Process Optimization Strategies Research Articles

A complementarity‐based vapor‐liquid equilibrium formulation for equation‐oriented simulation and optimization

AbstractVapor‐liquid equilibrium (VLE) is a cornerstone of computer‐aided process engineering (CAPE). Embedded within process system models, VLE calculations are inherently procedural with non‐smooth behavior that frequently requires discrete decisions. Traditionally, these features resist the incorporation of VLE within efficient, large‐scale equation‐oriented (EO) process simulation and optimization strategies. On the other hand, recent reformulation of VLE models through the incorporation of complementarity constraints has broadened its scope to deal seamlessly with phase transitions and even supercritical excursions in process simulation and optimization. In this study, we extend these VLE complementarity models to EO frameworks where procedural thermodynamic property libraries are still required. Here we develop an efficient, non‐intrusive, and intuitive “square‐flash” equation system that has been implemented within the IDAES Integrated Platform (IDAES‐IP). The effectiveness of this modular approach is demonstrated on case studies for non‐ideal flash calculations and distillation optimization, with disappearing phases and supercritical transitions.

Spring‐Like Ammonium Salt Assisting Stress Release for Low‐Temperature Deposited FAPbI3 Films Toward Flexible Photovoltaic Application

AbstractThe substrates of conventional flexible perovskite solar cells (FPSCs) are thermoplastic polymer material polyethylene naphthalate (PEN), which will deform during high temperature annealing process. In addition, lead iodide (PbI2) permanently formed and the substrate undergoes reversible deformation from 20 °C to 200 °C and back to 20 °C. Therefore, to balance the substrate supporting capacity and the crystalline quality of narrow band gap α‐phase formamidinium lead iodide (α‐FAPbI3), an annealing process of 120 °C for 30 minutes is determined. Additionally, there will also be a large number of gaps and lattice strain at the perovskite grain boundaries during the annealing process as the FAPbI3 phase transition is accompanied by much lattice shrinkage. As a result, 1,6‐hexanediammonium diiodide (HADI) is chosen to passivate the defects and release the stress of perovskite film. Therefore, a recorded 1.4% extended stretch rate of the flexible film is attained. Finally, the champion PCE of 21.14% under AM 1.5G and 31.52% under 1062 lux is achieved after HADI treatment, accompanied by a better long‐term and mechanical stability. This study provides annealing process optimization and stress relief strategies for the further development of narrow band gap FPSCs.

Experimental Investigation of EN-31 Steel Using VMC

This research paper presents an experimental investigation using the Vertical Machining Centre (VMC) for machining the EN31 material. The study looks at how different input factors, including feed, speed, and cut depth, affect the output factors, like the material removal rate (MRR) and surface roughness (SR). The Taguchi method is used as the optimization technique to identify the optimal combination of input parameters that lead to maximum MRR and minimum SR. The objective of the study is to establish the relationship between input and output parameters and to offer a workable strategy for machining process optimization. The study's findings will advance our understanding of EN31 material machining with VMCs and have real-world implications for the machining sector.

Exploring lean six sigma: A comprehensive review of methodology and its role in business improvement

In a highly competitive industrial landscape, organizations are increasingly adopting strategies to enhance product quality, with Lean Six Sigma emerging as a notable approach. This paper presents a comprehensive review of Lean Six Sigma, a synergistic approach combining the waste-reduction principles of Lean with the process optimization strategies of Six Sigma. The study underscores the importance of the Lean Six Sigma approach as a valuable tool for businesses, seeking process improvement and increased competitiveness and acknowledging that its applicability depends on an organization’s specific circumstances and needs. Furthermore, the paper critically assesses the benefits and potential criticisms of Lean Six Sigma, providing balanced insights into challenges to its implementation. By offering a comprehensive understanding of Lean Six Sigma, this review paper serves as a valuable resource for organizations aiming to enhance their operational efficiency, reduce cost, and improve customer satisfaction.

