Removal Of N-hexane Research Articles

Unlocking High-Throughput Plasma-Catalytic Low-Temperature Oxidation of n-Hexane over Single-Atom Ag1/MnO2 Catalysts.

The total oxidation of n-hexane, a hazardous volatile organic compound (VOC) emitted by the pharmaceutical industry, presents a significant environmental challenge due to limited catalyst activity at low temperatures and poor stability at high temperatures. Here, we present a novel approach that overcomes these limitations by employing single-atom Ag1/MnO2 catalysts coupled with nonthermal plasma (NTP). This strategy achieves exceptional performance in n-hexane oxidation at low temperatures, demonstrating 96.3% n-hexane removal and an energy yield of 74.1 g kW h-1 with negligible byproduct formation (O3 < 5 ppm, NO x < 20 ppm). In situ characterization of the plasma-catalytic system coupled with theoretical calculations revealed a synergistic mechanism for n-hexane oxidation. Reactive species generated by the NTP initiate the breakdown of n-hexane into smaller fragments. These fragments are then preferentially adsorbed onto the atomic Ag sites due to their favorable energetics, facilitating their subsequent oxidation. The incorporation of single Ag atoms not only enhances the selective adsorption of these NTP-generated intermediates but also accelerates the reaction kinetics. This work demonstrates the potential of single-atom catalysts coupled with NTP for efficient and environmentally friendly removal of VOCs at low temperatures. This approach offers a promising strategy for mitigating industrial air pollution and achieving cleaner air quality.

Electrochemical biofilter enhances performance of volatile organic compounds abatement

ABSTRACT An electrochemical biofilter (EBF) was developed for enhancing the removal of volatile organic compounds (VOCs) through current. The removal efficiency (RE) of toluene exhibited a notable increase of 15% while the biomass growth rate exhibited a corresponding decline of 46% under an optimal current intensity of 50 mA. Meanwhile, the efficacy of the EBF system was markedly enhanced upon the removal of n-hexane, styrene, dichloromethane, and diisobutylene. The results indicated that there was an 11% to 49% increase in RE and a 0% to 64% reduction in biomass growth rates under the influence of the current. The current stimulation inhibited the accumulation of microorganisms, thereby alleviating biofilm clogging. The relative abundance of gram-positive phyla, including Firmicutes and Actinobacteria, increased by 15% and 23%, respectively, while the traditionally dominant genera within the Proteobacteria phylum, such as Rhodococcus and Dokdonella, exhibited a decline. In addition, the presence of hydrogen peroxide, free chlorine, and superoxides in the leachate indicated that the oxidative reaction increased in EBF system. This study provides an attractive pathway for current stimulation to enhance degradation of VOCs and alleviate biofilm clogging.

Degradation of n-hexane by the high-throughput double dielectric barrier discharge: Influencing factors, degradation mechanism and pathways

The emission of volatile organic compounds (VOCs) is known to be a source of various environmental problems. N-hexane is a saturated aliphatic hydrocarbon that is a major precursor of ozone. For the decomposition of n-hexane, a novel double dielectric barrier discharge (DDBD) reactor design is developed and tested on a pilot scale. The factors influencing the plasma degradation of n-hexane have been thoroughly investigated. The degradation efficiency, carbon balance and nitrogen oxide concentration were measured and analysed. Through experiments, it was found that the maximum removal of n-hexane at an initial concentration of 2000 ppm and a flow rate of 5 L/min was 1544 ppm. The associated energy efficiency reached 67.71 ppm/J. The excited states of oxygen and nitrogen (O2+, O(3 s5S-3p5P), N2(C3Πu-B3Πg), N2+(B2Σu+-X2Σg+)) during n-hexane degradation were observed. Possible degradation pathways of n-hexane are proposed, and it is revealed that the active species play an important role in the formation of oxygen and nitrogen-containing volatile organic by-products. The results show that the pilot-scale design of the DDBD system provides a feasible way for the industrial treatment of n-hexane, and provides fundamental insights into the mechanism of plasma catalytic system operation.

