Investigation of CO2 Reaction with CaO and an Acid Washed Lime in a Packed-Bed Reactor

In this work, a mathematical model was developed for the prediction of packed-bed reactor behavior for CaO+CO₂ reaction based on the random pore model. A natural limestone and a modified sorbent using acetic acid washing were used for the experiments. The performances of these sorbents were initially determined using a thermogravimeter analyzer. Then, the reaction was accomplished in a packed-bed reactor for obtaining CO₂ breakthrough curves and investigation of model predictions. This model was able to successfully predict the effect of process conditions and solid texture on the breakthrough curves of the packed-bed reactor.     

Breakthrough analysis of carbon dioxide adsorption on zeolite synthesized from fly ash

Zeolite (FAZ) was synthesized by the fusion method using coal fly ash to adsorb carbon dioxide. The experimental adsorption was operated batchwise in a laboratory-scale packed-bed adsorber to obtain the breakthrough curves of CO₂ under conditions such as adsorption temperatures (20–80 °C), flow rates of gaseous mixture of carbon dioxide and nitrogen (40–100 cm³/min), and concentration of CO₂ (3000–10000 ppmv) at atmospheric pressure of 101.3 kPa. The influence of the experimental conditions, such as the gas flow rate, concentration of CO₂ and adsorption temperature on adsorption behavior, was discussed. The deactivation model, combined the adsorption with the deactivation of adsorbent, was used to analyze the physicochemical properties, such as the adsorption kinetics, capacity and heat of adsorption, by fitting the experimental data of the breakthrough curves to this model. The adsorptive activity and capacity of FAZ were as almost same as those of the commercial zeolite of Wako 4A.     

Adsorption of carbon dioxide onto PDA-CP-MS41 adsorbent

Carbon dioxide was adsorbed onto mesoporous adsorbent of PDA-CP-MS41, which was synthesized by CP-MS41 with propylene diamine, in a laboratory-scale packed-bed. Experiments were carried out at different adsorption temperatures (30–60 °C), amounts of adsorbent (1–3 g), and flow rates of nitrogen (15–60 cm³/min) to obtain the breakthrough curves of CO₂. These curves were tested by the deactivation model, which combined the adsorption of CO₂ and the deactivation of adsorbent particles. The adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data were fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

Adsorption of carbon dioxide onto BDA-CP-MS41

Carbon dioxide was adsorbed onto mesoporous adsorbent of butylene diamine immobilized CP-MS41 (BDA-CP-MS41), which was synthesized by chloropropyl functionalized MCM-41 (CP-MS41) with butylene diamine in a laboratory-scale packed-bed. The adsorber was operated batchwise with the charge of adsorbent in the range of 1–3 g to obtain the breakthrough curves of CO₂. Experiments were carried out at different adsorption temperatures (20–40 °C) and flow rates of nitrogen (10–20 cm³/min) to investigate the effects of these experimental variables on the breakthrough curves. The deactivation model was tested for these curves by combining the adsorption of CO₂ and the deactivation of adsorbent particles. The observed values of the adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

CO2 adsorption performance of polyethyleneimine-modified ion-exchange resin

A series of solid amine adsorbents were prepared by the template method with ion-exchange resin (D001) as the carrier and polyethyleneimine (PEI) as the modifier. The absorbents were characterized by energy disperse spectroscopy (EDS), scanning electron microscope (SEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) techniques. The effects of PEI loading, adsorption temperature and influent velocities on CO₂ adsorption capacity in a fixed-bed reactor were investigated. The results show that the solid amine adsorbent prepared by the template method had a better PEI dispersion, stability and CO₂ adsorption capacity. The maximum CO₂ adsorption capacity was 3.98 mmol·g^?1 when PEI loading was 30%, the adsorption temperature was 65°C and the influent velocity was 40 mL·min^?1. The CO₂ adsorption capacity decreased only by 9.50% after 10 cycles of adsorption–desorption tests. The study of kinetics indicates that both chemical adsorption and physical adsorption occurred in the CO₂ adsorption process. The CO₂ adsorption process included fast breakthrough adsorption and gradually approaching equilibrium stage. The particle internal diffusion process was the control step for CO₂ adsorption.     

