Purification of saponified waste liquor

The general composition of saponification waste liquor is about 80% water, 10% - 15% inorganic salt (NaCI), 6% - 10% glycerol, 0.1% - 1.0% fatty acid salt (Na salt), 0.1% - 0.5% NaOH. They are from nitrogenous compounds (proteins), phospholipids and resins, pigments, glycerol fermentation products such as propylene glycol (about 0.1% - 0.5%) etc. In the process of soap boiling, the content of fatty acid salts in the saponification waste liquor will increase greatly because of the insufficient salt concentration or the high free alkali in the waste liquor. It is noteworthy that the saponification waste liquor, especially the dilute glycerol recovered from the inferior oil, will produce fermentation phenomenon if the storage time is too long or the storage environment is unclean. Besides affecting the yield of glycerol, it will also affect the operation and control of the refining process (filtration, concentration of clear water and distillation of crude glycerol) and the quality of the product. Therefore, we should take seriously the purification operation of saponification waste liquid. The treatment of saponification waste liquid is divided into two parts: acid treatment and alkali treatment. The purification process of saponification waste liquor is shown in Figure 1.1.

1.1Acid treatment (including acid decomposition and acid decomposition of fatty acids)

The purpose of the acid treatment operation is to neutralize the free alkali in the saponification waste liquor and to decompose fatty acid salts to produce fatty acids.



Fatty acids and flocculants, such as ferric chloride, precipitate fatty acids to form metal salts：



In the acid treatment of saponification waste liquid, as flocculant, ferric chloride mainly has the following functions:



Formation of iron soap precipitation:



Isoelectric point coagulation: In addition to fatty acid salts, saponification waste liquor also contains amino acids, proteins, nitrides and other sodium salts, they are amphoteric compounds. They can form salts with acids and bases. The hydrolysis of ferric chloride is generated by hydrochloric acid.



Therefore, ferric chloride can change the Ph value of saponification waste liquid. Neutral dipole ions exist when Ph reaches a certain value. At this time, the solubility in water is the smallest, and this Ph value is isoelectric point of the substance. Adjusting the Ph value to the isoelectric point (if the colloid isoelectric point is Ph 5.2; the protein is Ph 4.6-4.9; the amino acid isoelectric point is Ph 2.9), such substances can be precipitated from the solution.

Electroneutralization: The impurities precipitated from acidic saponification waste liquor are in colloidal state. These impurities are negatively charged and can not agglomerate into large particles because of mutual repulsion. After adding ferric chloride, the iron ions are neutralized with the negatively charged impurities colloids, resulting in precipitation.

Adsorption: The atoms on the solid surface have certain surface energy and tend to adsorb some substances to reduce the surface energy. Iron soap and excess iron ions and alkali to form iron hydroxide are huge precipitates, with a large surface area, can adsorb a large number of impurities.

Several functions of ferric chloride are interrelated, interacting and restricting each other. Therefore, we must strictly control and strictly operate.

Saponification waste liquor is alkaline. First, HCI and H2SO4 are used to neutralize, neutral fat is skimmed, HCI or H2SO4 is added to PH3.5-4 under compressed air agitation, and black fat is still skimmed out (fatty acids and other impurities produced by acidification and decomposition of fatty acid salts are named because they are black, and black fatty acids can be treated to recover fatty acids).

Under the stirring of the compressed air, add FeCL3 solution (concentration is generally 38%) to PH3.5-4.2, continue to turn, 10 MIN after sampling and filtering, 10 ML filtrate added 2 drops of 5% FeCL3 solution, shake well, after 5 minutes should be no turbidity, if there is turbidity, then add FeCL3 solution and continue to test, must make the solution clear and transparent. However, if the Ph value is too low, the fatty acid iron salt will be dissolved and the treatment effect will be reduced. Therefore, it is necessary to carry out alkaline recovery operation (especially to treat the saponification waste liquor of low-grade oil and grease should be particularly careful, otherwise it will affect the filtration).

