Adsorption of two coffee aromas from synthetic aqueous solution onto granular activated carbon derived from coconut husks
Introduction
Aroma is one of the most important attributes of coffee. During the roasting process, several aroma compounds are formed by the pyrolysis of water-soluble components, such as sugars, amino acids and trigonelline. Volatile components of coffee are numerous and varied in their quality, potency and concentration; thus, each compound contributes to the overall aroma (Dart and Nursten, 1989). Some volatile components such as benzaldehyde have a pleasant odour, while others, such as acetic acid, have an unpleasant smell. Benzaldehyde (C6H5CHO) is an aromatic aldehyde naturally found in almonds and roasted coffee, and possesses the bitter odour of almond oil. Alternatively, the irritating odour of vinegar is attributed to acetic acid (C2H4O2) (Flament, 2002).
Soluble coffee processes including extraction, evaporation and drying result in the loss and degradation of aromas, reducing the quality of the final product. During these processes, aromas can be collected into aqueous waste streams and separated from wastewater. To allow aromas to be reincorporated into the final product (Varnam and Sutherland, 1994, Smith, 1989), pleasant-smelling compounds such as benzaldehyde must be separated from unpleasant compounds such as acetic acid. The recovery and/or separation of volatile compounds are usually achieved by expensive thermal treatments, which can damage the final product (Diban et al., 2007). Consequently, there is considerable interest in the development of alternative separation processes. Adsorption is a promising operation that has been used for the recovery and/or separation of organic compounds such as benzaldehyde and pyridine in waste water (Rajoriya et al., 2007, Lataye et al., 2008), phenylethyl alcohol, ethanol and acetic acid in fermentation broth (Fabre et al., 1996, Bowen and Vane, 2006), methyl mercaptan, ethyl acetate and furfural in coffee aroma (Sakano et al., 1996, Sakano et al., 1999, Lucas et al., 2004) and the main pear aroma from aqueous fruit juice (Diban et al., 2007).
The recent increase in coconut production, processing and consumption in Brazil has generated a large quantity of coconut husks residues. The disposal of these materials is expensive and may lead to environmental problems. An alternative application for this raw material is the conversion of coconut husks into activated carbon (Gratuito et al., 2008), which can be used as an adsorbent in many applications (Sekar et al., 2004, Hameed et al., 2008).
The application of granular activated carbon from coconut husks to the recovery and/or separation of coffee aromas in soluble coffee production is relatively rare. Currently, approximately 1000 different coffee aromas have been detected, and experts suggest that dozens of compounds have yet to be identified; thus, the development of alternative aroma separation and recovery processes is important.
Previous studies on the adsorption of benzaldehyde and acetic acid onto granular activated carbon derived from coconut husks have not yet been reported. The aim of this study was to evaluate the adsorption of volatile compounds in aqueous solution onto commercial grade granular activated carbon made from coconut husks. For this purpose, equilibrium batch experiments were performed in synthetic single-solute aqueous systems. The physical properties of the adsorbent were evaluated to better understand the adsorption process. Moreover, Langmuir, Freundlich and Temkin models were used to describe and predict single system adsorption behaviour. The equilibrium parameters obtained from monocomponent adsorption studies may be helpful to describe the behaviour of adsorption from mixtures, since the multicomponent isotherm models require the constants derived from single-solute adsorption isotherms for the data fitting (Choy et al., 2000).
Section snippets
Characterization of the adsorbent
Commercial grade granular activated carbon (GAC) derived from coconut husks was provided by Carbomafra Chemical Industries S.A. The Carbomafra® activated carbon (C 119) was produced via calcination and physical activation, and possessed a particle size distribution of 850–250 μm. Scanning electron microscopy (SEM) micrographs of the GAC were obtained with a scanning electron microscope (Jeol JSM-6360LV). The Brunauer–Emmett–Teller surface area (Brunauer et al., 1938), total pore volume and
Characterization of the adsorbent
According to technical specifications, the GAC employed in this study possessed a minimum hardness of 90% and an apparent density of 500 ± 50 kg m−3, allowing the adsorbent to be successively regenerated, which is desirable for industrial applications.
