Recovery Of Volatile Organic Compounds Research Articles

Low temperature conditioning and nitric oxide treatment reduced chilling injury and altered fatty acid metabolism of flat peaches

Low-temperature conditioning is a recognized method for alleviating chilling injuries in flat peaches. However, long-term low-temperature storage can mitigate volatile organic compounds, thereby limiting fruit availability. To improve the supply of flat peaches, we investigated the combined effects of low-temperature conditioning and nitric oxide treatment on various parameters including physiological quality, volatile organic compounds, fatty acids, associated enzymes, and genes involved in the fatty acid pathway with the transcriptome sequencing analysis. The results indicated that low-temperature conditioning coordinated with 10 µL L−1 nitric oxide treatment possessed higher firmness and vitamin C content and restricted the content of malonaldehyde and relative electrical conductivity, thus maintaining the overall quality of flat peaches. In the study, 10 µL L−1 nitric oxide was employed for subsequent experiments. Moreover, higher contents of volatile organic compounds were supported by increased contents of palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, alcohol dehydrogenase, hydroperoxide lyase, and up-regulated genes of LOX2, LOX3, LOX6, ADH2, and ADH3. In summary, nitric oxide treatment effectively facilitated the recovery of volatile organic compounds in flat peaches during cold storage. Therefore, low-temperature conditioning and nitric oxide treatment can be a promising strategy to prevent the loss of volatile organic compounds by modulating the fatty acid pathway and associated genes.

Multifactor orthogonal analysis on the desorption performances of P/N/S-doped activated carbon for acetone

As a widely used industrial material, the recovery of volatile organic compounds (VOCs) has great economic value and environmental significance. Improving the desorption performance of modified activated carbon in treating volatile organic compounds emissions is the key to the utilization of adsorbent and the recovery of adsorbate. In this study, five kinds of activated carbons and acetone were selected for orthogonal experiments to analyze the effect of multi-factors on the performances of major concern in engineering. The desorption process was divided into three zones, concentration fast rise zone, concentration fast decay zone and concentration slow decay zone, and quantitively evaluated for each zone. The results show that the enrichment ratio of SC800 is the highest in these sample, can reach 5.16, which is mainly affected by the chemical functional group with the highest adsorption energy, and is negatively correlated with the specific surface area. Combined the kinetic analysis and the quantitative evaluation of the total effects of chemical functional groups, the desorption rates are mainly related to the adsorbent surface saturation in the concentration fast decay zone and the total chemical effect in the concentration slow decay zone. In addition, the PC500 has the highest desorption efficiency of 69 %, which can be measured by the desorption activation energy.

Establishment of a headspace-thermal desorption and gas chromatography-mass spectrometry method (HS-TD-GC-MS) for simultaneous detection of 51 volatile organic compounds in human urine: Application in occupational exposure assessment

Volatile organic compounds (VOCs) are a group of ubiquitous environment pollutants especially released into the workplace. Assessment of VOCs exposure in occupational populations is therefore a crucial issue for occupational health. However, simultaneous biomonitoring of a variety of VOCs is less studied. In this study, a simple and sensitive method was developed for the simultaneous determination of 51 prototype VOCs in urine by headspace-thermal desorption coupled to gas chromatography-mass spectrometry (HS-TD-GC-MS). The urinary sample was pretreated with only adding 0.50 g of sodium chloride to 2 mL of urine and 51 VOCs should be determined with limits of detection (LODs) between 13.6 ng/L and 24.5 ng/L. The method linearity ranged from 0.005 to 10 μg/L with correlation coefficients (r) of 0.991 to 0.999. The precision for intraday and inter-day, measured by the variation coefficient (CV) at three levels of concentration, was below 15 %, except for 4-isopropyl toluene, dichloromethane, and trichloromethane at low concentration. For medium and high levels, recoveries of all target VOCs were within the standard range, but 1,1-dichloropropene and styrene, which were slightly under 80 % at low levels. In addition, the proposed method has been used to determine urine samples collected in three times (before, during and after working) from 152 workers at four different factories. 41 types of prototype VOCs were detected in workers urine. Significant differences (Kruskal-Wallis chi-squared = 117.18, df = 1, P < 0.05) in the concentration levels of VOCs between the exposed and unexposed groups were observed, but not between the three sampling times (Kruskal-Wallis chi-squared = 3.39, df = 2, P = 0.183). The present study provides an alternative method for biomonitoring and assessing mixed exposures to VOCs in occupational populations.