Glycerol Vs. Mineral Oil

Upon first inspection, glycerol and mineral oil appear to be identical (or at least very similar) compounds: They're both colorless, (mostly) odorless, and have mild lubricating properties that make them feel slippery when rubbed between the thumb and index finger. Chemically, however, they are very different compounds.

Chemistry

Mineral oil is a hydrocarbon, meaning it contains nothing except carbon and hydrogen, with each molecule typically containing somewhere between 15 and 40 carbon atoms. It typically has a density of about 0.8 g/mL (meaning 1 millileter of mineral oil would weigh 0.8 grams). Mineral oil is not soluble in water: If the two are mixed, they will form separate phases, with the mineral oil on top.

Glycerol, also known as glycerin or glycerine, is actually an alcohol. Its molecules only contain 3 carbons, and it has a density of about 1.3 g/mL. Unlike mineral oil, it is soluble in water. In fact, it is hygroscopic, meaning glycerol will actually absorb water vapor from the air.

Manufacture

Mineral oil is a byproduct of the crude-oil refining process.

Glycerol is produced by the saponification of animal fats. Saponification is the reaction between fats and strong bases (like lye) and is the primary reaction involved in the manufacture of soap; glycerol is a byproduct of the soap manufacturing process.

Medical Uses

Mineral oil is the primary ingredient of baby oil. It can also be taken orally as a laxative.

Glycerol is used in cough syrup (as a sweetener and thickener) and acts as a laxative in suppository form.

Food and Cosmetic Uses

Mineral oil is used in many topical creams and ointments.

Glycerol is used in foods as a sweetener and as a humectant (to keep foods moist). It is also used in toothpaste, shaving cream and soap.

Toxicity

Some mineral oils have been linked to cancer in animal studies involving exposure to oil mists.

Glycerol is not carcinogenic and is not believed to be toxic unless ingested in large quantities.

 

Purification of Crude Glycerol From Biodiesel

Crude glycerol is the by product produced throughout the biodiesel production process. However glycerol produced at this stage is crude glycerol which is about 80% pure and contains other contaminants like methanol, water, salt and soap. Crude glycerol has approximately about 45% glycerol, 10-15% water and methanol, 10-15% salt, and 30% soaps by weight2. This crude glycerol is not a highly valued chemical so a purification process must be done to make the crude glycerol into useful glycerol used for industrial application. Due to large supply of crude glycerol, purifying glycerol will maximise the biodiesel production profits. During the refinement process into technical grade glycerol, the methanol is evaporated from glycerol fraction. The salt, methanol, odors, and water are removed. Crude glycerol refine into technical grade glycerol gives <97% purity. The technical grade glycerol is much more useful for industrial application as it removes the high cost of toxic waste disposal which increases the value of the end product.

The purity of glycerol determines the value of glycerol, the higher the purity of glycerol the higher the market value for glycerol. Glycerol refinement will help biodiesel plants turn into a stronger profit with its refined glycerol’s since it cost less than fully refined grade. The refined grade greens the business as its takes less energy to produce and it is renewable. For this reason the demand for refining glycerol into technical grade glycerol and further has increased. The refining process is however currently expensive. USP (The United States Pharmacopeia) is highly purified glycerol, purity of glycerol >99.7%. This is a pharmaceuticals grade which is useful in cosmetics, personal care, food and other specialty application.

Typical Processes:

• Adsorption


• Vacuum Distillation


• Further purification


• Methanol Removal Step (Flash Evaporators or falling film evaporator)


• Neutralization Step (Soap Splitting)


• Crude glycerol


• Ion exchange

General process

There are many way to refine glycerol. Soap splitting is involved in all of the refining process as a glycerol pre-treatment step. The soap splitting involves to major separation step which removes methanol and salt. In all purification step process that are soap and other organic impurities need to be removed by centrifugation /filtration. Purification process can be done mainly in three steps.

