future science group 193 ISSN 1759-7269 10.4155/BFS.12.6 

### The primary objectives of this review are to cover impor

tant topics related to biodiesel, which include stan

dards, production, influence of chemical structure on fuel properties and traditional feedstocks. Of principal interest are the promising alternative oilseed feedstocks camelina ( Camelina sativa ) 

### and field pennycress ( Thlaspi

arvense ) 

### , which have hitherto attracted considerably less attention than algae and jatropha ( Jatropha curcas ). Also discussed are advantages and disadvantages of biodiesel relative to conventional petroleum diesel fuel (petro

diesel), energy balance, the influence of free fatty acids (FFAs) on production of biodiesel, phase distribution during transesterification 

### , optimum reaction conditions, the chemical structure of biodiesel and common fatty acids (FAs) typically encountered in biodiesel. With an emphasis on camelina and field pennycress, the current review differentiates itself from numerous predecessors by concentrating on alternative nonfood oilseed feed

stocks that thrive in temperate climates and, thus, may be produced in close proximity to human population (and energy consuming) centers. Definition Biodiesel is defined by the American Society for Testing and Materials (ASTM) as a fuel comprised of monoalkyl esters of long-chain FAs derived from vegetable oils or ani

mal fats, designated B100 and meeting the requirements of ASTM D6751. The European Standard (EN) 14214 (European Committee for Standardization) de facto defines biodiesel as fatty acid methyl esters 

### (FAMEs). Consequently, other materials such as neat vegetable oils, hydrocarbons prepared therefrom or Fischer–Tropsch diesel produced by gasification of biomass do not techni

cally qualify as biodiesel, despite their occasional reference as such. As the name implies, biodiesel is intended as a bio-based substitute or blend component for middle dis

tillate fuels (petrodiesel) for combustion in compressionignition (diesel) engines, and is therefore not suited for spark-ignition (gasoline) engines.

Biodiesel standards Two of the most influential biodiesel standards, ASTM D6751 in the USA and EN 14214 in the EU, are 

# Biodiesel from alternative oilseed feedstocks: camelina and field pennycress

Bryan R Moser* Biodiesel is prepared from lipids by transesterification with a monohydric alcohol and may serve as a replacement or blend component for conventional petroleum diesel fuel (petrodiesel). Advantages of biodiesel over petrodiesel include strongly positive energy balance, domestic and renewable origin, enhanced lubricity and biodegradability, superior flash point, negligible sulfur and aromatics content, and low environmental toxicity. However, high feedstock cost, reduced storage and oxidative stability, inferior volumetric energy content and poor cold-flow properties represent critical technical deficiencies relative to petrodiesel. This review covers biodiesel standards, production and optimum reaction conditions, the influence of free fatty acids on production, the influence of composition on fuel properties and traditional feedstocks. A particular emphasis is placed on the alternative oilseed feedstocks camelina ( Camelina sativa ) and field pennycress ( Thlaspi arvense ) as promising nonfood candidates with high oil contents that would not displace existing agricultural production and would flourish in temperate climates. 

# R eview

*Bio-Oils Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture, 1815 North University Street, Peoria, IL 61604, USA Tel.: +1 309 681 6511; Fax: +1 309 681 6524; E-mail: bryan.moser@ars.usda.gov Biofuels (2012) 3(2), 193–209Biofuels (2012) 3(2) future science group 194 

### Review Moser



### summarized in Tables 1 & 2 

### , respec tively. An additional ASTM standard covering blends of biodiesel from 6 to 20 vol% in petrodiesel, ASTM D7467, is summarized in Table  3



### . The US and European petrodiesel standards ASTM D975 and EN 590 permit up to 5 and 7 vol% biodiesel (B5 and B7), respectively. Biodiesel is approved for use as heating oil in both the EU and the USA, and is covered by ASTM D396 (up to B5) and EN 14213 (B100). Biodiesel certified as compliant with ASTM D6751 may be used as a blending component in ASTM D7467, D975 and D396. Correspondingly, biodie

sel must meet the specifications of EN 14214 in the EU before inclu

sion in petrodiesel, as mandated by EN 590.

The European biodiesel stan

dard, EN 14214, states that biodiesel is to be comprised of FAMEs, thus excluding other alkyl esters. In addi

tion, specifications such as iodine value, linolenic acid methyl ester content and polyunsaturated FAME con

tent (Table 2) 

### in EN 14214 limits feedstock choice for biodiesel production. ASTM D6751 defines biodiesel as monoalkyl esters prepared from vegetable oils or animal fats, thereby inadvertently excluding other lipid sources such as algae. Under consideration for future versions of ASTM D6751 is a change in phrasing that would ame

liorate this oversight. The official definition of biodiesel in ASTM D6751 ensures that critical moieties for fuel performance, such as monoalkyl esters and long-chain FAs, are included. Monoalkyl esters are specified because they impart favorable antiwear and biodegradability properties to biodiesel. Esters also ensure that kinematic viscosity (KV) (40°C) will be within the specified range. The long-chain FA requirement increases the probability that cetane numbers (CNs) will be above the minimum specified limit. Additionally, ASTM D6751 does not contain limits on iodine value, linolenic acid methyl ester content and polyunsaturated FAME content. Instead, fuel performance-based test methods are emphasized. However, it should be noted that EN 14214 contains the same performance-based specifications. Both ASTM D6751 and EN 14214 recommend that antioxidants be added to biodiesel immediately after its production to maintain stability.

Table 1. American Society for Testing and Materials D6751 biodiesel standard. Property Test method(s) Limits Units Flash point (closed cup) ASTM D93 93 min o C Alcohol control; One of the following shall be met: Methanol content EN 14110 0.2 max % mass Flash point ASTM D93 130 min o C Water and sediment ASTM D2709 0.050 max % volume Kinematic viscosity (40°C) ASTM D445 1.9–6.0 mm 2 /s Sulfated ash ASTM D874 0.020 max % mass Sulfur ASTM D5453 15 max ppm Copper strip corrosion ASTM D130 3 max Cetane number ASTM D613 47 min Cloud point ASTM D2500 Report o C Cold soak filterability ASTM D7501 360 max seconds Carbon residue ASTM D4530 0.050 max % mass Acid number ASTM D664 0.50 max mg KOH/g Free glycerin ASTM D6584 0.020 max % mass Total glycerin ASTM D6584 0.240 max % mass Oxidation stability EN 15751 3.0 min hours Phosphorous content ASTM D4951 0.001 max % mass Na plus K EN 14538 5 max ppm Ca plus Mg EN 14538 5 max ppm Distillation temperature, atmospheric equivalent temperature 90% recovered ASTM D1160 360 max o C

ASTM: American Society for Testing and Materials; EN: European Standard; max: Maximum; min: Minimum. Key terms Camelina ( Camelina sativa ): Also known as false flax or gold-of-pleasure, is a broadleaf oilseed flowering plant of the Brassicaceae family that grows optimally in temperate climates and is native to Eurasia. The seed oil content, along with various agronomic characteristics, renders it attractive as an alternative feedstock for production of biodiesel. Field pennycress ( Thlaspi arvense ): Also known as stinkweed or Frenchweed, is a winter annual belonging to the Brassicaceae family that is native to Eurasia but distributed throughout the world as a weed. With high seed oil content and favorable agronomics, it is an attractive nonfood alternative source of biodiesel.
Transesterification: Chemical process by which lipids are converted into biodiesel by treatment with a monohydric alcohol and catalyst at elevated temperature.

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 195 

### Advantages & disadvantages Miscible with petrodiesel in any proportion, biodiesel has numerous technical advantages over ultra-low sulfur diesel (<15 ppm S) fuel, which include: inherently good lubricity, low toxicity, domestic origin and production, derivation from renew

able feedstocks, higher flash point (safer handling), superior biode

gradability, negligible sulfur and aromatics content, strongly positive energy balance and lower overall exhaust emissions [1–3] 

### . In addition, biodiesel produced from soybean oil as well as waste greases, oils and fats meets or exceeds the required minimum GHG reduction stan

dards defined by the Renewable Fuels Standard (RFS2) in the USA [4] 

### . Important disadvantages relative to ultra-low sulfur diesel include: comparatively high feedstock cost, limited feedstock availability, infe

rior storage and oxidative stability, lower volumetric energy content, susceptibility to hydrolysis as well as microbial degradation, inferior cold flow properties and in some cases higher nitrogen oxides (NO

x 

### ) exhaust emissions [1–3] 

### . Many of the deficiencies of biodiesel may be mitigated through cold-flow improver [5–7] 

### and antioxidant [8–11] 

### additives, along with blending with petrodiesel [5,10–13] 

### and proper stor

age coupled with reduced storage time [13–15] 

### . Additional methods to enhance cold-flow properties of biodiesel include crystallization fractionation (win

terization) [16,17] 

### and transesterification with long- or branched-chain monohydric alcohols [18,19] 

### . Strategies to improve exhaust emissions include after-treatment tech

nologies such as selective catalytic reduction, exhaust gas recirculation, diesel oxidation catalysts and NO

x 

### or diesel particulate filters [20–22]



### .

Feedstock acquisition may account for up to 88% of production costs when biodiesel is prepared from refined commodity oils [23–25] 

### . A promising solution to the costprohibitive issue of high feedstock cost is employment of alternative feedstocks 

### of lesser value such as soapstocks, acid oils, tall oils, used cooking oils and waste restaurant greases, various animal fats, nonfood plant oils, and oils obtained from selected trees and shrubs. However, many low-value feedstocks may contain prohibitively high levels of FFAs, water and/or insoluble mat

ter, which negatively impact con

ventional production of biodiesel by homogenous alkaline catalysts if not removed beforehand [26]



### . Energy balance The net energy ratio (NER) is the amount of output energy divided by the needed input energy, and values greater than 1.0 are indicative of a positive energy balance (i.e., more energy is available than was required Table 2. EN 14214 biodiesel standard. Property Test method(s) Limits Units Fatty acid methyl ester content EN 14103 96.5 min % (mol/mol) Density (15°C) EN ISO 3675, EN ISO 12185 860–900 kg/m 3

Kinematic viscosity (40°C) EN ISO 3104 3.50–5.00 mm 2 /s Flash point EN ISO 2719, EN ISO 3679 101 min o C

Sulfur content EN ISO 20846, EN ISO 20884 10.0 max mg/kg

Carbon residue (10% distillation residue) EN ISO 10370 0.30 max % (mol/mol)

Cetane number EN ISO 5165 51.0 min Sulfated ash content ISO 3987 0.02 max % (mol/mol) Water content EN ISO 12937 500 max mg/kg Total contamination EN 12662 24 max mg/kg Copper strip corrosion (3 h at 50°C) EN ISO 2160 Class 1 Degree of corrosion

Oxidation stability (110°C) EN 15751 6.0 min h Cold filter plugging point EN 116 Variable o C Acid value EN 14104 0.50 max mg KOH/g Iodine value EN 14111 120 max g I 2 /100 g Linolenic acid methyl ester content EN 14103 12.0 max % (mol/mol) Polyunsaturated ( ≥ four double bonds) methyl esters EN 14103 1 max % (mol/mol)

Methanol content EN 14110 0.20 max % (mol/mol) Monoacylglycerol content EN 14105 0.80 max % (mol/mol) Diacylglycerol content EN 14105 0.20 max % (mol/mol) Triacylglycerol content EN 14105 0.20 max % (mol/mol) Free glycerol EN 14105 EN 14106 0.02 max % (mol/mol)

Total glycerol EN 14105 0.25 max % (mol/mol) Group I metals (Na and K) EN 14108 EN 14109 EN 14538 5.0 max mg/kg

Group II metals (Ca and Mg) EN 14538 5.0 max mg/kg Phosphorous content EN 14107 4.0 max mg/kg EN: European Standard; max: Maximum; min: Minimum.

