Fuel intermediates, agricultural nutrients and pure water from Kappaphycus alvarezii seaweed

Article abstract of DOI:10.1039/c3ra42919a

The present work reports a standalone integrated scheme for the production of 5-hydroxymethyl furfural (HMF) and potassium sulphate (K₂SO ₄) from granular biomass rich in the sulphated polysaccharide, κ-carrageenan. Fresh Kappaphycus alvarezii seaweed was crushed to expel the juice rich in KCl (0.7 m³ t^-1 of fresh seaweed) and granular biomass (0.04 t dry weight per t of fresh seaweed). The latter yielded κ-carrageenan through seawater extraction. HMF was derived from this phycocolloid through reaction with Mg(HSO₄)₂ acid catalyst and isolated in pure form. Galactose was a co-product which remained in the aqueous phase. The aqueous phase was recycled up to 10 times by maintaining a constant acid strength, and utilized thereafter for the recovery of K ₂SO₄. Selective crystallization of K₂SO ₄ was guided by the phase diagram and use was made of a part of the seaweed juice in this process. The spent aqueous phase rich in galactose was subjected to further reaction with HCl obtainable through bipolar electro-dialysis (ED) of seaweed juice. The reaction yielded levulinic acid (LA) and formic acid (FA) in nearly equal proportions. The processing of 1 t of granular biomass was computed to require 30.15 GJ of energy and would yield 0.18 t HMF, 0.056 t LA, 0.020 t FA, 0.27 t K₂SO₄, and 5.77 m³ pure water. The process energy requirement for the scheme can be met from additional supplies of granule (3.35 t). Combustion/gasification of this biomass would yield additionally 0.74 t glaserite fertilizer and the required amount of H₂SO₄ for Mg(HSO₄) ₂ preparation. The Royal Society of Chemistry.

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Paper
Fuel intermediates, agricultural nutrients and pure water from Kappaphycus
alvarezii seaweed
Dibyendu Mondal,a Mukesh Sharma,a Pratyush Maiti,b Kamalesh Prasad,a,b Ramavatar Meena,a,b Arup
K. Siddhanta,a,b Pragnya Bhatt,b Sushma Ijardar,b V. P. Mohandas,b Arup Ghosh,a,b K. Eswaran,b
Bharti G. Shahb and Pushpito K. Ghosha,b*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
The present work reports a standalone integrated scheme for the production of 5-hydroxymethyl furfural (HMF) and potassium sulphate
10 (K2SO4) from granular biomass rich in the sulphated polysaccharide, -carrageenan. Fresh Kappaphycus alvarezii seaweed was crushed
to expel the juice rich in KCl (0.7 m3/t of fresh seaweed) and granular biomass (0.04 t dry weight/t of fresh seaweed). The latter yielded
-carrageenan through seawater extraction. HMF was derived from this phycocolloid through reaction with Mg(HSO4)2 acid catalyst and
isolated in pure form. Galactose was a co-product which remained in the aqueous phase. The aqueous phase was recycled up to 10 times
by maintaining a constant acid strength, and utilized thereafter for the recovery of K2SO4. Selective crystallization of K2SO4 was guided
15 by the phase diagram and use was made of a part of the seaweed juice in this process. The spent aqueous phase rich in galactose was
subjected to further reaction with HCl obtainable through bipolar electro-dialysis (ED) of seaweed juice. The reaction yielded levulinic
acid (LA) and formic acid (FA) in nearly equal proportions. The processing of 1 t of granular biomass was computed to require 30.15
GJ of energy and would yield 0.18 t HMF, 0.056 t LA, 0.020 t FA, 0.27 t K2SO4, and 5.77 m3 pure water. The process energy
requirement for the scheme can be met from additional supplies of granule (3.35 t). Combustion/gasification of this biomass would yield
20 additionally 0.74 t glaserite fertilizer and the required amount of H2SO4 for Mg(HSO4)2 preparation.
