VOC Recovery Research Articles

Adsorption characteristics of water vapor on the hypercrosslinked polymeric adsorbent

Hypercrosslinked polymeric adsorbent is finding increased application as sorbents for removing the VOCs from gas steam. Due to the competitive adsorption between the water and VOCs, hence, it is important to understand the adsorption characteristics of water vapor on hypercrosslinked polymeric adsorbent. In this paper, the adsorption of water vapor on hypercrosslinked polymeric adsorbent with poly (styrene-divinylbenzene) matrix (HY-1) was investigated and compared with a commercial activated carbon (m-GAC) and activated carbon fiber (ACF). The results showed that HY-1 had minimal uptake of water until P/ P 0 was raised to 0.6, which is an indication of an extremely hydrophobic surface. Moreover, increasing the temperature induced the decrease of the water uptake and a rightward shift in the isotherm heel. The adsorption isotherms of water vapor on three adsorbents were fitted by the Cluster Formation Induced Micropore Filling model (CIMF model). The results indicated that the experimental data can be well-fitted by CIMF model. Based on this semiempirical modeling, the adsorptive contributions of primary sites and micropores were estimated qualitatively. In addition, the effect of water vapor on the adsorption of benzene onto three adsorbents was investigated. The breakthrough time of benzene on HY-1 decreased by 10.4% even if the relative humidity was 80%, while that of m-GAC and ACF decreased by17.2% and 38.9%, respectively. Therefore, HY-1 would be a particularly efficient and competitive adsorbent for VOCs recovery from the humid gas streams.

Simulation of VOCs Recovery Process by Absorption

Using a simulation program, an absorption process has been simulated of an air stream contaminated with acetone using water as absorbent and the subsequent recovery of the solvent by distillation. After verifying the effectiveness of the simulated process, the next step was to carry out an economic analysis at the level of equipment to assess the economic viability of the simulated recovery plant.

Polyurethane/polyethersulphone composite hollow fibers produced by simultaneous spinning of two polymer solutions

In this work, composite hollow fibers were prepared by simultaneous spinning of two polymer solutions using a triple orifice spinneret. The polymer solutions were composed of a rubbery (polyurethane) and a glassy (polyethersulfone) polymer to form skin and support, respectively. Hollow fibers with those features are eligible to be used in many applications, including VOC recovery, and as facilitated transport membranes, given that carriers can be incorporated in the rubbery layer. Different synthesis conditions were investigated and the hollow fiber morphologies were characterized by scanning electron microscopy. The results showed that it is possible to produce the polyurethane/polyethersulphone composite membranes, with adhesion between the top and the support layers, and with dense skin. The use of a volatile solvent in the polyurethane solution, such as THF, different from the solvent in the support solution, also allowed the formation of hollow fiber membranes with dense skin and complete adhesion between the polyurethane and the polyethersulphone layers.

Evaluation of VOC recovery strategies

Many manufactured items receive surface coatings for decoration and/or protection against damage. In a number of places along the production line emissions of (VOC) Volatile Organic Compounds can occur. Because VOC are a major contributor to photochemical smog, control of VOC emissions is a major concern for the industries' commitment to the environment. Approaches for process optimisation have a long tradition within chemical and process engineering for the systematic identification of cost- and resource-efficient production options. The challenge in the context of supply chain management is the optimal recovery and reuse of materials not only for single substances or energy flows in large chemical installations, but also for smaller production processes and various mass and energy flows within and between enterprises. Based on a case study from the industrial coating of bicycle frames, an approach for Multi Objective Pinch Analysis (MOPA) for the evaluation of overall recovery potentials for energy, water and VOC is presented. Moreover, a metric for resource efficiency is introduced as a measure for the possible savings potential and for the savings ultimately realised. This integrated approach requires a tight coupling of mass, energy, economic and environmental assessment methods and demands a highly interdisciplinary approach.

Psychrometric-like charts for the energy analysis of VOC recovery processes

Psychrometric-like charts for the energy analysis of VOC removal or recovery by means of combined adsorption and condensation were developed. These charts make use of conventional psychrometric parameters: dry-bulb temperature, specific mass content—or alternately mole fraction—, degree of saturation (relative “humidity”), enthalpy, etc., for toluene-nitrogen mixtures. In addition, they include information on the adsorption equilibrium, and particularly the adsorbed-phase enthalpy, in order to characterise the adsorbers behaviour. The graphical representations of unitary operations occurring in VOC treatment processes are presented: VOC condensation on a cool coil, adsorption or regeneration of an adsorber. This methodology is applied to a case study based on an indirectly heated and cooled adsorber and a heat pump. A proper design of this integrated process allows to use half of the heat available at the heat pump condenser, which is usually wasted.

