Linear Driving Force Approximation Research Articles

Simulation of a zeolite thermochemical heat storage reactor: Impact assessment of isotherm model selection

Efficient modeling of thermochemical heat storage reactors is required to predict their performance in various operating conditions and optimize their design. Such modeling necessitates an accurate description of the properties of storage materials, which is still challenging to this day. This paper specifically investigates the influence of the choice of the sorption isotherm model. To this aim, the Langmuir, Dubinin-Astakhov (DA) and modified Brunauer-Emmet-Teller (BET) isotherm models are studied. The 1D model of an open fixed bed reactor based on the hydration and dehydration of zeolite 13X is presented. The model couples heat and mass transfer and uses the linear driving force approximation. Experimental investigations are also performed to characterize the sorption equilibrium of the material, its adsorption kinetics at the reactor scale and the resulting heat storage performance. The model is validated simultaneously on the basis of mass and of heat transfer measurements (i.e., breakthrough and temperature curves).The BET isotherm is shown to be the most relevant for the description of water adsorption on zeolite 13X because it considers multilayer adsorption. It fits the experimental isotherm best. At the reactor scale, the modified BET model also provides the best results, closely followed by the DA model. Still, for consistent predictions, the characterization of the chosen sorbent (i.e., the experimental data used to correlate the isotherm model or the heat of sorption) is of utmost importance and the initial water loading must be adequately specified.

Experimental and modeling study of volatile organic compounds adsorption over zeolitic monolith adsorbent

In this study, a coupled mass and momentum model is developed and solved to describe the dynamic adsorption of a single adsorbate over honeycomb structured zeolite under industrial operating conditions. The Linear Driving Force approximation was used to predict the kinetics of adsorption to the solid-phase mass transfer and Navier Stokes equations were solved both radially and axially under laminar flow conditions through the honeycomb channels. To investigate the effect of key input parameters on model results, a sensitivity analysis was performed. Modeling and experimental results compared the effects of different initial concentrations and gas stream face velocities under a range of conditions to determine adsorption capacity, removal efficiency, and the 5% breakthrough time. Overall, the model output was in good agreement (less than 5% mean absolute relative error in concentration) with the experimental results under industrially relevant operating conditions. Modeling results illustrated that the radial velocity distribution over the monolith channels has an important effect on the shape of the breakthrough curve as well as the 5% breakthrough time. Both experimental results and modeling predictions showed that the long tails of the adsorption breakthroughs were the result of the non-uniform flow distribution, which resulted in delayed saturation of the outer honeycomb channels.

Synthesis of macroporous three-way catalysts via template-assisted spray process for enhancing mass transfer in gas adsorption

Catalyst particles with macroporous structures have been attracting much attention because of their high molecular diffusions and catalytic activities. In this study, macroporous-structured three-way catalyst (TWC) particles were synthesized via a template-assisted spray process followed by an additional heating process. Several process parameters, i.e., carrier-gas type, template size, and reaction temperature, were investigated to enable preparation of macroporous particles with controllable porous structures and interconnected pore networks. The mass transfer coefficients of the obtained macroporous TWC particles were assessed using the Linear Driving Force approximation to understand the effects of the macroporous structure on the mass transfer improvement. The results showed that the introduction of macropores into TWC particles enhances the mass transfer coefficient.

Arsenic adsorption by low-cost laterite column: Long-term experiments and dynamic column modeling

Arsenic (As) contamination of drinking water supplies is a major concern in many countries due to its large concentration in groundwater and high toxicity. In this study, batch adsorption experiments on a natural laterite adsorbent from Vietnam (NLTT) were firstly conducted, followed by four column adsorption experiments using NLTT working with synthetic water under different experimental conditions (initial arsenate As(V) concentration: 0.1 and 0.5 mg/L; bed height: 0.15 and 0.41 m). Results from the batch equilibrium adsorption study show that all three models - Sips, Langmuir, and Freundlich - fitted the experimental data very well. The Sips and Langmuir maximum adsorption capacities were 0.76 mg/g and 0.58 mg/g, respectively. At an As(V) concentration of 0.5 mg/L, adsorption breakthrough occurred at 28 h and 122 h for column heights of 0.15 m and 0.41 m, respectively. When As(V) concentration fell to 0.1 mg/L, the breakthrough times rose to 144 h and 240 h, respectively. A linear driving force approximation (LDFA) model incorporating the Sips equation was calibrated with data from the equilibrium and kinetic adsorption experiments and one column adsorption experiment (initial concentration: 0.1 mg/L; bed height: 0.15 m). The LDFA model with the calibrated model coefficients could predict the breakthrough curves and adsorption time in the three other column experiments and four household column filters used to treat As contaminated groundwater in Vietnam. The study revealed that application potential for NLTT in column adsorption studies and field trials to remove As(V) is significant despite this study having limited data. Subsequently, refining the model based on simulation of results is cost-effective, saves time and effort, and negates the need for multiple experiments to optimize filter conditions.

