be

nd

iesettlebleed teq

Biode lan

subst. These20, toa Sust7 [1]. As sche009. Hhe 5.7

biodiesel. To achieve 5.75% substitution according to the previoustarget would thus require 5.75% of all agricultural land under oil-seed rape, which is equivalent to 63% of arable land in Ireland.Food crops are grown on arable land and hence this raises theconict of land for food versus land for fuel.

The EU Renewable Energy Directive [6] states that biofuels to beused in 2020 will only be classied as biofuels if they contribute

greenhouse-gas (GHG) emissions savings of at least 60% compared

the largest fats and oils trading countries, inedible tallow and recy-cled greases have remained the lowest priced among the varioustypes of oil and fat, since records began in 1990 [7,8]. The producedquantity of tallow and greases is predicted to increase every year[9] as a result of increasing population, rising food consumptionand an increased demand for industrial products. It is estimatedthat the potential of UCO collectable in the EU is between700,000 and 1,000,000 t/a [10], which could account for up to20% of biodiesel produced in the EU (based on 4,890,000 t/a biodie-sel production in 2006 [11]).

* Corresponding author. Tel.: +353 21 490 2286; fax: +353 21 427 6648.

Fuel 89 (2010) 35793589

Contents lists availab

ue

.eE-mail address: jerry.murphy@ucc.ie (J.D. Murphy).it to 3% by 2010. The target of 10% by 2020 still remains as acommitment to achieving the EU targets [2]. The main reasonsfor this revision are the increase in global food prices, which islinked to the transfer of land from food to energy crops and alsodoubts as to whether biofuels are as environmentally friendly asoriginally thought [2]. The Republics biofuels sector producesonly 0.6% of all fuel, with a greater quantity being imported tomeet the biofuels target of 2.2% by 2008 [3,4]. A paper writtenby the authors [5] shows that 1% of total agricultural land is re-quired to satisfy 1% substitution of transport fuels with rapeseed

associated GHG emissions from crop production; for example agri-culture is responsible for 14% of the parasitic energy demand in ra-peseed biodiesel and 79% of the GHG emissions in the life cycleanalysis. Biofuels produced from wastes, residues, and by-productshave a signicantly better energy balance with less GHG emissionsthan biofuels produced from energy crops.

Tallow and used cooking oil (UCO) are considered to be renew-able and sustainable feedstocks for biodiesel production. Their rel-atively low costs contribute to a low biodiesel price and allowbiodiesel to compete economically with diesel. In the USA, one of1. Introduction

Ireland has set national targets towith biofuels in the transport sectorsubstitution by 2010 and 10% by 20ernments White Paper Deliveringfor Ireland, published in March 200fuels in retailed petrol and diesel wato the transportation market by 22008 the Irish government revised t0016-2361/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.fuel.2010.06.009itute conventional fuelstargets included 5.75%comply with the gov-ainable Energy Futuren obligation of 5% bio-duled to be introducedowever, in September5% target, and lowered

to conventional fuels. Using a life cycle analysis approach withoutallocation to co-products or by-products, Thamsiriroj and Murphy[5] calculated a GHG emissions reduction of 28.8% for biodieselproduced from Irish-grown rapeseed. The energy used in agricul-ture (e.g. ploughing, fertilizing) is the major energy-consumingprocess in rapeseed biodiesel production, releasing a signicantamount of GHG emissions in the biodiesel life cycle [5]. Recently,interest has been focused on transport fuels produced from resi-dues, wastes, and by-products. These feedstocks do not have theHow much of the target for biofuels canfrom residues in Ireland?

T. Thamsiriroj, J.D. Murphy *

Department of Civil and Environmental Engineering, University College Cork, Cork, Irela

a r t i c l e i n f o

Article history:Received 10 February 2009Received in revised form 11 January 2010Accepted 3 June 2010Available online 17 June 2010

Keywords:BiodieselTallowUsed cooking oil

a b s t r a c t

This study focuses on biodIreland has 8% of the EU caslaughter residues is availawastes and UCO is estimattial quantity of biodiesel isthe 2010 biofuels target.equivalent to 22% of arabl

F

journal homepage: wwwll rights reserved.met by biodiesel generated

l production from residues in particular tallow and used cooking oil (UCO).herd with less than 1% of the EU population. Thus a signicant quantity offor energy production. The total energy potential associated with slaughtero be 7.07 PJ/a; 61% of which is suitable for biodiesel production. The poten-uivalent to 2.1% of predicted transport fuel use in 2010; three quarters ofiesel production from these two residue streams may be expressed asd in Ireland under oilseed rape.

2010 Elsevier Ltd. All rights reserved.

le at ScienceDirect

l

l sevier .com/locate / fuel

businesses, and brown grease is the grease recovered from grease Alkalines, e.g. KOH and NaOH, are the most common catalystsused in the one-step process. The reaction is faster foralkaline- than for acid-catalyzed processes (only 30 min comparedto 18 h for the acid catalysis) [21,25]. However, the yield ofmethyl ester will substantially decrease if high FFA content feed-

Table 1SFA and FFA contents in some oils and fats.