55 its known applications, κ-carrageenan has been utilised for
Introduction
ethanol production .12-13 The seaweed also accumulates potassium
from seawater with K+/Na+ selectivity ratio in excess of 350. The
25 Whereas solar energy, wind energy, nuclear energy, hydroelectric
K+ is present as ca. 4 % (w/v) KCl in the juice and as counter ion
power, and geothermal energy can meet the demand for thermal
and electrical energy in part or in full,1-4 the production of liquid
in the polysaccharide.
fuels for sustainable mobility will remain critically dependent on
60
In the course of investigations to improve the ethanol
yield from the granular biomass,13 it was observed that
hydroxymethyl furfural (HMF), formic acid (FA) and levulinic
acid (LA) were formed as impurities during hydrolysis.14a Similar
observation was made by Meinita et al., who investigated the
biomass, even considering the future scenario of partial
30 replacement of conventional vehicles with electro-vehicles and
hybrids. Many types of terrestrial biomass have been used for
this purpose, but the potential of fast growing seaweeds remains
unexploited.5-8 Bioethanol and several other liquid fuels can be
readily produced from this alternative feedstock as essentially the
35 same chemical processes are involved as in the case of land-based
carbohydrate biomass conversion. These conversions typically
involve hydrolysis of polysaccharides to simple sugars and
further conversion of the sugars into ethanol through fermentation
or into other fuels through dehydration, rearrangement/
40 fragmentation and hydrogenation.6 Besides circumventing the
dilemma of land use competition for food and fuel, their
cultivation in the sea can be carried out without inputs of fresh
water, fertilizers and pesticides, and the polysaccharides present
in many cultivable seaweeds are easier to process for fuel than
45 cellulosic biomass.9 Countries such as India which have a long
coastline can better exploit their geographical advantage and look
to the sea for biomass.
65 inhibitory effect of these compounds on fermentation.14b The
production of such compounds may be of greater interest than
production of ethanol.6,15-19 Kim et al. have shown that a mixture
of HMF and LA can be obtained from agar. The process entailed
use of ionic liquid and chromium salt besides a solid acid
70 catalyst.6c The present work reports the production of HMF from
κ-carrageenan using benign Mg(HSO4)2 as catalyst.20,21 Whereas
Eq. 1 shows an idealised reaction with 100 % carbon utilisation
efficiency towards HMF formation, galactose was obtained as
co-product in the study and converted separately into LA and FA.
75 Other useful products – most importantly potassium sulphate
fertilizer
–
accrued from the integrated approach.20 The
neutralized aqueous stream after HMF recovery, along with a part
of the seaweed juice, were utilised for this purpose. Isolation of
K2SO4 formed via the reaction of Eq 2 was guided by the phase
80 diagram of reciprocal salt systems.22 It is proposed that the
process energy requirement can be met from seaweed biomass
itself.
The red seaweed, Kappaphycus alvarezii, is easy to
cultivate, exhibits prolific growth, and sequesters 17-20 t of
50 CO2/hectare/annum.10 One hectare of cultivation can generate
300 t of fresh biomass annually from which 210 m3 (70 % (v/w))
of juice and 12 t (dry basis) of granule (4 % w/w) are obtained.
The former finds application as leaf spray whereas the latter
yields κ-carrageenan, a linear sulphated polysaccharide.11 Besides
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60 concentration in the range of 0.33-0.63 M. The best result was
obtained with 0.48 M catalyst when similar κ-carrageenan
concentration and reaction conditions were adopted. Higher
catalyst concentration led to partial degradation of HMF and/or
competing reactions leading to formation of LA. This
65 concentration was therefore selected for the further studies.
