Fatty acid ester and glycerol are the important reactions in oil chemical industry. A variety of ester products can be obtained by this reaction. The most widely used products in industry are methyl ester of fatty acid and glycerol. Fatty acid methyl ester is an important basic oil chemical raw material. Many compounds can be derived from fatty acid methyl ester. Fatty acid methyl ester has always been the research object of oil chemical workers. In recent years, due to the fierce competition in the oil price war, the contradiction between fuel supply and demand has intensified, and the research of fuel substitutes has been widely carried out. The production of biodiesel has developed to a considerable scale. The production of biodiesel has directly impacted the structure of glycerol production.
The raw materials of biodiesel are oil and methanol or ethanol. For every 10 tons of biodiesel, 1 ton of glycerol by-product is produced. Vegetable oils such as rapeseed oil, soybean oil, palm oil, butter, industrial lard and other oils can be used, as well as various kinds of recycled oils, such as fried waste oil, refined oil foot recycled oil, etc. China has made great progress in the research and production of biodiesel. At present, there are 2 million tons of low-grade oil and fat in China. There are abundant raw materials for the production of biodiesel (low-grade fatty acid esters - methyl esters, ethyl esters). It is expected that biodiesel will develop rapidly to make up for the shortage of more than one million tons per year. The rapid development of biodiesel will provide abundant raw materials for glycerol production, which will inevitably attract the attention of the glycerol industry.
The alcoholysis process of oil and fat is to produce fatty acid esters and glycerol by alcoholysis of oil and low-carbon alcohols under the condition of alkaline catalyst. In order to obtain high ester conversion rate, the grease used should be degummed and deacidified so that the acid value is less than 0.5 mg KOH/g, and methanol should be anhydrous. The alcoholysis reaction can be carried out under pressure and high temperature (9.OMPa, 240 C, glycerol concentration up to 90%) or under normal pressure of 50-70 C. There are batch and continuous processes. Intermittent production, quick product turnaround, can be applied to a variety of oils and fats raw materials. Continuous type is suitable for large-scale production with low energy consumption. The concentration of alcoholic glycerol is much higher than that of oil-hydrolyzed sweet water, which can reach more than 70%.
In order to reduce the cost of raw materials, when low-grade oils (high acid value oils) are used, pre-esterification technology can be used to make free fatty acids into fatty acid esters, and then methyl esterification can be carried out. The alcoholysis reaction under pressure and high temperature has fast reaction speed, but it requires high equipment. In order to reduce the investment cost of equipment, the reaction device under low temperature and normal pressure is often used.
Oil, methanol and catalyst (sodium methanol, etc.) were put into the reactor in batches. The material remained boiling and refluxed for 2 to 3 hours at 70 (?) C. The ester conversion rate was above 95%. If the content of free fatty acid in oil is more than 2%, the oil must be alkali refined or pre-esterified with methanol (commonly used catalysts are H2SO4, HCl, p-toluene sulfonic acid, strong acid resin, etc.) to reduce the amount of catalyst and the content of soap in sweet water. The reactant is stationary in the settling stratifier and crude glycerol is separated. Methanol in crude glycerol is evaporated and reused by methanol evaporator, and crude glycerol is sent to the post-processing and refining process. A small amount of glycerol in methyl ester is recovered by heating crude methyl ester to recover methanol, then adding water to crude methyl ester to dilute acid (3% of the reaction mixture, the amount of acid is equal to that of catalyst), so as to wash out glycerol in methyl ester and decompose soap and catalyst in methyl ester. Static stratification, crude glycerol sent to the post-processing refining process.
Showing posts with label glycerol. Show all posts
Showing posts with label glycerol. Show all posts
Saturday, May 11, 2019
Thursday, March 7, 2019
The possibility and prospect of using glycerol as an energy feedstuff source for pigs
Corn is the main source of energy feeds for pigs. In recent years, both the increasingly rising price and also the tense supply of corn have influenced the development for the pig industry very severely. In order to accommodate with the states, people have been looking for alternative energy feeds actively, and have also conducted much extensive research. Among them, the possibility and prospect of using glycerol (a by-product of biodiesel production) as a source of energy feedstuff proposed by some countries have brought attention from the world.
According to statistics, the capacity of biodiesel under construction in China is up to 3 million t/ year. This means that large amounts of glycerol by-products will be produced worldwide. With the increase of biodiesel production, the quantity of its by-product glycerol also have increased accordingly, providing sufficient material base for the exploitation of glycerol.
Glycerol, a small molecule by-products, is a colorless, odorless, clear liquid, released during the process of biodiesel production. For livestock, fat intake from the fodder will be digested into glycerol and fatty acids in the digestive tract, which will be obtained and finally stored in the adipocytel as the most economical storage form in the body of livestock. And this could convert into heat energy when needed. Therefore, glycerol is one substance of the animal physiological system. Using glycerol as energy feed for livestock has become one of the hot research topics in this way for many countries.
