Continuous Flow Conditions Research Articles

Novel oily sludge treatment process: Based on biological leaching

The performance of bioleaching technology was studied for the demulsification, oil content reduction and efficient removal of heavy metals from oily sludge. A method was established for treating oily sludge from an oil refinery. Firstly, bioleaching bacteria were enriched and acclimated. The effects of substrate type (FeSO4·7H2O and Na2S2O3·5H2O), concentration and aeration conditions on treatment performance were investigated, with response surface methodology used to optimize the treatment process. Finally, the effects of operating parameters on heavy metal removal under continuous flow conditions were investigated. Results show that an optimal treatment effect was achieved when 5.00 g/L FeSO4·7H2O and 5.64 g/L Na2S2O3·5H2O were used as substrates and the aeration ratio (air-water ratio) was 14.53 L/L. Under these conditions, the oily sludge reduction rate was 51.76 %, and the oil removal rate was 57.67 %. The removal rates for Pb, Hg and Cu ranged between 40 % and 70 %, with a stable total heavy metal reduction rate of 50 %. These results show that bioleaching technology is feasible for the treatment of oily sludge and heavy metal removal, with good potential for practical application.

An integrated lab-on-a-chip platform for pre-concentration and detection of colorectal cancer exosomes using anti-CD63 aptamer as a recognition element

Colorectal cancer (CC) is one of the common causes of cancer-related deaths around the globe. Identification of a novel biomarker for CC is of paramount importance for early diagnostics and reducing its mortality. Among the most promising biomarker candidates, exosomes hold great potential for cancer diagnosis, management, and treatment. Exosomes are extracellular vesicles secreted from cells and they contribute to the intercellular communication, immune response and the pathogenesis of many diseases including cardiovascular diseases, neurodegenerative diseases, and cancer. Several methods have been developed/utilized for exosome isolation and purification. However, these methods are time-consuming and have low purification efficiency. In this work, we developed the “apta-magnetic biosensor” platform for isolation, purification and detection of exosomes from cell culture. Anti-CD63 aptamer, which is conjugated to the surface of magnetic nanobeads, was used as a recognition element. A dynamic separation system was used which employs a transverse magnetic field along a microfluidic channel. The channel was exposed to an alternate magnetic field which imposes alternate magnetic force onto the magnetic bead-exosome complex. The combination of the fluid flow and magnetic force generates several “alternate trapping and releasing” events under continuous-flow conditions with each event representing a washing cycle. The graphene coated onto the surface of the magnetic nanobeads was used as a quencher for the fluorescently labeled aptamer (OFF state) in the absence of the target. Upon the addition of CD63 target protein, the aptamer dissociates from the graphene and binds to the target hence increasing the fluorescence intensity (ON state). A calibration plot of variable concentrations of exosomes vs fluorescence intensity was obtained and the detection limit was calculated as 1457 particles/mL. The specificity of the sensor was tested using closely associated proteins. The results showed that the aptamagnetic isolation, pre-concentration of exosomes and quantification demonstrate great potential for various clinical applications.

Visible-Light-Induced Cascade Cyclization of 3-(2-(Ethynyl)phenyl)quinazolinones to Phosphorylated Quinolino[2,1-b]quinazolinones.

3-(2-(Ethynyl)phenyl)quinazolinones were designed and synthesized as a class of novel and efficient skeletons for phosphorylation/cyclization reactions. Under visible light irradiation, a series of phosphorylated quinolino[2,1-b]quinazolinones (35 examples, up to 87% yield) were first synthesized from 3-(2-(ethynyl)phenyl)quinazolinones and diarylphosphine oxides by using 4CzIPN as a photocatalyst under mild conditions. This reaction was also applicable under sunlight irradiation. Moreover, the reaction efficiency could be significantly improved under continuous-flow conditions.

