WO2015136554A1 - Process of spontaneous dewatering of feed solution using salt bitterns as draw solutions - Google Patents
Process of spontaneous dewatering of feed solution using salt bitterns as draw solutions Download PDFInfo
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- WO2015136554A1 WO2015136554A1 PCT/IN2015/000126 IN2015000126W WO2015136554A1 WO 2015136554 A1 WO2015136554 A1 WO 2015136554A1 IN 2015000126 W IN2015000126 W IN 2015000126W WO 2015136554 A1 WO2015136554 A1 WO 2015136554A1
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- WIPO (PCT)
- Prior art keywords
- bittern
- draw solution
- feed
- solution
- draw
- Prior art date
Links
- 239000000243 solution Substances 0.000 title claims abstract description 97
- 238000000034 method Methods 0.000 title claims abstract description 57
- 230000008569 process Effects 0.000 title claims abstract description 51
- 239000012527 feed solution Substances 0.000 title claims abstract description 40
- 150000003839 salts Chemical class 0.000 title claims abstract description 20
- 241000272875 Ardeidae Species 0.000 title abstract description 13
- 230000002269 spontaneous effect Effects 0.000 title description 5
- 238000009292 forward osmosis Methods 0.000 claims abstract description 90
- 241001131796 Botaurus stellaris Species 0.000 claims abstract description 84
- 235000011389 fruit/vegetable juice Nutrition 0.000 claims abstract description 62
- 235000007201 Saccharum officinarum Nutrition 0.000 claims abstract description 53
- 240000000111 Saccharum officinarum Species 0.000 claims abstract description 53
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 claims abstract description 42
- 239000012528 membrane Substances 0.000 claims abstract description 41
- CZMRCDWAGMRECN-UGDNZRGBSA-N Sucrose Chemical compound O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)O[C@@H]1[C@H](O)[C@@H](O)[C@H](O)[C@@H](CO)O1 CZMRCDWAGMRECN-UGDNZRGBSA-N 0.000 claims abstract description 37
- 229930006000 Sucrose Natural products 0.000 claims abstract description 37
- 239000005720 sucrose Substances 0.000 claims abstract description 36
- 230000004907 flux Effects 0.000 claims abstract description 22
- 229910052943 magnesium sulfate Inorganic materials 0.000 claims abstract description 21
- 235000019341 magnesium sulphate Nutrition 0.000 claims abstract description 21
- 230000003204 osmotic effect Effects 0.000 claims abstract description 18
- 230000000694 effects Effects 0.000 claims abstract description 15
- 238000001704 evaporation Methods 0.000 claims abstract description 13
- 239000000470 constituent Substances 0.000 claims abstract description 11
- 239000004952 Polyamide Substances 0.000 claims abstract description 10
- 230000008020 evaporation Effects 0.000 claims abstract description 10
- 229920002647 polyamide Polymers 0.000 claims abstract description 10
- 239000002131 composite material Substances 0.000 claims abstract description 9
- 239000010409 thin film Substances 0.000 claims abstract description 9
- 238000009792 diffusion process Methods 0.000 claims abstract description 8
- 229910052500 inorganic mineral Inorganic materials 0.000 claims abstract description 4
- 235000002639 sodium chloride Nutrition 0.000 claims description 25
- 238000010790 dilution Methods 0.000 claims description 15
- 239000012895 dilution Substances 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 10
- 238000010612 desalination reaction Methods 0.000 claims description 8
- 238000011084 recovery Methods 0.000 claims description 7
- 239000011780 sodium chloride Substances 0.000 claims description 7
- 239000012267 brine Substances 0.000 claims description 4
- 239000012452 mother liquor Substances 0.000 claims description 4
- 238000001223 reverse osmosis Methods 0.000 claims description 4
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims description 4
- 238000011282 treatment Methods 0.000 claims description 4
- 239000003610 charcoal Substances 0.000 claims description 3
- 238000000926 separation method Methods 0.000 claims description 3
- 238000005406 washing Methods 0.000 claims description 3
- 230000009467 reduction Effects 0.000 claims description 2
- 230000008929 regeneration Effects 0.000 claims description 2
- 238000011069 regeneration method Methods 0.000 claims description 2
- 239000002689 soil Substances 0.000 claims description 2
- 235000010755 mineral Nutrition 0.000 abstract description 2
- 239000011707 mineral Substances 0.000 abstract description 2
- 229960004793 sucrose Drugs 0.000 description 34
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 14
- 238000002474 experimental method Methods 0.000 description 14
- 241000609240 Ambelania acida Species 0.000 description 7
- 239000010905 bagasse Substances 0.000 description 7
- 230000008901 benefit Effects 0.000 description 7
- 229910001629 magnesium chloride Inorganic materials 0.000 description 7
- 239000013535 sea water Substances 0.000 description 5
- 239000003337 fertilizer Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
- 238000004821 distillation Methods 0.000 description 3
- 239000013505 freshwater Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 229940072033 potash Drugs 0.000 description 3
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Substances [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 3
- 235000015320 potassium carbonate Nutrition 0.000 description 3
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Substances BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 description 2
- 229910052794 bromium Inorganic materials 0.000 description 2
- 235000010633 broth Nutrition 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000000855 fermentation Methods 0.000 description 2
- 230000004151 fermentation Effects 0.000 description 2
- -1 ionic strength (I) Substances 0.000 description 2
- 229920002492 poly(sulfone) Polymers 0.000 description 2
- 239000001103 potassium chloride Substances 0.000 description 2
- 235000011164 potassium chloride Nutrition 0.000 description 2
- 230000003389 potentiating effect Effects 0.000 description 2
- 238000012552 review Methods 0.000 description 2
- 235000020374 simple syrup Nutrition 0.000 description 2
- 229910021653 sulphate ion Inorganic materials 0.000 description 2
- WZCQRUWWHSTZEM-UHFFFAOYSA-N 1,3-phenylenediamine Chemical compound NC1=CC=CC(N)=C1 WZCQRUWWHSTZEM-UHFFFAOYSA-N 0.000 description 1