Optimization Design of a Recovery System for an Automatic Spray Robot and the Simulation of VOC Recovery

A recovery system for an automatic spraying robot to conduct the spraying operation outdoors for ships is designed in this paper, which addresses the pollution problem of volatile organic compounds (VOCs) by employing the vacuum recovery method. The recovery system consists of the recovery hood, nozzle, and vacuum tubes. The recovery hood is the critical part of the recovery system and is designed with internal and external cavities, as well as four vacuum tubes for recycling VOCs. Based on the computational fluid dynamics (CFD) method, simulation in the time domain of the gas–liquid interaction, droplet evaporation, and wall impingement is conducted. To identify the better recovery performance, three vacuum recovery-hood schemes are designed, and their performance is compared. The numerical results show that the distance between the vacuum tubes and the intake gap has a significant impact on the VOCs’ recovery effect. One of the main reasons for the escape of VOCs is that the swirling airflows in the baffle plane act as vortices which may capture VOCs, causing the accumulation of VOCs beyond the capacity of the external cavity. Dividing the external cavity into four chambers with deflectors (with each chamber equipped with one vacuum tube only) can significantly reduce the leakage rate of the recovery system. The recovery system provides a theoretical solution for implementing the prevention and control of VOCs in shipyards as soon as possible.

Covalent organic frameworks filled Pebax hybrid membrane for efficient toluene/N2 separation

Hybrid membranes hold significant potential in the efficient recovery of aromatic volatile organic compounds (VOCs). The advanced fillers with high aromatics affinity and polymer compatibility are in urgent demand. In this study, covalent organic framework nanosheets (COFNs) were introduced into poly (ether block amide) (Pebax®2533) to fabricate hybrid membranes. The long-range ordered pore structure, tunable functional groups and organic attributes of COFNs enhanced the affinity of membrane towards aromatic VOCs, the transport of VOCs within the membrane as well as the interactions between COFNs and Pebax. The hybrid membrane filled with TpPa-COOH COFNs exhibited a noticeable improvement in both selectivity and permeability compared to pure Pebax membranes. Particularly, when the content of TpPa-COOH COFNs was at 4 wt%, the membrane demonstrated excellent separation performance for a 2.7 mol% toluene/N2 mixture, wherein the toluene permeability of membrane was 6.7 × 10−7 mol μm m−2 s−1 Pa−1 and the selectivity was 674. This study expanded the application scenarios of COFs-based hybrid membranes and provided a new approach for the design and fabrication of VOCs recovery membranes.

Optimization and Simulation Analysis of Furnace Structure for Regenerative Thermal Oxidizer

Volatile Organic Compounds (VOCs) significantly threaten the atmospheric environment. Currently, common methods for the recovery and treatment of VOCs include adsorption, solution absorption, photocatalytic oxidation, and high-temperature oxidation. Among them, the Regenerative Thermal Oxidizer (RTO) is a scheme for high-temperature oxidation treatment of VOCs, which applies aerospace heat transfer and combustion technology to the treatment of VOCs, and the removal efficiency of VOCs can reach over 99%. Considering the high temperature and possible instantaneous overpressure during the combustion process, a three-dimensional flow model of the bottom air distribution chamber and heat storage chamber was established to solve the technical difficulties of the gas flow field in the existing RTO and improve the safety and stability of the overall flow. Simulated the gas flow field and analysed the distribution pattern of the gas flow rate. In response to the uneven distribution of airflow caused by the pipeline layout, orifice plates were installed at the bottom of the furnace, and various orifice plate designs were considered. The results indicate that adding slanted orifice plates can improve flow conditions and enhance safety while meeting practical needs.