Selective hydrogenation of furfural using TiO2-Fe2O3/C from Ti-Fe-MOFs as sacrificial template: Microwave vs Continuous flow experiments

A TiO2-Fe2O3/C catalyst was synthesized utilizing Metal-Organic-Frameworks (MOFs) as a sacrificial template prepared by the solvothermal method and pyrolyzed in an inert nitrogen (N2) atmosphere. This material was characterized using various techniques, including X-ray diffraction, N2 porosimetry, and X-ray photoelectron spectroscopy; these techniques confirmed its transformation into TiO2-Fe2O3/C. TiO2-Fe2O3/C was employed in the hydrogenation of furfural using isopropanol and formic acid as hydrogen donors and solvents to produce furfuryl alcohol. This reaction has been studied under microwave irradiation and continuous flow conditions. Results obtained (70% conversion and 100% selectivity in a continuous flow reactor) represent a significant advance in the design of selective biomass-derived conversion strategies, taking into account the frequently uncontrolled reactivities of such molecules that result in several reaction byproducts. This provides the opportunity to continue discovering selective processes with promising applications for the advancement of green chemistry.

Examining fluid flow and solute transport through intersected rock fractures with stress-induced void heterogeneity

In this study, fluid flow and solute transport processes are assessed in three-dimensional (3-D) intersected rock fractures with stressed-induced void heterogeneity. Specifically, flow behaviors are examined in the intersected fractures with flow directions perpendicular and parallel to the intersection orientation. Then, transport behaviors are analyzed considering the classic continuous flow condition, and a new mixing ratio is proposed to better quantify the mixing process. Last, applicability of two-dimensional (2-D) representations of rock fractures for analyzing flow and transport is assessed by result comparison with the 3-D cases. The results show that fracture intersecting can enhance transmissivity of the single fracture as a result of locally enlarged aperture at the intersection and generation of more conducive flow paths, with latter being the main mechanism especially when under high stress. Moreover, it is found that transport behaviors can differ evidently in intersected fractures due to stress-induced void heterogeneity and anisotropy. For intersected fractures with obvious directional void heterogeneity, solute transport can become more nonuniform with occurrence of forced mixing caused by scattered flow channeling from the intersection. Compared to the actual 3-D cases, adopting the 2-D representations is generally found to produce transmissivity overestimation and mixing underestimation, due to inaccurate quantification of the 3-D flow and transport features. Considering the realistic stress-induced void heterogeneity for rock fractures, the findings of this work can further broaden our understanding of the flow and transport processes in underground fractured rock formations.

Visible-Light-Driven α-Hydroxymethylation of Ketones in a Continuous-Flow Microreactor

AbstractA visible-light-driven α-hydroxymethylation of ketones to generate the corresponding alcohols was achieved under continuous-flow conditions. MeOH was used as a green and renewable C1 source and solvent to enable the α-C(sp3)–H functionalization of ketones under irradiation by white LEDs. A flow microreactor operated under optimized conditions permitted this oxidation to proceed with a higher efficiency and a shortened reaction time of 215 minutes, which was improved ten times compared with the batch parallel reaction (36 h). Mechanism studies indicate the reaction proceeds by a radical pathway.

Development of Silicon Carbide-Supported Palladium Catalysts and Their Application as Semihydrogenation Catalysts for Alkynes under Batch- and Continuous-Flow Conditions

Silicon carbide (SiC)-supported palladium (Pd) catalysts [3% Pd/SiC and a 3% Pd-diethylenetriamine (DETA)/SiC complex] for chemoselective hydrogenation under batch- and continuous-flow conditions were developed. The alkyne, alkene, azide, nitro, and benzyloxycarbonyl-protected aromatic amine (N-Cbz) functionalities were chemoselectively reduced in the presence of 3% Pd/SiC. By contrast, benzyl ether, alkyl N-Cbz, epoxide, aromatic chloride, aromatic ketone, and tert-butyldimethylsilyl ether were tolerant to the 3% Pd/SiC-catalyzed hydrogenation. The combined use of 3% Pd/SiC and DETA demonstrated excellent chemoselectivity toward the semihydrogenation of various mono- and disubstituted alkynes under batch- and continuous-flow conditions. Furthermore, compared with the separate use of 3% Pd/SiC and DETA, the newly developed 3% Pd(DETA)/SiC-packed in a cartridge showed higher chemoselectivity toward the continuous-flow semihydrogenation of alkyne over 24 h.