- HNSDLXPSAYFUHK-UHFFFAOYSA-N 1,4-bis(2-ethylhexyl) sulfosuccinate Chemical compound CCCCC(CC)COC(=O)CC(S(O)(=O)=O)C(=O)OCC(CC)CCCC HNSDLXPSAYFUHK-UHFFFAOYSA-N 0.000 description 1
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 description 1
- 238000012695 Interfacial polymerization Methods 0.000 description 1
- 208000009989 Posterior Leukoencephalopathy Syndrome Diseases 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- UWCPYKQBIPYOLX-UHFFFAOYSA-N benzene-1,3,5-tricarbonyl chloride Chemical compound ClC(=O)C1=CC(C(Cl)=O)=CC(C(Cl)=O)=C1 UWCPYKQBIPYOLX-UHFFFAOYSA-N 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 239000002274 desiccant Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910052564 epsomite Inorganic materials 0.000 description 1
- IDGUHHHQCWSQLU-UHFFFAOYSA-N ethanol;hydrate Chemical compound O.CCO IDGUHHHQCWSQLU-UHFFFAOYSA-N 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000005048 flame photometry Methods 0.000 description 1
- 235000013305 food Nutrition 0.000 description 1
- 238000009432 framing Methods 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000003306 harvesting Methods 0.000 description 1
- 238000004128 high performance liquid chromatography Methods 0.000 description 1
- 239000012510 hollow fiber Substances 0.000 description 1
- 238000009616 inductively coupled plasma Methods 0.000 description 1
- 238000004255 ion exchange chromatography Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229940018564 m-phenylenediamine Drugs 0.000 description 1
- WRUGWIBCXHJTDG-UHFFFAOYSA-L magnesium sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Mg+2].[O-]S([O-])(=O)=O WRUGWIBCXHJTDG-UHFFFAOYSA-L 0.000 description 1
- BMQVDVJKPMGHDO-UHFFFAOYSA-K magnesium;potassium;chloride;sulfate;trihydrate Chemical compound O.O.O.[Mg+2].[Cl-].[K+].[O-]S([O-])(=O)=O BMQVDVJKPMGHDO-UHFFFAOYSA-K 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000009285 membrane fouling Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000010079 rubber tapping Methods 0.000 description 1
- 238000013341 scale-up Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 238000005382 thermal cycling Methods 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C13—SUGAR INDUSTRY
- C13B—PRODUCTION OF SUCROSE; APPARATUS SPECIALLY ADAPTED THEREFOR
- C13B20/00—Purification of sugar juices
- C13B20/16—Purification of sugar juices by physical means, e.g. osmosis or filtration
- C13B20/165—Purification of sugar juices by physical means, e.g. osmosis or filtration using membranes, e.g. osmosis, ultrafiltration
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L2/00—Non-alcoholic beverages; Dry compositions or concentrates therefor; Their preparation
- A23L2/02—Non-alcoholic beverages; Dry compositions or concentrates therefor; Their preparation containing fruit or vegetable juices
- A23L2/08—Concentrating or drying of juices
- A23L2/082—Concentrating or drying of juices by membrane processes
- A23L2/085—Concentrating or drying of juices by membrane processes by osmosis, reverse osmosis, electrodialysis
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L2/00—Non-alcoholic beverages; Dry compositions or concentrates therefor; Their preparation
- A23L2/70—Clarifying or fining of non-alcoholic beverages; Removing unwanted matter
- A23L2/72—Clarifying or fining of non-alcoholic beverages; Removing unwanted matter by filtration
- A23L2/74—Clarifying or fining of non-alcoholic beverages; Removing unwanted matter by filtration using membranes, e.g. osmosis, ultrafiltration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/002—Forward osmosis or direct osmosis
- B01D61/005—Osmotic agents; Draw solutions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/56—Polyamides, e.g. polyester-amides
-
- C—CHEMISTRY; METALLURGY
- C13—SUGAR INDUSTRY
- C13B—PRODUCTION OF SUCROSE; APPARATUS SPECIALLY ADAPTED THEREFOR
- C13B35/00—Extraction of sucrose from molasses
- C13B35/08—Extraction of sucrose from molasses by physical means, e.g. osmosis
Definitions
- the present invention relates to a process of extensive dewatering of sugarcane juice using bittern as draw solution through forward osmosis (FO).
- the present invention provides use of such abundant bittern as benign and potent draw solution in forward osmosis (FO).
- the invention relates to tapping the pent-up energy in these bitterns by virtue of their low water activity and high osmotic coefficients - for spontaneous dewatering of feed solutions.
- the invention relates to extensive dewatering of sugarcane juice coupled with the production of pure Epsom salt from the exhausted bittern to maximize gains.
- sucrose sucrose
- sucrose sucrose
- the raw juice expelled from the cane contains 9-12% (w/v) sucrose.
- the juice is stabilized to prevent decay, clarified to remove suspended solids, and then subjected to multiple effect evaporation to obtain sugar syrup containing50-60% sucrose by weight. Further concentration under vacuum yields a supersaturated solution, from which sucrose is crystallized upon seeding. Thermal energy for the process is largely met from bagasse.
- the main object of the present invention is to provide a process of extensive dewatering of sugarcane juice using bittern as draw solution through forward osmosis (FO).
- Another object of the present invention is to demonstrate a process of FO employing highly potent, abundant, cost-effective and benign sea bittern as draw solution.
- Another object is to employ high flux thin film composite polyamide membranes in the process.
- Another object is to achieve substantial energy saving through such a process.
- Another object is to concentrate the sugarcane juice to a similar level as obtained in the first stage of the conventional process employing multiple effect evaporation.
- Another object is to minimise exposure of feed to high temperatures.
- Another object is to demonstrate that sucrose loss in the process is minimal.
- Another object is to demonstrate that back diffusion of inorganic constituents from bittern to sugarcane juice is minimal.
- Another object is to utilize clarified juice so as to minimise fouling of the membrane.
- Another object is to show that simple water washing of the membrane restores the initial flux almost to its original value.
- Another object is to recover Epsom salt in purer form from the diluted bittern obtained in the course of FO.
