Chromatographic Analysis of Limonene and Linalool on Silica Gel in Supercritical Carbon Dioxide

ABSTRACT

Adsorption behavior of limonene and linalool, which are respectively the principal constituents of terpene and oxygenated compounds in citrus oil, on silica gel in the presence of supercritical carbon dioxide was analyzed by the tracer response method. In this study a two-column system was used to eliminate the effect of nonideal behavior at the sample injection. Adsorption equilibria and mass transport properties were evaluated by means of the moment method at pressures of 8.8–23.5 MPa and temperatures of 313–333 K. The adsorption equilibrium constant was larger for higher temperature and lower pressure when linalool was selectively adsorbed on silica gel. The apparent heat of adsorption ranged from –20 to 230 kj/mol. The Peclet number and the ratio of intraparticle effective diffusivity to molecular diffusivity were 0.013–0.257 and 0.002–0.716, respectively.     

Effect of Drying Method on Gas Adsorption Characteristics of Carbon Gel Microspheres

Abstract

The effect of drying method used in the preparation of carbon gel microspheres was studied by comparing the porous properties of carbon cryogel microspheres (CCM) and carbon xerogel microspheres (CXM), which were respectively obtained using freeze drying and hot air drying. CCM were found to possess higher mesoporosity than CXM because freeze drying was effective to suppress the shrinkage of the mesopores during drying. On the other hand, the microporosity of the carbon gel microspheres was hardly influenced by not only the drying method but also the synthesis condition. Although the amounts of nitrogen and oxygen adsorbed were almost the same, the adsorption rate of nitrogen on both CCM and CXM possessing ultramicroporous surfaces was much larger than that of oxygen, which indicated the applicability of the carbon gel microspheres to adsorbents for pressure swing adsorption (PSA) of air. The relations between the temperature and the amount of oxygen adsorbed showed the adsorption characteristics of CCM and CXM as adsorbents for temperature swing adsorption (TSA) were almost the same.     

Effect of KI and KOH Impregnations over Activated Carbon on H2S Adsorption Performance at Low and High Temperatures

In the present work, commercial-grade activated carbon was modified by steam activation to improve its surface properties for high temperature desulfurization. The modified sample was also further upgraded by impregnating with KOH and KI to promote the chemisorption with of H₂S. The H₂S adsorption performance was tested under the temperature range of 30–550°C using the temperature program adsorption technique to understand the effect of adsorption temperature on the material adsorption characteristic. It was found that at ambient temperature, the impregnation of activated carbon with KOH can promote the H₂S adsorption capacity of activated carbon, whereas the impregnation with KI does not provide a significant beneficial effect. At high adsorption temperature (upto 550°C), both KOH and KI impregnation considerably improve the H₂S adsorption performance of activated carbon in terms of the adsorption capacity and breakthrough time. It was revealed from N₂ adsorption, SEM and EDS measurement that the chemical reactions between H₂S and alkaline compounds (KOH and KI) are promoted at high temperature. Based on all experimental results, the equilibrium adsorption model using the linear isotherm was developed to predict the adsorption behavior of these sorbents in terms of equilibrium isotherm constant and mass transfer coefficient for later scaling-up process.     

Adsorption Characteristics of Polyvinylpyridine and Activated Carbon for Lactic Acid Recovery from Fermentation of Lactobacillus delbrueckii