Neutralisation involves in the 1st step which uses an acid to remove soaps and catalyst. FFA and salt will produce with the reaction of an acid with soap, and salt and water produces with the reaction with the base catalyst. Insoluble salt and FFA in the glycerol will precipitate out and some will be skimmed off. FFA and salt can also be eliminated by filtration. The colour of filtrate coming from neutralisation step is light brown or yellow colour. Removal of methanol is the purpose in 2nd step which is the preliminary stage of refining. Using a falling film evaporator or flash evaporators can be used to remove methanol from the glycerol. The advantage using a falling film evaporator is the short contact time and is better suited to this process because it decomposes due to temperature inclination of glycerol. The purity of glycerol is around 80% after the removal of methanol. In the 3rd step, a further purification of glycerol can be done by mixture of ion-exchange, vacuum distillation, adsorption, extraction and crystallisation, dialysis, precipitation. The glycerol is purified around >99.7% in the 3rd step of the purification.

Further purification

Ion exchange and concentration purification process

The ion exchange system uses cation, anion, and mixed bed exchangers to remove catalyst and other impurities. The removal of ionic substances by ion exclusion chromatography is the concentration step. Due to their charge, the ionic substances are repelled from the resin surface which stays in the liquid volume. The non-ionic substances are accommodated in the resins and pores. Anionic and cationic ion exchangers are exchanged for wash water, which first removes the ionic substances in the liquid and later the non-ionic substances. Negative anionic ion exchangers are exchanged for hydroxide ions where as positive cationic ion exchanged for hydrogen ions. The purification step is the next step which uses ion exchangers. The removal of odour and colour, inorganic salts, soap and fat components are done by the purification process.

For smaller capacity plants, ion exchange purification of glycerol is a good alternative to vacuum distillation. However for this process ion-exchange is not economical since high salt content of glycerol issued from biodiesel production. When the salt content is around 5-7 percent range the chemical regeneration costs becomes extremely high. The disadvantage of the ion- exchange is that it obstructs the process obtaining high purity glycerol and also the system is fouling by soaps and fatty acids. The other shortcoming is the necessity for water evaporation after purification, which results in additional losses of glycerin, carried over by water steam4.

Vacuum distillation

Vacuum distillation with steam injection, followed by activated carbon bleaching is the commonly practised method for the final purification of glycerol. Evaporation of components can be accomplished in vacuum distillation. Vacuum distillation is also known as low temperature distillation. Vacuum distillation is used as separator in some separation techniques because glycerol is sensitive to heat and the compound splits into water and decomposes. Due to high boiling point of glycerol an extreme deep vacuum should be used to distil glycerol from inorganic salt.

The advantages of vacuum distillation are that it is a commonly well established technology as it produces high purity glycerol in high yield. Another advantage is it is the reduced temperature requirement at lower pressures. Vacuum distillation could be used without heating the solution. The number of equilibrium stages needed can be reduced by utilizing the vacuum distillation. The disadvantage of this process is that distillation of glycerol has high capital cost and it is energy intensive. This is because glycerol heat capacity is high which demands a high energy input for vaporisation. The vacuum distillation cannot proceed out continuously and is accompanied by considerable losses of glycerol. It been suggested that vacuum distillation of glycerol is best suited to operations > 25 tons per day.

Column adsorption/crystallisation

An adsorption technique is an established technology for separating glycerol, ions, water and methanol. Odor and pigments can be eliminated by adsorption on activated carbon. Activated carbon in the adsorption process removes soluble substance from water. It is used to make the carbon extremely porous and therefore have a very large surface area available for adsorption. The large internal surface makes active carbon ideal for adsorption. The activated carbon functions longer when the pores are bigger. Using activated carbon is good in waste water cleaning. However activated carbon is expensive to regenerate the carbon.

Due to high pressure drop and high viscosity of crude glycerol, the operational cost of the column adsorption will be high. Chromatography separation is the new progress in adsorption techniques. Chromatography separation is used to separate small amounts of samples in laboratory. Some of the possible chromatography techniques are: ion exchanged chromatography, reversed phase, affinity chromatography and hydrophobic interaction, gel permeation or molecular sieves may be used as the solid stationary phase in column chromatography. Ion exchange chromatography as an adsorption provides an ionic environment which allows two or more solutes in the feed stream to be separated. Glycerol and water separation are based on particle size and affinity. Since water is difficult to separate from glycerol, a suitable type of adsorbent with respect to high separation efficiency at low pressure drops and at a high volume flow capacity is required.