Metabolic and Process Engineering for Producing the Peach-Like Aroma Compound γ-Decalactone in Yarrowia lipolytica

Due to its strong and unique peach-like aroma, γ-decalactone is widely used in dairy products and other foods or beverages. The oleaginous yeast Yarrowia lipolytica, which is generally regarded as safe, has shown great potential in the production of this flavor compound. Recently, the development of metabolic and process engineering has enabled the application of Y. lipolytica for the production of γ-decalactone. This Review summarizes the relevant biosynthesis and degradation pathways of Y. lipolytica, after which the related metabolic engineering strategies to increase the accumulation of γ-decalactone are summarized. In addition, the factors affecting γ-decalactone accumulation in Y. lipolytica are introduced, and corresponding process optimization strategies are discussed. Finally, the current research needs are analyzed to search for remaining challenges and future directions in this field.

A novel strategy for process optimization of a natural gas liquid recovery unit by replacing Joule–Thomson valve with supersonic separator

The natural gas liquid recovery is an important process in a gas plant to correct hydrocarbon dew point and earn profit. In this study, a natural gas liquid recovery unit operated based on the Joule–Thomson process was investigated and its performance was optimized. To improve the system performance, the plant configuration and intermediate pressure ratio were defined as the variables and maximization of the natural gas liquid recovery rate and maximization of exergy efficiency were defined as the objective functions. To improve the plant performance, the amount of natural gas liquid recovery rate should be increased. To achieve this goal, several scenarios for the intermediate pressure ratio and three new configurations were proposed for the investigated gas plant. In the proposed configurations, the supersonic separators with optimized structures were used instead of the Joule–Thomson process. It was observed that all three proposed configurations improved the natural gas liquid recovery rate compared to the existing configuration. For example, by installing two supersonic separators instead of second and third stage Joule–Thomson valve + low temperature separator, at the optimal operating condition, the natural gas liquid recovery rate increased about 390%. The influence of the intermediate pressure ratio on the phase envelope diagram, exergy efficiency, dew point depression and natural gas liquid recovery rate was also investigated. By comparing the influence of intermediate pressure ratio and modifying the plant configuration on the objective functions, it was observed that the system performance can be further improved by modifying the plant configuration.

Control-oriented dynamic process optimization of solid oxide electrolysis cell system with the gas characteristic regarding oxygen electrode delamination

Fast response, strong reliability, and high efficiency as the critical objectives of a solid oxide electrolysis cell (SOEC) system, which requires the system to operate under optimal operating conditions and switching manners. Therefore, various research has been carried out on its characteristic security. Most of them focus on the thermal characteristics security without further considering the security of gas characteristics regarding oxygen electrode delamination. However, this is one of the most critical degradations of SOEC. Herein, a novel SOEC system dynamic model with the gas characteristic regarding oxygen electrode delamination is proposed for the first time to optimize operation. Specially, the advantages are discussed through the optimization analysis of both the secure operation range regarding certain operating conditions and the steady-state operating points of the system. Subsequently, the dynamic process constraints of oxygen electrode delamination, fuel starvation, and power fast tracking during dynamic switching are investigated. The feasibilities of multi-step, parabola, and ramp schemes in solving the problems above are also evaluated. The outcomes show that the ramp scheme is preferred. Furthermore, the priority issue between oxygen electrode delamination and fuel starvation is studied, and corresponding dynamic process optimization strategies are developed for high and low initial power with a two-step switching method. After that, the dynamic process optimizations of two representative cases are investigated in detail. The optimization results show that the system efficiency is increased, and the safe ramp duration under the low initial power is significantly shortened. The findings of this study could provide a basis for developing control strategies for SOEC systems with fluctuating energy input.

