Table of Content

22 February 2019, Volume 19 Issue 1

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Editorial

Accumulation, development, pioneering and innovative-editorial from the Editor-in-Chief

Suojiang ZHANG

Chin. J. Process Eng.. 2019, 19(1):  1-2.  DOI: 10.12034/j.issn.1009-606X.219001

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来暑往，岁月如梭；历添新岁，春满山河！《过程工程学报》充满着勃勃生机，在充实与忙碌中，大步踏入了2019年。

Reviews

Progress in flame synthesis of carbon nanotubes

Weiwei HAN Peng WANG Yan WEI Huaqiang CHU Yong SUN Wenjian CAO

Chin. J. Process Eng.. 2019, 19(1):  3-13.  DOI: 10.12034/j.issn.1009-606X.218203

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Flame synthesis of carbon nanotubes is a novel, energy efficient and low cost method. The flame method can simultaneously provide the carbon source and heat source needed for the preparation of carbon nanotubes, and has the potential to prepare carbon nanotubes on a large scale, over the existing conventional methods. Tremendous progress has been achieved during the past 20 years on not only improving the yields of carbon nanotubes and move progressively towards their mass production, but also on gaining a profound fundamental understanding of the nucleation and the growth processes. However, controlling the synthesis of carbon nanotubes in the flame is still a huge challenge, due to the extremely complex environment. The purpose of the present review is not to list all the experiments reported in the literature, but rather to identify trends and provide a comprehensive summary on the role of selected parameters in the flame. In this work, the structure and properties of carbon nanotubes were introduced firstly, then the research progress of carbon nanotubes by diffusion and premixed flame, including co-flow diffusion flame, inverse diffusion flame, counter diffusion flame, single-face wall stagnation flame and double-face wall stagnation flame were summarized, and the vapor–liquid–solid, tip and base, hollow and solid growth mechanisms of carbon nanotubes were briefly described. The synthesis of carbon nanotubes based on a methane/air coaxial jet diffusion flame by our group was also introduced. Through SEM, XRD and TEM characterization, it was proved that metallic nickel played a catalytic role. The catalyst particles were coated inside the carbon nanotubes, and the flame synthesized carbon nanotubes were based on a vapor–liquid–solid growth mechanism. The diameter of carbon nanotubes was distributed between 50 nm and 90 nm with an average diameter of 65 nm. Finally, the research direction of the preparation of carbon nanotubes by flame method was prospected.

Research progress of ammonia adsorption materials

Junli WANG Shaojuan ZENG Neng CHEN Dawei SHANG Xiangping ZHANG Jianwei LI

Chin. J. Process Eng.. 2019, 19(1):  14-24.  DOI: 10.12034/j.issn.1009-606X.218171

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Ammonia is a typical toxic pollutant and also one of the main causes of the formation of PM2.5. The emission of industrial tail gases containing a large amount of ammonia not only seriously affects the environment and health of human beings, but also results in serious waste of ammonia sources if directly discharged into the atmosphere. Because of their abundant pore structures and large specific surface areas, good adsorption characteristics and mechanical stability, porous materials have attracted a lot of attention in gas adsorption, especially in ammonia removal. Different porous materials can effectively absorb ammonia through the physical or chemical interaction between ammonia and their special pore structures or action sites. The adsorption method for ammonia removal has the several advantages, such as high selectivity, easy recovery and low energy consumption, so it is widely used in many industrial processes. In this review, the recent research status and progress of ammonia removal using different porous materials were reviewed, mainly focused on the research around the ammonia adsorption performances of zeolite, silica gel, activated carbon, graphene oxide, porous organic polymer, covalent organic frameworks (COFs), metal?organic frameworks (MOFs) materials before and after modification, and the research progress of supported ionic liquids materials for ammonia separation in recent years was also introduced. Ionic liquids, as a class of green medium, have several unique advantages for ammonia removal, such as low vapor pressure, high gas selectivity, high thermal stability, tunable structures and properties. Supported ionic liquids materials can combine the characteristics of both ionic liquids and porous materials, which can break the traditional restriction of ionic liquids in industrial applications and providing a novel pathway for ammonia removal applications. Finally, given the main problems of the current development on ammonia removal and recovery using porous materials, the future research directions and solutions had been put forward.

Research progress on acidic catalyzed dehydrative formation of isosorbide from sorbitol

Jie DENG Jing YUAN Qin TONG Weiguo DAI Kunfeng ZHAO Yaofeng WANG Baohua XU Dannong HE

Chin. J. Process Eng.. 2019, 19(1):  25-34.  DOI: 10.12034/j.issn.1009-606X.218161

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Isosorbide is a biomass-derived functional diol, with wide applications in the synthesis of several pharmaceutical molecules and fine chemicals. It attracted much attention recently due to its potential applications in the polymer industry. The catalytic dehydration of sorbitol represents a key and challenging step in the synthesis of isosorbide from biomass. Up to now, the acid catalytic system has been extensively explored and significant progresses were made with respect to both of catalyst designing and process optimization. This review mainly provides the relationship between structure and activity of different acid catalyst types. The first section comprehensively introduces the acid-catalyzed dehydration of sorbitol to isosorbide and the mechanism involved. The following two sections describe the progresses made in the homogenous and heterogeneous catalysts, respectively. The homogeneous catalyst mainly includes Br?nsted mineral acids, Lewis acids and ionic liquids, and the focus of was put on the influence of acid sites, acidity, stability and reaction solvent to sorbitol dehydration. The heterogeneous catalyst mainly includes acid resin, zeolite, supported metal oxide, heteropolyacid, sulphate and phosphate metal oxides, acid polymer and macromolecule catalyst. In addition to acid sites, acidity and stability, the acid capacity, pore structure, and surface structure and nature also have importantly effects on the activity of heterogeneous catalyst. Moreover, the effects of preparation methods of heterogeneous catalysts on their properties will be discussed. This article pointed out that Br?nsted mineral acids of strong acidity provided better catalytic activity, which, however, had the worst corrodibility and are difficult to be recycled. Latest reported acidic ionic liquids with tunable acidity and non-volatility in principle enables catalyst recycling, which may become competitive catalysts to replace mineral acids. For the heterogeneous catalytic system, the catalytic activity is closely related to the composition and structure of catalysts launched. More researches about the relationship between structure and activity needs to be carried out to develop efficient solid catalyst.

