J Sci Food Agric 1997, 75, 117È124

Potential of Agricultural By-Product-BasedActivated Carbons for Use in Raw SugarDecolourisationM Ahmedna,1* M M Johns,1 S J Clarke,2 W E Marshall3 and R M Rao11 Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803,USA2 Audubon Sugar Institute, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA3 USDA, ARS, Southern Regional Research Center, PO Box 19687, New Orleans, LA 70179, USA

(Received 31 January 1996 ; revised version received 30 October 1996 ; accepted 10 March 1997)

Abstract : The physical (bulk density and hardness) and chemical (pH andmineral content) characteristics of granular activated carbons (GACs) made fromrice straw, pecan shells and hulls of soybean and rice were determined. Theadsorption properties (iodine test, molasses test and raw sugar decolourisationefficiency) of these by-product-based carbons were also evaluated. A commercialdecolourising carbon (Calgon CPG LF) was used as a comparison. Pecan-basedcarbons had bulk densities and hardness numbers higher than Calgon CPG LF.They also showed a mineral content and pH similar to or lower than the com-mercial carbon. The adsorption properties of the pecan-based carbons were,however, about 40% below that of the reference carbon. In contrast, rice (hulland straw)-based carbons exhibited good adsorption properties similar to thereference carbon in both iodine test and molasses test, but their ash content andtheir inherent pHs were higher than Calgon CPG LF. Both types of rice-basedcarbons were also more friable and had lower bulk densities than the commercialcarbon. However, rice-hull-based carbon was statistically as e†ective as CalgonCPG-LF in decolourising raw sugar solutions at the 5% conÐdence level. Of theby-product-based carbons evaluated, pecan-shell-based GACs would be mostsuitable as raw sugar decolourisers if their adsorption efficiencies could beimproved.

J Sci Food Agric 75, 117È124 (1997)No. of Figures : 4. No. of Tables : 3. No. of References : 14

Key words : activated carbon, agricultural by-products, raw sugar decolourisa-tion

INTRODUCTION

The use of activated carbon for the removal of undesir-able odours and Ñavours was Ðrst recorded more than200 years ago. Carbon adsorption is now commonlyused in the food processing industry, such as sugarreÐning, and for pollution control, as in wastewatertreatment. The extensive use of activated carbon is gen-erally attributed to its large surface area (up to2000 m2/g), making it a powerful adsorbent, capable ofadsorbing most organic and many inorganic contami-nants (Ying and Tucker 1990). Most activated carbons

* To whom correspondence should be addressed.

commercially sold are from non-renewable sources,such as coal. This includes the activated carbons used inraw sugar decolourisation. Activated carbons madefrom agricultural by-products (lignocellulosic material)are potential substitutes for commercial activatedcarbons currently used in raw sugar decolourisation.Almost any lignocellulosic material can be converted toan activated carbon. The literature mentions many pre-cursors for activated carbon, which include variouswoods, particularly in waste forms ; various forms of cel-lulose materials such as cane trash, bagasse, corn cobsand seed shells ; grain residues such as rice hulls ; reÐn-ing by-products such as molasses ; shells of nuts ; and

1171997 SCI. J Sci Food Agric 0022-5142/97/$17.50. Printed in Great Britain(

118 M Ahmedna et al

pits and pulp of fruits (Mantell 1946 ; Mattson andMark 1971 ; Laine et al 1989 ; Girgis et al 1994).

Activated carbons from agricultural by-productsmight have the advantage of o†ering an e†ective, lower-cost replacement for existing bone char or coal-basedgranular activated carbons (GACs) provided that theyhave similar or better adsorption efficiency. The effi-ciency of any activated carbon to adsorb the targetedcompounds (colour, ash, colloids) depends on severalfactors. These factors include the carbonÏs porosity,surface area, pore size distribution, bulk density, surfacechemistry, hardness, pH, particle density, particle size,amount of water soluble minerals and its total ashcontent (Hassler 1963 ; Nakhla et al 1994 ; Smisek andCerney 1970). Each of these characteristics may be ofspecial importance depending on the projected use. Forinstance, in the case of sugar decolourisation, thedecolourising carbon should possess a pore size dis-tribution favourable for adsorption of a mixture ofpolydispersed constituents from highly concentratedsugar solutions, including the pH-sensitive sugarcolourants, such as phenols and Ñavonoids. Suchcarbon should also have a low ash content, since ash isundesirable in the reÐned sugar. In fact, good sugardecolourising carbons should possess ash-removingproperties. In addition to the above examples, decolou-rising carbons should have sufficient hardness to endurethe mechanical action of the percolating liquor duringthe raw sugar decolourisation process.

