chapter 5 dimerization of unsaturated fatty acids/ methyl...
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Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
178
Chapter 5
Dimerization of unsaturated fatty acids/ methyl esters and alkali fusion
of ricinoleic acid
5.1 Background and objectives of investigations
The diverse and significant applications of dimer acids are presented under section
1.4 of Chapter 1. They have some unique properties and the chemical nature of these
acids can alter or modify condensation polymers in reference to elasticity, flexibility,
impact strength, hydrolytic stability, hydrophobicity and lower glass transition
temperatures. Therefore dimer acids present a special niche market area. Sebacic acid
finds variety of industrial uses in the field of plasticizers, lubricants, hydraulic fluids,
cosmetics etc. It is also used for the synthesis of polyester and polyamide and as an
intermediate for antiseptics. 2-Octanol is the feedstock for the production of flavouring
compounds. In spite of excellent commercial potential, the research papers and reports on
synthesis of these renewable oleochemicals are few in number. This reflects the necessity
of additional R & D inputs.
5.1.1 Synthesis and characterization of dimerized unsaturated fatty acids/ esters
The synthesis of dimer acids is subject of many international patents1-2
. The
product, as per patent and commercial literature, is well known in US industries since
1950. On the other hand, the manufacture of dimer acid is yet to commercialize in India,
barring some isolated but unsuccessful attempts e.g. Jayant Agro-organics Ltd., Mumbai.
US industries use tall oil as raw material for manufacture of dimer acid, which is not
available in India. Hence, it is essential to establish the dimer acid manufacturing process
based on indigenous raw materials. Thus DCO (dehydrated castor oil) and soyabean oil,
which are easily available at moderate cost in India, were selected as feedstock for dimer
acid synthesis. Oleic acid which was earlier used as raw material for epoxidation
(Chapter 3), was also examined as feedstock for dimer acid synthesis. High energy
consumption, low yield, poor colour etc. are some of the major drawbacks of clay
catalyzed, high temperature (> 3000C) and high pressure (400 psi) route used for the
industrial production of dimer acids. Hence accomplishment of dimerization at lower
reaction temperature and pressure was the major objective of investigations on acid
activated clay catalysed synthesis of dimer acids from oleic acid/ DCO fatty acids and
soya fatty acids/ methyl esters. Two routes were explored: high pressure clay catalysed
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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dimerization of fatty acids and low pressure clay catalysed dimerization of fatty esters.
The experimental conditions (multistage synthesis, catalyst concentration, reaction period,
temperature, steam pressure etc.) were optimized for higher yield (> 60%) and lighter
Gardner colour (< 5) of dimer acids.
5.1.2 Synthesis and characterization of 2-octanol and sebacic acid by alkali fusion of
sodium ricinoleate
Castor oil is an important non-edible renewable resource which should be
exploited as far as possible so that the edible oils can be freed for human consumption.
This is especially important in developing countries like India where food security poses a
challenge. In many countries with little or no petrochemical feedstock, castor oil will come
in handy as a versatile resource for industrial applications.
There are very few publications on synthesis of sebacic acid by alkali fusion of
castor oil3-6
. The sebacic acid yields were reported to be low. The present study reports
investigations on establishment of suitable reaction conditions and catalysts for alkali
fusion of ricinoleic acid- the principal fatty acid present in castor oil. Different transition
metal oxides were searched for their suitability as alkali fusion catalyst. One of the major
changes in material properties with reduction in size to nanometre range has been the
enormous increase in surface area per unit mass/ volume. The application of this concept
in catalysis, thus, results in production of catalysts of high activity and selectivity. Hence
in present study, zinc oxide was obtained in nano size form by using impinging solution
spray mode of synthesis and the resulting nanomaterial was explored as a catalyst for
alkali fusion of ricinoleic acid.
