Utilization of almond residues - IDC Technologies

18 Pages·2011·0.57 MB·English

December,2010 Vol.3No.4 1
Utilization of almond residues
Paul Chen1, Yanling Cheng1, Shaobo Deng1, Xiangyang Lin1,2,
Guangwei Huang3, Roger Ruan1,4
(1.CenterforBiorefining,DepartmentofBioproductsandBiosystemsEngineering,UniversityofMinnesota,
1390EcklesAvenue,St.Paul,MN55108,USA;
2.CollegeofBiologicalScienceandTechnology,FuzhouUniversity,Fuzhou350108,China;
3.AlmondBoardofCalifornia,Modesto,California,USA;
4.StateKeyLaboratoryofFoodScienceandTechnology,EngineeringResearchCenterforBiomassConversion,
MinistryofEducation,NanchangUniversity,Nanchang330047,China)
Abstract:Almondproductiongeneratesmillionsoftonsofresiduesinadditiontoalmondnuts. Almondresidues,including
shells, hulls, pruning, leaves, skin and inedible kernel disposition, are good feedstocks for production of bioenergyand other
valuable compounds. In this article, research on the utilization of almond residues as energy and non-energy feedstocks is
reviewed. Technical options for converting almond residues to energy and other valuable products are discussed. Several
commercialconversiontechnologiesareexamined. Needsforfurtherresearchanddevelopmentarerecommended.
Keywords:activatedcarbons,almond,anti-oxidants,bioenergy,biomass,biorefinery,gasification,heat,power,pyrolysis
DOI:10.3965/j.issn.1934-6344.2010.04.001-018
Citation: Paul Chen, Yanling Cheng, Shaobo Deng, Xiangyang Lin, Guangwei Huang, Roger Ruan. Utilization of almond
residues. IntJAgric&BiolEng,2010;3(4):1－18.
separatedandcollectedforcommercialuses. Theworld
1 Introduction
producesabout1.8milliontonsofalmondnuts. TheUS,
Almond (Prunus dulcis) is a mid-size tree of rose mainly California, accounts for around 45% of the
family. Almond fruit consists of the hull, shell, and world’s production. The 2010 California crop is
kernel (nut). The almond tree can grow to a height of forecasted to be 825,000 tons of almond nuts, which are
seven to ten meters. The edible kernel or nut is accompaniedbyequalamountofshells,twiceasmuchas
hulls, and half as much as pruning (Figure 1). Other
biomaterials maybegeneratedfromremovalof oldtrees,
Receiveddate:2010-11-08 Accepteddate:2010-12-09
Biograpies:PaulChen,PhD,SeniorResearchAssociate,Program treebranchesandleavescollectedduringhulling,inedible
Director, Food Science and food engineering, renewable energy, kernel disposition from grading process, and almond
biorefining. Email: [email protected]; Yanling Cheng, PhD,
skins from blanching process. Due to orchard age and
Associate Professor, Email: [email protected];
knock-down by wind, it is estimated that each year
Shaobo Deng, PhD, Senior Research Associate, Email:
[email protected]; Xiangyang Lin, PhD, Associate Professor, 20,000 acres of almond orchards may be removed.
Email:[email protected]; Based on 90 trees per acre and 200 kg mass per tree, by
Corresponding author: Roger Ruan, PhD, Yangtze Scholar
distributing over the total bearing acreage of 660,000
DistinguishedGuestProfessoratNanchangUniversity,Directorat
acres, each 1,000 acre of bearing orchard would generate
Center for Biorefining, and Professor at University of Minnesota.
Research areas: food science and nutrition, food engineering, tree mass of 545 tons annually. By estimation, each
renewable energy, biorefining, bioprocessing, and value-added
1,000acresofbearingalmondorchardcangeneratemore
process development. Dept. of BioProducts & BioSystems
than 4,800 dry tons of biomass annually at hulling and
Engineering, University of Minnesota, 1390 Eckles Ave. St Paul,
MN55108,USA. Tel: [phone]; Fax: [phone]. Email: shelling level including prunings and tree removal.
[email protected]. These residues, if processed and used wisely and
Vol.3No.4
efficiently, could provide substantial amount of heat and combustion,co-firing,activatedcarbons,etc. Morethan
power needed for almond handling and processing 450 scientific and technical papers and reports covering
(Figure 1). Additionally, advanced conversion periodsfrom1947to2010werefound. Abreakdownof
technologies mayproduce liquid and solid fuels and high the key categories is shown in Table 1. The
value materials and chemicals from these residues, categorization is not meant to be very strict and some
bringing extra income to producers and processors. overlapping exists among them. As you can see, the
Utilization of these almond residues will certainly majority of work is on extraction and use of antioxidants
enhance the economic viability and sustainability of the and making of activated carbons. There is not much on
almondproductionandprocessingindustries. energy uses of almond residues. Hulls and skins are
mainly for fractionation, extraction and recovery of
valuablecompoundswhilemostofshellsandpruningare
used for making activated carbons, and some for
combustion, pyrolysis, and gasification. From the
information accessible to us, we are not aware of any
largescalecommercialconversionoperationsintheUS.