Recent advance on the 2D Ti₃C₂T_x MXene materials in supercapacitor field

Xun ZHANG Pei LI Zhengde WANG Xianpeng WANG Wei ZHANG Jie TAN Yaohui Lü

Chin. J. Process Eng.. 2019, 19(1):  35-44.  DOI: 10.12034/j.issn.1009-606X.218142

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In recent years, two-dimensional (2D) MXene materials have attracted a great deal of research interests in the field of energy storage, due to their extraordinary physical/chemical properties. The investigation of the 2D Ti3C2Tx is the most prevalent. MAX phase is a kind of ternary nitrides and/or carbide, its chemical formula for Mn+1AXn (n=1~3), M represents the transition metal elements (such as Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, etc.), X is the carbon and/or nitrogen, A is main IIIA or IVA group elements. According to different n values, the crystal structure of MAX phase includes 3 types. In the MAX phase, the bonds of M?X and M?A are very strong. Therefore, it is impossible to separate the layers by cutting or other mechanical methods. However, because the M?A bond has higher chemical activity than the M?X bond, the single-layer/low-layer MXenes material can be obtained by chemical etching of M?A bond assisted auxiliary method, and the surface terminations are randomly distributed. Surface terminations play an important role in electrochemical performance. Therefore, how to control the type and quantity of surface terminations is an important part in the current research field. The fundamental structure of the MXene phase was introduced and the relationship between phase structure and performance was analyzed in this work. The electrochemical performances of Mxene phase materials improved by ion implantation, heat treatment, surface modification, electrode design and elemental doping were summarized. Meanwhile, in order to further improve the conductivity and cyclic stability of the materials, the application progress of the composites with carbon, oxide and polymer in the field of supercapacitor was briefly introduced. Phase structure, preparation and electrochemical properties of Mxene material were reviewed, the existing problems and future development direction for Mxene phase materials used in supercapacitor fields were pointed out.

A review on recycling of waste aluminum alloy

Xuan WEI Haijuan WANG Chunwei LIU Hongbin CAO Pengcheng YAN Zhi SUN

Chin. J. Process Eng.. 2019, 19(1):  45-54.  DOI: 10.12034/j.issn.1009-606X.218180

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Because of the low density, high strength, good corrosion resistance and other excellent properties, aluminum alloys have become the second widest used metal material. In recent years, more and more attention to the recycling of waste aluminum alloys has been paid, which not only effectively alleviates the global shortage of bauxite resource, but also contributes to the sustainable development of economy, environment, and energy. Due to the special working environment of aerospace industry, it has higher performance requirements for the aluminum alloy, i.e. strength, heat resistance, corrosion resistance and fatigue resistance. Therefore, the aerospace aluminum alloys contain many types of alloying elements and create higher recycling value. With decades of research and exploration, there are still problems limiting the recycling, such as unstable product quality, high burning rate, and severe oxidation. Heavy-medium separation, dual-chamber furnace smelting, and LARS metamorphic treatment technologies and equipments have been successively developed. This article summarized the types of commonly used aluminum alloys, the equipments and technologies used in the recycling process, including pretreatment, remelting regeneration, and refining. The status of recycling and utilization of aerospace aluminum was highlighted. Finally, the difficulties and future trends in the aluminum recycling industry were discussed and looked ahead.

Research progress on agglomeration mechanisms and fluidization behavior of cohesive particles

Hanlu QI Jiajun WANG Xueping GU Lianfang FENG

Chin. J. Process Eng.. 2019, 19(1):  55-63.  DOI: 10.12034/j.issn.1009-606X.218139

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Cohesive particles tend to bond together during fluidization due to the inter-particle force, which breaks down the normal fluidization and seriously affects factory production. In recent years, the research focus of cohesive granular flow has gradually transferred to the intrinsic agglomeration mechanisms and fluidization characteristics simulation study from the black-box-like experiments before. Taking studied scale as the cut-in point, the mechanical model, agglomeration criterion as well as fluidization experiment and simulation study of four kinds of cohesive forces (Van der Waals force, electrostatic force, solid bridge force and liquid bridge force) were reviewed on the particle scale and reactor scale. The functionary mechanisms of cohesive force and the fluidization behavior of cohesive particles were analyzed from the aspects of force, motion and kinetics. While the development of the four kinds of cohesive forces are in different stage according to the agglomeration mechanisms studies, the dynamic model as well as agglomeration process mechanisms will become the major tendency in this field. On the reactor scale, the discrete element method simulation coupled with cohesive force models will remain to play an important role in fluidization study. For the significant influence on simulation performance caused by the accuracy of the model like cohesive force model and drag model as well as the trends in three-dimensional simulation, the mechanical model and calculation ability will be two challenges in the future simulation research.

Flow & Transfer

Effects of hydrocyclone separation on purification of natural gas-hydrate slurry and sand remove

Shunzuo QIU Guorong WANG Guangshen WANG Shouwei ZHOU Qingyou LIU Lin ZHONG Leizhen WANG

Chin. J. Process Eng.. 2019, 19(1):  64-72.  DOI: 10.12034/j.issn.1009-606X.218154

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In view of the problem of low efficiency caused by the large amount of sand contained in the natural gas hydrate of the seabed in process of hydrates mining in the solid-state flow method, a novel separation process was presented based on the solid fluidization, and a hydrocyclone used for submarine gas-hydrate slurry was designed based on the properties of seabed gas-hydrate and the multiphase flow theory. The effects of particle (sands and gas-hydrate) size, inlet flux of slurry, and sands concentration in gas-hydrate slurry on separation efficiency and pressure drop were simulated by CFD. The results showed that the separation efficiencies of sand and gas-hydrate were more than 60%, and the maximum was 98.72%, the pressure drop was within 0.5 MPa, and the lowest was 0.03 MPa with the hydrocyclone at the conventional condition. The separation efficiency of sand increased first and then unchanged when particle size was increased. When inlet slurry flux was increased, the sand separation efficiency first increased and then decreased. When sand concentration in slurry was increased, the separation efficiency was always decreased. The separation efficiency of gas-hydrate increased first and then unchanged with increasing particle size and inlet slurry flux. When increasing sands concentration in slurry, the separation efficiency of gas-hydrate was decreased. The pressure drops in the overflow and underflow outlet were almost unchanged when particle size was increased, and increased with the sands concentration in slurry and inlet slurry flux increased. It was revealed and verified that the particle size, inlet slurry flux, and the sand concentration had great influence on the performance of the hydrocyclone. The separation performance was very good when the sand size was greater than 20 ?m, the hydrate size was greater than 40 ?m, the inlet slurry flux was about 5 m3/h, and the sand concentration was no more than 25vol%.