A number of testing methods have been developed inan attempt to evaluate the efficiency of decolourisingcarbons (Smisek and Cerney 1970). The basic principlebehind these methods is to apply appropriate standardtests to both a reference activated carbon and a candi-date activated carbon. Results of such tests will evaluatethe relative efficiency of the tested vs the referencecarbon.

The objective of this study was to characterise GACsprepared from agricultural by-products such as ricehulls, rice straw, pecan shells and soybean hulls. Thecharacteristics of the by-product-based carbons werecompared to a reference carbon, namely Calgon CPGLF, to determine how closely the properties of the by-

product-based GACs matched those of a good com-mercial decolourising carbon.

MATERIALS AND METHODS

Materials

Samples of GACs made from agricultural by-productswere furnished by the Southern Regional ResearchCenter (USDA-ARS, New Orleans, LA, USA). Table 1lists the conditions under which these carbons were pre-pared. Precursors were either mixed with molasses(1 : 1 w/w) or soaked in 50% (w/w) for 24 h.H3PO4They were then pyrolysed in or air for 1 h at theN2temperatures stated in Table 1. The activatedCO2carbons were activated at 800¡C for 6È10 h, until aburn-o† of 20È30% was reached. The pecan shellcarbon was chemically activated using in eitherH3PO4air or at 460¡C. The activated carbons were washedN2with 0É1 M HCl for 2 h, followed by a water rinse untilthe pH of the rinse water was above 6É0. The carbonswere dried at 50¡C before use.

The reference carbon (Calgon CPG LF) was providedby Calgon Carbon (Pittsburgh, PA, USA). This com-mercial GAC is made from bituminous coal and wasselected on the basis of the manufacturer recommen-dations as an excellent decolouriser of organic liquidssuch as raw sugar liquors (Calgon 1987). Calgon CPGLF was tested for its efficiency in raw sugar decolourisa-tion. It was found to be a better raw sugar decolouriserthan several other available commercial GACs.

Methods

Physical properties : apparent (bulk) density, hardnessApparent (bulk) density was determined by Ðlling a10-ml tube with dry activated carbon. The tubes werecapped, tamped to a constant (minimum) volume by

TABLE 1Precursors and pyrolysis conditions for the production of by-product-based

carbons

Precursors Binder or Charring/ Charring Activationadditive activation atmosphere atmosphere

temperature

Rice hulls Molasses 800¡C N2 CO2Rice straw Molasses 800¡C N2 CO2Soybean hulls Molasses 800¡C N2 CO2Pecan shells H3PO4 460¡C Air AirPecan shells H3PO4 460¡C N2 N2

Activated carbons in raw sugar decolourisation 119

tapping on a table, and weighed. The apparent densityof 40-mesh size activated carbon was calculated by

Apparent density (g/cm3) \

Weight of dry sample (g)Volume of packed dry material (cm3)

To determine hardness of the carbons, 2 g of 40-meshactivated carbon was weighed, placed in a 250-mlErlenmeyer Ñask, and 10 glass marbles (15 mm diam-eter, 5É41 g each) were then introduced into each Ñask.The Ñasks were capped and placed in an Aquathermwater-bath shaker (New Brunswick ScientiÐc Co,Edison, NJ, USA). The samples were shaken at 200 rpmfor 20 min at 25¡C and then screened through a40-mesh screen. The material retained by the screen wasweighed and the hardness number calculated as follows :

Hardness number \

Weight of carbon retained by screen (g)Initial sample weight (g)

] 100

Chemical properties : pH, mineral contentSuspensions of activated carbons in water (1% w/w)were heated to 90¡C and were subjected to continuousstirring for 20 min then cooled to room temperature.The pH of the suspension was subsequently determinedwith an Orion Research Digital Ionalyser, Model 601/A(Cambridge, MA, USA).

Total ash was determined using crucibles containing1 g of carbon placed overnight in a circulating air ovenset at 115¡C. After cooling in a desiccator, crucible andcontent were weighed and placed in a Jelrus furnace(Jelrus Technical Products, New Hyde Park, NY, USA).The samples were heated to 950¡C for 1É5 h with acurrent of air circulating over them. The crucibles werethen allowed to cool in a desiccator and weighed. Theresidue weight was calculated and reported as percent-age of ash.

