adcancements in solid acid

8/18/2019 Adcancements in Solid Acid

1/24

Correspondence to: Yogesh C. Sharma, Department of Applied Chemistry, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India.

E-mail: [email protected]

© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd

Review

69

Advancements in solid acid

catalysts for ecofriendly andeconomically viable synthesis

of biodiesel

Yogesh C. Sharma and Bhaskar Singh, Banaras Hindu University, Varanasi, India, John Korstad, Oral Roberts

University, Tulsa, OK, USA

Received July 27, 2010; revised version received August 27, 2010; accepted September 9, 2010

View online at Wiley Online Library (wileyonlinelibrary.com); DOI: 10.1002/bbb.253;

Biofuels, Bioprod. Bioref. 5:69–92 (2011)

Abstract: Solid acid (heterogeneous) catalysts have a unique advantage in esterification and transesterification reac-

tions which enhances the use of high acid value oil to be used as feedstock for synthesis of biodiesel. Various solid

acid catalysts such as resins, tungstated and sulfated zirconia, polyaniline sulfate, heteropolyacid, metal complexes,

sulfated tin oxide, zeolite, acidic ionic liquid, and others have been explored as potential heterogeneous catalysts.

The activity of the catalyst differs slightly resulting in moderate to high conversion and yield. The reuse of the solidcatalyst is governed by their deactivation, poisoning, and the extent of leaching in the reaction medium. The applica-

bility of these catalysts for synthesis of biodiesel along with their reusability aspect is discussed in this review.

© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd

Keywords: solid acid catalysts; calcinations; activity; leaching; reuse; biofuels

Introduction

D

evelopment o heterogeneous catalysts has been a

relatively recent area o research in the synthesis o

biodiesel. Te need or development o heterogene-

ous catalysts has arisen rom the act that homogeneous cat-

alysts used or biodiesel development pose a ew drawbacks.

Tese drawbacks include washing o biodiesel with water

to remove the catalyst present which results in wastewater

generation and loss o biodiesel as a result o water washing.

Heterogeneous catalysts have the benet o easy separation

rom the product ormed without requirement o wash-

ing. Reusability o the catalyst is another advantage o the

heterogeneous catalyst.Heterogeneous catalysts are categorized as solid acid and

solid base. Solid base catalysts include a wide group o com-

pounds in the category o alkaline earth meta l hydroxides,

hydrotalcites/layered double hydroxides, alumina loaded

with various compounds, zeolites, and various other com-

pounds showing high basicity coupled with active basic


2/2470 © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 5:69–92 (2011); DOI: 10.1002/bbb

YC Sharma, B Singh, J Korstad Review: Solid acid catalysts for biodiesel synthes

sites, pore size, and other parameters. Solid base catalysts

have been quite successul with high conversion and yield o

biodiesel obtained. However, they are sensitive to the pres-

ence o ree atty acids and thus solid acids have a preerence

over solid base catalysts. Excellent review papers on solid

catalysts are available.1–6 Tis review ocuses exclusively

on solid acid catalysts as potential heterogeneous catalysts

or biodiesel synthesis applied in recent publications. Solid

acid catalysts have been used in various industrial applica-

tions. Te solid acid catalysts differ in acidity, surace area,

mechanical resistance, thermal and hydrothermal stability,

and cost o production. Hence, a catalyst may be chosen

on the requirements needed or synthesis o a compound.

Nevertheless, they indeed are good alternates to the homo-

geneous catalysts such as H2SO4 and HF.5 Heterogeneous

solid acid catalysts can simultaneously catalyze esterica-

tion and transesterication reactions.6 Tus, the application

o such catalysts, which are effi cient in both o these reac-

tions, is preerable as most non-edible oil and waste cooking

oil possesses high acid value that cannot undergo alka line

transesterication without reduction in acid value. In such

eedstock with high acid value, biodiesel synthesis becomes a

two-step process with acid esterication reaction ollowed by

alkaline transesterication. In addition to their easy removal

and reusability, solid acid catalysts do not cause corrosionas ound with common acid homogeneous catalysts, such as

suluric acid. As the heterogeneous catalysts are insoluble

in the oil and methanol phase, they require high tempera-

ture or an optimum yield o biodiesel. Te application o

heterogeneous catalysts or production o biodiesel in the

industrial perspective warrants or minimal energy require-

ment. Tis can be achieved i the heterogeneous catalysts are

prepared easily and need moderate reaction conditions. Te

leaching aspect is another important criterion that governs

the suitability o a particular catalyst. Hence, there is a needor development o heterogeneous catalysts that can produce

biodiesel at conditions (e.g. temperature and pressure) com-

parable to that used in homogeneous catalysis.7 Tis review

deals with the recent publications dealing with catalyst

preparation, operating reaction conditions, reusability, and

easibility o the catalyst.

Solid base catalysts have higher catalytic perormance or

transesterication than solid acid. However, the latter is

preerred over the ormer because o simultaneous esterica-

tion and transesterication or eedstock possessing high

acid value.8

Solid acid catalyst

In general, a catalyst that is to be used or synthesis o

biodiesel should be selective, specic, and result in esteri-

cation/transesterication with high conversion and yield o

biodiesel. A solid acid catalyst should posses high stability,

numerous strong acid sites, large pores, a hydrophobic sur-

ace providing a avorable condition or reaction, and should

also be economically viable.

Resins and membranes

Ion-exchange resins are composed o copolymers o divinyl-

benzene, styrene, and sulonic acid groups grafed on ben-

zene. Teir catalytic activity depends strongly on swelling

properties as swelling capacity controls the reactant’s acces-

sibility to the acid sites and hence their overall reactivity.

Ion-exchange resins have ofen been used or esterication

as well as t ransesterication reactions. Tese ion-exchange

resins have a cross-linked polymeric matrix on which the

active sites or the esterication reaction are due to protons

bonded to sulonic groups.9 Te surace area and pore size

distribution o the resin is characterized by the content othe cross-linking component. Lower cross-linking is known

to cause higher swelling o ion-exchange resins. Swelling

capacity, in turn, controls the reactant’s accessibility to the

acid sites and thereby their total reactivity. Even with a low

swelling capacity, the ion-exchange resin has higher pore

diameter which can let the entrance o ree atty acids (FFAs)

to the inner surace o the catalyst leading to a better esteri-

cation reaction.

