Types Of Adsorption Isotherms Research Articles

Comparative analysis of anti-corrosive performance: Azure C dye vs. alternative Azure dyes on mild steel in 1 N HCl at elevated temperatures

Organic derivatives and dyes represent a promising and efficient class of corrosion inhibitors, demonstrating considerable potential in fulfilling the criteria for utilization as corrosion inhibitors. In the present study, the anti-corrosive impact of some Thiazines dyes: Azure A (D-1), Azure B (D-2) and Azure C (D-3), has shown a decelerative effect on mild steel in 1 N HCl environment and was investigated using experimental {Weight loss (WL), Electrochemical method and Atomic Force Microscope (AFM)} and theoretical {Density Functional Theory (DFT)} studies. It was found to have an efficiency in the order of D-3 (98.09 %) > D-1 (89.94 %) > D-2 (76.44 %) at elevated temperatures (338 K for 100 ppm concentration) deliberated through WL method. D-3 had greater stability than D-1 and D-2 at elevated temperatures which is indicative in the obtained experimental data. As examined via electrochemical and WL analysis, the cathodic type of inhibition mechanism and adsorption isotherm viz. Langmuir, Temkin and El-Awady were followed by all three dyes. Results of surface analysis and thickness of deposited layer by AFM agreed with other experimental outputs. A theoretical study for these thiazine dyes was probed employing DFT that illustrated the formation of a complex among the dyes and mild steel. The corrosion inhibition efficacy of dyes, as deduced from both experimental and theoretical data, aligns cohesively, thereby establishing a comparatively durable monolayer at the mild steel/medium interface, preventing steel deterioration in a specified range of temperatures.

Bridging the Adsorption Data and Adsorption Process by Introducing a Polynomial Structure To Accurately Describe IUPAC Isotherms, Stepwise Isotherms, and Stepwise Breakthrough Curves.

Porous heterogeneous adsorbents, those composed of multiple pore structures and surface chemical adsorption sites, can result in various gas or vapor adsorption isotherms, including five types of IUPAC adsorption isotherms and stepwise adsorption isotherms that have been difficult to model using a single adsorption equilibrium model. The limitation of the above equilibrium model further restricts the calculations of complex stepwise breakthrough curves. To bridge the adsorption data and adsorption process, it is important to first develop a simple model or method to describe these isotherms of various complex adsorption systems. In this work, assuming that the effect of the diffusion rate can be neglected under the static condition and the adsorption process is discontinuous, the number of adsorption isotherm inflection points can be used to represent the changed number of adsorption interactions. With the introduction of the polynomial structure, a series of empirical or semi-empirical polynomial adsorption models were developed. The N-site polynomial Langmuir-Freundlich equation could accurately fit common type I, II, III, IV, and V adsorption isotherms and complex stepwise adsorption isotherms covering various adsorbates, such as volatile organic compounds (VOCs), toxic industrial chemicals (TICs), water vapor, and carbon dioxide, as well as different adsorbents, such as metal/covalent organic frameworks (MOFs/COFs), zeolites, and porous carbons. Similarly, the introduction of a polynomial structure, such as the N-site polynomial Yoon-Nelson equation, was also successful in the description of interesting stepwise breakthrough curves. This work provides a more accurate adsorption equilibrium model to characterize all types of isotherms. As a foundation model, it is expected to be used to simulate the gas-solid adsorption process inside the fixed and fluidized beds packed with porous adsorbents.