活性焦汞吸附特性及动力学机理分析

通过固态吸附剂汞吸附效能测定系统进行了太西活性焦吸附单质汞的实验,考察单质汞Hg⁰入口浓度和温度对太西活性焦脱汞性能的影响并探讨了吸附机理。结果表明:在CO₂/N₂/O₂/NO/Hg⁰体系中,不同Hg⁰入口浓度获得的汞脱除效率曲线相似,脱除效率随Hg⁰入口浓度增大而增加;变入口浓度工况下,汞的吸附全过程遵循准二级动力学反应模型,该吸附过程以化学吸附为主;在反应温度从403 K升高到423 K的过程中,系统发生了化学吸附或者化学反应,423 K可作为活性焦的最佳除汞温度;Bangham方程可对变温工况下活性焦脱除单质汞的吸附过程进行准确描述,并获得不同温度下活性焦脱汞的吸附速率常数存在k_423K>k_463K>k_403K的关系。     

Enhancement of Energy Yield for Ozone Production via Packed-Bed Reactors

The present work aims to enhance the energy yield of ozone production via packed-bed reactors. It has been experimentally demonstrated that ozone concentration and corresponding energy yield achieved by packed-bed reactors are significantly higher than that achieved by DBD only. The so-called packed-bed reactor is constructed by packing granular dielectric pellets within a DBD reactor. Two kinds of dielectric materials including glass beads and Al₂O₃ pellets are tested. Experimental results indicate that an ozone generator packed with Al₂O₃ pellets results in a higher ozone production compared with one packed with glass beads. The maximum ozone production takes place when Al₂O₃ pellets with diameter of 2 mm are packed. The maximum ozone concentration, ozone production rate, and energy yield achieved in this study are 61 gO₃/m³, 3.7 gO₃/hr, and 173 gO₃/kWh, respectively. The highest ozone concentration and energy yield achieved with the packed-bed reactor are about 8 and 12 times high as those with DBD reactor, respectively. Although the packed-bed reactors have a shortcoming of high temperature, it can be solved by adding a cooling system and the ozone generation can be improved thereof. As a result, the packed-bed reactor is a promising and state-of-the-art technology for ozone generation based on this study.     

Adsorption of CO2 on Hydrotalcite‐like Compounds in a Fixed Bed

Abstract

The reduction of carbon dioxide emission from flue gases can be achieved using post‐combustion technologies, such as adsorption employing efficient solid sorbents. In this work, the adsorption of CO₂ on hydrotalcite‐like Al‐Mg compounds partially carbonated was studied using dynamic and static methods. The breakthrough curves were obtained at different flow gas rates in the range 60 to 100 mL/min and total pressure 1.0 atm. Different mixtures of CO₂ diluted in helium were used (3–20% v/v) at temperatures in the range 29 to 350°C. The experimental equilibrium data were described according to a Langmuir‐like equation. The capacity of adsorption presented a weak dependence on the temperature due to opposite effects of increasing of entropy and increasing of MgO (non‐carbonated) content in the adsorbent at high temperatures. The linear driving force model was suitable to describe the breakthrough curves. The dispersion and mass transfer coefficients were calculated by theoretical correlations and the model described quite very well the adsorption of CO₂ on hydrotalcite‐like compounds in a fixed bed in any temperature.     

Simultaneous Adsorption of SO2, NO,and CO2 by K2CO3‐Modified γ‐Alumina

The simultaneous adsorption of SO₂, NO, and CO₂ on K₂CO₃‐modified γ‐alumina under different operating conditions was studied in a fixed‐bed reactor. The experimental results showed that the influence of a temperature increase on the simultaneous adsorption of the three gases was complex and different from the effects seen when both chemical adsorption and competitive adsorption existed. An increase in O₂ concentration and small amounts of water could enhance the adsorption of SO₂ and NO while the adsorption of CO₂ was not influenced. The breakthrough curves of the simultaneous adsorption experiments suggested that the investigated adsorbent may be a good candidate for the simultaneous adsorption of SO₂, NO, and part of the CO₂ while the adsorption capacity for CO₂ still needs to be enhanced.     