Cation exchange resins (NKC-9, 001 × 7 and D61) were

tried by Feng et al.10

and ound to be effective in esterica-tion o high acid value (13.7 mg KOH/g) eedstock o waste

cooking oil (WCO) origin. NKC-9 had high water-adsorbing

capacity avoring its role in effective esterication. A high

average pore diameter o NKC-9 was helpul or reactants to

access the active sites o the resin resulting in greater than

90% conversion. Te reaction conditions were 6:1 (alcohol

to oil) molar ratio, 24 wt% o the catalyst at 64oC or 4 h

o reaction time. Te catalyst NKC-9 urther reused up to


3/24

© 2010 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 5:69–92 (2011); DOI: 10.1002/bbb 71

Review: Solid acid catalysts for biodiesel synthesis YC Sharma, B Singh, J Korsta

10 runs. Te activity o the catalyst in subsequent reuse

did not deteriorate, but rather it was enhanced. Tis has

been attributed to the breakdown o the resin particles by

mechanical agitation, which increased the surace area o

the resin. Afer 10 runs, there was loss o the catalyst dur-

ing separation which ultimately decreased the ree atty acid

(FFA) conversion, so new resin was added. Kitakawa et al .11

tried anion-exchange and cat ion-exchange resins as hetero-

geneous catalysts or batch and continuous transesterica-

tion reaction o triolein in an expanded bed reactor and

ound anion-exchange resin to perorm better than the cat-

ion-exchange resin. Te reason attributed to better perorm-

ance o anion-exchange resin was the higher adsorption

affi nity o alcohol on resin rather than tr iolein. Te lower

cross-linking density and smal ler particle size played more

signicant roles in enhancing the react ion rate than porosity

and caused high reaction and high conversion rates. A high

conversion o 98.8% was achieved with t he optimized reac-

tion conditions. Te catalytic activ ity decreased in the sub-

sequent run due to leaking o hydroxyl ions rom the resin.

A three-step regeneration method was adopted or the reuse

o the catalyst, and or our runs similar activity o the cata-

lyst was achieved. Ozbay et al .12 observed high average pore

diameter with high BE (Brunauer, Emmett, and eller)

surace area to be more effective than high swelling (lowcross-linking level) o ion-exchange resin (Amberlyst-15) in

esterication reaction with waste cooking oil as eedstock.

High pore diameter enabled the ree atty acid molecules

to enter the inner surace o the catalyst and enhance the

esterication rate. Although moderate conditions (60oC and

2% catalyst) were suffi cient or the reaction, the conversion

o FFA to biodiesel was low (45.7%). Tis low conversion is a

limitation o the study and urther enhancement o the reac-

tion conditions is warranted or the easibility o the catalyst

or esterication reaction.Gelular and microporous type ion-exchange resins (EBD

100, EBD 200, EBD 300) were studied by Russbueldt and

Hoelderich13 and ound to be successul or conversion o

high FFA oil to biodiesel. Te catalysts used were EBD-

100 (with gelular polymer matrix), EBD-200 and EBD-300

(microporous resins), and Amberlyst-15. Te low cross-

linking in EBD-100 caused high methanol uptake which

increased the catalyst volume 4.8 times by swelling in

methanol. Te other resins (EBD-200 and EBD-300) had

lower methanol uptake than EBD-100. 100% conversion

was obtained by EBD-100 and EBD-200 catalysts. With

EBD-300, 81% conversion was obtained. Te act ivity o the

catalysts decreased in subsequent runs and to almost negli-

gible in the ourth run. Te possible reason or deactivation

was attributed to the presence o salt contaminants in the

sunower oil which blocked the acid sites. Tus, desalting

the eedstock has been suggested as precursor or the

transesterication o the eedstock with ion-exchange resin

catalysts. Addition o small amounts o water was ound

to have only little inuence on the completion o the reac-

tion as water was trapped in the methanol phase, and not

on the methyl ester in the oil phase, which maintained high

conversion o eedstock to biodiesel.13 A cation-exchange

resin (D002) has been shown to effectively catalyze rapeseed

oil deodorizer distillate o high FFA value o 48.80 ± 1.46

wt% corresponding to acid value o 97.61 ± 1.87 mg KOH/g.

A high yield o 96% was obtained by 18 wt% catalyst at 9:1

alcohol to oil (A:O) molar ratio at 60oC or 4 h in a column

reactor. Te catalyst was reused effectively or 10 cycles with

a yield greater than 88%.14

A solid acid catalyst, poly vinyl alcohol (PVA) cross-linked

with sulosuccinic acid possessing sulonic acid groups or

transesterication o soybean oil, was ound to be effi cientand superior to commercial resins such as Naon membr-

anes and Dowex resins. Higher content o sulonic groups led

to better perormance by the PVA polymer cross-linked with

sulosuccinic acid. Better catalytic activity o PVA has also

been attributed to high swelling capability o PVA in oil and

less in methanol. Due to this, oil concentration was ound to

be more with PVA than with Naon, resulting in higher cata-

lytic activity with PVA as catalyst. Te reverse happened with

Naon membrane as catalyst, where swelling was observed

in methanol but not in soybean oil. Swelling o Naon mem-brane in methanol made the catalyst lipophobic, resulting

in a low reaction rate.15 Dowex monosphere 550 resin has

been effective or esterication and transesterication o oils

with higher FFA content. A conversion o 80% was obtained

at approximately 6:1 A:O molar ratio, 2 wt% catalyst, 45oC,

and 200 rpm stirring. Regeneration o the catalysts afer each

experiment was desired because the conversion was reduced

to 25% afer the rst run. However, a leaching study o the




catalyst wasn’t conducted, which could have provided an

insight into the heterogeneity o the catalyst.16

Te effect o water on the esterication o FFA by solid acid

catalyst has been studied by Park et al .17 Amberlyst-15 was

ound to be poisoned by the presence o water in the reaction

medium and its activity was substantially reduced in com-

parison to the homogeneous suluric acid catalyst. Te pres-

ence o water resulted in poor accessibility o reactants to

the acid sites. Tis was overcome by a two-step esterication

process (addition o resh methanol and cata lyst to the reac-

tants in the second step), which increased the react ion rate

and reduced the reaction time. In the case o H2SO4, pres-

ence o water up to 5 wt% was ound to be tolerable when the

methanol to oil ratio was 6:1.

Te synthesis o biodiesel rom silica unctionalized with

4-ethyl-benzene sulonic acid catalyst was carried out by

Aiba-Rubio et al.18 Leaching was ound to be predominant

in the rst run and slowed down in subsequent runs. A high

temperature o 150oC deterred regeneration o the catalyst

or reuse as the organosulonic acid sites were ound to be

combusted. A signicant difference in the activity o the

catalyst was observed between the rst and second runs,

whereas the reaction rate was ound to be similar or the

second, third, and ourth runs, which suggested that deac-

tivation o the catalyst occurred in the rst run. All o theproducts and reactants in general, and glycerol in particular,

were responsible or leaching o the catalyst. Tis leaching

was dominant in the rst run which has been attributed

either to the loss o active acid sites or activity o acid sites

in ormation o deactivating organic species. Tus, regen-

eration o the catalyst isn’t possible because the organosul-

onic group will be combusted. Ion-exchange resins have

also ound their applicability in purication o biodiesel

when a homogeneous catalyst, sodium methoxide, was

used. Although the ion-exchange resin wasn’t so effi cient inremoval o methanol, it brought the glycerol level to the EN

14214 specication.19 able 1 depicts the reaction conditions

o resins and membranes used as heterogeneous catalysts.