Adsorption Characteristics of 2,4-Dichlorophenoxybutric Acid Using Bamboo Activated Carbon in a Fixed Bed

Adsorption and desorption characteristics of 2,4-dichlorophenoxybutyric acid (2,4-DB) from aqueous solution on bamboo activated carbon (BAC) were studied in a fixed bed adsorber. The adsorption equilibrium capacity of 2,4-DB on BAC increased with decreasing initial pH of the solution and with a maximum adsorption capacity of 1.61 mol/kg. The adsorption rate of 2,4-DB on BAC could be best fitted by the pseudo first-order model. The adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of the 2,4-DB in a fixed bed. More than 95% desorption of 2,4-DB was obtained using distilled water.

Evaluation of activated carbons produced from Maize Cob Waste for adsorption-based CO2 separation and biogas upgrading

Two activated carbons (AC) resulting from CO2 activation of Maize Cob Waste (MCW) were investigated as adsorbent materials for biogas upgrading to bio-methane applying a biorefinery concept. The porous carbons were originated from different times of activation and the one resulting from 3 h with CO2 (MCW(PA)3 h) showed better textural properties, higher working capacity, and selectivity towards CO2 than the carbon resulting from 2 h of activation (MCW(PA)2 h), making it the best candidate for biogas purification. The adsorption equilibrium measurements of CO2 and CH4 on MCW(PA)3 h carbon showed that the Sips isotherm model, as well as the Adsorption Potential Theory (APT), can be confidently employed to accurately correlate the adsorption equilibrium data of the adsorbates employed. In the range of the partial pressures typical for biogas upgrading units, MCW(PA)3 h showed higher CO2 uptakes than the ones reported for coal-based commercial ACs and similar uptakes to the ones reported for bio-based ACs. Moreover, the axial dispersed plug-flow and Linear Driving Force (LDF) approximation for lumped solid-diffusion mass transfer model used for the prediction of the dynamic behaviour of the adsorbate-adsorbent system, provided a good agreement with the experimental results, demonstrating its applicability to the studied system. This work represents the basis of future modelling works of a Pressure Swing Adsorption (PSA) cycle based on the use of MCW(PA)3 h as adsorbent material and demonstrates the high potential of this novel material to be applied in biogas upgrading processes.

Continuous and selective copper recovery by multi-modified and granulated SBA-15

Continuous and selective recovery of copper (Cu) from heavy metal wastewater not only mitigates the pollution of environment but also can be applied for industrial field. Due to several advantages such as large pore size, easy modification, physical and chemical stabilities, mesoporous silica material, SBA-15, has been synthesized via hydrothermal reaction in this study. For enhancing the adsorption capacity and selectivity for Cu ions, prepared SBA-15 was modified with manganese loading and amine-grafting (MN-SBA) then granulated by alginic-acid (GMN-SBA), successfully. Adsorption capacities for heavy metals such as Cu, Zn, Ni and Mn were 2.11, 1.24, 1.74 and 1.25 mmol/g on MN-SBA and decreased to 1.23, 0.68, 0.86 and 0.65 when it was granulated. Even though the adsorption capacities of GMN-SBA for heavy metals decreased by 40–50%, it enabled easy regeneration and separation process when applied for continuous fixed-bed column adsorption mode. Specifically, the results demonstrated that GMN-SBA was able to be reused for 5 times while maintaining over 80% adsorption capacities. Fixed-bed adsorption results were well explained by dynamic adsorption model incorporated with linear driving force approximation (LDFA) model. The simulation of fixed-bed adsorption tests was proceeded in terms of bed length, feeding concentration and flow rate, and it showed the breakthrough times were shifted in the axis of time. In multi-component adsorption, LDFA model showed a high overshoot phenomenon of the breakthrough curves for Zn, Ni and Mn compared to Cu. This reflected the high affinity of Cu towards GMN-SBA compared to other heavy metals.