Due to its small molecular weight and molecules, glycerol is easily absorbed by the intestinal tract of livestock via simple diffusion. In the metabolic pathway, glycerol is used for energy production.
The latest study shows that the metabolizable energy (ME) of glycerol is close to its total energy (GE). This indicates that glycerol has a higher digestibility. With proper content, glycerol could improve the quality of pelleted feed, reduce both the energy costs in the pelletizing process, and also the powder in fodder and additives.
Some researchers have pointed out that because glycerol is sweet, it can improve the palatability of fodder.
Iowa State University conducted a series of animal experiments on using glycerol as an energy feed instead of corn. And its results shows that effect of glycerol is comparable to that of corn, with a promising prospect. Dutch Dr. Jannes Doppenberg thought glycerin would be a popular nutritive material as it's going to be a common ingredient, while other bio-fuel byproducts such as DDGS and rapeseed meal/press cake are low-energy and starch-deficient raw materials. William Dozier, an animal scientist at the USDA's agricultural research service (USDA-ARS), has pointed out that glycerol can be used as an alternative source of energy in fodder to reduce fodder costs, from a nutritional standpoint. A series of experiments confirmed that glycerol had the same energy value as corn.
Although using glycerol as an energy feed for pigs still with many problems that need to be further studied has not been commercialized on a large scale, the current researches and future development trend indicates that using glycerol as a source of energy for pig fodder has a great foreground.
According to statistics, the capacity of biodiesel under construction in China is up to 3 million t/ year. This means that large amounts of glycerol by-products will be produced worldwide. With the increase of biodiesel production, the quantity of its by-product glycerol also have increased accordingly, providing sufficient material base for the exploitation of glycerol.
Glycerol, a small molecule by-products, is a colorless, odorless, clear liquid, released during the process of biodiesel production. For livestock, fat intake from the fodder will be digested into glycerol and fatty acids in the digestive tract, which will be obtained and finally stored in the adipocytel as the most economical storage form in the body of livestock. And this could convert into heat energy when needed. Therefore, glycerol is one substance of the animal physiological system. Using glycerol as energy feed for livestock has become one of the hot research topics in this way for many countries.
Due to its small molecular weight and molecules, glycerol is easily absorbed by the intestinal tract of livestock via simple diffusion. In the metabolic pathway, glycerol is used for energy production.
The latest study shows that the metabolizable energy (ME) of glycerol is close to its total energy (GE). This indicates that glycerol has a higher digestibility. With proper content, glycerol could improve the quality of pelleted feed, reduce both the energy costs in the pelletizing process, and also the powder in fodder and additives.
Some researchers have pointed out that because glycerol is sweet, it can improve the palatability of fodder.
Iowa State University conducted a series of animal experiments on using glycerol as an energy feed instead of corn. And its results shows that effect of glycerol is comparable to that of corn, with a promising prospect. Dutch Dr. Jannes Doppenberg thought glycerin would be a popular nutritive material as it's going to be a common ingredient, while other bio-fuel byproducts such as DDGS and rapeseed meal/press cake are low-energy and starch-deficient raw materials. William Dozier, an animal scientist at the USDA's agricultural research service (USDA-ARS), has pointed out that glycerol can be used as an alternative source of energy in fodder to reduce fodder costs, from a nutritional standpoint. A series of experiments confirmed that glycerol had the same energy value as corn.
Although using glycerol as an energy feed for pigs still with many problems that need to be further studied has not been commercialized on a large scale, the current researches and future development trend indicates that using glycerol as a source of energy for pig fodder has a great foreground.
Thursday, January 17, 2019
Glycerol as a Feed Ingredient in Dairy Rations
Glycerol, also known as glycerin and glycerine or as propane-1,2,3-triol, 1,2,3-propanetriol, 1,2,3-trihydroxypropane, glyceritol, and glycyl alcohol, is a colorless, odorless, hygroscopic, and sweet-tasting viscous liquid. It is a sugar alcohol with a high solubility index in water. There are a wide range of applications for glycerol in the food, pharmaceutical, and cosmetic industries.
The term "bio-diesel" is used to describe the methyl or sometimes ethyl esters produced from oilseed crops. Every 10 gallons of biodiesel produced generates about 7.6 lb of crude glycerol. According to the National Biodiesel Board, the production of biodiesel in the United States over the next decade is expected to grow. As of April 2007, current annual production is 395 million gallons. Planned expansions in the biodiesel industry are expected to drive annual production to more than 1.1 billion gallons within the next 18 months, generating more than 800 million pounds of glycerol. Corresponding price projections suggest that glycerol could be priced competitively with grains as a source of energy for livestock. The value of glycerol in this regard may be further amplified with increasing diversion of corn and other grains to ethanol production. Although there is supporting evidence for use of glycerol for transition cows, there is little information that examines the use of glycerol as a macro-ingredient in rations for lactating dairy cows. This review will explore some of the attributes and issues pertinent to glycerol as a feed for lactating dairy cows and highlight results from a recent research study at Purdue University where the value of glycerol was examined as a replacement for corn grain.