Novel magnetic non-aqueous phase liquid with superior recyclability for efficient and sustainable removal of gaseous n-hexane using two-phase partitioning bioreactor

Two-phase partitioning biotechnology has been recognized as effective alternative in enhancing the purification of hydrophobic waste-gas. However, current available non-aqueous phases (NAPs) are either difficult to be recovered or exhibit low affinity for hydrophobic pollutants, causing secondary pollution, high operating costs, or limited removal efficiency. Herein, nano silicon oil-based ferrofluid (SOF), featured with high pollutants affinity and magnetism, was synthesized and employed as an innovative NAP liquid in airlift reactors for gaseous n-hexane removal. The removal efficiency of n-hexane (540 mg m−3) reached about 90.0% during 90-day operation, and the used SOF could be quickly recovered via magnetism with a high ratio of 95.6%. Mechanism analysis found, the microbial cell surface hydrophobicity was sustainably improved under the induction of SOF, allowing abundant bacteria adhered on SOF-water interface, thereby enhancing the n-hexane mass transfer directly from SOF to microorganisms. Furthermore, the microbial activity was accelerated, and potential n-hexane-degrading functional microorganisms might be domesticated.

Effects of bamboo-charcoal modified by bimetallic Fe/Pd nanoparticles on n-hexane biodegradation by bacteria Pseudomonas mendocina NX-1

The high hydrophobicity of n-hexane is the main reason why it is difficult to be removed biologically. In this study, the effects of bamboo-charcoal modified by bimetallic Fe/Pd (BBC) on n-hexane biodegradation by Pseudomonas mendocina NX-1 (PM) was investigated. The n-hexane removal efficiency was increased in the presence of BC. The highest n-hexane removal efficiency at 90.0% was achieved at 0.05 g L−1 BCE and 3 g L−1 NH4+ under pH 7.7 and 35 °C. Additionally, protein content (45.9 μg mL−1) and negative cell surface zeta potential (−26.4 mV) were increased during biodegradation process, with PM-BBC being 43.1 μg mL−1 and 19.1 mV. Bacterial growth was improved and maximum cell surface hydrophobicity was obtained after 20 h, which was 59.4% higher than the control with PM-BBC (37.7%) or PM (16.1%), showing biodegradation products of 1-butanol and acetic acid. The results indicate that BBC improved n-hexane biodegradation efficiency by promoting bacterial growth, reducing cell zeta potential, exposing hydrophobic proteins, and increasing cell surface hydrophobicity of bacterial strain NX-1. This investigation suggests that BBC-enhanced biodegradation can be promising to treat n-hexane-containing gas.

Mechanisms of N, N-dimethylacetamide-facilitated n-hexane removal in a rotating drum biofilter packed with bamboo charcoal-polyurethane composite

n-Hexane and N, N-dimethylacetamide (DMAC) are two major volatile organic compounds (VOCs) discharged from the pharmaceutical industry. To enhance DMAC-facilitated n-hexane removal, we investigated the simultaneous removal of multiple pollutants in a rotating drum biofilter packed with bamboo charcoal-polyurethane composite. After adding 800 mg·L−1 DMAC, the n-hexane removal efficiency increased from 59.4 % to 83.1 % under the optimized conditions. The maximum elimination capacity of 10.0 g·m−3·h−1n-hexane and 157 g·m−3·h−1 DMAC were obtained. The biomass of bamboo charcoal-polyurethane and the ratio of protein-to-polysaccharide in extracellular polymeric substances were significantly increased compared with the non-DMAC stage, which is attributed to increased carbon utilization. In addition, Na+ K+-ATPase was positively correlated with increasing electron transport system activity, which was 1.98 and 1.36 times greater. Hydrophilic DMAC improved the bioavailability of hydrophobic n-hexane and benefited bacterial metabolism. Co-degradation of n-hexane and DMAC system can be used for other volatile organic pollutants.