Key terms Fatty acid methyl ester: Also known as biodiesel, a methyl ester of a long-chain fatty acid normally produced during transesterification of plant oils or animal fats.
Alternative feedstock: Source of low-cost nonfood lipids for sustainable production of biodiesel with high oil content that ideally does not displace existing agricultural production. Commodity oils/fats represent traditional (or 1st generation) feedstocks but have competing food-related applications and are generally prohibitively expensive.Biofuels (2012) 3(2) future science group 196 

### Review Moser



### for production). Life cycle assessments of biodiesel pre

pared from soybean [3] 

### , palm [27] 

### and sunflower [28] 

### oils have yielded NERs of 4.5:1, 4.8:1 and 4.5:1, respec

tively. Differences in agricultural practices and other inputs are responsible for the variability of NER among feedstocks. Even within a given feedstock NER may vary, depending on the inputs and outputs selected for inclusion. For instance, NERs of 0.79:1 [29] 

### , 1.93:1 [30] 

### and 3.21:1 [31] 

### were reported for biodiesel prepared from soybean oil. The lowest value (0.79:1) was debunked by a subsequent study [32] 

### . The NER of 4.5:1 reported by Pradhan et al. [3] 

### represents an update to the Sheehan et al. [31] 

### study (3.2:1) by taking into consideration techno

logical advancements in agricultural practices, biodiesel production, pesticide use, and soybean yield and genet

ics. For comparison, the NER of petrodiesel is reported as 0.83:1 due to the high energy inputs required for extraction of crude oil from the Earth, transportation of crude oil across vast distances from oil fields to refinery locations and energy requirements of crude oil refinery operations [31]



### .
Production of biodiesel Biodiesel is produced via the transesterification reac

tion, whereby triacylglycerols (TAGs) react with shortchain monohydric alcohols with assistance provided by a homogeneous alkaline catalyst at elevated temperature to yield FA alkyl esters (FAAEs) and the co-product glycerol (Figure 1) 

### . In most cases methanol is used as a co-reactant, since it is normally the least expensive of the short-chain monohydric alcohols. In regions such as Brazil, where sugarcane is plenti

ful, ethanol is utilized to produce FA ethyl esters (FAEEs) because it is less expensive than methanol and widely available. Ethanol also has the added benefit of being bioderived when produced from fermentation of sug

ars, whereas methanol, on an indus

trial scale, is produced from natural gas (methane). Industrially, feedstock, alcohol and catalyst are mixed in continu

ously stirred tank reactors (CSTRs) until the reaction has reached equi

librium [33] 

### . Excess alcohol is used to drive the equilibrium toward the products (FAAEs). Often, two CSTRs are utilized in series (with glycerol removal in between) to ensure a high level of conversion to FAAEs. The alkaline catalyst is dissolved in the alcohol co-reactant prior to its addition to the CSTR containing the plant oil or animal fat to minimize the possibility that a con

centrated region of catalyst might come into contact with TAGs and promote unwanted soap formation. Separation of glycerol and biodiesel at the conclusion of the reaction is accomplished with a settling tank or with a disk centri

fuge. The glycerol stream is then acidified to neutralize residual catalyst and to decompose soaps into FFAs and inorganic salts. Alcohol entrained in the glycerol phase can be recycled through an evaporative process. The frac

tion containing FAAEs is also neutralized with acid, and alcohol is recovered, followed by washing with water and subsequent drying to provide the finished biodiesel prod

uct. Figure 2 

### provides a schematic depiction of traditional industrial biodiesel production.

The most significant parameters that determine compatibility of plant oils or fats with the traditional homogenous alkaline-catalyzed transesterification pro

cedure (Figure 2) 

### are FFAs and water content (Figure 3)



### . Typically, refined lipids contain very low percentages of FFAs (<0.05 wt%) and water (< 0.1 wt%) [34] 

### , so their direct conversion to biodiesel is readily accomplished. Crude lipids may have considerably higher percentages of these contaminants, so purification is required prior to the conventional homogenous, alkaline-catalyzed transesterification procedure depicted in Figure 2 

### . Water and FFA content can be reduced with physical refin

ing [34] 

### . Additionally, FFAs can be esterified to FAAEs prior to methanolysis to mitigate yield loss [2,25,26]



### . Table 3. American Society for Testing and Materials D7467 biodiesel–petrodiesel blend (B6–B20) standard. Property Test method(s) Limits Units Biodiesel content ASTM D7371 6–20 % volume Flash point (closed cup) ASTM D93 52 min °C One of the following must be met: Cetane index ASTM D976 40 min

Aromaticity ASTM D1319 35 max % volume Water and sediment ASTM D2709 0.050 max % volume Kinematic viscosity (40°C) ASTM D445 1.9–4.1 mm 2 /s Sulfur content ASTM D5453 15 max ppm Copper strip corrosion ASTM D130 3 max Cetane number ASTM D613 40 min Ramsbottom carbon residue ASTM D524 0.35 max % mass Acid value ASTM D664 0.30 max mg KOH/g Oxidation stability EN 14112 6.0 min h Ash content ASTM D482 0.01 max % mass Lubricity (HFRR, 60°C) ASTM D6079 520 max m m Cloud point or LTFT/CFPP ASTM D2500, D4539, D6371 Only guidance provided °C

Distillation temperature (90% recovered) ASTM D86 343 max °C

ASTM: American Society for Testing and Materials; CFPP: Cold filter plugging point; EN: European Standard; HFRR: High-frequency reciprocating rig; LTFT: Low temperature flow test; max: Maximum; min: Minimum.

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 197 

### Optimum reaction conditions In a seminal paper published in 1984, Freedman et al. elucidated the classic homogenous, alkaline-catalyzed reaction conditions for the methanolysis of anhy

drous, low-FFA (<0.50 wt%) TAGs to provide FAMEs and glycerol in an essentially quantitative yield [35]



### . Freedman et al. reported that a 6:1 molar ratio of metha

nol to TAG, 0.5 wt% homogenous alkaline catalyst (with respect to TAG), 600+ rpm agitation intensity and 1 h of reaction at 60°C produced FAMEs in high yields [35]



### . Numerous subsequent studies performed on a wide vari

ety of refined feedstock oils have essentially verified the optimum reaction conditions reported by Freedman et al. , utilizing modern statistical methods such as response surface methodology (RSM) [36,37] 

### . Reaction parameters normally investigated using RSM to give maximum yield of biodiesel include catalyst type and amount, reaction time and temperature and molar ratio of alcohol to oil. A representative recent example of reaction cond

itions optimized by RSM is the work of Rashid et al., in which sunflower oil methyl esters were prepared using 0.70 wt% KOH, at 50°C for 65 min with a molar ratio of methanol to oil of 6:1 to provide biodiesel in greater than 91% yield [37] 

### . As seen by comparison of the conditions elucidated by Freedman et al. to that of the example, the reaction conditions do not vary significantly after optimization by RSM.

Influence of FFAs Feedstocks containing a significant percentage of FFAs (>2 wt%) will render typical homogenous alkaline catalysts ineffective due to a deleterious side reaction (Figure 3) 

### in which the catalyst reacts with FFAs to pro

duce unwanted soap (sodium salt of FA) and water (or methanol in the case of sodium methoxide). Ultimately, reaction with FFAs deactivates the catalyst and signifi

cantly reduces biodiesel yield [2,26,33,38–44] 

### . In fact, alka

line-catalyzed transesterification will not occur at all, or will be significantly retarded, if the FFA content of the feedstock is 3 wt% or greater [40,41] 

### . Numerous studies reported that homogenous, alkaline-catalyzed metha

nolysis proceeds optimally when FFA content is below 0.50 wt% [35,40,45] 

### . However, the yield of biodiesel plum

mets to 6% with an increase in FFA content to 5.3 wt% [43] 

### . A further complicating factor of high FFA content is the production of water upon reaction with alka

line hydroxide catalysts (Figure 3) 

### . Water is particularly problematic because, in the presence of any remaining catalyst, it can hydrolyze biodiesel to produce additional FFAs and methanol (Figure 3) [42] 

### . Sodium and potassium salts of FFAs (soaps) also promote dissolution of FAMEs into the glycerolic phase during purification, thus fur

ther suppressing the final yield of biodiesel [46,47] 

### . If the percentage of FFAs is high enough, phase separation at the conclusion of methanolysis will not be possible [47]



### . Lastly, increasing the concentration of alkaline catalyst to counteract the effect of catalyst deactivation by FFAs is detrimental, as such a strategy merely accelerates unwanted hydrolysis of TAGs and FAEEs [46]



### .

In cases where FFA content is prohibitively high for direct conversion of lipids to FAMEs a two-step proce

dure is employed, whereby acid pretreatment is followed by transesterification with homogenous alkaline catalysts to produce FAMEs. Acid-catalyzed esterification of FFAs to FAMEs is normally conducted in the presence of heat, excess methanol and a catalytic amount of sulfuric acid [2,40,41,43,48–51] 

### . This two-step procedure readily accom

modates high FFA-containing, low-cost feedstocks for the preparation of biodiesel [40,41] 

### . Despite the additionalfixed capital and operational costs, the integrated twostep procedure is being increasingly applied industri

ally to prepare biodiesel from low-cost but high FFAcontaining feedstocks [38] 

### . As previously discussed, feedstock cost dictates biodiesel process economics, so less expensive but lower quality feedstocks may offset the increased capital investment in a dual-step facility. Several studies have conducted RSM-optimized methanolysis on acid-pretreated oils and verified that the reaction conditions do not vary significantly from those reported by Freedman et al. [35] 