Synthesis of an iron-titanium-carbon composite from slag high in titanium for removing arsenic particles from drinking water

The objective is to develop a novel iron-titanium-carbon composite using titanium-rich slag as a precursor material. This composite should demonstrate efficient arsenic removal capabilities for water-based treatments. The straightforward photochemical method is used to create a microporous iron-titanium/carbon composite by milling titanium-rich slag with activated carbon at room temperature. XRD, SEM, EDX, and N2 adsorption/desorption were used to describe it. This microstructure sorbent has excellent composition, surface area, and pore structure suitable enough to intake As(V) ions from drinking water at pH 6 with the adsorption capability of 86 mg/g. Among the many adsorption isotherm types examined, the Langmuir isotherm had the best fit with R2:0.9879. The intake of As(V) into the produced composite was most aptly stated by the Elovich model (R2:0.9899), according to the kinetic investigations. Given that, the synthesized micro-composite exhibits long-term stability and reproducibility over several regeneration cycles. Our findings displayed that the synthesized iron-titanium/carbon composite is effectively convenient for the elimination of As(V) with the effectiveness of recuperation of 95%.

Utilization of iron scrap into copperas and rambutan (Nephelium lappaceum L.) peel extract into environmentally friendly iron nanoparticles for hexavalent chromium removal and its kinetics

AbstractHexavalent chromium is a toxic pollutant that is very harmful to human health and the environment. One of the materials for hexavalent chromium removal is iron nanoparticles (INPs). In recent years, the manufacture of environmentally friendly INPs has been of great interest. In general, INPs are made using sodium tetra borane/NaBH4, which is expensive. The synthesis of INPs using NaBH4 also produces side products in the form of toxic boric acid and hydrogen gas which are explosive and flammable. In this study, INPs are made by using iron scrap waste into copperas which is then reacted with rambutan peel extract (RPE). The reaction between iron scrap and sulfuric acid until crystals are formed and then washed until blue‐green crystals are formed. The resulting crystal is made into a solution and then reacted with RPE. After forming a black solution, it was dried by spray drying. The resulting black powder was characterized by UV‐Vis Spectrophotometer, SEM‐EDX, FTIR, and XRD. The results showed that iron scrap can be synthesized into copperas with a Fe content of 19.84 ± 0.15%. RPE has a total phenol content of 877.39 ± 16.6 ppm/100 g rambutan skin or equivalent to 441.42 mg GAE/100 g rambutan skin. INPs can be made from copperas from iron scrap and RPE which have Surface Plasmon Resonance (SPR) characteristics at 214 nm absorption, particle size 20–70 nm. Hexavalent chromium removal using INPs was maximum at pH 3, hexavalent chromium concentration of 5 ppm, INPs concentration of 0.15 g/100 mL, and contact time of 10 min. The adsorption isotherm type of hexavalent chromium using iron nanoparticles can take place chemically or physically. The correlation coefficient showed that the model of Freundlich (R2 > 0.99) is more suitable than the model of Langmuir (R2 = 0.98) with an adsorption capacity of 91.74 mg iron nanoparticles/g hexavalent chromium. The use of INPs for hexavalent chromium removal is a promising and effective technology. These results can be an alternative to the production of environmentally friendly INPs by using materials from waste into useful materials for the prevention of environmental pollution.

Green corrosion and DFT studies of Ustilago maydis extract for carbon steel in sulfuric acid

A study on the use of Ustilago maydis extract as a green corrosion inhibitor for 1018 carbon steel in 0.5 m H2SO4 by using gravimetric, potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy electrochemical techniques at 25, 40 and 60 °C. Density functional theory (DFT) calculations were performed to know the relationship between inhibitor electronic properties and inhibition efficiency. Weight loss results indicated that Ustilago maydis was a good corrosion inhibitor with an efficiency that increased with its concentration but decreased with the temperature. However, the efficiency was around 60% because it was physically adsorbed on to the steel surface according to a Langmuir type of adsorption isotherm obtaining relatively low free energy values, which lied between −14.8 and −27 kJ/mol at 25 and 60 °C respectively. Activation energy decreased in presence of Ustilago maydis making corrosion process more difficult to occur. Potentiodynamic polarization curves showed a decrease in the corrosion current density in one order of magnitude and determined this extract as a cathodic type of corrosion inhibitor affecting. There was no evidence of a passive film, whereas the corrosion mechanism was controlled by the adsorption/desorption of some intermediate species and the double electrochemical layer resistance increased with the addition of the inhibitor. Gas chromatography showed that the main compounds found in this extract included D-Mannose, β-D-Glucopyranose,4-O-β-D-galactopyranosyl, Melibiose and Arabinose, whereas quantum chemical calculations by density functional theory analysis showed that Melibiose had the highest inhibition efficiency because it had the highest EHOMO value and lowest gap energy value, ∆E.