Heat transfer characteristics of self-wetting solution and nanotube surface

Xianghua SI Baisong HU Shaofeng ZHANG Dewu WANG Weiming YU

Chin. J. Process Eng.. 2019, 19(1):  73-82.  DOI: 10.12034/j.issn.1009-606X.218131

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A highly ordered nanotubes-surface was prepared on the surface of smooth titanium plates by anodic oxidation. The morphologies and the characteristics of nanotubes-surface and smooth surface were characterized by SEM, atomic force microscopy (AFM) and automatic contact angle measuring instrument. The preparation of self-wetting solution and the corresponding thermophysical determination were realized. The heat transfer performances of different surfaces (smooth surface and nanotubes-surface) coupled to different working fluids (distilled water and self-wetting solution) were investigated by the pool boiling experiment, making the comparation and analysis from different angles for the heat transfer effect using the distinct combination of conditions. At the same time, the mechanism of heat transfer enhancement between the nanotubes-surface and the self-wetting solution had been analyzed in micro and macro. The results showed that when the nanotubes-surface with super hydrophilicity and greater roughness was coupled with the self-wetting solution, the maximum heat transfer coefficient and critical heat flux can be as high as 11.963 kW/(m2?℃) and 623.706 kW/m2, respectively, which increased by 84.1% and 143.8% compared to the conventional smooth surface and distilled water coupling. The effects of the maximum heat transfer coefficient and critical heat flux enhancement to the heat transfer systems were slightly different between the nanotubes-surface and self-wetting solution, showing characteristics in coordination and enhancement of the boiling heat transfer performance. The nanotubes-surface had more effective vaporization core and better wettability. Combined with the special surface tension characteristics of self-wetting solution, the cold and hot liquid microcirculation was formed, which would facilitate the movement of hot and cold liquids, the secondary wetting in time, the drastic reduction in bubble diameter and the increasement in departure frequency, microbubbles appeared, increased system disturbances, effectively enhanced heat transfer performance. It was the main mechanism to increase the system's maximum heat transfer coefficient and critical heat flux density.

Numerical simulation on flow characteristics of heavy oil through circular-sectioned 90° bends

Xiaoyuan GU Fukui PAN Wenjie WANG Liming ZHANG

Chin. J. Process Eng.. 2019, 19(1):  83-90.  DOI: 10.12034/j.issn.1009-606X.218158

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The flow of heavy oil in circular-sectioned 90° bends was investigated. The local hydrodynamic performance was affected by heavy oil flow parameters and structure parameters of bend. Computational fluid dynamics (CFD) was used to numerical calculate the three-dimensional laminar flow for circular-sectioned 90° bends, and heavy oil was used as the research medium. The resistance of heavy oil was exported at temperature 50~70℃, Reynolds number 300~800, the inner diameter of pipe D=50.7~131.7 mm, bending ratio B=0.75~3.0. The mechanism of the local drag coefficient in bend was analyzed. The results showed that the local drag coefficient increased with the increase of temperature, the inlet Reynolds number decreased and D increased. The resistance decreased in the range of 0~15° in the bend because of the formation of double longitudinal vortices, and the scope of resistance decreased from 75° in the bend to 0.5D behind the bend because of the formation of four longitudinal vortex bend. The effect of local flow resistance was greater by bending ratio than the other. The maximum value of the local drag coefficient when B=0.75 was 28.35 times of that of B=3.0, however, the pipeline resistance between inlet and outlet was only 1.68 times. The reason was that there was a local low pressure region at 1.0D behind the bend when the bending ratio B≤1.0. Meanwhile, there was a flow vortex, and the peak of shear rate located 0.5D behind the bend. The conclusions can provide technical support, and the theoretical study about the secondary flow characteristics of heavy oil in the pipe can provide reference data for the design of heavy oil pipeline. The initial state parameters of heavy oil can be predicted in the engineering practice.

Pressure fluctuations in a gas-solid fluidized bed with rotating sieve tray type baffles

Yao SHI Dewu WANG Bin ZHAO Shaofeng ZHANG Kaiguang LIANG Shuhui MA

Chin. J. Process Eng.. 2019, 19(1):  91-101.  DOI: 10.12034/j.issn.1009-606X.218151

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Compared with the free bed, the gas?solid fluidized bed with rotating sieve tray type baffles has good performance in breaking the bubbles under different superficial gas velocities (Ug=0.04~1.14 m/s). The ideal operating conditions were then determined by some parameters, e.g. the flow phenomena, the standard deviation of differential pressure fluctuation and the standard deviation of pressure fluctuation. The results showed that, when the superficial gas velocity increased, the particles below the internals tended to move forward to the areas above the internals. It caused the bed height to decrease below the internals. Moreover, three flow types appeared below the internals under different superficial gas velocities. It directly determined if the internals worked in breaking bubbles. When Ug<0.44 m/s, the bed height kept high value below the internals. The bubbling fluidized bed appeared. It contained two sections: the bottom section with dense phase and the upper section with the alternant appearance of the dense phase and the large bubbles. At that time, the internals suppressed the growth of bubbles and can even break the bubbles. Compared with the free bed, the fludized bed with internals had lower standard deviation of differential pressure fluctuation and the standard deviation of pressure fluctuation. When 0.44≤Ug<0.66 m/s, the bed height became small below the internals. The turbulent fluidized-bed occurred. It included two sections: the bottom section with dense phase and the upper section with dilute phase. At that time, the internals had no direct influence on the bubbles. However, the dense phase at bottom reduced the pressure fluctuation intensity below the internals and a little above the internals. When Ug≥0.66 m/s, the turbulent fluidized-bed comprised one single section with dilute phase. The section with dense phase disappeared. The gas phase became the continuous phase below the internals. At that time, the internals had little influence on the bubbles, the bed pressure and the differential pressure fluctuation intensity.