Solution of a mathematical model for the concentration of a hexane solution of technical paraffin to obtain its food modification

For pectin-containing film structures, which are used for the production of biodegradable packaging materials and are hydrophilic in nature, their paraffinization, i.e., applying a thin layer of molten food paraffin to the surface of the film for subsequent protection of packaged food products from moisture and sunlight, will reduce the influence of external factors, primarily moisture, To rationalize the convective preconcentration of a hexane solution, it is necessary to select such regime parameters that will allow not only the removal of hexane with toxic components dissolved in it from the object of study in a relatively simple apparatus, but also significantly reduce the time for the process within temperature restrictions. The latter condition, in view of the complexity of the empirical determination of the temperature distribution in a thin layer of the object of concentration, is advisable to implement by solving the system of equations for the transfer of thermal energy and mass in partial derivatives, however, we can restrict ourselves to one equation for the transfer of thermal energy, using empirical kinetic dependences that describe the removal of n-hexane from the composition. The aim of the study was to adapt paraffin to a hexane solution and solve the model of heat and mass transfer during its concentration in order to exclude the possibility of reducing its temperature below the value of possible preliminary crystallization. The model was implemented numerically by the finite difference method. As a result of the solution, the intensity of the temperature front advancement along the height of the film of the hexanoparaffin composition was found with varying the proportion of paraffin in the process of its concentration with convective supply of thermal energy to it, i.e., it was adapted to the resulting solution and a mathematical model of heat and mass transfer was solved during its concentration to eliminate the likelihood of a decrease in its temperature below the value of possible pre-crystallization. The data obtained do not conflict with the known results of other researchers and can be successfully used for operational calculation and design of the designated processes and units.

Bamboo charcoal powder-based polyurethane as packing material in biotrickling filter for simultaneous removal of n-hexane and dichloromethane

Bamboo charcoal powder-based polyurethane (BC-PU) was firstly applied in biotrickling filter to treat n-hexane and dichloromethane (DCM) simultaneously. Maximum elimination capacity of 12.68 g m−3h−1 n-hexane was achieved and exceed 30.28 g m−3h−1 DCM could be degraded. BTF respond quickly to the mixed shock loadings, and recovered to 76% and 100% respectively in less than 1 h. By increasing inlet loading (IL) of DCM from 6.20 g m−3h−1 to 28.36 g m−3h−1, the removal efficiency of n-hexane decreased from 73.4% to 55.9% corresponding to the IL of 19.96 g m−3h−1. N-hexane degradation was inhibited by high IL of DCM due to enzymes competition for active sites. The growth of key microorganisms Mycobacterium sp., Hyphomicrobium sp. was stimulated and colonized. BC-PU is an innovative and applicable bio-based material in the process of biological purification, which could be widely applied to treat hydrophobic pollutants in the pharmaceutical industry.

Performance promotion and its mechanism for n-hexane removal in a lab-scale biotrickling filter with reticular polyurethane sponge under intermittent spraying mode

Mass transfer limitations commonly challenge biofiltration for n-hexane emissions due to its high hydrophobicity. In this study, a bench-scale biotrickling filter (BTF) packed with reticulated polyurethane sponge was evaluated for n-hexane removal at various organic loading rates (OLRs) (ranging from 15 to 60 g m−3 h-1) and gas empty bed contact times (EBCTs) (ranging from 30 to 7.5 s). The obtained results show that the designed BTF can effectively remove n-hexane under intermittent spraying mode of the nutrient solution and the reticulated configuration of the packing media, which resulted in the spatial development of mycelium and enhanced mass transfer of n-hexane. The mean maximum removal efficiencies (REs) of n-hexane were 92.6 ± 0.9 %, 86.7 ± 4.8 %, and 63.8 ± 3.3 % under the OLRs of 15.67, 30.20, and 61.59 g m−3 h-1, respectively. When the BTF was operated under gas EBCTs of 30, 15, and 7.5 s, average REs of 85.9 ± 5.7 %, 44.8 ± 6.3 %, and 31.2 ± 2.5 % were achieved. The BTF also showed a superior fluctuation resistance capability and prevented excessive biofilm accumulation due to the reticular configuration of the polyurethane sponge. Results present in this study could provide an alternative consideration for the practical industrial application in treating hydrophobic VOC like n-hexane.

