Laboratory-scale Reactor Research Articles

Unlocking higher methane yields and digestate nitrogen availability in soil through thermal treatment of feedstocks in a two-step anaerobic digestion

BackgroundThere is an increasing interest in using lignocellulosic feedstocks for biogas production. Treatment of these feedstocks prior to anaerobic digestion (AD) can enhance their accessibility to microorganisms involved in the process. To improve the digestion of recalcitrant feedstocks and boost biogas yields, many biogas plants now employ two-step AD systems, extending substrate residence times. However, the combined effect of feedstock treatment and two-step AD on methane yield and fertiliser value of digestates are underexplored. This study, therefore, evaluated the effectiveness of thermal treatment (TT) of pre-digested agricultural feedstocks before a secondary AD step on the carbon (C) and nitrogen (N) dynamics of digestates following application to soil. It also investigated the effects of TT on methane yields. Pre-digested feedstock (PDF) was treated at three different temperatures (70 °C, 120 °C and 180 °C) for 60 min, followed by parallel secondary AD steps using lab-scale continuous stirred-tank reactors (CSTR) and a batch test. Thermally treated feedstocks with and without a secondary AD step were applied to soil to study C and N dynamics and turnover for 2 months.ResultsTT at 180 °C increased ultimate CH4 yields by 7.2%; however, it decreased the net mineral N release in soil from 42 to 34% (of N input). Adding a secondary AD step increased the net mineral N release in soil from an average of 39% to 47% (of N input), with the effect of TT levelling off. Moreover, the secondary AD step significantly reduced C mineralisation rates from an average of 37% to 26% (of C applied).ConclusionsOverall, TT at 120–180 °C can improve biogas yields of recalcitrant feedstocks, but it may lead to the formation of refractory nitrogen compounds resistant to further degradation during AD, potentially resulting in a lower N fertiliser value of digestates.Graphical

Catalytic Oxidation of Kraft Lignin in a Trickle-bed Continuous Reactor.

For the first time, the catalytic oxidation of Kraft lignin over a solid heterogeneous catalyst was studied in a continuous lab-scale trickle-bed reactor. This catalytic process is able to depolymerize Kraft lignin and produce phenolic compounds of interest such as vanillin. The impact of operating conditions such as temperature, residence time, contact time, catalyst loading and lignin concentration was evaluated. The formation of vanillin, the main phenolic compound detected in reaction products, was favored at medium temperature (200°C), short contact time (< 1 gcat.min.gfeed-1), high catalyst loading (32 g) and low lignin concentration (5 g.L-1). The vanillin productivity is 30 times higher in a continuous fixed bed reactor than in a batch reactor.

Response of Metabolic Gene Panel to Organic Loading Stress in Propionate-Degrading Methanogenic Anaerobic Digesters

Propionate, a critical intermediate in anaerobic digestion, and its syntrophic removal, is sensitive to stress. To our knowledge, this study investigates for the first time the response of a metabolic gene panel to organic loading rate (OLR) stress in propionate-degrading methanogenic consortia in lab-scale upflow anaerobic sludge blanket (UASB) reactors. The experimental phases included stabilisation (1.4–2.8 g COD/L/day), electroactive enrichment, OLR shock (6 g COD/L/day), and early recovery. Quantitative PCR was used to assess the abundance of key functional genes (16SrRNA, mcrA, pilA, and hgtR). During stabilisation, ~200 mLCH₄/h was produced, the mcrA/16SrRNA ratio was 0.78–2.64, and pilA and hgtR abundances were 1.29–2.27 × 105 and 2.12–4.37 × 104 copies/gVS. Following the OLR shock, methane production ceased entirely, accompanied by a sharp decline in the mcrA/16S ratio (0.08–0.24) and significant reductions in pilA (1.43-log) and hgtR (1.34-log) abundance. Partial recovery of pilA and hgtR abundance (1.19 × 105 and 8.57 × 104) was observed in the control reactor after the early recovery phase. The results highlight the utility of mcrA, 16SrRNA, pilA, and associated ratios, as reliable indicators of OLR stress in lab-scale UASB reactors. This study advances the understanding of molecular stress responses in propionate-degrading methanogenic consortia, focusing on direct interspecies electron transfer in process stability and recovery.