Most biodiesel is currently produced by a reaction that utilizes a base catalyzed transesterification of the oil. For soy diesel production, soybean oil is reacted with an equal weight of a short chain alcohol (usually methanol but sometimes ethanol) in the presence of a catalyst (sodium hydroxide; caustic soda or potassium hydroxide; potash) to yield biodiesel and crude glycerol. This process requires low temperature and pressure, yields high conversion (98%) with minimal side reactions and reaction time, and results in direct conversion of soybean oil to biodiesel with no intermediate compounds. The biodiesel is separated from the glycerol by gravity separation or by centrifugation. Because most commercial biodiesel production utilizes a 6 to 1 molar ratio of alcohol to oil, or excess alcohol, to drive the reaction to completion, methanol can partition to the glycerol and biodiesel phases.
Alcohol is removed from biodiesel and glycerol phases by flash evaporation or by distillation to recover and re-use it. The resulting glycerol contains unused catalyst and soaps which are then neutralized by the addition of acid to produce crude glycerin containing 80 to 88% glycerol. Further purification of crude glycerin to 99% or higher purity is needed for use in the cosmetic and pharmaceutical industries. Impurities devalue crude glycerol; high levels of residual catalyst, salts, and methanol may be problematic in the using of glycerol as a livestock feed. Recent evaluation of crude glycerol from soy biodiesel production indicates a glycerol content of 76.2% and as much as 7.98% fat, 0.05% protein, and 2.73% ash. The latter was composed of 11 ppm Ca, 6.8 ppm Mg, 53 ppm P, and 1.2% Na .
Glycerin is generally recognized as safe for use in animal feed . Although food grade glycerol is safe in this regard, concerns have been expressed relative to contaminant levels in crude glycerol from biodiesel production. Methanol levels are of particular concern, and the methanol content of crude glycerol should be less than 0.5%. A recent regulatory letter issued by FDA indicates that methanol levels higher than 150 ppm could be considered unsafe for animal feed.
The use of glycerol in the treatment of ketosis was reported as early as 1954 , and evaluation of glycerol as well as propylene glycol as a ketosis treatment was further explored in the 1970s (Fisher et al., 1971, 1973). More recently, the value of glycerol has been examined as a preventative aid for metabolic problems associated with transition cows. Goff and Horst (2001) used up to 3 L in ketosis treatment and prevention, and DeFrain et al. (2004) fed 1.89 lb/day to transition dairy cattle. While these studies demonstrate the potential value of glycerol in treating ketosis, there is a lack of data to examine the value of glycerol as a primary ration ingredient for post-transition dairy cattle. Feeding rates for transition cows range from 5 to 8% of the dietary DM.
Feeding studies have typically been lower from 150 to 472 g/day . There are only a handful of studies with glycerol feeding rates that approach 5% or more of the ration on a dry matter (DM) basis. Schröder and Südekum (1999) fed 10% glycerol to dairy cattle, effectively replacing over one-half of the starch in the diet, without negatively affecting intake, ruminal digestibility, rumen microbial synthesis, or total tract nutrient digestibility in steers. Feeding 3.6% glycerol to mid-lactation dairy cows was without effect on intake, milk production, or gross milk composition but slightly altered the profile of fatty acids in milk and increased rumen propionate and butyrate concentrations at the expense of reduced acetate concentration . Feeding 1.89 lb/day of glycerol to +21 days relative to calving (5.4% of ration DM) did not have any effects on milk production or feed intake . Feeding 500 ml of glycerol, or approximately 3.1% of ration DM, from three weeks prior to calving through 70 days in milk caused an increase in milk yield and milk protein content . Taken together, these experiments indicate that glycerol may be added to diets for lactating cows to a level of at least 10% of DM without deleterious effects, and in some cases, beneficial effects on milk production and composition have occurred.
Because glycerol has not been used as a macro ingredient, the estimates of net energy of lactation (NEL) are not available for typical feeding scenarios. Schröder and Südekum (1999) reported estimates from 0.9 to 1.03 Mcal/lb with energy values decreasing for higher starch diets, and recently, DeFrain et al. (2004) reported 0.86 Mcal/lb when feeding glycerol in early lactation. There is uncertainty in the energy value for glycerol due to the amounts fed previously and unknown interactions with other ration components.