Synergism of andisol soil and foundry sand mixture as adsorbent of nickel (II) metal ion

A mixture of andisol soil and foundry sand as Ni2+ ion adsorbent was studied in this research. Andisol soil and foundry sand were activated using 3M NaOH. The characterizations of adsorbents were carried out by Fourier Transform Infrared Analyzer (FTIR), Scanning Electron Microscopy-mapping Energy Dispersive X-Ray (SEM-EDX), and Surface Area Analyzer (SAA). The mixture was made by mixing andisol soil and foundry sand with various compositions of 100:0, 75:25, 50:50, 25:75, and 0:100 (wt%). The adsorption of Ni2+ metal ion performed on pH solution of 3-7 and contact time of 10-110 minutes with the batch system. Based on the research, the optimum conditions for the adsorption of Ni metal in the adsorbent mixture of andisol soil and foundry sand were 75:25 (wt%) at pH 6 and contact time of 95 minutes with an adsorption capacity of 0.3967 mg/g and adsorption percentage 72.59%. Adsorption kinetics tend to follow pseudo-second-order. The type of adsorption isotherm is more dominant following the Langmuir isotherm. Nickel metal adsorption capacity in electroplating waste is 0.2777 mg/g.

Theoretical isotherm equation for adsorption-induced structural transition on flexible metal–organic frameworks

Flexible metal-organic frameworks (MOFs) exhibit an adsorption-induced structural transition known as "gate opening" or "breathing," resulting in an S-shaped adsorption isotherm. This unique feature of flexible MOFs offers significant advantages, such as a large working capacity, high selectivity, and intrinsic thermal management capability, positioning them as crucial candidates for revolutionizing adsorption separation processes. Therefore, the interest in the industrial applications of flexible MOFs is increasing, and the adsorption engineering for flexible MOFs is becoming important. However, despite the establishment of the theoretical background for adsorption-induced structural transitions, no theoretical equation is available to describe S-shaped adsorption isotherms of flexible MOFs. Researchers rely on various empirical equations for process simulations that can lead to unreliable outcomes or may overlook insights into improving material performance owing to parameters without physical meaning. In this study, we derive a theoretical equation based on statistical mechanics that could be a standard for the structural transition type adsorption isotherms, as the Langmuir equation represents type I isotherms. The versatility of the derived equation is shown through four examples of flexible MOFs that exhibit gate opening and breathing. The consistency of the formula with existing theories, including the osmotic free energy analysis and intrinsic thermal management capabilities, is also discussed. The developed theoretical equation may lead to more reliable and insightful outcomes in adsorption separation processes, further advancing the direction of industrial applications of flexible MOFs.

Utilization of Tea Waste Activated by Using Hydrochloric Acid as An Adsorbent for Calcium (II) Ions in Hard Water