- the present invention provides a process of dewatering of sugarcane juice through forward osmosis (FO) employing wasted salt bittern (mother liquor after separation of common salt) as draw solution wherein the said process comprising the steps of:
- bittern may be of natural origin or derived from sea-, lake- or sub-soil brine and having density in the range of 28-38 °Be with viscosity ( ⁇ ) in the range of 3-1 13 cP and osmotic coefficient in the range of 1.4-3.3;
- the temperature of feed solution was in the range of 15-45 °C and the inlet pressure at the feed side was 0.5-2.0 bar.
- the sugarcane juice had an initial concentration of sucrose in the range of 8-12% (w/v) and a final concentration of 15-60%) (w/v) after forward osmosis.
- the average flux during forward osmosis was in the range of 5- 15 L/(rri h).
- the loss of sucrose from feed solution to draw solution was 1-3 % (w/v).
- Figure 1 showed the photographic image of FO assembly used in the present invention.
- the present invention provides a process of FO employing sea bittern as draw solution, sugarcane juice as feed solution, and suitable membrane as solute barrier, the process comprising the following steps:
- salt bitterns are a source of pent-up energy by virtue of their low water activity and high osmotic coefficient.
- J n is the flux (L/(m 2 h))
- V t o and F tn are the volumes (L) of feed solution at zero time and at time interval n, respectively
- A is area (m 2 ) of the membrane.
- This example teaches the general FO process used in the present invention using sugarcane juice as feed and bittern as draw solution.
- the compositions and relevant physical properties are shown in Table 1 .
- Table 1 Chemical composition, ionic strength (I), water activity (w a ), osmotic coefficient ( ⁇ ) and viscosity ( ⁇ ) of the seawater bittern used in the FO studies cp (% w/v) M
- the raw juice was clarified by treating with 2 % activated charcoal followed by filtering, and the pH adjusted to ca. 8 through treatments with lime water.
- Thin film composite (TFC) polyamide membrane was used in FO experiments.
- the membrane comprised a polysulfone supporting layer and a polyamide skin layer prepared by interfacial polymerization of m-phenylenediamine and trimesoyl chloride.
- the membrane When operated in reverse osmosis mode for desalination of 2000 ppm aqueous NaCl feed, the membrane gave a flux of 26.45 L/(m 2 h) and salt rejection of 94.9% at 5 bar operating pressure.
- FO experiments were conducted with the same membrane in the FO set up shown in Figure 1.
- the active area of the flat sheet membrane was 0.0057 m .
- Membrane active layer facing both feed solution and draw solution was similar (5.3 cm x 10.7 cm) throughout all experiments and cross flow velocity was calculated to be 0.283 m s "1 .
- the ration of draw solution to feed solution was varied from 1 : 5 to 8: 1. After circulation for 3-5h the FO process was terminated.
- the bittern sample of Table 1 contains 21 % (w/v) of MgCl 2 as the principal constituent and other salts additionally.
- Two FO experiments were conducted with pure water as feed: In one experiment bittern was used as draw solution while in the other experiment a 21 % (w/v) pure MgCl 2 solution was used as draw. Whereas the
- the above objective is thermodynamically feasible in view of the reported values of 2.26 and 1 .05 of the osmotic coefficients of the bittern of Table 1 and 40 % sugarcane juice, respectively.
- This example teaches four-fold concentration of sucrose in sugarcane juice and 10% dilution of the bittern of Table 1 used as draw solution, taking 8:1 draw solution to feed solution ratio.
- sucrose concentration in draw solution was estimated after the experiment under Example 5. Loss of sucrose in the draw solution was estimated to be 1.8 %.
- Example 7 [0058] Back diffusion of salts from draw solution to feed solution may decrease the net osmotic pressure across the membrane and also affect adversely the further processing of the concentrated sugarcane juice. Accordingly, an assessment was made of Na + , K + , Mg 2+ , Ca 2+ Cl " , and S0 4 2" in the initial sugarcane juice and final sugarcane juice after FO experiment of Example 5.
- Clarified sugarcane juice contained 0.0064 % Na + , 0.016 % K + , 0.061 % Ca 2+ , 0.017 % Mg 2+ , 0.11 % CI " , and 0.068 % S0 4 2" before FO run and 0.103 % Na + , 0.01 % K + , 0.077 % Ca 2+ , 0.036 Mg 2+ , 0.36 % CI " , and 0.14 % S0 4 2" after FO run.
- Example 5 The experiment of Example 5 was repeated after rinsing the membranes thoroughly with de-ionized water. The decline in the initial flux was ⁇ 5%.
- This example teaches us the reuse of the membrane through simple water wash.
- the bittern of Table 1 was concentrated further in solar pans to separate out kainite mixed salt (KCl.MgS0 4 .3H 2 0) useful for recovery of potash.
- the mother liquor had a density of 36.3 °Be and its osmotic coefficient was 2.98.
- the average flux and final sucrose concentration were estimated to be 13.2 L/(m 2 h) and 1 1 .2% (w/v) after 5 hours of FO.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Water Supply & Treatment (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Biochemistry (AREA)
- Organic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Nutrition Science (AREA)
- Food Science & Technology (AREA)
- Polymers & Plastics (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The present invention relates to the use of abundant and generally wasted salt bitterns with high osmotic coefficient as draw solution in forward osmosis (FO). A conventional high flux thin film composite polyamide membrane was utilized for this purpose. With sugarcane juice as feed, its fourfold concentration was demonstrated with an energy saving of 97% compared to the energy requirement for conventional multiple effect evaporation. Sucrose loss from feed to draw was <3% and back diffusion of mineral constituents from bittern to feed was insignificant. using 33.5°Bé sea bittern as draw solution and an appropriate ratio of draw solution to feed solution, it was possible to value added the bittern in as much as the Epsom salt recovered from it after the FO process had a significantly higher purity than the original bittern. The invention can be applied to dewatering of other feeds using bittern as draw solution.
Description
PROCESS OF SPONTANEOUS DEWATERING OF FEED SOLUTION USING SALT BITTERNS AS DRAW SOLUTIONS
Field of invention
[0001] The present invention relates to a process of extensive dewatering of sugarcane juice using bittern as draw solution through forward osmosis (FO). Particularly, the present invention provides use of such abundant bittern as benign and potent draw solution in forward osmosis (FO). More particularly, the invention relates to tapping the pent-up energy in these bitterns by virtue of their low water activity and high osmotic coefficients - for spontaneous dewatering of feed solutions. Still more particularly, the invention relates to extensive dewatering of sugarcane juice coupled with the production of pure Epsom salt from the exhausted bittern to maximize gains.