5.2 Raw materials and chemicals
Oleic acid and ricinoleic acid were procured from s d fine Chem. Ltd., Mumbai
and Jayant Agro-organics Ltd., Mumbai, respectively. Soyabean and castor oil were
purchased from local market. Their fatty acid composition and other characteristics have
been reported in Table 3.1 of Chapter 3. Dehydration of castor oil was carried under
nitrogen atmosphere at 2300C for 2 hrs. It was accomplished by using two different
catalysts: conc. H2SO4 catalysing formation of product designated as DCO-I and
combination of sodium bisulphite and sodium sulphite catalysing the formation of product
designated as DCO-II, respectively. DCO/ soya fatty acids (FA) and methyl esters
(FAME) were prepared using procedure described under section 2.3.1 of Chapter 2.
Table 5.1 presents characteristics of these renewable feedstock.
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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Table 5.1 Physicochemical characteristics of raw materials used for dimerization and
alkali fusion
Feedstock RI AV HV IV
Oleic acid 1.450 193.76 -- 98.20
Methyl oleate 1.4521 1.5 -- -
Soya FA 1.4583 203.5 -- --
Soya FAME 1.4615 0.5
Ricinoleic acid 1.4703 175 150 88.1
DCO FA-I 1.472 205.4 -- 127.3
DCO FA-II 1.4805 204.6 -- 132.5
Catalysts for dimer acid synthesis: Fuller earth (mesh size 100), obtained from s. d. fine-
Chem. Ltd., Mumbai, was subjected to thermal activation at 1100C for 2 hrs and acid
activation by treatment with conc. H2SO4.
Catalysts for alkali fusion of ricinoleic acid: The transition metal oxides examined as
catalysts were lead monoxide, barium sulphate, zinc oxide and nano zinc oxide.
Preparation of nanozinc oxide
Zinc oxide nanoparticles were synthesized by carrying Tween 80 (polyoxyethylene (80)
sorbitan monooleate) stabilized caustic hydrolysis and oxidation of zinc nitrate solution in
impinging solution spray reactor, patented by Mishra and co-workers7. The use of this
reactor, incorporating external mixing two fluid nozzle for atomization of zinc nitrate
solution as well as caustic solution, and the corresponding procedure have been already
described under section 2.3.3 of Chapter 2 for the synthesis of nano lead chrome. Fig.5.1
portrays FESEM image of synthesized nano zinc oxide at a scale of 500 nm and provide
the evidence of the size stabilisation of zinc oxide in nanometer range. The FESEM
analysis in fact, substantiates the superiority of impinging solution spray in providing thin
film oxidation zone and the role played by Tween 80 surfactant in size and morphology
stabilisation of zinc oxide nanoparticles during their synthesis. The EDX spectrum
presented in Fig. 5.2 supported confirmation of zinc oxide formation (Zn and O peak) by
caustic hydrolysis and oxidation of zinc nitrate solution. The nitrogen peak showed
negligible presence.
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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Fig. 5.1 FESEM image of nano zinc oxide
Fig. 5.2 EDX spectrum of nano zinc oxide
5.3 Experimental methodology
5.3.1 Medium pressure clay catalysed dimerization of oleic acids, DCO fatty acids,
and soyabean fatty acids
The feed mixture composed of fatty acids, acid activated clay catalyst and water at specific
ratio, as given under Table 5.2 and Table 5.3, was transferred to a ½ lit high-pressure
stainless-steel autoclave (Amar Engineering, Mumbai) equipped with a magnetic
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motorised drive and an electrical heating system coupled with PID temperature controller.
Air above the reaction mixture was vented by nitrogen flushing under vacuum. Nitrogen
flow and vacuum was discontinued and the pressure vessel was sealed. The reaction
mixture was heated to the desired temperature (190-2500C) and maintained there at for
given period (1-5 hrs). The reaction mixture was cooled to room temperature and the
catalyst was separated from the crude product by filtration through a 60 mm fritted funnel
at 600C in oven. The catalyst residue was washed with acetone (50 ml) to recover the
adsorbed product. The filtrate- polymerized fatty acids were fractionated as monomer
(distillate) and dimer and higher oligomers (residue) by high vacuum distillation under
nitrogen flow. Distillation temperature and vacuum (1-5 mm Hg) were recorded and the
weight of both distillate (monomer) and residue (dimer + trimer) was determined.