New process route for glycerol purification

This process above can be either continuous or batch mode. The process consists of five separation steps: first reactor, second reactor, decanter, flash distillation column, and adsorption column. This new process  to be able to produce glycerol higher than 99.5% purity from typical crude glycerol.

First reactor:

The crude glycerol is preheated first before heading for the first reactor. The purpose of the first reactor is by reacting glycerol and methyl esters to produce methanol and glycerides. The water and methanol removed when nitrogen is sparged. The gas runoff stream is passed through a condenser. The nitrogen is recycled back to the reactor when water and methanol are condensed (separated) through a condenser.

Second reactor:

The purpose of this reactor is that the unreacted methyl esters are reacted to produce triglycerides and methanol. Wash water has glycerol, is also added to the 2nd reactor. From the 1st reactor the liquid effulent stream is heated to preserve the 2nd reactor at 120-160oc just like the 1st reactor. Wash water is recycled when water and methanol is separated from nitrogen.

Decanter:

The purpose of decanter placed after the reactor is to get rid of the oil layer from glycerol stream by reducing the pH below 7 and also skimming it from the glycerol layer. In this tank glycerol stream is mixed with the recycled stream from the bottom of the flash column.

Flash distillation column:

In the flash distillation, the top column (vapour fraction) product is about 80-90% of glycerol from the feed stream is to be condensing in two condensers in series. Condensing glycerol is used in the first condenser whereas water condensing used in the 2nd condenser that will be sent to waster water stream. The heavy compounds and glycerol comes out of the bottom product (liquid fraction) is pumped back to the decanter. To prevent glycerol and salts build up in the decanter, some of is purged.

Adsorption columns

Removing the trace impurities and colour is the last step of glycerol refining. Ion exchange resins and activated carbon can be used as adsorbent material. Glycerol is then purified into a storage tank.

Factors affecting acid treatment of saponified effluent

The factors affecting acid treatment are as follows.

1. Raw oil

The quality of saponification waste water depends on the quality of oils and fats. Generally, oils and fats contain protein, gum, pigment (chlorophyll, carotenoids, gossypol), resin, phospholipids, sterols, waxes and other impurities. If the oil has not been pretreated, these impurities will be salted out into the saponification waste liquor after the saponification, it not only affects the saponification waste liquor treatment, but also affects the quality of glycerol products.

2. influence of flocculants: The amount of ferric chloride is determined by the quality of saponified waste liquid during acid treatment.

In order to remove the impurities in the saponification waste water as much as possible, the pH and temperature of the solution must be controlled. The hydrolysis of 1mol ferric chloride produces 3mol hydrochloric acid. Under acidic conditions, the iron soap can be dissolved and the colloid of ferric hydroxide can be reduced. In this way, the precipitation of ferric chloride, electric neutralization, coagulation and adsorption at isoelectric point are reduced, and the impurities can not be completely removed. Therefore, the Ph control of general endpoints is more appropriate in 3.5-3.8. The average amount of ferric chloride is 0.3%-0.6% of saponification waste liquid. For the same waste liquor, the crude glycerol (fatty acid iron soap precipitated completely) obtained by increasing ferric chloride in proper amount has good quality and light color. However, the treatment cost is high, the filtration residue is much, and the filtration speed is slow. When the amount of ferric chloride is reduced, the amount of filter residue is low, the filtration speed is fast, and the cost is low. However, the coarse and sour color is deep and the quality is poor.