Impact of trace elements (total and labile fraction) on the anaerobic digestion activity and microbial community structure

Trace elements (TEs) in anaerobic digestion (AD) are known to be essential for optimal biogas production, but inhibitive in excessive concentrations. However, the mechanisms of inhibition are not fully understood. The effects of the addition essential TEs (Co, Cu and Ni) and a non-essential TE (Cd) on the microbial community structure of AD were studied in lab-scale reactors, using total TE concentrations that ranged from 0 to 100 μM. Reactor performance was assessed by monitoring biogas production. The labile fraction of TEs (the most bioaccessible species) was determined by diffusive gradients in thin-films technique. Prokaryotic community composition was characterized through high throughput sequencing (HTS) targeting archaea and bacteria and qPCR to evaluate changes in methanogens and metal resistance genes. Only a minor fraction of added TEs was labile and it decreased over time, with Ni being the most labile. Although only a minor fraction of spiked concentration was labile, all TEs inhibited biogas production at the highest spiking concentration (100 μM), with higher inhibition observed for Cd and Ni. HTS and qPCR revealed changes, particularly in archaea, with reduced relative abundance at higher TE concentrations. Shifts in prokaryotic communities suggest alterations in AD metabolic pathways. High inhibition of biogas was linked to reduced diversity, dominance of the bacterial genus Klebsiella and changes in the ratio acetoclastic / hydrogenotrophic methanogens. This study addresses a research gap in understanding how TEs inhibit AD, and provides a strategy to improve TE dosing by monitoring the labile fraction of TEs to avoid overdosing.

The Conversion of Ethanol to Syngas by Partial Oxidation in a Non-Premixed Moving Bed Reactor

An experimental investigation into the conversion of ethanol to syngas by partial oxidation in a non-premixed counterflow moving bed filtration combustion reactor was carried out. Regimes of conversion depending on the mass flow rates of fuel and air (separate feeding), as well as a granular solid heat carrier, were studied. Depending on the mass flow rate of the heat carrier, two combustion modes were realized—reaction trailing and intermediate—with different temperature patterns in the gas preheating, combustion, and cooling zones along the reactor. The product gas composition is far from the predictions of the equilibrium model; it contains substation fractions of methane and ethylene. Combustion temperature and conversion are limited by the relatively high level of heat loss from the laboratory-scale reactor. The effect of the heat loss can be reduced by enhancing the absolute flow rate of the reactants.

Thermal coupling study during the co-processing of coal and biomass in the lab-scale adiabatic reactor

A lab-scale adiabatic reactor has been self-made to characterize the coupled properties of heat and reactions during the co-thermal-processing of coal and biomass with steam or steam/O2 gasification agents. Results showed that the synergistic effects caused by heat transfer between corncob and coal at different mixing ratios were heavily determined by coal rank and gasification agent. During steam co-processing, the heat transfer from corncob char to adjacent bituminous coal char promoted the water-gas reaction on coal char and contributed to synergistic effects; the heat transfer from anthracite char to adjacent corncob char reduced the kinetic rate of the water-gas reaction on coal char and contributed to inhibitory effects, and the inhibitory effect caused by heat transfer was greater than the promotion effects of biomass mass transfer. The introduction of O2 diminished the impact of inter-particle heat transfer and altered the intensity of synergy, decreasing the values of synergy factor of bituminous coal/corncob blends by 17% and increasing the value of synergy factor of anthracite/corncob blends by 142.5%. This study provides sufficient support for the process conditions selection for the production of syngas with specific H2/CO molar ratios and the desired level of gasification performance.

Numerical Analysis of Spatial Distribution of Carbon in Methane Dry Reforming over Supported Nickel Catalyst in a Packed Bed Reactor

This study investigates carbon deposition during methane dry reforming over a nickel-based catalyst supported on alumina in a laboratory-scale fixed-bed reactor. Approximately 23.75 grams of catalyst were used, and simulations were performed using COMSOL 6.2 software. The reactor was simulated at isothermal wall conditions at four temperatures (650°C, 750°C, 850°C, and 950°C), with an equimolar CH₄ to CO₂ ratio in the feed. The results showed that while localized carbon deposition density increased with temperature, likely due to a higher local methane decomposition rate, the total amount of carbon deposited was inversely proportional to temperature. This suggests enhanced carbon gasification at higher temperatures. The total carbon deposited was estimated to be around 18 grams after 10,000 seconds of Time on Stream (TOS) at 650°C. As the temperature increased, the total carbon deposition decreased, although this reduction became negligible beyond 850°C. Furthermore, the hydrogen to carbon monoxide (H₂/CO) molar ratio peaked at over 1.1 at 650°C, dropped to approximately 0.76 at 750°C, and then rose back to 0.97 at 950°C. Steady-state operation was not achieved due to continuous carbon deposition and accumulation in the reactor. However, in the absence of carbon deposition, steady-state was reached around 100 seconds after the feed entered, at a velocity of 3 cm/s. Methane conversion reached 97% at 950°C.