Dynamic analysis of droplet impregnation microchannel in entry

Peisheng LI Xiaolong LIAN Ying ZHANG Wandong ZHAO Qiang LIU Min LU Peng DU

Chin. J. Process Eng.. 2019, 19(1):  102-109.  DOI: 10.12034/j.issn.1009-606X.218147

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Droplet impregnate microchannel was a widely existed phenomenon in microfluidic control, while the mechanism of dynamic motion during impact was not well addressed. A numerical model was developed using volume of fluid (VOF) method and the model was validated by experiments. In this work, the gas?liquid interface was captured using VOF method and the phenomenon of droplet impregnating microchannel was studied. Among the many simulation cases, it was found that the section width, contact angle, Re number and We number had significant influences. In the process, the effects of section width, contact angle, Re number and We number were studied in details. After comparing the results of each cases, it was clear that the cross section's width of the microchannel inlet had the most obvious impact on the process of the droplet impregnating in the microchannel. And it was found that the smaller the width was, the more difficult for the droplet to pass the microchannel after colliding with the entrance of the channel. When the microchannel's cross-sectional width was reduced to 0.2 mm, the effect of the static contact angle of the wall surface would appear. The larger the static contact angle of the wall, the greater the resistance of the droplet to microchannel. Under the condition of large static contact angle, the length of the liquid in the channel can be increased by appropriately increasing the Re number of the droplet so that the liquid passed through the microchannel. However, when the Re number reached 4000, jet phenomenon would happen. Then the liquid would flow through the microchannel in large quantities, and spread diameter would also increase significantly. As the We number decreased, the surface tension effect became obvious, the flow resistance in the microchannel became larger, and the liquid flowing through the microchannel would be more difficult, meanwhile the length of the infiltration was significantly reduced.

Numerical simulation on heat transfer in a cylindrical fluidized bed

Lijun WANG Shuping DUAN Lingfeng XU Jiajun SUN

Chin. J. Process Eng.. 2019, 19(1):  110-117.  DOI: 10.12034/j.issn.1009-606X.218119

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Based on the cylinder fluidized bed built by Shedid and Hassanto, a three-dimensional Euler–Euler simulation of the effect on the convective heat transfer characteristics between the fluidized particles and the inner heated surface was carried out under different operation conditions including particles sphericity, superficial gas velocity and initial solid packing height in the vertical fluidized bed. Moreover, the experimental average temperature had been chosen to test the validity of numerical average temperature. Contour plots of transient distribution of solid volume fraction and solid temperature have been obtained in fluidized bed on horizontal cross-section in order to understand the effects of hydrodynamic and flow patterns on heat transfer characteristics. The results showed that the solid phase concentration distributed from the initial centrally symmetric annular stratification to the final severely turbulent fluidization by observing contour plots of the solid-phase volume fraction on horizontal cross-section. Solid temperature decreased from center to periphery in the radial direction at initial state since the gas–solid heat exchange rate affected the particle temperature in the entire bed. The temperature distribution of particles was non-uniform on the annular region due to the bed without being fluidized. With the process of fluidization underway, the particles temperature distribution tended to be uniform in horizontal cross-section because the bed material heat transferred from the center's cylindrical heater wall to the bed. The effective thermal conductivity was used to calculate the individual gas and solid phase convective heat transfer coefficient from heater surface to fluidized beds. Not only the average temperature of both heating wall and fluid but the difference of the average temperature between wall and fluid were decreasing with increasing superficial gas velocity. It enhanced turbulence intensity and led to increase the heat transfer coefficient between heater surface and fluid with the same time. The solid average convective heat transfer coefficient growed up with the initial height increasing of the bed material due to the contact area enlargement of particles and the heated surface in the fluidized bed.

Reaction & Separation

Centrifugal field enhanced oil-water phase separate in Si/SiC separation process of silicon wire-saw waste

Zhankui WANG Dong WANG Zhi WANG Wenhui MA Xiaohan WAN

Chin. J. Process Eng.. 2019, 19(1):  118-125.  DOI: 10.12034/j.issn.1009-606X.218175

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An efficient process of separating silicon and SiC in silicon wire-saw waste was studied. According to the different surface properties of Si and SiC in silicon wire-saw waste, SiC was absorbed by emulsified diesel to achieve the goals of separating Si/SiC. Centrifugal force was applied to the emulsified slurry to enhance the separation of oil?water phase during phase separation process, so the time required of oil?water phase separation was shortened. Adjusting pH of the slurry to change zeta potential of particles, and then to control oil drops size. The relationships of Si/SiC separation effect and phase separation time with slurry pH value were studied respectively. The relationship between the apparent density of oil drops with SiC and the diameter of oil drops was found. Stress analysis of SiC on oil drops surface in centrifugal field was studied, and the movement of SiC on the surface of oil drops in centrifugal field was analyzed. The results showed that the smaller size of oil drops, the longer time of phase separation and better results of removal SiC at normal gravity field. The content of SiC in silicon powder was 4.23wt% at the pH of 7. When the oil drops diameter less than 64 μm, the oil droplets could not float in the slurry. Applying centrifugal force with a gravity coefficient of 10, 50, 100, 150, and 200 to the emulsified slurry, the effect of phase separation and Si/SiC separation with 2 min of centrifugal were investigated. When the gravity coefficient was 100 and pH was 7, the content of SiC in silicon powder was 5.47wt%, the separation time decreased from 460 min to 2 min. It was confirmed that the centrifugal force made SiC moved along the surface of the oil drops to the direction of centrifugal force, which resulted in a decreased of adsorption force.

Technology of lithium extraction from lepidolite through mechanochemistry activation

Mingming HE Haixia YOU Chunlong ZHAO Xiaohong ZHENG Hongbin CAO Zhi SUN

Chin. J. Process Eng.. 2019, 19(1):  126-135.  DOI: 10.12034/j.issn.1009-606X.218169