Superacid catalysts (Tungstated and sulfated

zirconia)

Acids that are stronger than Ho = –12 corresponding to

the acid strength o 100% H2SO4 are called ‘super acids’.

Common super acids include HF (a Brønsted acid) and BF3

(a Lewis acid).20 Zirconia has shown catalytic activity, and

also a good support or catalysts, owing to its high thermal

stability, stability under oxidizing and reducing conditions,

and the amphoteric character o its surace hydroxyl groups.

Sulated zirconia and tungstated zirconia are examples o

solid super acids and exhibited high catalytic activities

because o active acid sites.21 ungstated zirconia–alumina

(WZA), sulated tin oxide (SO4/SnO2; SO), and sulated

zirconia–alumina (SZA) were tried as solid super acid cata-

lysts or transesterication o soybean oil and esterication

o n-octanoic acid. More than 90% conversion during trans-

esterication was obtained at a temperature o 250oC with

WZA, with soybean oil as eedstock. During esterication o

n-octanoic acid, the catalysts WZA, SZA and SO showed

94, 99, and 100% conversion at 175oC. Conversion o WZA

and SZA catalyst urther increased to 100% at 200oC.22

Various solid acid catalysts such as Amberlyst-15, Naon-50,

supported phosphoric acid, sulated zirconia (SZ), tungstated

zirconia (WZ), zeolite Hβ, and ES-10 H, along with solid

base catalysts, were compared with that o conventional

homogeneous acid and base catalysts or transesterica-

tion o triacetin by Lopez et al .23 o obtain 50% conversion

with the solid acid catalysts, a large variance in time was

recorded. While only 10 min was needed or 50% conversiono triacetin, the times needed by the solid acid catalysts were

150, 330, 538, and 2047 min or Amberlyst-15, SZ, Naon-50,

and WZ, respectively. Te catalysts showed decrease in

triacetin conversion (40–67%) afer ve reaction cycles o 2 h

each. Te concentration o the species related to active sites

showed 80–95% o the original values and hence the cause

o deactivation was attributed to site blockage by adsorption

o intermediates and/or products ormed that are more polar

than the original reactants.

Esterication o acetic acid and transesterication otriacetin by tungstated zirconia (WZ) were perormed by

Lopez et al .24 Te effect o calcination temperature on the

experiments and the nature o active sites or esterication

and transesterication reaction were observed. When cal-

cined at 400oC, the X-ray diffractogram showed the catalyst

to possess amorphous structure and small crystallites o

tetragonal zirconia. At high ca lcination temperature (500–

800oC), the catalyst was comprised primari ly o tetragonal


5/24



phase o zirconia. At ≥800oC calcination temperature, crys-

talline WO3 particles were ormed. Increase in calcination

temperature resulted in loss o total surace area o the cata-

lyst which was due to loss o surace area o ZrO2 structure.

Tis resulted in transormation o tungsten oxide rom mon-

omeric to polymeric species. Calcination temperature was

ound to strongly inuence activity o the catalyst or both

the esterication and transesterication reactions, with the

optimum at 800oC. Loss o catalytic activity occurred due to

disappearance o heteropolyoxotungstate clusters, suggest-

ing it to be the catalyst active site.

Calcination temperature plays an important role in the

activation o the solid acid catalyst. A pioneering work on

this aspect has been done by Kiss et al .25 where calcination

temperature o 600–700oC has been ound to be optimum

or sulated zirconia catalyst or esterication o atty acids.

Modied zirconias, namely titania zirconia (iZ), SZ, and

WZ, have been used as heterogeneous catalysts or simul-

taneous esterication and transesterication by López

et al .26 Te optimum calcination temperature was ound to

be different or the three modied zirconias. Te optimum

calcination temperature was ound to be 500oC or SZ and

400–500oC or iZ. emperature higher than this results in

sulur loss, which decreases the catalyst’s surace area and

ultimately loss o its activity. Presence o sulate ions stabi-lizes the zirconia structure and increases the surace area.

O the three catalysts, WZ showed better activity over SZ

because o the easy generation o the ormer in the xed bed

reactor. Also, SZ will have to be re-impregnated with H2SO4

or its regeneration which could lead to leaching o sulur

and may be a hindrance in the production o biodiesel. iZ,

although suitable or transesterication, was not ound to be

suitable or esterication because o poisoning o its active

basic sites by carboxylic acids and hence has been reported

to be unsuitable or higher acid value eedstocks.Zirconia-supported isopoly tungstate (WO3/ZrO2) was

prepared by impregnation o ammonium metatungstate, and

was used or transesterication o sunower oil. Another

catalyst, zirconia-supported heteropoly tungstate was pre-

pared by the impregnation o silicotungstic acid and phos-

photungstic acid on zirconium oxyhydroxide. Te activity

o zirconia-supported isopoly tungstate was better than

zirconia-supported heteropoly tungstate. WO3/ZrO2 catalyst

calcined at 750oC gave 97% conversion o the eedstock to

biodiesel at 200oC with 15:1 methanol to oil molar ratio.

Te catalyst was reused successully afer separating and

calcined at 500oC or 3 h in air. Te catalyst was also used

to convert sesame and mustard oil to biodiesel, where con-

version o 93% and 95%, respectively, were obtained. Afer

removal rom the solution o methanol, the catalyst showed

minor conversion o 7% and displayed potential prospect as

a heterogeneous catalyst.27

WO3/ZrO2 was pelletized and used in packed-bed continu-

ous reactor by Park et al.28 or conversion o high FFA eed-

stock. Hexane and biodiesel were ound to be good solvents

to enhance the miscibility o the oil and methanol, resulting

in yield o 65% in 1 h but took substantial time (20 h) to rise

to 85%. However, the conversion decreased thereafer to 65%

when the reaction time was increased to 140 h. Te reason

attributed to this decreased yield with reaction time is the

deposition o soybean oil on the particles o the catalyst and

reduction o WO3 by the eedstock oleic acid. Te catalytic

activity was restored by calcination in air. Pelletized catalyst

resulted in less FFA conversion compared to that rom the

powdered catalyst due to reduced BE surace area and pore

size distribution. Te conversion o 65% was maintained or

140 h. Although Park et al.28 advocate packed-bed reactor or

large scale production o biodiesel using pelletized catalyst,a low yield in comparison to powdered orm deems urther

justication. Leaching o SZ and impact o alcohol on its

deactivation at higher temperature was carr ied out to see its

potential as a heterogeneous catalyst by Suwannakarn et al.29

It was ound that at 100oC almost 70% o the sulate ion

in the orm o sul uric acid was leached rom the solution,

exhibiting homogeneous nature o the catalyst. Te ability

o the sulate to leach rom sulated zirconia was attributed

to the presence o –OH groups in the alcohol. Suluric acid

reacted with alcohol to orm monoalkyl hydrogen sulateand dialkyl sulate.