Microbial community evolution in a lab-scale reactor operated to obtain biomass for biochemical methane potential assays

Biochemical methane potential (BMP) test is an important tool to evaluate the methane production biodegradability and toxicity of different wastes or wastewaters. This is a key parameter for assessing design and feasibility issues in the full-scale implementation of anaerobic digestion processes. A standardized and storable inoculum is the key to obtain reproducible results. In Uruguay, a local enterprise dedicated to design and install anaerobic digesters operated a lab-scale bioreactor as a source of biomass for BMP tests, using a protocol previously described. This reactor was controlled and fed with a mixture of varied organic compounds (lipids, cellulolytic wastes, proteins). Biomass was reintroduced into the reactor after BMP assays to maintain a constant volume and biomass concentration. The aim of this work was to evaluate how the microbial community evolved during this operation and the effect of storing biomass in the refrigerator. The composition of the microbial communities was analyzed by 16S rRNA amplicon sequencing using primers for Bacteria and Archaea. The methanogenic activity was determined, and the methanogens were quantified by mcrA qPCR. One sample was stored for a 5-month period in the refrigerator (4 °C); the activity and the microbial community composition were analyzed before and after storage. Results showed that applying the reported methodology, a reliable methanogenic sludge with an acceptable SMA was obtained even though the reactor suffered biomass alterations along the evaluated period. Refrigerating the acclimatized biomass for 5 months did not affect its activity nor its microbial composition according to the 16S rRNA gene sequence analysis, even though changes in the mcrA abundance were observed.Key points• The applied methodology was successful to obtain biomass suitable to perform BMP assays.• The microbial community was resilient to external biomass addition.• Biomass storage at 4 °C for 5 months did not alter the methanogenic activity.Graphical

Novel sparging strategies to enhance dissolved carbon dioxide stripping in industrial scale stirred tank reactors

Aerated stirred tank reactors are widely used in bio-process engineering and pharmaceutical industries. To supply the organisms with oxygen and control the pH value, oxygen is transferred from air bubbles into the liquid phase, and, at the same time, carbon dioxide is stripped from the liquid phase with the same gas bubbles. The volumetric mass transfer coefficients for oxygen and carbon dioxide are, therefore, of crucial importance for the design and scale-up of aerated stirred tank reactors. In this experimental work, the volumetric mass transfer coefficients for oxygen and carbon dioxide are investigated simultaneously to study their mutual influence. The mass transfer performance for oxygen and carbon dioxide is conducted in stirred tank reactors on the 3 L laboratory scale, 30 L pilot scale, and 15,000 L production scale. First, the influence of dissolved carbon dioxide on the oxygen mass transfer performance is investigated in a 30 L pilot scale stirred tank reactor. The results show that the volumetric mass transfer coefficient of oxygen is not affected by the concentration of dissolved carbon dioxide, but the total mass flux of oxygen decreases with increasing carbon dioxide concentration due to the decreasing partial pressure difference. With rising gassing rate and volumetric power input, both mass transfer coefficients for oxygen and carbon dioxide show the same increasing trend. Although this trend can also be observed when scaling down to the 3 L laboratory scale reactor, a significantly different effect must be considered for the scale-up to the 15,000 L industrial scale reactor. The limited absorption capacity for carbon dioxide of the gas bubbles during the long residence time in the industrial scale reactor is noticeable here, which is why the specific interfacial area is of negligible importance. This effect is used to develop a method for independent control of oxygen and carbon dioxide mass transfer performance on an industrial scale and to increase the mass transfer performance for carbon dioxide by up to 25%.