Dual Reflux PSA Process Applied to VOC Recovery as Liquid Condensate

A new pressure swing adsorption process was proposed for treatment of low-VOC-concentration air streams. Feed gas is supplied to the high pressure column at some intermediate position to divide it into an enriching and a stripping sections. A part of air stream leaving the high pressure column is returned to the low pressure column as stripping reflux while air stream leaving the low pressure column is returned totally to the high pressure column as enriching reflux. With this dual reflux policy, VOC vapor can be enriched in the enriching section up to a concentration high enough to be condensed in liquid state as well as VOC free air is produced in the stripping section. High efficiency of the dual reflux PSA was confirmed experimentally in a lab-scale unit with a model system of ethanol-activated carbon for various parameters such as half cycle time, feed rate, feed inlet position etc. The optimum feed inlet position was found experimentally and its behavior was interpreted based on an analytical simulation by short cycle time approximation.

Preparation of PDMS vi–Al 2O 3 composite hollow fibre membranes for VOC recovery from waste gas streams

A new PDMS vi–Al 2O 3 composite hollow fibre membrane has been developed by coating a PDMS vi-oligo film on the outer surface of an Al 2O 3 hollow fibre porous substrate prepared by a dry/wet phase inversion method. Microstructures of the composite membranes were examined using scanning electron microscopy (SEM), displaying a uniform PDMS vi-oligo coating layer, free of defects with a thickness of around 15 μm. Such composite hollow fibre membranes are suitable for VOC recovery from waste gas streams because of their high chemical stability. The separation performances of the PDMS vi–Al 2O 3 composite hollow fibre membrane were studied using chloroform in N 2 as a test vapour mixture. By analyzing the experimental data obtained at various conditions with a mathematical model derived, the permeabilities of chloroform and nitrogen in the PDMS vi polymer membrane were obtained. The effects of temperature, feed flow rate, vacuum pressure on the permeate side and feed concentration on the chloroform recovery were also investigated both experimentally and theoretically.

Automating hierarchical environmentally‐conscious design using integrated software: VOC recovery case study

AbstractTraditionally, chemical process design and optimization has mainly been based on economic considerations. Currently, the scope is being extended to include environmentally‐conscious process design (ECD). ECD will be facilitated by the emergence of integrated design methodologies and tools. The objectives of this paper are to present a hierarchical design methodology for environmentally‐conscious process design, and an integrated assessment and optimization software. An application for the recycle of VOCs from a gaseous waste stream is presented using this design methodology and software. Revenue increased and environmental impacts were reduced. The net present value for the optimum design is approximately $900,000, which is much higher than the base case design, −$2,498,200. A composite environmental index decreases from 1.19 × 10−4 in the base case to about 1.30 × 10−5 in the optimum case.This automated tool along with the embedded design methodology provides an effective and efficient way to perform environmentally‐conscious chemical process design and optimization.

VOC–air separations using gas membranes

AbstractVolatile organic components (VOC) are commonly emitted from chemical processes, ranging from dilute to concentrated streams. Membrane separation techniques are gaining increasing interest and acceptance for the recovery of VOCs. Various thin film composite membranes were experimentally assessed for the separation of gases and vapours. The membranes were used in a flat sheet configuration with a dense elastomeric silicone as the top layer on a porous polyether‐imide (PEI) or polyvinylidene‐fluoride (PVDF) support. Experimental results for pure substances and for binary mixtures were used to determine the permeability as a function of temperature and to calculate the selectivity towards nitrogen. Different models are available in the literature to predict the permeability of hydrocarbons and in this paper the free‐volume model is evaluated. The predictions from this model overestimate the experimental permeabilities, even after corrections through integrating the concentration polarisation and resistance of the porous support. A design method is developed to calculate the necessary surface area of the membrane separation module for a given flow rate, concentration, operating temperature and pressure, and the characteristic (experimental) permeability and selectivity of the membrane. This design is applied as an example to a butane–air system. Finally, current industrial applications are briefly reviewed.© 2003 Society of Chemical Industry

Minimization of water vapor interference in the analysis of non-methane volatile organic compounds by solid adsorbent sampling

