This document reviews various methods for purifying crude glycerol produced during biodiesel production. Crude glycerol contains impurities like methanol, soap, fatty acids and salts that must be removed. Common purification methods include neutralization to remove soap and acids, evaporation to remove methanol, and vacuum distillation. Emerging methods like ion exchange, activated carbon adsorption and membrane technologies are also discussed but have challenges to overcome like fouling and energy requirements. Overall the document provides an overview of progress in glycerol purification and the need for improved small-scale and economically viable processes.

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. 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. 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. 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. 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. Grades specification of glycerol
5

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. 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. 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. 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. 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. III. Purification and refinery
Vacuum Distillation
Ion Exchange Adsorption
Adsorption using
activated carbon
11

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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