Thermodynamic, economic, and environmental performance evaluation of boil-off gas condensate recovery by liquid nitrogen with power generation as byproduct

As stricter national standards for volatile organic compounds (VOCs) emissions are implemented, the emission of VOCs is a growing concern. There is an urgent necessary to optimize the existing condensate recovery system structure to meet national emission standards for boil-off gas. In existing VOCs recovery methods, the drawbacks include the frequent regeneration of adsorbent materials, limitations in the condensation recovery of isomers, and the lack of self-sufficiency in power generation. Therefore, a novel boil-off gas condensate recovery system by liquid nitrogen (LN) was proposed in this study. Based on the first and second laws of thermodynamics, a numerical optimization model of the system was established and the system performance of thermodynamic, economic and environmental was analyzed. The results show that the system achieves condensation and recovery of boil-off gas. The LN pump has an optimal outlet pressure. When the pressure is 1.95 MPa, the system achieves maximum net power output, and when the pressure is 0.85 MPa, the system achieves maximum LN savings. Additionally, the higher the ambient temperature, the greater the net power output. At lower ambient temperatures, the system supplies a greater cooling capacity. The system demonstrates good economic and environmental performance under higher ambient temperatures and outlet pressure of LN pump. When the pressure is 1.95 MPa, the system achieves the maximum net present value, standard coal savings and carbon dioxide emission reduction. The system has a maximum payback period of only 0.35 years. The system could be used in engineering applications to improve the overall performance of the liquefied natural gas plant.

Thermodynamic design and experimental study of a condensation recovery system for VOCs

During the storage and transportation process of crude oil on tankers, the light hydrocarbon components in liquid form have the tendency to evaporate and vaporize easily, resulting in wasted resources and environmental pollution. The current petroleum volatile organic compounds (VOCs) recovery system such as absorption and membrane separation applied to crude oil tankers is unable to fulfil the requirements of existing VOCs emission standards. In contrast, the condensation method of VOCs recovery technology has the benefit of a straightforward process principle, and the recovered liquid hydrocarbons can be utilized directly. It is thus vital to develop a condensation recovery system for petroleum VOCs that is compatible with crude oil tankers. To attain the condensation and recovery of the non-azeotropic gases, such as CH4, C2H6, C3H8, and N2 in the feed gas, this paper proposes a low-temperature VOCs condensation recovery system with graded cooling and liquefaction separation for crude oil tankers. The proposed system initially utilizes a R404A/R23 double-stage cascade refrigeration cycle to cool the VOCs below −75 ℃ to liquefy most heavy hydrocarbons. Then, a low-temperature nitrogen expansion cooling cycle is utilized to cool the VOCs to approximately −160 °C to recover the remaining light hydrocarbons. The condensation process is simulated by Aspen HYSYS to study the variable operating conditions. The recovery of total hydrocarbons in the outlet tail gas in the simulation results is analyzed and found to be up to 95.50 %. Under identical refrigeration capacity circumstances, decreasing the inlet pressure, increasing the inlet flow rate, and increasing the methane mole fraction in VOCs component, all lead to declining trends of total hydrocarbon recovery and methane recovery rate. Specifically, the effects of four different hydrocarbon component ratios on total hydrocarbon recovery and total cooling load are investigated at a constant nitrogen content and refrigeration capacity. Furthermore, the optimal design and analysis process for the flow path section of the turbine expander under the cryogenic conditions is discussed. The results demonstrate that the outlet temperature through the turbine expander is at least −172.1 °C, and the cooling capacity can be up to 4.5 kW with a margin of 80 %. Finally, through the comprehensive VOCs condensation recovery experiments, the proposed system successfully achieves the liquefied separation and recovery of CH4, C2H6, and other hydrocarbons. The recovery rate of the total hydrocarbons in the outlet tail gas reaches 96.21 %, conforming to the VOCs emission standards and regulations. The findings of this study provide a viable technical resolution in the field of petroleum VOCs recovery from crude oil tankers.

A complementary VOCs recovery system based on cryogenic condensation and low-temperature adsorption

The control of volatile organic compounds (VOCs) emission has a significant influence on the environment and human health. Liquid nitrogen (LN2) condensation is a highly efficient method for VOCs recovery with a wide range of applications, but it is poor in the treatment of light hydrocarbons, especially methane and ethane, and has some shortcomings such as high emission concentration and large carbon emissions. In this paper, a novel cryogenic condensation system combined with low-temperature adsorption was proposed. The low-temperature exhaust gas treated by cryogenic condensation equipment is introduced into an adsorption bed, resulting in lower temperature and higher adsorption capacity of the adsorption bed, which not only effectively improves the recovery rate of VOCs, but also solves the spontaneous combustion problem caused by the adsorptive heat effect of traditional room-temperature adsorption method. A thermodynamic calculation model was established, and related experimental verifications were carried out. The results show that the economic value of the recovered VOCs condensate is 1.24 times of the cost of consumed LN2 and the carbon emission reduction is 1683 t per year, achieving an acceptable breakthrough time of 16,971 s at an adsorption temperature of 198.15 K exceeding that at 238.15 K by a factor of 16 when the cryogenic condensation temperature is 138.15 K with a 600 m3/h of waste gas. The effects of cryogenic condensation temperature, adsorption temperature, inlet gas concentration, flow rate, and the proportion of components on the system performance are analyzed in detail.