Background and prior art
[0002] The spontaneous process of Forward Osmosis (FO) is utilized to concentrate various feed solutions. FO requires the use of a membrane for the selective passage of solvent - the solvent being water in the case of aqueous solutions - and a draw solution having higher osmotic coefficient than the feed to pull out solvent from the latter spontaneously. Bittern refers to the multi-electrolyte mother liquor that remains after common salt production from seawater, ca. 1 m3 of virgin bittern being generated per ton of salt. It is mostly discarded to sea or evaporated to higher densities in solar salt pans for recovery of marine chemicals such as bromine, Epsom salt (MgS04.7H20), potash (KC1, K2S04) and magnesium chloride, generating more concentrated bitterns from these processes.
[0003] Reference may be made to an article entitled "A review of draw solutes in forward osmosis process and their use in modern applications" by Chekli et al., (Desalination and Water Treatment 43 (2012) 167-184), providing valuable information regarding the selection criteria of suitable draw solutions for FO. No mention is made therein of salt bitterns.
[0004] Reference may be made to an article by Ge et al., (Draw solutions for forward osmosis processes: Developments, challenges, and prospects for the future, Journal of Membrane Science 442 (2013) 225-237), wherein various draw solutions used in FO have been documented. No mention is made therein of bittern.
[0005] Reference may be made to a review article by Bruggen and Luis (Forward osmosis: understanding the hype, Rev. Chem. Eng., 2014, DOI:10.1515/revce-2014- 0033), wherein the quest for an ideal draw solution is viewed as the "Holy Grail" of FO. No mention is made therein of the feasibility of using bittern as an ideal draw solution.
[0006] Reference may be made to the article by Shuren et al., (Robust and High performance hollow fiber membranes for energy harvesting from salinity gradients by pressure retarded osmosis, Journal of Membrane Science 448 (2013) 44-54), wherein synthetic seawater brine (1.0 M NaCl) was used as draw solution. No mention is made therein of use of bittern which is a much more concentrated multi-electrolyte solution.
[0007] Reference may be made to an article by J. Schrier (Ethanol concentration by forward osmosis with solar-generated draw solution, Solar Energy, DOI: 10.1016/j.solener.2012.01.027), wherein a simple, low-cost, and scalable alternative method of removing water from ethanol-water mixture using FO was explored. The draw solution used was aqueous brine that was regenerated by solar evaporation. However, these studies were carried out with pure salts. Further, no mention is made of use of bittern.
[0008] Reference may be made to an article by Cho et al. (Polyamide thin-film composite membranes based on carboxylated polysulfone microporous support membranes for forward osmosis, Journal of Membrane Science 445 (2013) 220-227), wherein, 1 M MgCl2 was used as draw solution for forward osmosis process. While MgCl2 is one of the constituents in bittern, no mention is made in the article of use of bittern as such.
[0009] Reference may be made to an article by Loeb et al. (Effect of porous support fabric on osmosis through a Loeb-Sourirajan type asymmetric membrane, J. Membrane Science., 1997, 129, 243-249), wherein FO studies were conducted with 6% and 12% (w/v) aqueous MgCl2 as draw solution. While MgCl2 is a principal constituent in bittern, no mention is made in the article of use of bittern which would be a far more cost-effective draw solution.
[0010] Reference may be made to an article by G. Lychnos et al. (Properties of seawater bitterns with regard to liquid desiccant cooling Desalination,2010, 250, 172— 178), wherein important thermodynamic properties of bitterns, such as activity coefficient, osmotic coefficient, etc., have been computed using various models. There is no mention of bittern utility in FO.
[0011] Reference may be made to the article by J. A. Fernandez-Lozano (Recovery of epsomite and sylvite from sea water bittern by crystallization, North. Ohio Geol. Soc.,1974, vol. 2, pp. 501-510), wherein the process of separation of Epsom salt from sea bittern is described. It is reported therein that the best yield and purity of the salt is achieved when sea bittern is evaporated to a density of 32.5-33.5 °Be, diluted thereafter with 10%) water, and chilled to 5 °C. There is no report in the prior art wherein this dilution is achieved by the process of FO.
[0012] Reference may be made to an article by Phuntsho et al. (Blended fertilizers as draw solutions for fertilizer-drawn forward osmosis desalination, Environmental Science & Technology 46 (212) 4567-4575), wherein use of blended fertilizers as draw solution in forward osmosis desalination has been disclosed. Although fertilizers may be attractive from a cost angle, their use will still be far costlier than use of wasted bittern. Moreover, fertilizers are unlikely to find acceptability as draw solutions for food applications such as concentration of sugarcane juice.
[0013] Reference may be made to the article on sucrose (sugar) in Wikipedia, wherein it is stated that sucrose is produced mainly from sugarcane. The raw juice expelled from the cane contains 9-12% (w/v) sucrose. The juice is stabilized to
prevent decay, clarified to remove suspended solids, and then subjected to multiple effect evaporation to obtain sugar syrup containing50-60% sucrose by weight. Further concentration under vacuum yields a supersaturated solution, from which sucrose is crystallized upon seeding. Thermal energy for the process is largely met from bagasse.
[0014] Reference may be made to the work done by Chang et al., (US 201201 18827A1 dated May 2012) with the title "Method of concentrating low titer fermentation broths using forward osmosis", wherein, a method for concentrating low titer fermentation broth using forward osmosis has been disclosed. However, there is no mention of use of FO for concentrating the sugarcane juice.
[0015] Reference may be made to an article by Castello et al. (Performance evaluation of sucrose concentration using forward osmosis, Journal of Membrane Science 338 (2009) 61-66), wherein sucrose solution was concentrated by forward osmosis process using NaCl as draw solution. Although sugarcane juice contains sucrose, no mention is made therein of concentration of sugarcane juice directly. Neither is there any mention of use of bittern as draw solution.