Bamboo Charcoal Powder-Based Polyurethane as Packing Material in Biotrickling Filter for Simultaneous Removal of N-Hexane and Dichloromethane

Bamboo Charcoal Powder-Based Polyurethane as Packing Material in Biotrickling Filter for Simultaneous Removal of N-Hexane and Dichloromethane

Effect of presence of hydrophilic volatile organic compounds on removal of hydrophobic n-hexane in biotrickling filters

Hydrophilic VOCs (volatile organic compounds) were applied to explore their positive influence on the elimination of the single hydrophobic VOC in biotrickling filters (BTFs). Comparison experiments were carried to evaluate the effect of 4-methyl-2-pentanone and toluene on the performance of BTFs for n-hexane removal. The results showed that the existence of 4-methyl-2-pentanone improved the removal performance of BTFs at short gas empty bed contact time (EBRT) of 15 s and low temperature of 10 °C. The degradation of n-hexane in the presence of 4-methyl-2-pentanone was slightly enhanced with a loading ratio of 6:1. When the mixing ratio was greater than 4, toluene significantly promoted the biodegradation of n-hexane with toluene loading rate less than 10 g m−3 h−1. Additionally, The promotion effect was not only reflected in the contents of proteins and polysaccharides, but also in the growth rates of microorganisms in biofilms. This work discussed the detailed effect between n-hexane and hydrophilic VOCs in BTFs, which would contribute to develop a more economical method to improve the removal performance of hydrophobic VOCs in BTFs.

Improved degradation of n-hexane vapours using a hybrid system, a photoreactor packed with TiO2 coated-scoria granules and a multilayer biofilter.

Biofiltration of hydrophobic and/or recalcitrant volatile organic compounds such as n-hexane is imperfect. In the present study, we applied a hybrid system consisting of a photoreactor packed with scoria granules coated with TiO2 and a biofilter to improve the removal efficiency of n-hexane from the air stream. The experimental results showed that the hybrid system provided higher removal efficiencies than the single biofilter process with an inlet n-hexane concentration range of 0.11-1g-3 for empty bed residence times (EBRTs) of 30-120s in the hybrid system. The removal efficiency of the single biofilter in EBRTs of 30, 60 and 120s was 10.06%, 21.45%, and 45.98%, respectively. When the photoreactor was included as a pretreatment system (with residence time of 7-27s) and the overall EBRTs of the system was adjusted to 30, 60 and 120s, the removal efficiency of the hybrid system was increased to 39.79%, 63.08%, and 92.6%, respectively. The mass ratio of carbon dioxide produced as an indicator for n-hexane degradation in the hybrid system and the biofilter alone was 1.9 and 1.28, respectively. Bacterial community analysis with sequence analysis of 16S rDNA in the biofilter biomass revealed that Pseudomonas and Bacillus as predominant bacterial species were responsible for n-hexane biodegradation. Therefore, the application of the hybrid system is advantageous in enhanced n-hexane removal from the air stream.

Enhanced biodegradation of n-hexane by Pseudomonas sp. strain NEE2

Pseudomonas sp. strain NEE2 isolated from oil-polluted soils could biodegrade n-hexane effectively. In this study, the secretory product of n-hexane biodegradation by NEE2 was extracted, characterized, and investigated on the secretory product’s enhanced effect on n-hexane removal. The effects of various biodegradation conditions on n-hexane removal by NEE2, including nitrogen source, pH value, and temperature were also investigated. Results showed that the secretory product lowered surface tension of water from 72 to 40 mN/m, with a critical micelle concentration of 340 mg/L, demonstrating that there existed biosurfactants in the secretory product. The secretory product at 50 mg/L enhanced n-hexane removal by 144.4% within 48 h than the control group. The optimum conditions for n-hexane removal by NEE2 were at temperature of 25–30 °C, pH value of 7–8, and (NH4)2SO4 as nitrogen source. Besides n-hexane, NEE2 could also utilize a variety of carbon sources. These results proved that NEE2 can consume hydrophobic volatile organic compounds (VOCs) to produce biosurfactants which can further enhance hydrophobic VOCs degradation.

Simultaneous degradation of n-hexane and production of biosurfactants by Pseudomonas sp. strain NEE2 isolated from oil-contaminated soils.