Development of a Moisture Pretreatment Device for the Accurate Quantitation of Water-Soluble Volatile Organic Compounds in Air

In air pollutant monitoring using sensors, moisture can adversely affect the analytical accuracy of volatile organic compounds (VOCs). Therefore, a new moisture pretreatment device (KPASS–Odor) for analyzing VOCs in the air was developed, based on frost and created by a desublimation process inside a cold tube. The performance of KPASS–Odor was compared with conventional devices (i.e., a NafionTM dryer and a cooler) through the measurements of low water-soluble VOCs (i.e., benzene, toluene, ethyl benzene, p-xylene, and styrene) and relatively high ones (i.e., methyl-ethyl ketone, methyl isobutyl ketone, butyl acetate, and isobutyl alcohol) using gas chromatography (GC) and sensor methods. Regarding the GC method, the recovery rates for KPASS–Odor and the cooler were &gt;95% and &gt;80%, respectively, at a flow rate of 500 mL/min for all compounds. For the NafionTM dryer, the recovery rates differed between low and high water-soluble compounds, which exhibited the rates ≥88% and ≤86%, respectively. In terms of the sensor method, the VOC recovery rates of KPASS–Odor and the NafionTM dryer were found to be &gt;90% and &lt;50%, respectively. Therefore, KPASS–Odor was determined to be the most suitable moisture pretreatment device for highly soluble VOCs of concern in this study.

Design of cascade refrigerant process utilizing CO2 and NH3 to remove volatile organic compounds

Volatile Organic Compounds (VOC) are organic substances that evaporate from crude oil. About 0.08–0.15 % of the crude oil loaded into the ship is released as VOCs, which indicates that 50–200 tons of VOC are generated per loading. The recovery of VOCs generated by crude oil loading is essential to avoid any environmental issues. In this study, we developed the VOCs recovery process based on the selective condensation of VOCs. The process was modeled using Aspen HYSYS V10, and economic evaluation methods including CAPEX, OPEX, and benefits obtained by utilizing VOCs were conducted to analyze the economic effect of increasing the condensation temperature. Moreover, this system was optimized to increase the efficiency of the refrigerant cycle at a predetermined condensation temperature based on an economic evaluation. We investigated carbon dioxide and ammonia, which is eco-friendly and can be used in ammonia-powered ships with on-board CCS system, to replace propylene refrigerant. COP (Coefficient of Performance) was optimized when modifying the design of the refrigerant process such as mixed refrigerant and cascade refrigeration. As a result, using a cascade refrigerant system with carbon dioxide and ammonia exhibits a higher process efficiency than that of the existing propylene refrigerant. Using the proposed cascade refrigerant system using carbon dioxide and ammonia will enable a more efficient and eco-friendly operation of the VOC recovery system

Sampling and recovery of ignitable liquid residues (ILRs) from fire debris using capillary microextraction of volatiles (CMV) for on‐site analysis

A new, fast, and ultra-sensitive headspace sampling method using the Capillary Microextraction of Volatiles (CMV) device is demonstrated for the analysis of ignitable liquid residues (ILRs) in fire debris. This headspace sampling method involves the use of a heated can (60°C) to aid in the recovery of volatile organic compounds (VOCs) from medium and heavy petroleum distillates. Our group has previously reported the utility of CMV to extract gasoline at ambient temperature in less than 5min in the field. This work evaluates the recovery and analysis of low mass loadings (tens of ng) of VOCs from charcoal lighter fluid, kerosene, and diesel fuel. Nonane, decane, undecane, tridecane, tetradecane, and pentadecane were selected for evaluation of recovery to represent these ILR classes. The face-down heated can headspace sampling technique was compared to the previously reported, non-heated, paper cup headspace sampling technique. Mass recovery improvements of 50%-200% for five of the six target compounds in diesel fuel were achieved compared to the non-heated sampling method. The average relative standard deviation (reported as % RSD) between the replicate trials decreased from an average of 28% to 6% when using the heated can method. Ignitable liquids were spiked onto burned debris in a live burn exercise and sampled using the heated can and paper cup headspace sampling techniques. The heated sampling technique reported here, for the first time, demonstrates an effective extraction method that when coupled to a portable GC-MS instrument allows for a sampling and analysis protocol in the field in less than 30 min.