Sulated zirconia catalysts were prepared using different

methods (such as solvent-ree precipitation) by Garcia et al .30

to examine their act ivity as heterogeneous catalysts. Only SZ

prepared by solvent-ree method gave an effi cient conversion

(98.6% in methanol and 92% in ethanol) o soybean oil to

biodiesel in 1 h reaction time at 120oC. Tis has been attrib-

uted to the high quantity o acid sites. Low conversion with




T a b l e 1 . R e s i n s a n d m e m b r a n e s a s h e t e r o g e n e o u s c a t a l y s t s

.

C a t a l y s t

F e e d s t o c k ,

A c i d v a l u e

M e t h o d o f

p r e p a r a t i o n

C h a r a c t e r i z a

t i o n

C a l c i n a t i o n

R e a c t i o n c o n d i t i o n s

C o n v e r s i o n

( C ) / Y i e l d

( Y ) ( % )

R e f e r e n c e s

T e m p e r a t u r e

( o C ) , t i m e ( h )

M o l a r r a t i o

( a l c o h o l

t o o i l )

R

e a c t i o n

t i m e ( h ) ;

t e m p e r a t u r e

( o C )

C a t a l y s t

a m o u n t

( w t % )

Z e o l i t e , I o n -

e x c h a n g e r e s i n ,

M e t a l o x i d e s

( s u l f a t e d

z i r c o n i a )

D o d e c a n o i c a c i d

S u l f a t e d z i r c o n i a c a t a -

l y s t : 5 0 g Z r O C l 2 . 8 H 2 O

w a s d i s s o l v e d i n

5 0 0 m l w a t e r f o l l o w e d

b y p r e c i p i t a t i o n o f z i r -

c o n i u m h y d r o x i d e a t

p H = 9 u s i n g a m m o n i a

s o l u t i o n . Z r ( O H ) 4 w a s

w a s h e d w i t h w a t e r

t o r e m o v e C l – i o n s .

Z r ( O H ) 4 w a s d r i e d 1 6 h

a t 1 2 0 o C a n d i m p r e g -

n a t e d w i t h 1 N H 2 S O 4

a n d c a l c i n e d i n a i r

S u l f a t e d z i r c o n i a

c a t a l y s t : S u r f a c

e

a r e a = 1 1 8 m

2 g

– 1

S p e c i fi c p o r e v o l u m e

= 0 . 0 9 9 c m

3 g –

1

A v e r a g e p o r e s i z e =

3 . 0 n m

6 5 0 , 3

3 : 1

1 , 1 4 0 – 1 8 0

3 . 0

C = 9 6

4

A m b e r l y s t 1 5 ,

1 6 ; R e l i t e C F S

S o y b e a n

R e s i n s w e r e d r i e d i n a

v e n t i l a t e d o v e n f o r 2 4 h

a t 1 0 0 o C

N o t d o n e

N o t d o n e

8 : 1

3 0 m i n , 1 2 0

5 g

C = 9 5

9

W a s t e f a t t y a c i d s

( O l e i n s ) , 5 0 %

A c i d i t y

C a t i o n -

e x c h a n g e r e s i n

( N K C - 9 , 0 0 1

× 7 , a n d D 6 1 )

W a s t e f r i e d o i l ,

1 3 . 7 m g K O H / g

N K C - 9 w a s w a s h e d

w i t h d e i o n i z e d w a t e r

a n d t r a n s f o r m e d w i t h 1

M H C l .

S u r f a c e a r e a =

7 7

m 2 / g A v e r a g e p

o r e

d i a m e t e r =

5 6 n m

N o t d o n e

6 : 1

4 , 6 4

2 0

C = 9 0

1 0

A n i o n / c a t i o n -


T r i o l e i n ( 6 3 %

p u r i t y ) ; R e s t p a r t

( 3 7 % w a s i m p u -

r i t y & u n r e a c t i v e )

A n i o n i c e x c h a n g e r e s i n

i n c h l o r i d e f o r m w a s

m i x e d w i t h 1 M N a O H

t o d i s p l a c e c h l o r i d e

i o n s w i t h h y d r o x y l i o n s .

N o t r e p o r t e d

N o t d o n e

1 0 : 1

4 , 5 0

4 0 ( i . e .

4 g )

C = 9 8 . 8

1 1

A c i d i c i o n -


( A m b e r l y s t &

D o w e x )

W a s t e c o o k i n g o i l

A c i d i t y = 0 . 4 1 –

0 . 4 7 w t % )

A m b e r l y s t & D o w e x

r e s i n s w e r e d r i e d i n

a n o v e n f o r 1 2 h a f t e r

m e t h a n o l w a s h i n g .

A m b e r l y s t ( A - 1 5 )

S u r f a c e a r e a = 5 3 m

2 / g

A v e r a g e p o r e d

i a m -

e t e r = 3 0 n m

P o r o s i t y = 3 3 %

N o t d o n e

2 0

v o l %

1 0 0 m i n , 6 0

2 . 0

C = 4 5 . 7

1 2

R e s i n i ) G e l u l a r

E B D 1 0 0 i i )

M a c r o p o r o u s

( E B D 2 0 0

E B D 3 0 0 ) i i i )

A m b e r l y s t - 1 5

S u n fl o w e r 0 . 6 %

F F A

R e s i n w a s d r i e d b y

w a s h i n g t h r i c e w i t h

w i t h 1 0 0 m l m e t h a n o l

f o r 1 h b e f o r e u s e .

M i c r o p o r e s i z e

=

1 n m M a c r o p o r e s i z e

= 1 0 0 n m I n n e r

s u r -

f a c e a r e a = 4 0 m

2 / g

S p h e r i c a l p a r t i c

l e o f

s i z e 0 . 5 m m d i a

m e t e r

N o t d o n e

N o t

m e n t i o n e d

2 4 , 1 2 0

1 . 0

C = 1 0 0

1 3

R a p e s e e d 0 . 6 %

F F A

U s e d f r y i n g o i l s

1 5 . 7 % F

F A


7/24



C a t i o n -


( D 0 0 2 , 0 0 2 C R ,

7 3 2 )

R a p e s e e d o i l d e o -

d o r i z e r d i s t i l l a t e ,

4 8 . 8 0 ± 1 . 4 6 w t %

F F A

T h e e x p e r i m e n t a l r e s i n

w a s i m m e r s e d i n 5 %

H C l - e t h a n o l m i x t u r e

s o l v e n t f o r 3 0 m i n . a n d

e l u t e d w i t h e t h a n o l

u n t i l n e u t r a l p H a n d

d r i e d i n a n o v e n a t

7 0 o C f o r 2 h

D 0 0 2 P a r t i c l e s

i z e =

0 . 0 5 m m , C r o s s l i n k -

i n g d e n s i t y = 3 2 %

N o t d o n e

9 : 1

4 , 6 0

1 8 . 0

Y = 9 6

1 4

0 0 2 C R P a r t i c l e

s i z e

= 1 . 2 5 m m , C r o

s s

l i n k i n g d e n s i t y =

3 8 %

7 3 2 P a r t i c l e s i z

e

= 1 . 0 2 m m , C r o

s s

l i n k i n g d e n s i t y = 3 5

± 1 %

P V A 5 , P V A 2 0 ,

P V A S S 2 0 :

c r o s s l i n k e d

w i t h s u l f o s u c -

c i n i c a c i d

S o y b e a n o i l

P V A S S 2 0 m e m b r a n e

w a s p r e p a r e d b y

e s t e r i fi c a t i o n o f 5 - s u l -

f o s a l i c i l i c a c i d o n t h e

r e m a i n i n g h y d r o x y l

g r o u p o f a c r o s s - l i n k e d

P V A m a t r i x

P V A S S 2 0 T h i c

k n e s s

= 0 . 1 4 m m

S w e l l i n g ( % ) i n

m e t h a n o l = 1 8 .