Glycerol is fermented to volatile fatty acids (VFA) in the rumen. Early reports of glycerol fermentation indicated that glycerol was almost entirely fermented to propionate . Other reports indicate an increase in acetic and propionic acids or increased propionic and butyric acids . In vitroglycerol fermentation using rumen fluid inoculum from cows adapted to glycerol feeding indicates increased production of propionate and butyrate at the expense of acetate . Studies using 14°C labeled glycerol indicate that that most of the glycerol was found in propionate . Rumen microbes adapt to glycerol feeding as the rates of glycerol disappearance from rumen fluid are more rapid after 7 days of glycerol feeding to donor animals used as a source of rumen-fluid . In studies where 15 to 25% glycerol was added, most of the glycerol disappeared within 6 hours .
The maximal rates of glycerol disappearance in the rumen determined using in vitro fermentors is 0.52 to 0.62 g/hour . There is lack of agreement for in vivo disappearance from the rumen by microbial metabolism. Estimates from disappearance of a 200 g dose of glycerol indicate that more than 85% of glycerol in the rumen disappears within 2 hours in cattle acclimated to glycerol feeding . Other data using a dose of 240 g of glycerol indicate rumen disappearance rates ranging between 1.2 to 2.4 g/hour . Likewise, there have been reports suggesting that a portion of the glycerol entering the rumen can be absorbed directly . The fate of any absorbed glycerol is metabolism in the liver and requires glycerol kinase , and this enzyme is responsible for channeling glycerol into the triose phosphate step of glycolysis/gluconeogenesis. When glucose demands are high, such as the case for lactating cows, the fates of absorbed glycerol or propionate produced by rumen fermentation are likely to be identical.
The objective of our experiment was to evaluate the value of glycerol as a replacement for corn grain in diets of lactating dairy cattle. Sixty lactating Holstein cows were housed in individual tie stalls at the Purdue Dairy Research and Education Center and adjusted to a basal diet for a 2-week period. Cows were then assigned to diets containing 0, 5, 10, or 15% glycerol (99.5% USP/FCC, Kosher grade) as a percentage of ration DM. The basal (0 glycerol) ration was balanced to meet or exceed NRC (2001) requirements and contained corn silage, alfalfa haylage, hay, dry-rolled corn, vitamins, and minerals (Table 1). Corn was replaced by an equivalent amount of food grade glycerol and corn gluten feed. The addition of corn gluten feed adjusted for the protein removed with corn grain. Diets were offered once daily for ad libitum intake (5 to 10% weigh-backs), feed refusals were measured daily, and feed intake was determined by difference. Cows were milked twice daily, and milk samples were obtained weekly at two consecutive milkings and analyzed for fat, protein, lactose, total solids, milk urea N, and somatic cells.
Glycerol was well tolerated by the cows, and there were no differences in DM intake or milk production when the entire 8-week experimental period is considered (Table 2). Feed intake was reduced by inclusion of 15% glycerol during the first 7 days of the trial. Negative effects on intake were only evident during the first week of the test, and differences were not detected for the subsequent 7 weeks. Recovery of intake within 7 days suggests that achieving a feeding rate of 15% glycerol might be best accomplished with a protocol that gradually introduces glycerol into the ration.
Milk production and composition were not altered in response to glycerol feeding with the exception of decreased milk urea nitrogen in response to glycerol. These changes were observed at all levels of glycerol feeding. Reduced MUN concentrations suggest improved use of dietary protein by rumen bacteria and reduced losses as ammonia. Cows fed the highest amount of glycerol gained the most weight during the 8-week feeding period. Cows fed 10 and 15% glycerol gained more weight than cows fed 5% glycerol or the control diet. Weight gain for the control cows and 5% glycerol did not differ.
Estimates of NEL for the diets were calculated from intake, production data, and body weight (BW) changes. The energy content of each ration was calculated for each cow over the experimental period using total energy expenditure (milk, maintenance, and BW gain) with DM intake. An estimate of NEL (Mcal/lb) for each diet was determined from NEL used (Mcal) divided by DM consumed for the corresponding interval. Estimated energy values for the diets were 0.70, 0.70, 0.71, and 0.72 ± 0.02 Mcal/lb and were not different (P = 0.90). The lack of differences in this regard suggests that glycerol can be substituted for corn without adjustments for the energy content. However, the feed energy value of crude glycerol is likely to be less than that of pure glycerol and must be adjusted for the levels and energy content of the impurities. It should be noted that the energy values of the TMR determined by chemical analysis in Table 1 are slightly higher than the estimates determined by difference of milk produced and BW change. These differences may reflect the effects of increasing intake and therefore passage rate to reduce the NE value of the rations.
Results from this study clearly indicate that glycerol is a valuable feed ingredient for lactating dairy cows. Glycerol can be included as a macro ingredient in diets for lactating dairy cows without any deleterious effects. Therefore, feeding glycerol in place of corn is an alternative strategy for formulating diets for lactating cows when corn is not priced favorably.
These data point to the feeding value of glycerol when fed in pure form; however, depending on the level and composition of impurities, the feeding value of crude glycerol cannot be inferred directly from these results.