Water soluble minerals were studied by electricalconductivity. To measure electrical conductivity, a 1%(w/w) carbonÈwater suspension was prepared. Themixture was stirred for 20 min, then the electrical con-ductivity of the suspension was recorded using a CDM3conductivity meter (Radiometer, Copenhagen,Denmark).

Adsorption properties : iodine and molasses testsThe amount of iodine adsorbed by a test carbon wasdetermined from a modiÐcation of the method ofHassler (1963). A stock solution of iodine was preparedby dissolving 2É7 g of and 4É1 g of KI in 1 litre ofI2deionised water. The solution was stored in the dark.Carbon (0É5 g) and 10 ml of 5% hydrochloric acid wereplaced in a 250-ml Ñask. The Ñask was swirled until the

carbon was wetted, and then 100 ml of stock iodinesolution was added and the mixture shaken for 5 min.A blank was prepared without adding carbon. Allsamples were Ðltered through Whatman No. 5 Ðlterpaper. Filtrate (50 ml) was titrated with 0É1 M sodiumthiosulfate using starch as an indicator. The percentiodine removed (PIR) by each carbon was calculated asfollows :

PIR \

ml thiosulfate used for blank[ ml thiosulfate used for sampleml thiosulfate used for blank

] 100

The above test was employed using an appropriatecarbon dosage between 0É2 and 0É5 g per 100 ml ofiodine solution.

The molasses test used was described by Hassler(1963) with modiÐcation. Blackstrap molasses (10 g)together with 15 g of disodium phosphate was dissolvedin 500 ml of water and sufficient phosphoric acid wasadded to give a pH of 6É5. The mixture was diluted to 1litre, then Ðltered through a thin layer of Ðlter aid in aBuchner funnel.

Test solution (50 ml) was put into a 250-ml beaker,0É5 g of carbon was added and the suspension stirred.Beakers were placed on a heating plate and the contentsbrought to the boil. A blank to which no carbon wasadded was prepared. The heated mixture was Ðlteredthrough Whatman No. 5 Ðlter paper and the colour ofthe Ðltrate measured using a Gilford Response-II (UV,VIS) spectrophotometer with a 10-mm cell. The wave-length used was 420 nm and the band width 0É2 nm.The above procedure was repeated using other weightsof carbon suitable to give an adsorption range of 70È90%.

The percent of adsorption was calculated by

PMCR\

Absorbance of blank[ Absorbance of sample with carbon

Absorbance of blank] 100

where PMCR is the percent molasses colour removed.

E†ectiveness of activated carbons in raw sugardecolourisationThe decolourisation test was a modiÐed version of thebatch-type decolourisation assay used by DominoSugar (Amstar 1993). ModiÐcations were the use of pH7É00 bu†ered solutions to prepare the standard sugarliquor, instead of deionised water, and an additional Ðl-tration of samples through 0É45-km membrane after Ðl-tration through Reeve Angel 202 Ðlter paper, which isspeciÐed by the original procedure.

120 M Ahmedna et al

Preparation of standard test liquor/decolourisationprocedure. Test liquors of 60^ 0É2 Brix were preparedby dissolving a sufficient quantity of white sugar in0É1 M 3-(N-morpholino)-2-hydroxypropane sulphonicacid (MOPSO) bu†er, previously adjusted to pH 7É00(Ahmedna et al 1997). The liquorÏs colour was adjustedby addition of blackstrap molasses to reach an absorb-ance reading of 0É5 at 420 nm. Finally, the pH of thetest liquor was checked to ensure that it was maintainedat pH 7É00.