[0016] Reference may be made to an article by S. Nene et al. (Membrane distillation for the concentration of raw cane sugar syrup and membrane clarified sugarcane juice, Desalination, 2002, 147, 157-160) which projects energy saving in sucrose production from sugarcane juice through the process of membrane distillation. Besides the fact that membrane distillation requires higher than ambient temperatures, no mention is made of the energy saving in the process.
[0017] Reference may be made to an article by S. Gul and M. Harasek (Energy Savings in Sugar Manufacturing with the Implementation of a new Membrane Process, http://
www.nt.ntnu.no/users/skoge/piOst/proceedings/pres201 1 -andicheap 10/
PRES 1 1/231 Gul. pdf, 2009), wherein a multi-stage reverse osmosis process, carried out at 32 bar pressure and 80 °C temperature, is disclosed for the concentration of
sugarcane juice. An energy saving ca. 86% was projected. However, no detailed methodology was presented. Besides the high expenditure on capital cost, the energy saving is lower than realised in the present invention of forward osmosis. Moreover, it is likely that the membrane fouling would be severe and membrane stability would be poor under the applied conditions.
[0018] Reference may be made to the article by Gao et al. (Determination of osmotic coefficients of aqueous solutions of polyhydroxylated compounds at various temperatures, Indian J. Chem., 2002, 41A, 1184-1 187) wherein it is reported that the osmotic coefficients of raw sugarcane juice (ca. 10% sucrose content) and concentrated sugarcane juice with 40%) sucrose content are 1.01 and 1.052, respectively.
[0019] Reference may be made to the article entitled by Mondal et al. (Four-fold concentration of sucrose in sugarcane juice through energy efficient forward osmosis using sea bittern as draw solution, RSC Adv., 2015, 5, 17872-17878) published after the priority date of the present application. It may be noted therein that bittern samples exhibit osmotic coefficient values in the range of 1.41-3.24 and can drive the forward osmosis of sugarcane juice to achieve substantially higher sucrose concentrations.
[0020] It will be evident from the prior art that there is no report of any process wherein abundant and wasted bittern is used as draw solution in forward osmosis. There is also no report of any process of forward osmosis aimed at concentration of sugarcane juice directly. Neither is there any example in the literature where the dilution of draw solution after forward osmosis is turned into an advantage.
Objects of the invention
[0021] The main object of the present invention is to provide a process of extensive dewatering of sugarcane juice using bittern as draw solution through forward osmosis (FO).
[0022] Another object of the present invention is to demonstrate a process of FO employing highly potent, abundant, cost-effective and benign sea bittern as draw solution.
[0023] Another object is to employ high flux thin film composite polyamide membranes in the process.
[0024] Another object is to achieve substantial energy saving through such a process.
[0025] Another object is to concentrate the sugarcane juice to a similar level as obtained in the first stage of the conventional process employing multiple effect evaporation.
[0026] Another object is to minimise exposure of feed to high temperatures.
[0027] Another object is to demonstrate that sucrose loss in the process is minimal.
[0028] Another object is to demonstrate that back diffusion of inorganic constituents from bittern to sugarcane juice is minimal.
[0029] Another object is to utilize clarified juice so as to minimise fouling of the membrane.
[0030] Another object is to show that simple water washing of the membrane restores the initial flux almost to its original value.
[0031] Another object is to recover Epsom salt in purer form from the diluted bittern obtained in the course of FO.
Summary of the invention
[0032] Accordingly, the present invention provides a process of dewatering of sugarcane juice through forward osmosis (FO) employing wasted salt bittern (mother liquor after separation of common salt) as draw solution wherein the said process comprising the steps of:
(i) evaporating pure sea bittern in solar pan to obtain draw solution wherein the bittern may be of natural origin or derived from sea-, lake- or sub-soil brine and having density in the range of 28-38 °Be with
viscosity (□) in the range of 3-1 13 cP and osmotic coefficient in the range of 1.4-3.3;
(ii) clarifying freshly expelled raw sugarcane juice as feed solution through treatment with 2-3 % charcoal;
(iii) maintaining the volume ratio of draw solution to feed solution from 1 :5 to 20: 1 ;
(iv) circulating the juice as feed solution and bittern as draw solution through a forward osmosis (FO) stack fitted with high flux thin film composite polyamide membrane for a period in the range of 3-5 hat temperature in the range of 15 °C to 45 °C to obtain de watered feed;
(v) subjecting the draw solution after FO for chilling at temperature in the range of to crystallize out Epsom salt.
[0033] In an embodiment of the present invention selective permeation of water during forward osmosis was effected using a thin film composite polyamide membrane with active membrane surface area 0.005-0.006 m2, which when operated in reverse osmosis mode for desalination of 2000-3000 ppm feed solution gave a flux of 25-30 L/(m h) and salt rejection of 93-96% at 5-8 bar operating pressure and flow rate of the pump 1.6-1.9 LPM.
[0034] In one embodiment of the present invention the temperature of feed solution was in the range of 15-45 °C and the inlet pressure at the feed side was 0.5-2.0 bar.
[0035] In another embodiment of the present invention the sugarcane juice had an initial concentration of sucrose in the range of 8-12% (w/v) and a final concentration of 15-60%) (w/v) after forward osmosis.
[0036] Still in another embodiment of the present invention the average flux during forward osmosis was in the range of 5- 15 L/(rri h).
[0037] In yet another embodiment of the present invention in comparison to concentration through multiple effect evaporation, an energy saving of 97% was computed for four-fold concentration of sugarcane juice by forward osmosis with
33.5 °Be sea bittern as draw solution, and 8: 1 volume ratio of draw solution to sugarcane juice in 3-5 h with both feed and draw solutions under constant recirculation.
[0038] In yet another embodiment of the present invention the loss of sucrose from feed solution to draw solution was 1-3 % (w/v).
[0039] In yet another embodiment of the present invention back diffusion of inorganic mineral constituents from bittern draw solution into sugarcane juice was insignificant.
[0040] In yet another embodiment of the present invention simple water washing of the membranes after forward osmosis helps their regeneration with < 5% reduction of initial flux.
