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.

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.

Table 1. Diet composition.

	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.

Table 2. Effect of glycerol on feed intake, milk production, body weight (BW) change, and body condition score (BCS) change.¹

	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.

Glycerin: High position slips When is the crazy fall?

Since the end of January 2018, the domestic glycerin market has continued to decline, the atmosphere of commercial investment has been relatively deserted, the market is prosperous, and the transaction price has been falling. The market is full of bearish atmosphere and limited operation.

From the price point of view, the 95% net water glycerin turnover in East China was 5800-6200 yuan / ton, and the 95% water glycerin turnover in South China was 6800-7000 yuan / ton, compared with the year-to-date, East China fell 1,300 yuan / ton And the decline was around 17.8%, while South China's decline was relatively small, the price fell 700 yuan / ton, a decline of 9.3%. What is the reason for the decline in glycerol prices?

First of all, the raw material external disk declines significantly and the cost support weakens.

Crude glycerin is mainly used as raw material for refined glycerin. From the perspective of external disk price, in January, the price of crude glycerin was in the range of 500-520 US dollars/ton, and the current outer disk price fell to 455-470 US dollars/ton, the low end. Prices fell by $45/ton, while high-end prices fell by $50/ton, and fell by around 9%-9.6%. The price of crude glycerin has been slowly declining, and the cost support of domestic workers has been significantly weakened.

Secondly, factory shipments continue to be under pressure

Under the influence of environmental protection, the domestic industrial plant started to operate at a low level. Although some of the factory's supply continued to be tight, but under the weak demand, the shipment continued to be under pressure, and some said that the goods were not smooth. At present, the factory offer is more confusing. Under the pressure of the downstream inquiries, the firm space is large and the center of gravity has fallen sharply.

Again, the demand is weak and the market is limited.

Epichlorohydrin, polyether, and paint coatings are the main downstream products of glycerin, and market operations are weak or continue to limit glycerin shipments. From the start of the downstream products in the past three months, the overall start-up is lower, and the epichlorohydrin starts less than 30%. Although the operating rate in February has increased, it is still operating at a lower level; the polyether device is terminated by the terminal. Due to the impact of shipments, the operating rate of the equipment has been declining; the paint and coating factory has been pressured by environmental inspections, and the start-up of the equipment has been limited. Some factories with smaller capacity are still parked.

From the price point of view, the price of epichlorohydrin and polyether dropped sharply. Its epichlorohydrin fell by 7,100 yuan/ton, a drop of 40.8%, while the price of polyether fell by 2,500 yuan/ton, a decrease of 17.61%.

In summary, the domestic glycerin market is weak in raw materials and demand, and there is no new news in the short-term, the industry's mentality continues to bearish, and when the domestic glycerin market declines?

Comprehensive utilization of biodiesel by-product crude glycerin

Biodiesel is a renewable, biodegradable, non-toxic, low-sulfur new fuel with similar performance to fossil fuel diesel, making it a clean renewable energy alternative to fossil fuels. In the actual biodiesel production process, for every 1 t of biodiesel produced, about 0.1 t of by-product glycerin is produced. According to the report “Oil World” in Hamburg, the global biodiesel production in 2015 was 29.1 million tons, reaching a record high of 32.8 million tons in 2016, a surge of 11% year-on-year, which resulted in a large amount of by-product crude glycerin. Therefore, while developing and producing biodiesel, improving the development and utilization of its by-product glycerin will increase the overall utilization and economy of the entire process, and also increase the source of glycerol.

Production of biodiesel by acid, alkali or enzyme catalyzed process, crude glycerol can be obtained after transesterification, and other glycerin in addition to glycerol, such as water, organic salts, inorganic salts, soap, methanol Or ethanol, pigments and trace amounts of catalysts and glycerides. To apply it to the food, cosmetics and pharmaceutical industries, it is necessary to refine crude glycerin. However, the current crude glycerin refining process is cumbersome, costly, and economically less feasible. Therefore, in order to increase the value of biodiesel by-product glycerin, it is possible to improve the comprehensive utilization value by improving the applicability of crude glycerin in the market and converting high-purity glycerin into high value-added products. Figure 1 shows various products that can be used in the production of biodiesel by-products, crude glycerol and high-purity glycerol. This paper begins with the comprehensive application of biodiesel by-product crude glycerin, and summarizes the current application status of crude glycerin from the fields of chemical products, fuel additives, hydrogen production, fuel cells, methanol or ethanol, and waste treatment. The application prospect of crude glycerin provides technical support for the sustainable development of biodiesel technology.