Oils and fats % Saturated fatty acids % Free fattyacids

Soybean 14.3 [22], 15.5 [23] 0.1% [22]Palm 43.4 [23], 47.0 [24] 0.4% [29]Rapeseed 4.1 [24], 5.1 [25] 0.02% [30]Jatropha 21.1 [23], 22.9 [26] 0.1% [26]

O O CH2 O C R1 CH3 O C R1 CH2 OH O O CH O C R2 + 3 CH3OH CH3 O C R2 + CH OH

O O CH2 O C R3 CH3 O C R3 CH2 OH

(Catalyst)

y / Fuel 89 (2010) 35793589traps and interceptors [14]. Finally, tallow is the term used for ani-mal fats obtained by either the melting process or rendering pro-cess [15]. Inedible tallow, generally produced from the renderingprocess, is a competitive feedstock in biodiesel production due toits low cost [14,1618].

3.2. Saturated fatty acid (SFA) content

Fats and oils are made up of 1 mol of glycerol and 3 mol of fattyacids, and are commonly referred to as triglycerides. There are alsominor quantities of monoglycerides and diglycerides in fats andThe 1st generation feedstocks for biofuels produced from en-ergy crops have resulted in concerns over change in land use andfood price increase. The next generation feedstocks need to be trulybenecial in a more sustainable manner; food supply should not beadversely affected and net environmental benets should result.Biodiesel production from tallow and used cooking oil has beendeveloped to a commercial scale in Ireland, and a facility with aproduction capacity of 30,000 t/a has been operational since mid-2008 [12]. Biofuels produced from residues (such as tallow andused cooking oil) are allowed a double count towards the biofuelstargets according to the Renewable Energy Directive [6].

2. Methodology and objectives

Initially this paper reviews the available processes for generat-ing biodiesel in the form of fatty acid methyl ester (FAME) fromresidues such as used cooking oil (UCO) and tallow, which are highin either free fatty acids (FFA) or saturated fatty acids (SFA) as com-pared to pure plant oil (PPO). An analysis is undertaken to estimatethe quantity of residues, which are readily available in Ireland andto estimate the potential production of biodiesel from suchsources. Of particular interest is the quantity of land that wouldneed to be under rapeseed to produce a similar quantity of biodie-sel; previous work by the authors [5] showed that 1355 L of biodie-sel is the average production of rapeseed biodiesel per hectare perannum in Ireland. This is especially important as only 9% of land inIreland is arable and thus there is extreme competition betweenfood and fuel. A sensitivity analysis is carried out by examiningthe readily available feedstock. Thus the paper has a number ofobjectives:

quantify animal by-products and used cooking oil inIreland;

estimate the proportion of the national biofuels target thatcan be met by biodiesel from residues;

calculate the land under oilseed rape required to producethe same quantity of biodiesel.

3. Biodiesel produced from animal fats and used cooking oil

3.1. Terminology

The term fats may be briey dened either as animal tissuedistended with greasy or oily matter, or as glyceride compoundsof fatty acids [13]. The former denition, which is mostly used inthis paper, species that fats are animal products. In the latter def-inition, the entire range of fats and oils from vegetables and ani-mals is included. Greases generally refer to solid or thick oil.Greases can be classied as yellow and brown greases. Yellowgrease is UCO collected from commercial or industrial cooking

3580 T. Thamsiriroj, J.D. Murphoils [1921]. Primarily, there are two types of fatty acids, saturatedand unsaturated fatty acids. SFA content in animal fats is typicallyhigher than in most type of vegetable oils. However, in UCO it canvary by a wide range, depending on the usage and properties of theoriginal oil. Table 1 shows the SFA content of some fats and oils. Alarge variation can be seen in UCO (1190% SFA). High SFA contentcauses the oil to solidify at room temperature.

3.3. Free fatty acid (FFA) content

The FFA content of oil feedstocks is a key parameter in deter-mining the viability of the transesterication process. For fatsand oils with an FFA content of less than 23%, feedstock pretreat-ment is not required and alkaline-catalyzed transesterication canbe simply performed. The higher the acidity of the oil, which isassociated with higher FFA content, the lower the conversion ef-ciency of biodiesel through alkaline catalysis [14,33]. Rendered tal-low and UCO normally contain a signicant quantity of FFA (seeTable 1). The upper value is between 15% and 20% FFA for renderedtallow [15,34]. For UCO, the FFA content is typically less than 15%[14]. With these high FFA content feedstocks, alternative transeste-rication methods to the simple one-step, alkali-catalyzed processshould be considered in order to achieve a high yield of biodiesel.

3.4. Transesterication methods

Transesterication is a chemical reaction which involves themixing of a fat or oil with an alcohol in the presence of a catalystto produce fatty acid esters (biodiesel) and glycerol. It transformsthe large, branched molecular structure of the bio-oils into smaller,straight-chain molecules, with fuel characteristics similar to thoseof regular diesel. Methanol is the most commonly used alcohol be-cause of its low price compared to other alcohols [14,17,19,3537].The transesterication reaction of a triglyceride and methanol isoutlined by the chemical reaction in Fig. 1.

3.5. Reduced yield from alkaline-catalyzed transesterication of highFFA feedstock

Animal fats Lard 39.3 [19], chicken fat 32.0 [16], beeftallow 45.6 [19], mutton tallow 61.1 [16]

Inedibletallow: 11.220% [31]

Used cookingoil

11.8 [27], 13.6 [22], 90.9 [28] 1.8 [28], 5.6%[32]Triglyceride Methanol Methyl ester Glycerol

Fig. 1. Transesterication reaction.

(Fig. 3b), thus resulting in additional soap products. The presenceof water causes further saponication (Fig. 3c), which also pro-duces more soap [21]. Hence, one-step, alkaline-catalyzed transe-sterication is not an appropriate process for high FFA contentfeedstocks.