[0041] In yet another embodiment of the present invention use of sea bittern of 32.5- 33.5 °Be as draw solution, and its dilution by 9-1 1% in the course of forward osmosis, permits the recovery of Epsom salt (MgS04.7H20) in 95-99% purity upon chilling to 5 °C, compared to a purity level of 80-85% obtained with the undiluted bittern as such.
Brief description of drawing
[0042] Figure 1 showed the photographic image of FO assembly used in the present invention.
Detailed description of the invention
[0043] The present invention provides a process of FO employing sea bittern as draw solution, sugarcane juice as feed solution, and suitable membrane as solute barrier, the process comprising the following steps:
(i) evaporating virgin sea bittern in solar pans to desired density;
(ii) clarifying freshly expelled raw sugarcane juice;
(iii) computing the ratio of draw solution to feed solution to achieve the required extent of dewatering of feed and dilution of draw;
(iv) circulating the juice as feed solution and bittern as draw solution through a FO stack fitted with high flux thin film composite polyamide membrane;
(v) monitoring the extent of dewatering of feed by measuring its volume from time to time;
(vi) terminating the process when desired extent of dewatering is achieved;
(vii) subjecting the draw solution after FO to chilling to crystallize out Epsom salt;
(viii) recovering other marine chemicals such as potash and bromine optionally as desired, or discarding the spent bittern to sea.
[0044] The novel and inventive steps related to the present invention are as follows:
1. Recognising that salt bitterns are a source of pent-up energy by virtue of their low water activity and high osmotic coefficient.
2. Recognising further that forward osmosis is one application wherein this energy locked up in bittern can be put to use in uncomplicated manner.
3. Recognising further that, to effect an efficient FO process, osmotic coefficient of the draw solution is critical whereas its purity is a non-issue. Hence, the use of multi-electrolyte bitterns pose no difficulty, while being advantageous from cost and availability considerations.
4. Identifying a rare example where the dilution of draw solution during FO is an advantage rather than a disadvantage, in as much as Epsom Salt recovered from the diluted bittern has substantially higher purity.
5. Devising suitable equations to guide the selection of draw solution to feed solution ratio to achieve fourfold concentration of sugarcane juice, on the one hand, and 10% dilution of bittern for purer Epsom salt, on the other hand.
[0045] Materials and methods: Raw sugarcane juice, without any additives, was obtained from a local juice parlor (Juice centre, Waghawadi road, opposite to SBI bank, Bhavnagar, 364002).
[0046] The solvent flux (Jn) across the FO membrane was calculated from the equation:
, _ Vto -Vtn
Jn A(t0 -tn)
In this equation, Jn is the flux (L/(m2h)), Vto and Ftnare the volumes (L) of feed solution at zero time and at time interval n, respectively, and A is area (m2) of the membrane.
[0047] Concentrations of Mg2+ and Ca2+ were estimated by EDTA titration, K+ and Na+ by flame photometry (Cole-Parmer Instrument Company Chicago, Model 2655- 00, Digital flame Analyzer), and S04 2" and CI" by ion chromatography (Dionex 500) or classical techniques. Back diffusion of draw solution constituents into feed solution was studied using an inductively coupled plasma optical emission spectrometer (ICP- OES, Perkin Elmer, Optima 2000). Sucrose concentration was determined by high performance liquid chromatography employing Aminex-HPX-87P (BioRad, USA) column.
EXAMPLES
[0048] The following examples serve to provide the best modes of practice for the present invention, and should not be constructed as limiting the scope of the invention Example 1
[0049] This example teaches the general FO process used in the present invention using sugarcane juice as feed and bittern as draw solution. Virgin sea bittern obtained after recovery of common salt (procured from M/s Tata Chemicals Limited, Mithapur) was further evaporated in solar pan to a density of 33.5 °Be (°Be = 145( 1 - 1 /p), where p= specific gravity). The compositions and relevant physical properties are shown in Table 1 .
Table 1 : Chemical composition, ionic strength (I), water activity (wa), osmotic coefficient (φ) and viscosity (η) of the seawater bittern used in the FO studies
cp (% w/v) M
33. 5.4 2.83 2.03 7.42 BDL 23.48 8.42 12.0 0.6 2.26 a
5 4 0
BDL=1 ielow detection limit
[0050] The raw juice was clarified by treating with 2 % activated charcoal followed by filtering, and the pH adjusted to ca. 8 through treatments with lime water. Thin film composite (TFC) polyamide membrane was used in FO experiments. The membrane comprised a polysulfone supporting layer and a polyamide skin layer prepared by interfacial polymerization of m-phenylenediamine and trimesoyl chloride. When operated in reverse osmosis mode for desalination of 2000 ppm aqueous NaCl feed, the membrane gave a flux of 26.45 L/(m2h) and salt rejection of 94.9% at 5 bar operating pressure. FO experiments were conducted with the same membrane in the FO set up shown in Figure 1. The active area of the flat sheet membrane was 0.0057 m . The feed ( sugarcane juice) and draw ( sea bittern) solutions, maintained at room temperature (22 ± 2 °C), were circulated (KEMFLO pumps) through the kit at a flow rate of 1.8 LPM and the operating pressure at the feed side was 1 bar. Membrane active layer facing both feed solution and draw solution was similar (5.3 cm x 10.7 cm) throughout all experiments and cross flow velocity was calculated to be 0.283 m s"1. The ration of draw solution to feed solution was varied from 1 : 5 to 8: 1. After circulation for 3-5h the FO process was terminated. Example 2
[0051] The bittern sample of Table 1 contains 21 % (w/v) of MgCl2 as the principal constituent and other salts additionally. Two FO experiments were conducted with pure water as feed: In one experiment bittern was used as draw solution while in the other experiment a 21 % (w/v) pure MgCl2 solution was used as draw. Whereas the
2 2 pure water flux was 5.5 L/(m h) with the former, the latter gave a flux of 4.4 L/(m h). This example teaches us that to affect an efficient FO process, osmotic coefficient of the draw solution is of crucial importance- and it would be higher in the former in
view of the other salts present additionally - and purity of the solute is of no importance. On the other hand, use of bittern as draw solution is more practical and cost effective than use of pure salts.