Entrained-flow gasification characteristics of plastic waste pyrolysis oil

Plastic waste (PW) pyrolysis is a promising method in chemical recycling technology; however, PW pyrolysis oil cannot be used directly because of its high contaminant content. Entrained-flow gasification (EFG) is a suitable method for removing contaminants from pyrolysis oil and enhancing the conversion compared with fixed bed or fluidized bed gasification. We examined the basic characteristics of PW pyrolysis oil through EFG with the variation of O2/fuel ratios from 0.6 to 1.4 and steam/fuel ratio from 0.4 to 0.7 at 600–900°C in a lab-scale reactor. The H2 composition and Cold Gas Efficiency (CGE) showed the highest when the O2/fuel ratio was 0.8. The Carbon Conversion Efficiency (CCE) showed the highest values when the ratio was 1.4. C2-C3 gases tended to decrease at higher temperatures because of the thermal cracking of hydrocarbons. In the experiments with the variation of steam/fuel ratio, CO2 concentration decreased with increasing temperature from 600 to 800°C because of the reverse water-gas-shift reaction. The residence time was calculated to review the reaction conditions and was found to be 4.2–7.3 seconds. The experimental data from a lab-scale EFG can serve as fundamental data for the scale-up of integrated pyrolysis and gasification systems.

Draft genome sequence of Ferrimicrobium acidiphilum strain YE2023, isolated from a pulp of bioleach reactor.

We report the draft genome sequence of Ferrimicrobium acidiphilum strain YE2023, isolated from a pulp of a laboratory-scale bioleach reactor. The genome is 3,221,954 Mbp long with a guanine-cytosine content of 58.16%.

Population Dynamics and Key Influencing Factors of Microthrix parvicella Caused Sludge Bulking

Given the frequent occurrence of the sludge bulking phenomena caused by Microthrix parvicella （M. parvicella） overgrowth during the low-temperature period in the full-scale municipal wastewater treatment plant, the filamentous bacteria dynamics of the M. parvicella population were systematically investigated during the completed bulking period using the multi-dimensional integrated filamentous monitoring method combined with the molecular quantitative method. A lab-scale reactor was constructed and successfully simulated bulking phenomena under the low-temperature condition. The trend of dominant filamentous bacterial shift and the main influencing parameters were estimated during the bulking period, to verify the key factors for filament growth and extinction of the sludge bulking phenomenon in the full-scale plant. The results showed that the bulking-caused M. parvicella was characterized by significant changes in the diversity of filamentous bacteria, and the dominant filamentous bacterial succession was reflected in the competition between the skeleton filamentous bacteria Type 0092 and Type 0041 and M. parvicella. At lower temperatures, sludge loading was an important controlling factor for the competitive growth advantage of M. parvicella： when the temperature was lower （approximately 15°C）, low sludge loading [0.05 kg·（kg·d）-1] could lead to the stabilized elevation of M. parvicella, and with the loading increased to 0.1 kg·（kg·d）-1 or more, M. parvicella populations showed a targeted decline despite the presence of the low temperature factor.

Chemical looping gasification of vinegar residue with enhanced LD slag composite Ca-Fe oxygen carrier for syngas production

Biomass chemical looping gasification (BCLG) is an emerging technology that enables waste co-processing into clean energy. A laboratory-scale vertical fixed-bed reactor was used to conduct CLG experiments with vinegar residue (VR) as a biomass fuel, and the effect of enhanced LD slag composite Ca-Fe material as an oxygen carrier (OC) on the production of syngas from BCLG was investigated. This study analyzed the influence of LD slag proportion, kinds of OC, and operational conditions (temperature, oxygen carrier/biomass (OC/B) ratio, and steam/biomass (S/B) ratio) on gasification performance. Results indicate that the syngas yield under the gasification operating conditions at about 850 °C, OC/B = 1, and S/B = 2.5 obtained 1.36 Nm3/kg, the CCE and CGE achieved about 80.82 % and 98.16 %, respectively, and the H2/CO molar ratio was as high as 2.57. The OCs multi-redox cycle test revealed that after undergoing 10 redox cycles under the conditions mentioned above, the gas yield, CCE, and CGE were reduced to varying extents, but still maintained impressive reactivity. The mechanism analysis showed that the performance degradation of the LD slag composite Ca-Fe OC during the multi-cycle process was related to its agglomeration due to thermal stress and steam. This study provides a new perspective on the synthesis of low-cost OCs and the co-utilization of solid wastes.