Cover Feature: Continuous Flow Single‐Atom Catalysis: A Viable Organic Process Technology? (ChemCatChem 21/2022)

The Cover Feature shows a flow reactor employing a single-atom catalyst schematically represented. In their Perspective, M. Pagliaro, C. Della Pina and R. Ciriminna try to answer the question: “Is single-atom catalysis under continuous flow conditions a technically and economically viable organic process technology?” Early results actually suggest valuable insight en route to its industrial uptake in the production of fine and specialty chemicals. Reviewing selected examples of the first utilization of single-atom catalysts (SACs) under continuous-flow conditions, the authors provide evidence that SACs are not different from state-of-the-art supported metal nanoparticle catalysts in affording significantly higher TOFs than the same catalysts in batch reactor conversions. Furthermore, continuous flow conditions enhance the lot-to-lot consistency and dramatically lowers production time thug improving customer delivery. More information can be found in the Perspective by M. Pagliaro, C. Della Pina and R. Ciriminna.

A Bipolar Membrane-Integrated Electrochlorination Process for Highly Efficient Ammonium Removal in Mature Landfill Leachate: The Importance of ClO• Generation.

Electrochemical oxidation has been demonstrated to be a useful method for removing biorefractory organic pollutants in mature landfill leachate but suffers from low efficiency in eliminating ammonium because of its resistance to being oxidized by HO• or free chlorine (FC) at decreased pH. Here, we propose a new bipolar membrane-electrochlorination (BPM-EC) process to address this issue. We found that the BPM-EC system was significantly superior to both the undivided and divided reactors with monopolar membranes in terms of elevated rate of ammonium removal, attenuated generation of byproducts (e.g., nitrate and chloramines), increased Faradaic efficiency, and decreased energy consumption. Mechanistic studies revealed that the integration of BPM was helpful in creating alkaline environments in the vicinity of the anode, which facilitated production of surface-bound HO• and FC and eventually promoted in situ generation of ClO•, a crucial reactive species mainly responsible for accelerating ammonium oxidation and selective transformation to nitrogen. The efficacy of BPM-EC in treating landfill leachates with different ammonium concentrations was verified under batch and continuous-flow conditions. A kinetic model that incorporates the key parameters was developed, which can successfully predict the optimal number of BPM-EC reactors (e.g., 2 and 5 for leachates containing 589.4 ± 5.5 and 1258.1 ± 9.6 mg L-1 NH4+-N, respectively) necessary for complete removal of ammonium. These findings reveal that the BPM-EC process shows promise in treating ammonium-containing wastewater, with advantages that include effectiveness, adaptability, and flexibility.

Electrochemical Regioselective Sulfenylation of 2H-Indazoles with Thiols in Batch and Continuous Flow.

A novel electrochemical cross-dehydrogenative C-S bond coupling of aryl thiols with 2H-indazole is reported. Thiol-functionalized 2H-indazoles were synthesized under catalyst-, oxidant-, and metal-free conditions with innocuous hydrogen as the sole byproduct at ambient temperature. Furthermore, continuous electrochemical flow conditions using a graphite/Ni flow cell were used to obtained 3-(arylthio)-2H-indazole compounds on a gram scale within the residence time of 39 min. Detailed mechanistic studies including control experiments and cyclic voltammetry are provided to support the radical-radical cross-coupling pathway.

Continuous Flow Single‐Atom Catalysis: A Viable Organic Process Technology?**

AbstractHeterogeneous catalysis under continuous flow conditions is increasingly used by the chemical industry to synthesize fine chemicals. Is single‐atom catalysis under flow a technically and economically viable organic process technology? Early results suggest valuable insight en route to the industrial uptake of single‐atom catalysis in the production of fine and specialty chemicals.

Simple Enzyme Immobilization for Flow Chemistry? An Assessment of Available Strategies for an Acetaldehyde-Dependent Aldolase.