Example 3
[0052] An FO experiment was subsequently conducted with 6% sucrose as feed solution and the bittern of Table 1 as draw solution. The initial ratio of feed solution to draw solution was 5 : 1 v/v. Sucrose concentration in the feed solution rose to 10.8% (w/v) after 5 hours of FO. The average flux was estimated to be 10.8 L/(m2h).
This experiment teaches us the concentration of sucrose by FO wherein bittern is used as draw solution.
Example 4
[0053] The bittern of Table 1 was chilled to 5 °C whereupon Epsom salt crystallized out. Its purity was 80-85%. When the bittern was diluted with fresh water (bittern to fresh water ratio = 10: 1 v/v), the purity of the Epsom salt rose to >95%.
This example teaches us that dilution of bittern with 10% fresh water is beneficial, for recovery of Epsom salt in purer form.
Example 5
[0054] This example teaches FO-based four-fold increase in sucrose concentration in sugarcane juice (initial sucrose concentration = 10.5%) using the bittern of Table 1 as draw solution, with 10% dilution of the latter so as to recover purer Epsom salt as taught in Example 4. The above objective is thermodynamically feasible in view of the reported values of 2.26 and 1 .05 of the osmotic coefficients of the bittern of Table 1 and 40 % sugarcane juice, respectively. Considering initial volume of feed solution = (V 1 )F, initial sucrose concentration in feed solution = (C 1 )F, final volume of feed solution =(V2)F, final sucrose concentration in feed solution = (C2)F, initial volume of draw solution = (V 1 )D and final volume of draw solution = (V2)D, the following relationships (eqsl a-g) enabled computation of (V 1 )D : (V 1 )F to satisfy both objectives of fourfold concentration of sucrose in sugarcane juice (feed solution) and
10% dilution of draw solution (bittern of Table 1) simultaneously, neglecting sucrose loss.
(C2)F = 4 X (C1)F (considering 4-fold concentration) (la)
(V1)F X (C1)F = (V2)F X (C2)F = (V2)F x 4 x (C1)F (lb) Hence, (V2)f = 0.25X(V1)F (lc)
Permeate volume during FO = (VI )F - 0.25 (Vl)F= = 0.75 (V1)F (Id) (V2)b = (V1)D+ 0.75 (V1)F = 1.1 X (V1)d
(Considering 10% dilution of draw solution) (le)
Hence, 0.1 (V1)D = 0.75 (VI )F (I f) i.e., (Vl)D/(Vl)F = 7.5 . (lg)
[0055] An experiment was carried out accordingly with 250 mL of charcoal-treated sugarcane juice as feed solution and 2 L of the bittern of Table 1 as draw solution. After 4h of FO with continuous recirculation, volume of feed solution was found to be 50-60 mL and the sucrose concentration in dewatered juice was found to increase to 40.6%,i.e., by a factor of ca. 4, with average flux of 8.2 L/(m2h). The volume of the draw solution increased by ca. 10% in line with the objective stated above.
This example teaches four-fold concentration of sucrose in sugarcane juice and 10% dilution of the bittern of Table 1 used as draw solution, taking 8:1 draw solution to feed solution ratio.
Example 6
[0056] The sucrose concentration in draw solution was estimated after the experiment under Example 5. Loss of sucrose in the draw solution was estimated to be 1.8 %.
[0057] This example teaches negligible crossover of sucrose from feed solution to draw solution during FO, and justifies the neglect of sucrose loss in the framing of eqs l a-g under Example 5.
Example 7
[0058] Back diffusion of salts from draw solution to feed solution may decrease the net osmotic pressure across the membrane and also affect adversely the further processing of the concentrated sugarcane juice. Accordingly, an assessment was made of Na+, K+, Mg2+, Ca2+ Cl", and S04 2"in the initial sugarcane juice and final sugarcane juice after FO experiment of Example 5. Clarified sugarcane juice contained 0.0064 % Na+, 0.016 % K+, 0.061 % Ca2+, 0.017 % Mg2+, 0.11 % CI", and 0.068 % S04 2" before FO run and 0.103 % Na+, 0.01 % K+, 0.077 % Ca2+, 0.036 Mg2+, 0.36 % CI", and 0.14 % S04 2"after FO run.
[0059] This example teaches us that, notwithstanding the substantial presence of Na+, K+, Mg2+, CI", and S04 2"in the bittern of Table 1, concentrations of the above ions in the concentrated sugarcane juice after FO were minimal, i.e., unwanted back diffusion was minimal.
Example 8
[0060] A comparative assessment was made of the energy requirement for four-fold concentration of sugarcane juice through the conventional process of multiple effect evaporation arid the FO process in Example 5, and the saving of bagasse (in most sugarcane industries the thermal/electrical energy requirement is met by combustion/ gasification of bagasse) in the FO process. Assuming commercial scale operation, the requirement of electrical energy to concentrate 1 m3 sugarcane juice to 0.25 m3 by FO is only 7.33MJ, (which is equivalent to 37 MJ of calorific value) whereas the same extent of concentration through multiple effect evaporation (MEE) requires 867 MJ of thermal energy. Considering a calorific value of 19 MJ per kg of bagasse, and 65 % thermal efficiency, 71 kg of bagasse must be sacrificed for 4-fold concentration of 1 m3 of juice through MEE. Thus the net saving in bagasse - which can be put to alternative uses - would be 69 kg per m of sugarcane juice processed, i.e., a saving of ca. 97.2%. The basis of the calculations is explained in the article by Mondal et al. (RSC Adv., 2015, 5, 17872-17878).
This example teaches 97 % saving of bagasse during initial concentration of sugarcane juice by FO using bittern as draw solution as compared to multiple effect evaporation.
Example 9
[0061] 2.2 L of the ca. 10% diluted draw solution after the FO run in Example 5 was chilled to 5 °C to recover Epsom salt. The purity of the recovered Epsom salt was >98 % with 47 % yield on sulphate basis. A control experiment was conducted with the bittern of Table 1 as such. 45 % (sulphate basis) of Epsom salt was recovered in this case with 83-84% purity.
[0062] This example teaches value addition of draw solution after FO in as much as the purity of Epsom salt recovered from the draw solution (bittern) improves as a result of its spontaneous dilution in the course of FO.