The term "bio-diesel" is used to describe the methyl or sometimes ethyl esters produced from oilseed crops. Every 10 gallons of biodiesel produced generates about 7.6 lb of crude glycerol. According to the National Biodiesel Board, the production of biodiesel in the United States over the next decade is expected to grow. As of April 2007, current annual production is 395 million gallons. Planned expansions in the biodiesel industry are expected to drive annual production to more than 1.1 billion gallons within the next 18 months, generating more than 800 million pounds of glycerol. Corresponding price projections suggest that glycerol could be priced competitively with grains as a source of energy for livestock. The value of glycerol in this regard may be further amplified with increasing diversion of corn and other grains to ethanol production. Although there is supporting evidence for use of glycerol for transition cows, there is little information that examines the use of glycerol as a macro-ingredient in rations for lactating dairy cows. This review will explore some of the attributes and issues pertinent to glycerol as a feed for lactating dairy cows and highlight results from a recent research study at Purdue University where the value of glycerol was examined as a replacement for corn grain.
Glycerol Production and Quality Concerns
Most biodiesel is currently produced by a reaction that utilizes a base catalyzed transesterification of the oil. For soy diesel production, soybean oil is reacted with an equal weight of a short chain alcohol (usually methanol but sometimes ethanol) in the presence of a catalyst (sodium hydroxide; caustic soda or potassium hydroxide; potash) to yield biodiesel and crude glycerol. This process requires low temperature and pressure, yields high conversion (98%) with minimal side reactions and reaction time, and results in direct conversion of soybean oil to biodiesel with no intermediate compounds. The biodiesel is separated from the glycerol by gravity separation or by centrifugation. Because most commercial biodiesel production utilizes a 6 to 1 molar ratio of alcohol to oil, or excess alcohol, to drive the reaction to completion, methanol can partition to the glycerol and biodiesel phases.
Alcohol is removed from biodiesel and glycerol phases by flash evaporation or by distillation to recover and re-use it. The resulting glycerol contains unused catalyst and soaps which are then neutralized by the addition of acid to produce crude glycerin containing 80 to 88% glycerol. Further purification of crude glycerin to 99% or higher purity is needed for use in the cosmetic and pharmaceutical industries. Impurities devalue crude glycerol; high levels of residual catalyst, salts, and methanol may be problematic in the using of glycerol as a livestock feed. Recent evaluation of crude glycerol from soy biodiesel production indicates a glycerol content of 76.2% and as much as 7.98% fat, 0.05% protein, and 2.73% ash. The latter was composed of 11 ppm Ca, 6.8 ppm Mg, 53 ppm P, and 1.2% Na .
Glycerin is generally recognized as safe for use in animal feed . Although food grade glycerol is safe in this regard, concerns have been expressed relative to contaminant levels in crude glycerol from biodiesel production. Methanol levels are of particular concern, and the methanol content of crude glycerol should be less than 0.5%. A recent regulatory letter issued by FDA indicates that methanol levels higher than 150 ppm could be considered unsafe for animal feed.
Glycerol for Transition Cows at Low Inclusion Levels
The use of glycerol in the treatment of ketosis was reported as early as 1954 , and evaluation of glycerol as well as propylene glycol as a ketosis treatment was further explored in the 1970s (Fisher et al., 1971, 1973). More recently, the value of glycerol has been examined as a preventative aid for metabolic problems associated with transition cows. Goff and Horst (2001) used up to 3 L in ketosis treatment and prevention, and DeFrain et al. (2004) fed 1.89 lb/day to transition dairy cattle. While these studies demonstrate the potential value of glycerol in treating ketosis, there is a lack of data to examine the value of glycerol as a primary ration ingredient for post-transition dairy cattle. Feeding rates for transition cows range from 5 to 8% of the dietary DM.
Feeding Studies Using Higher Inclusion Levels of Glycerol
Feeding studies have typically been lower from 150 to 472 g/day . There are only a handful of studies with glycerol feeding rates that approach 5% or more of the ration on a dry matter (DM) basis. Schröder and Südekum (1999) fed 10% glycerol to dairy cattle, effectively replacing over one-half of the starch in the diet, without negatively affecting intake, ruminal digestibility, rumen microbial synthesis, or total tract nutrient digestibility in steers. Feeding 3.6% glycerol to mid-lactation dairy cows was without effect on intake, milk production, or gross milk composition but slightly altered the profile of fatty acids in milk and increased rumen propionate and butyrate concentrations at the expense of reduced acetate concentration . Feeding 1.89 lb/day of glycerol to +21 days relative to calving (5.4% of ration DM) did not have any effects on milk production or feed intake . Feeding 500 ml of glycerol, or approximately 3.1% of ration DM, from three weeks prior to calving through 70 days in milk caused an increase in milk yield and milk protein content . Taken together, these experiments indicate that glycerol may be added to diets for lactating cows to a level of at least 10% of DM without deleterious effects, and in some cases, beneficial effects on milk production and composition have occurred.