### . An advantage to esterification of FFAs as opposed to their removal by refining is that the yield of biodiesel is higher in the two-step case of esterification/transesterification because FAs are not removed from the system. Instead, they are converted into the desired product. O O O R O

R O

R O + 3R'OH R OR ' O

TA G Alcohol

Glycerol O OH O R O

R O

DA G +

R OR ' O
HO OH O

R O MA G +

R OR ' O
HO OH OH + R'= −CH 3 (nor mally)

R OR'

O
= biodiesel k 1
k 2

k 3 k 4

k 5 k 6



### Figure 1. Transesterification of triacylglycerols to fatty acid alkyl esters (biodiesel) and glycerol. DAG: Diacylglycerol; MAG: Monoacylglycerol; TAG: Triacylglycerol.Biofuels (2012) 3(2) future science group 198 

### Review Moser



### Phase distribution during methanolysis Because TAGs are not soluble in methanol, methanolysis commences as two immiscible phases [52–54] 

### . Illustrative of this is the fact that only 5.7 g of soybean oil is soluble in 1 l of methanol at 30°C with vigorous agitation. With an increase in temperature to 40°C, the solubility of soybean oil increases to 7.5 g after vigorous agitation [54] 

### . The alkaline catalyst is exclusively dissolved in the polar methanol phase at the onset of methanolysis and only interacts with TAGs at the interface of the phases unless sufficient agitation is intro

duced [52,53] 

### . Stirring of adequate intensity causes TAG transport into the methanol phase where they are rapidly converted into FAMEs and glycerol (Figure 1) 

### . Once the diacylg

lycerol (DAG) and monoacylglycerol (MAG) intermediates are formed in sufficient quantity, they act as emulsifiers to improve mass transfer of TAGs into the methanolic phase. When near completion, methanoly

sis transforms into another biphasic system that consists of ester-rich (FAME) and glycerol-rich phases. At this stage, catalyst and metha

nol are preferentially soluble in the more polar glycerolic phase [52,55]



### . The phases readily partition once the reaction is complete and agi

tation is ceased, which facilitates purification of FAMEs. Zhou and Boocock demonstrated that 42.0% of residual methanol was located in the FAME-rich phase, whereas the remaining 58.0% was in the glyc

erolic phase. Additionally, 94.2% of sodium methoxide catalyst was in the glycerolic phase. As expected, 97.7% of glycerol partitioned into the denser glycerolic phase and 99.0% of FAMEs separated into the ester-rich phase [53]



### .
Chemical structure & common FAs The chemical structure of biodiesel (FAMEs) consists of methanol esteri

fied to FAs. The FA moiety is derived from TAGs, which are triesters of glycerol with three FAs attached via ester linkages to the glycerol backbone (Figure 1)



### . Palmitic (hexadecanoic), stearic (octadecanoic), oleic (9 Z -octadecenoic), linoleic (9 Z ,12 Z -octadecadienoic) and linolenic (9 Z

,12 Z ,15 Z -octadecatrienoic) acids are the five most commonly encountered FAs in plant oils [1,2,56] 

### . However, other FAs are occasionally encoun

tered in significant quantities in a limited number of plant oils. For instance, erucic (13 Z -docosenoic) acid is an important constituent in plant oils from the Brassicaceae 

### family, of which wild mustard [57] 

### and high-erucic acid rapeseed oil are examples. Other exam

ples include capric (decanoic) acid-containing cuphea ( Cuphea viscosissima x Cuphea lanceolata ) [58] 

### oil, lauric CSTR

#1 Oil Methanol Catalyst

Separator Crude FAME Neutralizatio n

Acidification Acid
FFA glycero l Crude

Methanol removal Methanol removal

Glycerol,
∼ 85% Distillation Wet methanol Wet methanol

Methanol Wate r

Wate r wash Dirty wate r Water Dryer Biodiesel

CSTR

#2 Catalyst

Methanol

Salts Separator

Crude FAME



### Figure 2. Industrial production of biodiesel from feedstocks with low free fatty acids and water content. Depicted are two CSTRs in sequence with glycerol removal in between. Methanol recovered after distillation can be recycled. CSTR: Continuously stirred tank reactor; FAME: Fatty acid methyl ester; FFA: Free fatty acid.

Key term
Brassicaceae: Herbaceous family of flowering plants with high seed oil content that is generally compatible with fallow lands. Widely distributed throughout the northern temperate climate zone and includes rapeseed/ canola.

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 199 

### (dodecanoic) acid-containing coconut [59] 

### , palm kernel [60] 

### and babassu [60] 

### oils, petroselenic (6 Z -octadecenoic) acid-containing coriander ( Coriandum sativum ) oil [49] 

### , and 5 Z -eicosenoic acid-containing meadow

foam ( Limnanthes alba ) oil [61] 

### . Listed in Table 4 

### is the distribution of common FAs encountered in plant oils.

Influence of chemical structure on fuel properties Fuel properties of biodiesel are largely determined by FA composition, with other factors such as presence of contaminants and minor components playing lesser roles [2,56,62] 

### . As a result, fuel properties of biodiesel vary depending on FA composition. Such dependence of fuel properties on chemical structure may inform genetic modification of oilseed crops for optimum composition to yield the most favorable biodiesel fuel properties [63]



### . Fuel properties directly impacted by FA composition include low cold-flow properties, oxidative stability, KV and CN [1,2,56,62] 

### . Minor components in biodie

sel and feedstock lipids are defined as naturally occur

ring nonpolar unsaponifiable species and may include tocopherols, tocotrienols, phospholipids, steryl gluco

sides, wax esters, chlorophyll, fat soluble vitamins and hydrocarbons (such as squalene, carotenes and poly

cyclic aromatic hydrocarbons) [34,64,65] 

### . Contaminants in biodiesel are defined as transesterification and may include FFAs, soaps, TAGs, DAGs, MAGs, alcohol, catalyst, salts, glycerol, metals and water.

The cold-flow properties of biodiesel are impacted by chain length, degree of unsaturation, double-bond geometry and ester head group. As seen in Table 5 

### , higher melting points (MPs) are obtained as the chain length of saturated FAMEs is extended (C12:0, MP 4.3°C; C18:0, MP 37.7°C) [66] 

### . Compounds of identical chain length exhibit progressively lower MPs as the content of double bonds increases, as evidenced by the MPs of C18:0 (37.7°C), C18:1 (-20.1°C), C18:2 (-43.1°C) and C18:3 (-52°C) [66] 

### . Double-bond geometry is another important factor influencing MP. The orientation of double bonds in nearly all natural oils is the cis - con figuration. However, trans- isomers may be chemically introduced through catalytic partial hydrogenation or unnatural other means [67,68] 

### . Isomerization to the transconfiguration results in a modified 3D geometry that is manifested by higher MPs relative to the correspond

ing cis -isomers. Illustrative of this is a comparison of the MPs of methyl elaidate (methyl 9 E -octadenenoate) and methyl oleate, which are 9.9 and -20.1°C, respec

tively [66] 

### . The influence of ester head group on MP is illustrated by methyl, ethyl, propyl and butyl esters of stearic acid, which have MPs of 37.7, 33.0, 28.1 and 25.6°C, respectively [66] 

### . In general, FAEEs exhibit lower MPs as the number of carbons (up to eight) in the ester head group is increased. Because biodiesel is a mixture of FAAEs with a wide range of MPs, initial crystal growth that occurs upon cooling of biodiesel to sub-ambient conditions is primarily caused by crystalli

zation of higher melting constituents [16] 

### . As mentioned previously, alkyl esters other than methyl do not qualify as biodiesel according to EN 14214. Oxidative stability of biodiesel is principally influ

enced by degree of unsaturation (number of double bonds), with factors such as double-bond location and geometry also playing roles. The rate of autoxida

tion primarily depends on the number and location of methylene-interrupted double bonds contained within the hydrocarbon backbone of FAAEs. Bis -allylic methy

lene positions found in methyl linoleate (carbon 11) and methyl linolenate (carbons 11 and 14) contain C-H bonds with lower dissociation energies (more labile hydrogens), and are, therefore, considerably more prone to hydrogen abstraction than allylic, especially saturated methylene positions. FAAEs with a higher + NaOH

(or NaOCH 3 ) R OH

O
R O − Na + O

+ H 2 O (or CH 3 OH ) FFA Soap R OCH 3

O

Biodiesel + H 2 O + CH 3 OH R OH

O

FFA

[2 ] [1 ]



### Figure 3. Deleterious side reactions caused by the presence of water and free fatty acids. Hydrolysis of biodiesel (reaction 1) to yield FFAs and methanol. Formation of soap from reaction of FFAs with alkali catalyst (reaction 2). FFA: Free fatty acid.

Table 4. Systematic, common and shorthand names of fatty acids in biodiesel feedstocks. Systematic Common Shorthand
Decanoic Capric C10:0 Dodecanoic Lauric C12:0 Tetradecanoic Myristic C14:0 Hexadecanoic Palmitic C16:0 9 Z

-hexadecenoic Palmitoleic C16:1 9c Octadecanoic Stearic C18:0 9 Z

-octadecenoic Oleic C18:1 9c 9 Z

,12 Z -octadecadienoic Linoleic C18:2 9, 12c 9 Z

,12 Z ,15 Z -octadecatrienoic Linolenic C18:3 9, 12, 15c Eicosanoic Arachidic C20:0 11 Z -eicosenoic Gadoleic C20:1 11c Docosanoic Behenic C22:0 13 Z -docosenoic Erucic C22:1 13c Tetracosanoic Lignoceric C24:0Biofuels (2012) 3(2) future science group 200 

### Review Moser



### number of methylene carbons allylic to double bonds are vulnerable to autoxidation. Particularly susceptible to autoxidation are bis -allylic methylene positions, as evidenced by relative rates of oxidation of 1, 41 and 98 for ethyl esters of oleic (2 methylene positions), linoleic (2 methylene and 1 bis -allylic position), and linolenic (2 methylene and 2 bis -allylic positions) acids, respectively [69] 

### . In another report, the relative rate of oxidation is reported as 1, 27 and 77, respectively [70] 

### . These results are confirmed by examination of the induction peri

ods (IPs) (EN 14112, 110°C) (Table 5) 

### of methyl esters of stearic (>40 h), oleic (2.5 h), linoleic (1.0 h) and linolenic (0.2 h) acids [71] 

### . Autoxidation commences with production of resonance-stabilized alkyl radicals through allylic hydrogen abstraction caused by an initiator (e.g., heat, light, metals and peroxides) [72]



### . Consequently, superior oxidative stability is generally observed in biodiesel prepared from feedstocks with relatively high saturated FA content and/or relatively low polyunsaturated FA content.

