Abstract
The adsorption of gallic acid on active carbons of different ranks with different pore structure and chemical state of the surface is investigated. The regularities and features of the adsorption process are established. It is revealed that the adsorption isotherm of gallic acid from the aqueous solution with activated carbon of AG-OB-1 rank refers to the L-type isotherms by Giles's classification, and AC adsorption isotherm of ABG and Purolat-Standard ranks - to the S-type isotherms. L-type isotherm gives evidence concerning the flow of physical adsorption. With S-type isotherm is the adsorption described, at which the strength of the interaction between the solute and the adsorbent is less than the force of interaction between the adsorbed molecules, which can be explained by the formation of hydrogen bonds. It was found that the maximum adsorption of gallic acid with carbon sorbents changes in the following sequence - Purolat-standard > ABG > AG-OV-1. The mechanism of adsorption of gallic acid on active carbons is offered. Proceeding from the structure, the chemical state and the main adsorption parameters of active carbon, we can assume that the adsorption of gallic acid has physical nature. It can take place in pores, both due to dispersion interaction (of van der Waals forces) and due to the interaction between the active carbon surface functional groups, containing oxygen with carboxyl and hydroxyl groups of gallic acid. The values of adsorptive capacity testify to the dependence of the adsorption efficiency on the structure and physical-chemical properties of the sorbent. It has been determined that by the absorption of gallic acid specific interaction makes greater contribution. It is shown that the results obtained can be applied to create adsorption technologies on removing gallic acid from the sewage containing individual components and from the mixture with other polyphenols, including beer wort.
Highlights
Gallic acid (3.4.5-trihydroxybenzoic acid) is one of the most common plant acids
Where X is the concentration of gallic acid in mg/dm3, found from the graph; Val is the aliquot of the test solution, cm3; Vmf is the volume of measuring flask, cm3
Where Г0 is adsorbent maximum adsorptive capacity, mole/g; K is the universal gas constant, J/mole·K; T is temperature, K; E is characteristic adsorption energy, J/mole; β is coefficient of affinity; Cр is equilibrium concentration of the solution, mole/dm3; Cs is the concentration of saturated solution, mole/dm3; Vm is molar volume of the adsorbent, cm3/mole; W0 is the limiting volume of the adsorption space cm3/g
Summary
As a part of the plant usually in a bound form (esters, polymers) it is a precursor to a number of polyphenolic substances [1] This acid is contained in the sewage of pharmaceutical factories, it is present as a component in the beer wort. Glucose esters with condensed gallic acid can be considered as tannins of dual nature, because they contain hydrolyzable fragments These completely non-hydrolyzable tannins are derived from flavonols. The difference of applied technology consists in replacing the traditional two-step process of carbonizing the raw material in an inert atmosphere, followed by activation for one-step process of air carbonization/activation This reduces the final price of the sorbent due to the reduction of energy consumption for its production [3]. The aim of the study was to investigate the adsorption of gallic acid by active carbons different in their structure and nature, to identify the possibility of their use in the process of improving the quality of beer
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