Enzyme immobilization is a technology that enables (bio-)catalysts to be applied in continuous-flow systems. However, there is a plethora of immobilization methods available with individual advantages and disadvantages. Here, we assessed the influence of simple and readily available methods with respect to the performance of 2-deoxy-d-ribose-5-phosphate aldolase (DERA) in continuous-flow conditions. The investigated immobilization strategies cover the unspecific attachment to carriers via epoxides, affinity-based attachment via metal ion affinity, StrepTag™-StrepTactin™ interaction as well as the covalent affinity attachment of an enzyme to a matrix tethered by the HaloTag®. The metal-ion-affinity-based approach outperformed the other methods in terms of immobilized activity and stability under applied conditions. As most enzymes examined today already have a HisTag for purification purposes, effective immobilization may be applied, as simple as a standard purification, if needed.

Discovering of the photocatalytic performance of BiFeO3/BNQDs immobilized polyester filters for efficient continuous-flow elimination of recalcitrant antibiotic via PMS activated process

Finding effective and practical elimination systems for harmful contaminants is a challenging issue and thereby, construction of scalable materials has gained attention in advanced oxidation processes. Herein, BiFeO3 (BFO) perovskites were first incorporated with boron nitride quantum dots (BNQDs) via impregnation technique and then the BFO/BNQDs catalysts were immobilized on commercial polyester (PE) filters via dip-coating method (BFO/BNQDs@PE). It was aimed to enhance the photocatalytic performance of perovskite catalyst via incorporation of BNQDs and restrict the disadvantages of powder form of catalysts via immobilization on filter. SEM images revealed that the BFO/BNQDs particles were uniformly coated on the polyester fiber. The XRD pattern demonstrated that the immobilization process did not alter the crystal structure of perovskite. The catalytic performance of the system was investigated via degradation of tetracycline-hydrochloride (TC-HCl) in batch as well as continuous flow conditions and the dual-effect catalytic system was generated by introducing peroxymonosulfate (PMS) agent to the antibiotic solution. The TC-HCl degradation efficiencies under PMS-activated system were calculated as 49.3% and 70% for BFO@PE and BFO/BNQDs@PE, respectively. The high-efficiency removal was assigned to the hindered recombination rate owing to electron capturing ability of PMS and quantum confinement effect of BNQDs. In addition, the immobilization of BFO/BNQDs particles on PE filter enabled more active surface sites for the target TC-HCl molecules, resulting enhanced photodegradation efficiency. The photocatalytic degradation mechanism was explained in detail and the reusability of catalytic filters was investigated. Under flow conditions, 91.3% removal was still achieved by BFO/BNQDs@PE catalytic filter until 7 h of visible light irradiation, verifying successful immobilization of BFO/BNQDs particles as well as its high reusability. This study contributes to the hybridization of quantum dots with scalable materials for treatment of recalcitrant pollutants with industrial interest.

Visible light-driven complete photocatalytic oxidation of organic dye by plasmonic Au-TiO2 nanocatalyst under batch and continuous flow condition

The present work demonstrates a facile hydrothermal synthesis of Plasmonic Au–TiO2 nanocatalyst followed by its successful application for complete photocatalytic dye degradation (oxidation) in batch and continuous flow process under natural sunlight as well as visible and UV light. The Au-TiO2 nanocatalyst was synthesized by a hydrothermal method at basic pH conditions. It was meticulously analyzed by a variety of spectroscopic (UV-Vis, Raman, FTIR, PL, Powder XRD, ED-XRF, XPS), microscopic (FE-SEM with elemental mapping, TEM), and thermal (DSC) techniques. The characterization results showed that monodisperse Plasmonic Au(0) nanoparticles with a mean diameter of 12 ± 1 nm are homogeneously deposited on Anatase TiO2 crystals. The nanocatalyst showed complete photocatalytic degradation of various dye compounds (Eosin Yellowish, Indigo Carmine, Methyl Orange, Methylene Blue, and Rhodamine B) under visible light or sunlight as confirmed through UV-Vis spectra, mass spectral study, and TOC analysis of dye solutions. A continuous flow process using a specially designed photoreactor was accomplished with a long catalyst lifespan, easy processibility, and low cost. Easy synthesis of the catalyst, its very detailed characterization, and its efficient catalytic studies to completely degrade various dye molecules under visible light source in the absence of any added oxidizer (O2, H2O2, KMnO4, Organic peroxides) and the demonstration of continuous flow process are significant highlights of the present work. A plausible mechanistic pathway is also presented in line with the previous literature reports and presently observed phenomenon.