3.6. Acid-catalysed processes for feedstock with high FFA

A one-step transesterication process may be applied to highFFA content feedstocks using an acid as a catalyst. Sulfuric acid(H2SO4) is a commonly chosen catalyst. The reaction of the one-step, acid-catalyzed transesterication process is also based onFig. 1. Although the reaction can produce a high yield of biodiesel,the reaction is relatively slow and a reactor is required to with-stand an acidic environment [39]. Alkaline-catalyzed transesteri-

Fig. 2. Yield of methyl esters related to %FFA [14].

T. Thamsiriroj, J.D. Murphy / Fuel 89 (2010) 35793589 3581(a) Dehydrolysis reaction O O

HO C R + KOH K+ -O C R + H2O stocks are used. An example of the reduced yield in the one-step,alkaline-catalyzed transesterication is outlined in Fig. 2. Whenadding an alkaline catalyst, FFA reacts with the catalyst to formsoap and water in a dehydrolysis reaction (Fig. 3a) [38]. Watercan further react with methyl esters to produce more FFA

no soap is produced in the process. On the other hand, the produc-

Free fatty acid Potassium Hydroxide Potassium soap Water

(b) Hydrolysis reaction O O CH3 O C R + H2O HO C R + CH3OH

Methyl ester Water Free fatty acid Methanol

(c) Saponification reaction O O

CH2 O C R1 K+ -O C R CH2 OH O O

CH O C R2 + 3 KOH K+ -O C R + CH OH O O

CH2 O C R3 K+ -O C R CH2 OH Triglyceride Potassium Hydroxide Potassium soap Glycerol

Fig. 3. (a) Dehydrolysis reaction, (b) hydrolysis reaction and (c) saponicationreaction.

(a) Esterification reaction O HO C R + CH3OH CHFree fatty acid Methanol M

(b) Combined esterification and transes O

CH2OCR1

O O

n CHOCR2 + m HOCR4 + (3n+m) CH3OH O

CH2OCR3

Triglyceride Free fatty acid Methanol

(H2SO4)

(Lip

Fig. 4. (a) Esterication reaction and (b) combined CH2OH

O

(3n+m) CH3OCRn + n CHOH + m H2O

CH2OH

ase)tion cost of lipase catalysts is higher than that for alkaline catalysts[33,42]. Renewable diesel may also be generated using hydrogena-tion; the end product is not FAME but synthetic diesel. It is veryattractive to petroleum rening companies but is not discussedfurther in this paper.

Table 2 outlines some studies dealing with high FFA content tal-low and UCO. Most of the processes are viable for these oil feed-

O

3 O C R + H2O ethyl ester Water

terification reactions cation is much more effective in terms of reaction rate. Thisadvantage of alkaline catalysts can be applied to high FFA contentfeedstocks through a two-step transesterication process. In therst step, pretreatment known as esterication (Fig. 4a) uses anacid catalyst to convert FFA into biodiesel; the remainder of the tri-glycerides are subsequently transesteried to biodiesel in the sec-ond step using an alkaline catalyst [21,38].

3.7. Alternative transesterication methods for feedstock with high FFA

The supercritical methanol method is an alternative to thetransesterication of oil feedstocks with high FFA content. A cata-lyst is not required in the process; as a result, the wastewater con-taining acid or alkaline can be avoided in the washing process. Thereaction rate is relatively high; a residence time of between 12.5and 50 min is required. However, the reaction has a high energydemand as high temperatures and pressures are required (at least250 C and 10 MPa) [35,40].

Enzymatic catalysts like lipases are also used in transesterica-tion. Triglycerides and FFA can be enzymatically transesteried tobiodiesel in a one-step process because lipases catalyze bothtransesterication and esterication reactions (Fig. 4b) [41]. Hence,FFA contained in oil feedstocks can be completely converted to bio-diesel, and the difculty of recovering glycerol is also overcome as Methyl ester Glycerol Water

esterication and transesterication reactions.

Acste

Ta960

0.1

H2

1 h90

ence

CO

.882

.684.5[493 [3[32.5 [35.83

y / Fustocks, except the one-step, alkaline-catalyzed transestericationprocess. The yield of biodiesel is unacceptably low and this processis not therefore feasible for commercial production.

3.8. Fuel quality

Biodiesel is required to comply with the EN 14214 standard

Table 2Processing conditions and biodiesel yield.

Alkaline catalysis (one-step) [31]

Acid catalysis (one-step) [43]

Feedstocks Tallow UCO%FFA in feedstock 20 5.6Process

temperature(C)

55 65

Process pressure(MPa)

0.1 0.1

Catalyst used KOH H2SO4

Residence time 1 h 48 hBiodiesel yield (%) 34.5 97.8

a Two stages of pretreatment by acid-catalyzed esterication with resid

Table 3Fuel properties of biodiesel.

Properties Tallow U

Density (kg/L) 0.877 [47] 0Viscosity (mm2/s) 5.0 [48] 4Cetane number 58.0 [47] 5Cold lter plugging point (C) 8 [48] 1Pour point (C) 9 [48] Cloud point (C) 11 [48] 1Acid value (mg KOH/g) 0.44 [48] 0Iodine value 53.6 [48] 8

3582 T. Thamsiriroj, J.D. Murph[46]. The fuel properties of biodiesel produced from tallow andUCO can be different from those of biodiesel from virgin oils be-cause of the higher FFA and SFA contents of recycled oils. FFAand SFA affect many important fuel parameters including cetanenumber (CN), cold ow properties, acid value, and iodine value.Some fuel properties are presented in Table 3 and discussed below:

Cetane number indicates the ignition properties of the fuel. It isgenerally dependent on the composition of the fuel and can impactthe engines startibility, noise level, and exhaust emissions. Thehigher the cetane number, the more efcient the ignition [53,54].Biodiesel from high SFA content feedstocks has a higher cetanenumber, which has a positive impact on the diesel engine [55].