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The demand for lithium resources has increased significantly in recent years due to the rapid development of hybrid electric vehicles, plug-in-vehicles and so on. To alleviate the shortage of lithium resources in China, the lithium extraction from lithium-containing minerals has received widely attention. As an important lithium-containing minerals, lepidolite has a stable mineral structure. Therefore, it is difficult to extract valuable metals from lepidolite efficiently. Based on the understanding of the stable mineral structure of lepidolite, direct leaching lithium from minerals with dilute sulfuric acid and limestone calcination-sulfuric acid leaching method are adopted to realize the activation and separation of lithium from minerals. However, the extraction of lithium by these methods are complicated, besides, the comsumption of medium is great, and a large amount of residues and waste water are produced during these processes. In this paper, the mechanochemical activation was introduced to activate the transformation of inert Li?O coordination structure in lepidolite under the condition of K2SO4 as an additive, then dilute acid was used to achieve efficient separation of lithium. Various parameters including type and amount of additive, milling time and ball-to-concentrate mass ratio in the mechanochemical activation process as well as the acid concentration, liquid-to-solid ratio, stirring speed, temperature and time in the leaching process were optimized and the mechanism was further discussed. The results showed that the mechanochemical process destroyed the structure of Si?O?K and reduced the effect of the Si?O coordination on the Li?O coordination structure, resulted in a decrease in the Li?O bond strength and an increase in its reactivity. Under the optimum conditions (lepidolit-to-additive mass ratio 5:1, ball mill speed 500 r/min, ball-to-concentrate mass ratio 20:1, ball milling time 3 h, sulfuric concentration 15vol%, liquid-to-solid ratio 4 L/g, temperature 80℃ and stirring speed 200 r/min), the leaching rate of Li was 99.1%. With this research, it is expected to provide a new approach for short range extraction and efficient utilization of lepidolite.

Selectively extract astaxanthin from wet biomass of Haematococcus pluvialis

Xiaoli REN Lin CHEN Runzhi LI Tianzhong LIU

Chin. J. Process Eng.. 2019, 19(1):  136-143.  DOI: 10.12034/j.issn.1009-606X.218102

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Microalgae Haematococcus pluvialis is the richest natural source of astaxanthin and has become the primary source for astaxanthin production so far. However, its thick resistant cell wall probably represents the biggest barrier for target compound extraction. Therefore, high energy-consuming and cost-intensive downstream processes such as cell disruption and drying are required to improve extraction efficiency. In the present study, an approach to selectively extract astaxanthin and lipid using aqueous ethanol from algal biomass of H. pluvialis with moisture content of 80%, following a pre-process of acidic hydrolysis cell wall disruption, was proposed. Experiments for parameters optimization and for investigation of mechanism of this approach to improve extraction performance were also carried out. The results showed that polar fractions (mainly chlorophyll and polar lipids) and neutral fractions (mainly carotenoids and triglyceride) were selectively extracted in different extraction cycles, thus fraction extraction was achieved as consequence of the change of ethanol concentration in different extraction cycles. Solvent or solvent mixtures with moderate polarity act out better selectivity and efficiency for carotenoids (mainly astaxanthin), i.e. extraction using ethanol/ethyl acetate mixture gave a total yield of carotenoids reaching 25.31 mg/g of dry weight, a recovery rate of 69.35% and a high content ratio of carotenoids to chlorophyll of 10.6. With assistant of acidic cell-wall disruption, the extraction efficiency of astaxanthin and lipid were significantly improved, in particular, the total yield of lipid reached 418 mg/g dry weight and the recovery rate of lipid reached 97% under the optimal acidic hydrolysis cell-wall disruption conditions of HCl 1 mol/L, temperature of 60℃ and time 60 min. The extracted astaxanthin and fatty acid maintained their chemical stability during extraction process. Therefore, this approach for selectivity extraction astaxanthin and triglyceride from wet algal biomass was demonstrated, and could be an alternative with multiple benefits including extraction efficiency improvement and cost reduction, for astaxanthin production from algal biomass of H. pluvialis.

Treatment technology of waste phosphor by sulfation-roasting-leaching

Huan TIAN Menglong ZHANG Li LAI Zhuo ZHAO

Chin. J. Process Eng.. 2019, 19(1):  144-150.  DOI: 10.12034/j.issn.1009-606X.218156

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At present, in view of the existing problems in waste phosphor, such as lower comprehensive utilization and serious environmental pollution caused by improper handling, the method of sulfation-roasting?leaching was used to pre-treatment waste phosphor according to its problems to explore the effect of roasting temperature on the form of materials, roasting temperature and concentrated sulfuric acid addition on rare earth leaching. A preliminary environmental assessment of the process was carried out. The results showed that with the optimum leaching conditions which were roasting temperature of 300℃, roasting time of 120 min, concentrated sulfuric acid?waste phosphor mass ratio of 1.85, leaching temperature of 25℃, leaching time of 120 min and liquid?solid mass ratio of 2:1, the sulfation-roasting?leaching rate of rare earth oxides were Y2O3 98.82%, Eu2O3 97.39%, CeO2 96.58% and Tb4O7 98.77%. The material after sulfation-roasting?leaching indicated that sulfation-roasting can decompose rare earth into soluble sulfate and phosphate, and ensure that the slag was environmentally friendly and low slag. Concentrated sulfuric acid addition gave greater impact on the leaching of four kinds of rare earth, while roasting temperature brought larger influence on the leaching of CeO2 and Tb4O7, leaching rates increased from 40.18% and 37.18% at 200℃ to 96.58% and 98.77% 300℃, respectively. Waste phosphor calcined at 300℃ will not produce harmful gases such as SO2 and SO3 through the discussion of the emission of gas during the roasting process, the main gases released during roasting were water vapor and volatile sulfuric acid, and the material loss was about 10%. This process avoided the production of a large amount of sulfur-containing, fluorine-containing, strongly acidic waste gas and refractory roasting waste residue in the roasting process, and reduced environmental pollution and waste of rare earth resource, the new process has good prospects for industrial applying.

Density functional analysis on extracting of zinc by HA and HNAPO

Xingguo LUO Chang WEI Xingbin LI Zhigan DENG Ziyu ZHUANG Cunxiong LI

Chin. J. Process Eng.. 2019, 19(1):  151-158.  DOI: 10.12034/j.issn.1009-606X.218157