Immobilization of Functionalized epi-Cinchonine Organocatalysts on Controlled Porous Glass Beads: Applications in Batch and ­Continuous Flow

AbstractA well-known squaramide-cinchonine organocatalyst was immobilized in a controlled way onto three types of commercial porous glass beads EziG™ (EziG OPAL, EziG Amber, and EziG Coral) and applied in asymmetric Michael reactions. The performance of the immobilized catalysts was evaluated under batch and continuous-flow conditions, showing promising results in both approaches. In batch reactions, 0.8 and 1.6 mol% of the immobilized cinchonine-squaramide provided the products with excellent yields (up to 99%) and enantioselectivities (up to 99% ee). These excellent results were also verified in the case of continuous-flow reactions, where also 0.8 and 1.6 mol% of the catalyst immobilized onto the glass beads afforded the product with extraordinary yields (up to 99%) and very high enantioselectivities (up to 97% ee). The immobilized catalysts could be recycled (up to seven cycles) using both approaches.

A Solid Alkylation: Highly Recyclable, Flow Chemistry‐Ready, Resin‐Supported Thioimidazoliums Alkylate Sulfur‐Centered Nucleophiles

AbstractA series of readily regenerable thioimidazolium‐based ionic liquids, which can transfer alkyl groups to nucleophiles, are immobilized on crosslinked polystyrene beads. Different alkyl groups can be loaded onto the resin, highlighting the tunability of the material. The efficiency of these materials is demonstrated by their screening against a series of nucleophiles, showing a particular preference for thiols. Finally, these materials were evaluated for use under continuous flow conditions. The flexibility, ease of use, safety, and recyclability of these alkylating resins shows promise for their use in large scale and automated applications.

Optimization of reaction conditions for hydrodeoxygenation of bio-glycerol towards green propylene over molybdenum-based catalyst

The present work refers to the one–step gas phase complete glycerol deoxygenation to propylene, under continuous flow conditions. The effect of the reaction parameters (temperature, hydrogen partial pressure P°H2, hydrogen to glycerol partial pressure ratio P°H2/ P°glyc, LHSV and W/F) was investigated over an 8.7 wt% molybdenum catalyst supported on black carbon. The main physicochemical properties of the catalyst (surface area, crystal phases, reducibility and thermal stability) in fresh, reduced and used form were determined. The extensive testing of the catalyst under variable reaction conditions proved the high activity of the catalyst in reduced state towards C-O bonds scission and more importantly, the high selectivity towards propylene which in most of the cases was the only carbon containing product in the gas phase. Partially deoxygenated liquid products were identified, such as 2-propenol, the intermediate for propylene formation along with its isomer propanal, and its hydrogenated form, 1-propanol. Response surface methodology was applied to examine the binary effects of process parameters (P°H2, P°H2/ P°glyc, LHSV and W/F) on the responses (propylene yield, propylene rate and combined yield of propanal and 1-propanol) followed by the optimization of the reaction. The empirical process models developed for each response accurately fitted the experimental data. The validation of the model showed that the experimental data at the proposed optimum reaction conditions were very close with the predicted ones, confirming its adequacy. Under optimum reaction conditions (P°H2 = 30 bar, P°H2/P°glyc = 80, LHSV = 1 h−1, W/F = 422 gcat/molglych, T = 280 °C and Ps =60 bar) glycerol is selectively converted to propylene achieving 71 % propylene yield (2 mmolesC3H6/gcath rate) at compete glycerol conversion.

Visible-Light-Promoted Synthesis of 1,3-Dicarbonyl Sulfoxonium Ylides.