9

N o t d o n e

N o t

m e n t i o n e d

– , 6 0

N o t

m e n t i o n e d

N o t

m e n t i o n e d

1 5

D o w e x m o n o -

s p h e r e 5 5 0 A

I d e a l f r y i n g o i l

( 1 0 % O

l e i c a c i d )

F F A = 1 0 . 6 8 4 %

N o t d o n e

N o t d o n e

N o t d o n e

6 . 1 2 8 : 1

2 , 4 5

2 . 2 6 7

w t %

C = 8 0

1 6

S o y b e a n o i l

S i l i c a f u n c -

t i o n a l i z e d w i t h

4 - e t h y l - b e n -

z e n e s u l f o n i c

g r o u p s

S u n fl o w e r

C o m m e r c i a l g r a d e

P a r t i c l e s i z e = 4 0 – 6 3

µ m

N o t d o n e

6 : 1

5 , 1 5 0

1 . 5 w t %

Y = 6 0

1 8

T a b l e 1 . C o n t i n u e d

C a t a l y s t

F e e d s t o c k ,

A c i d v a l u e

M e t h o d o f


C h a r a c t e r i z a

t i o n



C o n v e r s i o n

( C ) / Y i e l d

( Y ) ( % )

R e f e r e n c e s


( o C ) , t i m e ( h )

M o l a r r a t i o

( a l c o h o l

t o o i l )

R

e a c t i o n

t i m e ( h ) ;


( o C )

C a t a l y s t

a m o u n t

( w t % )




ethanol has been attributed to the presence o 0.44% water

in ethanol compared to 0.08% in methanol. Conversion

with ethanol urther increased to 96% when reaction was

carried out or 6.5 h. However, the limitation observed with

SZ was leaching o sulate ions which resulted in signicant

deactivation o the catalyst when reused. No conversion was

obtained with conventional zirconia, whereas standard sul-

ated zirconia prepared by precipitation and impregnation

method gave a poor conversion o only 8.5 ± 3.8% under the

same conditions.

Lou et al.31 reported on sulated zirconia and niobic acid

(Nb2O5.nH2O) used as catalysts or esterication and trans-

esterication o waste cooking oils with high (27.8 wt%) FFA

content to give a low yield o 44 and 16%, respectively, in

14 h reaction time. WO3/ZrO2, SO42–/ZrO2, and Amberlyst

15 were used as heterogeneous catalysts by Park et al.,32 with

all catalysts giving 93% conversion o FFA-bearing used

cooking oil. However, SO42– was leached in the reaction

medium using SO42–/ZrO2 as catalyst, lessening its applica-

tion as a catalyst. Among the three catalysts, 20 wt% WO3/

ZrO2 showed high catalytic activity and structura l stability.

WOx/ZrO2 in nanoparticle size supported on MCM-41 silica

exhibited acidic properties and was ound to be suitable or

esterication o oleic acid. 100% conversion was obtained

with WO3 loading o 15–20 wt% afer activation at 700oC.Te catalyst was ound to be stable even afer being operated

at 200oC and was reusable or our cycles without leaching o

tungsten. However, the reaction conditions were a problem.

A high molar ratio o 67:1 A:O or 24 h reaction time and

18.7 wt% o catalyst at 65oC was needed or completion o

the reaction. High amount o methanol and high reaction

time increases the overall production cost o biodiesel.33 A

similar loading o WO3 on ZrO2 (i.e. 20 wt%) was observed

to be optimum or 96% FFA conversion rom waste acid oil

by Park et al .34

under optimized reaction conditions, whichincluded 9:1 A:O molar ratio, 0.4 g o catalyst/ml o oil, at

150oC or 2 h. Although tungsten leached in the reaction, the

catalytic activity was unaffected.

Te catalytic activity and stability o sulated zirconia and

sulated titanium oxide were improved by addition o lanth-

anum.35 SO42–/ZrO2–iO2/La

3+ prepared by precipitation

and impregnation method or synthesis o biodiesel showed

95% conversion effi ciency and decreased to only 5% even

afer ve runs. Loading lanthanum on the surace o ZrO2–

iO2 changed the chemical state o exterior atom and also

strengthened the interaction o SO42– with ZrO2–iO2. Te

catalyst was observed to be stable or the purpose o its reuse

and its activity was ound to be better than SO42–/ZrO2–iO2

catalyst. Li et al.36–37 observed the same SO42–/ZrO2–iO2/

La3+ to work effectively or soapstock as eedstock. Te con-

version effi ciency o esterication and transesterication was

ound to be 98.02 and 97.25% respectively, under moderate

reaction conditions. Te catalyst SO42–/ZrO2–iO2/La

3+

was also observed to be effective or simultaneous esterica-

tion and transesterication o oil containing 60 wt% FFAs.

Te catalyst developed was reused or ve times without

any treatment and the yield observed afer ve cycles was

90.20 wt%, which is near the 92.8% yield obtained afer the

rst cycle. Kansedo et al .38 prepared biodiesel rom Cerbera

odollam using sulated zirconia catalyst. Although optimi-

zation o variables affecting the reaction was not taken in

account, a high yield o 83.8% was obtained.

A carbon-based solid acid catalyst was prepared by Shu

et al .39 by carbonizing vegetable oil asphalt and petroleum

asphalt. Te high catalytic activity observed owing to its

high density and stabil ity o acid sites, loose irregular net-

work, and the hydrophobic property o its carbon sheets

that prevented the hydration o –OH groups in the pres-ence o water. Te low surace area o 7.48 m2 g–1 was an

indication that –SO3H groups were in the interior o the

catalyst. Te large pores size o 43.90 nm was helpul or

the reactants to diffuse into the interior o the catalyst.