Table1 Breakdownofliteraturesearchresults
Category Hits
Shells (activated carbons, absorbents/filters,
Figure1 Utilizationofalmondresiduesandwastes gasification, pyrolysis, combustion, antioxidants, 106
culturemedia/composite/bedding,carbohydrates)
Thisarticlewillprovideareviewofpriorworkonthe Byresidue Hulls(feed,antioxidants,fiber,gums/polysaccharides, 65
type triterpenoids,filter)
utilization, especially energy uses, of almond residues
Pruning(combustion,pyrolysis,gasification,activated
15
carbons)
reported in the scientific and technical literatures, and an
Skin(antioxidants) 55
assessmentoftechnologyoptionsforbiomassprocessing.
Gasification(shells,pruning) 7
Energy
Pyrolysis(shells,pruning) 14
2 Prior research on utilization of almond uses
Combustion/co-firing(shells,pruning) 6
residues Antioxidants(hulls,skins) 76
Non-energy Activatedcarbonsandbiochar(shells,hulls,pruning) 43
2.1 Literaturesearch uses Absorbents/filters(hulls,shells) 11
Others(culturemedia,feed,carbohydrates,lipids,etc) 55
We searched several major publication databases
including CAB, FSTA, Agricola, AGRIS, Academic 2.2 Energyuses
Search Premier, PubMed, Google Scholar, etc, with Table 2 shows the chemical compositions and Higher
searchtermssuchasresidues,shells,hulls,pruning,skins, Heating Values (HHV) of major almond residues. The
fractionation, antioxidants, phenolics, flavanoids, HHVs are comparable with that of forest residues
absorbent/absorption, filtration, gasification, pyrolysis, (18.4MJ/kg).
Table2 UltimateandproximateanalysesandtheHigherHeatingValue(HHV)ofalmondresidues[1]
Ultimateanalysis/% Proximateanalysis/%
HHV/
Residue MJ·kg-1
C H N Cl S Ashe Moisture VolatileMatter FixedC
Shell 50.5 6.6 0.21 0.05 0.006 0.6 3.3 80.3 15.8 18.2
Pruning 51.3 6.5 0.77 0.05 0.035 1.2 10.6 72.2 15.9 18.2
Hull 43.0 5.7 3.28 0.01 0.008 3.6 11.3 71.2 13.9 16.2
AscanbeseenfromTable2,differentcomponentsof Therefore, different technologies may need to be
the almond residues have different composition, employed for their utilization. For example, due to the
especially the hull as compared with shell and pruning. relatively high nitrogen content in the hull, high
December,2010 Utilizationofalmondresidues Vol.3No.4 3
temperature gasification maynot be appropriate since the Gonzalezetal[7]combustedthreealmondresidues(shells,
NO content in flue gas may be too high, and low pruning, and hulls) with a mural boiler under different
x
temperature pyrolysis may be more appropriate for the conditions. The residues were made into pellets of
conversion, and both catalytic deoxygenation and 5mmindiameterand20mminlength. Theresearchers
denitrogenation may be required for the pyrolytic bio-oil found that the pruning and shells burned similar to wood
upgrading. pellets but the hulls did not burn as well. The boiler
Almond residues have a energy content in the range efficiencies obtained with the maximum fuel mass flow
of 16-18 MJ/kg[1], comparable with the energy content (100%) and minimum draught (0%) were 88.3%, 85%,
levels of other lignocellulosic biomass[2]. Shells and 78.5% for the pruning, shell, and hulls pellets,
hulls are readily available on processing sites. respectively, compared with 90.5% for the wood pellets.
Therefore, almond residues are an excellent alternative They also studied mixtures of different almond residues
source of bioenergy for use on site. Nonetheless, both and wood wastes. Mixtures with pruning seem to
scientific research and commercial use of almond performbetterthanothers.
residues as energy are very limited. Combustion, Almond shells had lowest N and S, suggesting that
gasification,andpyrolysisarethefocusofpriorresearch. the shells are a fuel with lowest NO and SO emission.
x x
No scientific report on biological conversion (e.g., Almond residues tend to have high alkaline compounds
fermentation) of almond residues has been found in the which cause combustor surface fouling and corrosion.
literature. Both almond shells and hulls are considered high fouling
Combustion is the easiest way to generate heat and fuels[11]. Another study suggested that the low lignin
power from almond residues. The heat and power content in almond shells contributed to the relatively low
generated may be used in the operations within almond heating value of almond shells compared with olive husk
processing plants, and the surplus electricity generated and walnut, hazelnut, and sunflower shells when
may be sold to local power grids. Direct combustion is combusted[4].
theburningofbiomassinairtoconvertbiomassintoheat, No study has been conducted to understand the
mechanical power, or electricity using various devices, particle size and density of almond residues on
e.g., stoves, furnaces, boilers, steam turbines, and combustion characteristics. In general, burning rate and
turbo-generators. Direct combustion is simple and ignition speed increase with decreasing particle size.