The effect of double-bond location on oxidative sta

bility is evidenced by comparison of the IPs (110°C) of methyl petroselinate (IP = 3.5 h) and methyl ole

ate (IP = 2.5 h) [71] 

### . Analogously, methyl 5 Z -eicosenate (IP = 69.4 h) is considerably more stable to oxidation than methyl oleate (IP = 14.8 h) at 90°C [73] 

### . It would stand to reason that biodiesel fuels enriched in FAMEs with unsaturation located close to the ester head group would have superior oxidative stability relative to the more typical 9-ene FAMEs. This supposition is verified by comparison of FAMEs prepared from coriander and meadowfoam oils to soybean oil methyl esters (SME). Methyl esters prepared from meadowfoam oil, which is enriched in up to 64.2 wt% 5 Z -eicosenoic acid, has an IP (110°C) of 66.9 h [61] 

### . The IP (110°C) of coriander oil methyl esters, which is enriched in >68% petroselenic acid, is 14.6 versus 5.0 h for SME [49]



### .

Double-bond geometry ( cis- vs trans- isomers) impacts oxidative stability, which is illustrated by the contrasting IPs of FAMEs of oleic (2.5 h) and elaidic (7.7 h) acids [71]



### . Trans- isomers are thermodynamically more stable than the corresponding cis -isomers, which explains their enhanced oxidative stability relative to cis -isomers. Biodiesel fuels that contain trans -FAAEs exhibit higher oxidative stability than those with a simi

lar number of entirely cis double bonds. For instance, partially hydrogenated SME (7.7% trans- FAME, 16.4% saturated FAME and 44.7% polyunsaturated FAME) yielded an IP of 6.2 h (110°C) versus 2.3 h for SME (0%

trans , 16.9% saturated and 59.8% polyunsaturated) [67]



### .

Chain length and degree of unsaturation principally affect KV of FAMEs. As seen in Table 5 

### , KV increases with increasing chain length among otherwise similar constituents. For instance, saturated FAMEs of lau

ric (C12:0), myristic (C14:0), palmitic (C16:0) and stearic (C18:0) acids have KVs of 2.43, 3.30, 4.38 and 5.85 mm 2 

### /s, respectively. Lower KVs are observed with increasing double-bond content among otherwise similar constituents, as noted by the FAMEs of stearic (C18:0, 5.85 mm 2 

### /s), oleic (C18:1, 4.51 mm 2 

### /s), linoleic (C18:2, 3.65 mm 2 

### /s) and linolenic (C18:3, 3.14 mm 2 

### /s) acids. Double-bond orientation also impacts KV, which is illustrated by comparison of methyl elaidate (5.86 mm 2 

### /s) and methyl linoelaidate (5.33 mm 2 

### /s; methyl 9 E , 12 E -octadecadienoate) to the corresponding cis- isomers (methyl oleate and linoleate) [74]



### .

KV is strongly temperature dependent, as higher KVs are reliably observed as the temperature of measurement is incrementally decreased [48,75–78] 

### . For instance, an increase in the KV of SME from 4.15 to 11.75 mm 2 

### /s is observed as the temperature is lowered in 10°C incre

ments from 40 to 0°C [74] 

### . In addition, the KV of field pennycress oil methyl esters increases from 5.24 mm 2 

### /s at 40°C to 8.65 mm 2 

### /s at 20°C, 16.70 mm 2 

### /s at 0°C and 35.52 mm 2 

### /s at -10°C [48] 

### . Similar results are obtained with low sulfur (30 ppm S) diesel fuel, with values of 2.90, 3.64, 4.55, 6.21 and 8.58 mm 2 

### /s at 40, 30, 20, 10 and 0°C, respectively [76] 

### . Increased viscosity of biodiesel at low (subambient) temperatures is of concern because Table 5. Fuel properties of fatty acid alkyl esters commonly found in biodiesel. Fatty acid ethyl esters MP † ( o C) KV ‡ (mm 2 /s) IP § (h) CN ¶

C12:0 ME 4.3 2.43 >40 67 C12:0 EE -1.8 2.63 # # C14:0 ME 18.1 3.30 >40 # C14:0 EE 12.5 3.52 # # C16:0 ME 28.5 4.38 >40 86 C16:0 EE 23.2 4.57 # 93 C16:1 ME -34.1 3.67 2.1 51 C16:1 EE -36.7 # # # C18:0 ME 37.7 5.85 >40 101 C18:0 EE 33.0 5.92 >40 97 C18:0 BE 25.6 7.59 # 92 C18:1 ME -20.1 4.51 2.5 59 C18:1 EE -20.3 4.78 3.5 68 C18:1 BE -34.8 5.69 # 62 C18:2 ME -43.1 3.65 1.0 38 C18:2 EE -56.7 4.25 1.1 40 C18:3 ME -52 3.14 0.2 23 C18:3 EE -61.7 3.42 0.2 27

† Data from [92]

. ‡ Data from [100]

. § Data from [97]

. ¶ Data from [106]

. # Not determined or reported. BE: Butyl ester; CN: Cetane number; EE: Ethyl ester; IP: Induction period; KV: Kinematic viscosity; ME: Methyl ester; MP: Melting point.

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 201 

### it may cause potentially excessive fuel injection pres

sures during initial engine warm-up. Furthermore, fuel starvation of diesel engines may result as the biodiesel fuel moves more slowly through filters and fuel lines at subambient temperatures [76,78] 

### . Several methodologies to predict KV of biodiesel based on FAAE composition are reported. These procedures essentially consist of a weighted average method utilizing the FA composition and KVs of individual FAAEs to provide a calculated KV [75,78] 

### . Lastly, the blend percentage of biodiesel in petrodiesel can be determined from KV if the values for neat biodiesel and petrodiesel are known [77]



### . CN is a dimensionless measure of diesel fuel ignition performance and is obtained by comparing it to refer

ence fuels in a standardized engine test. As a primary indicator of diesel fuel quality, CN is directly related to the ignition delay diesel fuels experience upon injection into combustion chambers of diesel engines. Ignition delay is defined as the period of time, expressed in degrees of crank angle rotation, between the start of fuel injection and the start of combustion. Higher CNs are observed with shorter ignition delay and vice versa. Hexadecane, trivially referred to as cetane, is arbitrarily assigned a CN of 100 and is the high-quality reference standard of the cetane scale. At the other end of the cetane scale is 2,2,4,4,6,8,8-heptamethylnonane, which has a long ignition delay time and an arbitrarily assigned CN of 15. Typical CN testing is in the range of 30 to 65. CN is conceptually similar to octane number (ON) and fuels with low CNs will have high ONs, and vice versa. As evidenced by the end points of the CN scale, branching reduces CN. Other factors influencing CN include chain length and degree of unsaturation, with higher CNs observed for longer chain compounds and those with lower degrees of unsaturation. Illustrative of this is a comparison of methyl esters of lauric (67), pal

mitic (86) and stearic (101) acids (Table 5) 

### . Furthermore, methyl esters of stearic (101), oleic (59), linoleic (38) and linolenic (23) acids demonstrate the influence of unsaturation on CN [79]



### .
Commercial feedstocks A desire among liquid transportation fuel-import

ing countries to reduce their dependence on foreign sources of energy has resulted in the implementation of numerous governmental incentives and mandates for domestic production and consumption of alterna

tive biofuels. Such policies, along with other factors, have resulted in a rapid increase in worldwide biodie

sel production capacity. However, it does not appear possible to meet the increased production capacity and mandated demand with traditional sources of biodie

sel prepared from commodity lipids. For example, it is estimated that if all US soybean production were dedicated to biodiesel, only 6% of diesel demand would be satisfied [30] 

### . The US Energy Information Administration estimates that 1.170 billion l of bio diesel was pro

duced in the USA in 2010, versus 34 million l in 2001 [201] 

### . Production peaked in 2008 at 2.567 billion l. For 2011, production is expected to show a rebound to a level near the historical high, owing to retroactive reinstatement of the lapsed US$1.00 per gallon biodiesel tax credit by the US Federal govern

ment. The US Energy Policy Act of 2005 included an RFS1 that mandated 28 million l of renewable fuels be blended into energy supplies by the end of 2012. The Energy Independence and Security Act of 2007 (EISA) made significant changes in the structure and magnitude of the renewable-fuel program. The revised statutory requirements of EISA specify the volumes of cellulosic biofuel, biomass-based diesel, advanced biofuels, and total renewable fuel that must be used in transportation fuel yearly from 2010 to 2022. The EISA fuel program, designated RFS2, mandates the use of a total of 57.5 billion l per year of renewable fuel by 2012 and 136.3 billion l per year by 2022.

A recent report by Tilman et al. [80] 

### identified sev

eral feedstock categories that hold the most promise as sources of biofuels with much lower life cycle GHG emissions than traditional fossil fuels and that do not compete with food production: perennial plants grown

on fallow lands 

### , crop residues, sustainably harvested wood and forest residues, double crops and mixed crop

ping systems, as well as municipal and industrial wastes. The four major biodiesel feedstock categories are micro

algae, oilseeds, animal fats and various low-value waste materials such as used cooking oils, greases and soap

stocks. With regard to oilseeds, desirable characteristics include adaptability to local growing conditions (e.g., rainfall, soil type and latitude), regional availability, high oil content, favorable FA composition, compat

ibility with existing farm infrastructure and practices, minimal agricultural inputs (water, fertilizer and pes

ticides), definable growth season, uniform rates of seed maturation, markets for co-products, compatibility with agriculturally undesirable lands and suitability for off-season rotation with conventional commodity crops [2,48,49,61] 

### . Biodiesel prepared from feedstocks that meet all or most of the above criteria hold the greatest promise as alternatives to petrodiesel.