The feasibility of recycling the acidic aqueous layer
Eq 1
Eq 2
K2SO4.MgSO4.6H2O + 2KCl
2 K2SO4 + MgCl2
was studied next, taking 100 g κ-carrageenan (6.1 % (w/w)
moisture content) in 10 lots of 10 g each. After each cycle, the
aqueous layer was extracted with ethyl acetate and the HMF yield
70 and selectivity estimated by HPLC (Figures S4-S5). The total
yield of isolate was 36.05 g, with purity of 92 % based on HPLC
assay. The cycle-wise data are plotted in Figure 1B. It can be
seen that, as observed with H2SO4 (Figure 1A), there was a sharp
rise in the yield of HMF over the first two cycles. Thereafter, the
75 yield was similar with a standard deviation of 0.16 g for cycles
3-10. The residual HMF in the aqueous phase after each cycle
was also analysed directly by HPLC and its amount after cycles 1
and 2 were estimated to be 0.51g and 0.24 g, respectively (Figure
S6). For cycles 3-10 the values ranged from 0.19-0.28 g. Thus
80 whereas in the first cycle, 15.4 % of total HMF remained in the
aqueous phase, there was no such loss in the second cycle as
HMF concentration in aqueous phase was already at the
saturation limit; if anything, its solubility was slightly reduced
due to salting out effect which may have additionally led to some
85 of the HMF from cycle 1 being accounted for in cycle 2. Thus the
substantial difference in the HMF yields between first and second
cycles could be rationalised.
Results and Discussion
5
The granular mass obtained from K. alvarezii comprises cellulose
and -carrageenan present in similar proportions. The hot
aqueous extractive was filtered to separate out the cellulosic
matter and thereafter -carrageenan was isolated through
precipitation with isopropyl alcohol (IPA). The sulphate content
10 was 21.5 % (w/w), which matched well with the expected value
of 22.64 % (w/w) for a structure bearing one sulphate half ester
per repeating unit of pristine -carrageenan (MW = 424). The
potassium content was 7.7 % (w/w) which indicated that the
counter ion for ca. 85 % of the half ester groups of the repeating
15 units was K+, the remaining being Na+ primarily. Characteristic
bands due to 4-sulphate and 3,6-anhydro galactose were seen in
the IR spectrum (Figure S1). Co-production of HMF and K2SO4
in integrated manner from the pristine -carrageenan via Eqs 1
and
2 was considered an attractive proposition and the
20 methodology was formulated accordingly. The residual mass
after recovery of the carrageenan was dried and gave a calorific
value of 14.6 MJ/kg with negligible ash formation.
HMF synthesis
25
A
Although several methods for HMF synthesis have been listed in
a recent review on the subject – including synthesis in ionic
liquids and other non-aqueous media23 – aqueous H2SO4 was
considered initially in the present scheme as it could be obtained
30 through combustion of the granules. This is discussed below. The
H2SO4 concentration was varied from 0.1N to 0.9N and the
reactions were conducted with 5 % (w/v) -carrageenan under
autoclave condition at 105°C (see SI for details, Figure S2). HMF
was recovered through its extraction with ethyl acetate. In
35 comparison to the 100 % carbon utilisation efficiency for the
idealised reaction of Eq 1, the best result obtained was 49% of
isolated HMF at 0.3N acid concentration (Table 1). Lower
concentrations gave less reaction while at higher concentrations
HMF was found to degrade to LA (Figure S3). Maintaining acid
40 concentration thereafter at 0.3N, the reaction time was increased
to 2 h which raised the yield of HMF to 52.6 % with only
marginal drop in selectivity (entry 7, Table 1). Further increase
of the time to 3 h was found to be deleterious (entry 8, Table 1),
due to the degradation of HMF to LA. Thereafter a study was
45 conducted with 0.3N H2SO4 to ascertain recyclability of the
acidic aqueous layer after HMF extraction. The HMF yield rose
in the second cycle and then remained steady till the fifth cycle.
Beyond this, the yield and selectivity dropped markedly (Figure
1A). With the assumption that the decline was due to build up of
50 KHSO4 over the cycles on account of hydrolytic cleavage of the
sulphate moiety in the substrate (Eq 1), it was decided to maintain
the acid concentration constant over the cycles through
neutralization of the excess acid generated. However, since
H2SO4 would be converted to bisulphate during neutralization, a
55 better option would be to use bisulphate catalyst initially itself.
