At present, the biggest problem in lignin research is how to achieve efficient depolymerization of lignin, which is mainly due to the structural instability of lignin. In view of this problem, the natural structure of lignin, the structural changes of lignin in the process of separation and depolymerization were summarized and the specific effects of structural changes of lignin on the depolymerization process were also discussed. Literature survey shows that maintaining the structural integrity of lignin plays a key role in promoting the depolymerization of lignin, and put forward the prospect of the development trend of lignin depolymerization.
In order to study the rapid start⁃up of biofilters in seawater recirculating aquaculture systems, this study investigated the removal effects of seawater biological fluidized bed on pollutants under different hydraulic retention time (HRT) and temperature conditions, and explored the impact on initiation of seawater biological fluidized bed. The results show that: HRT=1 h experimental group can achieve material conversion and return to equilibrium more quickly, which is suitable for membrane loading; the high temperature conditions (28 ℃) are suitable for fluidized bed initiation, and the biofilm attachment growth can be observed more quickly.
The detection of explosive nitro compounds is a key research topic in the field of environmental pollution control and public safety. The luminescent platinum complexes [Pt(ppy)(CH3CN)2]ClO4 with high fluorescence quantum efficiency was applied as fluorescent probe to detect nitrocompound 4⁃nitrotoluene (4⁃NT). The fluorescence emission intensity of [Pt(ppy)(CH3CN)2]ClO4 decreased gradually until quenching with the addition of 4⁃NT. The detection efficiency KSV of 40.2 L/mmol was obtained by fitting experimental data with Stern⁃Volmer equation, and the minimum limit of detection was 1.83×10-6 mol/L. It is confirmed by spectrum experiment and DFT calculation that the detection mechanism of 4⁃NT by [Pt(ppy)(CH3CN)2]ClO4 was investigated to be synergistic effect of energy transfer and electron transfer.
TG was used to study the thermogravimetric behavior of Fushun oil shale at different heating rates in argon atmosphere. Four thermal kinetic models, DAEM model, Coats⁃Redfern method, FWO method and Doyle method, were compared and analyzed. The results show that the results of different dynamic model analysis are different: Coats⁃Redfern method, activation energy (E) has little change, and E belongs to the average value in a certain temperature range, which increases with the increase of heating rates as a whole. E is 109.40 kJ/mol when the heating rate is 20 ℃/min. The E of the DAEM model, the Doyle method, and the FWO method all increase with the increase of conversion rate. In addition, the E obtained by the DAEM model and the FWO method are relatively close, the DAEM model has the highest coefficient of determination. Therefore, the DAEM model is the most suitable for the kinetic analysis of Fushun oil shale pyrolysis among four thermodynamic analysis methods.
Surface enhanced Raman spectroscopy (SERS) is a technique widely used in detecting analytes at low concentrations and could provide structural information at the sametime. It is necessary to find the optimal particle size, shape and spatial distribution to optimize the SERS substrate. Current research efforts are focused on fabricating new kind of nanocomposite using as SERS substrates. Porous materials have long been employed as SERS substrate because of their unique features, the porosity that enable them as efficient adsorbents for target molecule. The porous α⁃Fe2O3 was used as solid support. In this paper, porous nano α⁃Fe2O3 was synthesized by hydrothermal method using porous α⁃Fe2O3 as solid carrier, and then calcined into Fe, so that there were porous channels on the surface of Fe. PATP aqueous solution and melamine aqueous solution were used as probe molecules. By adjusting the size of Au nanoparticles and investigating its influence on SERS performance, the optimum performance of 50 nm Au was obtained.The structures and compositions of the nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X⁃ray diffraction (XRD), and N2 adsorption. Our research illustrates a new kind of porous Fe2O3⁃Ag nanocomposite, that could be used as effective SERS substrate to adsorb and detect trace level of target analyte.
A strategy for the formation of amide bonds with one side protection of diamine was reported. A method was found to obtain a large number of mono⁃side protective diamines. When the reaction temperature was 0 ℃, adding the protective group to diamine solution slowly did not need catalyst to synthesize tert⁃butyl N⁃(6⁃aminohexyl)carbamate. The reaction had strong selectivity and good universality. The reaction had strong selectivity and good universality. This process can selectively and efficiently obtain the single amino protection product. The excessive diamine can be recycled and utilized, which improves the utilization rate of raw materials. It is a green and environment⁃friendly reaction.