Two-phase flow effect on methane conversion in pyrolysis reactors embedding molten salts or metals

In this work, we numerically investigate the impact of flowrate, sparger and reactor geometry on methane conversion in lab-scale cylindrical pyrolysis reactors embedding molten salts or metals. A multiscale approach is enforced, where a diffusion-reaction model yielding the conversion vs time within a single rising bubble is combined with the average residence time of gas bubbles obtained through the two-phase turbulent bubbly flow model. We find that the relative size of the sparger and the height-to-diameter ratio of the molten medium are key parameters for controlling the average residence time of the bubbles, which always results lower than that predicted by the terminal velocity of a single bubble rising in an overall static melt. The highest relative discrepancy (order 300%) between the single-bubble estimate and the CFD-based residence time is found in the case of molten salts in low-aspect ratio reactors fed by small spargers. The physical mechanism underpinning the influence of geometric parameters on the overall conversion is addressed in detail, together with the impact of two-phase flow effects on the estimation of bubble size in laboratory scale bubble reactors.

CO2-free production of hydrogen via pyrolysis of natural gas: influence of non-methane hydrocarbons on product composition, methane conversion, hydrogen yield, and carbon capture

Methane pyrolysis represents a CO2-free hydrogen production route that enables simultaneous carbon capture. While the majority of previous studies in the field focus on pure CH4 as feed gas stream, commercial processes will typically rely on natural gas as feedstock that contains also non-methane hydrocarbons such as ethane, propane, and n-butane. Therefore, the present study evaluates how CH4 conversion, H2 selectivity, product composition, and solid carbon yield evolve when using either pure CH4 or synthetic natural gas (SNG) as feed gas stream for a thermal pyrolysis process in a lab-scale high-temperature reactor. For this, industrially viable conditions are applied, namely temperatures between 1000 °C and 1600 °C, residence times between 1 s and 7 s, and molar H2 dilution ratios between 1:1 and 4:1. Although the use of SNG results in slightly lower hydrocarbon conversions because the additional components in SNG result in a higher effective H2 dilution ratio compared to a CH4-only feed, the non-methane hydrocarbons in the SNG have a positive effect on both H2 selectivity and solid carbon yield. Taking existing mechanistic understanding into account, these positive effects are attributed to radicals formed from the non-methane hydrocarbons, which facilitate dehydrogenation steps from ethane to ethylene and hereby increase the relative amount of H2 originating from CH4. The introduction of a carbonaceous fixed bed further benefits the performance of the pyrolysis process and ultimately enables to capture more than 98% of carbon in its solid form under industrially viable process conditions.

Urine luck: Environmental assessment of yellow water management in buildings for urban agriculture

The increasing global demand for agricultural production poses challenges to maintain the needs for critical fertilizers such as nitrogen. This study explores the potential of human urine as a source of renewable nitrogen for fertilizer production. Through a life cycle assessment, three different urine management strategies were compared: (S1) an artificial wetland, (S2) an on-site lab-scale aerobic reactor for nitrogen recovery, and (S3) a centralized wastewater treatment plant. While scenario S2 had the highest impacts in 6 out of 8 categories, an advantage in marine eutrophication was identified. S2 showed high energy demand (750 kg MJ-eq) and ecotoxicity (602 kg 1.4-DCB-eq.) mainly due to energy requirements. Nitrogen production exceeded 2.3 times the yearly nitrogen demands of the building tomato production. Upscaling S2 reduces impacts up to 2 times, lowering the payback time from 29 to 13 years. Therefore, implementing large-scale nitrogen recovery systems in cities is encouraged.

Fluidized Bed Reactors for energy recovery from biomass and wastes: a data-driven approach towards the development of digital twins for real time control and monitoring

Abstract The application of machine learning (ML) techniques for the control and development of digital twins for a fluidized bed reactors represents a significant advancement in process engineering. In this study, the integration of data-driven models trained using computational fluid dynamics (CFD) simulations, is explored for developing and optimizing the lab-scale fluidized bed reactor operations. By leveraging the collection of data generated from CFD simulations, data-driven algorithms, based on the Singular Value Decomposition (SVD) and Gaussian processes for regression, are trained to predict the gas-solid flow patterns under different operating condition. The data-driven models presented, serve as efficient reduced order model (ROM) surrogate for computationally expensive CFD simulations, enabling real-time predictions and control strategies for fluidized bed reactors, facilitating continuous monitoring, optimization, and predictive maintenance. Moreover, the ROM can effectively capture the complex relationships within the reactor system, with an overall error &lt; 10% even without precise knowledge of the underlying physical phenomena. The synergistic combination of ML techniques and CFD simulations offers valuable insights into complex multiphase flow phenomena and reactor dynamics, leading to improved process control, energy efficiency, and overall performance of fluidized bed reactors. This approach holds great promise for accelerating innovation and sustainability in chemical and energy industries.