Samples of 100 g of 60 Brix sugar liquor wereweighed into 250-ml beaker. A TeÑon stirring bar wasplaced in each beaker. Beaker containing test liquorwere covered with watch glasses and placed in a water-bath at 81 ^ 1¡C. Samples were subject to moderatestirring and heating until the test liquor reached80 ^ 1¡C. At this point, 1 g of GAC was added to eachsample. Stirring at 160 rpm was continued for 20 min,the liquor temperature maintained at 80 ^ 1¡C. At theend of 20 min, samples were removed and Ðlteredthrough a Buchner plastic funnel containing ReevesAngel 202 Ðlter paper. About 1% (w/w) of Ðlter aid (No3 diatomaceous earth) was added to the Ðltrate. Fil-trates containing Ðlter aid were moderately stirred andheated until they reached 70¡C. The samples were thenÐltered through a membrane Ðltration assembly con-taining Reeves Angel 202 Ðlter paper and an adsorbent,Amberlite XAD-7 (Rhom and Haas Co, Philadelphia,PA, USA). The Ðltrates were transferred to 250-mlbeakers, their Brix measured, and their pH adjusted to7É00, if necessary. Prior to colour measurement, Ðltrateswere passed through a 0É45-km membrane to eliminatethe black colour caused by suspended carbon, very Ðnecarbon particles generated by carbon attrition. Thecolour of all samples was then measured at 420 nm by aGilford Response-II (UV-VIS) spectrophotometer usinga 10-mm cell. Along with the activated carbon samples,a blank containing the test liquor alone was subjectedto the same experimental conditions. The colour of theblank after stirring and Ðltration represents the originalcolour of the standard test liquor and was used for thecalculation.

The percent colour removed by activated carbonswas calculated by,

Percent colour removed\

Colour of blank[ Colour of sample with carbon

Colour of blank] 100

where, in each case, colour is calculated as follows :

Colour \

(1000 ] Sample absorbance)(Corrected RDS] Corrected RDS density)

ICUMSA units

where RDS is the refractometric dry substance or per-centage of soluble solids (Brix) ; Corrected RDS densityis the relative density of sugar solution (20 vs 4¡C) ; andCorrected RDS is the Sample RDS] Correction factor,where

Correction factor \

Raw sugar weightASolvent RDS

100] Solvent weight

B] Raw sugar weight

RESULTS AND DISCUSSION

Physical and chemical characteristics of activatedcarbons

Table 2 shows that the activated carbons prepared frompecan shells had pH values similar to the reference com-mercial carbon. The remaining carbons were alkalinewith pH values above 9. Carbon made from rice hullsshowed the lowest conductivity value (90 kS/cm) of theby-product-based material. Pecan shells pyrolysed and

TABLE 2Chemical properties (conductivity, pH and ash content) of activated

carbonsa

Carbons pH Conductivity Ash content(kS/cm) (% dry weight)

Calgon CPG LF 7É15 ^ 0É06 25 ^ 3É5 4É75 ^ 0É07Pecan shells/air 7É76 ^ 0É01 170 ^ 15 3É15 ^ 0É07Pecan shells/N2 6É45 ^ 0É28 340 ^ 07 5É15 ^ 0É07Rice hulls 9É60 ^ 0É17 90 ^ 04 49É75 ^ 0É21Rice straw 9É75 ^ 0É52 150 ^ 35 22É85 ^ 0É07Soybean hulls 9É50 ^ 0É27 300 ^ 50 19É45 ^ 0É49

a Values given are means of four estimations and standard deviation.

Activated carbons in raw sugar decolourisation 121

activated in atmosphere and soybean hulls had theN2highest conductivities, 340 and 300 kS/cm, respectively.With the exception of pecan-shell-derived carbonpyrolysed and activated in air atmosphere, the ashcontent of all by-product-based carbons was higherthan the reference carbon. Rice-straw- and rice-hull-derived carbons had the highest ash content, 22É85 and49É75% respectively. The high ash content of rice strawand rice hulls can be explained by the presence ofbinder and their inherent mineral content, especiallytheir richness in silica (Mantell 1946). The low ashcontent of pecan carbons is due to the inherently lowash content common to most lignocellulosics and to theabsence of binder in their preparation.

The pH variation among carbons may be explainedby the percent ash content and by the speciÐc mineralcontent. Carbons with pH of about 7 had low ash con-tents, while those with a pH above 9 showed a high ashcontent. In this regard, Hassler (1963) reported that thepH of most commercial carbons is due to inorganicconstituents originating from the precursor or addedduring manufacture. Therefore, the lower pH andmineral content of pecan-shell-based carbons may beattributed to the absence of the high ash molassesbinder used in their preparation. Similarly, the high ashmolasses binder used for the rice and soybean carbonsmay explain their richness in minerals and the highmineral content may have contributed to the relativelyhigh pHs. The activation environment can also providean explanation to the observed di†erence in pH amongthe tested carbons. According to Mattson and Mark(1971), alkaline pHs are characteristic of carbons acti-vated with Such an explanation is applicable inCO2 .the present case, since rice and soybean derived carbonswere activated with and have high pH values. TheCO2results of electrical conductivity indicated that, eventhough the tested samples were acid washed, substantialamounts of potentially water soluble minerals remain inthe carbons. Such high leachable mineral contents areunacceptable when the carbons are to be used for com-mercial sugar decolourisation. Consequently, moreextensive washing with acid would be necessary toreduce the amount of water soluble minerals to a levelsimilar to that of the reference carbon.

