Badanie fizykochemicznych właściwości chemicznie modyfikowanych węgli aktywnych

• Autorzy: Repelewicz M. , Choma J.

Warianty tytułu

EN

Study of physicochemical properties of chemically modified activated carbons

• Języki publikacji: PL

Abstrakty

PL

Badano fizykochemiczne właściwości węgli aktywnych otrzymanych przez modyfikację węgla handlowego poprzez osadzanie depozytu węglowego z rozkładu chlorku metylenu. Na podstawie niskotemperaturowej adsorpcji azotu wyznaczono podstawowe parametry struktury porowatej. Stosując metodę Boehma, wyznaczono stężenie powierzchniowych grup funkcyjnych zawierających tlen. Metodą inwersyjnej chromatografii gazowej (IGC) wyznaczono izotermy adsorpcji alkoholi alifatycznych od C=1 do C=4 oraz benzenu i chloroformu. Na podstawie otrzymanych izoterm adsorpcji obliczono wartości izosterycznego ciepła adsorpcji qst. Stwierdzono istotny wpływ depozytu węglowego na właściwości strukturalne i powierzchniowe węgla aktywnego.

EN

Physicochemical properties of activated carbons prepared by chemical modification of a commercial active carbon were studied. The modification consisted in forming so-called carbon deposit from methylene chloride pyrolysis. The obtained modified activated carbons contained carbon deposit within the range of 7.28 to 20.91% by weight. The basic parameters of porous structure were calculated by means of low-temperature nitrogen adsorption. The specific surface, determined by BET method within the range of relative pressures (p/p0 0.01 to 0.2, is going down regularly from 790 m2/g (the commercial carbon) to 360 m2/g (the carbon containing 20.91% by weight carbon deposit). Moreover, the micropore volume (calculated by means Barrett, Joyner and Halenda method) changes also regularly from 0.34 to 0.15 cm3/g, similarly as total pore volume from 0.40 to 0.19 cm3/g. The results point out that, forming a carbon deposit has a great influence on the pore structure of the carbon materials, and during the modification adsorptive properties to nitrogen are getting worse markedly. Using the Boehm method the concentration of surface acidic functional groups containing oxygen such as: carboxylic, lactic, carbonyl and phenyl groups, were determined. The total concentration of surface functional groups is almost the same for the studied carbons except carbon possessing 20.91% by weight carbon deposit (here the concentration is smaller). On the other hand, the carbons differ in the concentration of individual groups. This effect is most visible in the concentration of carboxylic groups: the commercial carbon contains 0.016 mmol/g carboxylic groups and the all modified carbons contain about 0.55 mmol/g of these groups. Adsorption isotherms of aliphatic alcohols (C=1 to C=4), benzene and trichloromethane on all studied carbons were determined by means of inverse gas chromatography (IGC). The measurements were carried out by a Mera-Elmet type N-504 chromatograph, using a thermoconductometic detector (TCD), helium as a carrier gas, within the temperature range from 333 to 493 K. The adsorption isotherms were calculated by the peak profile method by graphic integration of an individual chromatogram. The measurements of adsorption isotherms at various temperatures permit to calculate isosteric adsorption heat (qst). It can be said generally that the isosteric adsorption heat is going up with the degree of surface covering. If the degree of surface covering is small, the magnitude of heat effect depends mainly on interaction between adsorbate-adsorbent. Whereas for the increasing degree of surface covering there can be additional adsorbate--adsorbate interaction. Additionally, the molecules of aliphatic alcohols can create hydrogen bonds with the carbon surface having adequate surface functional groups. The obtained values of isosteric adsorption heats are about 60 kJ/mol to the extent of degree of surface covering to 30 μmol/g. It can suggest that the dominant adsorption mechanism is physical adsorption.

Słowa kluczowe

PL

węgiel aktywny; modyfikacja depozytem węglowym; niskotemperaturowa adsorpcja azotu; powierzchniowe grupy funkcyjne; metoda IGC

EN

activated carbon; carbon deposit; low-temperature nitrogen adsorption; concentration of surface functional groups; IGC method

• Wydawca: Wydawnictwo Politechniki Częstochowskiej
• Czasopismo: Inżynieria i Ochrona Środowiska
• Rocznik: 2005
• Tom: T. 8, nr 1
• Strony: 5--17
• Opis fizyczny: Bibliogr. 13 poz.

Twórcy

autor

Repelewicz M.

• Akademia Świętokrzyska, Instytut Chemii, ul. Chęcińska 5, 25-020 Kielce

autor

Choma J.

• Akademia Świętokrzyska, Instytut Chemii, ul. Chęcińska 5, 25-020 Kielce

Bibliografia

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