Energy Value for Glycerol
Because glycerol has not been used as a macro ingredient, the estimates of net energy of lactation (NEL) are not available for typical feeding scenarios. Schröder and Südekum (1999) reported estimates from 0.9 to 1.03 Mcal/lb with energy values decreasing for higher starch diets, and recently, DeFrain et al. (2004) reported 0.86 Mcal/lb when feeding glycerol in early lactation. There is uncertainty in the energy value for glycerol due to the amounts fed previously and unknown interactions with other ration components.
Rumen Metabolism of Glycerol
Glycerol is fermented to volatile fatty acids (VFA) in the rumen. Early reports of glycerol fermentation indicated that glycerol was almost entirely fermented to propionate . Other reports indicate an increase in acetic and propionic acids or increased propionic and butyric acids . In vitroglycerol fermentation using rumen fluid inoculum from cows adapted to glycerol feeding indicates increased production of propionate and butyrate at the expense of acetate . Studies using 14°C labeled glycerol indicate that that most of the glycerol was found in propionate . Rumen microbes adapt to glycerol feeding as the rates of glycerol disappearance from rumen fluid are more rapid after 7 days of glycerol feeding to donor animals used as a source of rumen-fluid . In studies where 15 to 25% glycerol was added, most of the glycerol disappeared within 6 hours .
The maximal rates of glycerol disappearance in the rumen determined using in vitro fermentors is 0.52 to 0.62 g/hour . There is lack of agreement for in vivo disappearance from the rumen by microbial metabolism. Estimates from disappearance of a 200 g dose of glycerol indicate that more than 85% of glycerol in the rumen disappears within 2 hours in cattle acclimated to glycerol feeding . Other data using a dose of 240 g of glycerol indicate rumen disappearance rates ranging between 1.2 to 2.4 g/hour . Likewise, there have been reports suggesting that a portion of the glycerol entering the rumen can be absorbed directly . The fate of any absorbed glycerol is metabolism in the liver and requires glycerol kinase , and this enzyme is responsible for channeling glycerol into the triose phosphate step of glycolysis/gluconeogenesis. When glucose demands are high, such as the case for lactating cows, the fates of absorbed glycerol or propionate produced by rumen fermentation are likely to be identical.
Feeding Experiments with Glycerol
The objective of our experiment was to evaluate the value of glycerol as a replacement for corn grain in diets of lactating dairy cattle. Sixty lactating Holstein cows were housed in individual tie stalls at the Purdue Dairy Research and Education Center and adjusted to a basal diet for a 2-week period. Cows were then assigned to diets containing 0, 5, 10, or 15% glycerol (99.5% USP/FCC, Kosher grade) as a percentage of ration DM. The basal (0 glycerol) ration was balanced to meet or exceed NRC (2001) requirements and contained corn silage, alfalfa haylage, hay, dry-rolled corn, vitamins, and minerals (Table 1). Corn was replaced by an equivalent amount of food grade glycerol and corn gluten feed. The addition of corn gluten feed adjusted for the protein removed with corn grain. Diets were offered once daily for ad libitum intake (5 to 10% weigh-backs), feed refusals were measured daily, and feed intake was determined by difference. Cows were milked twice daily, and milk samples were obtained weekly at two consecutive milkings and analyzed for fat, protein, lactose, total solids, milk urea N, and somatic cells.
| Glycerol (% of DM) | ||||
|---|---|---|---|---|
| Ingredient | 0 | 5 | 10 | 15 |
| Corn silage | 31.94 | 31.94 | 31.94 | 31.88 |
| Alfalfa haylage | 10.00 | 10.00 | 10.00 | 9.98 |
| Alfalfa hay | 12.16 | 12.16 | 12.16 | 12.14 |
| Soybean hulls | 7.66 | 7.66 | 7.66 | 7.64 |
| 48% soybean meal | 6.62 | 6.62 | 6.62 | 6.61 |
| Roasted soybeans | 5.40 | 5.40 | 5.40 | 5.39 |
| Fish meal | 0.66 | 0.66 | 0.66 | 0.66 |
| Urea | 0.30 | 0.30 | 0.30 | 0.30 |
| Megalac-R®1 | 0.98 | 0.98 | 0.98 | 0.98 |
| Corn, ground | 20.00 | 14.20 | 8.40 | 2.79 |
| Glycerol | - | 5.00 | 10.00 | 14.97 |
| Corn gluten meal | - | 0.80 | 1.60 | 2.40 |
| Mineral/vitamin | 4.28 | 4.28 | 4.28 | 4.27 |
| Chemical analysis, % of DM2 | ||||
| Crude protein | 18.1 | 17.5 | 17.9 | 18.1 |
| ADF | 19.1 | 19.2 | 19.4 | 19.3 |
| NDF | 30.9 | 32.4 | 29.7 | 31.0 |
| NEL, Mcal/lb | 0.77 | 0.76 | 0.77 | 0.77 |
| Ca | 1.03 | 1.01 | 1.06 | 1.05 |
| P | 0.41 | 0.39 | 0.41 | 0.41 |
| Mg | 0.34 | 0.31 | 0.32 | 0.33 |
| K | 1.88 | 1.85 | 1.88 | 1.88 |
| Na | 0.25 | 0.24 | 0.28 | 0.27 |
| 1Church and Dwight Co. Inc., Princeton, N.J. 2DM = dry matter, ADF = acid detergent fiber, NDF = neutral detergent fiber, and NEL = net energy for lactation. | ||||
Glycerol was well tolerated by the cows, and there were no differences in DM intake or milk production when the entire 8-week experimental period is considered (Table 2). Feed intake was reduced by inclusion of 15% glycerol during the first 7 days of the trial. Negative effects on intake were only evident during the first week of the test, and differences were not detected for the subsequent 7 weeks. Recovery of intake within 7 days suggests that achieving a feeding rate of 15% glycerol might be best accomplished with a protocol that gradually introduces glycerol into the ration.