The minimum miscible pressure is one of the important parameters of CO2 injection in oil field. In order to determine the minimum miscible pressure between crude oil and CO2 in the tight reservoir of lucaogou formation, jimusar sag, Xinjiang, the laboratory slim tube test and interfacial tension test were carried out. The results show that the MMP measured by slim tube test in Xinjiang tight oil reservoir is 18.70 MPa, slightly higher than the MMP measured by the interfacial tension experiment, which is 18.44 MPa. The difference between the two is 1.4%, and both lower than the reservoir pressure of 43.00 MPa. Therefore, CO2 and crude oil can be miscible under the reservoir conditions. When the equilibrium pressure increases, the IFT decreased more as more CO2 dissolved in crude oil. When the system equilibrium pressure increased from 0.73 MPa to 28.46 MPa, the IFT value between crude oil and CO2 decreased from 22.62 mJ/m2 to 1.83 mJ/m2. When the equilibrium pressure was between 0.73 MPa to 13.33 MPa, the dissolution of CO2 in crude oil took the leading role. However, when the equilibrium pressure was between 15.84 MPa to 28.46 MPa, the extraction of light components in crude oil took the leading role, and the interaction mechanism between crude oil and CO2 changes from CO2 solubility to CO2 extraction of light components at the pressure of 13.67 MPa. Through the experimental study, the understanding of the MMP of the target reservoir and the microscopic interaction mechanism between crude oil and CO2 is deepened, which provided theoretical support for the formulation of CO2 injection development of the target reservoir.
Based on the research results in gas field developmment, this paper summarized the development of optimization at domestic and foreign from two aspects: Infilled well deployment, piped network design, pointed out the difficulties and development directions of each part, and provided reference for gas field mining. The analysis points out that there are some difficulties in algorithmic improvement and well pattern density identification in the deployment of infill wells. Further research is needed in the deployment direction of shale gas field infill wells. Model establishment and algorithm improvement are the difficulties in pipe network research, further study of three⁃dimensional terrain relief layout analysis is required.
With the rapid advancement of ecological civilization construction in China, energy utilization methods such as recycling industrial waste heat and developing clean energy have gradually received widespread attention in the market. In this paper, a dual⁃loop cycle⁃kalina (DORC⁃KC) cogeneration system based on LNG cold energy utilization was designed. In addition, a new method for reducing acid gas emissions from industrial waste heat was proposed. Through the construction of the system thermodynamic model, the key thermodynamic parameters affecting the system carbon capture were analyzed in detail. The results show that the top cycle in the double cycle uses cyclopentane as the working fluid. By increasing the evaporation temperature and evaporation pressure, the maximum net output of the system is 367.9 kW,and the thermal efficiency is 33.29%. In the Kalina cycle, factors such as flux and concentration have a positive impact on system efficiency. The optimal thermal efficiency is 15.42% and the cold energy recovery efficiency is 20.65%. The reduction in compression pressure reduces the amount of circulating water but increase the quantity of the liquefaction of CO2. When the compression pressure is 472 kPa, the system has the highest exergy efficiency of 34.30%, carbon capture rate of 47.00%, and the amount of recycled water recovered is 167 616 t.
In order to explore the flow characteristics of vertical pipe in the deep⁃sea horizontal pipe⁃catenary system, in this paper, aiming at an oil and gas field in the south China sea, the influence of diameters, total flow rate, water cut and outlet pressure were simulated. The results show that the position of the flow state in the pipe is the boundary, and the influence of each influencing factor on the flow state parameters in the pipe shows different changes, but the temperature distribution along the pipe is not affected by the relevant factors; From the perspective of the research scope of the above four parameters, the influence process of each parameter is divided into different stages. The influence of pipe diameter is divided into two stages: D=0.06~0.12 m and D=0.12~0.50 m, the total flow of Q=0.001~0.030 m3/s and Q=0.100~0.300 m3/s, the water content of w=10%~25% and w=25%~30%, and the outlet pressure is divided into three stages, including 0~5.0, 5.0~7.0, 7.0~10.0 MPa.
