Five types of concrete were produced: one reference concrete with natural aggregates, two concrete mixes with recycled coarse aggregate (RCA) replacement ratios of 50% and 100%, and two concrete mixes with recycled fine aggregate (RFA) replacement ratios of 50% and 100%. The specimens were exposed to 300 °C, 600 °C and 800 °C for 3 h. The test results showed that, due to the existence of the recycled aggregates, the post-fire performance of RACFST stub columns was lower than the corresponding normal CFST specimens under the same maximum temperature suffered, and the RACFST specimens with RCA had a better behaviour than those with RFA under the same recycled aggregate replacement ratio.     

Role of CeO2–ZrO2 in diesel soot oxidation and thermal stability of potassium catalyst

Potassium nitrate catalysts supported on different oxides (CeO₂, Ce_0.5Zr_0.5O₂ and ZrO₂) were prepared for diesel soot combustion. The ageing treatment was performed at 800 °C for 24 h and the catalytic activity was evaluated by a temperature-programmed oxidation technique. The results demonstrated that, compared with CeO₂ and ZrO₂, Ce_0.5Zr_0.5O₂ presented good redox properties, a high surface area and available potassium-holding capacity at an elevated temperature. For aged K/Ce_0.5Zr_0.5O₂, the combustion temperature of soot particle was 359 °C under tight contact conditions and 455 °C under loose contact conditions. Thus, ceria–zirconia mixed oxides were considered as good candidate supports for diesel soot oxidation catalysis.     

A theoretical analysis of cohesive energy between carbon nanotubes,graphene and substrates

Explicit solutions for the cohesive energy between carbon nanotubes, graphene and substrates are obtained through continuum modeling of the van der Waals interaction between them. The dependence of the cohesive energy on their size, spacing and crossing angles is analyzed. Checking against full atom molecular dynamics calculations and available experimental results shows that the continuum solution has high accuracy. The equilibrium distances between the nanotubes, graphene and substrates with minimum cohesive energy are also provided explicitly. The obtained analytical solution should be of great help for understanding the interaction between the nanostructures and substrates, and designing composites and nanoelectromechanical systems.     

The return of drilling fluid in large diameter horizontal directional drilling boreholes

The return of drilling fluid (drilling mud) in large diameter horizontal directional drilling (HDD) boreholes is a very important issue related to mud pressure, cuttings transport and pull back force, but this problem has not been fully solved in previous research due to the complexity and uncertainty of downhole conditions. The calculation methods of mud pressure loss in the borehole annulus are briefly introduced and the equation using a Power Law model is adopted to study the drilling mud return. A typical reaming hierarchy of a large diameter HDD project has been used to study the return direction of drilling mud and volumes of drilling mud return to the exit and entry points. The research results disclosed that the drilling mud can return to both exit and entry points at the same time, with a large majority of the drilling fluid returning to the exit point if the reamer is closer to the exit point, and vice versa. A parametric study has been conducted to find out the effect of changing parameters in the calculation equation on the drilling fluid return. The drilling mud return for those boreholes with the exit point and entry point located at different elevations has also been discussed. Finally, different types of reamers and other factors such as borehole collapse and borehole shape were taken into the consideration of drilling mud return.     

零碳及碳中和燃料内燃机应用进展

通过一台改进的单缸轻型柴油机,研究3种进气压力(120、150和180 kPa)下燃料的滞燃期、十六烷值与进气压力的耦合对柴油机碳氢化合物(HC)排放的影响。使用纯柴油(B00)、B20燃料(按质量分数混合20%正丁醇和80%纯柴油的燃料)和B20+EHN (B20中添加0.7%质量分数的2-乙基己基硝酸盐)作为燃料进行实验研究。对B00和B20+EHN的碳氢排放进行比较,可知在进气氧浓度高于13%时,HC排放差值几乎不随进气氧浓度发生变化,不同压力的HC排放差异基本维持在 0~1 g/(kw·h)范围内。对B20和B20+EHN的碳氢排放进行比较,可知在 120、150 和 180 kPa 的入口压力下,临界氧浓度分别为 16%、15%和 13%,缸内燃烧温度和燃烧持续期是影响两种燃料HC排放差异的主要因素,当进气氧浓度值低于各进气压力下的临界点时,不同的十六烷值引起的缸内燃烧温度差异加大了HC 排放的差异,随着氧浓度的降低,缸内燃烧温度的影响程度增大。