Applicability of linear driving force (LDF) mass transfer model for heavy metal biosorption in packed bed column

Adsorption technique for industrial effluent treatment as well as recovery of valuable components have been widely accepted for application. Since then, many researches on adsorption field have been established to investigate the economical yet having high separation efficiency of adsorbent for specific purpose. Biosorbent, for instance have shifted the focused of researches due to their abundant existence that can be easily converted into adsorbent, and some showed promising separation properties. However, the study on the biosorbent adsorption usually limited until the isotherm determination in batch experimental study. The dynamic behaviour of the system requires the experimental set-up in packed bed column, which is primarily controlled by the mass transfer mechanism. Mathematical expression describing the system is very useful as preliminary estimation of the system dynamic behaviour, provided by several input parameters such as isotherm parameters and mass transfer coefficients. Linear driving force (LDF) model approximation has proved its reliability to describe the dynamic behaviour of a system over a wide range of adsorption process. By taking three (3) experiments adsorption system on packed bed, the respective systems were simulated employing LDF approximation to obtain the dynamic behaviour of the system. The breakthrough curves were simulated by using the simplified mathematical model of LDF approximation. It is shown that the predicted LDF approximation give acceptable agreement to the experimental data with error of less than 15%, provided with mass transfer coefficient predicted from correlation. Overall, this work proved that it is possible to accurately determine the behaviour of the system using LDF approximation accompanied with the predicted mass transfer coefficient (MTC) from correlation and accurately determined adsorption isotherm for continuous system. Therefore, the mass transfer approximation is further used for evaluation of industrial-scaled packed bed column.

Supercritical CO2 extraction of pelletized oilseeds: Representation using a linear driving force model with a nonlinear sorption isotherm

This work develops a general, predictive model for the SuperCritical (SC) CO2 extraction of pelletized oilseeds. Cumulative SC-CO2 extraction curves of small (S, dp = 2.5 mm) and large (L, dp = 4.0 mm) cylindrical evening primrose seed pellets were modeled simultaneously using a Linear Driving Force (LDF) approximation modified to consider the nonlinear oil partition between CO2 and the substrate and extrapolated using the actual solubility of oil in CO2 at extraction conditions (40 °C and 45 MPa). Model best-fitting parameter was a single interparticle porosity (εp) of pellets considering equilibrium conditions after static extraction, and mass transfer kinetics during dynamic extraction. The adaptation of general model to bisized mixtures containing 25–75% S-pellets, predicted experimental results better than a monosized version (same Sauter mean diameters) because of the negative impact on overall cumulative extraction curves of slow-extracting L-pellets. Finally, a simplified version of the general model was developed that neglected the intraparticle porosity (εp = 0) and used a microstructural factor (FM∝(εp)−2) in the general model as the best-fitting parameter. This simplified model saved 33% of computational time at the expense of overestimating extraction rates, particularly at the beginning of the diffusion-controlled period, which diminished as εp decreased and FM increased.

Selective copper extraction by multi-modified mesoporous silica material, SBA-15

Selective copper (Cu) recovery from wastewater mitigates environmental pollution and is economically valuable. Mesoporous silica adsorbents, SBA-15, with amine-grafting (SBA-15-NH2) and manganese loading along with amine-grafting (Mn-SBA-15-NH2) were fabricated using KMnO4 and 3-aminopropyltriethoxysilane. The characteristics of the synthesized adsorbents were evaluated in detail in terms of its crystal structure peaks, surface area and pore size distribution, transmission electron microscope and X-ray photoelectron spectroscopy. The results established the 2.08mmol/g of Cu adsorption capacity on Mn-SBA-15-NH2. Furthermore, in a mixed heavy metal solution, high selective Cu adsorption capacity on Mn-SBA-15-NH2 (2.01mmol/g) was achieved while maintaining 96% adsorption amount as that of a single Cu solution. Comparatively, Cu adsorption on SBA-15-NH2 decreased by half due to high competition with other heavy metals. Optimal Cu adsorption occurred at pH5. This pH condition enabled grafted amine group in Mn-SBA-15-NH2 to form strong chelating bonds with Cu, avoiding protonation of amine group (below pH5) as well as precipitation (above pH5). The adsorption equilibrium well fitted to Langmuir and Freundlich isotherm models, while kinetic results were represented by models of linear driving force approximation (LDFA) and pore diffusion model (PDM). High regeneration and reuse capacity of Mn-SBA-15-NH2 were well established by its capacity to maintain 90% adsorption capacity in a multiple adsorption-desorption cycle. Cu was selectively extracted from Mn-SBA-15-NH2 with an acid solution.