Formate-facilitated recovery of wastewater anammox granular sludge from oxygen inhibition: Effects and mechanisms

Oxygen leakage due to poor reactor sealing or accidental aeration can have detrimental impacts on the performance of wastewater anammox processes. Strategies of restoring functionality of anammox consortia are scarce, and providing appropriate chemical reducing reagents may help reduce oxidative damage. This study characterized the responses of anammox granular sludge (AnGS) to oxygen inhibition, and identified formate as an effective promoter capable of facilitating activity recovery, while other organics (acetate, glucose, methanol) were less effective. Upon 12 h of air exposure (DO: 1.2 ± 0.1 mg/L), the total nitrogen removal efficiency of a lab-scale AnGS reactor decreased from 85.15 % to 45.46 %. Compared with natural recovery (without chemical addition), potassium formate at 10 mg COD/L for 3 days significantly increased the total nitrogen removal efficiency, both in the short-term (66.68 % vs 57.09 %, 3 days post inhibition) and long-term (82.34 % vs 72.88 %, 30 days post inhibition). By examining sludge morphology, metagenome and transcriptome, the following potential mechanisms were proposed: 1) rapidly decreasing intracellular ROS; 2) enhancing nitrite turnover; 3) maintaining granular sludge integrity; 4) facilitating interspecies metabolic interactions. The ability of formate to facilitate sludge recovery from oxygen inhibition also implies its potential in mitigating other oxidative stresses in wastewater anammox reactors.

Effect of High-Rate Aeration in the Electrocoagulation Treatment of Pharmaceutical and Synthetic Textile Industrial Wastewater Effluents

Despite the extensive literature on the effects of implementing aeration in the electrocoagulation (EC) treatment of industrial wastewater, few studies evaluate the performance of this technique at high aeration rates. In this work, we present the outcomes derived from EC treatment of pharmaceutical and synthetic textile wastewater effluents in two lab-scale reactors with and without aeration, each equipped with different electrode combinations of aluminium and iron (Al/Al, Al/Fe, and Fe/Fe). In the non-aerated EC reactor, maximum chemical oxygen demand (COD) reductions of 56% and 80% were achieved for the pharmaceutical and textile effluents, respectively, with up to 100% removal of turbidity and colour with the Al/Al combination. The installation of high-rate aeration to prevent sludge accumulation on the electrode surface markedly reduced residence times and enhanced the COD removal in the pharmaceutical effluent. However, this implementation potentially reduced the process efficiency for thesynthetic textile effluent as prolonged operation led to flocculation breakdown and subsequent re-dissolution of the contaminants in the water.

Application of continuous stirring tank reactor for controllable synthesis of Cu7S4 nanocrystals

As a typical model for a chemical reactor in industry, the continuous stirring tank reactor has been widely used in waste-water treatment, industrial catalysis, and biological fermentation as well as great application prospects in the synthesis of nanomaterials. In this report, a convenient lab-scale continuous stirring tank reactor was assembled and utilized to synthesize Cu7S4 nanocrystals by injecting cupric bromide and sulfur solution in the presence of ascorbic acid and polyethyleneimine at 60 °C. The morphology control of Cu7S4 nanocrystals was accomplished by simply adjusting the agitation speed. Cu7S4 nanofibers with an average diameter of 48 ± 4.42 nm and a length of several micrometers were obtained at 80 rpm. Cu7S4 nanoplates with a thickness of 89 ± 13.56 nm and a plane size of 103 ± 16.47 nm were synthesized at 90 rpm, and the size of the nanoplates was regulated by continuously increasing the agitation speed from 90 rpm to 1000 rpm. Furthermore, the influences of two additional conditions (the mean residence time and the concentration of the feed solution) on the morphology of Cu7S4 nanocrystals, were also investigated. Therefore, these results could facilitate the understanding of the behaviors of CSTR in the synthesis of Cu7S4 nanocrystals and could also provide an important reference for the continuous synthesis of other nanoparticles.