Refractive index (RI), TLC (developing solvent- ether:hexane:acetic acid::6:4:1)
and FTIR analysis were used as a qualitative tool for confirmation of dimerization. Colour
of the product was recorded using Gardner colour. In addition, AV, IV and SV
characteristics of the product were recorded.
5.3.2 Clay catalysed dimerization of soyabean FAME and methyl oleate under
nitrogen atmosphere
The feed mixture composed of FAME and clay catalyst (no water was charged) at specific
ratio, as given under Table 5.2 and Table 5.3, was placed into a 500 ml three neck flask
equipped with a magnetic stirrer and an electrical heating system coupled with energy
regulator. After ensuring thorough dispersion of catalyst, nitrogen sparging was initiated
through the mixture followed by heating the reaction mixture to the given temperature
(230-2500C). Constant N2 bubbling rate was maintained throughout the reaction period (5-
6 hrs) and during cooling.
The corresponding results of both processes are recorded in Table 5.2 and Table
5.3.
5.3.3 Synthesis of 2-octanol and sebacic acid by alkali fusion of sodium ricinoleate
Preparation of sodium ricinoleate:
In situ neutralisation of ricinoleic acid was carried out by refluxing the mixture of
ricinoleic acid and 2 N alc. NaOH for 4 hrs in a 500 ml four neck flask equipped with
mechanical stirrer and reflux condenser. The alcohol was thereafter removed under
reduced pressure to obtain sodium ricinoleate.
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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Alkali fusion of sodium ricinoleate
Reaction set up: The reaction assembly consists of 500 ml four neck flask supported with
electrical heating system with energy regulator and mechanical stirrer with speed
controller. One neck carries thermometer pocket to record reaction temperature. The other
neck was connected with Claisen head, spiral condenser with chilled water circulation and
receiver. The thermometer placed in thermometer pocket of claisen head measures the
temperature at which 2-octanol (by product of alkali fusion) gets distilled from the
reaction mixture.
Alkali fusion process: The reactor was charged with sodium ricinoleate, NaOH and heavy
paraffin oil at 2:1:6 wt ratio. The reaction mixture was heated to 2500C and maintained
there at for 6 hrs under distillative set up. TLC [developing solvent- benzene:acetic
acid:water::5:4:1 and visualization of spots using bromocresol green solution under
heating], FTIR and NMR analysis were conducted to assess the completion of the reaction.
2-Octanol was separated from the reaction mixture by in situ distillation.
Separation and purification of sebacic acid from the bottom product: The solid
product from the reactor was diluted with hot water in a glass beaker and acidified to pH
6.0 with conc. hydrochloric acid. The floating oily layer carrying white mineral oil and
monobasic fatty acids was recovered using separating funnel. The remaining aqueous
layer was acidified to pH 2.0 using conc. hydrochloric acid and then cooled. The white
solid was washed with warm water. The sebacic acid was extracted using ethanol and the
solvent was recovered using rotary evaporator. Recrystalization from ethanol afforded the
pure product. Purity of sebacic acid was further confirmed by determining its acid value
and melting point.
5.4 Analytical and Instrumental techniques for characterization of dimer acids, 2-
octanol and sebacic acid
Estimations of Acid value (AV), Hydroxy Value (HV), Iodine Value (IV), and
Saponification Value (SV) were performed using the procedures given under section
2.4.1.1, 2.4.1.2, 2.4.1.3, and 2.4.1.4, respectively of Chapter 2.
Refractive Index (RI): RI analysis of Dimerized products was carried using Abbe
Refractometer.
Colour (Gardner): It was determined by matching visually the colour of the product with
calibrated colour glasses in Gardner Colour Comparator.