A novel visible-light-promoted coupling of diazoketones with sulfoxonium ylides, employing a violet light-emitting diode, is described under both batch and continuous flow conditions. This transformation permits the direct synthesis of synthetically useful 1,3-dicarbonyl sulfoxonium ylides (33 examples, 21-85% yields), by means of an acylation from the in situ and selective generation of ketenes. The reaction performed under flow conditions proved to be very efficient, providing the 1,3-dicarbonyl sulfoxonium ylides with higher yields and shorter reaction times.

Efficient peroxymonosulfate activation of immobilized Fe–N–C catalyst on ceramsite for the continuous flow removal of phenol

Nowadays, developing environmentally friendly catalysts with both low cost and high efficiency was still a challenge in actual organic wastewater purification. Herein, the Fe–N–C catalyst was successfully immobilized on solid waste derived ceramsite for efficient degradation of phenol under continuous flow conditions by activating peroxymonosulfate (PMS). After the introduction of ceramsite, the microstructure of Fe–N–C catalyst was changed from granular structure to worm-like structure, promoting the dispersion of the nanoscale catalyst and providing more reactive sites. Therefore, the phenol removal rate and mineralization rate of the obtained 0.5FNNC within 30 min were up to 96.79% and 71.79%, respectively. In addition, the degradation rate of the optimal composite (0.5FNNC)/PMS system was about 4.06 times higher than that of bare Fe–N–C/PMS system. Intriguingly, the Fe ion leaching from 0.5FNNC during the degradation reaction was significantly lower than bare Fe–N–C owing to the strong catalyst-support chemical bonding. Based on electron paramagnetic resonance, quenching experiments, X-ray photoelectron spectroscopy analysis and electrochemical analysis, it was indicated that the non-radical processes (1O2 and high valent iron-oxo species) should be responsible for the phenol degradation. Meanwhile, the possible phenol degradation pathways were proposed, and the intermediates were evaluated for ecotoxicity by ECOSAR. Finally, a preliminary economic analysis of this process was carried out. Overall, this work would provide a new strategy for the construction of ceramsite based multi-pore composite catalysts and the large-scale application of persulfate oxidation technology in organic wastewater treatment.

Quality Minimization of Agricultural Drainage Water for Irrigation Water Reuse Using Coconut Shell Activated Carbon

Nutrients and organic pollutants draining from agricultural fields are the leading sources of surface water quality impairment. Activated carbon (AC) produced from agricultural crop residues has great success in the sequestration of hazardous substances from wastewaters. This study evaluates the potential of coconut shell activated carbon for agricultural drainage water quality minimization; pH adjustment, and excess nitrate and sulphate adsorption. Agriculture drainage water samples were collected and analyzed for Electrical conductivity, Total Dissolved Solids, Chloride, Sodium, Sulphate, Bicarbonate, Nitrate – Nitrogen, and pH. Coconut shells were sourced locally and carbonized at 500°C (± 5°C) for one hour in a muffle furnace. The char produced was ground, sieved, and activated with potassium hydroxide (KOH). The porosity and morphological structures of the AC were examined using a Scanning Electron Microscope. The effect of contact time (30, 60, 90, and 120 min), temperature (20 and 40°C), and adsorbent dosage (1, 1.5, 2, and 2.5 g) were examined using batch studies. The analysis of the drainage water shows the water is highly alkaline and contains sulphate and nitrate above FAO benchmark values. The SEM analysis indicates that the stability and mesoporosity of the carbonaceous material were enhanced by KOH activation. The pH value of the treated water decreased from 9.94 (highly alkaline) to 7.92. The use of 1 g (10 g/l) of coconut shell AC has the highest amount of nitrate and sulphate per unit quantity of AC (4.1 and 2.98 mg/g respectively). The adsorption process peaked at 30 mins contact time with 99.8% and 98.8% nitrate and sulphate removal efficiency, respectively. The process is temperature dependent; nitrate adsorption performs slightly better at 40°C; sulphate adsorption at 20°C. More research effort is needed to ascertain the performance and applicability under continuous flow conditions.