Laser Additive Manufacturing of High-Strength Aluminum Alloys: Challenges and Strategies

Metal additive manufacturing (AM)-fabricated high-strength aluminum (HS-Al) alloys (2xxx, 6xxx, and 7xxx) tend to produce fatal metallurgical defects such as porosity and cracks. Since Al is the most important lightweight structural material in automotive and aviation industries, successful printing of HS-Al alloys is in high demand. Therefore, this review focuses on the formation mechanisms and research advancements to address these metallurgical defects. Firstly, the process optimization strategies, including AM parameter optimization, hybrid AM processes, and post-processing treatment, and their effectiveness and limitations have been reviewed thoroughly. However, process optimization can address defects such as porosity, surface roughness, and residual stresses but has limited effectiveness on cracking alleviation. Secondly, the research efforts on composition modification to address cracking in AM of HS-Al alloys are critically discussed. Different from process optimization, composition modification alters the solidification dynamics in AM of HS-Al alloys and hence is considered the most promising route for crack-free printing.

Integrating 1G with 2G Bioethanol Production by Using Distillers’ Dried Grains with Solubles (DDGS) as the Feedstock for Lignocellulolytic Enzyme Production

First-generation (1G) bioethanol is one of the most used liquid biofuels in the transport industry. It is generated by using sugar- or starch-based feedstocks, while second-generation (2G) bioethanol is generated by using lignocellulosic feedstocks. Distillers’ dried grains with solubles (DDGS) is a byproduct of first-generation bioethanol production with a current annual production of 22.6 million tons in the USA. DDGS is rich in fiber and valuable nutrients contents, which can be used to produce lignocellulolytic enzymes such as cellulases and hemicellulases for 2G bioethanol production. However, DDGS needs a pretreatment method such as dilute acid, ammonia soaking, or steam hydrolysis to release monosaccharides and short-length oligosaccharides as fermentable sugars for use in microbial media. These fermentable sugars can then induce microbial growth and enzyme production compared to only glucose or xylose in the media. In addition, selection of one or more suitable microbial strains, which work best with the DDGS for enzyme production, is also needed. Media optimization and fermentation process optimization strategies can then be applied to find the optimum conditions for the production of cellulases and hemicellulases needed for 2G bioethanol production. Therefore, in this review, a summary of all such techniques is compiled with a special focus on recent findings obtained in previous pieces of research conducted by the authors and by others in the literature. Furthermore, a comparison of such techniques applied to other feedstocks and process improvement strategies is also provided. Overall, dilute acid pretreatment is proven to be better than other pretreatment methods, and fermentation optimization strategies can enhance enzyme production by considerable folds with a suitable feedstock such as DDGS. Future studies can be further enhanced by the technoeconomic viability of DDGS as the on-site enzyme feedstock for the manufacture of second-generation bioethanol (2G) in first-generation (1G) ethanol plants, thus bridging the two processes for the efficient production of bioethanol using corn or other starch-based lignocellulosic plants.

SimDFBA: A framework for bioprocess simulation and development

Many efforts have been made to model bio-processes and investigate the main effective parameters using conventional known softwares. The main shortcoming of such models is that the bioreactor is considered a black box. Such simplification causes uncertainty in following different metabolic pathways of microorganisms. This study presents a new method for simulating bio-processes by integrating available conventional simulation softwares such as ASPEN PLUS and MATLAB. The former is used to simulate common process equipment, and the latter is employed to model Bio-reactor. Besides, the Bio-reactor is modeled mathematically with Dynamic Flux Balance Analysis (DFBA) concept using the metabolic network reconstruction model. This framework will simultaneously provide a rigorous basic model of both upstream and downstream equipment. This approach can also be used as a toolbox to implement process optimization and modern control strategies on the bio-processes. A syngas fermentation bioprocess case study was chosen to implement the new framework.