ABSTRACT

Polyvinylpyridine (PVP) and activated carbon were examined for the adsorption characteristics pertinent to their application in lactic acid fermentation. For PVP the linear adsorption constant, K_ad , was between 0.7 and 1.0 for an equilibrium pH range of 3 to 9. The pH was adjusted by acid/base addition, similar to pH control in fermentation. The values of K_ad> in the pH-adjusted systems were much lower than that reported for pure lactic acid solutions, i.e., about 9.7. Furthermore, no clear effect of pH was observed. These are attributed mainly to the competition of anions (Cl～ and lactate) for the adsorption sites of protonated pyridinal N. Its adsorption capacity was also found to decrease with the base regeneration (by about 14% each time) after being contacted with the culture broth. These limit its potential application in lactic acid fermentation. Activated carbon was much more effective in lactic acid/lactate adsorption than PVP. At pH 5.5 (optimal for fermentation), the value of K_ad of activated carbon was about 7. The adsorption further favored lower pH under acid (HC1) addition. Activated carbon has been reported to adsorb glucose. However, the presence of glucose in 0–70 g/L was found in this study to have an insignificant effect on lactate adsorption. Cells of Lactobacillus delbrueckii also adsorbed rapidly on activated carbon. This cell adsorption had a negative effect on lactate adsorption.     

Adsorption of CO2 on Zeolite 13X and Activated Carbon with Higher Surface Area

In this work, adsorption isotherms and adsorption kinetics of CO₂ on zeolite 13X and activated carbon with high surface area (AC-h) were studied. The adsorption isotherms and kinetic curves of CO₂ on the adsorbents were separately measured at 328 K, 318 K, 308 K, and 298 K and with a pressure range of 0–30 bar by means of the gravimetric adsorption method. The mass transfer constants and adsorption activation energy E_a of CO₂ on the adsorbents were estimated separately. Results showed that at very low pressure the amounts adsorbed of CO₂ on the zeolite 13X was higher than that on the AC-h, while at higher pressure, the amounts adsorbed of CO₂ on the AC-h was higher than that on the zeolite 13X since the AC-h has a larger surface area and a larger total pore volume compared to the zeolite 13X. The adsorption kinetics of CO₂ can be well described by the linear driving force (LDF) model. With the increase of temperature, the mass transfer constants of CO₂ adsorption on both samples increased. The adsorption activation energy E_a for CO₂ on the two adsorbents decreased with the increase of pressure. Furthermore, at low pressure the E_a for CO₂ adsorption on the zeolite 13X was slightly lower than that on the AC-h, while at higher pressure the E_a for CO₂ adsorption on the zeolite 13X was higher than that on the AC-h.     

Regeneration of Activated Carbon Loaded with Toluene by Supercritical Carbon Dioxide

Abstract

Activated carbon loaded with toluene was regenerated by supercritical carbon dioxide. The adsorptive capacities after several regeneration cycles were still close to that of virgin carbon and remained stable. The effects of temperature, pressure, and flow rate on regeneration efficiency were studied. It was found that the operations at higher pressures were more favorable for regeneration, but the optimal operating temperature depended on pressure. The interphase mass transfer resistance was insignificant during regeneration. A one-parameter mathematic model assuming linear desorption kinetics is proposed which agrees well with the experimental data. The adsorption rates of activated carbon regenerated by the supercritical regeneration method and the steam regeneration method are compared in this study. It was found that the supercritical regeneration method is superior to the steam regeneration method.     

Adsorption of Methane,Ethane, Ethylene,and Carbon Dioxide on High Silica Pentasil Zeolites and Zeolite-like Materials Using Gas Chromatography Pulse Technique

Abstract

Adsorption of methane, ethane, ethylene, and carbon dioxide in H-ZSM-5, Na-ZSM-5, H-ZSM-8, Na-ZSM-8, Silicalite, and ALPO-5 at 303–473 K has been investigated using a gas chromatography pulse technique. The zeolites have been compared for the heat of adsorption of the adsorbates at near zero adsorbate loading and also for the specific retention volume (or thermodynamic adsorption equilibrium constant) of ethane, ethylene, and carbon dioxide relative to that of methane. Among the zeolites, ALPO-5 has a high potential for the separation of methane, ethane, ethylene, and carbon dioxide from their mixture.     

Adsorption of H2, CO2, CH4, CO,N2 and H2O in Activated Carbon and Zeolite for Hydrogen Production

Abstract

The design of a layered pressure swing adsorption unit to treat a specified off-gas stream is based on the properties of the adsorbent materials. In this work we provide adsorption equilibrium and kinetics of the pure gases in a SMR off-gas: H₂O, CO₂, CH₄, CO, N₂, and H₂ on two different adsorbents: activated carbon and zeolite. Data were measured gravimetrically at 303–343 K and 0–7 bar. Water adsorption was only measured in the activated carbon at 303 K and kinetics was evaluated by measuring a breakthrough curve with high relative humidity.     