Linear Driving Force Approximations as Predictive Models for Reactive Sorption

Herein, the utilization of linear driving‐force approximations as predictive models for hydrogen sulfide removal on a commercial copper‐based sorbent is assessed. Sorption experiments are carried out in a fixed‐bed reactor at different flow conditions, temperatures, total pressures, and inlet hydrogen sulfide concentrations. For large pellet sizes (≥800 μm), quasi‐chemical linear driving‐force approximations, that are first order in both bulk gas‐phase concentration and solid‐phase capacity, effectively model contaminant breakthrough curves. Experimentally determined rate parameters (10.7 ± 0.7 s−1 and 6.5 ± 0.5 s−1 for 800 and 1000 μm‐sized particles, respectively) reflect those determined from pore diffusion within pellets. For small pellet sizes (≤212 μm), linear driving‐force approximations, that are zero order in bulk gas‐phase concentration but first order in solid‐phase capacity, model contaminant breakthrough curves; and rate parameters reflect reaction and diffusion at reactive interfaces rather than bulk or pore diffusion. These studies demonstrate that linear driving‐force approximations can model experimentally determined trace hydrogen sulfide removal parameters. Alternatively, under conditions where bulk and/or pore diffusions are limiting, the rate parameters can be calculated from known engineering theories (e.g., the Chapman–Enskog relation or the Wilke–Chang correlation).

A model for transient diffusion in bidisperse pore structures

A bidisperse model for transient diffusion and adsorption processes in porous materials is presented in this paper. The mathematical model is solved by numerical methods based on finite elements combined with the linear driving force approximation. A criterion based on the model to identify the diffusion controlling mechanism (macropore diffusion, micropore diffusion, or both) is proposed. The effects of different adsorption isotherms (linear, Freundlich, or Langmuir) on the concentration profiles and on curves of fractional uptake versus time are investigated. In addition, the influences of model parameters concerning the pore networks on the fractional uptake are studied as well.

Adsorption of vanillic and syringic acids onto a macroporous polymeric resin and recovery with ethanol:water (90:10 %V/V) solution

In this work the adsorption of vanillic (VA) and syringic (SA) acids onto the nonpolar resin SP700 was investigated aiming to collect data to evaluate their separation from a lignin oxidation mixture containing other phenolic compounds. The respective adsorption equilibrium isotherms in aqueous solutions were assessed at three different temperatures 288, 298 and 333 K and experimental results were fitted with Bi-Langmuir isotherm model. Maximum adsorption capacities of 0.486 g g−1dry resin and 0.407 g g−1dry resin were obtained for VA and SA, respectively.Dynamic studies at different temperatures and feed concentrations were performed and a mathematical model comprising the Bi-Langmuir equilibrium isotherm, axial dispersed plug flow, intraparticle mass transfer resistance expressed with linear driving force approximation with no temperature gradients and constant porosity along the bed successfully described the adsorption concentration histories at the outlet of the fixed bed.More than 83% of each phenolic acid was readily eluted within 5 min elution with ethanol:water (90:10 %V/V) solution allowing obtaining a final concentrated solution with 5.8–11.7 g L−1.

Chemisorption and kinetic mechanisms of elemental mercury on immobilized V2O5/TiO2 at low temperatures.