Room temperature synthesis of monolithic MIL-100(Fe) in aqueous solution for energy-efficient removal and recovery of aromatic volatile organic compounds.

The removal and recovery of volatile organic compounds (VOCs) are widely used in many industrials. Unfortunately, most conventional porous materials not only have low VOCs uptake, but also need to be regenerated at relatively high temperature. Metal-organic frameworks (MOFs) have great potential for the removal and recovery of VOCs as their record-breaking gas adsorption capacity, easy regeneration, tunable pore structure and functional groups. Whereas, powdered MOFs are hardly implemented in industrial fields owing to their low bulk density and high pressure drop. Exploring a green method to prepare granular MOFs for the removal and recovery of VOCs is still a challenge. Herein, we report the room temperature green synthesis of a stable Fe-based MOF monolith by using water as the solvent without applying high pressure and chemical binders. The static and dynamic experiments show that the optimized centimeter-scale monolith has high porosity and mechanical strength, and exhibits much better adsorption performance for representative aromatic VOCs (benzene, toluene and p-xylene), than commercial activated carbon and activated carbon fiber under the same conditions. Remarkably, as-synthesized monolith can be rapidly regenerated at lower temperature. These results clearly demonstrate the advantages of MOF monoliths in removing and recovering VOCs, and also provide new insight into the effects of drying temperature, washing and centrifugation procedures on MOF shaping.

Superoleophilic conjugated microporous polymer nano-surfactants for realizing unprecedented fast recovery of volatile organic compounds.

A pervaporation membrane with fast and selective permeation is key to improving the recovery efficiency of volatile organic compounds from water. Here, we synthesize a new type of nanofiller-conjugated microporous polymer (CMP) to fabricate polydimethylsiloxane (PDMS)-based mixed matrix membranes (MMMs) and explore their application in the recovery of organic solvents from water via pervaporation. Due to their good dispersibility in the dope solvent and compatibility with PDMS, uniform MMMs without discrete particle phases or aggregates are prepared. Interestingly, CMP nanosheets play a unique role as a nano-surfactant in enhancing both the sorption and diffusion coefficients, realizing unprecedented fast recovery of organic solvents from water. The total flux of the as-fabricated membranes can be enhanced from 74.8 to 406.2 kg μm-2 h-1 and the separation factor αethyl acetate/water is increased from 118.7 to 526.6 when using 5 wt% ethyl acetate aqueous solution as the feed at 50 °C. In addition, the CMP-incorporated PDMS membranes are also effective in recovering a wide range of organic compounds from water, including ethanol, acetone, tetrahydrofuran and acetonitrile.

Comparative studies on the toluene sorption performance over silicalite-1 zeolites with different morphologies

The silicalite-1 zeolites with different morphologies (spherical-like, plate-like, and brick-like) were synthesized successfully to study the toluene sorption. The results demonstrate that morphology has a significant and different effect on toluene adsorption under dry or wet conditions. The dynamic adsorption capacities follow S–S (spherical-like silicalite-1) > P–S (plate-like silicalite-1) > B–S (brick-like silicalite-1) under the dry condition (303 K). For the wet condition (RH = 50%, 303 K), the order of the dynamic adsorption capacities is P–S > S–S > B–S. Silicalite-1 zeolites were tested for five adsorption-regeneration cycles to study the reusability and their performance remained stable above 85% after five cycles. The calculated rate constants of Yoon-Nelson model and Weber-Morris (W-M) intra-particle diffusion model reveal that there is less diffusion resistance in P–S. The findings may provide valuable information on zeolite-based adsorbents for adsorption removal or recovery of volatile organic compounds.