Increased catalytic activity was observed or the second

run and decreased subsequently in the third run. Increase

in catalytic activity has been attributed to swelling o the

catalyst in the presence o swelling agent. Te leaching o

–SO3H groups was the cause o decreased catalytic activity

in the third run. Leaching o sulate has also been reportedby Petchmala et al.,40 where conversion o eedstock to

methyl esters decreased rom 90.1% to 35.0% in the next

run. Although the catalytic activity o the catalyst can be

restored by re-impregnation with suluric acid and re-

calcination, the leached sul ate in the product may cause

biodiesel to get off-specication. able 2 depicts the reaction

conditions o tungstated and sulated zirconia used as het-

erogeneous catalyst.


9/24




T a b l e 2 . T u n g s t a t e d a n d s u l f a t e d z i r c o n i a a s h e t e r o g e n e o u s

c a t a l y s t s

C a t a l y s t

F e e d s t o c k ,

A c i d v a l u e

M e t h o d o f


C h a r a c t e r i z a t i o n



C o n v e r s i o n

( C ) / Y i e l d

( Y ) ( % )

R e f e r e n c e s


( o C ) , t i m e ( h )

M o l a r r a t i o

( m e t h a n o l

t o o i l )

R e a c

t i o n t i m e

( h ) ; t e m p e r a t u r e

( o C )

C a t a l y s t

a m o u n t

( w t % )

T u n g s t a t e d

z i r c o n i a -

a l u m i n a

( W O 3 / Z r O 2 )

S o y b e a n o i l

n - o c t a n o i c a c i d

M i x t u r e o f h y d r a t e d

z i r c o n i a p o w d e r ,

h y d r a t e d a l u m i n a ,

a q u e o u s a m m o n i u m

m e t a t u n g s t a t e s o l u -

t i o n a n d d e i o n i z e d

w a t e r w a s p r e p a r e d

a n d t h e n k n e a d e d f o r

2 5 m i n . t o s h a p e i n t o

p e l l e t s a n d d r i e d a t

1 3 0 o C a n d c a l c i n e d

N o t d o n e

8 0 0 , 1

4 0 : 1

2 0 , 3 0 0

4 g

C > 9 0

2 2

4 . 5 : 1

2 0 , 2 0 0

4 g

C = 1 0 0

S u l f a t e d

z i r c o n i a a n d

o t h e r M i x e d

m e t a l o x i d e s

D o d e c a n o i c a c i d

F i r s t s t e p :

H y d r o x y l a t i o n o f

z i r c o n i u m , t i t a n i u m ,

a n d t i n c o m p l e x e s

S e c o n d s t e p :

S u l f o n a t i o n w i t h

H 2 S O 4 f o l l o w e d b y

c a l c i n a t i o n i n a i r

Z r O 2 / S O 4 2 – S u r f a c e

a r e a : 1 1 8 m 2 / g ,

p o r e v o l u m e : 0 . 0 9

8

c m 3 / g ; S u l f u r c o n -

t e n t : 2 . 3 %

6 5 0 , 4

3 : 1

1 , 1 3 0 – 1 5 0

3 . 0

C = 9 0 %

2 5

Z i r c o n i a

s u p p o r t e d

i s o p o l y a n d

h e t e r o p o l y

t u n g s t a t e s

( H P A )

S u n fl o w e r ,

S e s a m e , M u s t a r d

Z i r c o n i u m o x y h y d r o x -

i d e w a s p r e p a r e d b y

h y d r o l y s i s o f z i r c o n y l

c h l o r i d e s o l u t i o n a n d

d r i e d a t 1 2 0 o C f o r

1 2 h , p o w e r e d , a n d

a g a i n d r i e d f o r 1 2 h

S u r f a c e a r e a = 7 0

m 2 / g , S u r f a c e d e n

-

s i t y = 6 . 4 W n m 2 ,

A c i d i t y = 2 . 6 0 N H 3

n m 2

7 5 0 , 4

2 0 : 1

5 , 2 0 0

3

C = 9 7

2 7

W O 3 / Z r O 2

( p e l l e t t y p e )

U s e d V e g e t a b l e o i l

Z r O 2 p e l l e t s w e r e

s t e a m e d a t 1 9 0 o C

w i t h a m m o n i u m

m e t a t u n g s t a t e ( a q ) .

T h e m i x t u r e w a s s t i r -

r e r f o r 2 h a n d a f t e r

r e m o v i n g . e x c e s s

w a t e r , i t w a s c a l c i n e d

B E T S u r f a c e a r e a

= 4 0 m 2 / g , A v e r a g

e

p o r e s i z e = 1 1 0 Å

8 0 0 , 5

N o t g i v e n

N o t g

i v e n

N o t g i v e n

C = 7 0

2 8

S - Z r O 2

S o y b e a n o i l

Z r O 2 C l 2 . 8 H 2 O w a s

m i x e d w i t h ( N H 4 ) S O 4

f o r 2 0 m i n . a t 1 : 6

m o l a r r a t i o i n a g a t e

m o r t a r

S - Z r O 2 w a s f o u n d

t o b e a m o r p h o u s ;

B E T s u r f a c e a r e a

=

1 2 6 m 2 / g

6 0 0 , 5

2 0 : 1

1 , 1 2 0

5

9 8 . 6 ( M )

3 0

9 2 . 0 ( E )


11/24



W O 3 / Z r O 2

S o y b e a n o i l ( 4 w t %

o l e i c a c i d )

W O 3 / Z r O 2 w a s p r e -

p a r e d b y i m p r e g -

n a t i n g Z r ( O H ) 4 w i t h

a m m o n i u m m e t a t u n g -

s t a t e s o l u t i o n

W O 3 a n d Z r O 2 w e

r e

c r y s t a l l i n e i n n a t u r e .


. 1

m 2 / g a t 3 0 w t %

W O 3 l o a d i n g .

8 0 0 , N o t g i v e n

9 : 1

2 , 7 5

0 . 2 9 g / m l

o f o i l

C = 9 3

3 2

S O 4

2 – / Z r O 2

S O 4

2 – / Z r O 2 p r e p a r e d

b y d e h y d r a t i o n o f

H 2 S O 4 a n d Z r ( O H ) 4

A m b e r l y s t 1 5

A m b e r l y s t 1 5 w a s o f

c o m m e r c i a l g r a d e

M C M - 4 1

S i l i c a

s u p p o r t e d

W O 3

O l e i c a c i d

S i / Z r m o l a r r a t i o =

5 : 1 , Z r - M C M - 4 1 w a s

s t e a m e d a t 1 9 0 o C

f o r 4 h t o g e n e r a t e

s u r f a c e O H g r o u p s .