Mg(HSO4)2 was chosen since it was inexpensive to prepare from
H2SO4 and Mg(OH)2 and also to facilitate recovery of K2SO4 (see
K2SO4 recovery section). Table 2 provides data on the reaction
with the above catalyst. HMF formation was sensitive to catalyst
90
B
Fig. 1 Bar diagram of (A) HMF content in ethyl acetate fraction
with 0.3 N H2SO4 as catalyst and reuse of the acidic aqueous
phase and (B) HMF and galactose yield for 10 cycles with reuse
95 of acidic aqueous phase (10g κ-carrageenan was added in each
cycle, catalyst was 200 mL 0.48 M Mg(HSO4)2 and reaction
condition was 105ºC for 1h in autoclave (standard deviation :
0.16 g for cycles 3-10).
2
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Taking the total HMF formation (34.47 g on 100 % purity basis)
results. Under the experimental conditions adopted for HMF
production from -carrageenan, galactose gave virtually no
15 HMF.24This accounted for its steady build up over the 10 cycles
as shown in Figure 1B.
into consideration, the carbon conversion efficiency worked out
to 61.8 %. An attempt was made thereafter to account for the
remaining carbon in -carrageenan. Galactose was found to be a
co-product of the reaction (Figure S7), and it can be seen from
Figure 1B that its concentration grew almost linearly over the 10
cycles. The total amount of galactose formed was estimated to
be 20.84 g corresponding to a carbon utilisation efficiency of 26.1
% on κ-carrageenan basis. Thus the total carbon utilisation
5
A mechanism is proposed in Figure 2 to rationalise the
co-formation of HMF and galactose from -carrageenan in the
relative proportions indicated. As can be seen from the figure,
20 one part of the repeating unit possesses a 1,3 linked α-D-
galactopyranose unit sulphated at the C-4-position whereas the
other part comprises a 1,4 linked strained β-D-3,6-anhydro
galactose unit. On acid induced cleavage of the glycosidic
linkages,6c these two units are assumed to form the
10 towards formation of HMF and galactose was 88.0 %. A second
experiment conducted with 100 g -carrageenan over 10 cycles,
and a third with 120 g -carrageenan over 6 cycles, gave similar
25
Table 1 Data on yield and selectivity of HMF formation from κ-carrageenan in autoclave as a function of H2SO4 concentration
Entry
Amount of feed (κ-
carrageenan) taken
g/(mmol)
Catalyst
H2SO4 (N)
Solvent H2O (mL)
Time (h)
HMF (% of Selectivity of HMF
carbon
utilisation)
in organic part (%)a
1
2
3
4
5
6
7
8
20
20
20
20
20
20
20
20
1
1
1
1
1
1
2
3
NR
<20
49
NR
low
100
68
1/(2.36)
1/(2.36)
1/(2.36)
1/(2.36)
1/(2.36)
1/(2.36)
1/(2.36)
1/(2.36)
0.1
0.2
0.3
0.5
0.7
0.9
0.3
0.3
41
34
54
30
50
52.6
50.8
98
91
aGC selectivity
30
Table 2 Data on yield and selectivity of HMF formation from κ-carrageenan in autoclave as a function of Mg(HSO4)2 concentration
Entry
Amount of feed (κ-
carrageenan) taken g/(mmol)
Solvent H2O
(mL)
Catalyst
Mg(HSO4)2 (M)
Time
(h)
HMF (% of
carbon
Selectivity of HMF in
organic part (%)a
utilisation)
1
2
3
4
5
6
7
2.5/(5.9)
2.5/(5.9)
2.5/(5.9)
2.5/(5.9)
5/(11.8)
5/(11.8)
5/(11.8)
50
50
0.33
0.38
0.43
0.48
0.48
0.53
0.63
1
1
1
1
1
1
1
NR
NR
99
99
99
99
80
78
25.5
32.8
42.3
43
50
50
100
100
100
31
27
35
aGC selectivity
intermediates 1 and 2, respectively. 2 may rearrange to 4 upon
carbocation intermediate 3 which too can generate HMF. The
addition of H2O. Relief of ring strain would provide the driving 45 formation of HMF via the two pathways would explain the
force for the facile conversion of 4 into HMF. 1 can either yield
40 galactose and KHSO4 by pathway (i) or it can give the
greater than 50 % carbon utilisation efficiency from
carrageenan. The criticality of optimizing the acid strength was
-
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on account of the competition among the different pathways and
the hydration/dehydration sequences involved which are strongly
acid sensitive.