Specific energy consumption and quality of Citrus hystrix leaves treated using convective and microwave vacuum methods

This study compared the effects of three drying techniques on Citrus hystrix leaves: convective hot air drying (CAD), microwave vacuum drying (MVD), and convective hot air pre-drying followed by microwave vacuum finishing drying (CPD-MVFD). As a control, freeze-drying (FD) was employed. As a result, the modified Page model best described the drying kinetics of C. hystrix leaves. Furthermore, CPD-MVFD significantly lowered the specific energy consumption by 51.6%. Meanwhile, MVD, at density of 12 W/g, retained the greatest antioxidant capacity, TPC content and volatile compounds. In physical terms, CPD-MVFD and MVD performed best in retaining the color characteristics of C. hystrix leaves under all circumstances. Finally, all samples were microbiologically stable. In conclusion, it is suggested that MVD with a power density of 12 W/g be used for drying C. Hystrix leaves, due to its low specific energy consumption, strong antioxidant and TPC capacity, and good recovery of volatile organic compounds.

Plasma Polymerized Coatings on Hollow Fiber Membranes-Applications and Their Aging Characteristics in Different Media.

In the past 30 years, plasma polymerization has emerged as a versatile technique for depositing ultrathin nanocoating on a variety of substrates for applications that range from providing lubricity to the substrate, protection from harsh environments, promoting adhesion, surface modification to applications of coating in ultrafiltration and gas separation membranes. Applications in the field of volatile organic compound (VOC) recovery and membrane distillation have also gained importance in recent years. Most of these applications use silicone and fluorosilicone-based plasma polymers that provide versatility, good separation characteristics, and long-term stability to the membrane. However, plasma polymers are known to age with time. The current study focuses on the aging behavior of silicone and fluorosilicone plasma polymers in different environments that include air, ionized air, heat, aqueous solutions of inorganic chemicals, as well as harsh solvents such as hexane, dichloromethane (DCM), and toluene. Membrane gas permeance and gas selectivity were used to quantitatively measure the aging behavior of the coatings on gas separation membranes, while water and VOC flux were used to measure the effect of aging for membranes designed for membrane distillation and VOC separation. It was found that while all plasma polymers of this study showed changes in membrane gas permeance on exposure to air, they fundamentally retained their membrane separation characteristics in all the studied environments. Significant changes in gas permeability characteristics were observed on exposure of the membranes to organic solvents like dichloromethane, 2-propanol, hexane, and toluene, which are attributed to dimensional changes in the hollow fiber substrate rather than changes in plasma polymer characteristics. Ionized air was also found to have a significant effect on the gas permeability characteristic of the membranes, reducing the gas permeance by as much as 50% in some cases. This is attributed to accelerated oxidation and crosslinking of the polymer in ionized air. XPS studies showed an increase in the oxygen content of the polymer on aging. Differences were found in the aging behavior of polymer coatings made from different monomers with long-chain monomers such as hexamethyltrisiloxane offering more stable coatings. The cross-link density of the polymer also influenced the aging behavior, with the more cross-linked polymer showing a lesser influence on aging in a chemical environment. No significant effect of aging was found on applications of these polymer coatings in the field of membrane distillation, pervaporation, and VOC removal, and a stable performance was observed over a long period of time. It was also noted that the selection of co-monomers played a significant role in membrane distillation, with polymers forming fluoro co-monomers giving better results. The current study also demonstrated the usefulness of plasma polymers in controlling the pore size of microporous membranes that can find useful applications in bio-filtration and VOC recovery.

Study of the Dissolution and Diffusion of Propane, Propylene and Nitrogen in Polydimethylsiloxane Membranes with Molecular Dynamics Simulation and Monte Carlo Simulation

Volatile organic compounds (VOCs) are important sources of atmospheric pollutants on account of their high recycling value. The membrane of dense silicone rubber polydimethylsiloxane (PDMS) has wide-ranging prospects for the separation and recovery of VOCs. In this study, PDMS membrane body models were established in BIOVIA Materials Studio (MS) to simulate VOCs with C3/N2 gases, and to study the structure of PDMS membranes and the dissolution and diffusion process of gas in the membranes. The free volume fraction (FFV), cohesive energy density (CED), radial distribution function (RDF), diffusion coefficient and solubility coefficient of C3H8, C3H6 and N2 in PDMS membranes were calculated, and the permeability coefficients were calculated according to these values. At the same time, the effects of temperature and mixed gas on the dissolution and diffusion of C3/N2 in PDMS membranes were investigated. The results show that the mass transfer process of C3 in PDMS membranes is mainly controlled by the dissolution process, while that of N2 is mainly controlled by the diffusion process. In a C3/N2 mixed gas system, there is a synergistic relationship between gases in the diffusion process, while there is competitive adsorption in the dissolution process. With an increase in temperature, the diffusion coefficients of the three gases in PDMS gradually increase, the solubility coefficients gradually decrease, and the overall permeability selectivity coefficients of the gases gradually decrease. Therefore, low-temperature conditions are more conducive to the separation of C3/N2 in PDMS membranes. The simulation results of the permeability selectivity coefficients of pure C3 and N2 in PDMS are similar to the experimental results, and the relationship between the micro- and macro-transport properties of PDMS membranes can be better understood through molecular simulation.

