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Progress, prospect and challenges in glycerol purification process


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Glycerol purification process

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Progress, prospect and challenges in glycerol purification process

  1. 1. Progress, prospect and challenges in glycerol purification process: A review M.S. Ardi, M.K. Aroua, N. Awanis Hashim Presented By: Bijaya K. Uprety PhD (Biotechnology) student
  2. 2. Introduction • Biodiesel production produce ~10 % w/w of crude glycerol. • Increase in biodiesel production  Increase in crude glycerol. • Surplus crude glycerol Decrease in price of pure glycerol • Conversion of crude glycerol into value added products is essential to maintain the sustainability of biodiesel production. 1 a. Almeida, J. R. M., Fávaro, L. C. L., & Quirino, B. F. (2012). Biodiesel biorefinery: opportunities and challenges for microbial production of fuels and chemicals from glycerol waste. Biotechnology for Biofuels,
  3. 3. Utilization of glycerol in these products requires one with high quality and purity Series of purifications of crude glycerol are usually required preferably prior to further processes Present purification technology seems to be not feasible for small and medium scale industries. 2
  4. 4. Composition of crude glycerol However, almost every crude glycerol contains, Glycerol Light solvent (Methanol or ethanol, water) Soap Fatty acid methyl esters (FAME i.e. biodiesel) Glycerides (i.e. to mono, di & tri-glycerides), Free fatty acids (FFA) Ash Variations in biodiesel production methods variation in composition of crude glycerol The impurities such as soap, methanol, water, salts, MONG (100- Glycerol%-Water %- Ash) have more tendencies to concentrate in the glycerol phase during phase separation of biodiesel phase and glycerol phase. Commonly used Catalyst: Basic catalyst  Fast reaction, mild reaction Solvent: Methanol Cheaper, High reactivity, no azeotropes formation 3
  5. 5. Effect of impurities on glycerol utilization Impurities on glycerol In Phytase production by pichia pastoris  Reduced cell density at 70 g/l initial concentration of CG In DHA production by Algae from CG; Soap & Methanol  Negatively influence the productivity High salinity Inhibit microbial activity in anaerobic digestion of CG Presence of heavy metals make it unsuitable for pharmaceutical and food application Methanol is toxic to health and environment Hydrogen production by Rhodopseudomonas palustris; Presence of saponified fatty acid (SFA) Inhibitory effect on photofermentative growth 4
  6. 6. Grades specification of glycerol 5
  7. 7. Glycerol Purification Technology Purification method varies  Crude glycerol from different feed stock have different composition Purification Method also depends on  the usage of glycerol and the effect of impurities on the process Purification techniques in Biodiesel plant are adapted  from existing soap making industries that utilizes vacuum distillation and other treatments such as ion exchange and activated carbon. 6
  8. 8. General Purification steps of crude glycerol Neutralization Removal of fatty acids & simultaneous removal of non-glycerol products via. precipitation Evaporation Concentrate the solution & removal of Alcohol Purification and refining step  achieved to the desired degree vacuum distillation, ion exchange, membrane separation and adsorption. Neutralization Stripping Vacuum Distillation Filtration/Centrifugation USP Glycerin Crude Glycerol 7
  9. 9. I. Neutralization Most common pretreatment method  involves acidifying with Strong acid to remove Catalyst and Soaps Acid + Soap  Free fatty acids (skimmed off) Acid + Base catalyst (NaOH, KOH)  Salt + Water Acidification process usually separates the crude glycerol into 3 layers: 1. free fatty acids  Top layer (Separated using separated funnel) 2. glycerol rich layer Middle & 3. Inorganic salts Bottom (Decantation) 8
  10. 10. Kongjao et al. Repeated acidification (H2SO4, pH 1-6) of crude glycerol derived from waste used oil biodiesel plant  increases glycerol –rich layer As a part of their proposed strategy to economize biodiesel production, various researchers have tried to optimize the acidification process Some Relevant Researches on neutralization step Tianfeng et al. Acidification (5.85% H3PO4 ) of crude glycerol derived from waste cooking oil  enhanced glycerol –rich layer 40% to 70% at pH 5 or 6 Javani et al. proposed that crude glycerol to go through saponification and produce potassium phosphate as by-product using repeated acidification. 9
  11. 11. II. Methanol removal Excess methanol is used during transesterification to enhance the yield Excess methanol distributes between the methyl-ester and crude glycerol phase. However, due to toxicity of methanol on environment & health it has to be removed and recycled back CG can be treated under vacuum conditions using a rotary evaporator at 50-90 0C for more than 2 h In industry, commonly evaporator or flash unit is employed Falling film evaporators recommended as best  as it keeps shorter contact time Prevents glycerol decomposition Glycerol concentration after methanol removal= ~85% 10
  12. 12. III. Purification and refinery Vacuum Distillation Ion Exchange Adsorption Adsorption using activated carbon 11
  13. 13. Vacuum Distillation At higher temperature glycerol property changes, >200 0C, Polymerization into polyglycerol >160 0C & slightly acidic condition, dehydration Thus, purification has to be done in vacuum where the pH, temperature and pressure must be controlled. Can oxidize into glycerose, glyceraldehydes and di-hydroxylacetone Most common method of purification??? 12
  14. 14. Optimum pH was found to be less than 5 Yong et al. reported simple distillation at 120–126 0C (pH 3.5)would yield around 141 g glycerol/kg of glycerol residue (~14% yield, purity 96.6%) However, distillation is energy intensive process. High-energy input requirement of vaporization and creates thermal decomposition due to high specific heat capacity of glycerol which makes the process costly. 13