Anaerobic Digestion of Cereal Rye Cover Crop

The rapid growth of cover crop planting area in the U.S. helps with erosion control, soil health, control of greenhouse gases, and also provides abundant biomass for the production of bioenergy and bioproducts. Given the cover crops’ compositional heterogeneity and variability, a tolerate platform technology such as anaerobic digestion (AD) is preferred but has not been widely used for cover crop biorefining. This study evaluated the biogas and methane yields from six cereal rye (Secale cereale L.) cover crops grown in the Midwest, using both bench- and pilot-scale anaerobic digesters. The effects of two critical factors, the total solids (TS) content and ensiling, on digester performance were also investigated. Methane yields of 174.79–225.23 L/kg-VS were obtained from the bench-scale tests using cereal rye as the mono feedstock. The pilot-scale test with no pH adjustment showed a slightly higher methane yield. Ensiling increased the methane yield by 23.08% at 6% TS, but disturbed AD at 8% TS, and failed AD at 10% and 15% TS. Findings from this study would help farmers and the biorefining industry to determine the baseline performance and revenue of cereal rye AD and to develop strategies for process control and optimization.

Understanding the abnormal effects of ultrasonic vibration on tool wear and surface generation in Zr-based bulk metallic glass cutting

Bulk metallic glasses (BMGs), which represent an emerging popular class of alloys, are regarded as difficult-to-cut materials. Ultrasonic vibration-assisted cutting (UVAC) has been reported as an effective method to improve the machinability of such materials. In UVAC, it is widely accepted that, the larger the ultrasonic amplitude, the better the processing outcome, i.e., lower cutting force, lower surface roughness and longer tool life. However, this study demonstrates that the cutting performance of BMGs can be enhanced only if the ultrasonic amplitude is within a carefully-determined window. Due to the high hardness, high elastic limit, and inhomogeneous deformation of BMGs, an excessive ultrasonic amplitude would violate the cutting performance of UVAC. On the one hand, the increase of ultrasonic amplitude can increase the cutting-in speed and actual cutting distance of the tool, which, due to the extreme hardness and elastic limit of BMGs, might lead to severe tool wear in the form of abrupt fracture and rapid flank abrasion, respectively. On the other hand, the increase of ultrasonic amplitude can increase the instantaneous maximum cutting speed of the tool, which, due to the inhomogeneous deformation of BMGs, might lead to local melting of the BMG. When the instantaneous cutting speed reaches a critical value, local material melting takes place on the newly generated surface, which will induce the deterioration of surface quality due to the formation of dimples and periodic micro-pools during UVAC. Based on the theoretical and experimental results, the process window of UVAC of BMGs has been identified. A process optimization strategy is proposed by synergistically considering the surface quality, tool life, and machining efficiency. Additional confirmatory experiments reveal that UVAC can effectively reduce the cutting force and surface roughness of BMGs if the process parameters are well-matched within the identified window. • UVAC improves the machinability of BMGs, unless an excessive vibration amplitude. • An analytical model of UVAC tool failure was established and verified by experiments. • The unique properties of BMGs induce the abnormal failure of UVAC tool. • Feathered dimples and micro-pools were found, the mechanism is revealed. • the process window and optimization strategy of UVAC of BMGs were proposed.

Application of nanomaterials in anaerobic digestion processes: A new strategy towards sustainable methane production

Anaerobic digestion is an established biomass conversion technology that is renewable, environmentally friendly, and technologically robust. However, to turn it into a more profitable and sustainable business model, stringent research into process optimization strategies is required. As a result, there is a continuous search for strategies and pathways to improve process stability as well as product quality and yield and to decrease the production of inhibitory compounds. More recently, nanoparticles have been utilized as catalysts to enhance the performance of anaerobic digestion technologies. The current paper provides a state-of-the-art review on utilizing nano-catalysts in the biomass anaerobic digestion process. The potential of several kinds of nano-catalyst has been discussed to enhance biogas production with a cost-effective approach. The results of this research suggest that while nanoparticle supplementation is a promising strategy, further research is required to address the energetic, technological, and economical utilization of nanoparticles in anaerobic digestion processes.