employs well-developed, commercially-available But in certain velocity range, larger particles may burn
technology. Therefore it is not surprising that biomass faster than smaller particles[12,13]. The ignition front
combustion is responsible for over 90% of the current speed is inversely proportional to the bulk density, while
production of bioenergy. Combustion appears to be a the burning rate tends to decrease linearly with bulk
natural choice to get into the energy use of almond density[12]. Data on the effect of moisture content of
residues. However, only a few studies attempted to almondresiduesoncombustionarenotavailable.
understand the combustion characteristics of almond Gasification of almond residues has been attempted
residues in different situations and for different by a few researchers[14-20]. Gasification is a process in
purposes[3-10]. which lignocellulosic feedstocks are converted to a
Although burning of almond residues sounds really combustible gas mixture called “synthesis gas (syngas)”
simple, there are a number of factors which could have or “producer gas”through partial oxidation reactions at
significant impact on the burning characteristics and high temperatures typically ranging from 700 to 1,100
efficiency and equipment fouling. The particle size and degree centigrade. Some earlier researchers used the
distribution, density, moisture content, proximate and term “pyrolysis” but in fact they meant gasification
ultimate analysis, and volatile matters are important according to the conditions they used[14,15,20]. Syngas
physical and chemical properties of combustion fuels. can be burned to produce heat or used in gas engines or
Vol.3No.4
gas turbines to generate electricity. Gonzalez et al[1] to the reactor head. The experiments conducted in both
estimated that a gasifier with a processing capacity of studiesusedverysmallamountsofsamplesrangingfrom
1,400 kg of almond residue/h will be able to generate a few milligrams to a few grams, representing ideal
3.99 MW thermal from gasification of almond residues. situation which could be rather different than at larger
Gas yield and quality and emission of pollutants are the scales. Tong et al[18] gasified three unpretreated/
major concerns of biomass gasification, which may vary unprocessed rice husk, wood wastes, and almond shells
with type and moisture content of feedstock, type of usingafullscalegasifier. CO,H ,CH ,andunsaturated
2 4
gasifier,gasificationconditions,etc. hydrocarbons C H are the major product gas
n m
Font et al[14] used a sand fluidized bed to gasify fine components with CO being the highest at around 15%.
particles (0.297–0.500-mm) of almond shells at The syngas from almond shell had the highest high heat
745–950℃. The highest gas yield was obtained at value. TheyfoundthattheCOandCH yieldsfromrice
4
890℃ for ca. 2.3 s. The gas consisted of 1.5% H , huskandalmondincreasedwithincreasingcarbonfeedin
2
8.3% CH , 4% C H , 45% CO, 28% CO , 0.7% C H , the range of 200–400 kg/hr but the composition of the
4 2 4 2 2 6
and 0.5% C H (dryweight basis). Theresearchers also hydrocarbon gases were not affected by the carbon feed
3 6
used a Pyroprobe 100 pyrolyzer to study the effect of rate. Almond shells yielded higher H than rice husk
2
particle size, temperature, and catalysts impregnated in because almond shells were higher in moisture content
the almond shell samples. They found that the particle (17.2%) than rice husk (12.7%), which may be attributed
sizeswithintherangetested(0.21to0.84mm)anduseof to the fact that hydrogen is produced from hydrolysis.
catalysts did not have significant effect ongas yields, but The product gas consisted of a range of polluting gases
the hydrocarbon yields increase with temperature. In (Table 3). Product gas from almond shells had higher
another similar study[15], these researchers concluded that NO but lower SO and tar than the gases from rice husk
x 2
the primary decomposition occurs on the bed and the andwoodwastes.
crackingoftarstakesplaceinthehotzoneabovethebed
Table3 Concentrationsofgaspollutants,tarcontent,andpercentageofCO andO[18]
2 2
Ricehusk Almondshell Woodwaste
700℃ 750℃ 800℃ 850℃ 600℃ 700℃ 800℃ 900℃ 650℃ 700℃ 750℃ 850℃
NOx/ppm 475 278 139 641 847 1.066 1.227 595 431 370 151 53
SO2/ppm 555 0 0 280 0 0 0 0 119 80 29 5
PM10/mg·m-3 2.8 9.4 0.5 1.3 21.5 0.9 13.0 0.7 30.9 2.4 2.1 1.0
PM2.5/mg·m-3 2.4 8.5 0.4 1.2 18.4 0.8 12.8 0.7 27.8 1.7 1.7 0.9
Tar/mg·L-1 64.8 13.7 3.7 4.6 3.7 3.7 2.0 1.8 1.8 11.9 5.4 4.9
CO2/% 13.4 15.7 15.3 15.3 13.7 14.3 13.5 13.6 16.8 16.1 16.1 17.0
O2/% 1.5 0.8 2.1 0.7 1.6 1.5 1.4 1.9 1.8 1.5 1.0 0.6
Rapagna and Latif[16] reported their study on steam increase over the entire temperature range (600–800℃),
gasificationofgroundalmondshellsusingafluidizedbed never reaching that attained by the smaller particle
gasifier. Use of steam is to enhance gas reforming and systems, indicating the significance of extra- and/or
further gasification of char (water-gas shift reaction) to intra-particle thermal resistances for particles larger than
increase the yields of H , CO, and CH . Their results 1 mm in diameter. The total gas yields reported in their
2 4
indicate that gas yields were affected byparticle size and study ranged from 0.5 to 1.55 m3/kg biomass with
temperature. However, for smaller particle sizes, hydrogendominating(around50%byvolume).