Traditional commodity oilseed feedstocks predomi

nately include soybean, rapeseed/canola, palm and sunflower oils, with lesser contributions from coconut, corn, cottonseed and peanut oils [2] 

### . Also of signifi

cance are waste cooking oils derived from commodity lipids, as well as low-grade tallow obtained from animal Key term
Fallow land: Cropland that is not seeded for a season. May also refer to land that is not suitable for agricultural production and is thus perpetually fallow.Biofuels (2012) 3(2) future science group 202 

### Review Moser



### rendering. Alternative (i.e., nontra

ditional) feedstocks are normally pursued out of necessity in regions where more traditional plant oils are not locally available, as part of a concerted effort to reduce depen

dence on imported petroleum or because an abundance of marginal land is available for cultivation of low-input agricultural products.
Promising alternative feedstocks Algae and jatropha have attracted considerable interest as alternative feedstocks for pro

duction of biodiesel due to their purportedly high lipid densities (l/ha) [81–84] 

### . Because of the propensity of jatropha to produce toxic substances, along with its preference for arid climates and algae’s complicated and expensive production and extraction systems, these feedstocks will not be considered here. Furthermore, the principal FAs in these feedstocks are fully saturated, which has significant deleterious implications for cold weather performance of the resulting biodiesel fuels [1,81–84] 

### . Some strains of algae are enriched in polyunsat

urated FAs, which is excellent for cold weather perfor

mance but abysmal for oxidative stability and CN, and is, therefore, not desirable from a fuel property stand

point. Instead, lesser-known alternatives with adaptabil

ity to temperate climate zone 

### s will be considered, such as camelina and field pennycress. Temperate climates are of particular interest because they encompass Europe, North America, most of Asia and portions of the Middle East, Africa, Australia and South America. As a result, the majority of the energy-consuming human popula

tion, along with our collective associated energy infra

structure, resides mostly within the temperate climate zones. It therefore stands to reason that energy crops should thrive in relatively close proximity to human population centers.

Members of the Brassicaceae family are particu

larly attractive as alternative feedstocks because they evolved to thrive in, and originated mostly within, the northern temperate climate zone [85] 

### . Many members also produce seeds with high oil content and include commercially important species such as Brassica napus (rapeseed), Brassica oleracea (e.g., broccoli, cabbage and cauliflower), Brassica rapa (turnip), Raphanus sativus (common radish), Amoracia rusticana (horseradish) and the model organism Arabidopsis thaliana . This family of economically important flowering plants (Angiosperms) is also known as Brassicas, mustards, the crucifers or the cabbage family. The older scientific classification of the Brassicaceae was Cruciferae, which means ‘cross bearing’ and is descriptive of the four petals of mustard flowers that resemble a cross. The Brassicaceae consist mostly of herbaceous plants with annual, biennial or perennial lifespans, and includes 338 genera and 3709 species [85] 

### . Oilseeds derived from winter annuals are especially attractive feedstocks in temperate climates as they are often high in oil content, require few agricul

tural inputs, are compatible with existing farm infra

structure, can flourish on otherwise fallow land, have definable growth seasons and uniform seed-maturation rates, and can be harvested in spring, thus not displac

ing existing food production while simultaneously augmenting oil supply and providing ground cover to prevent soil erosion. Historically, members of the Brassicaceae family have attracted interest as cover crops for weed manage

ment due to favorable characteristics such as soil ero

sion mitigation, disruption of pest cycles and increased nutrient cycling [86] 

### . In addition, all mustards contain glucosinolates 

### , which are secondary metabolites with sulfur and nitrogen and are derived from glucose and an amino acid. Glucosinolates are not toxic but are enzy

matically hydrolyzed to yield a variety of products with beneficial biofumigation properties, including isothio

cyanates, nitriles, oxazolidinethiones, organic cyanates and epithionitriles. Myrosinase, the enzyme responsible for hydrolysis, is separated intracellularly from the glu

cosinolates until cellular damage occurs through events such as mowing, grazing, freezing, tillage or root death [87,88] 

### . Although beneficial due to their biofumingation properties, glucosinolates, if present in sufficient con

centration, may render seed meal 

### unsuitable as a feed supplement for livestock animals, as higher amounts in feed can lead to goiter and other adverse health effects [86–89] 

### . Such unsuitability may render the seed meal of lower monetary value while simultaneously suppressing the profitability of biofuels production from such crops. A strategy to overcome this drawback is to use low-level (<10%) blends of glucosinolate-containing seed meals in seed meals of nonglucosinolate-containing origin, to provide a protein source for animals with an acceptable level of glucosinolates while concomitantly consum

ing Brassicaceae seed meals. Another approach is the employment of glucosinolate-containing seed meals as biofumigants to inhibit growth of weeds, which may be useful to organic farmers seeking green practices for pest control [90,91]



### .
Camelina Camelina, also known as false flax or gold-of-pleasure, is a broadleaf oilseed flowering plant of the Brassicaceae family that grows optimally in temperate climates. Camelina may be grown in a variety of climatic and soil conditions as a spring or summer annual or as a Key terms Temperate climate zones: Latitudes that lie between the tropics and the polar circles; where the majority of the human population resides.
Glucosinolates: Class of secondary metabolites found in species of the Brassicaceae that contain sulfur and nitrogen and are derived from glucose and an amino acid.
Seed meal: Solid material enriched in protein that is obtained when lipids are expelled or extracted from seeds. Seed meals are valuable ingredients in livestock feed formulations.

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 203 

### biannual rotational winter crop. Cultivated in Europe sporadically since the Bronze Age, camelina has several beneficial agronomic attributes: short growing season (85–100 days), compatibility with existing farm prac

tices, and tolerance of cold weather, drought, semi-arid conditions and low-fertility or saline soils. Camelina also has lower water, pesticides and fertilizer require

ments than traditional commodity oilseed crops (e.g., apeseed/canola, soybean and sunflower). Moreover, camelina is well adapted to the more northerly regions of North America, Europe and Asia. As such, it may serve in a rotational cycle in the Northern Hemisphere where winter wheat ( Triticum spp.) is typically planted, thus facilitating disruption of undesirable weed and pest cycles [92,93] 

### . The yield of camelina at maturity is 1500–3000 kg seeds/ha. The lipid content of indi

vidual seeds ranges between 36 and 47 wt% [65] 

### . The resulting yield of camelina oil is thus calculated to be 540–1410 kg/ha, which, as seen in Table 6 

### , surpasses the yield of soybean oil and is approximately equal to that of rapeseed oil. a -linolenic acid comprises 32–40 wt% of the FA composition of camelina oil (Table 7) 

### . Other FAs in quantities above 10 wt% include linoleic, oleic and 11-eicosenoic acids [12,65,92–95]



### .

Extraction of oil from camelina seeds by mechanical expeller yields a seed meal that consists of approximately 10% residual oil, 45% crude protein, 13% fibers, 5% minerals and other minor constituents such as gluco

sinolates and vitamins [92] 

### . The concentration of glu

cosinolates in dry camelina seeds ranges from 13 to 36 μmol/g with a mean concentration of 24 μmol/g [96]



### . Consequently, camelina meal can

not exceed 10 wt% of the total food ration given to feedlot cattle and chickens in the USA. However, a ceiling of 10% represents significant market potential where a large num

ber of livestock animals is located, thus representing an important revenue stream for camelina meal.

The FFA content of crude cam

elina oil is sufficiently low to allow for direct conversion to FAMEs, thereby eliminating the need for acid pretreatment. However, a higher yield of FAMEs was reported when pretreatment was performed [12,95] 

### . Camelina oil was successfully converted into biodiesel by the classic homogeneous base-catalyzed method, as well as with heterogeneous metal oxide catalysts, both with andwithout microwave irradiation and at noncatalytic suband super-critical conditions employing co-solvents with methanol [12,95,97–100] 

### . The fuel properties (Table 8) 

### of camelina-based biodiesel are similar to those of biodiesel prepared from soybean oil, thus indicating its accept

ability for use as biodiesel [12,95] 

### . It should be noted, based on the relatively high content of polyunsaturated FAMEs contained in camelina oil-derived biodiesel, that antioxidant additives would be needed to meet the oxidative stability specifications contained in ASTM D6751 and EN 14214. However, both ASTM D6751 and EN 14214 recommend that antioxidants be added to all biodiesel fuels immediately after their produc

tion, regardless of the feedstock from which they were prepared. Additionally, FAEEs prepared from camelina oil along with FAMEs were evaluated as blend com

ponents in petrodiesel (<15 ppm S). Camelina-based petro diesel blends exhibited fuel properties comparable to the analogous soybean-based blends [12]



### . Field pennycress Field pennycress is a winter annual belonging to the Brassicaceae family that is also known as stinkweed or French weed. Native to Eurasia but with an extensive distribution throughout the world, field pennycress is Table 6. Yield of plant oil from several feedstocks.

Common name Latin binomial Oil content/seed (wt%) Seed yield (kg ha -1 year -1 ) Oil yield (kg ha -1 year -1 ) Camelina Camelina sativa 36–47 1500–3000 540–1410 Field pennycress Thlaspi arvense 20–36 1120–2240 224–806 Jatropha Jatropha curcas 27–40 2000–5000 540–2000 Oil palm Elaeis guineensis 4000–10,000 Rapeseed Brassica napus 40–44 2680–3390 965–1342 Soybean Glycine max 18–22 2140–2840 347–562



### Table 7. Distribution of principal fatty acids in several plant oils. Fatty acid Camelina Field pennycress Canola Palm Soybean C16:0 6.8 3.1 4.6 41.9 10.5 C18:0 2.7 0.5 2.1 4.6 4.1 C18:1 9c 18.6 11.1 64.3 41.2 22.5 C18:2 9c, 12c 19.6 22.4 20.2 10.3 53.6 C18:3 9c, 12c, 15c 32.6 11.8 7.6 0.1 7.7 C20:1 11c 12.4 8.6 Trace None Trace C22:1 13c 2.3 32.8 None None None Others 5.0 9.7 1.2 1.9 1.6Biofuels (2012) 3(2) future science group 204 

### Review Moser



### highly adapted to a wide variety of climatic conditions [48,90,91,101–103] 

### . Normally considered to be an agricul

tural pest (weed) by farmers, field pennycress readily grows from fall to spring with none or minimal agricul

tural inputs (fertilizer, pesticides and water). Because of its growth habit, it can be successfully planted and harvested without disrupting annual soybean produc

tion, thus not displacing existing agricultural produc

tion. In addition, field pennycress is tolerant of lands not otherwise suited for agricultural production, does not compete with the food chain, is compatible with existing farm infrastructure and practices, and has high seed oil content (20–36 wt%) [48,90,91,101,102]



### . The typical yield from wild populations is 1420 kg seed/ha, although 1120–2240 kg/ha is the expected range due to variability in various climatic and soil conditions along with inputs and other factors [48,90]



### . The resulting yield of field pennycress oil is thus cal

culated to be 224–806 kg/ha, which, as seen in Table 6 

### , surpasses the yield of soybean oil but is lower than that for rapeseed oil. Erucic acid is the principal component of field penny cress oil (Table 7) 

### . The remaining FA dis

tribution consists mostly of oleic, linoleic and linolenic acids [48,90,102] 

### . Current agronomic efforts are focused on increasing oil yield, lowering erucic acid content and reducing the growing season to enable rotation with corn [90]



### . The concentration of glucosinolates in pennycress seed and its seed meal is sufficient to serve as a volatile biofumigant [91] 