FTIR spectroscopy: FTIR analysis was performed using procedure and instrument
described under section 2.4.2.1 of Chapter 2.
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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1HNMR spectroscopy: Model AVANCE III 400 Ascend Bruker, BioSpin International
AG, Switzerland was used for NMR analysis.
FESEM and EDAX: FESEM and EDAX analysis were performed using equipment setup
and procedure outlined under section 2.4.2.6 of Chapter 2.
5.5 Results and discussion
5.5.1 Clay catalysed dimerization of unsaturated fatty acids/ esters
Two different feedstocks were examined, monounsaturated oleic acid and
polyunsaturated soya/ DCO fatty acids. These two feedstocks follow different routes
(Diels Alder route and hydrogen exchange route)8,9
for dimerizations owing to the
differences in number of double bonds. In all, 14 different batches were conducted to
understand the influence of nature of feedstock, reaction temperature (T), holding period
(t) and clay catalyst loading on progress of dimerization.
5.5.1.1 Dimerization of oleic acid/ methyl oleate
Table 5.2 reports results of dimerization of oleic acid and methyl oleate. TLC
analysis, which exhibited 3 distinct spots-monomer, dimer and trimer, iodine value (IV)
and refractive index (RI) analysis formed the basis of understanding of the progress of the
reaction. Retention of acid value (AV) and saponification value (SV) of dimer close to
those of oleic acid indicated the success in control of decarboxylation reactions during
dimerization. There were marked increases in the RI with rise in reaction time t and
temperature T. These increases in RI with t and T are the indicative of rise in the viscosity
and molecular weight with dimerization10,11
. Evaluation of results of batch D1 against
those of D2 reflected the influence of increase in reaction temperature on rise in RI. But
high reaction temperature caused darkening of product. Moreover, slight drop in AV and
SV of dimer acid was observed. Batch D3 was conducted for longer reaction period but
with reduced catalyst quantity. Extended reaction period compensated for lower catalyst
usage as evidenced by slight increase in RI over that of batch D2. Lower catalyst usage
permitted better control of decarboxylation reaction for same steam pressure and higher
yield (lower product loss during filtration). The extended period, on the other hand,
resulted in higher energy requirement. There was also marginal rise in colour due to longer
holding time at high temperature. In order to reduce the energy consumption, two stage
synthesis- first stage of high temperature and second stage of lower temperature (batch
D4) was planned. Dimerization is a two step process8: the first stage is slow
(isomerisation, rearrangement) and requires higher temperature. Second stage is formation
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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Table 5.2 Clay catalysed dimerization of oleic acid and methyl oleate
IV of O.A. = 98.2, RI of O.A. = 1.450, RI of methyl oleate = 1.4521
Dimerization parameters Characterization of crude Dimerized
product
Batch Catalyst
(wt%)
Temp.
(0C)
Time
(hr)
Steam
pressure
(psig)
AV SV IV RI Gardner
Colour
D1 2 220 1 350 186.4 195.1 73.6 1.454 2
D2 2 240 1 520 182.1 192.7 73.2 1.456 5
D3 1.2 240 5 500 188.4 198.5 74.8 1.457 6
D4 1.2
240
(1.5hr),
200 (1hr)
2.5 500-240 181.6 194.4 71.5 1.457 4
D5 (Methyl
oleate) 5 250 6
Under N2
atm. - 187.2 83.8 1.458 1
Fig. 5.3 FTIR overlay spectra of a) oleic acid, b) oleic acid dimer (D4), c) methyl
oleate dimer (D5), d) soya FAME dimer (D9) and e) soya FA dimer (D8)
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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of acyclic dimer; it is relatively fast and could be accomplished at lower temperature. The
overall benefit of two stage synthesis is the reduction in reaction period and improvement
in the product colour while retaining product Characterizations similar to those of batch
D3 (identical RI). Thus batch D4 represented the best optimisation with reference to the
quality of dimer and overall process economics.