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In order to analyse extraction mechanism of Zn(II) from ammonia/ammoniacal solution, density function theory (DFT) calculation at the level of B3LYP/6-31G+(d, p) were used to predict the geometry structures, vibrational frequencies, frontier orbitals energy, chemical potential and charge distribution of the 1-phennyl-1,3-sebacic-diketone (Mextral54-100, HA), 2-hydroxy-5-nonylacetophenone dioxime(Lix84I, HNAPO) and corresponding Zn(II) extracted complexes. The DFT calculation results were used to predict the extraction ability and compared with the experiment values. The results showed that during the process of extracting zinc by HA and HNAPO, the O and C atoms on enol-form of HA, the C and N atoms on oxime, the O atom on phenol of HNAPO, which accounting for the highest contribution to the molecular frontier orbitals. In the infrared spectrum of extractants and complexes, the stretching vibration peak of the C=C double bond on the HA showed red-shifted, the intensity of the distortion vibration peak of the C=N double bond on the oxime group changed, and the characteristic absorption peak of the phenolic hydroxyl group on the HNAPO disappeared after extraction reaction, indicating that the enol form, oximido and phenolic hydroxyl group were the active centers during extraction process. After extracted zinc, the bond molecule length and molecule angle changed, Zn(II) replaced enol-form hydrogen and with oxygen atom to form coordination bond, the C=O double bond stretched during zinc extraction process by HA. Besides, Zn(II) replaced phenolic hydroxyl H atom and reacted with O and N atoms to form coordination bonds, the benzene and Zn(II) were on the same plane of zinc extracted HNAPO molecule. The ΔE (ΔELUMO–HOMO) and electronegativity of HA were lower than HNAPO. The chemical potential was higher than HNAPO, which indicated that the extraction capacity was in the order of HA>HNAPO. The experimental results were in good agreement with the theoretical prediction results.

Process & Technology

Preparation of porous Ni-Fe-Sn electrode by electrodeposition and its electrocatalytic behavior of oxygen evolution

Ying GAO Yihui WU Lianke ZHOU Chunsheng MA

Chin. J. Process Eng.. 2019, 19(1):  159-164.  DOI: 10.12034/j.issn.1009-606X.218214

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Oxygen evolution reaction (OER) is one of the core reactions in the field of electrochemistry and subjected to a lot of studies for many years. But it is still one of the most complicated electrochemical processes and of practical importance. Specifically, the development of efficient and low-cost non-precious catalyst for the OER is still a key challenge for the renewable energy research community. In this study, electrodeposited porous nickel?iron?tin (Ni–Fe–Sn) alloy on Cu foil as an efficient OER electrocatalyst in alkaline medium was introduced. The obtained alloy was analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), respectively. The OER electrocatalytic performance of Ni–Fe–Sn alloy was investigated by linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CP) in 30wt% KOH solution. In addition, the Ni–Fe–Sn alloy was further tested as anodes for alkaline water electrolysis during at least 12 h with good stability. The results showed that the obtained Ni–Fe–Sn alloy was composed of Ni3Sn2 and FeNi3 phases. The EDS result of Ni–Fe–Sn alloy showed the existence of three elements (Fe, Ni and Sn). SEM images displayed that the surface of the Ni–Fe–Sn alloy had porous structure, which provided more active sites for the OER. OER measurements demonstrated that the Ni–Fe–Sn alloy was highly effective for the OER with a low overpotential of 261 mV to reach 10 mA/cm2 and a small Tafel slope of 69.9 mV/dec. The excellent electrocatalytic activity, long-term stability and facile preparation method enabled Ni–Fe–Sn alloy to be a viable candidate for its widespread use in various water-splitting technologies. The better OER activity of Ni–Fe–Sn alloy in comparison to Ni–Fe alloy originated from higher electrochemical active surface area (ECSA) and the improved mass/electron transport capability due to synergetic effect between Ni, Fe, and Sn.

Performance degradation model and prediction method of real-time remaining life for high temperature ceramic filter tube

Longfei LIU Zhongli JI Xin LUAN

Chin. J. Process Eng.. 2019, 19(1):  165-172.  DOI: 10.12034/j.issn.1009-606X.218183

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High-temperature ceramic filter tube is composed of a support body with a large pore size and a membrane structure with a small pore size. In practical applications, it has a lot of dust with particle size smaller than 1 ?m, which can move through the membrane structure and deposit the support body finally. It can't be removed by pulse jet cleaning effectively. Particle deposition within the support body and the compression of residual dust cake are responsible for the decreasing permeability and increasing residual pressure drop of high temperature ceramic filter tubes. In this work, on the basis of particle deposition within the filter medium and the compression of residual dust cake can't be measured directly, Bayesian estimation theory was used to establish a state-space model to describe the ceramic filter tubes degradation process using the residual pressure drop measured in the filtration system. This method can incorporate the latest residual pressure drop data and update the model parameter timely, the remaining life of the ceramic filter tube was predicted in real time. At the same time the failure probability density distribution of the remaining life of the ceramic filter tube and the change rate of degeneration status of the ceramic filter tube were predicted. By analyzing the actual data of the ceramic filter tube residual pressure drop from high-temperature experiment device and shell coal gasification process respectively, the prediction accuracy of the remaining life increased gradually with the increase of the residual pressure drop data, the accuracy of the prediction at the later stage was higher than 95%, and the ceramic filter tubes change rate of degradation status gradually decreased. This was consistent with the conclusion that the residual pressure drop of ceramic filter tube increases fast at the early stage and slow at the late stage.

Efficient absorption of dichloromethane using imidazolium based ionic liquids

Wenliang WU Tao LI Hongshuai GAO Dawei SHANG Wenhui TU Binqi WANG

Chin. J. Process Eng.. 2019, 19(1):  173-180.  DOI: 10.12034/j.issn.1009-606X.218162

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In recent years, environment problems have been a hot issue of concern to the public. Chlorinated volatile organic compounds such as dichloromethane (DCM) have been a serious threat to the public health and environment as hazardous chemical substances. Solving these problems has become an urgent issue in nowadays society. Ionic liquids (ILs) are supposed to be potential solvents to absorb gases due to their unique structures and properties, which have exhibited excellent absorption capacity in NH3, SO2, CO2 and other gases. In this paper, a series of conventional ILs including [Bmim][BF4], [Bmim][PF6], [Bmim][DCA], [Bmim][SCN], [Bmim][NTf2], [Emim][SCN], [BPy][SCN] were synthesized and used as absorbents for dichloromethane (DCM) capture at different temperatures and partial pressures. The absorption capacities of DCM by ILs were measured by a highly sensible microbalance-intelligent gravimetric analyzer (IGA). It was found that [Bmim][SCN] has the highest absorption capacity to DCM (1.46 g/g, 303.15 K, 60 kPa) among these investigated ILs, and the absorption capacity of [Bmim][SCN] had no obvious decline after five absorption?desorption cycles. The densities and viscosities of [Bmim][SCN] with different mass fraction of DCM absorbed were measured in this work as well. And with the increase of the mass fraction of DCM absorbed, the density of DCM absorbed [Bmim][SCN] increased slightly, while the viscosity decreased dramatically. In addition, mechanism of DCM absorption by [Bmim][SCN] was investigated through FT-IR and 1H?NMR, implying the interaction between DCM and [Bmim][SCN] was physical interaction. Furthermore, the interactions between cations or anions of ILs and DCM were investigated by quantum chemical calculation, which demonstrated that the anions of ILs had a more significant influence on the absorption capacity than cations, on account of the strong hydrogen bond interaction between anion and DCM, which has a great agreement with the results of experiment. This work will provide a new sight for designing more competitive ILs for DCM capture.