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Abstract

Single and multicomponent fixed-bed adsorption of CO₂, N₂, and CH₄ on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO₂ and the loadings of CH₄ and N₂ are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO₂ is one order of magnitude faster than for CH₄ and N₂.     

Experimental and theoretical study on H2/CO2 separation by a five-step one-column psa process

An experimental and theoretical study is performed for bulk separation of H₂/CO₂ mixture (70/30 volume %) by PSA process with zeolite 5A, a process widely used commercially in conjunction with the catalytic steam reforming of natural gas or naphtha. For the optimized adsorption conditions of PSA, the characteristics of adsorption/desorption characteristics have been studied through breakthrough and desorption experiments under various conditions. The purge-to-feed ratio is important to the H₂ product purity only at a long adsorption step time. H₂ could be concentrated from 70% in the feed to 99.99% at H₂ recovery of 67.5%. The results of all five steps in PSA are successfully predicted by the LDF model considering an energy balance and nonlinear isotherm. For the model, the effective diffusivities (D,) are obtained separately from the uptake curves of H₂ and CO₂. The Langmuir-Freundlich isotherm is used to correlate the experimental equilibrium data and is very well fitted to the results.     

CO2 capture capacity of CaO in long series of pressure swing sorption cycles

One promising method for the capture of CO₂ from point sources is through the usage of a lime-based sorbent. Lime (CaO) acts as a CO₂ carrier, absorbing CO₂ from the flue gas (carbonation) and releasing it in a separate reactor (calcination) to create a pure stream of CO₂ suitable for sequestration. One of the challenges with this process is the decay in calcium utilization (CO₂ capture capacity) during carbonation/calcination cycling. The reduction in calcium utilization of natural limestone over large numbers of cycles (>250) was studied. Cycling was accomplished using pressure swing CO₂ adsorption in a pressurized thermogravimetric reactor (PTGA). The effect of carbonation pressure on calcium utilization was studied in CO₂ with the reactor operated at 1000 °C. The pressure was cycled between atmospheric pressure for calcination, and 6, 11 or 21 bar for carbonation. Over the first 250 cycles, the calcium utilization reached a near-asymptotic value of 12.5-27.7%, depending on the cycling conditions. Pressure cycling resulted in improved long-term calcium utilization compared to temperature swing or CO₂ partial pressure swing adsorption under similar conditions. An increased rate of de-pressurization caused an increase in calcium utilization, attributed to fracturing of the sorbent particle during the rapid calcination, as observed via SEM analysis.     

Preparation of Core-Shell SAPO-34 Adsorbent on Ceramic Particles; Improvement of CO2 Separation from Natural Gas

Fine crystals of SAPO-34 were synthesized by preparation of sol-gel precursor and hydrothermal process. The produced crystalline phase and the crystal shapes were analyzed by XRD patterns and SEM images. The core-shell adsorbent was prepared by the formation of the fine layer of SAPO-34 on the surface of the inert ceramic particles using the same synthesis parameters and hydrothermal conditions by in situ crystallization. The prepared core-shell SAPO particles were tested in dynamic adsorption experiments of a mixture of 5% CO₂ and 95% CH₄ at 298 K and 0.1 MPa, and their performance was compared with pure powders of SAPO-34 in the same adsorption operational conditions. The longer breakthrough time, sharper breakthrough curves, and higher CO₂ adsorbed amount were observed using core-shell SAPO-34 particles as adsorbent rather than using pure particles of SAPO-34. It is concluded that the production of a thin layer of SAPO-34 on cheap and inert porous ceramic particles is preferred rather than using higher amounts of SAPO-34 powders pelleted or binded with inert material in dynamic adsorption processes for the separation of CO₂ from natural gas.     