Water vapor can be a significant interference in the analysis of air for non-methane volatile organic compounds (NMVOCs) using solid-adsorbent sampling techniques. The adsorbent materials used in sampling cartridges have different hydrophobic characteristics, and it is therefore necessary to characterize solid-adsorbent cartridges over a wide range of humidity. Controlled humidity experiments were performed to assess the extent of water vapor interference when samples are collected onto AirToxics solid-adsorbent cartridges. It was found that elevating the temperature of the cartridge to 10 °C above the temperature of the air sample greatly reduced water vapor adsorption and interferences and resulted in ≥90% recovery of NMVOCs, biogenic VOCs and chlorofluorocarbons. Similar collection efficiencies were obtained at ambient temperature by reducing the relative humidity to ≤60% in the sample by dilution with dry, scrubbed ambient air. A procedure also was developed and optimized for dry-purging cartridges prior to analysis. However, under optimized conditions, significant losses of C 3–C 5 compounds still occurred under highly humid conditions. It was determined that these losses were due to reduced retention during sampling rather than loss during the dry purge procedure. The dry purge method was shown to be adequate at high humidities for sampling NMVOCs with retention indices greater than 500.

Recovery of VOCs from high‐volume, low‐VOC‐concentration air streams

AbstractHigh‐volume, low‐VOC‐concentration air streams are produced by a broad range of industries. The most widely used treatment technology is carbon adsorption, which produces dilute aqueous waste streams as a secondary waste, is difficult to adapt to particulate‐containing streams, and is too expensive to be applied by some industries. Scrubbing the air with an absorbent liquid is economical, but limited to scrubbing with water due to the expense and difficulty of regenerating nonaqueous scrubbing liquids. A low‐volatility organic scrubbing liquid regenerated by a stripper/membrane vapor‐separation unit was used to remove VOCs from the dilute air stream. The technical and economic feasibility of the scrubbing/stripping/membrane separation hybrid process was evaluated in laboratory tests with a pilot‐scale system. The unit, operated with model‐contaminated gas streams containing 100 to 2,000 ppm methylene/chloride, removed 95% of the methylene chloride in the feed air as a condensed liquid. The experimental data show that the process offers significant cost and operating benefits over other technologies for streams in the 500 to 2,000 ppm VOC concentration range. It can be applied to treating effluent air streams from painting, degreasing, and printing operations.

Comparative Environmental Assessments of VOC Recovery and Recycle Design Alternatives for a Gaseous Waste Stream

Comparative Environmental Assessments of VOC Recovery and Recycle Design Alternatives for a Gaseous Waste Stream

Comparative Environmental Assessments of VOC Recovery and Recycle Design Alternatives for a Gaseous Waste Stream

Decisions involving chemical process design, including selection of technologies and operating conditions, should integrate environmental considerations. The assessment methodology presented in this article includes nine environmental and human health impact indices, a “level I” multimedia fate and transport model, and an air emissions estimation calculator based on emission factors and correlations. The methodology and software tool was used to evaluate two case studies involving mixed-solvent recovery from a gaseous waste stream utilizing output from a commercial process simulator. The assessment methodology was applied for two evaluations: (a) separation technology selection and (b) choice of process operating conditions. It was found that two adsorption technologies with either steam stripping or vacuum regeneration are superior to three absorption technology configurations based on environmental and health indices. With suitable weightings, a single process composite index was defined and served as ...

A Laboratory Method to Investigate Gaseous Emissions And Solids Decomposition During Composting Of Municipal Solid Wastes

A laboratory method was developed to quantify CO2, NH3 and VOC yields and to follow solids decomposition during composting of MSW or its components. All organic substrates were shredded, water and nutrients were added to near optimum levels prior to composting, and composting was continued until feed materials reached approximately the full extent of decomposition. Twenty five L stainless steel digesters were used and aluminum packing was mixed with the wastes to facilitate airflow. Thermophilic temperatures were maintained and air supplied in excess. Nutrients were added to reach an initial C/N ratio of approximately 30. CO2 and NH3 gases in the exit air stream were captured in alkaline and acidic solutions, respectively, and quantified through titration on a cumulative basis. VOC traps, prior to the gas traps, captured emitted volatile organic compounds, which were quantified on a cumulative basis. Solids were analyzed for hot water soluble matter, fats and lipids, cellulose, hemicellulose and lignin/humus. Food wastes, yard wastes and mixed paper produced approximately 368, 220 and 153 g C-CO2/dry kg and approximately 40.5, 4.6 and 2.0 g N NH3/dry kg of starting material, respectively. VOC volatilization profiles had a decreasing trend with composting. Partially composted MSW produced 8.2 mg/dry kg of 8 selected VOCs. CO2, NH3 and VOC recovery tests resulted in efficiencies of 98.6%, 97.6% and 94.6% respectively. Reproducibility of the solids decomposition and gaseous emissions measurements was observed. Carbon and nitrogen mass balance closures ranged from 85.5% to 117.1% and 32.2% to 175% respectively.