differences in gas yield and distribution practically Another important processing variable is air flow rate
disappeared in high temperature range, whereas for which determines the oxygen input into the system. A
particles above 1 mm in diameter the yield continued to higherflowrate(higheroxygeninput)producesmoregas
December,2010 Utilizationofalmondresidues Vol.3No.4 5
butlessliquidandsolidchars(Table4)[17]. Equivalence feedboard, or reactor. Almond shells and walnut
ratio, which is the ratio of actual amount of oxygen pruning were tested with air as the gasifying agent and
supplied to the theoretical amount of oxygen required for electrical resistance heater to heat the reactor during
completecombustion,isanotherparametertoindicatethe start-up. The heater is kept under low energy discharge
oxygenconcentrationinthefeedgas. Tongetal[18]used during experiments. Good agreement between the
equivalence ratios in the range of 6%–16% in their study modelsimulationdataandoperationaldatawasfound.
butdidnotinvestigatetheeffectsofdifferentequivalence Syngas clean-up and conditioning has been identified
ratioonthegasyieldandcomposition. as a key technical barrier to the commercialization of
biomass gasification technologies and has the greatest
Table4 Influenceoftheairflowrateonthefractionyields
impact on the cost of clean syngas[21,22]. No efforts on
andHHVofthecarbonaceousresiduesfromgasificationof
almondhulls[17] clean-up and upgrading of syngas from gasification of
almondresidueshavebeenreportedintheliterature.
Fractionsyields/%
Airflowrate HHVchar
/cm3·min-1 /MJ·kg-1 Pyrolysis is a process to produce liquid fuels or
Char Liquid Gas
50 38.2 24.0 37.8 23.8 bio-oil from organic materials with combustible gas
100 24.2 23.0 52.8 22.2 (similar to syngas from biomass gasification) and char
200 19.0 12.1 68.9 21.1
solid (“bio-char”) being the byproducts. During
400 18.0 10.4 71.6 21.1
pyrolysis, biomass is degraded to small gaseous
The fractional yields and gas composition vary with molecules at medium high temperature (300–600℃) in
type of residue (Tables 5 and 6)[17]. Pruning and shells the absence of oxygen leaving char solid behind.
produce more gas and less solid chars than hulls. The Pyrolysis of biomass at high temperature is not well
gases produced from pruning and shells had a higher understood. Some suggest a five-step process: (1)
HHV than that from peel, which maybe attributed to the biomass is heated, (2) volatiles evolve from the organics,
differenceinH ,CO,andCH yields. andcarbonizationoccurs,(3)outflow ofhot volatilesand
2 4
cooler unpyrolyed fuel volatiles (4) volatiles condense to
Table5 Influenceoftheresiduetypeonthefractionyields
liquid (tar) with incondensable gas, and (5) autocatalytic
andHHVofthecarbonaceousresidues[17]
secondary reactions (decomposition or repolymerization)
Fractionsyields/%
Residue H/MHJV·ckhga-1r takeplace[23].
Char Liquid Gas
The product fraction ratio of bio-oil:char:gas varies
Shell 11.1 13.6 75.3 25.2
primarily with heating rate and biomass composition.
Pruning 10.0 12.1 77.9 26.2
Peel 19.0 12.1 68.9 21.1 The ratios of bio-oil:char:gas for gasification, slow
pyrolysis, and fast pyrolysis are 5:10:85, 30:35:35, and
Table6 Influenceoftheresiduetypeonthegasproduction 75:12:13, respectively. The bio-oil produced may be
andHHV[17]
refined into liquid fuels or converted to other chemicals.
Gasproduction/mol·kg-1ofpeel HHV Thegascanbeusedassyngastogenerateheatandpower.
Residue /MJ·Nm-1
H2 O2 N2 CO CO2 CH4 C2H2 C2H4 C2H6 The char can be used as soil amendment agent and
Shell 10.9 2.0 37.1 9.5 7.8 4.2 0.06 0.61 0.17 6.5
fertilizer or made into activated carbons. Biomass
Pruning 9.6 1.9 37.9 11.9 7.8 3.6 0.05 0.65 0.11 6.4
pyrolysis has not been broadly commercialized.
Peel 7.9 2.3 35.7 9.0 7.4 2.6 0.03 0.65 0.18 5.8
Complexity and instability of bio-oil are the key barriers
There is only one paper related to the modeling of to the commercialization of biomass pyrolysis. It is
fluidized bed gasification[19]. The author developed a worth noting at this point that pyrolysis is widelyused to
comprehensive simulation program of moving and produce activated carbons from organic materials
fluidized-beds (CSFB or CSFMB) to generate including almond residues. More discussion on this
temperature, gas, and reaction rate profiles in the bed, or topicwillbeprovidedintheactivatedcarbonsection.