Evaluating isotherm models for the prediction of flue gas adsorption equilibrium and dynamics

We evaluated isotherm models for the precise prediction of adsorption equilibrium and breakthrough dynamics. Adsorption experiments were performed using pure N₂, CO₂ and their binary mixture with an activated carbon (AC) material as an adsorbent. Both BET and breakthrough measurements were conducted at various conditions of temperature and pressure. The corresponding uptake amount of pure component adsorption was experimentally determined, and parameters of the four different isotherm models, Langmuir, Langmuir-Freundlich, Sips, and Toth, were calculated from the experimental data. The predictive capability of each isotherm model was also evaluated with the binary experimental results of binary N₂/CO₂ mixtures, by means of sum of square errors (SSE). As a result, the Toth model was the most precise isotherm model in describing CO₂ adsorption equilibrium on the AC. Based on the breakthrough experimental result from the binary mixture adsorption, non-isothermal modeling for the adsorption bed was performed. The breakthrough results with all of the isotherm models were examined by rigorous dynamic simulations, and the Toth model was also the most accurate model for describing the dynamics.     

Removal of calcium and magnesium from LiHCO3 solutions for preparation of high-purity Li2CO3 by ion-exchange resin

This paper describes the results from an experimental study of the purification of LiHCO₃ solution which is used to produce high-purity Li₂CO₃ by ion exchange. Generally, there are some amounts of Ca²⁺ and Mg²⁺ in the LiHCO₃ solution whose contents exceed the requirements to produce qualified high-purity Li₂CO₃, so they need to be removed from the solution. There are many methods available to remove divalent metal ions from solutions, among which the ion exchange is the most simple and efficient one. Investigations of the performance of the chelating resin Amberlite IRC747 for its adsorption for Ca²⁺ and Mg²⁺ in LiHCO₃ solutions were conducted. Batch studies showed that the SDM-A model could describe the adsorption isotherm data well, and the Kannan particle diffusion model could describe the exchange kinetics properly. The study for column operation showed that breakthrough points of Ca²⁺ and Mg²⁺ both advanced with increasing the feed flow rate, and the penetration function model could describe the effluent curves adequately. HCl and LiOH of 1 mol·L^− 1 respectively were used to regenerate resins with good effect. This study will provide the basic reference for process operation and the reactor design to purify the LiHCO₃ solution by ion exchange.     

Methanol synthesis from CO2 and H2 in multi-tubular fixed-bed reactor and multi-tubular reactor filled with monoliths

This work investigates the impact of catalyst structuring into particles or monoliths on methanol production from only CO₂ and H₂ at a large scale. Methanol synthesis in multi-tubular reactors is evaluated using packed-bed and monolithic reactors by modeling heat and mass transfer in each reactor. The obtained simulation results show that, at low gas hourly space velocity (GHSV = 10,000 h⁻¹), the performances of both reactor technologies are similar. In this case, the packed-bed reactor technology is the most appropriate technology due to its simplicity of installation and operation. At high GHSV (25,000 h⁻¹), the packed-bed reactor technology is limited by a considerable pressure drop that causes an important loss in productivity due to thermodynamic equilibrium, whereas the monolithic reactors exhibit negligible pressure drop and achieve far better performances.     

Separation of CO2/CH4 mixtures with the MIL-53(Al) metal–organic framework

Adsorptive separation of CH₄/CO₂ mixtures was studied using a fixed-bed packed with MIL-53(Al) MOF pellets. Such pellets of MIL-53(Al) were produced using a polyvinyl alcohol binder. As revealed by N₂ adsorption isotherms, the use of polyvinyl alcohol as binder results in a loss in overall capacity of 32%. Separations of binary mixtures in breakthrough experiments were successfully performed at pressures varying between 1 and 8 bar and different mixture compositions. The binary adsorption isotherms reveal a preferential adsorption of CO₂ compared to CH₄ over the whole pressure and concentration range. The separation selectivity was affected by total pressure; below 5 bar, a constant selectivity, with an average separation factor of about 7 was observed. Above 5 bar, the average separation factor decreases to about 4. The adsorption selectivity is affected by breathing of the framework and specific interaction of CO₂ with framework hydroxyl groups. CO₂ desorption can be realised by mild thermal treatment.     