Iodine value is a measure of total unsaturation within a mixtureof fatty acids. It is expressed in grams of iodine which reacts withdouble bonds in a 100 g oil sample. The limitation of unsaturatedfatty acid is necessary due to the fact that heating the unsaturatedfatty acids results in polymerization of glycerides. This can lead tothe formation of deposits or deterioration of the lubrication. Theiodine value is also important in measuring the oxidation stabilityof fuels. The oxidation stability decreases with the increasing con-tent of polyunsaturated methyl esters [32,51]. Biodiesel from highSFA content feedstocks has a lower iodine value, which also has apositive impact on the diesel engine.

Acid value is a measure of the number of acidic functionalgroups in a sample, and is measured in terms of the quantity ofpotassium hydroxide required to neutralize the sample [14]. Thepresence of acid affects fuel aging. High acid value in fuel may becaused by either high FFA content in oil feedstocks or by theamount of acid added in the transesterication process [21,33]. Acase of high acid value caused by the amount of added acid wasstudied by Rice and Frohlich [31]; a two-stage transestericationprocess was selected in the study, in reverse order to the typicalprocess, i.e. alkaline-catalyzed transesterication in the rst step,followed by acid-catalyzed esterication in the second step. Thebiodiesel product had an acid value as high as 1.5 mg KOH/g (lim-ited to less than 0.5 mg KOH/g in the EN 14214 standard). Biodieselfrom high FFA content feedstocks has a higher acid value, whichhas a negative impact on the diesel engine.

id, alkaline catalysis (two-p) [44]

Supercriticalmethanol [43]

Lipase catalysis[45]

llow UCO UCO5.6 8.5350 50

43 0.1

SO4, NaOCH3 No Immobilized lipasePS-30

, 1 h, 8 ha 4 min 18 h.2 96.9 94

time of 1 h each, and 8 h for alkaline-catalyzed transesterication.

Rape seed oil EU biodiesel standard

[32] 0.882 [50] 0.860.90[32] 4.58 [50] 3.55.0[32] 52.9 [50] >51.0] 10 [51] 2] 15 [52] ] 0 [52] 2] 0.16 [51]

highly saturated and unsaturated methyl esters; blending diesel

only economically feasible at a scale above 100,000 t/a, and only

1774/2002 [68], animal by-products that are not intended for hu-

a substitute for fossil fuel. It is often co-incinerated in power gen-

Three categories of animal by-products are dened in the EURegulation EC 1774/2002 [68].

Category 1 materials are animal by-products that are regarded asa high-risk of TSE (Transmissible spongiform encephalopathies).All category 1 materials must be either incinerated; rendered andsubsequently incinerated; co-incinerated; or buried under strictconditions.

Category 2 materials are animal by-products that still possess arisk (but not a TSE risk). This category covers materials not in-cluded in category 1 or 3. There are more options for the disposalof category 2 materials than for category 1.

Category 3 materials are animal by-products that possess a lowrisk. These by-products are derived from animals considered tbut not chosen for human consumption. This category includesby-products from the slaughter process: degreased bones; formerfoodstuffs of animal origin devoid of an infectious risk to humansand animals; fresh sh by-products; and catering waste other thanthat of international transport origin. Materials in this third cate-

y / Fuvirgin vegetable oils with a maximum FFA content of 0.25% aresuitable for the process [62,64].

4. Tallow, and used cooking oil (UCO)

4.1. The rendering process

Rendering is the recycling of raw material tissue from animalsused for food and waste cooking fats and oils from all types of eat-ing establishments into a variety of value-added products. Duringthe rendering process, heat, separation technology, and lteringare applied to the material using various processes. Heat is usedin the cooking process. The temperature and duration of the cook-with biodiesel helps to reduce PM emissions because of the in-creased oxygen content [60].

3.10. Technology at commercial scale

It is found that most of the commercial biodiesel processingplants are currently based on the homogenous, alkaline-catalyzedprocess. Sodium and potassium hydroxides are traditional cata-lysts, but potassium hydroxide is preferable as potassium soap issofter than sodium soap and, unlike sodium soap, does not blockthe bottom of the separation funnel. Another advantage of potas-sium hydroxide is the potential to recover potash fertilizer, whichcreates an added value. The use of sodium or potassium methox-ides is also increasing. They have an advantage over the sodiumand potassium hydroxides in that they reduce side reactions, suchas saponication, resulting in an improved biodiesel yield [14,62].

The acid-catalyzed transesterication process has been provento be technically feasible for high FFA content oils. It is less com-plex than the alkaline-catalyzed transesterication process and istherefore a competitive alternative to commercial biodiesel pro-duction using the alkaline-catalyzed process [63]. However, be-cause of the slow reaction rate, acid catalysts are only used inthe esterication reaction in the pretreatment stage of the two-step process. In commercial biodiesel production, the two-stepprocess commonly uses sulfuric acid to esterify oil feedstocks priorto the alkaline-catalyzed transesterication. This process offers alarge potential to process high FFA content oils. Some examplesof industrial technology using the two-step process include BDI,CMB, DSB, and Energea [62].