Water is an important natural resource for human survival. Groundwater in calcareous soil areas contains high levels of Ca(HCO3)2 and Mg(HCO3)2 salts and will have a negative impact if consumed continuously. In this study, an adsorption method using tea waste (Camellia sinensis) was conducted to reduce the concentration of Ca(II) ions that cause water hardness. Tea waste was activated with 0.1 N HCl for 24 hours. Tea waste was characterized by Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM). Determination of optimum conditions was carried out at pH variations of 4, 6, and 8, with contact times of 30 minutes, 60 minutes and 90 minutes, and adsorbent weights were 0,5 grams, 1 gram, 1.5 grams and 2 grams. Tea waste with the best optimum conditions was tested on Ca(II) solutions of various concentrations from 30, 50, and 70 mg/L respectively to determine the maximum capacity for Ca(II) metal ions and the type of adsorption isotherm. Then applied to well water samples analyzed by Inductively Coupled Plasm (ICP) to determine the capacity of Ca(II) that can be absorbed by each adsorbent. The results showed that to utilize 0.1 N HCl-activated tea waste as an adsorbent for Ca(II) metal ions were optimum at pH 8, with a contact time of 30 minutes and an adsorbent weight of 0.5 grams. The maximum adsorption capacity was obtained at Ca(II) solution concentration of 70 mg/L with an adsorption capacity value of 6.704 mg/g. The adsorption isotherm corresponding to the tea waste adsorbent is the Freundlich isotherm (r2 = 0.9199). The highest absorption of Ca(II) metal ions in well water samples from the concentration of Ca(II) metal ions was 72.7702 mg/L to 4.877 mg/L, with adsorption efficiency of 93.3% and adsorption capacity of 6.7893 mg/g.

Synthesis, Characterization and Corrosive Inhibition Study of Phenylamino Cyclohexenone: Mild Steel Corrosion Studies in Acidic Medium

The present study reveals the greener synthesis and corrosion inhibition study of phenylamino cyclohex-2-enone (PAC) derivatives. Microwave assisted synthesis is one of the safe and environmental friendly method to synthesize cyclohex-2-enone compounds in presence of sodium bisulphate used as a catalyst and it is a highly economical one. The cyclohex-2-enone compounds corrosion inhibitive effect proved with the help of its weight loss. Synergetic process, electro chemical impedence and potentiodynamic polarization studies was carried out for the target compounds. The structures of synthesized cycloexenone compounds were elucidated with the help of IR, 1H and 13C NMR. The type of adsorption isotherm was confirmed by using synergetic process. The synergetic process was done by observing the correlation between halides and inhibitor. The final results show that the compounds follow the Langmuir adsorption isotherm.

A COMPARISON OF KINETIC STUDIES OF KAOLIN CLAY AND RICE HUSKS FOR CIPROFLOXACIN ADSORPTION

Objective: to compare the absorption of this drug on two surfaces of Iraqi kaolin and rice husks, which are considered environmentally friendly natural products and available locally. Methods: Ciprofloxacin adsorption from an aqueous solution was studied with respect to contact time, pH, and concentration. 30 min was determined to be the equilibrium time. Increasing the drug concentration on both adsorbents increased the adsorption rate, and the data fit well into a pseudo-second-order model. The solution concentration was analysed by UV-visible spectroscopy. Then the amount of adsorption was calculated, as well as the study of the reaction kinetics for both surfaces. The rice husk adsorbent showed faster removal with higher uptake than the Kaolin clay in both SGF and SIF solutions. Results: The adsorption isotherms of type (S4, S2) were found on the surface of rice husks and kaolin clay type (L3, L4) in stomach and intestine fluids, respectively. On Iraqi kaolin clay, adsorption is well described by the pseudo-second-order model, and the Tempkin adsorption isotherm provides a good fit for the Stomach. Whereas adsorption on rice husk is well described by the Freundlich isotherm, which is a good fit for the intestine. the adsorption is predominantly physical. The best maximum adsorption capacities were calculated on both surfaces in the following order: stomach-kaolin>intestinal fluids-rice husks>stomach-rice husks>intestinal fluids-kaolin. Conclusion: Both kaolin and rice husk are possible adsorbents that could be used to get antibiotics out of water.