The presence of surfactants in biofilters could enhance hydrophobic VOC removal. In this study, blood agar plate, methylene blue agar plate and a culture with n-hexane as the only carbon source were used to screen strains that could biodegrade n-hexane and produce biosurfactants simultaneously. The effects of n-hexane concentration on n-hexane removal and biosurfactant production were also investigated. Results showed that such a strain identified to be Pseudomonas sp. Strain NEE2 was successfully isolated from oil-polluted soils. The biosurfactants production by this strain were dependent on the initial concentration of n-hexane (132-2640 mg/L). At the concentration of 2640 mg/L of n-hexane, the biosurfactants promoted n-hexane removal. At 132 mg/L of n-hexane, n-hexane removal efficiency on day 2 exceeded 60%. The synergistic mechanisms of n-hexane removal and biosurfactant production by Pseudomonas sp. Strain NEE2 were discussed including the enhanced mass transfer from gas to liquid phase, within the biofilm phase and biodegradation at the presence of biosurfactants as well as the consequently enhanced production of the biosurfactants. These results in this study proved that it is possible for microorganisms utilizing the synergistic effect of hydrophobic VOC degradation and biosurfactant production for cost-effective hydrophobic VOC removal in biofilters.

Superior activity of Cu-NiWO4/g-C3N4 Z direct system for photocatalytic decomposition of VOCs in aerosol under visible light

We successfully used Cu to dope into the NiWO4 crystal to prevent the fast recombination or increase the lifetime of the photo-induced h+ and e− of the material. Then, the synthesized Cu-NiWO4 was successfully hybridized with g-C3N4 to form Cu-NiWO4/g-C3N4 direct Z system for novel photocatalytic decomposition of n-hexane under vis-light. In the formed Cu-NiWO4/g-C3N4 Z direct system, photo-induced e− in Cu-NiWO4 CB associated with photo-induced h+ in g-C3N4 VB maintaining e− in g-C3N4 CB and h+ in Cu-NiWO4 VB, thereby synthesized photocatalysts formed abundant available e− and h+ amounts even excited by vis-light and the formed e− and h+ pairs exhibit suitable redox potentials for reactions with O2 and H2O, respectively, to produce strong oxidative radicals for advanced photocatalytic degradation of n-hexane. The highest removal efficiency and degradation degree of n-hexane photocatalyzed by Cu-NiWO4/g-C3N4 were 96.8 and 96.3%, respectively. The synthesized Cu-NiWO4/g-C3N4 material also demonstrated strongly stability during long time n-hexane removal.

Enhanced biodegradation of n-hexane from the air stream using rhamnolipid in a biofilter packed with a mixture of compost, scoria, sugar beet pulp and poplar tree skin

Biofiltration of n-hexane vapors with and without using rhamnolipid biosurfactant was investigated on a laboratory scale biofilter packed with compost, scoria, sugar beet pulp, and poplar tree skin at empty bed residence times (EBRT) of 30, 60 and 120s for a period of 131 days. Acclimation of microorganism in the biofilter was achieved in 31 days with an average n-hexane concentration of 0.269 gm −3 and EBRTs of 120s. The results demonstrated that average removal efficiencies (RE) for the corresponding EBRT with n-hexane loading rates (IL) of 6.7–137 gm −3 h −1 were 18.7 ± 1.67%, 28.9 ± 4.06% and 46.8 ± 8.2% without biosurfactant. While, the average REs in presence of the biosurfactant were 23.98 ± 4.08%, 42.4 ± 9.7% and 85.13 ± 10.44% at EBRTs of 30, 60 and 120s, respectively. About 53% of n-hexane removal was related to the segment 1 of the biofilter, where the bacterial and fungi population of its biofilm was 2 × 10 15 and 1.3 × 10 9 CFU g −1 (dry weight), respectively, which was significantly more than the other segments. For all the tested inlet concentrations, the RE was significantly increased by increasing EBRT and decreasing IL of n-hexane. The results of this study confirm the efficiency enhancement of rhamnolipid in biofiltration of hydrophobic compounds such as n-hexane from air streams. • Biofiltration of n-hexane vapors was investigated in the presence and absence of rhamnolipid biosurfactant. • Removal efficiency of n-hexane increased from 46 to 86% in the presence of rhamnolipid. • About 53% of n-hexane removal was related to the segment 1 of the biofilter. • Increasing the biofiltration of hydrophilic compounds by rhamnolipid.