Heterogeneous catalyzed transesterication through solid alka-line or solid acid catalysts has also been developed to the produc-tion stage at commercial scale. The technology known as Esterp-H process was developed by Institut Franais du Ptrole (IFP) andcommercialized by Axens. The main advantages of the processare the production of high quality glycerol with over 98% purityand the fact that the disposal of salts resulting from catalyst usageis not required. The biodiesel yield is close to 100%. However, it istemperature. This could lead to an increase in combustion temper-ature and NOx emission levels [61]. However, a model simulationby Yuan et al. [59] shows that the increased NOx emissions are alsoinuenced by earlier start of injection and shorter ignition delay.These factors result in higher NOx emission levels for methyl estershigh in unsaturated fat than for methyl esters high in saturated fat[59]. Biodiesel from high SFA content feedstocks therefore has apositive impact on NOx emission levels.

Particulate matter (PM) emissions relate to the oxygen contentof fuels. There is no signicant difference in PM emissions between

T. Thamsiriroj, J.D. Murphing process are critical and so are the primary determinants of thequality of the nished products [65,66]. The diagram in Fig. 5 illus-trates the rendering process. The principle rendering process usederating plants or used in cement manufacturing [34]. The ban onthe feeding of MBM to farmed animals in the EU has been in placesince its introduction in 2000 [70].

4.3. Animal by-productsman consumption must be cooked using one of ve different op-tions. The most applicable option is cooking at 133 C and 3 barfor 20 min, with the particle size of starting material 650 mm [68].

4.2. Tallow, and meat and bone meal (MBM)

All rendering system technologies include the collection andsanitary transport of raw material to a facility, where it is pro-cessed into a consistent particle size and conveyed to a cookingvessel, which can be either continuous-ow or of batch congura-tion. Fat is separated from the cooked material via a screw presswithin a closed vessel. The fat known as tallow is stored and trans-ported in tanks. After the cooking and fat separation stages, thecrackling (which includes protein, minerals, and some residualfat) is further processed by moisture removal and grinding to pro-duce meat and bone meal (MBM) [65,69]. MBM is currently used asin the EU is pressure-cooking. According to the EU Regulation EC

Raw materials

Sizing Heat processing (Time x Temperature)

Press

Fat clean-up

Protein

Grinding

Storage/Load out

Fig. 5. Rendering process [67].

el 89 (2010) 35793589 3583gory can be used for pet-food production, animal feed for non-food-producing animals, or technical products after appropriateprocessing in an approved category 3 processing plant [69].

4.4. Use of tallow from animal by-products as a source of biodiesel

Tallowproduced fromall three categories is permitted to be usedfor biodiesel production according to the EU Regulation EC 92/2005[71]. Scientic studies in recent years have conrmed that crude,unltered tallow produced by a rendering procedure is safe frominfectivity, even if the starting materials contain a high concentra-tion of pathogenic prions and the 133 C/3 bar/20 min condition isnot achieved. The downstream biodiesel is considered safe [72,73].

4.5. Cleaning process for used cooking oil (UCO)

UCO can be used as a rawmaterial for many applications includ-ing biodiesel and a variety of oleochemical products such as surfac-tants, plasticizers, cosmetics and lubricants [74]. It can be useddirectly as fuel in a modied diesel engine. In animal feed produc-tion, the use of UCO as a raw material has been banned in the EUsince 2004 [31]. Most of the UCO collected from restaurants and

rides, and phospholipids [76]. A cleaning process separates the

people [78]). About 90% of beef produced in Ireland is exported,mainly to EU countries. More than 85% of Irish cattle outputs areslaughtered in Ireland; the remainder are exported live [79]. Morethan 50% of the total carcass weight of livestock and poultry ani-mals slaughtered in Ireland is from the slaughtering of cattle (seeTable 4).

There are currently nine licensed rendering plants in Ireland.These plants are classied as follows: ve category 1 and four cat-

Rendering plants accept animal carcasses, such as heads, feet, offal,

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Table 4Carcass weight of animals slaughtered in Ireland [78].

(000 t) 2000 2001 2002 2003 2004 2005 2006 Average

Cattle 577 579 540 568 564 546 572 563.7Pig 230 240 230 219 204 205 209 219.6Sheep 83 78 67 63 72 73 70 72.3Poultry 123 123 122 123 128 129 123 124.4Total 1013 1020 959 973 968 953 974 980

3584 T. Thamsiriroj, J.D. Murphy / Fuel 89 (2010) 35793589water and solid portion from the oil, but the impurities in the oil re-quire further processing (e.g. transesterication and separationsteps) to make it suitable for industrial applications. The cleaningprocess includes steam injection (heating the oil), coarse screening,and centrifugation to eliminate the ne portion and water [31]. Thewater-soluble impurities which dissolve in water can be removedby washing the oil with water or water vapour. The oil may alsobe neutralized by adding alkali but this must be in a small quantityin order to avoid the production of a lot of soap. More detail on oilcleaning techniques can be found in Ref. [77].