| Glycerol (% of DM) | ||||||
|---|---|---|---|---|---|---|
| Item | 0 | 5 | 10 | 15 | SEM | P2 |
| Milk production, lb/day | 81.4 | 81.2 | 82.1 | 80.0 | 1.3 | 0.71 |
| Feed intake, lb/day | 52.8 | 53.9 | 54.1 | 53.0 | 1.2 | 0.82 |
| Efficiency, milk/feed, lb/lb | 1.56 | 1.52 | 1.52 | 1.53 | 0.04 | 0.85 |
| Milk fat, lb/day | 2.93 | 2.81 | 2.92 | 2.80 | 0.14 | 0.88 |
| Milk protein, lb/day | 2.19 | 2.28 | 2.33 | 2.28 | 0.09 | 0.78 |
| Milk lactose, lb/day | 3.66 | 3.71 | 3.88 | 3.68 | 0.18 | 0.84 |
| Milk solids, lb/day | 9.50 | 9.53 | 9.85 | 9.47 | 0.43 | 0.91 |
| SCC, 1000 cells/ml | 275 | 490 | 137 | 144 | 111 | 0.10 |
| Milk urea N, mg/dl | 12.5a | 10.9b | 10.7b | 10.2b | 0.4 | <0.05 |
| Milk fat, % | 3.70 | 3.52 | 3.58 | 3.58 | 0.11 | 0.69 |
| Milk protein, % | 2.79 | 2.84 | 2.86 | 2.89 | 0.06 | 0.62 |
| Milk lactose, % | 4.64 | 4.62 | 4.70 | 4.66 | 0.07 | 0.89 |
| Milk solids, % | 12.05 | 11.89 | 12.03 | 12.04 | 0.19 | 0.91 |
| BCS change3 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.91 |
| BW change, lb3 | 69.4a | 89.6ab | 109.3b | 113.5b | 10.2 | <0.05 |
| 1SEM = standard error of mean; SCC = somatic cell count. 2Probability that treatment means are equal. 3Change observed over the 8 weeks of the trial. abMeans with different superscripts differ (P < 0.05). | ||||||
Milk production and composition were not altered in response to glycerol feeding with the exception of decreased milk urea nitrogen in response to glycerol. These changes were observed at all levels of glycerol feeding. Reduced MUN concentrations suggest improved use of dietary protein by rumen bacteria and reduced losses as ammonia. Cows fed the highest amount of glycerol gained the most weight during the 8-week feeding period. Cows fed 10 and 15% glycerol gained more weight than cows fed 5% glycerol or the control diet. Weight gain for the control cows and 5% glycerol did not differ.
Estimates of NEL for the diets were calculated from intake, production data, and body weight (BW) changes. The energy content of each ration was calculated for each cow over the experimental period using total energy expenditure (milk, maintenance, and BW gain) with DM intake. An estimate of NEL (Mcal/lb) for each diet was determined from NEL used (Mcal) divided by DM consumed for the corresponding interval. Estimated energy values for the diets were 0.70, 0.70, 0.71, and 0.72 ± 0.02 Mcal/lb and were not different (P = 0.90). The lack of differences in this regard suggests that glycerol can be substituted for corn without adjustments for the energy content. However, the feed energy value of crude glycerol is likely to be less than that of pure glycerol and must be adjusted for the levels and energy content of the impurities. It should be noted that the energy values of the TMR determined by chemical analysis in Table 1 are slightly higher than the estimates determined by difference of milk produced and BW change. These differences may reflect the effects of increasing intake and therefore passage rate to reduce the NE value of the rations.