T u n g s t e n w a s i n c o r -

p o r a t e d b y i m p r e g n a -

t i o n t e c h n i q u e u s i n g


s t a t e a q . s o l u t i o n a n d

t h e n d r i e d a t 6 0 o C

M e s o p o r o u s

s t r u c t u r e

7 0 0 , 2

6 7 : 1

2 4 , 6 5

1 8 . 7 w t %

C = 1 0 0

3 3

W O 3 / Z r O 2

W a s t e a c i d o i l

( D a r k o i l ) F F A =

5 4 . 9 %

W O 3 / Z r O 2 w a s p r e -

p a r e d b y i m p r e g -

n a t i n g Z r ( O H ) 4 w i t h


s t a t e s o l u t i o n


. 7

m 2 / g P o r e s i z e =

1 3 0 . 1

Å

8 0 0 , 5

9 : 1

2 , 1 5 0

0 . 4 0 g / m l

o f o i l ( 2 0

w t % )

C = 9 6

3 4

S O 4

2 – /

Z r O 2 - T i O 2 /

L a

3 +

R a p e s e e d o i l f e e d -

s t o c k F F A = 2 0 1 . 1

m g K O H / g

T i C l 4 a n d L a ( N O 3 ) 3

w e r e a d d e d t o

a q . s o l u t i o n o f

Z r O C l 2 . 8 H 2 O . C o n c .

N H 4 O H a n d t h e

m i x t u r e w e r e s t i r r e d

v i g o r o u s l y t o p H

9 – 1 0 a n d k e p t f o r

2 4 h . T h e p r e c i p i t a t e

w a s w a s h e d w i t h

d e i o n i z e d w a t e r u n t i l

C l – i n t h e fi l t r a t e w a s

r e m o v e d . T h e c a k e

f o r m e d w a s d r i e d

a t 1 1 0 o C f o r 1 2 h .

T h e p o w e r e d c o m -

p l e x o x i d e w a s t h e n

i m p r e g n a t e d w i t h

0 . 5 M H 2 S O 4 f o r 2 4 h

a n d fi l t e r e d .

5 5 0 , 3

5 , 6 0

5 . 0 w t %

C > 9 5

3 5


C a t a l y s t

F e e d s t o c k ,

A c i d v a l u e

M e t h o d o f





C o n v e r s i o n

( C ) / Y i e l d

( Y ) ( % )

R e f e r e n c e s


( o C ) , t i m e ( h )

M o l a r r a t i o

( m e t h a n o l

t o o i l )

R e a c t i o n t i m e


( o C )

C a t a l y s t

a m o u n t

( w t % )




S O 4

2 – /

Z r O 2 – T i O 2 /

L a

3 +

S o a p s t o c k

N o t g i v e n

N o t g i v e n

N o t d o n e

1 5 : 1

4 , 6 0

5 . 0 w t %

C > 9 5

3 6

S O 4

2 – /

Z r O 2 – T i O 2 /

L a

3 +

A c i d o i l F F A = 6 0

w t % (

1 1 9 . 5 8 m g

K O H / g )

T i C l 4 a n d L a ( N O 3 ) 3

w e r e a d d e d t o

a q . s o l u t i o n o f

Z r O C l 2 . 8 H 2 O . T h e

m i x t u r e a n d N H 4 O H

( c o n c . ) s o l u t i o n w a s

p r e p a r e d b y v i g o r -

o u s l y s t i r r i n g a t p H

9 - 1 0 a n d k e p t f o r

2 4 h . T h e p r e c i p i t a t e

w a s t h e n w a s h e d

w i t h d e i o n i z e d w a t e r

a n d fi l t e r e d u n t i l

C l - i n t h e fi l t r a t e w a s

r e m o v e d . T h e c a k e

o b t a i n e d a f t e r fi l t r a -

t i o n w a s t h e n d r i e d

a t 1 1 0 o C f o r 1 2 h .

T h e p o w d e r e d c o m -

p l e x o x i d e w a s t h e n

i m p r e g n a t e d w i t h

s u l f u r i c a c i d o f 0 . 5 M

f o r 2 4 h a n d fi l t e r e d .

T h e s a m p l e w a s t h e n

d r i e d a n d c a l c i n e d

t o p r e p a r e S O 4

2 – /

Z r O 2 – T i O 2 / L a 3 +

N o t g i v e n

5 5 0 , 3

1 5 : 1

2 , 2 0 0

5 . 0 w t %

Y = 9 0 ; C =

9 6 . 2 4

3 7

S u l f a t e d

z i r c o n i a

a l u m i n a

C e r b e r a .

O d o l l a m

( S e a M a n g o )

N o t g i v e n

N o t g i v e n

4 0 0 , 2 . 5

8 : 1

, 1 8 0

5 . 0 w t %

Y = 8 3 . 8 %

3 8

C a r b o n i z e d

a n d s u l -

f o n a t e d

v e g e t a b l e o i l

a s p h a l t ( V - C -

6 0 0 - S - 2 1 0 )

W a s t e o i l

C a r b o n - b a s e d s o l i d

a c i d c a t a l y s t s w e r e

p r e p a r e d f r o m c a r -

b o n i z e d v e g e t a b l e o i l

a s p h a l t a n d p e t r o -

l e u m a s p h a l t .

S u r f a c e a r e a = 7 . 4 8

m 2 g - 1 A v e r a g e p o

r e

d i a m e t e r = 4 3 . 9 0 n m

N o t d o n e

1 8 . 2 : 1

2 . 5 , 2

6 0

1 . 0 w t %

C = 8 9 . 9 3

3 9

P e t r o l e u m

a s p h a l t c a t a -

l y s t ( P - C -

7 5 0 - S - 2 1 0

a n d P - C -

9 5 0 - S - 2 1 0 )


C a t a l y s t

F e e d s t o c k ,

A c i d v a l u e

M e t h o d o f





C o n v e r s i o n

( C ) / Y i e l d

( Y ) ( % )

R e f e r e n c e s


( o C ) , t i m e ( h )

M o l a r r a t i o

( m e t h a n o l

t o o i l )

R e a c t i o n t i m e


( o C )

C a t a l y s t

a m o u n t

( w t % )


13/24



was ound to esteriy oleic acid and stear ic acid as well.

ungsten HPA catalysts are active or esterication as well

as transesterication reactions. Te activity o the catalyst

was tried in homogeneous as well as heterogeneous media.

Among the homogeneous catalysts were HPA hydrates,

H3PW12O40.25H2O, and H4SW12O40.25H2O. Te heteroge-

neous catalyst used was Cs2.5H0.5PW12O40. Suluric acid had

better activity t han HPA in homogeneous medium, whereas

Amberlyst-15 perormed better than HPA in heterogene-

ous medium. In heterogeneous medium, the HPA catalysts

were leached. Tis can be avoided by severe pre-treatment o

the catalyst, but the resultant activity o the cata lyst will be

affected.48 Heterogenized HPAs such as H3PW12O40/SiO2,

Cs2HPW12O40, and H3PW12O40/SiO2 were studied as cata-

lysts or transesterication o rapeseed oil. Tese catalysts

possessed Brønsted acidity o high strength and catalyt ic

activity, better than H2SO4 and H3PO4, but the acid strength

didn’t necessarily correlate with catalytic activity. Te cata-

lyst was prepared by precipitation steps using precursor

solutions. Te precipitate was recovered by centriugation

and then water washed. Based on the method o preparation,

Cs2HPW12O40 offered good resistance to leaching o active

phase present in the catalyst.49

Te sol-gel hydrothermal method was used to prepare

mesoporous polyoxometalate tantalum pentoxide compositesolid acid catalyst (H3PW12O40/a2O5) and tried or esteri-

