Francisco Salvador

A new method for regenerating activated carbon by thermal desorption with liquid water under subcritical conditions

Abstract A new procedure for regenerating activated carbon based on thermal desorption with liquid water under subcritical conditions (300 °C and 120 atm) is proposed. The method was assayed with three types of activated carbons exhausted with phenols (phenol and 4-nitrophenol), textile dyes (sirius red C.I.: 29080 and orange II C.I.: 15510) and pesticides (carbofuran and atrazine). In all cases, total recovery of the adsorption capacity was achieved, even after seven regenerations. The mechanism and factors involved in regeneration were investigated using the TPD technique in liquid phase. The differences and advantages of this procedure as compared with others, such as thermal regeneration or regeneration with supercritical CO2 are discussed.

Effect of regeneration treatment with liquid water at high pressure and temperature on the characteristics of three commercial activated carbons

Abstract The regeneration of three commercial activated carbons by thermal desorption with liquid water at 320°C and 150 atm, in the absence of oxygen, was investigated. The efficiency of this procedure was evaluated by measuring the rate and the amount of substance retained in successive cycles of adsorption–regeneration. The efficiency of the treatment was found to be very high. The study was conducted with the adsorption of two compounds differing greatly in their molecular sizes: phenol and an azo dye (direct red 79 C.I. 29065). In all three carbons a slight increase in the adsorptive power was observed with respect to the original carbons; this is attributed to the cleaning or opening of closed pores. The carbons exhausted with phenol showed the greatest difficulty in regenerating because part of the phenol may be chemically adsorbed. The effect of the treatment on the textural and chemical characteristics of the original carbons was also investigated using N2 adsorption isotherms, mercury porosimetry, pycnometry, scanning electron microscopy and acid-base titration. The alterations found were not very significant, except for a slight increase in the true density, total pore volume and the acidity of the treated carbons.

Study of the desorption of phenol and phenolic compounds from activated carbon by liquid-phase temperature-programmed desorption

Abstract The thermal desorption in water of phenol, 2-dichlorophenol, 2,6-dichlorophenol, 4-nitrophenol and 2,6-dichloro-4-nitrophenol adsorbed onto an activated carbon is studied by temperature-programmed desorption (TPD) in liquid phase and by temperature-programmed adsorption-desorption (TPAD). The TPAD thermograms indicate that the desorption in water of the five compounds is complete before a temperature of 300 °C is reached. The five phenolic compounds are stable below 260 °C. Application of the interruption test shows that diffusion controls the desorption of these compounds in water. High-temperature adsorption isotherms and TPAD thermograms indicate that readsorption occurs during thermal desorption. Study of TPAD permits the calculation of the activation energies of adsorption and desorption. The values of these energies afford values for the adsorption bonding energy that lie within the range of the hydrogen bond.

Adsorption of phenol on supercritically activated carbon fibres: effect of texture and surface chemistry.

The influence of texture and surface chemistry on the phenol adsorption capacity of activated carbon fibres (ACFs) was studied. ACFs were prepared by carbonization of a phenolic textile fibre under nitrogen flow, followed by activation with H(2)O and CO(2) (under atmospheric pressure and supercritical state). The materials were characterised by N(2) and CO(2) adsorption, and by temperature programmed desorption studies. A strong correlation between the amount of adsorbed phenol and the micropore volume has been observed. The relationship between surface oxygen concentration and amount of physisorbed and chemisorbed phenol was assessed, and it was shown that higher amounts of surface oxygen groups decreased the phenol chemisorption capacity of ACFs.

A review of the application of the BET equation to experimental data: the C parameter

Here we offer a review of the BET plot proposing other linear transformations of the original equation, with a view to checking the model. Comparative study of the results obtained with the different equations leads to the conclusion that the C constant of the BET equation cannot be constant; instead it varies with the amount of molecules adsorbed. We describe how to determine the values of C as a function of surface coverage. These values are compared with the molar adsorption enthalpies obtained using the isosteric method. The similarity of the results allows us to confirm the energetic meaning attributed to C. The variation in C with surface coverage also serves to explain the different types of isotherm, including Types III and V, and why the BET plot is only linear for a limited stretch of the isotherm.

Comparative study of non-isothermal methods in linear and non-linear temperature variation

A method is proposed for the treatment of data from non-isothermal kinetic experiments with non-linear variation of temperature with time. A comparative study was carried out between this and the linear method on application to a chemical reaction in solution.AbstractПредлагается метод обработки данных, полученных в неизотермических кинетических экспериментах с нелинейным изменением температуры во времени. Данный метод сравнивается с линейным методом при использовании их для химических реакций в растворе.

Kinetics of reactions in solution: Method for the treatment of data from non-isothermal chemical kinetic experiments

A new method is proposed for the treatment of kinetic data derived from non-isothermal kinetic experiments for the determination of the parameters of the Arrhenius equation. The results obtained from its application show the excellent precision of this method.AbstractПредлагается новый метод обработки кинетических данных неизотермических кинетических исследований с целью получения параметров уравнения Аррениуса. Результаты, полученные с помощью данного метода, указывают на превосходую точность этого метода.

Conversion of a resistant pollutant, phenol, into green fuels by gasification using supercritical water compressed up to 1000 bar

For green sustainable chemistry, it is crucial to investigate the destruction of such a common pollutant as phenol. This study reports the gasification of phenol with steam and supercritical water (SCW) and shows that gasification under high-pressure SCW is a method that destroys and efficiently converts phenol into valuable products. To the best of our knowledge, the widest pressure range ever investigated in this field is utilized, i.e., from atmospheric pressure steam to SCW at 1000 bar. The high temperature used (700 °C) leads to fast degradation of phenol under all the conditions studied but the amount of phenol gasified does strongly depend on pressure. During gasification, polymeric compounds such as naphthalene and phenanthrene are generated. They play a key role in the proposed degradation–gasification mechanism since they are difficult to degrade and can lead to the formation of char. High-pressure SCW can more efficiently degrade and gasify such polymeric compounds compared to steam. Then, the supercritical fluid leads to the conversion of a greater amount of phenol into gas than steam: 68% of the pollutant is gasified at 750 bar and 700 °C after 16.5 min with no generation of pollutant by-products, except CO2. Furthermore, the gaseous stream contains the valuable green gases H2 and CH4. The use of highly compressed SCW implies not only the production of more gases but also the enrichment of the gas mixture in H2 and CH4. H2 and CH4 concentrations up to 35 and 30%, respectively, are obtained at 1000 bar.

A model for the characterization of supported catalysts by temperature-programmed desorption with readsorption and heterogeneity

A model has been developed in which the thermogram is the net balance of the overall desorption-adsorption process. The equations necessary for its application are proposed and the model is tested using a simulation program.

Determination of activation energy in enzymatic reactions by a single non-isothermal kinetic experiment

A non-isothermal kinetic method with linear heating was applied to enzymatic catalysis and rapidly provided the activation energy. The results obtained showed the excellent precision of the method.AbstractНеизотермический кинетический метод с линейным нагревом применялся к знзиматическому катализу. Таким образом, быстро могут быть определены знергии активации. Полученные результаты свидетельствуйт о превосходной точности метода.