Results from this study clearly indicate that glycerol is a valuable feed ingredient for lactating dairy cows. Glycerol can be included as a macro ingredient in diets for lactating dairy cows without any deleterious effects. Therefore, feeding glycerol in place of corn is an alternative strategy for formulating diets for lactating cows when corn is not priced favorably.
These data point to the feeding value of glycerol when fed in pure form; however, depending on the level and composition of impurities, the feeding value of crude glycerol cannot be inferred directly from these results.
Saturday, November 10, 2018
Purification of sweet water
Because of the different process of splitting decomposition, the concentration and impurities of glycerol in sweet water differ greatly with catalysts hydrolyzed at low temperature and atmospheric pressure, medium temperature and pressure, and without catalysts hydrolyzed at medium pressure and high pressure, so the purification methods are also different. The following two parts are introduced:
The quality of sweet water without splitting decomposition of oil depends on the quality of the oil. After degumming and alkali refining, there are few impurities in the sweet water after pyrolysis, and the concentration of glycerol is between 10% and 25%. The purification method is also simple.
Purification operation method: Now the sweet water is heated to about 70 degrees Celsius, static settlement as far as possible, the upper layer of fat is skimmed out. If the sweet water is opaque (especially in medium temperature and medium pressure hydrolysis operation, when the hydrolysis depth is low, or when the high pressure hydrolysis interface is controlled low), it shows that there are more incomplete hydrolysis of fat mixed, inorganic acid or salt can be added a little to destroy its emulsification. Separation of fat. Otherwise, the effect of sweet water treatment is not good, which not only affects the evaporation of purified water, but also makes the filtration difficult.
At 60-70℃, Na2CO3 solution was added to the compressed air, and the PH value was controlled at about 9. CaCO3 precipitation was formed and precipitated. The purified water was purified after filtration.
When refined glycerol is not produced by distillation, the second clean water can be decolorized by activated carbon adsorption, and then purified by ion exchange resin to obtain pure purified sweet water. The refined glycerol with more than 98% glycerol content can be obtained by direct evaporation and concentration of purified sweet water treated by ion exchange resin.
Compared with distilled glycerol, refined glycerol without distillation has poor thermal stability and colour, but the recovery of glycerol is greatly improved. It is necessary to study carefully whether the low quality sweet water with more impurities is treated with ion exchange resin.
Protein and other impurities in sweet water are easy to ferment and deteriorate. They are not suitable for long-term storage. Sweet water should be purified and treated in time. In order to reduce glycerol loss, the sweet water container can be cleaned regularly.
Aluminum salts have a good effect on fatty acid treatment, and the adsorptive effect of the formed fatty acid aluminium salts is also good. Aluminum salts are mostly used abroad to treat fatty substances in sweet water, and quicklime is mostly used in China. If conditions permit, aluminium salts are also worth considering.
- Purification of Sweet Water without Catalyst
The quality of sweet water without splitting decomposition of oil depends on the quality of the oil. After degumming and alkali refining, there are few impurities in the sweet water after pyrolysis, and the concentration of glycerol is between 10% and 25%. The purification method is also simple.
Purification operation method: Now the sweet water is heated to about 70 degrees Celsius, static settlement as far as possible, the upper layer of fat is skimmed out. If the sweet water is opaque (especially in medium temperature and medium pressure hydrolysis operation, when the hydrolysis depth is low, or when the high pressure hydrolysis interface is controlled low), it shows that there are more incomplete hydrolysis of fat mixed, inorganic acid or salt can be added a little to destroy its emulsification. Separation of fat. Otherwise, the effect of sweet water treatment is not good, which not only affects the evaporation of purified water, but also makes the filtration difficult.
At 60-70℃, Na2CO3 solution was added to the compressed air, and the PH value was controlled at about 9. CaCO3 precipitation was formed and precipitated. The purified water was purified after filtration.
When refined glycerol is not produced by distillation, the second clean water can be decolorized by activated carbon adsorption, and then purified by ion exchange resin to obtain pure purified sweet water. The refined glycerol with more than 98% glycerol content can be obtained by direct evaporation and concentration of purified sweet water treated by ion exchange resin.
Compared with distilled glycerol, refined glycerol without distillation has poor thermal stability and colour, but the recovery of glycerol is greatly improved. It is necessary to study carefully whether the low quality sweet water with more impurities is treated with ion exchange resin.
Protein and other impurities in sweet water are easy to ferment and deteriorate. They are not suitable for long-term storage. Sweet water should be purified and treated in time. In order to reduce glycerol loss, the sweet water container can be cleaned regularly.
Aluminum salts have a good effect on fatty acid treatment, and the adsorptive effect of the formed fatty acid aluminium salts is also good. Aluminum salts are mostly used abroad to treat fatty substances in sweet water, and quicklime is mostly used in China. If conditions permit, aluminium salts are also worth considering.
Wednesday, October 31, 2018
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
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.
Tuesday, October 30, 2018
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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