Dimerization of methyl oleate required employment of higher reaction temperature
and longer reaction period to attain the similar extent of dimerization. The only advantage
with use of methyl oleate as feedstock for dimerization is the feasibility of conduction of
reaction at atmospheric pressure. The colour of the dimer was also lighter.
FTIR spectra of oleic acid, Dimerized oleic acid and methyl oleate dimer have
been depicted in Fig. 5.3. Oleic acid spectrum showed stretching frequency at 2926 cm-1
and 3005 cm-1
due to =CH- alkene group while spectrum of oleic acid dimer exhibited
2854 cm-1
and 2924 cm-1
corresponding to the -CH- alkane stretching and 1363-1458 cm-1
-CH- alkane bending frequencies. The peak at 1654 cm-1
corresponding to C=C stretching
frequency in oleic acid IR spectrum was disappeared in dimer acid spectrum which
provided the confirmation of the dimerization of oleic acid and methyl oleate.
5.5.1.2 Dimerization of soya fatty acids/ methyl esters and DCO fatty acids
Table 5.3 reports the results of dimerization of soya and DCO fatty acids.
Dimerization of soya fatty acids at 2300C for 3 hrs (batch D6) resulted in yield of dimer at
13% after distillation. Addition of acid activated clay catalyst @ 4% (batch D8)
accelerated the dimerization reaction for same reaction T and t. Thus one observed 80.8%
rise in yield over that for batch D6. There was slight drop in AV. Batch D8 was conducted
at lower reaction temperature of 1900C; other parameters were same as those maintained
for batch D7. The product yield and RI was marginally declined. On the other hand,
improvement in product colour was noticed. Thus when it is essential to obtain better
product colour at reduced energy consumption, batch D8 is preferred to batch D7. Batch
D9, conducted using soya methyl ester, reported lowest dimerization yield (10%) and
lower RI (1.467) in spite of higher catalyst loading and extended reaction period. The
colour of the dimer, however, was superior and distillation of dimer was feasible at lower
temperature. The results on dimerization of soya FAME and methyl oleate have indicated
the necessity of employment of more effective activation of clay catalyst or altogether
different catalyst.
FTIR spectra of dimerized soya fatty acids and FAME have been shown in Fig.
5.3. Replacement of =CH- alkene stretching frequencies by -CH- alkane stretching and -
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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CH- alkane bending frequencies and the disappearance of C=C stretching frequency in
dimer acid IR spectrum proved the formation of dimer.
For similar reaction conditions, dehydrations of castor oil (categorised as A and B),
were accomplished by employing two different sets of dehydration catalysts- conc. H2SO4
and sodium sulphite + sodium bisulphite. Dehydration of castor oil removes hydroxyl
group at 12th
position of ricinoleate in combination with hydrogen at 11th
or 13th
position
yielding, thus, conjugated or nonconjugated double bond configuration, respectively.
Second catalyst accelerated the dehydration of castor oil (DCO-II) for higher RI (higher
conjugation/ trans isomerisation) and IV (more completeness of dehydration) [Table 5.1].
Taking clue from batch D6 (blank reaction for soya FA), dimerization of DCO FA-I was
performed at higher temperature of 2200C for longer duration of 4 hrs (batch D10). It
resulted in enormous rise in yield over batch D6 (353.8%). Besides employment of higher
temperature and extended reaction period, change in feedstock was also responsible for the
increase in dimerization yield. The superiority of DCO over soyabean fatty acids as
dimerization feedstock was primarily due to the presence of conjugated fatty acids in
former feedstock. Diels Alder dimerization of polyunsaturated fatty acids like DCO/ soya
fatty acids is a two step reaction- conjugation (slow, first order rate determining step)
followed by cyclisation to yield dimer (fast, second order reaction)8,9
. D11 and D12
represented two catalyzed short duration process versions of blank run D10: batch D11
employed lower catalyst loading at higher reaction temperature (but lower than blank run
temperature of 2500C) while batch D12 was operated at lower temperature and higher
catalyst loading. The results of the two batches in terms of RI and dimer yield were found
to be identical. Thus the two process variations D11 and D12 provided options to the
manufacturer: either operate at lower temperature and take the benefit of reduced energy
consumption or perform batch at lower catalyst usage and achieve better colour and ease
of filtration. The dimerization of DCO-II was performed at two different catalyst loadings
2% (batch D13) and 4% (batch D14). For same reaction period (t) of 3 hrs and temperature
(T) of 2200C, doubling of catalyst loading permitted rise in dimerization yield by 3.2%.