### . Both hexane-extracted and mechani

cally expelled field pennycress seed meals release allyliso

thiocyanate (AITC) when placed in contact with water. Myosinase is the enzyme responsible for decomposition of glucosinolates into AITC, which is the aglycone of sinigrin (the principal glucosinolate in field pennycress). Interestingly, sinigrin is nontoxic but its degradation product, AITC, is toxic to both plants and animals. Field pennycress seed meal is effective at inhibiting the germination and growth of weed seeds in laboratory testexperiments, as well as in test plots, due to the growthinhibitory activity of AITC. When incorporated at 1.0 wt% into soil, seed meal containing AITC completely inhibited the appearance of weeds. This practice may prove useful to organic farmers who wish to use green practices for weed control within field plots [91] 

### . As a result of its high glucosinolate content, AITC-containing seed meal cannot be directly used as a component in feed for livestock animals. However, if the myrosinase enzyme responsible for biological conversion of sinigrin to AITC is deactivated, then field pennycress seed meal is suitable as an animal feed, as it would be free of AITC. Deactivation of myrosinase is performed by passing field pennycress seeds through a commonly available seed conditioner. The seed conditioner denatures myrosinase by subjecting the seeds to elevated temperature (85°C) for an extended period of time (24 h). An additional advantage of seed-conditioned field pennycress seeds is that a higher yield of oil is obtained when passed through a mechanical expeller relative to unconditioned seeds, due to extraction efficiency increases related to the increased surface area of conditioned seeds. In summary, seed-conditioned field pennycress seed meal is suitable as an animal feed supplement because it does not contain AITC [87,91,101,104–106]



### . The content of FFAs in crude field pennycress oil is sufficiently low to allow for direct conversion to FAMEs following the classic homogenous, alkaline-catalyzed methodology, thereby eliminating the need for acid pretreatment. However, a higher yield of FAMEs was reported when pretreatment was performed [48] 

### . The cold-flow properties (Table 8) 

### of field pennycress-based biodiesel indicate significantly improved low-tem

perature fluidity relative to camelina and commodity oil-derived FAMEs. Such a result has important impli

cations for use of biodiesel during winter months in tem

perate climates where ambient temperatures regularly reach 0°C or lower [48] 

### . However, the high content of methyl erucate (C22:1 13c) in field pennycress-derived biodiesel results in a higher KV (5.24 mm 2 

### /s at 40°C) than that typically reported for commodity-derived FAMEs (4.10–4.50 mm 2 

### /s at 40°C). The value obtained for field pennycress-derived biodiesel (5.24 mm 2 

### /s) is not within the range specified in EN 14214 (3.5–5.0 mm 2 

### /s) but is within the ASTM D6751 limit (1.9–6.0 mm 2 

### /s). Methods to lower KV include reduction of methyl eru

cate content through genetic modification, breeding techniques or simply through blending with less-viscous FAMEs [107]



### . Table 8. Selected fuel properties of biodiesel prepared from camelina and field pennycress oils, compared with soybean-, canola- and palm oil-based biodiesel fuels.
Camelina Field pennycress Canola Palm Soybean Cloud point (°C) 3 -10 0 17 0 Pour point (°C) -4 -18 -9 15 -3 Cold filter plugging point (°C) -3 -17 -7 12 -4 Induction period, 110°C (h) 2.5 4.4 6.4 10.3 5.0 Kinematic viscosity, 0°C (mm 2 /s) 4.15 5.24 4.42 4.58 4.12

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 205 

### Executive summary
Biodiesel fuel standards



###  The American biodiesel standard is American Society for Testing and Materials D6751 and the European biodiesel standard is EN 14214. Advantages & disadvantages of biodiesel



###  Advantages: domestic and renewable, inherent lubricity, low toxicity, high flash point, superior biodegradability, negligible sulfur and

aromatics content, lower overall exhaust emissions and positive energy balance.



###  Disadvantages: oxidative and storage stability, low temperature operability, high feedstock cost, lower volumetric energy content and

susceptibility to hydrolysis as well as microbial degradation. Energy balance



###  The net energy ratio (NER) for biodiesel prepared from soybean oil is 4.5:1.



###  NER may vary depending on feedstock as well as with inputs and outputs selected for study. Optimum reaction conditions



###  A sixfold molar excess methanol is needed along with 0.5 wt% catalyst (with respect to triacylglycerols [TAGs]) to ensure that the

transesterification reaction proceeds to completeness. Influence of free fatty acids



###  Free fatty acids (FFAs) react with homogeneous alkaline catalysts to form soap and water.



###  FFAs irreversibly quench homogenous alkaline catalysts and reduce yield when present in concentrations above 2 wt%.



###  FFAs promote dissolution of biodiesel into the glycerolic phase during purification, thus further depressing the final yield of biodiesel. Phase distribution during methanolysis



###  Methanolysis commences as two immiscible phases as a result of the low solubility of TAGs in methanol.



###  Diacylglycerol and monoacylglycerol intermediates serve as emulsifiers to improve mass transfer.



###  When near completion the reaction transforms into a second biphasic system consisting of ester- and glycerol-rich phases. Chemical structure & common FAs



###  Biodiesel consists of methanol esterified to FAs.



###  FAs are derived from TAGs of plant oils and animal fats, which consist of three FAs esterified to a glycerol backbone.



###  The five most common FAs in plant oils are palmitic, stearic, oleic, linoleic and linolenic acids. Influence of chemical structure on fuel properties



###  Fuel properties are determined by the component fatty acid methyl esters that comprise biodiesel.



###  Monounsaturated fatty esters strike a balance between cold-flow properties, oxidative stability, kinematic viscosity and cetane number. Traditional feedstocks



###  Up to 88% of the cost of biodiesel production is attributed to feedstock acquisition if refined commodity oils are utilized.



###  The most common feedstock in the USA is soybean oil. Canola and palm oils are most common in Europe and the tropics, respectively. Promising alternative feedstocks



###  Desirable characteristics of alternative feedstocks include adaptability to temperate climates, high oil content, favorable FA composition,

compatibility with existing farm practices, low agricultural inputs, definable growth season, uniform seed maturation rates, potential markets for byproducts, adaptability to fallow lands, not competing with the food chain and not displacing existing agricultural production.



###  Members of the Brassicaceae family are of particular interest because the above criteria are met. Historically, Brassicas have been used as

cover crops to prevent soil erosion and for weed management. Rapeseed is a commercially significant example from this family. Camelina



###  The yield of camelina oil is 540–1410 kg/ha, which surpasses soybean oil and is approximately equal to rapeseed.



###  Camelina seed meal contains 13–36 μmol/g of glucosinolates, which is sufficient to restrict its use as a livestock feed supplement to no

more than 10 wt%.



###  The primary FA in camelina oil is linolenic acid, with linoleic, oleic and 11-eicosenoic acid also present in significant quantities.



###  The fuel properties of camelina-based biodiesel are similar to those of biodiesel prepared from soybean oil, thus implicitly indicating its

acceptability for use as biodiesel.



###  Antioxidant additives would be needed to meet the oxidative stability specifications listed in American Society for Testing and Materials

D6751 and EN 14214. Field pennycress



###  The yield of field pennycress oil is 224–806 kg/ha, which surpasses the yield of soybean oil but is lower than that reported for rapeseed oil.



###  Field pennycress seed meal may be used as a livestock feed supplement if myrosinase is first denatured prior to lipid extraction.



###  Erucic acid is the principal component. Other FAs in quantities above 10 wt% include oleic, linoleic and linolenic acids.



###  The cold-flow properties of field pennycress biodiesel indicate significantly improved low-temperature fluidity relative to camelina and

commodity oil-derived fatty acid methyl esters. Conclusion



###  Problems remaining to be solved include relatively poor cold-flow properties, poor oxidative and storage stability, and high feedstock cost.



###  Development of alternative feedstocks with favorable agronomic traits that do not compete with food production and do not have

food-related applications show great promise to enhance biodiesel production while simultaneously improving process economics.Biofuels (2012) 3(2) future science group 206 

### Review Moser



### Conclusion Biodiesel exhibits several important technical advan

tages over petrodiesel, but resolution of technical issues would greatly facilitate its market acceptance and pen

etration. Outstanding technical deficiencies of biodiesel relative to petrodiesel include cold-flow properties as well as oxidative and storage stability. From an eco

nomic standpoint, deployment of low-cost alternative feedstocks would significantly improve biodiesel process economics. Commodity oilseed crops are relatively expensive, in many cases do not have optimum FA compositions, have competing food-related applications and, in some cases, the lipids are not obtained in high yields from seeds. Development of alternative feedstocks with favorable agronomic traits that do not compete with food produc

tion and do not have food-related applications have great promise, especially if they have high oil density (kg/ha) and can be grown in close proximity to human popula

tion centers. Two such examples are camelina and field pennycress, which both belong to the Brassicaceae family and can overwinter on otherwise fallow farm

land with minimal agricultural inputs. The resulting biodiesel fuels from these alternative feedstocks com

pare favorably with esters produced from traditional commodity fats and plant oils.
Future perspective From a policy standpoint, it is anticipated that the next 5–10 years will see an increase in the number of bio

diesel usage mandates at both the B5 and B20 levels and that governments (both local and national) will increase already existing mandates. Such actions will acceler

ate the acceptance and adoption of biodiesel while simultaneously stimulating rural economies around the world. It is anticipated that the primary market for biodiesel in the near- to long-term future is as a blend component in petrodiesel, although secondary markets for B100 may lie in niche applications such as farm equipment, marine or underground applications, as well as in environmentally sensitive areas such as national parks. From a technical aspect, new devel

opments in separation methods (such as membranes and ion-exchange resins) will facilitate purification of biodiesel while also increasing final product quality. Improved purification methods, such as membranes and resins, may also reduce the amount of wastewater generated during biodiesel production, thus represent

ing an important environmental advancement. Further breakthroughs may include implementation of new and existing heterogeneous catalyst technologies in an effort to economically convert feedstocks high in FFA content into high-quality biodiesel in high yield, thereby avoid

ing the classic two-step esterification/transesterification protocol commonly utilized today. Lastly, discovery and further development of existing alternatives to commodity lipids will enhance feedstock availability while simultaneously reducing feedstock cost for pro

duction of biodiesel, both of which will combine to result in increased global biodiesel production for the foreseeable future.

Disclaimer Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture. The US Department of Agriculture is an equal opportunity provider and employer.



### Financial & competing interests disclosure The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manu

script. This includes employment, consultancies, honoraria, stock ownership or options, expert t estimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.