Vol.3No.4
The first reported study of pyrolysis of almond range of 0.500–0.297 mm were pyrolyzed using the
residueswasdonebyFontatal.[24]. In theirstudy, flash fluidizebedreactor. Theliquid yieldreachedashighas
(fast) pyrolysis of almond shells (1–3 grams) was carried 65% at 610℃ at high heating rate, which is 20% higher
out at 400–710℃ with a small experimental fluidize bed than the liquid yield obtained with slow pyrolysis. At
reactor with a diameter of 66 mm and the Pyroprobe 100 very high temperature, liquid yield was reduced because
analyzer. Almond shells were washed, dried, crushed, gasification and cracking was enhanced. In general, a
andsievedtoproducethreesetsofsampleswithdifferent very slow pyrolysis produces very high amount of char
particle size ranges (0.500–0.297, 0.297–0.210, 0.210– solids[25-27], which is desirable for making high energy
0.105 mm). The effect of particle size on gasification density chars as fuel or precursors of activated carbons.
was evaluated using the Pyroprobe 100 analyzer in These results are in good agreement with Gonzalez et
another study[14], and samples with particle sizes in the al[28](Table7).
Table7 Fractionyields,proximateanalysis,andHHVofthecharsandHHVofthebio-oils[28]
Variabletemp Fractionyields/% Proximateanalysis/%a HHV/MJ·kg-1 HHVb/MJ·kg-1
/℃ chars Bio-oils
Char Liquid Gas Fieldcarbon Volatiles Ash
300 47.3 41.3 11.4 60.4 38.4 1.2 26.3 13.7(23.6)
400 30.6 53.1 16.3 76.9 21.2 1.8 28.2 14.1(23.3)
500 26.0 49.3 24.7 85.9 12.1 2.0 29.0 12.4(24.5)
600 23.5 44.3 32.2 91.4 5.8 2.8 29.0 12.0(24.6)
700 21.7 36.3 42.0 92.4 4.7 2.9 27.4 11.6(24.7)
800 21.5 31.0 47.5 93.9 3.1 3.0 25.8 11.3(24.7)
Heatingrate Fractionyields/% Proximateanalysis/%a HHV/MJ·kg-1 HHVb/MJ·kg-1
/K·min-1 chars Bio-oils
Char Liquid Gas Fieldcarbon Volatiles Ash
5 26.3 51.5 22.3 94.3 3.7 2.0 29.0 12.4(24.2)
10 24.9 50.5 24.3 95.8 2.2 2.0 28.2 12.8(24.0)
15 22.8 50.5 26.7 95.3 2.8 1.9 28.4 13.0(24.1)
20 22.1 49.9 28.0 93.7 3.7 2.6 28.4 13.7(23.7)
Note:awt%ondrybasis;bbetweenbracketsaregiventhewatercontentofbio-oils.
In order to evaluate the potential applications of However, separation and recovery of high value
different fractions from pyrolysis of almond residues, chemicals from the bio-oil will require complex and
Gonzalez et al characterized physical and chemical expensive processes, and the bio-oil is suitable for use as
properties of bio-oil, char, and gas produced from heating oil but its high water content viscosity,
pyrolysis of almond shells[28]. They found that the char corrosiveness, and instability, and poor ignition
hadahighfixed-carboncontent(>76%)aswellasahigh characteristicsmakeitunsuitableforuseastransportation
heating value and therefore it could be used as solid fuel. fuelswithoutfurtherupgradingandrefining.
Withalargespecificsurfacearea,thecharisanexcellent Post-pyrolysis upgrading is a common approach to
precursor for making activated carbons. The gas improvingandstabilizingbio-oils. Upgradingprocesses
composition was very similar to the syngas from may involve physical or chemical methods. Solvent
gasification, indicating that pyrolytic gas can be used to blending and filtration are physical upgrading
heatthepyrolysisreactorortogenerateheat/electricityin methods[29-34], but theyare not veryeffective. Chemical
agas-turbine/vapor-turbinecombinedcycle. Thebio-oil upgradingemployscatalytic crackingandreformingsuch
fraction is composed of mainly aliphatic and aromatic as hydrotreatment and thermal cracking to de-oxygenate
hydrocarbons and hydroxyl and carbonyl compounds, the bio-oil. Recent research in this area has made
suggesting that the bio-oil is a good source of chemicals incrementaladvancesinimprovingthebio-oilquality.
of industrial interest, and also can be used as liquid fuel. The idea of changing the product chemical profiles
December,2010 Utilizationofalmondresidues Vol.3No.4 7
using catalysts during pyrolysis instead of post-pyrolysis positive effect on the quality of the organic phase was
upgrading has been tested by many researchers. This noticed, and research has been directed towards the
idea is based on the assumption that some interventions design of selective catalysts for either increasing the
mayinduceand/oraltercertainchemicalreactionsinStep production of specific compounds (e.g. phenols) or
2 of the five-step process described above, resulting in minimizingtheformationofundesirablecompounds(e.g.