10
5
Fig 2 Proposed mechanism of HMF formation from κ-carrageenan
was not pronounced. The mother liquor after recovery of K2SO4
15 Utilisation of aqueous layer
contained the by-product galactose obtained during HMF
50 synthesis and resembled molasses in appearance.
A. K2SO4 recovery
The neutralized spent aqueous phase (0.25 L) obtained from the
experiment with 120 g -carrageenan was found to contain 6.9 g
2-
20 K+, 10.6 g Mg2+ and 50.6 g SO4 as the main inorganic
2-
constituents. SO4 was derived both from the substrate and
catalyst employed, and its total amount was in good agreement
with the expected value of 53.2 g. When expressed in terms of the
concentrations of K2SO4 and MgSO4, the values were computed
25 to be 8.42 and 42.05 mol/1000 mol H2O, respectively (Table S1).
The above composition fell within the schoenite (K2SO4.
MgSO4.6H2O) field in the Lowenherz phase diagram (Figure 3,
point 1). To effect the conversion of Eq 2, seaweed juice was
added into the solution to shift the equilibrium of the composition
30 to K2SO4 field (point 2). Progressive forced evaporation gave 1.5
L of distilled water in total. The water, after treatment through
carbon filter, had a pH of 7.1 and was free of any odour. The
value of total dissolved solids (TDS) was 80 mg.L-1, the TOC
was 17.53 mg.L-1 (the corresponding value for potable water
35 consumed routinely was 32.79 mg.L-1) and the heavy metal
concentration was less than 0.02 ppm. Evaporation of the water
shifted the equilibrium of the composition progressively from
point 2 to point 7 in Figure 3. 66.8 g K2SO4 (73 % yield on
sulphate basis) (Table S1) was obtained and its powder XRD
40 matched well with the standard (Figure S8). Further evaporation
gave a composition which fell in the KCl field (Figure 3, point 8).
The observed trends suggest that the effect of dissolved sugars
55 Fig 3 Experimental data points of composition of spent aqueous
phase after HMF recovery (filled circle 1), after addition of
seaweed juice containing KCl (filled circle 2) and subsequent
evaporation in stages (filled circles 3-8) superimposed on the
Lowenherz representation of the phase diagram at 25oC for
60 reciprocal salt pairs. The orthogonal axes indicate concentrations
of the salts in mol/1000 mol H2O.22
45
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experiment, the flue gas released from combustion of washed
granule at 800oC in a tubular furnace under continuous air flow
was bubbled through 800 mL distilled water. The pH of the water
60 reduced to 2.6 and titration gave an acid strength of 0.0067 N.
B. Levulinic acid synthesis from by-product galactose
The synthesis of LA from cellulose, starch, other polysaccharides
and sugars is well known. 63.1 % yield of LA was reported from
cellulose employing a polymeric ionic liquid.25a Reactions are
also reported with sucrose, starch, cellulose and chitosan, with
yields in the range of 32-46 % employing HCl catalyst.25b-f LA
has also been synthesized from galactose, derived from Gelidium
amansii. A yield of 41.4% was obtained at 160oC using 5 %
H2SO4 catalyst.25g Synthesis of LA from galactose obtained as
5
10 by-product during HMF synthesis from -carrageenan would be
of interest. HCl, which can be obtained from seaweed juice
through bipolar electrodialysis (bipolar ED) (Figure S9), was
selected as the catalyst of choice. An experiment was undertaken
with the neutralized aqueous layer from the experiment of Figure
15 1(B). The solution was desulphated and reacted under autoclave
condition at 105°C for 1h using 2.5 M HCl as catalyst. 11.06 g
LA and 4.02 g FA were obtained in 82.4 % and 76.2 % yield,
respectively, considering the reaction of Eq. 3 (Figure S10). Both
products are valuable commodity chemicals. The two together
20 can also yield
valerolactone, a molecule with diverse
Fig 4 Combustion of granules in a solid fuel fired boiler
applications, including as fuel additive.17 Production of LA from
the galactose present in the molasses after recovery of K2SO4 was
also studied. The isolated yield of LA in ethyl acetate extract was
64.7 %. The aqueous fraction after recovery of LA may be
25 treated to recover Mg(OH)2 required in Mg(HSO4)2 synthesis,
and the filtrate utilised for fortification of the juice.26
65
Eq 3
30
Energy computation
The energy requirement for implementation of the above
processes was computed. Individual data for the different steps
35 are provided in Table 3. It can be seen that, to obtain HMF,
K2SO4, LA, formic acid and pure water in integrated manner,
30.15 GJ of energy would be required per ton of granules
processed. Of this amount, 2.67 GJ can be met from the solid
residue obtained during extraction of -carrageenan. The
40 remaining energy can be sourced from unprocessed granule, with
additional gains as discussed below.