5. Potential energy associated with selected residues in Ireland

5.1. Tallow and MBM

The total number of livestock (i.e. cattle, pigs, and sheep)slaughtered in Ireland is estimated to be about 9 million annually(Fig. 6). This is twice the population of the country (4.42 million

0

2000

4000

6000

8000

10000

12000

1990 1991 1992 1993 1994 1995 1996 1997

No.

of a

nim

als

slau

ghte

red

(thou

sand

hea

ds)fried food processing lines is currently delivered to biofuel andoleochemical industries. The quality of this UCO may be expectedto vary depending on the original oil types, cooking practices, wasteoil storage methods, and collection systems [75]. After collection,the oil is transferred to large holding tanks where it is blended withother waste oils; however, the quality is very inconsistent. Theimpurities present in UCO consist primarily of FFA, polymers, chlo-Y

Fig. 6. Number of livestock slaexcess fat, excess meat, hides, skin, feathers, and bones. In Ger-many, on average 35% of the live weight of all animal species istransported to inedible rendering plants [82]. If this gure is trea-ted as the quantity of animal by-products available to the render-ing process, the tallow and MBM potentially available in Irelandare calculated as 92,600 and 156,300 t/a respectively (Table 5).This compares favourably with the 2006 production gures(88,000 and 151,000 t/a).

5.2. Biogas from paunch content

If we consider slaughter waste, it is important to also considerthe element of slaughter waste which is suitable for digestionand conversion to biogas/biomethane. Belly grass, which is diges-tive tract content (stomach content) obtained from cattle, is nor-mally removed in slaughterhouses in the form of dischargedslurry. Belly grass is classied as a category 2 material under the

CattlePigSheepTotalegory 3. There are no category 2 plants currently licensed in thecountry [80]. In 2006, 558,000 t/a of animal by-products were usedto produce 151,000 t/a of MBM and 88,000 t/a of tallow in Ireland[81]. Based on these gures, approximately 16% of the by-productquantity can be converted to tallow and 27% to MBM, while 57% islost in the process [34]. The percentage of losses in the renderingprocess is high, because the major component of animal by-prod-ucts is water. Animal carcasses can contain up to 68% water [82].ear

ughtered in Ireland [78].

EUpe[8 -se -tio rbo(Dsimstar -idth -m -lio

Biogas produced from stomach content: 12.48 mil-

yo -ca rfoth -tit /a woi r20 -culated gure (20.8%) will be further used to estimate a more up-

Pig

21977

285

b

y / Fulion mn3/a (6.93 million mn

3 CH4/a)

SheepAverage No. of sheep slaughtered (20002006): 3,593,000

sheep/a

Stomach content @5 kg/sheep @11%DS @80%VS

@85%VSdest: 0.37 kg VSdest/sheep

Biogas produced from stomach content: 1.34 million mn3/

a (0.75 million mn3 CH4/a)

PigAverage No. of pigs slaughtered (20002006): 2,918,000

pig/a

Stomach content @7 kg/pig @10%DS @80%VS

@85%VSdest: 0.48 kg VSdest/pig

Biogas produced from stomach content: 1.39 million mn3/

35.3

in19in(2wspanRegulation EC 1774/2002. Land-spreading of this material isrmissible in Ireland under the same regulations as manure3]. It can be used in pet-food production [82] and also possses the potential to produce biogas through anaerobic digesn. About 92 kg of stomach content may be expected pevine, 7 kg per pig and 5 kg per sheep [84,85]. The dry solidsS) content of the material from the various animals is veryilar, i.e. 11% DS for cattle and sheep, and 10% DS for pigs

omach content. For all animals, the gures of 80% and 85%e used for volatile dry solids (VS) content and volatile dry sols destroyed (VSdest) respectively [84]. The biogas potential frome stomach content of these farmed animals in Ireland is estiated to be 15.21 million mn3/a of biogas @55.5% CH4 (8.45 miln mn3 CH4/a) (Box 1). This is equivalent to 0.32 PJ/a.

Box 1. Biogas potential from animals stomach content.CattleAverage No. of cattle slaughtered (20002006): 1,814,000

cattle/a

Stomach content @92 kg/cattle @11%DS @80%VS

@85%VSdest: 6.88 kg VSdest/cattle

Destruction of 1 kg VS = 1 mn3 biogas @55.5% CH4

From Table 4.Average values in Europe modied from [82].16% by-products as tallow (000 t/a)27% by-products as MBM (000 t/a)Table 5Potential of animal by-products in Ireland.

(Data 20002006) Cattle

Average carcass wt (000 t/a)a 563.7Carcass wt as % of live wt (%)b 54Average live wt (000 t/a) 1043.935% live wt as by-products (000 t/a)

a

T. Thamsiriroj, J.D. Murpha (0.77 million mn CH4/a)

Total biogas potential:15.21 million mn3/a (8.45 million mn3 CH4/a)

. Used cooking oil (UCO)

A study done by the Irish Universities Nutrition Alliance [86]vestigating the habitual food consumption of Irish people from97 to 1999 showed that on average Irish people had a daily fattake of 87.1 g/day (31.79 kg/a). About 82% of this fat intake6.07 kg/a) is considered to be from vegetable oils and animal fats,hich are used in a variety of food categories including meats,reads, cake and biscuits, confectionery, breads, potato products,d others. The remaining 18% of fat intake is fats from milk anddated quantity of recoverable cooking oil in the followingparagraph.

Fig. 7, which outlines the quantity of vegetable oils and animalfats consumed per person from 1990 to 2003, indicates a signi-cant drop in animal fat consumption after 1998. This is due to achange in peoples habitual consumption. The decrease in animalfat consumption has been associated with an increase in vegetableoil consumption. The historical data show that the total oil and fatconsumption has never dropped below 25 kg/capita/a. Hence, thisgure may be used as the bottom line to calculate the potentialrecoverable quantity. Most oils and fats associated with food resi-dues collected from households are disposed to landll sites, com-posting plants, and wastewater treatment systems. As a result, notall of the total quantity produced is collectable. Only around two-thirds are believed to be realistically collectable in Ireland [88]. Thepotential collectable UCO in Ireland is thus estimated to be15,300 t/a (see Box 2), compared to the reported collected quantityof 9381 t in 2006 [89]. Hence, a further 5919 t/a could be collectedwith a better collection network and a more economically viableusage.