Aluminum salt is a good flocculant. When treating saponification waste liquid, aluminum hydroxide is formed by reaction with free alkali. Aluminum hydroxide is a kind of flocculant colloid with strong adsorption. At the same time, aluminum ions react with fatty acids to form fatty acid aluminum salts. Aluminum salt flocculants can completely remove higher fatty acids. The removal rate of fatty acids is also very high. The removal rate of hydrophilic impurities such as protein and amino acids can reach 80%. When using aluminium salt, the temperature should be controlled at 40-80 C, and the PH should be controlled at 4.5. But when treated with H2SO4 and AL2 (SO4) 3, Na2so4 is formed. If NA2SO4 is used in the salting out of soap glue, its effect is only half of that of Naci. Therefore, when the amount of Na2SO4 in the recovered salt exceeds 20%, the salting out effect of soap cooking operation will be affected, so it needs to be replaced. In addition, the price of aluminum salt is relatively high, so the Chinese soap making industry mostly uses FeCL3 solution.

3. Treatment temperature: When the treatment temperature is low, the coagulation and adsorption effect of iron soap precipitation formed by FeCl3 is better. The longer the static time is, the more black fatty acid is separated. In the same way, the water quality is lighter, but the filtration speed is slower. The acidification treatment temperature is 50-60 degrees.

Control points of acid treatment operation: Take 10ML filtrate into test tube, add 2 drops of 5% ferric chloride solution, shake well and place for 5 minutes. Observe that there should be no turbidity or precipitate in the filtrate. Otherwise, the ferric chloride solution should continue to be added. When Ph has reached 3.5, it is necessary to return to alkali, adjust PH with alkali, make the treatment solution alkaline and then add ferric chloride solution to treat Ph up to 3.8-4.2, until the filtrate is not turbid. When adding pH to pH value, a small test should be carried out to determine the amount of alkali added.

Sources of Glycerine

Glycerine, also called glycerol or glycerin, is an odorless chemical used as an additive in many pharmaceutical products and cosmetics. Glycerine is used in body care products as a lubricant to increase the ease of product application and as a humectant to draw moisture into the skin. Although all glycerine performs a similar function in cosmetics and products, it can be derived from numerous sources.

Animal Fats

One source of glycerine is a byproduct of animal fat soaps. Glycerol from animal fats comes from animal triglycerides, one type of fat molecule commonly found in animal blood and the major component of an animal's fatty tissue, according to the Children's Hospital of Pittsburgh. Each triglyceride molecule contains three fatty acid chains, all connected to the glycerol backbone. During soap making, the bonds holding the fatty acids onto the glycerol are broken, giving off glycerine as a byproduct. Glycerine obtained from animal products is often labeled "glycerine."

Vegetable Oils

If you are concerned about consuming animal by products, you may also find products containing vegetable glycerine. Plants lipids are also typically stored as triglycerides. Plant triglycerides often differ from animal triglycerides because of their fatty acid chains; plant triglycerides commonly contain unsaturated fatty acid chains that form a bent shape, which allows the lipid to form a liquid oil at room temperature. Plant glycerine is obtained as a byproduct of soap making using plant oils. Many products that use vegetable oils as a source of glycerine may indicate that they are free of animal products or list "vegetable glycerine" as an ingredient.

Petroleum

In some cases, glycerine may come from a synthetic source, generated in the laboratory as a product of chemical reactions beginning with petroleum. However, the market for synthetic glycerine has diminished over time, since glycerine from natural sources is readily available as a byproduct of several industrial processes, including soap making and biodiesel production, reports "Biodiesel Magazine." As the demand for synthetic petroleum dwindles, the magazine reports, it is likely that natural glycerine will be used in more industries.

Chemically there are Five Grades of Glycerine

USP GLYCERIN(E) is a clear, almost colorless product for uses requiring glycerine of high purity with taste and odor characteristics desirable for pharmaceutical and food purposes. The designation USP is an abbreviation of U.S. Pharmacopeia and signifies that the glycerine thus designated meets or exceeds the standards established in U.S.

Pharmacopeia (USP XXII, 1990) monograph, Glycerin. The USP designation has official legal status in the United States since the U.S. Pharmacopeia has been incorporated by reference in various statutes and regulations governing drug and medical practices, of which the federal Food. Drug. and Cosmetic Act is the most significant. USP glycerine is commonly available commercially at anhydrous glycerol content levels of 96%.99.0% and 99.5%. Concentrations above 99.5% are also available commercially.