Fig 5 Powder XRD of potash rich fertilizer (two principal phases
were glaserite [K3Na(SO4)2] (A) and K2SO4 (B)) in the form of
70 ash obtained after combustion of dry granules at 550°C. Search
match analysis was performed with high score plus software
using ICDD-JCPDF data base.
Combustion of granules
45 The use of unprocessed granule as fuel is proposed to meet the
process energy requirement (Figure 4). The granules had a
calorific value of 2825 kcal/kg (11.87 MJ/kg) and 3.35 t would be
needed to meet the thermal energy requirement, assuming 65 %
thermal efficiency. Ignition of the granule provided useful
50 products additionally. Ash was obtained in 22 % (w/w) yield and
2-
CO32-, SO4 and Cl- were not detected in any substantial amount
75 whereas SO42- was detected by BaCl2 test after addition of H2O2.
Quantitative measurements gave 0.0256 g SO42-/g of granule. For
the experiment of Figure 1B with 100 g κ-carrageenan, the
requirement of H2SO4 was 18.62 g. The granule amount which
would be needed for process energy is 670 g, yielding 17.52 g
80 H2SO4 through combustion, i.e., the requirement and production
of H2SO4 are closely matched.27 Small amount of electrical
energy required for bipolar ED too can be met from the granule
through controlled gasification. The standalone integrated scheme
for total utilization of fresh K. alvarezii is shown in Figure 6.
85
2-
weight percentages of K, Na and SO4 were 37.3 %, 5.9 % and
55.6 %, respectively, while the chloride amount was negligible.
Its powder XRD revealed a mixed composition of K3Na(SO4)2
(glaserite) and K2SO4, in 9:1 ratio (w/w) (Figure 5). The ash may,
Eq 4
55
therefore, find direct application as K+S fertilizer. In a separate
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Table 3 Computation of input energy for processing of 1 t of K. alvarezii granule into useful products. Calculations were based on the
laboratory scale data.
Sr. no Parameter
Energy requirement (GJ)
Autoclaving of granules followed by separation to obtain ~3.8 %
6.26
1.
solution of pristine κ-carrageenan and solid residue.
Gel pressing to 8 % κ-carrageenan concentration
0.58
7.23
3.13
2.63
2.
3.
4.
5.
Distillation of IPA used for κ-carrageenan precipitation
HMF synthesis from κ-carrageenan
Distillation of EtOAc used for HMF extraction
Multiple effect distillation for K2SO4 production and water recovery
7.8
6.
7.
LA synthesis from molasses
(i) Energy requirement for autoclaving
(ii)Energy requirement for distillation of EtOAC
0.28
0.45
(iii) HCl and KOH production from KCl rich seaweed juice by bipolar 1.79
ED
Total energy requirement for 1-7
30.15
8.
5
Fig 6 Integrated scheme for total utilisation of fresh Kappaphycus alvarezii red seaweed
10
15
20
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Conclusion
55 Experimental Section
The present study set out to demonstrate the production of HMF
and K2SO4 fertilizer from the fast growing cultivable seaweed, K.
alvarezii. The overarching principles adopted while formulating
the strategy may be stated as follows:
General consideration
Reference samples of HMF and LA were purchased from TCI
(Tokyo Chemical Industry Co., LTD), Tokyo, Japan while 98 %
60 H2SO4, 12 N HCl and Mg(OH)2 were purchased from S.D Fine
Chemicals, Mumbai, India. All chemicals were of analytical
grade and were used as received without further purification.