Mathematical modeling of low salinity waterflooding in sandstone reservoirs: Enhanced Oil Recovery by multicomponent cation exchange

Low salinity waterflooding is the injection of water with a smaller salt concentration than the connate water. The control of the pH of injection water, and the amount of dissolved monovalent and divalent cations in the water affect the cation exchange in the reservoir and the mobilization of residual oil. In this work, the solution for the problem of low salinity slug injection driven by seawater considering three dissolved cations and pH effects is described. It was considered that the cations and H+ adsorbed on the rock follow a Langmuir adsorption isotherm type. The adsorption parameters of the cations depend on the water pH. The mathematical problem is split into three parts: a pH equation, a one-phase chromatographic system, and a scalar equation. First, the pH problem is solved, and its solution is used to calculate the one-phase chromatographic problem, and both results are applied in the scalar equation solution. Next, the solution is mapped onto the space-time plane. The solution shows that due to the high adsorption rate, the pH effects take place close to the injection point. Moreover, the high contrast between the adsorption rates of hydrogen and the other cations creates small regions where salinity changes. Cations separation in the porous media, similar to a chromatographic cycle, lead to the generation of several small oil and water banks along the porous media. The oil banks contain residual oil which was mobilized by the cation exchange. The analytical solution was compared with experimental data, showing close agreement. These results, mainly the relation between pH and salinity, and the appearance of water and oil banks along the flooding are new and important to the design of this chemical enhanced oil recovery technique.

Surprising Use of the Business Innovation Bass Diffusion Model To Accurately Describe Adsorption Isotherm Types I, III, and V

Using adsorption isotherm data to determine heats of adsorption or predict mixture adsorption using the ideal adsorbed solution theory (IAST) relies on accurate fits of the data with continuous, mathematical models. Here, we derive an empirical two-parameter model to fit isotherm data of IUPAC types I, III, and V in a descriptive way based on the Bass model for innovation diffusion. We report 31 isotherm fits to existing literature data covering all six types of isotherms, various adsorbents, such as carbons, zeolites, and metal-organic frameworks (MOFs), as well as different adsorbing gases (water, carbon dioxide, methane, and nitrogen). We find several cases, especially for flexible MOFs, where previously reported isotherm models reached their limits and either failed to fit the data or could not sufficiently be fitted due to stepped type V isotherms. Moreover, in two instances, models specifically developed for distinct systems are fitted with a higher R2 value compared to the models in the original reports. Using these fits, it is demonstrated how the new Bingel-Walton isotherm can be used to qualitatively assess the hydrophilic or hydrophobic behavior of porous materials from the relative magnitude of the two fitting parameters. The model can also be employed to find matching heats of adsorption values for systems with isotherm steps using one, continuous fit instead of partial, stepwise fits or interpolation. Additionally, using our single, continuous fit to model stepped isotherms in IAST mixture adsorption predictions leads to good agreement with the results from the osmotic framework adsorbed solution theory that was specifically developed for these systems using a stepwise, approximate fitting, which is yet far more complex. Our new isotherm equation accomplishes all of these tasks with only two fitted parameters, providing a simple, accurate method for modeling a variety of adsorption behavior.

Experimental and theoretical investigations on the inhibition of mild steel corrosion by capsaicin derivatives in hydrochloric acid

The protective properties of two capsaicin derivatives named N,N'-((4‑hydroxy-2,5,6-trimethyl-1,3-phenylene)bis(methylene))diacrylamide and N,N'-((5‑chloro-2,4-dihydroxy-1,3-phenylene)bis(methylene))diacrylamide in hydrochloric acid for mild steel were investigated. Electrochemical experiments showed that the inhibition efficiency of the two capsaicin derivatives as mixed inhibitors reached 96.24% and 93.71% at 0.3 g/L, respectively. Surface observations show that the capsaicin derivatives adhere firmly to the mild steel by forming a barrier. These two inhibitors fit the Langmuir adsorption isotherm and mixed adsorption type. The computational studies (DFT and MD) provide excellent support for the experimental results of both inhibitors.