  15. 15. Ion exchange adsorption Several types of impurities such as fatty acid, inorganic salt and free ion impurities can be removed from crude glycerol by using ion exclusion purification techniques. Lever Brothers Company plant (May 1951, California, soap lye purification ) Purification capacity: 26,600 lbs of crude glycerol/day  first early commercial application of ion exchange unit for crude glycerol Four-stage unit consisted of three cation–anion exchangers and a mixed-bed Exceptionally high quality glycerol produced, comparable to high-grade distilled glycerol. 14
  16. 16. Initial belief  technique provides advantages over conventional distillations cheap and high quality products Later it was found that the technique results in poor separation due to fewer exchange sites per unit volume (smaller exclusion factor). Improvement based on this technique (biodiesel plant)gel type acidic ion exchange resin beads  Used to eliminate several types of salts such as fatty acid salts (5–50%), inorganic salts (1–5%) and free ions impurities 15
  17. 17. Ismail et al  Utilized resin type AmberliteIRN-78 and Amberlite200 to purify crude glycerol & its effectiveness measured HPLC analysis of purified glycerol showed single peak with smooth baseline However, for crude glycerol purification to be viable, issues concerning the ion exchange method such as fouling by fatty acids, oils and soaps, regeneration of the beds and large quantities of waste-water produced needs further improvement. 16
  18. 18. Adsorption using activated carbon Mainly used as the finishing step to further refine the purified glycerol; reduce the color, as well as reducing some fatty acids and other components Manosak et al.  sequential-refining stages using commercial activated carbon Concluded: Dose α Color removal of refined crude glycerol Hunsom et al. Among the 15 sets sludge (waste water plant) derived activated carbon KOH-800AC exhibited the highest efficiency to adsorb impurities in pre-treated crude glycerol 17
  19. 19. Membrane separation technology Simple & energy efficient separation technique Driving force of the most isothermal membrane separation process involves the difference in concentration or electrical potential and hydrostatic pressure. Commonly employed MST ( in food, chemical & biotechnology) 1.Microfiltration 2. Ultrafiltration 3. Nanofiltration 4. Reverse osmosis 5. Electrodialysis Selection of these membrane techniques depends upon the nature of compounds to be separated Recently employed in biodiesel industries environmental friendly, usage of water in water washing step is avoided 18
  20. 20. Application of membrane separation technology in glycerol refining Membrane separation technology in purification of glycerol is developed by EET Corporation Use patented technology of High Efficiency Electro-Pressure Membrane (HEEPM™) Integrated nanofiltration and/or reverse osmosis units to obtain single synergistic unit operation. 19
  21. 21. Mah et al. Investigated the ability of membrane GE PVDF 30 Kda to remove palm oil & oleic acid from glycerol at different concentration and pH conditions good result obtained Jeromin et al.  Proposed application of pressure driven membrane technology eg. Ultrafiltration to remove unreacted oil or fat in glycerol rich solution Similarly, Lazarova tested different types of membrane to purify pre-treated crude glycerol derived from biodiesel production. However, Problems such as fouling of membranes, durability, availability of suitable membrane for specific operations still persists. Various research are still ongoing to make this process commercially implementable. 20
  22. 22. Hybrid membrane Recently development of hybrid membranes combining organic and inorganic materials have been explored to improve membrane performance Hybrid membranes has shown  Better mechanical and thermal properties due to inorganic part  Better flexibility due to organic part Zulfikar et al.  Enhancing silica content of Poly(methyl methacrylate) (PMMA)- SiO2 composite membranes  enhanced water permeability Crude glycerol purification process could be benefitted if desired characteristics could be endowed upon membrane. E.g.: Water permeability increase would improve the permeation of water soluble material through the membranes 21
  23. 23. Membrane distillation Another emerging technology to purify glycerol. Unlike others, it is a thermally driven membrane process Selectivity of membranes used based on the retention of liquid water & permeability for free water molecules (water vapor). Temperature difference between the two bounding surfaces Partial water vapor pressure difference between two bounding surfaces (ensures that the vapor developing at the membrane surface follows the pressure drop) Commonly employed membranes hydrophobic (PVDF, PTFE)  0.1 to 0.5 µm pore size. Permeate Feed 22
  24. 24. Advantages over other conventional methods  It uses relatively lower energy compared to distillation, reverse osmosis and pervaporation  Lower membrane fouling  Lower operating pressure compared to pressure-driven membrane and lower operating temperature in comparison with conventional evaporation. Possesses a technical drawback in terms of having low transmembrane flux compared with reverse osmosis 23
  25. 25. Challenges of crude glycerol utilization & purification Development of new approaches and alternatives as to ensure the sustainability of biodiesel production industries is still needed. Design of economical method for the purification crude glycerol to more usable state for its utilization. Need of improvement in biodiesel production process itself less use of alcohol, avoiding using homogeneous catalyst (produce large amount of salt, large operation cost and expensive separation procedure). To obtain vegetable oil and alcohol with considerably anhydrous properties and have a low free fatty acid content, because the presence of water or free fatty acid or both promotes soap formation. 24
  26. 26. Conclusion Crude Glycerol purification is the necessary for the sustainability of biodiesel production Various techniques are being explored for purification process Even though costly and energy intensive, vacuum distillation remains the method of choice in most of the prevailing biodiesel plant Membrane separation technology is the emerging technology and possess a promising future Search for more economical purification techniques are still required 25