Reagent grade EtOAc and IPA were used in the process whereas
HPLC grade solvents were used for HPLC and GC-MS analysis.
65
5
(1) Realise the full potential of the biomass
(2) Identify and exploit synergies
(3) Avoid chemical inputs which do not form part of the
product portfolio
(4) Generate catalysts as part of the integrated process
(5) Make the operation standalone.
10
Analytical Methods
Calorific value was determined by digital Bomb calorimeter
(Toshibha India). FT-IR spectra of carrageenan were recorded on
a Perkin-Elmer Spectrum GX (FT-IR System, USA) instrument.
70 HMF was characterized by GC-MS and HPLC. GC-MS spectra
were recorded on Shimadzu GC-MS QP 2010. HMF, galactose,
LA and formic acid were quantified by HPLC (Waters Separation
Module 2695, USA) assay. Total sugar concentration present in
the hydrolysate was estimated spectrophotometrically by phenol-
75 sulphuric acid method. Sulphate was estimated gravimetrically;
Cl- was estimated using titration method; sodium and potassium
were estimated by flame photometry. Powder x-ray diffraction
(XRD) measurements were performed on X`pert MPD power X-
ray diffractometer using CuKα radiation operating at 40 KV and
80 30 mA. Data were collected in the range of 2 to 80º 2 with a
step size of 0.05º2 sec. Search match analysis was performed
with high score plus software using ICDD-JCPDF data base.
Total organic carbon content was measured on an Elementar,
Liqui TOC machine.
As would be evident from Figure 6, these objectives
15 were achieved and useful synergies identified while developing
the integrated scheme. Mg(HSO4)2 was found to be a mild and
efficient catalyst for HMF synthesis. It also had a role to play in
K2SO4 recovery from the aqueous stream. Fresh water of desired
quality was a co-product, a portion of which can be recycled in
20 the process. The surplus would be a precious commodity in
water-stressed coastal locations. The aqueous stream additionally
gave LA and FA using HCl as the catalyst. HCl can be generated
from seaweed juice through bipolar ED. The combined carbon
utilisation efficiency was 83.0 % for the formation of HMF, LA
25 and FA from κ-carrageenan. The spent aqueous stream may be
utilised to fortify the seaweed juice having utility as leaf spray.
Controlled combustion of 3.35 t granule per t of granule
processed can provide the thermal energy to drive the integrated
process, besides also yielding H2SO4 and a second potash
30 fertilizer of commercial importance. The former would regenerate
Mg(HSO4)2 through reaction with recycled Mg(OH)2.
Considering overall usage of granule to be 4.35 t, the product
portfolio shown in Table 4 would be obtained. Given that it is
inexpensive to raise the biomass, external inputs of energy and
35 chemicals are minimal, and considering the commercial value of
the products derived, the process should be economically viable
and merits scale up. To process 1 t of granule per day for 0.18 t
HMF and co-products (Table 4) in a bio-refinery, the annual
requirement of granule would be ca. 1590 t, inclusive of the
40 granule amount for process energy. This amount is obtainable
from cultivation over 125-150 hectare in coastal waters. The
small requirement of electrical energy to drive the bipolar ED
process too can be met from the granule through gasification. The
process would thus be self-sustainable. If the challenges of
45 cultivation on large scale can be dealt with successfully, the
scheme proposed offers considerable opportunity to source the
products listed in Table 4 with negligible carbon footprint.
85
Extraction of -carrageenan from granules
250 g of K. alvarezii granules (ca. 8 % moisture content) obtained
from the fresh seaweed after expelling the seaweed juice
mechanically was taken in 5L seawater and autoclaved at 105ºC
90 and 30 kPa pressure for 60 minutes. The contents were hot
centrifuged to obtain 70 g of residue (30.4 % yield on dry granule
basis) having calorific value of 3473 Kcal/kg. 120 g of pristine -
carrageenan having ~8 % moisture content (48.02 % yield w/w)
was obtained from the hot aqueous extract through precipitation
95 with IPA (extract : IPA = 1:2 v/v). The IPA was distilled from the
filtrate and recycled. The moisture content of -carrageenan
varied in the range 6-8 % (w/w).