The iodine number provides information on the internal surface of activated carbon and is determined by the iodine adsorption capacity of the material. Every milligram of iodine adsorbed by the material represents 1 m2 of internal surface. For the
Conclusion
The results of the present study revealed that Carbomafra® granular activated carbon derived from coconut husks was an effective adsorbent for the removal of benzaldehyde from aqueous solution. Moreover, benzaldehyde was removed from solution more efficiently than acetic acid, indicating that coconut husks GAC possessed a high affinity for benzaldehyde. The pseudo-second-order kinetic model provided an adequate representation of the kinetic of acetic acid adsorption, while the kinetic of
Acknowledgments
The authors are grateful for the scholarship provided by CAPES/REUNI, the research grant and support of the Graduation Program of Food Technology (Federal University of Paraná, Curitiba, Brazil) and the activated carbon supplied by Carbomafra S.A.
References (39)
- et al.
Preparation and characterization of activated carbon from oil palm wood and its evaluation on methylene blue adsorption
Dyes and Pigments
(2007) - et al.
A kinetics and thermodynamics study of methylene blue adsorption on wheat shells
Desalination
(2006) - et al.
Granular activated carbon for the recovery of the main pear aroma compound: viability and kinetic modeling of ethyl-2,4-decadienoate adsorption
Journal of Food Engineering
(2007) - et al.
Adsorption characteristics of activated carbons obtained from corncobs
Colloids and Surfaces A
(2001) - et al.
Experimental and statistical analysis of trichloroethylene adsorption onto activated carbon
Chemical Engineering Journal
(2010) - et al.
Thermodynamic study of fatty acids adsorption on different adsorbents
Journal of Chemical Thermodynamics
(2007) - et al.
Production of activated carbon from coconut shell: optimization using response surface methodology
Bioresource Technology
(2008) - et al.
Adsorption isotherm, kinetic modeling and mechanism of 2,4,6-trichlorophenol on coconut husk-based activated carbon
Chemical Engineering Journal
(2008) - et al.
Adsorption thermodynamics of carbofuran on Sn (IV) arsenosilicate in H+, Na+ and Ca2+ forms
Colloids and Surfaces
(1987) - et al.
Extraction of benzaldehyde from fermentation broth by pervaporation
Process Biochemistry
(1996)
Pyridine sorption from aqueous solution by rice husk ash (RHA) and granular activated carbon (GAC): parametric, kinetic, equilibrium and thermodynamic aspects
Journal of Hazardous Materials
Adsorption isotherms for ethylacetate and furfural on activated carbon from supercritical carbon dioxide
Fluid Phase Equilibria
Kinetics and equilibrium adsorption study of lead(II) onto activated carbon prepared from coconut shell
Journal of Colloid and Interface Science
Competitive adsorption of cadmium(II) and nickel(II) metal ions from aqueous solution onto rice husk ash
Chemical Engineering and Processing
Adsorptive removal of phenol by bagasse fly ash and activated carbon: equilibrium, kinetics and thermodynamics
Colloids and Surfaces A
Ethanol, acetic acid, and water adsorption from binary and ternary liquid mixtures on high-silica zeolites
Langmuir
Adsorption of gases in multimolecular layers
Journal of the American Chemical Society
Langmuir isotherm models applied to the multicomponent sorption of acid dyes from effluent onto activated carbon
Journal of Chemical and Engineering Data
Cited by (33)
Alginate-modified surfactants functionalized metal-organic framework-based fluorescent film sensors for detection and adsorption of volatile aldehydes in water
2024, International Journal of Biological MacromoleculesHigh surface area and supermicroporous activated carbon from capsicum (Capsicum annuum L.) industrial processing pulp via single-step KOH-catalyzed pyrolysis: Production optimization, characterization and its some water pollutants removal and supercapacitor performance
2022, Diamond and Related MaterialsExtraction of carotene from crude hybrid palm oil using polymeric resin
2020, Journal of Food EngineeringCopper adsorptive removal from aqueous solution by orange peel residue carbon nanoparticles synthesized by combustion method using response surface methodology
2019, Journal of Environmental Chemical EngineeringCitation Excerpt :The Temkin adsorption isotherm, considered chemisorption of an adsorbate onto the adsorbent [53], among the alternative model provides the better fit to experimental data. This suggests that the adsorption of Cu2+ on to OPCM is a chemisorption process, and indicates that the surface of the adsorbent is energetically heterogeneous [54]. As seen in Table 7a, the monolayer adsorption capacity according to the Langmuir model is 16.64 mg/g, which is in good agreement with the experimental value.