Plasmolysis-Inspired Nanoengineering of Functional Yolk-Shell Microspheres with Magnetic Core and Mesoporous Silica Shell.

Yolk-shell nanomaterials with a rattle-like structure have been considered ideal carriers and nanoreactors. Traditional methods to constructing yolk-shell nanostructures mainly rely on multistep sacrificial template strategy. In this study, a facile and effective plasmolysis-inspired nanoengineering strategy is developed to controllably fabricate yolk-shell magnetic mesoporous silica microspheres via the swelling-shrinkage of resorcinol-formaldehyde (RF) upon soaking in or removal of n-hexane. Using Fe3O4@RF microspheres as seeds, surfactant-silica mesostructured composite is deposited on the swelled seeds through the multicomponent interface coassembly, followed by solvent extraction to remove surfactant and simultaneously induce shrinkage of RF shell. The obtained yolk-shell microspheres (Fe3O4@RF@void@mSiO2) possess a high magnetization of 40.3 emu/g, high surface area (439 m2/g), radially aligned mesopores (5.4 nm) in the outer shell, tunable middle hollow space (472-638 nm in diameter), and a superparamagnetic core. This simple method allows a simultaneous encapsulation of Au nanoparticles into the hollow space during synthesis, and it leads to spherical Fe3O4@RF@void-Au@mSiO2 magnetic nanocatalysts, which show excellent catalysis efficiency for hydrogenation of 4-nitrophenol by NaBH4 with a high conversion rate (98%) and magnetic recycling stability.

Effects of anionic surfactant on n-hexane removal in biofilters

The biodegradability of three anion surfactants by biofilm microorganisms and the toxicity of the most readily biodegradable surfactant to biofilm microorganisms were examined using batch experiments, and the optimal concentration of SDS for enhanced removal of hexane was investigated using two biotrickling filters (BTFs) for comparison. Results showed that SDS could be biodegraded by microorganisms, and its toxicity to microorganisms within the experimental range was negligible. The best concentration of SDS in biofiltration of n-hexane was 0.1 CMC and the elimination capacity (EC) of 50.4 g m−3 h−1 was achieved at a fixed loading rate (LR) of 72 g m−3 h−1. When an inlet concentration of n-hexane increased from 600 to 850 mg m−3, the removal efficiency (RE) decreased from 67% to 41% by BTF2 (with SDS) and from 52% to 42% by BTF1 (without SDS). SDS could enhance hexane removal from 43% (BTF1) to 60% (BTF2) at gas empty-bed residence time (EBRT) of 7.5 s and an inlet concentration of 200 mg m−3.

Biosorption of Pb(II) Ions from Aqueous Solutions by Waste Biomass from Biotrickling Filters: Kinetics, Isotherms, and Thermodynamics

AbstractA dried biomass wasted from biotrickling filters has been prepared for removing lead [Pb(II)] ions from aqueous solutions. The kinetics, isotherms, and thermodynamics of Pb(II) ion biosorption by the dried biomass were investigated. The results showed that the maximum Pb(II) ion biosorption capacity of a dried biomass was 160.0 mg/g at 25°C according to an evaluation using the Langmuir equation, which was fitted well to the adsorption data. The results of the kinetic studies revealed that the adsorption process followed the pseudo second-order model. The calculated thermodynamic parameters of ΔS°, ΔH°, and ΔG° suggested that the adsorption of Pb(II) ion was endothermic and spontaneous. Fourier transform infrared spectroscopy (FT-IR) analysis illustrated that the amide group and the hydroxide group affected Pb(II) ion removal significantly. This study demonstrated that a dried biomass wasted from biotrickling filters for the removal of n-hexane could be successfully used as adsorbent for the treat...

Performance and biofilm characteristics of a gas biofilter for n-hexane removal at various operational conditions

The effects of operational parameters including nitrate concentration,n-hexane inlet concentration and gas empty bed residence time (EBRT) on long-term removal performance ofn-hexane were discussed.