Investigation of Pollutant Adsorption by Synthesized CuO Nanosorbents Based on Accurate Analysis of Different Types of Adsorption Isotherms

Investigation of Pollutant Adsorption by Synthesized CuO Nanosorbents Based on Accurate Analysis of Different Types of Adsorption Isotherms

Eco-Friendly Synthesized of CuO Nanoparticles Using Anchusa strigosa L. Flowers and Study its Adsorption Activity

Environmentally friendly copper oxide nanoparticles (CuO NPs) were prepared with a green synthesis route via Anchusa strigosa L. Flowers extract. These nanoparticles were further characterized by FTIR, XRD and SEM techniques. Removing of Gongo red from water was applied successfully by using synthesized CuO NPs which used as an adsorbent material. It was validated that the CuO NPs eliminate Congo red by means of adsorption, and the best efficiency of adsorption was gained at pH (3). The maximum adsorption capacity of CuO NPs for Congo red was observed at (35) mg/g. The equilibrium information for adsorption have been outfitted to the Langmuir, Freundlich, Temkin and Halsey adsorption isotherm types. The temperature thermodynamic parameters like ΔG°, ΔH° and ΔS° have been calculated.

Experiments‐Guided Modeling of MCM‐41: Impact of Pore Symmetry on Gas Adsorption

AbstractAmong mesoporous ordered silica‐based materials, MCM‐41 is widely employed in both experimental and computational investigations of gas adsorption. Specific surface area and pore size distribution are typically obtained by analyzing the N2 adsorption isotherm. To this aim, different models and theories are available, and which one is more accurate is under debate. On the computational side, the in silico model ought to match the characteristics of real samples and reproduce the macroscopic performance. While the typical hexagonal symmetry is usually considered, the tetragonal one is sometimes applied without any explained rationale. Interestingly, during the last decade, the preparation of mesoporous silica‐based materials with rare tetragonal symmetry is reported, indeed, but these are never tested as gas sorbents. In the present work, computer models with different symmetry are compared for their ability to reproduce the available experimental data from real samples. The combination of grand‐canonical Monte Carlo and molecular dynamics simulations is used to probe the differences at the microscopic level. The surface‐adsorbed gas molecules are differently ordered and a different type of N2 adsorption isotherm is correspondingly found.

Adsorption equilibrium of ammonia and water on porous adsorbents at low pressure: Machine learning-based models

Ammonia is a harmful gas in semiconductor cleanrooms. Activated carbons are widely used to remove ammonia. However, the existence of ambient moisture significantly impacts ammonia adsorption on adsorbents. Therefore, it is necessary to understand their adsorption performance on activated carbons to improve the product yield in semiconductor cleanrooms. Although many ammonia and water adsorption performance studies have been conducted, there has been little experimental research on low-pressure ammonia and water adsorption performance. In this study, several traditional isotherm models were applied to fit experimental isotherm data. The double-site (DS) Langmuir isotherm model provided good performance for ammonia adsorption on M-1, M-3, and M-4. The Toth isotherm model provided the best fit for ammonia adsorption on M-2. The Dubinin–Serpinsky (DS) isotherm model provided the best fit for water adsorption on the four investigated materials even at low pressure. In regard to predicting adsorption capacity, the previous prediction approach may limit the accuracy of the models by using a single set of characteristics to predict the adsorption capacity at different pressures. To solve this, an attention-based recurrent neural network (RNN) is proposed in this study. The attention mechanism is able to assign different weights to each material characteristic for different partial pressures. Due to this strength, the attention-based RNN realizes the prediction of adsorption isotherms by only taking material characteristics as inputs. The mean absolute percentage error (MAPE) of the attention-based RNN model in the prediction of adsorption capacity was 4.09%–18.68% and 3.68%–20.58% for ammonia and water, respectively, indicating that the well-trained model provides a reasonable prediction. The results predicted by the attention-based RNN model are consistent with the experimental data in terms of adsorption isotherm type, further confirming the reliability of the RNN model.

