A general relationship between adsorption of hydrocarbons and their polarizabilities on activated carbon

In this investigation a trial was made to find out a general relationship between the adsorptive characteristics of aliphatic and aromatic hydrocarbons and their electronic polarizabilities on a steam activated carbon of high surface area and microporous structure. The adsorption of these aliphatics and aromatics were carried out at high temperature using microchromatographic method. A general reationship between the high temperature adsorption of hydrocarbons on activated carbon and their electronic polarizabilities and consequently the electronic polarization was found.     

Biocatalytic Heterogeneous Processes of the Esterification of Saturated Fatty Acids with Aliphatic Alcohols

Heterogeneous biocatalysts prepared by immobilizing a recombinant lipase from Thermomyces lanuginosus on mesoporous inorganic supports—silica (SiO₂), alumina (Al₂O₃), and titania (TiO₂)—are comparatively studied in the esterification of fatty acids with aliphatic alcohols. It is found that the T. lanuginosus lipase adsorbed on silica has the highest esterifying activity, while the lipase adsorbed on titania is completely inactivated. SiO₂-based catalysts have high activity and stability in the esterification of saturated fatty acids containing 4–18 carbon atoms (C4–C18) with aliphatic alcohols (C5–C16) in organic solvents (hexane and diethyl ether). The catalysts operate in this reaction for several tens of reaction cycles (>40) without loss of activity. The recombinant rPichia/lip lipase immobilized on silica exhibits the most pronounced specificity for its first substrate, a fatty acid. For instance, the rate of synthesis for esters of low molecular weight acids (С4–С6) is three to four times slower than for the esters of acids with more than seven carbon atoms. The catalyst has a relatively broad specificity for the second substrate, an aliphatic alcohol. It is found that the ester of enanthic acid (C7:0) and butanol (C4) is synthesized at the maximum rate.     

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.     

Selective adsorption of organic homologues onto activated carbon from dilute aqueous solutions: Solvophobic interaction approach: Part IV. Effect of simple structural modifications with aliphatics

Preferential adsorption of organic compounds onto activated carbon from dilute aqueous solutions is studied to develop a comprehensive theoretical basis for predicting the adsorption of structurally different isomers for different homologous series. The fundamental multidimensional approachof the solvophobic (cϕ) thermodynamic theory is further refined and used to correlate the extent of adsorption for the comprehensive theory with the overall standard net free energy change (ΔG^net/RT) for the association-adsorption reaction in solution, and for the simplified theory with the cavity surface area of the solute (TSA). Experimental adsorption isotherms of two homologous series (12 aliphatic alcohols and 21 aliphatic ketones) were measured and used to test and compare the cϕ theory with seven independent parameters characterizing the sorbates. Several experimental innovations for measuring equilibrium adsorption isotherms are introduced to reduce the possible loss of sorbate during the procedure and to provide reproducible and reliable results. Comparing the coefficients of linear correlation (r), the results for 12 aliphatic alcohols give greater than 99% confidence that the r-values are different for ΔG^net/RT and molecular weight (MW). For the 15 aliphatic ketones, greater than 90% confidence interval is obtained for different r-values for TSA and MW. These results support the contention that simple structural modifications of aliphatic homologous compounds can be used to predict the effect of solute-solvent-sorbent interactions on adsorption. The cϕ theory can thus be used to rank-order adsorption intensity of these compounds from the aqueous phase onto activated carbon.     

High surface area-activated carbon from Glycyrrhiza glabra residue by ZnCl2 activation for removal of Pb(II) and Ni(II) from water samples

A high-surface-area activated carbon was prepared by chemical activation of Glycyrrhiza glabra residue with ZnCl₂ as active agent. Then, the adsorption behavior of Pb(II) and Ni(II) ion onto produced activated carbon has been studied. The experimental data were fitted to various isotherm models. According to Langmuir model, the maximum adsorption capacity of Pb(II) and Ni(II) ions were found to be 200 and 166.7 mg g⁻¹, respectively, at room temperature. Kinetic studies showed the adsorption process followed pseudo second-order rate model. High values of intra-particle rate constants calculated shows the high tendency of activated carbon for removal of Pb(II) and Ni(II) ions.     

Description of adsorption of polar substances on microporous adsorbents using the modified Polanyi-Dubinin potential theory

Mechanism of adsorption of lower aliphatic alcohols and amines on active carbon surfaces has been studied. Interpretation of the results required application of the modified Polanyi-Dubinin potential theory. A basic difference in adsorption of alcohols and amines has been found. Thus, the degree of alcohols association is lower in the adsorbed phase than in the liquid phase, whereas the reverse is observed for amines.     