Equilibrium and absorption kinetics of carbon dioxide by solid supported amine sorbent

The equilibrium and conversion‐time data on the absorption of carbon dioxide (CO₂) with amine‐based solid sorbent were analyzed over the range of 303–373 K. Data on CO₂ loading on amine based solid sorbent at these temperatures and CO₂ partial pressure between 10 and 760 mm Hg obtained from volumetric adsorption apparatus were fitted to a simple equilibrium model to generate the different parameters (including equilibrium constant) in the model. Using these constants, a correlation was obtained to define equilibrium constant and maximum CO₂ loading as a function of temperature. In this study, a shrinking core model (SCM) was applied to elucidate the relative importance of pore diffusion and surface chemical reaction in controlling the rate of reaction. Application of SCM to the data suggested a surface reaction‐controlled mechanism for the temperature of up to 40°C and pore‐diffusion mechanism at higher temperature. Published 2011 American Institute of Chemical Engineers AIChE J, 2011     

Adsorption of Radon from a Humid Atmosphere on Activated Carbon

Abstract

Temperature and relative humidity can influence the adsorption capacity of radon on activated carbon to a great extent, depending on the physical properties of the carbon. Experiments were carried out to measure the radon uptake by an activated carbon in the presence of water vapor in a specially designed adsorption apparatus. The radon concentrations in the gas and solid phases were measured simultaneously once the adsorption equilibrium and the radioactive equilibrium between the radon daughter products were reached. The experiments in the presence of water vapor were carried out using two approaches. In one case the activated carbon was preequilibrated with water vapor prior to exposing it to radon. In the other case the carbon was exposed to a mixture of water vapor and radon. The uptake capacity for radon decreased substantially when both components were introduced together compared to when carbon was preequilibrated with water.     

Adsorption and Desorption of Carbon Dioxide and Nitrogen on Zeolite 5A

The adsorption equilibrium data of CO₂ and N₂ at (303, 333, 363, 393, 423) K ranging 0-1 bar on zeolite 5A is reported. The pressure and temperature range covers the operating pressure in adsorption units for CO₂ capture from power plants. Experimental data were fitted by the multi-site Langmuir model. The adsorbent is much more selective to CO₂: loading at 303 K and 100 kPa is 3.38 mol/kg while loading of N₂ at the same pressure is 0.22 mol/kg. The Clausius-Clapeyron equation was employed to calculate the isosteric enthalpy of adsorption. The fixed-bed adsorption and desorption of carbon dioxide and nitrogen on zeolite 5A pellets has been studied. A model based on the bi-LDF approximation for the mass transfer, taking into account the energy and momentum balances, had been used to describe the adsorption kinetics of carbon dioxide and nitrogen. The model predicted satisfactorily the breakthrough curves obtained with carbon dioxide–nitrogen mixtures. Desorption process (consisting of depressurization, blowdown, and purge) was also performed. Following the feasibility of concentration and capture of carbon dioxide from flue gases by Pressure Swing Adsorption (PSA) process was simulated. A CO₂ recovery of 91.0% with 53.9% purity was obtained using a five-step Skarstrom-type PSA cycle.     