HMF synthesis from -carrageenan
100
(A) 10 g of -carrageenan was taken in 200 mL of 0.48 M
Mg(HSO4)2 (optimized condition) and autoclaved at 105ºC for 1
h. The product mixture was extracted with ethyl acetate. KHSO4
(3.21 g; 23.6 mmol) released during hydrolysis of -carrageenan
from the previous batch was neutralized with Mg(OH)2 (0.68 g,
105 11.8 mmol) and 10 g of -carrageenan was once again added into
the aqueous phase and the procedure repeated utilising recycled
ethyl acetate for extraction. After 10 cycles, 36.05 g of HMF was
isolated having 92 % purity by HPLC assay. The concentrations
of residual HMF and galactose in aqueous stream were also
110 estimated by HPLC without extraction from the aqueous solution.
The experiment was conducted in duplicate and the results were
comparable.
(B) The experiment at (A) above was repeated with 20 g of
-carrageenan taken in 300 mL of 0.48 M Mg(HSO4)2. 6 cycles
115 were carried out at the end of which 42.5 g of HMF was isolated.
The aqueous phase measuring 250 mL was neutralized with
Mg(OH)2 and the total sugar in it was estimated to be 33.6 g with
80 % galactose. The inorganic constituents in the aqueous phase
Table 4 Details of products and their corresponding amounts
50 obtainable from processing of 1 t of K. alvarezii granule using
3.35 t additional granule as energy source.
Product
Amount
0.18 t
0.056 t
0.020
5-hydroxy methyl furfural
Levulinic acid
Formic acid
Potassium suphate
Glaserite
Leaf spray
0.27 t
0.74 t
68.93 m3
5.77 m3
Fresh water
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DOI: 10.1039/C3RA42P91a9gAe 8 of 9
after neutralization were as follows: K+, 6.9 g; Mg2+, 10.2 g and 65 the combustion experiments, Mr. C. Paliwal determined the
SO42- 50.6 g,
calorific values, and Mr. A. Seth shared useful data for energy
computation. Several suggestions made by the referees were
incorporated in the revised manuscript. DM thanks CSIR for
award of fellowship. The work was supported as an in-house
70 project funded by CSIR, New Delhi.
K2SO4 recovery from neutralized aqueous stream after
extraction of HMF and seaweed juice with simultaneous
production of pure water
5
Recovery of K2SO4 was based on the phase diagram of reciprocal
salts of quaternary system (Figure 3). The concentrations of
K2SO4 and MgSO4 in the neutralized aqueous phase from (B)
above were computed to be 8.42 and 42.05 mol per 1000mol of
10 H2O. Into this solution 1.8 L of seaweed juice containing 4.14 %
(w/v) KCl was added and the contents subjected to progressive
evaporation in a rotavap to recover K2SO4 in pure form.
Affiliation of authors
a AcSIR- Central Salt & Marine Chemicals Research Institute, G.
B Marg, Bhavnagar-364002 (Gujarat), India
75 b CSIR-Central Salt & Marine Chemicals Research Institute,
G.
B Marg, Bhavnagar, 364002, Gujarat, India. E-mail:
pkghosh@csmcri.org ;Fax: +91-278-2567562; Tel: +91-
2782569496
†Electronic Supplementary Information (ESI) available:. See
Levulinic acid synthesis from galactose co-produced during
15 HMF synthesis
The aqueous stream from HMF synthesis was neutralized and
desulphated using CaCl2. 160 mL filtrate containing 20.84 g of
galactose was taken and acidified with concentrated HCl to an
acid strength of 2.5 M HCl and then reacted in an autoclave under
20 similar conditions adopted for HMF synthesis. 11.06 g of
levulinic acid and 4.06 g of formic acid was found to be present
(HPLC assay) in the aqueous layer.
80 DOI: 10.1039/b000000x/
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65
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