Gypsum scale formation and inhibition kinetics with implications in membrane system

Water desalination using membrane technology is one of the main technologies to resolve water pollution and scarcity issues. In the membrane treatment process, mineral scale deposition and fouling is a severe challenge that can lead to filtration efficiency decrease, permeate quality compromise, and even membrane damage. Multiple methods have been developed to resolve this problem, such as scale inhibitor addition, product recovery ratio adjustment, periodic membrane surface flushing. The performance of these methods largely depends on the ability to accurately predict the kinetics of mineral scale deposition and fouling with or without inhibitors. Gypsum is one of the most common and troublesome inorganic mineral scales in membrane systems, however, no mechanistic model is available to accurately predict the induction time of gypsum crystallization and inhibition. In this study, a new gypsum crystallization and inhibition model based on the classical nucleation theory and a Langmuir type adsorption isotherm has been developed. Through this model, it is believed that gypsum nucleation may gradually transit from homogeneous to heterogeneous nucleation when the gypsum saturation index (SI) decreases. Such transition is represented by a gradual decrease of surface tension at smaller SI values. This model assumes that the adsorption of inhibitors onto the gypsum nucleus can increase the nucleus superficial surface tension and prolong the induction time. Using the new model, this study accurately predicted the gypsum crystallization induction times with or without nine commonly used scale inhibitors over wide ranges of temperature (25–90 °C), SI (0.04–0.96), and background NaCl concentration (0–6 mol/L). The fitted affinity constants between scale inhibitors and gypsum show a good correlation with those between the same inhibitors and barite, indicating a similar inhibition mechanism via adsorption. Furthermore, by incorporating this model with the two-phase mineral deposition model our group developed previously, this study accurately predicts the gypsum deposition time on the membrane material surfaces reported in the literature. We believe that the model developed in this study can not only accurately predict the gypsum crystallization induction time with or without scale inhibitors, elucidate the gypsum crystallization and inhibition mechanisms, but also optimize the mineral scale control in the membrane filtration system.

ADSORPSI ASAM LEMAK BEBAS PADA MINYAK JELANTAH DENGAN TiO2/ZEOLIT ALAM

This research was conducted to determine the ability of TiO2/natural zeolite in adsorbing free fatty acids in used cooking oil. The studies included the synthesis of TiO2/natural zeolite adsorbent, characterization, and its application to adsorb free fatty acids with variations of contact time, oil volume, and adsorbent mass. The adsorbents’ functional groups were characterized by FTIR, active site by acid-base titration, and surface area by adsorption of methylene blue. The best character of adsorbent was TiO2/natural zeolite 9:100 which had a basicity active site of 11.6048 x 1020 sites/g and a surface area of ??45.6979 m2/g. The results showed that the optimum adsorption process occurred at a contact time of 60 minutes with an oil volume of 100 mL and an adsorbent mass of 0.30 grams resulting in an adsorption capacity and adsorption efficiency (%EE) of (1,00 ± 0.00) mg/g and (79.57 ± 0.17)%, respectively. The type of adsorption isotherm that occurred was Freundlich isotherm with a correlation coefficient (R2) of 0.9910 and Gibbs free energy (?G0) of -3.5571 kJ/mol, which indicated the adsorption process occurred spontaneously and it was a physical adsorption (heterogeneous and multilayers pores).
 Keywords: adsorption, adsorption isotherm, free fatty acids, TiO2/natural zeolite, used cooking oil.

Effect of different drying conditions on physicochemical, morphological, and rehydration properties, and adsorption characteristics of dried crab stick by‐product

The underspecification product obtained from crab stick production is considered as a crab stick by-product. To extend its shelf life, frozen storage is required but this process is costly due to electricity consumption. Then, the process for producing a shelf-stable crab stick by-product was focused in this study to reduce the cost of storage. For this experiment, the by-product (73% wet basis) was dried using different drying conditions such as freeze drying and convective hot air drying at 50, 60 and 70oC. The qualities of dried products including physicochemical, morphological and rehydration properties and adsorption characteristics were assessed. The results found that freeze drying was the best drying method to preserve dried sample qualities. Moreover, convective hot air drying at 70 and 60oC gave better qualities (higher porosity, % reconstruction and rehydration properties and less hardness) compared to 50oC. Adsorption isotherm types II and III were observed in this study.