Box 2. Potential of UCO in Ireland.

Oils/fats used for food activities: 25 kg/capita/a

Recoverable quantity @20.8%: 5.2 kg/capita/a

Collectable quantity @66.67%: 3.46 kg/capita/a

Population of Ireland 2008: 4,422,100 people

Potential collectable UCO in Ireland: 15.3 thousand t/a5.4

ucstcelainbianalpo(Lgurt, cheeses, and vegetables. Records from the FAO (Fig. 7) indite that the average quantity of oils and fats used in Ireland food consumption activities (both direct and indirect), betweene same period (19971999) was 32.93 kg/capita/a. Of this quany, 16.16 kg/capita/a was from vegetable oils and 16.77 kg/capitaas from animal fats [87]. The estimation of recoverable cooking

l is outlined in Table 6 to be 6.86 kg/capita/a, accounting fo.8% of the total quantity for food consumption activities. The calSheep Poultry Total

.6 72.3 124.4 98049 70

.2 147.6 177.7 1654.457992.6

156.3

el 89 (2010) 35793589 3585. Total energy produced from animal by-products and UCO

Three different biofuels can be produced from animal by-prod-ts including inedible tallow, MBM, and biogas from animalsomach content. Tallow can be used as a direct fuel in boilers (ex-pt tallow produced from category 1 material under the EU regu-tion EC 1774/2002 which strictly requires incineration or co-cineration) and for biodiesel production, while MBM is a goodomass energy source [82]. Biogas can be upgraded to biomethaned consequently to bio-CNG which is used as a transport fuel. It isso a source of energy for heat production and combined heat andwer (CHP) production systems [9094]. The lower heating valueHV) of tallow is reported to be 39.8 GJ/t; the gure may also be

tential quantity of tallow is met by the existing production of tal-low, while only 61% is met by the existing collection of UCO. Based

1996Ye

fats u

TaRe

Fat eaten sourced from oils/fats 26.07

y / Fuel 89 (2010) 35793589@82%Quantity used for food activities 32.93 16.16 (49.1%) 16.77 (50.9%)Recoverable quantity 6.86 3.37a 3.49a

% average recoverable oils/fats = 20.8% (i.e. 6.86/32.93)

aasthmfro

loprPast[8of34Hofum

5.

is

an1990 1991 1992 1993 1994 1995

Fig. 7. Quantity of oils and

ble 6coverable quantity of cooking oil.

Period 19971999 (kg/capita/a) Total Vegetableoils

Animal fats

Fat eaten 31.790

5

10

15

20

25

30

35

Oils

and

fats

qua

ntiti

es/c

apita

/a (k

g)

3586 T. Thamsiriroj, J.D. Murphsumed for UCO. For MBM, the LHV is about 15.7 GJ/t [82], whilee energy content of biogas (@55.5% CH4) is approximately 21 MJ/n3 [84]. The total energy potential is estimated to be 6.46 PJ/am animal by-products and 7.07 PJ/a if UCO is included (Box 3).

Box 3. Total energy potential.

Tallow @92,600 t/a @39.8 GJ/t: 3.69 PJ/a

MBM @156,300 t/a @15.7 GJ/t: 2.45 PJ/a

Biogas @15.21 million mn3/a @21 MJ/ mn

3: 0.32 PJ/a

Total energy from animal by-products: 6.46 PJ/a

UCO @15,300 t/a @39.8 GJ/t: 0.61 PJ/a

Total energy from animal by-products and UCO: 7.07 PJ/a

Of this energy potential, 60.8% (4.3 PJ/a) is associated with tal-w and UCO. Therefore, tallow and UCO are the most signicantoducts among the residues to produce biofuels in Ireland.unch content is considered to be an excellent and plentiful feed-ock for biomethane production through anaerobic digestion4,9094]. However, it may produce up to only 4.5% (0.32 PJ/a)the total energy potential explored here. MBM accounts for.7% (2.45 PJ/a) of the total energy potential, which is signicant.wever it has found favour as a displacement for conventionalels for thermal energy production in industries such as cementanufacturing.

5. Substitution of biodiesel based on potential production

Final energy consumption in the road transport sector in Irelandpredicted to be 188.15 PJ/a in 2010 [95]. With the new national

Assuming a direct relationship between the quantity used for food activitiesd the recoverable quantity.on the conversion efciency of 95% from oils/fats to biodiesel,102,505 t/a of biodiesel could be potentially produced from thefeedstocks (scenario 1, Table 8). Such biodiesel quantity could sub-stitute 2.1% of transport fuels in 2010, which would account forabout three quarters of the target (3% substitution). This is alsoequivalent to 85,970 ha of arable land (21.5% of the countrys ara-ble land) under oilseed rape if used for biodiesel production inIreland.

5.6. Sensitivity analysis

Three scenarios are examined in relation to the quantities of tal-low and UCO used for biodiesel production.