Factors Influencing The Adsorption Of Gold-Iodide Onto Activated Carbon

Abstract

Activated carbon has found increasing application during the past decade as an adsorbent for gold from cyanide leached pulps. As result of practical and theoretical advancements in recent years, the carbon-in-pulp (CIP) process has become the preferred method for gold extraction from cyanided slurries. Lately, environmental considerations have led to the investigation of alternative leaching processes. One group of lixiviants studied is the halogens, such as bromine, chlorine, and iodine. It is the aim of this paper to investigate the factors influencing the adsorption of gold from iodide solutions onto a coconut-shell-type activated carbon. Equilibrium loadings on the carbon indicated clearly that gold-iodide has a higher loading profile than has gold cyanide. The Freundlich isotherm fitted the equilibrium curve for gold-iodide adsorption on carbon. The experimental results indicated that the pH level, iodide, and dissolved oxygen concentration had little or no influence on the kinetic and equilibrium parameters in a film diffusion model. However, the initial gold, iodine, and tri-iodide concentrations altered both the rate and equilibrium of gold-iodide adsorption significantly. Scanning electron microscopy showed that elemental gold deposited on the carbon surface influences the high film transfer coefficients obtained for gold-iodide adsorption.     

Equilibrium Modeling of Ternary Adsorption of Phenols onto Modified Activated Carbon

The prediction of adsorption equilibria in multicomponent systems is of prime importance. Therefore, the equilibrium adsorption data for the following multicomponent systems have been studied. The present paper deals with the simultaneous removal phenol (P), 4-chlorophenol (CP), 4-nitrophenol (NP) and catechol (C), resorcinol (R), hydroquinone (HQ) onto modified activated carbon (MAC) from ternary mixtures. The BET surface area of SC was found to be 934 m²/g, whereas BJH adsorption/desorption surface area of pores is 53.03/58.15 m²/g. The equilibrium adsorption data were obtained at different initial concentrations (C₀ = 50–1000 mg/L), 12 h contact time, 30°C temperature, MAC dosage of 10 mg/L at solution pH. Equilibrium isotherms for the ternary adsorption of P–CP–NP and C–R–HQ onto MAC have been analyzed by using non-modified Langmuir, modified Langmuir, extended Langmuir, extended Freundlich and Sheindorf–Rebuhn–Sheintuch (SRS) models. The competitive Sheindorf–Rebuhn–Sheintuch (SRS) model fits for both ternary adsorption equilibrium data satisfactorily and adequately.     

Nonisothermal adsorption in a single spherical pellet having bidispersed pore structures

ZSM-5 and Y-zeolite as adsorbents for the adsorption of ethanol vapor were used to investigate the nonisothermal adsorption. Diffusivity and equilibrium constant in the pellet having both micro-and macropores were represented as a function of temperature to establish a nonisothermal model. More rapid adsorption rate was found in the early stage of adsorption in nonisothermal model than that in isothermal model. But the time taken to reach the equilibrium state from the start of adsorption was nearly the same for both models. As diffusivity in macropore became larger than that in micropore, the adsorption had a more rapid rate and a higher maximum temperature rise. The lower value of equilibrium constant showed a more rapid adsorption rate, but a lower maximum temperature rise. The maximum temperature rise of pellet up to 20‡C above the ambient temperature was found. When the adsorption rate curves from the experimental data are compared with those from the modeling, a deviation was obtained at a high uptake ratio while a good fitting was found in the early stage of adsorption.     

Adsorption of Pb(II) by Peanut Hull Carbon from Aqueous Solution

Abstract

Carbon prepared from peanut hulls (PHC) has been used for the adsorption of Pb(II) over a range of initial metal ion concentrations (10–20 mg/L), agitation times (5–140 minutes), adsorbent dosages (5–100 mg/100 mL), and pH values (1.5–10.0). Adsorption of Pb(II) obeyed the Langmuir isotherm. The applicability of the Lagergren kinetic model has also been investigated. Quantitative removal of 20 mg/L Pb(II) by 0.3 g carbon per liter aqueous solution was observed in the pH range of 3.0 to 10.0. A comparative study with a coal-based commercial granular activated carbon (CAC) showed that the adsorption capacity of PHC was 18 times larger than that of CAC.     