differentchemicalprofilesofthevolatiles. Thisismuch acids, carbonyls). Our more recent study[43] evaluated
like an in situ upgradingof the biomass pyrolysis vapors, the effects of metal oxides, salts, and acids including
i.e., evolved volatiles from thermal decomposition of K Cr O , Al O , KAc, H BO , Na HPO , MgCl , AlCl ,
2 2 7 2 3 3 3 2 4 2 3
organics react directly and immediately on the catalysts CoCl , and ZnCl on microwave assisted pyrolysis of
2 2
pre-mixedwiththebiomassfeedstock[35-38]. Suchinsitu corn stover and aspen wood pellets. The catalyst solids
catalytic upgrading of the biomass pyrolysis vapors is werepre-mixedwiththepelletspriortopyrolysis. KAc,
alsoknownascatalyticpyrolysis. Catalyticpyrolysisof Al O , MgCl , H BO , and Na HPO were found to
2 3 2 3 3 2 4
almond residues was studied by several increase the bio-oil yield by either suppressing charcoal
researchers[24,39-41]. Font and co-workers[24] screened yield or gas yield or both. These catalysts mayfunction
four basic catalysts and six acidic catalysts with which as a microwave absorbent to speed up heating or
groundalmondshellswereimpregnatedpriortopyrolysis. participate in “in situ upgrading”of pyrolytic vapors
Acidic catalysts especially FeCl and CoCl produced a during the microwave-assisted pyrolysis of biomass.
3 2
significant shifting in the liquid composition. High GC-MS analysis of the bio-oils found that chloride salts
concentrations of furfural were obtained and acetic acid promoted a few reactions while suppressing most of the
was reduced. Both basic and acidic catalysts reduced otherreactionsobservedfor thecontrolsamples. At8 g
total liquid yields but seemed to favor water production. MgCl per 100 biomass level, the GC-MS total ion
2
They further studied the effects of the ratio of catalyst to chromatograms of the bio-oils from the treated corn
biomass and the ways catalysts were mixed with stover or aspen show only one major furfural peak
biomass[41]. Furfural production and acetic acid accountingforabout80%oftheareaunderthespectrum.
reduction were enhanced with increased catalyst amount. We conclude that some catalysts improve bio-oil yields,
Pretreatment of biomass with HCl or NaOH prior to and chloride salts in particular simplify the chemical
catalystapplicationsdidnotmakeasignificantdifference. compositions of the bio-oils and therefore improve the
On the other hand, adding catalysts to the almond productselectivityofthepyrolysisprocess.
residues through wet impregnation was much effective 2.3 Non-energyuses
thanphysicallymixingthedrysolids. Itappearsthatthe 2.3.1 Antioxidants
acidic catalysts promote dehydration reactions, leading to A paper by Esfahlan et al published on Food
increased formation of 2-furaldehyde and water in the Chemistry in 2010 provides an excellent overview of
liquidphase[40]. non-energyusesofalmondresidues[44]. Thepaperhasa
Research on other biomass feedstock also shows that strong emphasis on antioxidants. The authors tabulated
catalytic pyrolysis usually produces additional water and the data from the literatures on the key antioxidants such
coke-solid residue and thus reduces the yield of the as vanillic, caffeic, p-coumaric, ferulic acids (after basic
organic phase of the bio-oil. Our study found that hydrolysis), quercetin, kaempferol, isorhamnetin (after
chlorides favor production of light oil and especially acidic hydrolysis), delphinidin and cyanidin (after
watersolublesandmetal-oxidesfavorheavyoil,andthus n-butanol/HClhydrolysis)aswellasprocyanidinsB2and
total oil yield, while nitrates favor gas production[42]. B3 in different parts of almond fruits. Table 8 is a
Bio-oils from current catalytic pyrolysis processes are summaryshowing the total phenolics indifferent parts of
still not up to the industrystandards, primarily due to the almond fruits. Antioxidants in almond residues may be
still complex chemical composition. However, a extractedwithethanol,methanol,andwarmwater[45-49].
Vol.3No.4
The high amount of antioxidants in the skin and hull the bioactive compounds such as phenolics may be low
may be a result of natural evolution for the purpose of due to the association of many phenolics with cellular
protecting the oil-rich almonds from oxidation by structures. Phenolic compounds can range in size from
penetrating atmospheric oxygen. Almond extracts were monomers to long-chain polymers such as tannins, and
foundtoslowdownoxidativeprocessesinfoodproducts. usually exist bound to carbohydrates or as part of
Medical studies found that phytochemicals in almonds repeating subunits of high molecular weight[50-52].
inhibited DNA niching and human LDL cholesterol Without certain physical and chemical “liberation”
oxidation. Antioxidants are regarded as a powerful treatments, the phenolics may not have sufficient in vitro
disease and aging fighting weapon because they protect bioactivities. Second,the crude fibers are so coarse that
human cells from attacks by free radicals from food they will not have the benefits of dietary fibers and may
consumptions, smoking, and radiation, thanks to their also compromise the sensory attributes of the food
strong antiviral, anti-inflammatory, anti-allergic, products containing these fibers. Finally, the residues
anti-mutagenic, anti-carcinogenic, and many contain flavor spoiling compounds which must be
anti-cholesterolemic activities. Therefore, extracts from removedbeforetheybecomeacceptablebyconsumers.