However the rise in yield was not proportionate and even batch D13 could be explored as
better process option. Comparison of results (RI and % yield) of batch D13 with those of
batch D11 established the supremacy of DCO-II as feedstock over DCO-I; former carried
higher magnitude of unsaturation (high IV) and probably higher conjugation/ trans isomers
as reflected through RI values (Table 5.1). Thus the synergistic combinations of sodium
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
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bisulphite and sulphite exhibited better catalytic effectiveness over conc. H2SO4 in terms
of conjugation isomerisation during dehydration of castor oil.
Thus, the overall results in Table 5.2 and 5.3 demonstrated the control of
decarboxylation at lower steam pressure. DCO fatty acids yielded more dimer than
soyabean fatty acids and oleic acid under similar conditions (catalyst concentration,
temperature, time). Dimerization of DCO fatty acids achieved 60-65% yield at lower
catalyst usage, (2-4%) moderate reaction temperature (1800-230
0C) and shorter duration of
3 hrs. DCO with high conjugation (DCO-II) gave more yield of dimer than one with less
conjugation (DCO-I). Another important consideration is the colour of the dimerized
product. Very marginal colour deepening could be observed at the end of the reaction. The
reaction product at the end of 65% conversion was pale yellow with Gardner colour 7.
This can perhaps be further improved by using appropriate additives such as antioxidants
or carbon bleaching. The results also displayed the diversity of options that manufacturers
can exercise- reduced catalyst loading at higher reaction temperature or lower reaction
temperature at higher catalyst loading. Moreover the results represented the suitability of
indigenous non edible materials such as DCO as feedstock for dimer acid production in
India.
5.5.2 Alkali fusion of sodium ricinoleate
As per the mechanism of alkali fusion of castor oil illustrated under section 1.5 of
chapter 1 (Fig. 1.9), the presence of suitable catalyst, which may work as oxygen donor,
favours the oxidation reaction of aldehyde of decanoic acid. The traditional preparation
process of sebacic acid based on high temperature, red lead catalysed alkali fusion of
ricinoleic acid, due to the use of thinner o-cresol and toxic catalyst lead oxide, shows
serious environmental pollution and toxicity concerns emphasizing the need for
establishment of alternative cleaner process. Moreover the use of red lead catalyst affects
product colour. Accordingly numbers of transition metal compounds were examined as
catalysts. Excess alkali was used to promote sebacic acid. Safer white mineral oil having a
boiling range of 300-4000C was used to reduce the reaction mixtures viscosity and thus
improve mixing. The results of investigations are presented in Table 5.4.
The normally expected theoretical yields of 2-octanol and sebacic acid from alkali
pyrolysis of castor oil containing 84% ricinoleic acid are 35.7 and 43.6%, respectively3.
ZnO exhibited better cracking catalytic effectiveness as shown by the results of batch SB2
(36.7% yield of theoretical output) in comparison to those of uncatalysed batch SB1 (7.6%
yield of theoretical output). The melting point and AV of products were matching to the
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
189
Table 5.3 Clay catalysed dimerization of soya FA/ FAME and DCO FA
Batch
Dimerization parameters Characterization of crude
Dimerized product
Vacuum Distillation parameters and
results
Catalyst
(wt%)
Temp.