CP GLYCERINE or chemically pure glycerine is generally understood to be of the same quality or grade as USP glycerine,but this term is considered generic in the United States because it does not reflect compliance with any official quality requirements or specifications a s does the USP designation.

FOOD GRADE GLYCERINE in the United States meets the requirements outlined in the monograph Glycerin contained in the Food Chemicals Codex prepared by the Committee on Food Protection of the National Research Council. Food grade requirements are similar to USP standards. Within the European Economic Community, glycerine for use in food products must comply with Council Directive 78/663/EEC which specifies the standards of purity for emulsifiers,stabilizers thickeners, and gelling agents for use in foods.

HIGH GRAVITY GLYCERINE is a designation used in the United States for a commercial grade of glycerine that is clear,almost colorless and conforms to Federal Specification 0-G-491C issued November 14, 1983 by the General Services Administration. This product also conforms to Standard Specification for High-Gravity Glycerin, D-1257, issued by the American Society for Testing and Materials (ASTM). This grade must contain not less than 98.7% glycerol. It is commonly supplied at not less than 99.O% concentration.

DYNAMITE GLYCERINE in the United States meets all the High Gravity grade specifications except color, but it cannot be darker than the Federal Color Standard. In Europe, glycerine for use in explosives is defined by Specification 21D for dynamite glycerine issued by the Nobel Explosives Company Ltd. The British Standards Institution has also issued a standard specification for this grade of glycerine as British Standard Specification for Dynamite Glycerol.

New use of crude glycerin in biodiesel

Glycerol (also known as glycerin) is a major byproduct in the biodiesel manufacturing process. In general, for every 100 pounds of biodiesel produced, approximately 10 pounds of crude glycerol are created. As the biodiesel industry is rapidly expanding, a glut of crude glycerol is being created. Because this glycerol is expensive to purify for use in the food, pharmaceutical, or cosmetics industries, biodiesel producers must seek alternative methods for its disposal. Various methods for disposal and utilization of this crude glycerol have been attempted, including combustion, composting, anaerobic digestion, animal feeds, and thermochemical/biological conversions to value-added products. The objective of this article is to provide a general background in terms of waste glycerol utilization.

Characterizations of Glycerol Waste

Crude glycerol generated from biodiesel production is impure and of little economic value. In general, glycerol makes up 65% to 85% (w/w) of the crude stream (Gonzalez-Pajuelo et al. 2005; Mu et al. 2006). The wide range of purity values can be attributed to different glycerol purification methods or different feedstocks used by biodiesel producers. For example, Thompson & He (2006) have characterized the glycerol produced from various biodiesel feedstocks. The authors found that mustard seed generated a lower level (62%) of glycerol, while soy oil had 67.8 % glycerol, and waste vegetable oil had the highest level (76.6 %) of glycerol.

Methanol and free fatty acids (soaps) are the two major impurities contained in crude glycerol (Thompson & He 2006). The existence of methanol is due to the fact that biodiesel producers use excess methanol to drive the chemical transesterification to completion, and do not recover all the methanol. The soaps, which are soluble in the glycerol layer, originate from a reaction between the free fatty acids present in the initial feedstock and the catalyst (base).i.e.,

 

In addition to methanol and soaps, crude glycerol also contains a variety of elements such as calcium, magnesium, phosphorous, or sulfur. Thompson & He (2006) reported that the elements present in the glycerol of different feedstock sources (such as canola, rapeseed, and soybean) were similar. Calcium was in the range of 3-15 ppm, magnesium was 1-2 ppm, phosphorous was 8-13 ppm, and sulfur was 22-26 ppm. However, when crambe (a perennial oilseed plant) was used as feedstock, crude glycerol contained the same elements, but at vastly different concentrations. Schröder & Südekum (1999) also reported the elemental composition of crude glycerol from rapeseed oil feedstock. Phosphorous was found to be between 1.05 % and 2.36 % (w/w) of the crude glycerol. Potassium was between 2.20 % and 2.33%, while sodium was between 0.09% and 0.11%. Cadmium, mercury, and arsenic were all below detectable limits.