### References Papers of special note have been highlighted as:

n of interest

n n of considerable interest

1 Knothe G. ‘Designer’ biodiesel: optimizing fatty ester composition to improve fuel properties. Energy Fuels 22, 1358–1364 (2008).

n Reports that monounsaturated fatty acids (FAs), such as oleic and palmitoleic, are the most desirable with regard to fuel properties. Also noted are shorter-chain FAs, such as decanoic. 2 Moser BR. Biodiesel production, properties, and feedstocks. In vitro Cell Dev. Biol. Plant 45, 229–266 (2009).

3 Pradham A, Shrestha DS, McAloon A et al. Energy Life-Cycle Assessment of Soybean Biodiesel

. US Department of Agriculture, Washington, DC, USA (2009).

4 US EPA. EPA Finalizes Regulations for the National Renewable Fuel Standard Program for 2010 and Beyond

. US EPA, Washington, DC, USA (2010).

5 Moser BR, Cermak SC, Isbell TA. Evaluation of castor and lesquerella oil derivatives as additives in biodiesel and ultra low sulfur diesel fuel. Energy Fuels 22, 1349–1352 (2008).

6 Moser BR, Erhan SZ. Branched chain derivatives of alkyl oleates: tribological, rheological, oxidation, and low temperature properties. Fuel 87, 2253–2257 (2008).

7 Soares VLP, Nascimento RSV, Albinante SR. Ester-additives as inhibitors of the gelification of soybean oil methyl esters in biodiesel. J. Therm. Anal. Calorim. 97, 621–626 (2009).

8 Dunn RO. Antioxidants for improving storage stability of biodiesel. Biofuels Bioprod. Bioref. 2, 304–318 (2008).

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 207 9 Moser BR. Efficacy of myricetin as an antioxidant additive in methyl esters of soybean oil. Eur. J. Lipid Sci. Technol. 110, 1167–1174 (2008).

10 Tang H, Wang A, Salley SO, Ng KYS. The effect of natural and synthetic antioxidants on the oxidative stability of biodiesel. J. Am. Oil Chem. Soc. 85, 373–382 (2008).

11 Dinkov R, Hristov G, Sratiev D, Aldayri VB. Effect of commercially available antioxidants over biodiesel/diesel blends stability. Fuel 88, 732–737 (2009).

12 Moser BR, Vaughn SF. Evaluation of alkyl esters from Camelina sativa oil as biodiesel and as blend components in ultra low sulfur diesel fuel. Bioresour. Technol. 101, 646–653 (2010).

n n Reports the fuel properties of biodiesel prepared from camelina oil.

13 McCormick RL, Westbrook SR. Storage stability of biodiesel and biodiesel blends. Energy Fuels 24, 690–698 (2010).

14 Bondioli P, Gasparoli A, Bella LD, Tagliabue S, Toso G. Biodiesel stability under commercial storage conditions over one year. Eur. J. Lipid Sci. Technol. 105, 735–741 (2003).

15 Moser BR. Influence of extended storage on fuel properties of methyl esters prepared from canola, palm, soybean and sunflower oils. Renew. Energ. 36, 1221–1226 (2011).

16 Dunn RO. Crystallization behavior of fatty acid methyl esters. J. Am. Oil Chem. Soc. 85, 961–972 (2008).

17 Lee I, Johnson LA, Hammond EG. Reducing the crystallization temperature of biodiesel by winterizing methyl soyate. J. Am. Oil Chem. Soc. 73, 631–636 (1996).

18 Lee I, Johnson LA, Hammond EG. Use of branched-chain esters to reduce the crystallization temperature of biodiesel. J. Am. Oil Chem. Soc. 72, 1155–1160 (1995).

19 Foglia TA, Nelson LA, Dunn RO, Marmer WN. Low-temperature properties of alkyl esters of tallow and grease. J. Am. Oil Chem. Soc. 74, 951–955 (1997).

20 Soltic P, Edenhauser D, Thurnheer T, Schreiber D, Sankowski A. Experimental investigation of mineral diesel fuel, GTL fuel, RME and neat soybean and rapeseed oil combustion in a heavy duty on-road engine with exhaust gas after treatment. Fuel 88, 1–8 (2009).

21 Fernando S, Hall C, Jha S. NO

x reduction from biodiesel fuels. Energy Fuels 20, 376–382 (2006).

22 Lopez JM, Jimenez F, Aparicio F, Flores N. On-road emissions from urban buses with SCR + urea and EGR + DPF systems using diesel and biodiesel. Transportation Res. D 14, 1–5 (2009).

23 West AH, Posarac D, Ellis N. Assessment of four biodiesel production processes using HYSY. Plant Bioresour. Technol. 99, 6587–6601 (2008).

24 Haas MJ, McAloon AJ, Yee WC, Foglia TA. A process model to estimate biodiesel production costs. Bioresour. Technol. 97, 671–678 (2006).

25 You YD, Shie JL, Chang CY et al. Economic

cost ana lysis of biodiesel production: case in soybean oil. Energy Fuels 22, 182–189 (2007).

26 Canacki M, Sanli H. Biodiesel production from various feedstocks and their effects on the fuel properties. J. Ind. Microbiol. Biot. 35, 431–441 (2008).

27 Angarita EEY, Lora EES, da Casta RE, Torres EA. The energy balance in the palm oil-derived methyl ester (PME) life cycle for the cases in Brazil and Columbia. Renew. Energ. 34, 2905–2913 (2009).

28 Kallivroussis L, Natsis A, Papadakis G. The energy balance of sunflower production for biodiesel in Greece. Biosystems Eng. 81, 347–354 (2002).

29 Pimentel D, Patzek TW. Ethanol production using corn, switchgrass, and wood; biodiesel production using soybean and sunflower. Nat. Resour. Res. 14, 65–76 (2005).

30 Hill J, Nelson E, Tilman D, Polasky S, Tiffany D. Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels. Proc. Natl Acad. Sci. USA 103, 11206–11210 (2006).

31 Sheehan J, Camobrecco V, Duffied J, Grabowski M, Shapouri H. Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus. NREL Final Report SR-580–24089 . National Renewable Energy Laboratory, Goldon, CO, USA (1998).

32 Pradhan A, Shrestha DS, Van Gerpen J, Duffied J. The energy balance of soybean oil biodiesel production: a review of past studies. Trans. ASABE 51, 185–194 (2008).

33 Van Gerpen J. Biodiesel processing and production. Fuel Process. Technol. 86, 1097–1107 (2005).

n Comprehensive review on biodiesel production and processing.
34 O’Brien RD. Fats and oils. In: Formulating and Processing for Applications (3rd Edition)

. CRC Press, Boca Raton, FL, USA, 8–196 (2009).

35 Freedman B, Pryde EH, Mounts TL. Variables affecting the yields of fatty esters from transesterified vegetable oils. J. Am. Oil Chem. Soc. 61, 1638–1643 (1984).

n n Seminal paper on optimum reaction conditions for the production of biodiesel.
36 Rashid U, Anwar F. Production of biodiesel through optimized alkaline-catalyzed transesterification of rapeseed oil. Fuel 87, 265–273 (2008).

37 Rashid U, Anwar F, Arif M. Optimization of base catalytic methanolysis of sunflower ( Helianthus annus ) seed oil for biodiesel production by using response surface methodology. Ind. Eng. Chem. Res. 48, 1719–1726 (2009).

38 Lotero E, Liu Y, Lopez DE, Suwannakarn K, Bruce DA, Goodwin JG Jr. Synthesis of biodiesel via acid catalysis. Ind. Eng. Chem. Res. 44, 5353–5363 (2005).

n Comprehensive review on synthesis of biodiesel using various acid catalysts.

39 Narasimharao K, Lee A, Wilson K. Catalysts in production of biodiesel: a review. J. Biobased Mat. Bioenerg. 1, 19–30 (2007).

n Comprehensive review on homogeneous and heterogeneous acid and base catalysts for production of biodiesel.

40 Canacki M, Van Gerpen J. Biodiesel production via acid catalysis. Trans. ASAE 42, 1203–1210 (1999).

41 Canacki M, Van Gerpen J. A pilot plant to produce biodiesel from high free fatty acid feedstocks. Trans. ASAE 46, 945–954 (2003).

42 Kwiecien J, Hajek M, Skopal F. Combined effect of water and KOH on rapeseed oil methanolysis. Bioresour. Technol. 101, 3121–3125 (2010).
43 Naik M, Meher LC, Naik SN, Das LM. Production of biodiesel from high free fatty acid Karanja ( Pongamia pinnata ) oil. Biomass Bioenerg. 32, 354–357 (2008).

44 Haas MJ. Improving the economics of biodiesel production through the use of low value lipids as feedstocks: vegetable oil soapstock. Fuel Process Technol. 86, 1087–1096 (2005).
45 Sanli H, Canakci M. Effects of different alcohol and catalyst usage on biodiesel production from different vegetable oils. Energy Fuels 22, 2713–2719 (2008).

46 Fr ő hlich A, Rice B. Sources of methyl ester yield reduction in methanolysis of recycled vegetable oil. J. Am. Oil Chem. Soc. 86, 269–275 (2009).
47 Fr ő hlich A, Rice B, Vicente G. Theconversion of low grade tallow into biodieselgrade methyl ester. J. Am. Oil Chem. Soc. 87, 825–833 (2010).Biofuels (2012) 3(2) future science group 208 

### Review Moser

48 Moser BR, Knothe G, Vaughn SF, Isbell TA. Production and evaluation of biodiesel from field pennycress ( Thlaspi arvense L.) oil. Energy Fuels 23, 4149–4155 (2009).

n n Reports the fuel properties of biodiesel prepared from field pennycress oil.
49 Moser BR, Vaughn SF. Coriander seed oil methyl esters as biodiesel fuel: unique fatty acid composition and excellent oxidative stability. Biomass Bioenerg. 34, 550–558 (2010).

50 Sharma YC, Singh B, Korstad J. High yield and conversion of biodiesel from a nonedible feedstock ( Pongamia pinnata ). J. Agric. Food Chem. 58, 242–247 (2010).

51 Rashid U, Anwar F, Moser BR, Knothe G. Moringa oleifera oil: a possible source of biodiesel. Bioresour. Technol. 99, 8175–8179 (2008).

52 Zhou W, Boocock DBG. Phase behavior of the base-catalyzed transesterification of soybean oil. J. Am. Oil Chem. Soc. 83, 1041–1045 (2006).

53 Zhou W, Boocock DBG. Phase distribution of alcohol, glycerol, and catalyst in the transesterification of soybean oil. J. Am. Oil Chem. Soc. 83, 1047–1052 (2006).
54 Boocock DGB, Konar SK, Mao V, Sidi H. Fast one-phase oil-rich processes for the preparation of vegetable oil methyl esters. Biomass Bioenerg. 11, 43–50 (1996).