Modeling of the Temperature Variation Effects on the Polymerization Reactions of Phenolics on Granular Activated Carbon

Abstract

The effect of temperature variation on the kinetics of adsorption and adsorption-reaction combination of phenol and o-cresol on granular activated carbon (GAC) was evaluated throughout this study. Batch experiments were performed under oxic and anoxic conditions at temperatures of 8, 21, and 35°C. The results showed that the equilibration time for physical adsorption increased with the decrease in temperature and occurred in the time range of 7.5–11 days for the adsorption-reaction combination (oxic cases). The polymerization reactions lagged by about 10 hours under all of the temperature values. Diffusivity coefficients in the anoxic cases increased proportionally with temperature, with the highest difference between oxic and anoxic diffusivities at a temperature 35°C. The homogeneous surface diffusion model (HSDM) accurately predicted the anoxic batches and deviated from the oxic data. Temperature increases the adsorption and polymerization reaction rates, and thus the predictivity of the HSDM for both oxic and anoxic batches improves. Under controlled dissolved oxygen (DO) and temperature conditions, the isotherm and batch equilibrium capacities matched with a maximum deviation of 4%. The effect of temperature on the rate of the DO-induced enhancement was found to follow a self-retardant reaction model. The developed model showed strong predictive capability for the temporal formation of polymers.     

改性活性炭对甲基橙的吸附

用盐酸和氨水对活性炭进行改性获得改性活性炭,将其用于处理甲基橙废水,考察了改性条件、振荡速度和温度等因素对甲基橙吸附性能的影响,采用吸附等温模型和吸附动力学模型进行拟合,并分析吸附过程的热力学特征. 结果表明,盐酸改性活性炭对甲基橙的吸附效果优于氨水改性活性炭,在甲基橙初始浓度60 mg/L、溶液体积50 mL、温度20℃、振荡速度100 r/min、盐酸改性活性炭投加量0.2 g时,24 h基本达到吸附平衡,甲基橙去除率为93.7%. 不同温度下,盐酸改性活性炭对甲基橙的吸附符合Langmuir(RC2>0.95)和Freundlich(RC2>0.97)吸附等温模型,饱和吸附量达112.7 mg/g. 热力学参数DG0<0,DH0>0,DS0>0,表明盐酸改性活性炭对甲基橙的吸附是自发吸热反应,其吸附动力学可用准二级动力学方程描述,随振荡速度增加,吸附速率常数增加.     

Accelerated Adsorption with Activated Carbon Fiber

Abstract

The properties of a new type of polyamphoteric activated carbon fiber (ACF) were investigated theoretically and experimentally. Results are compared with those from granular activated carbon (GAC) and ion-exchange resin (IER) materials. The adsorption rate of ACF was found to be two orders of magnitude higher than that of the GAC and one order of magnitude higher than that of the IER.     

Phase equilibria of long chain n-alkanes in supercritical ethane: Review,measurements and prediction

The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carbon atoms in supercritical ethane were studied to determine if the phase equilibrium pressure can be predicted from the number of carbon atoms and system temperature. It has previously been shown that for the phase equilibria of heavy n-alkanes in supercritical propane there exists, at constant temperature and mass fraction, a linear relationship between the number of carbon atoms and the bubble/dew point pressure. Published data in the temperature range 310–360 K was obtained from a literature survey and, where required, additional data was measured using a high-pressure equilibrium cell. It was found that linear relationships exist and that these relationships can be used to predict the phase equilibrium pressure within 4% of experimental values.     

Adsorption of Pyridine from Aqueous Solution by Surface Treated Carbon Nanotubes

Abstract

The surface treatment of multi‐walled carbon nanotubes (MWCNTs) with acid, heat, ultrasonic, and polyvinyl alcohol has been examined. The original CNTs and four treated CNTs were first used as adsorbents to remove pyridine from water and the adsorption isotherms of pyridine on CNTs were studied. At the same time, the effect of pH, temperature, and the adsorption kinetics on the adsorption of pyridine were also evaluated. The experiments show that the adsorption of pyridine on different CNTs is mainly a physical process and the data fit the Freundlich adsorption isotherm well. The short time needed to reach equilibrium as well as the high adsorption capacity of pyridine suggests that CNTs possess highly potential applications for pyridine removal from water.