almond residues have a great potential to become natural Elis et al[52] reported that lipids and phenolics are
food preservation additives and dietary/nutriceutical encapsulated by cell walls. Mechanical disruption,
supplements. chewing, and digestion ruptured only the first layer of
cells at the fractured surface. In fecal samples collected
Table8 Contentoftotalphenolicsindifferentpartsof
fromsubjectsconsumingthealmonddiet,theyfoundthat
almond[44]
thecotyledonarycellsremainedintact. Theintracellular
Almondfruit Totalphenolics
References
parts content contents would not be released for digestion without
16.1±0.4e Amarowiczetal.(2005) breaking the cell walls. Harrison and Were[50] used
8.1±1.75a SiriwardhanaandShahidi(2002)
Kernel gamma irradiation to increase phenolic content and
8±1b Wijeratneetal.(2006)
8±1b Siriwardhana(2006) antioxidant effect of almond skin. They found that
87.8±1.75a SiriwardhanaandShahidi(2002)
irradiation at 4kGy (trial I) and 12.7kGy (trial II)
88±2b Wijeratneetal.(2006)
Skin increased the yield of total phenolic content as well as
88±2b Siriwardhana(2006)
413－342f Monagasetal.(2007) enhanced antioxidant activity of almond skin extracts.
Shell 2.2c Moureetal.(2007) SimilarresultsweredemonstratedbyTeetsetal[53]. The
38.0±3.30d Jahanbanetal.(2009)
increase in phenolic content and antioxidant activity is
71.1±1.74a SiriwardhanaandShahidi(2002)
71±2b Wijeratneetal.(2006) attributed to the cleavage of covalent bonds, which
Hull
71±2b Siriwardhana(2006)
liberates and activates the low molecular weight phenolic
78.2±3.41d Jahanbanetal.(2009)
compoundsfromtheirglycosylatedforms[51].
Zone:amgcatechinequivalents/gethanolicextract.bmgquercetinequivalents/g
ethanolic extract. c g gallic acid equivalents/100 g shells. d mg gallic acid Prasetyoetal[51]andTeetsandco-workers[54,55]tested
equivalents/g methanolic extract. e mg catechin equivalents/g 80% aqueous
the antioxidation effects of electron beam irradiated
acetoneextract.fμg/g.
almond skin on meat products. They successfully
While most of the research has been focused on the demonstrated that the antioxidants liberated by the
bioactivity of extracts from almond residues, there are irradiation reduced the oxidation related reactions.
benefits of using processed almond residues directly as These findings suggest that there are opportunities to
additives to food products. First, this would apply processed almond residues directly to food
significantly reduce the costs associated with extraction productswithoutextraction.
and purification. Second, dietary and soluble fibers in 2.3.2 Activatedcarbons
theresiduesareutilized. However,thesebenefitsdonot The second greatest non-energy use of almond
come without challenges. First, the bioavailability of residues is manufacture of activated carbons. World
December,2010 Utilizationofalmondresidues Vol.3No.4 9
demand for virgin activated carbon is forecasted to activation, steam activation, CO activation, and acid
2
expand 5.2 percent per year through 2012 to 1.2 million activation have been tested on almond residue derived
metric tons. The US is the second largest activated carbons[60,61,70,72]. CO is the most common chemical
2
carbon producer in the world. Activated carbons are activationmethod,partlybecauseitiscleanandlowcost.
primarily used for water treatment. Other major Toles et al[60] studied both the CO and steam activation
2
applications includeseparation and purification processes processes combined with an air oxidation step in the
for gaseous or aqueous solution systems and catalytic production of granular activated carbons (GAC) from
processes (catalyst and catalyst support). The quality almondshells. Theylookedatthesurfacearea,attrition,
andsuitabilityofactivatedcarbonsdependonthespecific surface charge, copper ion (Cu+2) uptake, adsorption of a
surface area, pore size, pore structure, volume, ash mixture of six polar and non-polar organic compounds
content[56]. and estimated cost of carbon production as a function of
Activated carbons are made mostly from coal and different treatment combinations (pyrolysis temperature
woods. Agricultural byproducts and residues are and time, activation temperature and time, activation
inexpensive alternatives, and nutshells have been the method, oxidization). They concluded that the
most used agricultural residues for making activated steam-activated, unoxidized and oxidized carbons appear
carbons[56]. Almond shells have been used frequently tobethemosteconomicalGACstomanufactureandalso
for activated carbon manufacture[26,57-68]. Almond the most economical for removal of copper ions and
pruning has also been used to make activated organic compounds. They presented cost analysis
carbons[26,69-71]. The activated carbons produced from assumptions (Table 9) and results (Table 10) in their
fruit shells and stones have high surface areas and highly paper, which may be of interest to the readers of the
developed micropore structure compared with the present review and are therefore included here for
commercialtypesandthosefromusedtires[56]. reference. The largest difference between the two
Manufactureofactivatedcarbonsinvolvesremovalof activationmethodsisinthe electricityusageaccordingto
moisture and volatiles from biomass through thermal Table9.