Materials Engineering

Synthesis and properties of poly(triazole ester) resins

Bo PAN Luyu WANG Haijun WANG Songda JIANG Liqiang WAN Xufeng HAO Jie TIAN Farong HUANG

Chin. J. Process Eng.. 2019, 19(1):  181-188.  DOI: 10.12034/j.issn.1009-606X.218145

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As a new kind of resin system, polytriazole resin has lots of excellent properties, including excellent low temperature curing property, excellent thermal property and low vacuum outgassing rate, which is expected to be used as matrix resins in the application of satellites. In recent years, we have carried out a series of studies on the polytriazole resin systems. Different kinds of polytriazole resin are prepared by changing the chemical structure of azides and alkynyl compounds, reaction degree, main chain or side chain, etc. In this work, we hope to explore the effect of ester groups on curing behavior and thermodynamic properties of polytriazole resin system. Comparing the properties of three new polytriazole resin, we try to find a way for the development of a higher performance polytriazole resin. Dipropargyl succinate (DPS), dipropargyl isophthalate (DPIP) and dipropargyl phthalate (DPP) were synthesized by esterification. Three kinds of poly(triazole ester) (PTAE) resins were designed and synthesized from DPS, DPIP, DPP and multifunctional azides (TAMTMB) through thermal polymerization. T700 carbon fiber-reinforced PTAE composites were prepared and characterized. The processing properties, curing behaviors and mechanical properties of resins were investigated. The results revealed that PTAE resins had good processing properties and could be cured at a low temperature (80℃) . The glass transition temperatures (Tg) of the cured PTAE resins were greatly influenced by the structure of the crosslinked backbone, which was higher than 140℃. Flexural strength of the cured PTAE resins was higher than 170 MPa. Flexural strength of the T700 carbon fiber-reinforced PTAE composited at ambient temperature arrived at over 1500 MPa. From the above results, the introduction of ester group did not change the low temperature curing characteristics of polytriazole resin, and the mechanical properties of polytriazole resin did not change remarkably. Three kinds of poly(triazole ester) were expected to be used as the resin matrix of high performance composites.

Evaluation of dispersion of functionalized graphene in solvents by Hansen solubility parameters

Jianqiang LIU Jing MA

Chin. J. Process Eng.. 2019, 19(1):  189-194.  DOI: 10.12034/j.issn.1009-606X.218195

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Graphene as a kind of two-dimensional material is consisted of sp2 carbon atoms, which exhibits excellent properties, such as electronic, electrical, mechanical and thermal properties. However it is easy to form aggregation and difficult to dissolve in solvents because of its unique structure, so that the application is greatly limited. So far, most of the work reported on the dispersion of graphene without assistant of functionalization mainly in N,N-dimethylformamide (DMF) and 1-Methyl-2-pyrrolidinone (NMP), but preparation of graphene dispersion in other organic solvents is an vital step in application. In this work, graphene was surface modified by sodium alginate (SA) and polyvinylpyrrolidone (PVP) to restrain graphene aggregation and improve its dispersion in organic solvents. The functionalized graphene was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), Raman spectroscopy and X-ray diffraction (XRD). The dispersion of functionalized graphene in solvents was explored, and Hansen solubility parameters (HSPs) of functionalized graphene was calculated depending on their dispersion. The results showed that the functionalized graphene was successfully prepared. After surface functionalization, the dispersion of functionalized graphene in solvents was significantly changed compared with graphene and two kinds of functionalized graphene had good dispersion in water. Furthermore, HSPs and radius of HSPs sphere of functionalized graphene were changed. ?D and ?H increased and ?P decreased. These change indicated that the polar of graphene was weaken after functionalized, and its dispersion in non-polar solvents was improved. Furthermore, the increasement of radius of HSPs sphere indicated that functionalization expanded the dispersion scope of graphene in solvents.

Optimizing preparation of Ce-Cu/TiO₂ hollow microspheres with uniform particle size distribution and its photocatalysis and humidity control performance

Hao ZHANG Yuandi XU Xiuyu LIU

Chin. J. Process Eng.. 2019, 19(1):  195-201.  DOI: 10.12034/j.issn.1009-606X.218194

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Cerous nitrate Ce(NO3)3?6H2O and cupric nitrate Cu(NO3)2?3H2O were used as modifier to make Ce–Cu/TiO2 hollow microspheres. The preparation scheme of Ce–Cu/TiO2 hollow microspheres with uniform particle size distribution was optimized by conducting uniform design and building BP neural network model. Particle size distribution of Ce–Cu/TiO2 hollow microspheres was tested and characterized by laser particle size analyzer (LPSA), the microstructure was characterized by SEM and TEM, the pore structure was tested by brunauer–emmett–teller surface areas analyzer (BET). Humidity performance of Ce–Cu/TiO2 hollow microspheres with uniform particle size distribution was tested by isothermal absorption–desorption, the photocatalysis performance was tested by ultraviolet–visible spectrophotometer (UV–Vis). Finally, optimal technology parameters of Ce–Cu/TiO2 hollow microspheres were obtained. The results showed that the magnetic stirring rate (VMS), dropping rate of solution B added to solution A (VAB), dropping rate of solution D added to solution C (VCD), calcination heating rate (VTC), and calcination temperature (TC) were 910 r/min, 1.32 mL/min, 0.86 mL/min, 2.47℃/min and 485℃, respectively. Besides, for Ce–Cu/TiO2 hollow microspheres with uniform particle size distribution, other sizes were shown as follows: d10 =103.74 nm, d50=141.46 nm and d90 =188.84 nm. Particle size distribution interval of d90–d10 was 85.10 nm. It was also proved that Ce–Cu/TiO2 hollow microspheres with uniform particle size distribution had good photocatalysis and humidity control performance. Specifically, degradation rate of formaldehyde gas was 21.6%~53.9% after 1~6 h, and equilibrium moisture content under the relative humidity of 32.28%~84.34% reached 0.0364~0.2746 g/g accordingly. The above research provided certain theoretical basis and technical support for further systematic research on particle size distribution of Ce–Cu/TiO2 hollow microspheres and photocatalysis–humidity control performance.