To investigate the effect of low temperature and catalyst filling pattern on the adsorption of Hg° by DeNOx equipment, the chemisorption and kinetic mechanisms of Hg° adsorption on 5-30%V2O5/TiO2 immobilized on glass beads at 100-160 °C were investigated. The effects of the reaction temperature, influent Hg° concentration, and V2O5 doping amount on the adsorption efficiency and capacity for Hg° were explored. The active sites for Hg° adsorption were further identified. Additionally, the adsorption kinetics were modelled using the linear driving force approximation, Fick's diffusion model, and pseudo-second-order kinetic model. Finally, the influence of immobilization on the adsorption of Hg° was also investigated. Experimental results showed that the bridged oxygen atom of V-O-V played a key role in the adsorption of Hg°. The Hg° adsorption efficiencies decreased from >90% to 40% as the reaction temperature increased from 120 °C to 160 °C for 20%V2O5/TiO2, while the adsorptive capacities for Hg° were highly influenced by the influent Hg° concentration and V2O5 doping amount. 20%V2O5/TiO2 had the highest adsorptive capacity of 2547 μg Hg°/g V2O5/TiO2 at 160 °C. The kinetic results showed that the linear driving force approximation model fit the Hg° adsorption better than the other models. The diffusion resistance increased significantly for the immobilized catalysts because the external mass transfer coefficient decreased by more than 1200-fold.

Adsorption model development for mass transport characteristics of MFEP structure by physisorption method

A novel heterogeneous contacting structure, microfibrous entrapped particles (MFEP) structure, was developed to intensify chemical processes including heterogeneous catalytic reactions and the gas–solid adsorption process. MFEP is characterized by its extremely high heat and mass transfer efficiency, which is critical for thermal and/or mass transfer limited reactions. To investigate the mass transport characteristics of MFEP, a physisorption (hexane adsorption onto activated carbon) was used as a probe process. A theoretical adsorption model was developed based on the linear driving force approximation and constant pattern behavior. Mass transfer mechanisms including external diffusion, intraparticle molecular diffusion, Knudsen diffusion, and surface diffusion, were considered in the model. This model was then used to analyze the experimental breakthrough data and calculate the mass transfer coefficient. The experimental results showed that for MFEP with a particle diameter of approximately 200 µm, the volumetric mass transfer coefficient is more than 10 times higher than that of a packed bed. Combining the experimental results and theoretical analysis, it was also found that in the particle diameter range of 2000 to 100 µm, the system’s mass transfer resistance is primarily the result of both the external and internal mass transfer resistances. This leads to the conclusion that decreasing the particles size can effectively increase the mass transfer rate. However, when the particle size is less than 100 µm, axial dispersion becomes the rate-limiting resistance, potentially reducing the residence time of the adsorbate in the adsorbent bed. The current study was aimed at understanding the mass transfer behavior in the MFEP structure, and optimizing of MFEP for specific heterogeneous contacting applications.

Gradient elution behavior of proteins in hydrophobic interaction chromatography with U-shaped retention factor curves

Protein retention in hydrophobic interaction chromatography is described by the solvophobic theory as a function of the kosmostropic salt concentration. In general, an increase in salt concentration drives protein partitioning to the hydrophobic surface while a decrease reduces it. In some cases, however, protein retention also increases at low salt concentrations resulting in a U-shaped retention factor curve. During gradient elution the salt concentration is gradually decreased from a high value thereby reducing the retention factor and increasing the protein chromatographic velocity. For these conditions, a steep gradient can overtake the protein in the column, causing it to rebind. Two dynamic models, one based on the local equilibrium theory and the other based on the linear driving force approximation, are presented. We show that the normalized gradient slope determines whether the protein elutes in the gradient, partially elutes, or is trapped in the column. Experimental results are presented for two different monoclonal antibodies and for lysozyme on Capto Phenyl (High Sub) resin. One of the mAbs and lysozyme exhibit U-shaped retention factor curves and for each, we determine the critical gradient slope beyond which 100% recovery is no longer possible. Elution with a reverse gradient is also demonstrated at low salt concentrations for these proteins. Understanding this behavior has implications in the design of gradient elution since the gradient slope impacts protein recovery.

Single sphere model fitting of supercritical carbon dioxide extraction from Quercus infectoria galls

Q. infectoria galls, locally knowns as ‘manjakani’ in Malaysia and Indonesia, is a traditional medicine commonly used for postpartum recovery due to its strong astringency. The astringent properties of Q. infectoria galls is due to the high amount of tannin available in the extract. In this study, supercritical carbon dioxide (SC-CO2) with the presence of absolute methanol (1:3 w/v) was used for the extraction of Q. infectoria galls. The SC-CO2 extraction of the galls involve the diffusion and mass transfer process, represented by the value of diffusion coefficient (De) and the external mass transfer coefficient (kf). Single sphere model (SSM) was adapted and fitted into the experimental data, and De was found to be in the range of 0.91 ×10-11 to 9.99 × 10-11 m2/s. The linear driving force approximation was used to determine the kf values, which calculated to be in the range of 4.60 ×10-6 m/s to 9.50 ×10-6 m/s. SSM also pointed out that the SC-CO2 extraction of Q. infectoria galls is governed by internal diffusion with Biot number (Bi) greater than 10.