(0C)
Time
(hr)
Steam
pressure
(psig)
AV RI Gardner
Colour
Distillation
pressure,
mm Hg
Distillation
Temp, 0C
% yield of dimer and
trimer
Dimerization of soya FA and FAME
D6 0 230 3 120-140 192.6 1.4765 7 0.5 188-190 13
D7 4 230 3 120-140 190.7 1.4783 7 0.5 180-196 23.5
D8 4 190 3 100 190.7 1.4772 5 0.5 180-194 22.6
D9
(FAME) 5 230 4
Under N2
atmosphere
SV
177.5 1.467 1
1-2 160-190 10
Dimerization of DCO FA-I
D10 0 250 4 160 195.0 1.475 7 1-2 180-200 59
D11 2 230 3 140 192.7 1.479 6 0.5 174-188 60
D12 4 180 3 100 193.4 1.479 5 0.5 174-188 60
Dimerization of DCO FA-II
D13 2 220 3 100-110 200.4 1.49 7 1-2 170-210 63
D14 4 220 3 100-110 198.7 1.492 7 0.5 170-202 65
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
190
theoretical values of pure sebacic acid. In a similar manner, other transition metal
compounds such as lead mono-oxide (PbO) and BaSO4 demonstrated moderate catalytic
effectiveness similar to that of ZnO (batch SB2). But the overall results were still lower
than the expected industrial breakeven yields (at least 70.0% yield of theoretical output).
Batch SB3 involved the use of heavy white oil as the diluents and an
environmental friendly nano zinc oxide catalyst. When ZnO was obtained in nanoform
(refer section 5.2 and Fig. 5.1 and 5.2 for further details), the catalytic activity for
oxidation of aldehyde to decanoic acid and selectivity of suppressing the other forward
reaction of hydrogenation of aldehyde were found to be enhanced as demonstrated by the
results. Sebacic acid yield of 79.6% of theoretical output and the purity of 99.0% after
separation and recrystalisation (based on NMR analysis) were attained.
Fig. 5.4 and Fig. 5.5 presented the overlay FTIR and NMR spectra, respectively of
purified sebacic acid obtained from batch SB3. In Fig. 5.4, the band at 1744 cm-1
is
assigned to the C=O stretching vibration of the carboxylic groups of sebacic acid. NMR
spectrum depicted in Fig. 5.5 confirmed the formation of sebacic acid on the basis of
matching of same with NMR of standard sebacic acid. δ 2.3 ppm corresponded to the
proton adjacent to carbonyl group (α proton) while δ 1.6 ppm and δ 1.3 ppm are related to
β proton and γ proton, respectively. δ 0.9 ppm is related to δ protons. Overlay FTIR
spectra of 2- octanol obtained from three different batches (SB1-3) are presented in Fig.
5.6. It displayed the broad peak at 3342 cm-1
corresponding to the stretching frequency of
OH group which thus conformed the formation of 2-octanol.
Table 5.4 Alkali fusion of sodium ricinolate
Diluent:Paraffin oil (Heavy):NaOH:Na ricinoleate::2:1:6
Batch
code
Reaction parameters Characteristics of sebacic
acid
Characteristics of
2-octanol
T, 0C
Time,
hrs
Catalyst
@ 0.5%
by wt.
Acid
value
Melting
point, 0C
% Yield
Boiling
point, 0C
%Yield
SB1 250 6 -- 523 132 2.7 180 2.4
SB2 250 6 ZnO 526 128 13.1 180 9.6
SB3 250 6 nano
ZnO
530 130 28.4 180 20.7
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
191
Fig. 5.4 FTIR overlay of sebacic acid
Fig. 5.5 1HNMR spectrum of sebacic acid (batch SB3)
Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013
192
Fig. 5.6 FTIR overlay of 2-octanol
Thus using nano zinc oxide as the catalyst and heavy white mineral oil as the
diluent, a clean preparation process of sebacic acid by alkaline cracking ricinoleic acid
was established.
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