processes,andactivationofthecarbonaceouscompounds 2.3.3 Othernon-energyuses
through physical, chemical, and steam treatments[56]. Almond residues have been used directly or after
Pyrolysis is the most common process to produce some treatments as absorbents for removal of metals and
precursors from making activated carbons. Both dyes[73-78], feed[79-92], culture media[93-104], and raw
temperature and heating rate are two most important materials for extraction of xylo-oligosaccharides[105-109],
processingparametersfollowedbyinertgasflowrateand polysaccharides[105,110,111], and dietary fibers[90,112].
residencetime. Asdiscussedearlier,pyrolysisproduced These uses are beyond the scope of this review.
morecharsolidsatlowtemperatureandlowheatingrate. Interested readers are encouraged to read the review
The purpose of activation is to oxidize remaining papersbyEsfahlanetal[44]andotherreferencesprovided.
organicssothattheporousstructureisfurtherenhanced.
Marcilla et al[65] used a two-stage thermal process to Table9 Assumptionsmadeforscaled-up,productioncost
comparisons[60]
produce activated carbons from almond shells. In the
Inputsandconsumptions Steamactivation CO2activation
first stage, almond shells were heated at 275 to 400℃ at
Shellinput/kg·d-1 13.636 13.636
the low heating (3–4℃/min) followed by a second stage
CO2usage/kg·d-1 — 13.636
at the high rate (ca. 3,000℃/min) up to 850℃. The Waterusage/ft3·d-1 25 —
products treated this way exhibited a better porous Naturalgasusage/ft3×106·d-1 61.8 78.8
Electricityusage/KWH·d-1 4,075 7,501
structurethanthoseobtainedtreatedwithasingleheating
Carbonyield/% 16 16
up to 850℃ at both heating rates. The second heating
Operatingdays/year 320 320
step in the two-stage process may act as an activation Activeoperatinghours/d 24 24
Dailycarbonoutput/kg·d-1 2,180 2,180
treatment. Other activation methods such as air
Vol.3No.4
Table10 Productionandadsorptioncostestimatesfor of almond residues with or without treatments appears to
steam-activatedandcarbondioxide-activatedalmondshell be the easiest option but it may not capture the best
GACs[60]
values of these residues. Therefore, extraction and
Treatmentb Pr/oSd·ukcgti-o1n C/Su·2+madosl-o1rCptuio2+n aOdsrograpntiicosn thermochemical conversions have the best potential to
/S·mol-1 bringextraincometoalmondproducersandprocessors.
Steamactivation
While combustion is an easy and feasible option,
1-7-2-8(7.0mL/min) 1.54 4.16 2.96
most of the large almond processors could use only a
1-7-2-8(7.0mL/min-ox.) 1.91 3.67 3.60
fractionoftheresiduestosupplytheheatfortheiron-site
1-8-2-8(7.0mL/min) 1.54 4.40 2.40
1-8-2-8(7.0mL/min-ox.) 1.91 4.78 3.14 operations. Therefore combustion has limited potential
CO2activation for almond processing facilities. Gasification faces a
1-7-2-8(75%CO2) 2.56 6.74 4.63 similarsituation. Thegasproducedmustbeusedlocally
1-7-2-8(7%CO2-ox.) 2.93 5.05 5.59 becausestorageandtransportationofthegastoelsewhere
Note: a Adsorption cost estimates were determined from the production cost
are economically and technically impractical. Unless
values (S/kg) and the amounts of Cu2+ or total organics adsorbed (mol/kg). b
Treatmentconditionsconsistofnumbersequences1-7-2-8,etc.whichreferto low cost syngas reforming processes can be devised,
pyrolysistimes(1h)andtemperatures(700℃)andactivationtimes(2h)and
gasification will limit its use to small scale almond
temperatures(800℃).
producers and processors. Pyrolysis is technically less
mature than combustion and gasification. However, it
3 Technologyoptions
has a great potential in converting solid almond residues
3.1 Individualtechnologies to transportable liquid fuels and activated carbons. The
Inadditiontowhathavebeendiscussedabove,awide syngas produced from the pyrolysis process may be used
range of other technologies may be used to convert to power the pyrolysis itself and other operations on site.
almond residues to different forms of energy, chemicals, R & D efforts are needed to develop cost effective
and materials (Figure 2). However, the unique physical equipment and improve the quality and stability of
and chemical properties of almond residues make pyrolytic liquid through manipulating the pyrolysis
fermentation and anaerobic digestion unfit options. Use conditionsandpost-pyrolysisupgrading.
Note:DME:DimethylEther;F-T:Fischer-Tropsch;CHP:CombinedHeatandPower
Figure2 Bioenergyfrombiomassthroughdifferentpathways[113]