A Simple Method for the Determination of Adsorption Kinetic Parameters Using Recycle Fixed-Bed Adsorber

This study focuses on the development of a novel analysis technique for determining the intraparticle diffusivity $$(D_{\mathrm{S}})$$ and fluid film mass transfer coefficient $$(k_\mathrm{F})$$ from a concentration history curve of a recycle fixed-bed reactor without using the linear driving force approximation and empirical equations for the estimation of $$k_\mathrm{F}$$ . The recycle fixed-bed method requires lesser amounts of working fluid for experiment purposes, which is an advantage over the usual fixed-bed method. Based on the characterization results of the concentration history curves, simulated by rigorous numerical calculations, a novel analysis technique was established. The $$D_{\mathrm{S}}$$ value can be determined from the experimentally obtained time at which the concentration of the curve is minimal $$(t_{C\mathrm{min}})$$ . The $$k_\mathrm{F}$$ value can be determined from the $$D_{\mathrm{S}}$$ value and Biot number (Bi), which can be estimated from the experimental ratio of the maximum concentration to the minimum concentration $$(c_{\max }/c_{\min })$$ . The $$D_{\mathrm{S}}$$ and $$k_\mathrm{F}$$ values of phenol adsorption on an activated carbon material were determined experimentally using the proposed analysis method. This method enables the determination of reliable adsorption kinetic parameters through a simple and economical experiment. However, appropriate experimental data must be acquired under regulated experimental conditions, especially in the case of fluctuation of the concentration history curve.

Adsorption and desorption dynamics of CF4 on activated carbon beds: Validity of the linear driving force approximation for pressure-changing steps

Adsorption and desorption dynamics of CF4 on an activated carbon bed were studied experimentally and theoretically, focusing on pressure-changing steps. The theoretical model used the ideal adsorbed solution (IAS) theory and the linear driving force (LDF) approximation as equilibrium and mass transfer models, respectively. Adsorption breakthrough curves of raw CF4 gas (500, 1,000, and 1,500 ppm) were well predicted by the theoretical model and the diffusion time constant for CF4 was found to be 3.3×10−3 s−1 from breakthrough curve fitting. Changes in the CF4 concentration during depressurization could be easily predicted using the above mathematical model when the half-cycle time (θ c ) was above 0.1. However, significant discrepancies were observed between the predicted CF4 concentrations and the experimental data when θ c was 0.1. Nakao and Suzuki also reported that proportional constant of LDF approximation (=KD e /R p 2) needs to be modified when θ c is less than 0.1.

Pressure swing adsorption for biogas upgrading. A new process configuration for the separation of biomethane and carbon dioxide

Pressure swing adsorption (PSA) is an interesting technology for biogas upgrading, due to compactness of the equipment, low energy requirements, low capital cost, and safety and simplicity of operation. Unfortunately, some shortcomings penalize its diffusion in comparison with other technologies; in particular, conventional PSA has a low methane recovery and cannot compete in this field with other processes such as amine scrubbing; furthermore, it produces an off gas stream with a significant methane content, which requires further treatment to avoid the emission of residual methane into the atmosphere. In this framework, this study focuses on the feasibility of a PSA based separation process able to obtain a biomethane stream suitable to be injected in the natural gas grid (CO2 <3% by volume) with a high methane recovery and an almost pure CO2 stream (CO2 > 99%). The proposed process uses Zeolite 5A as adsorbent material in two PSA units; the biogas is fed to the first unit which produces biomethane; the off gas of the first unit is sent to a second PSA unit which separates carbon dioxide from a residual gas stream, recycled to the first to enhance methane recovery. A dynamic non-isothermal model, based on the linear driving force approximation, is employed to demonstrate the technological feasibility of the separation units and to assess the performance of the whole process. In particular a methane recovery greater than 99% can be obtained with energy consumption of about 1250 kJ per kg of biomethane.