From Table 3, rice-straw- and rice-hull-derivedcarbons had, respectively, the lowest density (0É27 and0É36 g/ml) and the lowest hardness number (73É22 and30É3%). In contrast, pecan-shell-based carbonsexhibited densities and hardness numbers higher thanthose of the reference carbon.

Based on their ash, hardness and density, pecan-shell-based carbons were similar to the reference carbon,whereas the rice and soybean derived carbons weremore friable and had higher ash. The similarities inphysical and chemical characteristics of pecan-shell-derived carbons to the commercial sample make themsuitable choices as GAC for raw sugar decolourisation.

TABLE 3Physical properties (bulk density and hardness number) of

activated carbonsa

Activated Apparent density Hardness numbercarbon (g/ml, 40 mesh size) (% survival)

Calgon CPG LF 0É46 ^ 0É01 74É12 ^ 1É68Pecan shells/air 0É49 ^ 0É01 83É41 ^ 1É32Pecan shells/N2 0É51 ^ 0É01 77É18 ^ 1É43Rice hulls 0É36 ^ 0É01 30É30 ^ 1É68Rice straw 0É27 ^ 0É01 73É22 ^ 0É55Soybean hulls 0É40 ^ 0É02 81É35 ^ 1É17

a Values given are means of four estimations and standarddeviation.

Adsorption properties

The percent of iodine removed by an activated carbonis an indicator of its ability to adsorb low-molecular-weight compounds. Carbons that can remove a highpercentage of iodine normally have a high surface areaand are e†ective at removing odour and taste com-pounds (Hassler 1963). Figure 1 shows that the highestiodine adsorption was achieved by the carbons madefrom rice straw and pecan shells (air). Of the sixsamples, carbon from soybean hulls gave the lowestiodine removal. Calgon CPG LF and carbons derivedfrom rice straw and pecan shells exhibited similar(N2)

Fig 1. Percentages of iodine removed by activated carbons(iodine test).

122 M Ahmedna et al

Fig 2. Percentages of molasses colour removed by activatedcarbons (molasses test).

percentages of iodine removal. The observed di†erencesin iodine adsorption among carbons generally reÑectdi†erences in their surface areas. A higher degree ofiodine adsorption indicates a higher surface area and a

Fig 3. Relative efficiency by-product based carbons indecolourising raw sugar solutions of 60 Brix.

Fig 4. Average percentage of sugar colour removed by acti-vated carbons in a sugar solution of 10 Brix (* \ signiÐcantly

di†erent from Calgon CPG LF at P\ 0É05).

largely microporous structure (Gergova et al 1993). Thecarbons made from pecan shells probably contained ahigh amount of microporosity that was due to theinherent structure of pecan shells and/or developedduring the low temperature pyrolysis employed(Gergova et al 1994 ; Girgis et al 1994). Such highmicroporosity would explain why both pecan shellcarbons were efficient in adsorbing iodine.

The molasses test is generally an indicator of an acti-vated carbonÏs ability to adsorb colour bodies, espe-cially sugar colourants. Carbons with high relativepercent molasses colour removal are potentially gooddecolourisers. Calgon CPG LF (reference carbon) hadthe highest percent molasses colour removal, followedby the carbons made from rice hulls, rice straw andpecan shells as shown by Fig 2. The lowest molas-(N2),ses colour adsorption was exhibited by the carbons pre-pared from soybean hull and pecan shell (air), which didnot exceed 20% colour removal even at the highestcarbon dosage. Two general properties of activatedcarbon can explain the observed di†erences in molassescolour adsorption among the tested carbons. Theseproperties are (1) the pore-size distribution and surfacearea of the material, and (2) the chemical reactivity ofthe carbon surface (Mattson and Mark 1971). Ingeneral, activated carbons with a range of larger tosmaller pores have the highest molasses colour removal.The presence of large and small pores implies a favour-able pore size distribution for adsorption of polydis-