Environment & Energy

Transition metal Mn substitutes polyoxometalates for catalytic alcoholysis of waste PET

Pengtao FANG Bo LIU Qing ZHOU Junli XU Yu DING Changliang JIAN Minglan GE Junying MA Xingmei Lü

Chin. J. Process Eng.. 2019, 19(1):  202-208.  DOI: 10.12034/j.issn.1009-606X.218178

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Poly(ethylene terephthalate) (PET) is a kind of thermoplastic polymer resin and has been widely used in many fields because of its excellent thermodynamics and mechanics performance, such as synthetic fiber, plastic film, food packaging, water and soft-drink bottles and so on. However, with the extensive use of PET materials and their inherently hard-to-degrade characteristics, our environment is facing significant challenges in environmental protection and resource reuse. Therefore, it is very necessary to carry out research on the recycling of PET. The recycling methods for PET are mainly divided into physical and chemical methods. Since chemical methods can degrade PET into raw materials and then reuse them, these methods have received more and more attention. Alcoholysis is a relatively mild method in chemical methods with the advantages of mild reaction conditions and easy separation of products. In order to achieve rapid and gentle degradation of PET and to obtain high conversion and selectivity, ethylene glycol was chosen as a solvent and polyoxometalate (POM) as catalysts for degradation of waste PET. In this study, a kind of transition-metal-substituted POM Na12[WZnMn2(H2O)2(ZnW9O34)2] with a sandwich structure was synthesized and it was used to catalyst the alcoholysis of poly(ethylene terephthalate) (PET). The effects of reaction time, reaction temperature, and the amount of catalyst on PET degradation were researched, the conditions was optimized. The results showed that PET could be 100% degraded at 190℃ for 80 min under the conditions of catalyst amount was 1.0wt% of PET and mass ratio of PET to ethylene glycol (EG) was 1:4, the yield of bis(hydroxyethyl) terephthalate (BHET) achieved 84.42%. In addition, in order to determine the structure and properties of the degradation products, the degradation products were characterized by NMR, IR, TGA, DSC, HPLC and other instruments. The final experimental results showed that the catalyst can efficiently catalyze the alcoholysis reaction of PET and obtain high-purity BHET products.

Electricity production and microbial community change of anaerobic sludge

Jianjun DING Xiaowei PENG Yejun HAN

Chin. J. Process Eng.. 2019, 19(1):  209-215.  DOI: 10.12034/j.issn.1009-606X.218152

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The production of methane by anaerobic fermentation is the main treatment mode of organic waste such as wastewater, but subsequent processes of carbon dioxide separation, methane storage and transportation have restricted its application. Microbial fuel cells can directly convert the chemical energy of organic waste into electrical energy, and converting the traditional anaerobic fermentation methanogenesis process of organic waste into electricity production process, which is a greener and more environmentally friendly process and has broad application prospects. In present study, a microbial fuel cell (MFC) with good performance was constructed by using an anaerobic activated sludge as inoculum. High-throughput sequencing was used to analyze the changes of bacteria and archaea before and after MFC operation. The results showed that when the external 1000 Ω resistor was used, the output voltage reached 0.62 V, the output power reached 1247 mW/m2, and the internal resistance was 143 Ω, the Coulomb efficiency was 9.9%, the COD removal rate of the sludge in anode chamber reached 64% after MFC operation. When the sludge was treated by MFC, only the electron was produced instead of traditional CH4 and H2, thereby avoiding problems such as CO2 separation, CH4 storage and transportation in the methanogenesis process. The composition of archaea was relatively stable, while the bacterial flora changed significantly. Compared with the original anaerobic sludge, the MFC microbial diversity index decreased, while the dominant bacteria group became more obvious. The dominant bacteria Firmicutes and Proteobacteria were accepted as the common electric producing bacteria. Klebsiella, which is directly related to MFC's ability to produce electricity, is enriched and became a dominant genus with a relative abundance of 16.73%. In addition, Hydrogenophaga is also abundantly enriched, which may be a novel electrogenic microorganism. This study provided theoretical and technical support for the conversion of organic waste into electrical energy through anaerobic treatment.

Influence of the initial pressure on formation characteristics of CO₂ hydrate in quartz sand below freezing point

Jinping LI Yang LI Ze YAO Xuemin ZHANG Juanjuan HUANG Jian KANG

Chin. J. Process Eng.. 2019, 19(1):  216-222.  DOI: 10.12034/j.issn.1009-606X.218118

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The permafrost region contains a large amount of natural gas hydrate resources. Carbon dioxide replaces methane to recover gas hydrates in the frozen soil, can not only obtain a large amount of natural gas resources, but also can save carbon dioxide gas and reduce the greenhouse effect caused by carbon dioxide emissions. It is a very promising gas hydrate extraction methods. At present, there are few studies on the carbon dioxide replacement of natural gas hydrates by methane production in the permafrost region, and the formation and decomposition characteristics of methane hydrate and carbon dioxide hydrate in the permafrost region have not yet been revealed. In this work, the occurrence condition of frozen quartz sands sleet shape to simulate permafrost gas hydrate, experimental study on effect of stress on carbon dioxide hydrate formation characteristics, several experimental groups were carried out respectively in 271 K, which the generated pressure of carbon dioxide above or below liquefaction pressure in 300 mL high pressure hydration reactor. The results showed that carbon dioxide below freezing temperatures in quartz sand pressure without liquefaction, the higher the initial pressure, the faster the hydration reaction rate and the earlier the pressure will reach the stable state. But above liquefaction pressure, the more the amount of carbon dioxide was filled, the faster the hydration reaction rate was. From the overall trend, the pressure acted as a driving force of the hydration reaction. The higher the pressure, the more formation of carbon dioxide hydrate was, and the higher the final conversion rate was. Therefore, when carbon dioxide was used to replace methane hydrate in the permafrost region, it was necessary to control the pressure below the liquefaction pressure or to inject excess carbon dioxide, and the final conversion rate will increase dramatically.