Existing collection of oils and fats. The most up to date data aretarget of 3% biofuel substitution by 2010, this equates to 5.64 PJ/ain Ireland. If the target was to be met solely by biodiesel, 164.5 mil-lion L/a would be required (based on the biodiesel energy contentof 34.32 MJ/L). The existing production of tallow and UCO is about88,000 and 9400 t/a, respectively (Table 7). About 95% of the po-

1997 1998 1999 2000 2001 2002 2003ar

Total oils and fatsVegetable oilsAnimal fats

sed for food in Ireland [87].the collected tallow and UCO (Table 7). This is available fromtwo national reports; the 2007 EPA national waste report [89]and the 2003 SEI report on UCO and animal fats [88]. These guresare considered the mean case for production (not all produced fatis collected) and are included as scenario 2 in the middle column ofTable 8.

Potential production of oils and fats. The collected quantity ofUCO according to the EPA report [89] is 9381 t/a. The SEI report[88] states that only two-thirds of the produced UCO is col-lected; this would yield a potential production gure of about14,000 t/a. Our analysis generates (Section 5.3) a theoretical g-ure for recoverable UCO of 15,300 t/a, which indicates that ouranalysis is close to the expected value. The collection networkmay improve if a viable UCO biodiesel market exists. Our analy-sis on tallow indicates that production exceeds collection by 5%

Table 7Feedstock potential for biodiesel production.

(000 t/a) Tallow UCO Total

Potential quantity 92.6 15.3 107.9Existing productiona 88 9.4 97.4

a Based on the gures in 2006.

Range of values.With respect to Table 8 it may be noted that thebiodiesel may substitute between 1% and 2.1% of transport fuel

[5] Thamsiriroj T, Murphy JD. Is it better to import palm oil from Thailand toproduce biodiesel than to produce biodiesel from indigenous Irish rape seed?Appl Energ 2009;86:595604.

n of

[95]

y / Fuwith scenarios ranging from present export levels to collection oftotal produced oils.

6. Conclusions

This paper focuses on the use of residues to produce biodiesel.Tallow and used cooking oil (UCO) are examined as sources of bio-diesel which may substitute for oilseed rape. Rapeseed biodieselrequires extensive quantities of land to meet biofuel targets. Ire-land has a signicant quantity of livestock in comparison to itspopulation. The slaughter industry is a very important industry;for example beef exports account for 90% of beef production. ThusIreland has a rich source of biodiesel in the form of slaughter(Table 7); this is not unlikely. These values are included as sce-nario 1 in Table 8.

Oils and fats presently exported. Tallow may be used in animalfeed, soap manufacture, biodiesel production and oleochemicalindustries. In Ireland in 2003, 54% of collected tallow was usedas a substitute for mineral oil in the rendering industry while theremainder was exported [96]. Thus, conservatively 44,800 t/a oftallow should be readily available for biodiesel production. In2006, 50% of UCO (4686 t) was exported. This should also be read-ily available for biodiesel production.

Table 8Potential contribution of tallow and UCO to biodiesel based on three scenarios.

Scenario 1: potential productioand fats

Total oils/fats quantity (t/a) 107,900Total biodiesel produced @95% (t/a) 102,505Biodiesel energy value (GJ/t) 39Biodiesel gross energy (PJ/a) 4.0Transport fuel required in 2010 (PJ/a) 188.15Biodiesel substitution in 2010 (%)a 2.1Equivalent arable land required under oilseed

rape (kha/a)b85.97

Equivalent percent arable land (%)c 21.5Equivalent percent agricultural land (%)d 1.9

a Based on 188.15 PJ of the transport energy (petrol and diesel) required in 2010b Based on gross energy of biodiesel produced from rape seed at 46.5 GJ/ha/a [5].c Based on the total 400 kha of arable land in Ireland [90].d Based on the total 4.45 million ha of agricultural land in Ireland [90].

T. Thamsiriroj, J.D. Murphwastes. Tallow and meat and bone meal (MBM) can be producedfrom animal by-products through the rendering process. Biogascan also be produced from the paunch content removed in theslaughterhouse as a raw material. It is estimated in this study that92,600 t/a of tallow and 156,300 t/a of MBM are potentially avail-able in Ireland. There is also potential for biogas from 205,000 t/aof paunch content. Of the energy potential in these residues,60.8% is associated with tallow and UCO and is suitable for biodie-sel production. Biomethane from the paunch content is limited to4.5% of the total energy potential explored. MBM accounts for34.7% of the total energy potential, which is signicant. HoweverMBM has found favour as a displacement for conventional fuelsfor thermal energy production in industries such as cementmanufacturing.

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T. Thamsiriroj, J.D. Murphy / Fuel 89 (2010) 35793589 3589

How much of the target for biofuels can be met by biodiesel generated from residues in Ireland?IntroductionMethodology and objectivesBiodiesel produced from animal fats and used cooking oilTerminologySaturated fatty acid (SFA) contentFree fatty acid (FFA) contentTransesterification methodsReduced yield from alkaline-catalyzed transesterification of high FFA feedstockAcid-catalysed processes for feedstock with high FFAAlternative transesterification methods for feedstock with high FFAFuel qualityEmissions from biodiesel fuelTechnology at commercial scale

Tallow, and used cooking oil (UCO)The rendering processTallow, and meat and bone meal (MBM)Animal by-productsUse of tallow from animal by-products as a source of biodieselCleaning process for used cooking oil (UCO)

Potential energy associated with selected residues in IrelandTallow and MBMBiogas from paunch contentUsed cooking oil (UCO)Total energy produced from animal by-products and UCOSubstitution of biodiesel based on potential productionSensitivity analysis

ConclusionsAcknowledgementReferences