Activated carbons in raw sugar decolourisation 123

persed colourants. It also implies a larger availablesurface area. The system of macropores would serve asavenues for the rapid di†usion of colour bodies to thesmaller pores where they are adsorbed. These structuresfavourably enhance both the adsorption and reacti-vation characteristics (Calgon 1987). The pore structureof activated carbons made from agricultural by-products are dependent upon the pyrolysis temperature,the composition and structure of the raw materials andthe method of activation. By-product-based carbonsprepared using high pyrolysis temperatures and CO2activation (ie rice hull and rice straw) are likely to havea mainly macroporous structure (Rodriguez-Reinosoand Molina-Sabio 1992 ; Gergova et al 1994). In con-trast, those prepared at low temperatures without CO2(ie pecan shells) are known to exhibit a predominantlymicroporous structure (Girgis et al 1994). The chemicalreactivity of the carbon surface was not investigated,however, and may have played a role in the adsorptionbehaviour of each carbon.

E†ectiveness of agricultural by-product-based carbons inraw sugar decolourisation

In agreement with previous molasses test results (Fig 2),GACs made from rice hull and rice straw had the bestdecolourising power, with a relative efficiency of about85% of that achieved by the reference carbon. Pecanshell carbons were about 65% as efficient, and thesoybean derived carbon was about 50% as efficient (Fig3). Similarities between the results of the molasses testand those of the sugar decolourisation assays areexpected, since the molasses test is generally consideredas an indicator of an activated carbonÏs ability toremove colourants from aqueous solutions.

A study was conducted to evaluate the e†ect of thetype of activated carbon on the percent colour removedfrom a more dilute sugar solution of 10 Brix (Fig 4). Thepercent colour removed by Calgon CPG LF and ricehull carbon were not signiÐcantly di†erent but were dif-ferent from all the other carbons at P\ 0É05. DuncanÏsranking of the six activated carbons placed both CalgonCPG LF and rice-hull-derived carbon as the bestdecolourisers. The remaining carbons were all signiÐ-cantly di†erent from Calgon CPG LF at P\ 0É05 andranked in the following order : pecan shell (pyrolysed in

shell (pyrolysed in air)[ soybean hull. TheN2) [ pecanpercentage of sugar colour removed by each activatedcarbon was higher, however, than those reached in thestandard batch-type decolourisation assay containingsugar solutions at higher Brix.

CONCLUSIONS

The by-product-based activated carbons exhibited dif-ferences in their physical, chemical and adsorptionproperties. These dissimilarities were caused by di†er-

ences among precursors or induced by manufacturingconditions. When compared with the commercialcarbon, Calgon CPG LF, as a reference, the by-product-based carbons can be divided into three groupsfor their potential as sugar decolourisers :

(1) carbons with good colour adsorption propertiesbut unsatisfactory physical and chemical charac-teristics (this group includes carbons that userice straw and rice hull as precursors) ;

(2) carbons with moderate colour adsorptionproperties but good physical and chemical char-acteristics (this group includes the activatedcarbons made from pecan shells) ; and

(3) carbons with poor colour adsorption propertiesand unsatisfactory physical and chemical charac-teristics (soybean hull-derived carbon is in thisgroup).

In terms of sugar decolourisation, only rice-hull-basedcarbon was found to be similar to the reference carbon,despite its poor physical and chemical properties. Sta-tistical analysis showed that the percentage of colourremoved from solutions by the reference carbon was notsigniÐcantly di†erent from that removed by rice-hull-derived carbon at the 5% level of signiÐcance. Furtherimprovements of this carbon should target (1) lower ashcontent, (2) higher bulk density and (3) better resistanceto mechanical abrasion (hardness). In contrast togroups 1 and 2, soybean hull-based carbon was thepoorest sugar decolouriser and appears to be a poorcandidate for future improvements. Because of theirphysical and chemical characteristics, pecan-shell-basedcarbons would be ideal as raw sugar decolourisers iftheir adsorption efficiencies could be enhanced.

ACKNOWLEDGEMENTS

The authors would like to thank the USDA Agricultu-ral Research Service for supporting this project underSpeciÐc Cooperative Agreement No 58-6435-121entitled “Carbonaceous materials made from agricultu-ral by-products and their use in cane sugar productionÏ.

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