cation reaction o lauric acid, which resulted in 99.9% yield

with 7:1 alcohol to oil molar ratio at 78 ± 2oC or 3 h reaction

time. ICP-AES analysis o the reaction solution afer removal

o catalyst conrmed that the catalyst was not leached. Upon

regeneration o the catalyst by boiling ethanol and wash-

ing with hexane overnight, 95.6–94.8% ester yields were

obtained afer successive runs, and its reusability was con-

rmed.50 A heteropoly solid acid catalyst (H4PNbW11O40/

WO3-Nb2O5) has been shown by Katada et al.51

to have highcatalytic activity when used or transesterication o triolein

and methanol/ethanol. Calcination at 500oC gave the best

results. Te high activity o the cata lyst has been attributed

to strong Brønsted acidity, bearing ester yield o 81%. Te

catalyst also worked in the presence o water in 95% ethanol.

Tus, crude alcohol can be used in the reaction, resulting

in lower production costs or biodiesel. Te dissolution o

the catalyst was undetectable or niobium and low (




or tungsten. A xed-bed continuous ow reaction has been

proposed or large-scale production o biodiesel using the

catalyst, with easy separation.

Niobium oxide has been used to impregnate heteropoly

tungstate by Srilatha et al.52 12-tungstophosphoric acid

(PA) was impregnated on niobium oxide or this purpose.

Acid strength was ound to increase with PA content and

was optimum with 25 wt% loading on Nb2O5. A high con-

version o methyl esters (99.1 and 97.3%) were observed

with palmitic acid and sunower oil, respectively with 4 h

reaction time at 65oC. Moderate calcination temperature

o 400oC was adequate or the perormance o the catalyst.

emperatures higher than 400oC or calcination led to deg-

radation o PA to metal oxides, thus decreasing the cata-

lytic activity.

Zhang et al.53 used microwave-assisted transesterica-

tion reaction to produce biodiesel by heteropolyacid cata-

lyst (Cs2.5H0.5PW12O40) rom Xanthoceras sorbifolia oil.

Te method resulted in a high yield (>96%) in only 10 min

o reaction time with 1.0 wt% o oil, 12:1 methanol to oil

molar ratio, at 60oC o optimized reaction conditions. Te

presence o our exchangeable protons and the distribution

o alkal i cation in the Keggin network prompted Pesaresi

et al.54 to try low amount o Cs loading on heteropoly

acid (H4SiW12O40) and ound that Cs loading >0.8 perKeggin resulted in heterogeneous activity o the cata lyst.

A high yield o 99% was obtained using heteropoly acid

(Cs2.5H0.5PW12O40) tried by Li et al.55 or transesterica-

tion o Eruca Sativa oil possessing FFA o 3.5%. Although a

longer reaction time was taken or completion o the reac-

tion, the other variables were moderate such as methanol to

oil molar ratio o 6:1, 85 × 10 –3:1 (catalyst to oil) weight ratio,

at 65oC.

a2O5 has been incorporated on Keggin-type heteropoly

acid by sol-gel co-condensation method by Xu et al.56

as ahybrid catalyst or preparation o biodiesel. Te incorporation

o a2O5 on the heteropoly acid resulted in enhanced activ-

ity o the catalyst. Te hydrophobic nature o the catalyst has

been enhanced by hydrophobic alkyl group such as methyl or

phenyl. Te Keggin structure was ound to disperse homo-

geneously throughout the hybrid catalyst. Te catalyst was

reused or subsequent runs and wasn’t leached in the reaction

medium and was easily desorbed rom the glycerol.

Pure hydropoly (H3PW) ollows the homogeneous catalytic

pathway because o its solubility in ethanol. o make the

catalyst heterogeneous, the heteropoly acid was supported

with zirconia (ZrO2) by Oliveira et al.42 or conversion o

oleic acid to methyl esters taking ethanol as solvent. Te het-

eropoly acid was ound to be well dispersed over the support,

and only the monoclinic phase o ZrO2 was detected. 20 wt%

o H3PW loaded on ZrO2 provided 88% conversion o oleic

acid with 10 wt% o catalyst in with 6:1 A:O molar ratio in

4 h. Some amount o the catalyst (8 wt%) was leached in the

solution. Te catalyst when reused afer washing with n-hex-

ane, drying, and calcination at 300oC or 4 h resulted in 70%

conversion. Silver has been doped over heteropoly acid to

orm AgxH3-xPW12O40, with Ag content varying rom 0.5

to 3 by Zieba et al.43 Te FIR analysis indicated no change

in structure o Keggin anions o the heteropoly acid when

the protons were replaced by the silver cations. With silver

content x > 1, only one phase o silver salt with good crystal-

linity was observed. With silver content x = 0.5, a two-phase

mixture o silver salt and crystalline hydropoly acid was

observed. Te catalyst loading up to x = 1 showed leaching

o the catalyst silver loaded heteropolyacid leading to the

homogeneous pathway reaction. Loading x > 1 resulted in

lowering o homogeneous nature and occurrence o het-

erogeneous pathway. Te homogeneous catalytic activityresulted in gel-type material which had to be immobilized

on a support to make the catalyst. Heteropoly acid has been

used or simultaneous esterication and transesterication

reaction by Baig et al.57 or synthesis o biodiesel. Although

a high temperature o 200oC and a high molar ratio was

adopted, the biodiesel obtained ull led the specications o

ASM. Te reaction condition o heteropolyacids as hetero-

geneous catalysts is given in able 3.

Pyrone complexes with metalsA group o pyrone complexes were used as catalyst by

Abreu et al.58. Sn(3-hydroxy-2-methyl-4-pyrone)2(H2O)2,

Pb(3-hydroxy-2-methyl-4-pyrone)2(H2O)2, Zn(3-hydroxy-

2-methyl-4-pyrone)2(H2O)2 were develop a homogeneous

catalyst or transesterication using various oils. Among

the three pyrone complexes, tin complex showed a com-

paratively high yield o 35.6 and 37.1% with babassu and

soybean oil respectively. Te maximum yield with lead and


15/24



T a b l e 3 . H e t e r o p o l y a c i d s a s

h e t e r o g e n e o u s c a t a l y s t s .

C a t a l y s t

F e e d s t o c k M

e t h o d o f p r e p a r a t i o n




C o n v e r s i o n

( C ) / Y i e l d

( Y ) ( % )

R e f e r e n c e s


( o C ) , t i m e ( h )

M o l a r

r a t i o

( m e t h a n o l

t o o i l )

R e a c t i o n

t i m

e ( h ) ;


( o C )

C a t a l y s t

a m o u n t

( w t % )

H 3 P W

adcancements in solid acid

Documents