Removal of strontium from aqueous solutions by adsorption onto activated carbon: kinetic and thermodynamic studies

This work reports the adsorption of strontium from aqueous solutions onto activated carbon. Various factors such as pH, initial concentration of strontium, particle size and temperature were considered. The optimum conditions obtained were: pH value = 4.0, contact time = 8 h, initial concentration of Sr(II) = 100 mg/l, particle size = 270 μm and temperature of 293.15 K. The adsorption of strontium(II) on activated carbon follows pseudo-first order kinetics and the energy of activation E_a calculated using the Arrehenius equation was found to be 3.042 kJ/mol.The adsorption isotherms could be fitted by the Langmuir model with the maximum adsorption capacity Q_o being 5.07×10^–4 mol/g at 293.15 K. A dimensionless separation factor R_L was used to judge the favourable adsorption. The values of the mass transfer coefficient β_L (cm/s) at different temperatures indicated that the velocity of mass transfer of Sr(II) ions onto activated carbon was slow. The intraparticle diffusion mechanism is of great importance in determining the overall rate of removal and the negative entropy of activation ΔS^# value 145.13 J/mol K, reflects that no significant change occurs in the internal structure of activated carbon during adsorption of strontium(II). The Gibbs free energy ΔG°_ads values range from –36.61 kJ/mol to –41.75 kJ/mol at 293.15–333.15 K, which show the physical adsorption properties of activated carbon and indicate the feasibility of the process.     

Adsorptive Removal of Organic Acids and Furans from Hydrothermal Treatment Process of Biomass

Abstract

Hydrothermal treatment of plant biomass using subcritical water is one of the pretreatment methods for producing valuable chemicals such as D-glucose for producing bio-alcohol. However, this treatment causes side reactions and produces by-products such as organic acids and furans which may inhibit the production of alcohols in the following step. In this study, the adsorption process is applied to remove by-products from products solution. As adsorbents, Cellufine A-200, A-800, DIAION WA21J, and activated carbon were used. Among them, Cellufine A-200 selectively adsorbed organic acids and activated carbon showed the best adsorption performance for furans. DIAION WA21J adsorbed both organic acids and furans.     

Removal of organic matter by coagulation enhanced with adsorption on PAC

The removal of humic acids and phenol from model solution by coagulation and adsorption on powdered activated carbon (PAC) was investigated. A PAX XL-69 polyaluminum chloride was applied as a coagulant. The adsorption of humic acids and phenol on activated carbon for single- and bi- component solutions was studied. It was found that coagulation without PAC addition was less effective than the adsorption-coagulation integrated system. Coagulation enhanced with adsorption on activated carbon was more effective when coagulation was preceded by adsorption than when the two processes were carried out simultaneously. The best results were obtained at pH 7. Phenol and color were removed pletely, UV₂₅₄ absorbance was reduced by about 99% and COD-Mn was reduced by 81-89%.     

Substrate specificity of the lipase fromCandida parapsilosis

Substrate specificity of the acyltransferase activity of the lipase (EC 3.1.1.3) fromCandida parapsilosis CBS 604 was studied in aqueous media. The specificity toward both acid and alcohol parts of a large number of acylglycerols and aliphatic esters was investigated. This lipase showed a high activity in the presence of esters with long-chain fatty acids and particularly unsaturated fatty acids with acis-Δ9 double bond. It was observed that the activity profile depended not only on the alcohol part of the acyl ester, but also on the temperature of the reactant medium. The best lipid substrates had their melting point between −40 to +20°C, 14 to 18 carbon atoms in the acyl group and 1 to 4 carbon atoms in the alkyl group. The enzyme, defined as an acyltransferase in a previous paper, showed a high affinity for primary and secondary alcohols with a short carbon chain (1 to 5 carbon atoms) as acyl acceptors. The influence of free alcohols in the reactant medium on the hydrolysis and alcoholysis activities of the enzyme is discussed. Two phenomena seem to be involved, depending on the alcohol: competition with water for the acyltransfer reaction and lipid substrate dilution when the alcohol places at the oil/water interface.     

活性炭表面负载金属离子对其吸附苯并噻吩的影响

主要研究了活性炭表面负载不同的金属离子对其吸附苯并噻吩的影响.通过浸渍法分别将6种不同的过渡金属离子负载在活性炭表面上,用静态吸附法测定了苯并噻吩硫化物在改性活性炭上的吸附等温线,应用软硬酸碱理论分析和讨论了其吸附能力的差异.结果表明,活性炭表面负载Ag^＋、Ni^2＋、Cu^2＋或Zn^2＋离子,可提高活性炭吸附苯并噻吩硫化物的能力,而活性炭表面负载Fe^3＋或Co^3＋离子,反而降低了活性炭吸附苯并噻吩硫化物的能力,这主要是活性炭表面的酸碱性质发生变化.采用密度泛函数理论法计算结果表明,苯并噻吩的电负性χ为2.638,属软碱类物质;由于Ag^＋为软酸,活性炭负载Ag^＋离子,增加了其局部表面的软酸,从而增强了对苯并噻吩硫化物的吸附;由于Ni^2＋、Cu^2＋和Zn^2＋离子属交界酸,负载Ni^2＋、Cu^2＋、Zn^2＋离子增加了活性炭表面的交界酸,也在一定程度上提高了其表面对苯并噻吩硫化物的吸附;当活性炭表面负载了硬酸性Fe^3＋或Co^3＋离子,其局部表面硬酸增大从而降低了其对苯并噻吩的吸附.     