CO2 Adsorption by Modified Palm Shell Activated Carbon (PSAC) Via Chemical and Physical Activation and Metal Impregnation

The aim of this study was to verify the ability of nickel-impregnated palm shell activated carbon (PSAC) for CO₂ adsorption and compare its performance with the chemically and physically activated PSAC. Sodium hydroxide and CO₂ were used as activating agents for chemical and physical activation, respectively. Nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) was used as a precursor for metal impregnation. The effect of different chemical loadings (NaOH: 20–50 wt%), metal impregnation (Ni(NO₃)₂·6H₂O: 16–28 wt%), and heat treatment time (1–4 h) was studied as parameters. Adsorption capacity was calculated using breakthrough graphs. The effect of humidity on CO₂ adsorption and desorption of CO₂ was also investigated in this study. The results revealed that chemically modified PSAC yields the highest adsorption capacity (48.2 mg/g) compared to other methods of activation. Interestingly, it was found that the adsorption capacity of nickel-impregnated PSAC was similar to other types of metal-impregnated activated carbon. Humidity gave a negative effect on CO₂ adsorption. In summary, results showed that chemical activation is an efficient technique to modify PSAC for CO₂ adsorption.     

Dynamic CO2 adsorption performance of internally cooled silica‐supported poly(ethylenimine) hollow fiber sorbents

The dynamic adsorption behavior of CO₂ under both nonisothermal and nearly isothermal conditions in silica supported poly(ethylenimine) (PEI) hollow fiber sorbents (Torlon®‐S‐PEI) is investigated in a rapid temperature swing adsorption (RTSA) process. A maximum CO₂ breakthrough capacity of 1.33 mmol/g‐fiber (2.66 mmol/g‐silica) is observed when the fibers are actively cooled by flowing cooling water in the fiber bores. Under dry CO₂ adsorption conditions, heat released from the CO₂‐amine interaction increases the CO₂ breakthrough capacity by reducing the severity of the diffusion resistance in the supported PEI. This internal resistance can also be alleviated by prehydrating the fiber sorbent with a humid N₂ feed. The CO₂ breakthrough capacity of prehydrated fibers is adversely affected by the release of the adsorption enthalpy (unlike the dry fibers); however, active cooling of the fiber results in a constant CO₂ breakthrough capacity even at high CO₂ delivery rates (i.e., high adsorption enthalpy delivery rates). In full RTSA cycles, a purity of 50% CO₂ is achieved and the adsorption enthalpy recovery rate can reach ～72%. Studies on the cyclic stability of uncooled fiber sorbents in the presence of SO₂ and NO contaminants indicate that exposure to NO at 200 ppm over 120 cycles does not lead to a significant degradation of the sorbents, but SO₂ exposure at a similar high concentration of 200 ppm causes 60% loss in CO₂ breakthrough capacity after 120 cycles. A simple amine reinfusion technique is successfully demonstrated to recover the adsorption capacity in poisoned fiber sorbents after deactivation by exposure to impurities such SO₂. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3878–3887, 2014     

Contribution to emission reduction of CO2 by a fluidized-bed membrane dual-type reactor in methanol synthesis process

In this work, a fluidized-bed membrane dual-type reactor was evaluated for CO₂ removal in methanol synthesis process. The feed synthesis gas is preheated in the tubes of the gas-cooled reactor and flowing in a counter-current mode with reacting gas mixture in the shell side. Due to the hydrogen partial pressure driving force, hydrogen can penetrate from feed synthesis gas into the reaction side through the membrane. The outlet synthesis gas from this reactor is fed to tubes of the water-cooled packed-bed reactor and the chemical reaction is initiated by the catalyst. The methanol-containing gas leaving this reactor is directed into the shell of the gas-cooled reactor and the reactions are completed in this fluidized-bed side. A two-phase dynamic model in bubbling regime of fluidization was developed in the presence of long-term catalyst deactivation. This model is used to compare the removal of CO₂ in a FBMDMR with a conventional dual-type methanol synthesis reactor (CDMR) and a membrane dual-type methanol synthesis reactor (MDMR). The simulation results show a considerable enhancement in the CO₂ conversion due to have a favourable profile of temperature and activity along the fluidized-bed membrane dual-type reactor relative to membrane and conventional dual-type reactor systems.