A multi-scale and multi-objective optimization strategy for catalytic distillation process

This work aims to establishing a multi-scale and multi-objective optimization strategy for the catalytic distillation process. Firstly, the catalyst layer efficiency factor correlation that embraces the influence of the catalyst layer structure was obtained and then coupled with the process simulation to establish a multi-scale model for the catalytic distillation process. On this basis, genetic algorithm was employed to realize the multi-objective optimization. The hydrolysis process of methyl acetate in the reactive dividing wall column was investigated. The equipment parameters and operational conditions of the catalytic distillation column, and the structure parameters of the catalyst layer are optimized simultaneously. The results indicated that the minima of the total annual cost, the gas emission cost and the exergy loss decrease by 19.26%, 23.11% and 67.27%, respectively, by comparing with the counterparts obtained from the single-factor sensitivity analysis. Furthermore, the catalyst cost decreases by 30.88% per year.

Structured 3D Printed Dry ECG Electrodes Using Copper Based Filament

Commercial wet Silver and Silver Chloride electrodes are used to monitor electrocardiogram (ECG) signals in numerous bioimpedance applications. These electrodes are frequently single-use components that adhere to the skin through an adhesive surface. This sticky surface is infamous for generating skin irritations during the replacement and removal of electrodes, making the process uncomfortable for the patient. Because this type of electrodes is inappropriate in many measuring situations, the applicability of dry electrodes is investigated.This study introduces the use of a copper-based filament (Electrifi) with the highest reported conductivity (0.006 Ω.cm) in biomedical applications, showcasing the process parameters of 3D printed, semi-flexible and wearable dry electrodes to monitor ECG signals. The effect of the printing-process parameters (bed and nozzle temperatures, surface infill pattern) on the electrical performance is thoroughly investigated (10 parameters and >100 electrode samples) to find the highest conductivity and lowest impedance of the printed electrodes. The influence of ten process parameters on the resistivity of printed electrode samples with three different surface structures (namely concentric, rough, and flat as shown in Fig. 1a) and different thicknesses have been experimented. The analyzed parameters play a significant role in the electrodes’ impedance and conductivity values. Choosing a proper setup of these parameters can enhance the bio-impedance measurements of dry electrodes similar to ranges of wet electrodes and even below.The flow of this study was divided into two main stages. First, electrodes of 15 mm diameter and 2 mm thickness were 3D printed with three surface structures, each with six temperature settings, including two nozzle temperatures (140 and 150 °C) and three bed temperatures (40, 60, and 80 °C). At this point, non-optimized electrodes are recognized. Second, another optimization strategy was presented, which involves experimenting with electrodes of 15 mm diameter and 0.5 mm thickness with two surface structures (concentric and flat), each with two temperature settings, including two nozzle temperatures (140 and 150 °C) and one bed temperature (80 °C).A 2D profilometry is provided, showcasing the effect of printing parameters on the electrodes' surface roughness. Keithley and Agilent semiconductor device analyzers were used to record the impedance measurements; both can acquire complex impedance spectra per second in a frequency range from 20 kHz to 400 kHz. The excitation current was set to 20 µA. This study investigates the behavior of 2 stacked electrodes. For this purpose, two binder clips were used to securely hold the two electrodes, resulting in uniform force distribution. The resistance measurements are performed using the same equipment under a fixed frequency at 400 kHz that is then converted into conductivity given the electrodes' cross-sectional area and thickness to be 177 mm2 and 2 mm (or 0.5 mm), respectively.The process parameters significantly affect the electrodes surface structures, specifically the bed temperature (Tbed). The roughness of the structured surfaces (concentric and rough) was observed to be increasing with the increase in bed temperature. However, the roughness of the flat surface remained unchanged under all temperature parameters. The impedance measurements of the 2 mm thick electrodes decreased significantly over frequency, showing a capacitive behavior (Fig. 1b). This is due to the air gap created between the structured electrodes, parasitic factors from the devices themselves, and external factors such as light, airflow, and movement that influenced the measurement. The conductivity measurements are depicted in Fig. 1c, unlike the rough surface electrode, which uses additional ironing parameters, the flat and concentric surface electrodes are printed with the same process parameters, resulting in equivalent resistance and conductivity values. Thus, the concentric and flat structures of Tbed = 80 °C and Tnozzle = 140 and 150 °C showed the best performance among all samples. Decreasing the thickness to 0.5 mm of the concentric and flat structures and using the optimum bed and nozzle temperatures generated better and stable results with higher sensitivity and lower impedance measurements.In conclusion, this study confirms that different electrode structures and printing temperatures significantly influence the electrodes' functionality, conductivity, and impedance measurements. Defining the optimum printing parameters for the electrodes' material is fundamental to obtain stable and reliable measurements. With a new insight into the electrical behavior of the copper-based Electrifi filament, process optimization and new printing strategies can be studied for the single-process fused filament fabrication (FFF) 3D printing to create functional and sensitive electrodes. Figure 1. A) Images of the three 3D printed electrodes surfaces: flat (left), concentric (middle), and rough (right). B) Impedance measurement of the concentric structure at different frequencies. C) Conductivity measurements of the electrodes with three different surfaces. Figure 1