A composite hollow fiber membrane-based pervaporation process for separation of VOCs from aqueous surfactant solutions

The separation and recovery of VOCs from surfactant-containing aqueous solutions by a composite hollow fiber membrane-based pervaporation process has been studied. The process employed hydrophobic microporous polypropylene hollow fibers having a thin plasma polymerized silicone (PDMS) coating on the outside diameter, trichloroethylene (TCE) as the model contaminant and sodium dodecyl sulfate (SDS) as the surfactant. The feed solution was passed through the fiber bore; the shell side had vacuum. The process operating parameters, e.g., feed flow rate, TCE and SDS concentrations, were varied over a wide range to investigate their effect on the process performance. Depending on the concentration of the surfactant, separation of VOCs can be achieved via two different conditions, namely, wetted pore and non-wetted pore. The resistances-in-series concept successfully applied earlier to the TCE–water system has been extended to the TCE–SDS–water system for both wetted pore and non-wetted pore conditions. Results will be provided also for a more complex feed solution containing alcohols and the hydrophilic polymer, xanthan gum.

VOC Recovery through Microwave Regeneration of Adsorbents: Process Design Studies

ABSTRACT Process design studies are described for a new type of VOC recovery system which uses microwave heating to regenerate adsorbents. Microwave regeneration systems create a highly concentrated effluent from which the VOCs can be recovered by condensation at near-ambient temperatures. Important design considerations, predicated on experimental work and model development, are identified and discussed. Parametric studies are then described that identify the optimal adsorbent selection, operating cycle, recovery configuration, regeneration pressure, regeneration final coverage, and column configuration. In general, it was found that microwave regenerated adsorption systems favor the use of low dielectric loss-factor polymeric adsorbents and operation under low pressure conditions (about 5 torr absolute pressure).

VOC recovery process

VOC recovery process

Pollution prevention through process integration: systematic design tools

Overview of Pollution Prevention and Process Integration. Modeling of Individual Mass Exchange Units for Environmental Applications. Synthesis of Mass Exchange Networks. Graphical Techniques for Mass Integration: Segregation,Recycle, Interception, and Unit Manipulation. Optimization Techniques for Mass Integration. Synthesis of Reactive Mass Exchange Networks. Combined Heat and Mass Integration. Design of Heat-Induced Separation Networks. Recovery of VOCs. Modeling and Design of Membrane Systems. Environmentally-Benign Chemistry and Species. Subject Index.

Recovery of VOCs from surfactant solutions by pervaporation

Surfactant-based processes are emerging as promising technologies to enhance conventional pump-and-treat methods for remediating soils contaminated with nonaqueous phase liquids (NAPLs), primarily due to the potential to significantly reduce the remediation time. In order to reuse the surfactant, thereby making the process more economical, the NAPLs must be separated from the surfactant solution. Pervaporation was identified as a potential technology for removing volatile NAPLs from surfactant solutions. Initial tests with 1,1,1-trichloroethane (TCA) in an aqueous solution of the non-ionic surfactant Triton X-100 showed that the surfactant had a negligible effect on both flux and selectivity at concentrations of up to four times the critical micelle concentration (4×CMC). Further tests with a 40×CMC surfactant solution yielded moderately lower TCA fluxes and selectivities than comparable aqueous solutions without surfactant. The reduced pervaporation performance at higher surfactant and TCA concentrations were found to result from two effects: (1) increases in the viscosity of the solution, which increases the liquid-side boundary layer mass transfer resistance and (2) partitioning of TCA into the micelles, thereby reducing the effective extramicellar concentration. Despite these reductions in performance, pervaporation was found to be quite capable of removing this volatile NAPL from the surfactant solutions.

Recovery of Volatile Organic Solvent Compounds from Air by Ceramic Membranes

Defect-free γ-Al2O3 and La2O3-modified γ-Al2O3 membranes were prepared for recovery of acetone from nitrogen by multilayer diffusion and capillary condensation mechanisms. There existed an optimum range for acetone permeance (∼8 × 10-7mol/m2·s·Pa) and acetone−nitrogen separation factor (∼1000) with respect to membrane temperature or feed composition. Hysteresises of acetone permeability and separation factor were also found between desorption and adsorption. The La2O3-modified γ-Al2O3 membrane appears to be the most effective for use in the VOC recovery process as compared to polymeric, Vycor, and unmodified γ-Al2O3 membranes.