Example 10
[0063] The experiment of Example 5 was repeated after rinsing the membranes thoroughly with de-ionized water. The decline in the initial flux was <5%.
This example teaches us the reuse of the membrane through simple water wash.
Example 11
[0064] The bittern of Table 1 was concentrated further in solar pans to separate out kainite mixed salt (KCl.MgS04.3H20) useful for recovery of potash. The mother liquor had a density of 36.3 °Be and its osmotic coefficient was 2.98. When the experiment of Example 3 was repeated with this bittern in place of the bittern of Table 1 , the average flux and final sucrose concentration were estimated to be 13.2 L/(m2h) and 1 1 .2% (w/v) after 5 hours of FO.
[0065] This example teaches us that the further concentration of the bittern of Table 1 to higher densities can enhance its performance as draw solution.
[0066] Advantages of the invention
The advantages of the present invention are:
(i) For high volume, low value applications, suitable draw solutions will be required that are abundant and cost-effective. The draw solution must also possess high osmotic coefficient to drive the required extent of concentration of a feed. Abundant salt bitterns, which are for the most part simply discarded to sea, satisfy these criteria.
(ii) By virtue of their very high osmotic coefficients, the bitterns provide a means of extensive dewatering of feed solution with sustained flux.
(iii) 97% energy saving demonstrated for fourfold concentration of sugarcane juice compared to the energy required in the conventional process of multiple effect evaporation.
(iv) Whereas in most examples in the prior art, the diluted draw solution has to be once again concentrated for recycle, this may not be necessary in the case of the bitterns in view of their abundance; the spent bittern may simply be discarded and its dilution may be an advantage for discharge.
(v) Use of bittern as draw solution would be useful in many FO applications,, considering the benign nature of the constituents of bittern and the excellent suppression of back diffusion of mineral constituents from draw solution to feed solution demonstrated in the course of the invention.
(vi) The process is amenable to scale up.
(vii) By undertaking the process at room temperature, it is feasible to avoid thermal cycling which may be an advantage for heat sensitive constituents.
(viii) Identification of 32.5-33.5 °Be sea bittern as an ideal draw solution, which would be relatively easy to procure, and which benefits from controlled dilution during FO in as much as it raises the purity of Epsom Salt obtained from it upon chilling.
Claims
1. A process of dewatering of sugarcane juice through forward osmosis (FO) employing wasted salt bittern (mother liquor after separation of common salt) as draw solution wherein the said process comprising the steps of:
(i) evaporating pure sea bittern in solar pan to obtain draw solution wherein the bittern may be of natural origin or derived from sea-, lake- or sub-soil brine and having density in the range of 28-38 °Be with viscosity (□) in the range of 3-1 13 cP and osmotic coefficient in the range of 1.4-3.3;
(ii) clarifying freshly expelled raw sugarcane juice as feed solution through treatment with 2-3 % charcoal;
(iii) maintaining the volume ratio of draw solution to feed solution from 1 :5 to 20: 1 ;
(iv) circulating the juice as feed solution and bittern as draw solution through a forward osmosis (FO) stack fitted with high flux thin film composite polyamide membrane for a period in the range of 3-5 having temperature in the range of 15 °C to 45 °C to obtain dewatered feed;
(v) subjecting the draw solution after FO for chilling at temperature in the range of to crystallize out Epsom salt.
2. The process as claimed in Claim 1 , wherein selective permeation of water during forward osmosis was effected using a thin film composite polyamide membrane with active membrane surface area 0.005-0.006 m2, which when operated in reverse osmosis mode for desalination of 2000-3000 ppm feed solution gave a flux of 25-30 L/(m2h) and salt rejection of 93-96% at 5-8 bar operating pressure and flow rate of the pump 1.6-1.9 LPM.
3. The process as claimed in Claim 1 , wherein the temperature of feed solution was in the range of 15-45 °C and the inlet pressure at the feed side was 0.5-2.0 bar.
4. The process as claimed in Claim 1 , wherein the sugarcane juice had an initial concentration of sucrose in the range of 8-12% (w/v) and a final concentration of 15-60% (w/v) after forward osmosis.
5. The process as claimed in Claim 1 , wherein the average flux during forward osmosis was m the range of 5-15 L/(m h).
6. The process as claimed in Claim 1 , wherein, in comparison to concentration through multiple effect evaporation, an energy saving of 97% was computed for four-fold concentration of sugarcane juice by forward osmosis with 33.5 °Be sea bittern as draw solution, and 8: 1 volume ratio of draw solution to sugarcane juice in 3-5 h with both feed and draw solutions under constant recirculation.
7. The process as claimed in Claim 6, wherein the loss of sucrose from feed solution to draw solution was 1 -3 % (w/v).
8. The process as claimed in Claims 1 , wherein back diffusion of inorganic mineral constituents from bittern draw solution into sugarcane juice was insignificant.
9. The process as claimed in Claims 1 , wherein simple water washing of the membranes after forward osmosis helps their regeneration with < 5% reduction of initial flux.
10. The process as claimed in Claims 1 , wherein use of sea bittern of 32.5-33.5 °Be as draw solution, and its dilution by 9-1 1 % in the course of forward osmosis, permits the recovery of Epsom salt (MgS04.7H20)in 95-99% purity upon chilling to 5 °C, compared to a purity level of 80-85% obtained with the undiluted bittern as such.
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| CN105533381A (en) * | 2015-12-07 | 2016-05-04 | 广西农垦糖业集团股份有限公司 | High nutrition pure solid saccharum officinarum juice and preparation method thereof |
| CN105533383A (en) * | 2015-12-07 | 2016-05-04 | 广西农垦糖业集团股份有限公司 | Solid sugarcane juice with high general flavone content and preparation method thereof |
| CN107376667A (en) * | 2017-08-25 | 2017-11-24 | 上海城市水资源开发利用国家工程中心有限公司 | A kind of method and device for preparing the amphibious performance CTA films of nanofiltration/just permeating |
| WO2019161444A1 (en) * | 2018-02-22 | 2019-08-29 | Ambrosios Kambouris | Systems and methods for the preparation of plant derived products using osmosis techniques |
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