Deactivation Mechanisms of Engineering Adsorbents for VOCs Adsorption and the Lifetime-Prolonging Strategy

Adsorption–desorption process has been considered as a promising way for both the removal and recovery of volatile organic compounds (VOCs) from waste gases. However, during the engineering applications of the adsorbents, they would be deactivated or deteriorated. Herein, the deactivation mechanisms of different engineering VOC adsorbents (activated carbons and silica gels) by different processes or parameters have been investigated. It is found that the deactivation of adsorbents is mainly attributed to the following reasons: accumulation of VOCs in the pores, breaking of the pore structures due to the frequent-changing of processing conditions, occupation of the pores by water or other impurities, and so forth. For the temperature swing adsorption (TSA) process, the performance of adsorbents would be deteriorated by (i) the accumulation of VOCs due to incomplete desorption or (ii) the collapse of the pore structure of adsorbents (e.g., activated carbons and microporous silica gel) due to frequent cooling and heating between adsorption and desorption, respectively, leading to the deactivation of adsorbents. This phenomenon could be weakened when the pores in the adsorbents increased (e.g., the mesoporous silica gel, SG B). For the vacuum swing adsorption (VSA) process, the pore structure of adsorbents was slightly influenced during the adsorption–desorption cycles. The decrease in the adsorption capacity of adsorbents was mainly ascribed to the accumulation of VOC chemicals in the pores. In addition, in the TSA or VSA process, when the water vapor was present, the adsorption performance of adsorbents will be significantly reduced due to the occupation of adsorption sites by the water, resulting in faster deactivation. Considering the processing cost and lifetime of adsorbents, the TSA and VSA are combined together herein. The results show that, compared with the single TSA and VSA, the combined VSA–TSA process could be applied to different VOCs and improve the desorption rate of the adsorbents greatly at lower energy consumption and longer lifetime.

In-situ catalytic fast pyrolysis of reed as a sustainable method for production of porous carbon as VOCs adsorbents

In this work, preparation of carbon adsorbents for recovery of volatile organic compounds (VOCs) by in-situ catalytic fast pyrolysis was investigated. Less emission of carbon gases, less consumption of energy and being fast and facile make the process as a green and sustainable method for production of the carbon adsorbents. Carbon nanostructures were prepared by fast pyrolysis of NiCl2 impregnated reed at 600℃. The porosity of the carbon product was improved by ZnCl2 post activation. Moreover, a highly porous carbon was synthesized by fast pyrolysis of the reed contained NiCl2 and ZnCl2 at 600℃. The carbon products were studied by different analysis methods including FE-SEM, TEM, Raman and FT-IR spectroscopy, BET and TGA. Also, the biogas and the bio-oils obtained as by-products were characterized using GC and GC-Mass instruments. FE-SEM and TEM images showed that the biochar obtained from fast pyrolysis of NiCl2 impregnated reed is a hybrid of carbon nanofibers and graphene (CNFs/G). By post-activation of the CNFs/ G hybrid using ZnCl2, the specific surface area was increased from 34.58 m2/g to 105.68 m2/g. However, by in-situ activation process using NiCl2 and ZnCl2, a product with a specific surface area of 1544.5 m2/g was produced. Adsorption/ desorption of VOCs on the commercial activated carbon and also the post activated CNFs/G hybrid and the in-situ activated product were (122.8/ 74.49), (64.5/ 63.1) and (643.6/ 428.1) mg/gadsorbent, respectively. GC-mass analysis of the bio-oils revealed that they contained invaluable chemicals including furfural (30.63—56.22%wt.) and acetic acid (35.51–51.44%wt.).