Modelling of continuous drying of heat-sensitive pharmaceutical granules in a horizontal fluidised bed dryer combined with a screw conveyor at steady state

• A novel FBD has been investigated for continuous drying of pharmaceutical granules. • A relatively simple and practical model has been developed to predict the continuous dryer operation. • This model contributes to facilitating process scaling up and gaining insight on process optimization strategies. • Usefulness of the work relies on the need of process intensification through continuous manufacturing in pharmaceutical industry. Continuous manufacturing improves productivity in terms of efficiency, flexibity and quality. However, the pharmaceutical industry still heavily relies on batch operations; extensive R&D work is required to convert the current processes into continuous ones. This work presents a phenomenologigcal modelling approach for continuous drying of pharmaceutical granules in a novel fluidised bed dryer (FBD) combined with a screw conveyor. A hybrid model methodology has been adopted to describe the drying kinetics of the target granules: (1) a phenomenological model for the constant-drying rate period and (2) an empirical one for the falling rate period. The model was first validated by batch drying results and then was extended to the corresponding continuous drying condition. The particle residence time distributions (RTDs) have been determined by the pulse-tracer injection method. Then, a dispersion model has been developed based on the RTD measurements and the drying kinetics that allows predicting the continuous drying results at a steady state. The solids flow has been considered as a plug flow moving from the inlet to outlet with moderate axial dispersion, and the back-mixing term has been expressed through an experimental dispersion coefficient. The influences of several parameters are studied towards process optimisation and scale-up. The increase of air temperature and velocity were efficient on reducing the final moisture content. The increase of the feeding rate enhanced the energy efficiency. And the increase of the internal rotation rate enhanced the process stability and reduced the overheating effect.

Optimal Strategy for Supplier Selection in a Global Supply Chain Using Machine Learning Technique

This paper proposes an optimization strategy for the best selection process of suppliers. Based on recent literature reviews, the paper assumes a selection of commonly used variables for selecting suppliers and using logistic regression algorithm technique to build a model of optimization that learns from customer requirements and supplier data and then makes predictions and recommendations for best suppliers. The supplier selection process can quickly at times turn into a complex task for decision-makers to deal with the growing number of suppliers. But logistics regression technique makes the process easier in the ability to efficiently fetch customer requirements with the entire supplier base list by predicting a list of potential suppliers meeting the actual requirements. The selected suppliers make up the recommendation list for the best suppliers for the requirements. And finally, graphical representations are given to showcase the framework analysis, variable selection, and other illustrations about the model analysis.

Enhancing Algal Yield and Nutrient Removal from Anaerobic Digestion Piggery Effluent by an Integrated Process-Optimization Strategy of Fungal Decolorization and Microalgae Cultivation