The crude glycerol derived from alkali-catalyzed transesterification usually has a dark brown color with a high pH (11-12). When pH is adjusted to a neutral range, soaps will be converted into free fatty acids, as shown in the following equation

 

The free fatty acids in the crude glycerol stream results in a cloudy solution. After settling for a period of time, this cloudy solution will be separated into two clear phases, with the top layer being the free fatty acid phase, and bottom layer the glycerol phase.

New Uses For Glycerol Waste

There are various outlets for disposal and utilization of the crude glycerol generated in biodiesel plants. For large scale biodiesel producers, crude glycerol can be refined into a pure form and then be used in food, pharmaceutical, or cosmetics industries. For small scale producers, however, purification is too expensive to be performed in their manufacturing sites. Their crude glycerol is usually sold to large refineries for upgrading. In recent years, however, with the rapid expansion of biodiesel industry, the market is flooded with excessive crude glycerol. As a result, biodiesel producers only receive 2.5-5 cents/lb for this glycerol . Therefore, producers must seek new, value-added uses for this glycerol.

There have been many investigations into alternative uses of crude glycerol. Combustion, composting, animal-feeding, thermo-chemical conversions, and biological conversion methods for glycerol usage and disposal have all been proposed. Johnson and Taconi (2007) reported that combustion of crude glycerol is a method that has been used for disposal. However, this method is not economical for large producers of biodiesel. It has also been suggested that glycerol can be composted  or used to increase the biogas production of anaerobic digesters . DeFrain et al. (2004) attempted to feed biodiesel-derived glycerol to dairy cows in order to prevent ketosis, but found that it was not useful.

Also, Lammers et al. (2008) studied supplementing the diet of growing pigs with crude glycerol. This study found that the metabolizable-to-digestible energy ratio of glycerol is similar to corn or soybean oil when fed to pigs. Therefore, the study concludes that “crude glycerol can be used as an excellent source of energy for growing pigs,” but also cautions that little is known about the impacts of impurities in the glycerol. Furthermore, Cerrate et al. (2006) have had some success with feeding glycerol to broiler chickens. Birds fed 2.5 % of 5% glycerin diets had higher breast yield than the control group, but the authors caution that there is still concern about methanol impurities in the glycerol.

Converting crude glycerol into valued-added products through thermo-chemical methods or biological methods is an alternative for utilizing this waste stream. It has been reported that glycerol can be thermochemically converted into propylene glycol , acetol , or a variety of other products. Cortright et al. (2002) have developed an aqueous phase reforming process that transforms glycerol into hydrogen. Virent Energy Systems is currently trying to commercialize this technology and claim that sodium hydroxide, methanol, and high pH levels within crude glycerol help the process.

For biological conversions of crude glycerol, the glycerol serves as a feedstock in various fermentation processes. For example, Lee et al. (2001) have used glycerol in the fermentation of Anaerobiospirillum succiniciproducens for the production of succinic acid. The fermentation of E. coli on glycerol leads to the production of a mixture of ethanol, succinate, acetate, lactate, and hydrogen. Glycerol can also be converted to citric acid by the yeast Yarrowia lipolytica. It has been reported that this organism produces the same amount of citric acid when grown on glucose or on raw glycerol. Rymowicz et al. (2006) found that acetate mutant strains of Y. lipolytica can produce high levels of citric acid while producing very little isocitrate. Furthermore, it has been shown that Clostridium butyricum can utilize biodiesel-derived glycerol to produce 1,3-propanediol  in both batch and continuous cultures. During the fermentation process, the organism also produces byproducts of acetic and butyric acid . The researchers at Virginia Tech also developing algal fermentation processes to convert crude glycerol into high value omega-3 polyunsaturated fatty acids