Cocoa (Theobroma cacao) shell-based activated carbon by CO2 activation in removing of Cationic dye from aqueous solution: Kinetics and equilibrium studies

Cocoa shell (CS) was used as a low-cost precursor for production of activated carbon (AC) and evaluated for its ability to adsorb Methylene Blue (MB) dye. Cocoa shell-based pellets were carbonized at 800 °C and subjected to 850 °C under a flow of CO₂ in different activation times. The cocoa (Theobroma cacao) shell-based activated carbon (CSAC) showed moderate surface area with the average pore size 2.7 nm. CSAC also displays the presence of aliphatic, aromatic hydrocarbons and near absence of C–O, carboxylic acid, and the –COOH functional group. Only the presence of O–H groups was detected. The influences of adsorption time and initial dye concentration on adsorption performance have been measured in a batch system. The results are well described by the Freundlich and Langmuir isotherms. The results from the kinetic study show that MB adsorption follows pseudo-second-order and Boyd models, which indicated the MB adsorption on the CSAC was controlled by film diffusion.     

活性炭表面含氧官能团对水中卤乙酸吸附去除的影响

为了改善极性、亲水性卤乙酸(HAAs)分子在非极性、疏水性活性炭上的吸附性能,利用N₂等温吸附实验、X射线光电子能谱实验（XPS）、HAAs等温吸附实验等方法,对几种不同产地的活性炭孔隙结构、表面元素形态结构组成,以及HAAs吸附性能进行了研究,考察了活性炭孔结构及含氧官能团对HAAs吸附性能的影响.活性炭表面含氧官能团对HAAs的吸附性能影响显著,当活性炭表面含氧官能团组成较小时,其HAAs吸附能力较强.     

Determination of pore size distribution and adsorption of methane and CCl4 on activated carbon by molecular simulation

A combined method of grand canonical Monte Carlo (GCMC) simulation and statistics integral equation (SIE) for the determination of pore size distribution (PSD) is developed based on the experimental adsorption data of methane on activated carbon at ambient temperature, T=299 K. In the GCMC simulation, methane is modeled as a Lennord-Jones spherical molecule, and the activated carbon pore is described as slit-shaped with the PSD. The well-known Steele’s 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. Covering the range of pore sizes of the activated carbon, a series of adsorption isotherms of methane in several uniform pores were obtained from GCMC. In order to improve the agreement between the experimental data and simulation results, the PSD is calculated by means of an adaptable procedure of deconvolution of the SIE method. Based on the simulated results, we use the activated carbon with the PSD as the prototype of adsorbent to investigate adsorption. The adsorption isotherms of methane and CCl₄ at 299 K in the activated carbon with the PSD are obtained. The adsorption amount of CCl₄ reaches 20 mmol/g at ambient temperature and pressure. The results indicate that the combined method of GCMC and SIE proposed here is a powerful technique for calculating the PSD of activated carbons and predicting adsorption on activated carbons.     

Role of microporosity and surface functionality of activated carbon in methylene blue dye removal from water

Activated carbons have been prepared from jute stick by both chemical and physical activation methods using zinc chloride and steam, respectively. They were characterized by evaluating surface area, iodine number, pore size distribution, and concentration of surface functional groups. The chemically activated carbon largely featured micropore structure, while the physically activated carbon mainly featured macropore structure. The specific surface area of chemically and physically activated carbons was 2,325 and 723 m ² /g, while the iodine number was 2,105 and 815mg/g, respectively. The concentration of surface functional groups was determined by Boehm titration method, which suggested that different types of surface functional groups are randomly distributed on chemical activated carbons, while it is limited for physical activated carbon. The microporosity along with surface functional groups provided a unique property to chemically activated carbon to adsorb Methylene Blue dye to a large extent. The adsorption of dye was also affected by the adsorption parameters such as adsorption time, temperature and pH. Comparatively, higher temperature and pH significantly facilitated dye adsorption on chemically activated carbon.     

Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties

High surface area activated carbons were prepared by simple thermo-chemical activation of Jatropha curcas fruit shell with NaOH as a chemical activating agent. The effects of the preparation variables, which were impregnation ratio (NaOH:char), activation temperature and activation time, on the adsorption capacity of iodine and methylene blue solution were investigated. The activated carbon which had the highest iodine and methylene blue numbers was obtained by these conditions as follows: 4:1 (w/w) NaOH to char ratio, 800 °C activation temperature and 120 min activation time. Characterization of the activated carbon obtained was performed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherm as BET. The results present that the activated carbon possesses a large apparent surface area (S_BET = 1873 m²/g) and high total pore volume (1.312 cm³/g) with average pore size diameter of 28.0 Å.     

Intermediates from the microbial oxidation of aliphatic hydrocarbons

Oxidation of aliphatic saturated and unsaturated hydrocarbons by bacteria, yeasts, and fungi leads to the production of a variety of intermediates, e.g., mono- and dicarboxylic acids, primary alcohols, isomeric alcohols and their corresponding ketones, diols, epoxides, and hydroxy acids. Further degradation of isomeric ketones in two species ofPseudomonas occurs by a flavoprotein monooxygenase leading to the formation of ester intermediates. In the case of 2-tridecanone→undecyl acetate, the esterase active on the acetate ester also has been characterized. Oxidation of pristane gives rise to several branched chain intermediates of varying carbon length. Products from other branched chain hydrocarbons are also presented. Oxidation of hydrocarbons that are not growth substrates but are nonetheless oxidized by microorganisms is reviewed. The examples presented reiterate the fact that microorganisms are a metabolically diverse group capable of altering an incredibly wide array of organic compounds of which aliphatic and alicyclic hydrocarbons as a class represent but one example.     

脱气预处理条件对木质活性炭比表面积和孔容积分析结果影响初探

在测定木质活性炭比表面积和孔容积前,先对活性炭进行脱气预处理,研究预处理条件(脱气温度和脱气时间)对活性炭的比表面积和孔容积的影响,并将所测结果与仪器推荐条件下所测结果进行对比分析。研究结果表明：脱气温度和脱气时间对于物理法木质活性炭比表面积和孔容积分析结果影响较小,这是因为物理法活性炭制备温度高,官能团少,结构以微孔为主,吸附类型以物理吸附为主,吸脱附速度较快。物理法活性炭预处理条件以脱气温度150℃脱气3 h为宜,相较于ASAP 2460使用说明所推荐的350℃和24 h的预处理条件,明显缩短预处理时间,降低电耗,提高了检测效率。脱气温度和脱气时间对化学法木质活性炭比表面积和微孔分析结果影响较大,适宜的预处理条件为300℃脱附12 h。主要是因为磷酸法活性炭制备温度较低,杂原子较多,表面化学基团丰富,发生物理吸附的同时易发生化学吸附,需要较高的温度和较长的时间才能脱气完全,当脱气温度过高时,孔道内的吸附质发生炭化形成炭质微粒堵塞孔道,同时部分物理吸附在更高的活化能下转化为化学吸附,使分析结果有所下降。     

新型微波适应型复合活性炭的研制及其微波再生性能

微波再生技术被广泛认为是一种高效、节能的绿色再生技术。本文通过引入高热导率物质--膨胀石墨制备出新型微波适应型复合活性炭,解决目前活性炭在微波脱附过程中存在的温度梯度问题,同时开发VOCs活性炭吸附-微波再生技术。结果表明,制得的复合活性炭具有与普通商业活性炭相当的吸附性能,且其热导率提高6倍。同时,其甲苯脱附活化能为18.08 kJ·mol^-1,低于其在商业活性炭上的微波脱附活化能（24.84 kJ·mol^-1）25%以上;相同微波功率下,其脱附床层温度低于实验室制备的普通活性炭10～30℃。所制备的高热导率复合活性炭不仅具有良好的吸附性能,而且具有很好的微波适应性。     

乙二酸和苯甲酸在活性炭上的脱附行为

低挥发性有机酸不仅自身污染环境而且显著促进颗粒污染物形成,对其吸脱附性能的研究有助于这类物质的控制。采用程序升温脱附(TPD)技术对乙二酸、苯甲酸在活性炭(AC)上的脱附行为进行了研究。结果表明,吸附主要发生在粗微孔(0.7~2 nm)、细微孔(<0.7 nm)中,对应TPD曲线中的吸附位Ⅰ、Ⅱ。粗微孔对乙二酸、苯甲酸的脱附活化能为101.63、112.43 kJ·mol^-1,吸附量均大于总吸附量的91%。细微孔对乙二酸、苯甲酸的脱附活化能为118.01、130.87 kJ·mol^-1,吸附量均小于总吸附量的9%。细微孔吸附强度高于粗微孔,但吸附量远低于粗微孔,因为细微孔对吸附质的迁移阻力较大,仅少量吸附质能进入细微孔中。苯甲酸在迁移中受到阻力较乙二酸大,在细微孔中吸附量更小,表现为分子筛分作用。