The corrosion behavior of auxiliary anode under the combined action of alternating current density and cathodic protection were studied. Firstly, the corrosion rate and corrosion image were analyzed by immersion experiment, and the corrosion process was determined. Secondly, the electrochemical behaviors of the auxiliary anode under different conditions were analyzed by electrochemical test, and the corrosion behaviors of the auxiliary anode under different conditions were characterized according to the change of its corrosion kinetic parameters. The results show that the corrosion product layer formed under lower alternating current density overlays on the surface to slow down the corrosion, while the higher alternating current density can break down the corrosion product layer to activate the corrosion reaction. The cathodic protection current causes the corrosion product layer to be in the constant destruction and the generation process, further promotes the corrosion reaction. The results of immersion experiment are in good agreement with those of electrochemical test.
The wormlike sealing ring is located in the sealed groove of Dn1160 type pressure sintering furnace, which is prone to tear and damage.This article uses the finite element analysis method to nonlinear contact analysis of wormlike ring. The Von Mises stress and contact stress of worm⁃shaped rings are numerically simulated by Ansys software, and the results are compared.The cracking failure characteristics and easy tearing positions of worm⁃shaped rings under different parameters and working conditions are obtained. At the same time, the research results of predecessors are consulted to further optimize ring sealing ability.Finally, the research results provide a new idea for the design and optimization of the same kind of seal ring.
The Stress concentration is the main reason of damage to ferromagnetic metal pipelines. Through effective detection,the use status of metal pipelines can be predicted and the safety of equipment can be effectively guaranteed. The ferromagnetic effect of the material under stress is analyzed by the energy balance theory of ferromagnetic materials. The 3D simulation model of ferromagnetic materials is built by simulation software based on the metal band theory, and the magnetic effect characteristics of the system under tension stress are calculated. The weak magnetic field detecting sensor based on differential symmetrical structure is designed and manufactured. The stress concentration system of different types of pipelines is detected by the stress detection system based on the weak magnetic sensor. The stress concentration is verified by other stress detection methods. The results show that the weak magnetic sensor can effectively detect the weak magnetic field signal on the pipeline surface, and the weak magnetic field signal shows violent fluctuation characteristics in the stress concentration region. Various detection methods verify the effectiveness of the weak magnetic stress detection. Weak magnetic stress detection technology can effectively detect pipeline stress concentration caused by defects or deformation.
In order to further improve the corrosion resistance of S32750 super duplex stainless steel, the passivation treatment was carried out by nitric acid passivation. The corrosion resistance of S32750 super duplex stainless steel was investigated by electrochemical polarization curve, electrochemical impedance spectroscopy, Mott⁃Schottky curve and immersion method,and the corrosion surface morphology of the sample surface before and after corrosion was observed. The results show that the nitric acid passivation time has a significant effect on the corrosion resistance of S32750 super duplex stainless steel passivation film. When the passivation time is less than 120 minutes, the longer the passivation time, the smaller the corrosion rate is, and the better the passivation film corrosion resistance is.
This paper studies the stability of complex network systems with nonlinear coupled nodes. For the network coupying matries,the switching points of sub⁃systems discrete points in complex networks by using method that the Nimensinal complex network system transformed into the form of kronecker product.Then based on the Lyapunov function method, sufficient conditions for the stability of complex network systems are obtained. Based on the Lyapunov stability determination method, sufficient conditions for satisfying the stability of complex network systems are obtained. Finally, numerical examples are given to verify the effectiveness of the design method.
Voice forgery is detected by digital audio watermarking and pattern recovery techniques. The three methods used by digital watermarking mode for speech signal forgery detection are replacement, insertion and deletion. If some changes are made to the speech signal, the watermark mode will also change, and the mode recovery can be used to measure or detect whether the speech signal has been modified or forged. The proposed method uses the cyclic pattern embedding to overcome synchronizing problems of previous detection techniques. In addition, pattern recovery enhances the robustness to compression. This method has been tested and verified using six recording devices, which was used for collecting verbal data. The speech signals were sampled at the rate of 8 kHz and digitized at 16 bits resolution. Randomly chosen regions were substituted, removed, and compressed in MP3 at the rate of 16 kbps as well as in CELP at the rate of 11.5 kbps. The experiment shows the perfect detection for three kinds of forgeries and it proved the validity of the proposed method.