55 Di Felice R, De Faveri D, De Andreis P, Ottonello P. Component distribution between light and heavy phases in biodiesel processes. Ind. Eng. Chem. Res. 47, 7862–7867 (2008).
56 Knothe G. Improving biodiesel fuel properties by modifying fatty ester composition. Energ. Environ. Sci. 2, 759–766 (2009).

57 Jham GN, Moser BR, Shah SN et al. Wild Brazilian mustard ( Brassica juncea L.) seed oil methyl esters as biodiesel fuel. J. Am. Oil Chem. Soc. 86, 917–926 (2009).

58 Knothe G, Cermak SC, Evangelista RL. Cuphea oil as a source of biodiesel with improved fuel properties caused by high content of methyl decanoate. Energy Fuels 23, 1743–1747 (2009).

59 Schober S, Steidl I, Mittelbach M. Ester content evaluation in biodiesel from animal fats and lauric oils. Eur. J. Lipid Sci. Technol. 108, 309–314 (2006).

60 da Silva RB, Neto AFL, dos Santos LSS et al. Catalysts of Cu(II) and Co(II) ions adsorbed in chitosan used in transesterification of soy bean and babassu oils – a new route for biodiesel synthesis. Bioresour. Technol. 99, 6793–6798 (2008). 61 Moser BR, Cermak SC, Knothe G. Biodiesel from meadowfoam ( Limnanthes alba L.) seed oil: oxidative stability and unusual fatty acid composition. Energy Environ. Sci. 3, 318–327 (2010).

62 Knothe G. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl

esters. Fuel Process Technol. 86, 1059–1070 (2005).

n Reviews the significance of FA composition on fuel properties of biodiesel.
63 Kinney AJ, Clemente TE. Modifying soybean oil for enhanced performance in biodiesel blends. Fuel Process Technol. 86, 1137–1147 (2005).

64 Bondioli P. Nature of some insoluble materials recovered from biodiesel samples. Eur. J. Lipid Sci. Technol. 111, 814–821 (2009).
65 Gunstone FD, Harwood JL. Occurrence and characterization of oils and fats. In: The Lipid Handbook (3rd Edition). Gunstone FD, Harwood JL, Dijkstra AJ (Eds). CRC Press, Boca Raton, FL, USA, 37–142 (2007).

66 Knothe G, Dunn RO. A comprehensive evaluation of the melting points of fatty acids and esters determined by differential scanning calorimetry. J. Am. Oil Chem. Soc. 86, 843–856 (2009).
67 Moser BR, Haas MJ, Winkler JK et al. Evaluation of partially hydrogenated methyl esters of soybean oil as biodiesel. Eur. J. Lipid Sci. Technol. 109, 17–24 (2007).

68 Bouriazos A, Sotiriou, S, Vangelis C, Papadogianakis G. Catalytic conversions in aqueous media. Part 4. Selective hydrogenation of polyunsaturated methyl esters of vegetable oils for upgrading biodiesel. J. Organomet. Chem. 695, 327–337 (2010).
69 Holman RT, Elmer OC. The rates of oxidation of unsaturated fatty acids and esters. J. Am. Oil Chem. Soc. 24, 127–129 (1947).

70 Gunstone FD. The Chemistry of Oils and Fats. Sources, Composition, Properties and Uses. CRC Press, Boca Raton, FL, USA, 150–168 (2004).

71 Moser BR. Comparative oxidative stability of fatty acid alkyl esters by accelerated methods. J. Am. Oil Chem. Soc. 86, 699–706 (2009).

72 Porter NA, Caldwell SE, Mills KA. Mechanisms of free radical oxidation of unsaturated lipids. Lipids 30, 277–290 (1995).

n Comprehensive review on mechanisms of lipid oxidation chemistry.

73 Isbell TA, Abbott TP, Carlson KD. Oxidative stability index of vegetable oils in binary mixtures with meadowfoam oil. Ind. Crops Prod. 9, 115–123 (1999). 74 Knothe G, Steidley KR. Kinematic viscosity of biodiesel fuel components and related compounds. Influence of compound structure and comparison to petrodiesel fuel components. Fuel 84, 1059–1065 (2005).

75 Krisnangkura K, Yimsuwan T, Pairintra R. An empirical approach in predicting biodiesel viscosity at various temperatures. Fuel 85, 107–113 (2006).
76 Knothe G, Steidley KR. Kinematic viscosity of biodiesel components (fatty acid alkyl esters) and related compounds at low temperatures. Fuel 86, 2560–2567 (2007).

77 Yuan W, Hansen AC, Zhang Q, Tan Z. Temperature-dependent kinematic viscosity of selected biodiesel fuels and blends with diesel fuel. J. Am. Oil Chem. Soc. 82, 195–199 (2005).

78 Joshi RM, Pegg MJ. Flow properties of biodiesel fuel blends at low temperatures. Fuel 86, 143–151 (2007).

79 Knothe G, Matheaus AC, Ryan TW 3rd.Cetane numbers of branched and straightchain fatty esters determined in an ignition quality tester. Fuel 82, 971–975 (2003).

80 Tilman D, Socolow R, Foley JA et al. Beneficial biofuels – the food, energy, and environment trilemma. Science 325, 270–271 (2009).

81 Chisti Y. Biodiesel from microalgae. Biotechnol. Adv. 25, 294–306 (2007).

n Important review on biodiesel prepared from microalgae.

82 Ahmad AL, Yasin NHM, Derek CJC, Lim JK. Microalgae as a sustainable energy source for biodiesel production: a review. Renew. Sustain. Energ. Rev. 15, 584–593 (2011).

83 Koh MY, Mohd. Ghazi TI. A review of biodiesel production from Jatropha curcas L. oil. Renew. Sustain. Energ. Rev. 15, 2240–2251 (2011).

84 Juan JC, Kartika DA, Wu TY, Hin TYY. Biodiesel production from jatropha oil by catalytic and non-catalytic approaches: an overview. Bioresour. Technol. 102, 452–460 (2011).

85 Franzke A, Lysak MA, Al-Shehbaz IA, Koch MA, Mummenhoff K. Cabbage family affairs: the evolutionary history of the Brassicaceae. Trends Plant Sci. 16, 108–116 (2011).

86 Haramoto ER, Gallandt ER. Brassica cover cropping for weed management: a review. Renew. Agric. Food Sys. 19, 187–198 (2004).

87 Fahey JW, Zalcmann AT, Talalay P. The chemical diversity and distribution of glucosinolates and isothiocyanates among plants. Phytochemistry 56, 5–51 (2001).

### Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 209 88 Halkier BA, Gershenzon J. Biology and biochemistry of glucosinolates. Annu. Rev. Plant Biol. 57, 303–333 (2006).

89 Griffiths DW, Birch ANE, Hillman JR. Antinutritional compounds in the Brassicaceae – analysis, biosynthesis, chemistry and dietary effects. J. Hort. Sci. Biotech. 73, 1–18 (1998).

90 Isbell TA. US effort in the development of new crops (lesquerella, pennycress, coriander and cuphea). Proc

. J

. Chevreul 16, 205–210 (2009).

91 Vaughn SF, Isbell TA, Weisleder D, Berhow MA. Biofumigant compounds released by field pennycress ( Thlaspi arvense ) seedmeal. J. Chem. Ecol. 31, 167–177 (2005).

92 Zubr J. Oil-seed crop: Camelina sativa

. Ind. Crops Prod. 6, 113–119 (1997).

93 Moser BR. Camelina ( Camelina sativa L.) oil as a biofuels feedstock: golden opportunity or false hope? Lipid Technol. 22, 270–273 (2010).
94 Zubr J, Matthaus B. Effects of growth conditions on fatty acids and tocopherols in Camelina sativa oil. Ind. Crops Prod. 15, 155–162 (2002).

95 Frohlich A, Rice B. Evaluation of Camelina sativa oil as a feedstock for biodiesel production. Ind. Crops Prod. 21, 25–31 (2005).

n n First report on the production of biodiesel from camelina oil. 96 Schuster A, Friedt W. Glucosinolate content and composition as parameters of quality of Camelina seed. Ind. Crops Prod. 7, 297–302 (1998).

97 Patil PD, Gude VG, Deng S. Biodiesel production from Jatropha curcas , waste cooking, and Camelina sativa oils. Ind. Eng. Chem. Res. 48, 10850–10856 (2009).

98 Patil PD, Deng S. Transesterification of Camelina sativa oil using heterogeneous metal oxide catalysts. Energy Fuels 23, 4619–4624 (2009).

99 Patil PD, Gude VG, Deng S. Transesterification of Camelina sativa oil using supercritical and subcritical methanol with cosolvents. Energy Fuels 24, 746–751 (2010).

100 Patil PD, Gude VG, Camacho LM, Deng S. Microwave-assisted catalytic transesterification of Camelina sativa oil. Energy Fuels 24, 1298–1304 (2010).

101 Vaughn SF, Palmquist DE, Duval SM, Berhow MA. Herbicidal activity of glucosinolate-containing seed meals. Weed Sci. 54, 743–748 (2006).

102 Moser BR, Shah SN, Winkler-Moser JK, Vaughn SF, Evangelista RL. Composition and physical properties of cress ( Lepidium sativum L.) and field pennycress ( Thlaspi

arvense L.) oils. Ind. Crops Prod. 30, 199–205 (2009). 103 Sharma N, Cram D, Huebert T, Zhou N, Parkin IAP. Exploiting the wild crucifer Thlaspi arvense to identify conserved and novel genes expressed during a plant’s response to cold stress. Plant Mol. Biol. 63, 171–184 (2007).

104 Daxenbichler ME, Spencer GF, Carlson DG, Rose BG, Brinker AM, Powell RG. Glucosinolate composition of seeds from 297 species of wild plants. Phytochemistry 30, 2623–2638 (1991).

105 Moyer JR, Hironaka R. Digestible energy and protein content of some annual weeds, alfalfa, bromegrass, and tame oats. Can. J. Plant Sci. 73, 1305–1308 (1993).

106 Ullrich I, Jahn-Deesbach W. Proteingehalt und proteinzusammensetzung verschiedener unkrautarten. Angew. Bot. 58, 255–266 (1984).

107 Moser BR. Complementary blending of meadow foam seed oil methyl esters with biodiesel prepared from soybean and waste cooking oils to enhance fuel properties. Energy Environ. Sci. 4, 2160–2167 (2011).



###  Website

201 US EIA. Monthly Energy Review January 2012, Table 10.4 Biodiesel Overview. www.eia.gov/totalenergy/data/monthly/pdf/ sec10_8.pdf