The dark brown anaerobic digestion piggery effluent (ADPE) with a large amount of ammonium generally needs high dilution before microalgae cultivation due to its inhibiting effects on algal growth. Due to the strong decolorization of fungi by degrading organic compounds in wastewater, the process-optimization integrated strategy of fungal decolorization of ADPE and subsequent microalgae cultivation with ammonium-tolerant strain may be a more reliable procedure to reduce the dilution ratio and enhance algal biomass production, and nutrient removal from ADPE. This study determined a suitable fungal strain for ADPE decolorization, which was isolated and screened from a local biogas plant, and identified using 26s rRNA gene sequence analysis. Subsequently, ADPE was pretreated by fungal decolorization to make low-diluted ADPE suitable for the algal growth, and conditions of microalgae cultivation were optimized to achieve maximum algal yield and nutrient removal from the pretreated ADPE. The results showed one promising locally isolated fungal strain, Nanchang University-27, which was selected out of three candidates and identified as Lichtheimia ornata, presenting a high decolorization to ADPE through fungal pretreatment. Five-fold low-diluted ADPE pretreated by L. ornata was the most suitable medium for the algal growth at an initial concentration of ammonium nitrogen of 380 mg L−1 in all dilution treatments. Initial optical density of 0.3 and pH of 9.0 were optimal culture conditions for the algal strain to provide the maximum algal yield (optical density = 2.1) and nutrient removal (88%, 58%, 65%, and 77% for the removal rates of ammonium nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand, respectively) from the pretreated ADPE. This study demonstrated that fungal decolorization and subsequent microalgae cultivation could be a promising approach to algal biomass production and nutrient removal from ADPE.

Enhanced extracellular β-mannanase production by overexpressing PrsA lipoprotein in Bacillus subtilis and optimizing culture conditions.

In this study, first, β-mannanase gene man derived from Bacillus amyloliquefaciens CGMCC1.857 was cloned and expressed in Bacillus subtilis 168 to generate B. subtilis M1. However, the extracellular β-mannanase activity of B. subtilis M1 was not very high. To further increase extracellular β-mannanase extracytoplasmic molecular chaperone, PrsA lipoprotein was tandem expressed with man gene in B. subtilis 168 to yield B. subtilis M2. The secretion of β-mannanase of B. subtilis M2 was enhanced by 15.4%, compared with the control B. subtilis M1. Subsequently, process optimization strategies were also developed to enhance β-mannanase production by B. subtilis 168 M2. It was noted that the optimal temperature for β-mannanase production (25°C) was different from the optimal growth temperature (37°C) for B. subtilis. Based on these findings, a two-stage temperature control strategy was proposed where the bacterial culture was maintained at 37°C for the first 12 h to obtain a high rate of cell growth, followed by lowering the temperature to 25°C to enhance β-mannanase production. Using this strategy, the extracellular β-mannanase activity reached 5016 ± 167 U/ml at about 36 h, which was 19.1% greater than the best result obtained using a constant temperature (25°C). The result of this study showed that PrsA lipoprotein overexpression and two-stage temperature control strategy were more efficient for β-mannanase fermentation in B. subtilis.

Dynamic growth/etching model for the synthesis of two-dimensional transition metal dichalcogenides via chemical vapour deposition

The preparation of two-dimensional transition metal dichalcogenides on an industrially relevant scale will rely heavily on bottom-up methods such as chemical vapour deposition. In order to obtain sufficiently large quantities of high-quality material, a knowledge-based optimization strategy for the synthesis process must be developed. A major problem that has not yet been considered is the degradation of materials by etching during synthesis due to the high growth temperatures. To address this problem, we introduce a mathematical model that accounts for both growth and, for the first time, etching to describe the synthesis of two-dimensional transition metal dichalcogenides. We consider several experimental observations that lead to a differential equation based on several terms corresponding to different supply mechanisms, describing the time-dependent change in flake size. By solving this equation and fitting two independently obtained experimental data sets, we find that the flake area is the leading term in our model. We show that the differential equation can be solved analytically when only this term is considered, and that this solution provides a general description of complex growth and shrinkage phenomena. Physically, the dominance suggests that the supply of material via the flake itself contributes most to its net growth. This finding also implies a predominant interplay between insertion and release of atoms and their motion in the form of a highly dynamic process within the flake. In contrast to previous assumptions, we show that the flake edges do not play an important role in the actual size change of the two-dimensional transition metal dichalcogenide flakes during chemical vapour deposition.