1 Crude glycerin is used to prepare various chemical products
Using biodiesel by-product crude glycerin as raw material, it can be used to prepare a variety of chemical products, such as 1,2-propanediol, 1,3-propanediol, polyester and polyglycerin. They are important chemical raw materials and products and have a wide range of uses in all aspects.

1.1 1,2-propanediol
1,2-propanediol is an important chemical raw material. Preparation of 1,2-propanediol from crude glycerol is usually carried out by chemical catalytic hydrogenolysis. YUAN et al. used Cu/Mgo as a catalyst to catalyze hydrogenolysis of glycerol to 1,2-propanediol. The preparation method of the catalyst was investigated. It was found that when the catalyst was prepared by coprecipitation, the activity was the highest and the conversion of glycerol was up to The selectivity of 72%, 1,2-propanediol was 97.5%, and the conversion of glycerol was further increased to 82% by the addition of a trace amount of NaOH. CHIU et al [7] used a two-step process to prepare 1,2-propanediol from glycerol. First, glycerol produced intermediate acetol under normal pressure, and then acetol was hydrogenated to form 1,2-propanediol under the action of copper chromate catalyst. The rate reached 75%. Studies have shown that the technology of catalytic hydrogenation of glycerol to bio-based 1,2-propanediol has made great progress, but in order to maintain the high activity of the catalyst, the purity of glycerol is generally required to be high, and further processing and purification of crude glycerol is required. .

1.2 1,3-propanediol
1,3-propanediol is an important intermediate for organic synthesis and an important raw material for the synthesis of polyester PTT (polytrimethylene terephthalate). With the continuous promotion of biodiesel technology, the production of 1,3-propanediol by biological methods using crude glycerol as a raw material has attracted wide attention from researchers all over the world. Several strains for the production of 1,3-propanediol have been reported in the literature, such as Klebsiella pneumoniae, Lactobacillus brevis, Citrobacter freundii, Clostridium butyricum, Pasteur. Clostridium Clostridiumpasteurianum et al. Hu Qiulong et al used the biodiesel by-product glycerol as raw material, Klebsiella as a strain, and fermented 1,3-propanediol to investigate the production efficiency and economic feasibility of different purity glycerol. The experiment found that the refined glycerol (purity > 98) %), crude glycerin A (purity 83%), crude glycerin B (purity 78%) and crude glycerol C (purity 68%) were converted to 1,3-propanediol by 52.38%, 48.08%, 45.22%, respectively. And 39.95%, through the rough evaluation of economic benefits, the crude glycerol A and B production unit 1,3-propanediol cost is lower, while the refined glycerin and crude glycerin C cost is higher. MARIA et al. improved the Clostridium butyricum by metabolic engineering and obtained a recombinant strain DG1. It was found that when glycerol is used as a substrate, 1,3-propanediol can be efficiently fermented and produced at a higher capacity. At a rate of 3g/(L·h), it can be operated continuously for a long time. ANAND et al. used Klebsiellapneumoniae ATCC15380 as a strain, biodiesel by-product crude glycerol as raw material, and fermented to produce 1,3-propanediol. The yield of propylene glycol was 56g/L, and the molar conversion of glycerol was 0.85. The fermentation broth was isolated and purified. A 1,3-propanediol product with a purity of 99.7% is obtained, and as a raw material, a PTT product can be successfully produced to meet the polymerization level requirement.

The production of 1,3-propanediol by biological method has the characteristics of mild reaction conditions, low environmental pollution, and renewable resources. However, its large-scale industrialization still has certain difficulties. The main limiting factors are the high cost of raw materials and the cost of separation and purification process. High, and the production of 1,3-propanediol from crude glycerol is an effective way to reduce the cost of raw materials.

1.3 DHA and PHA
DHA is a kind of ketose which is very beneficial to the human body and is widely used in cosmetics, medicine, food additives and other industries. Using glycerol as a raw material, the production of DHA by microbial metabolism has the characteristics of mild reaction conditions, high raw material utilization rate and high product purity. CHI et al. used crude glycerol as a substrate to ferment DHA with Schizochytrium limacinum microalgae. It was found that crude glycerol can maintain the growth of microalgae and produce DHA. Under the best experimental conditions, the highest yield of DHA is 4.9g. /L, the cell dry weight is 22.1g / L, so the use of crude glycerol as a substrate, microalgae fermentation DHA is a viable solution for the production of DHA. Compared with the chemical preparation of DHA, the microbial process is simple and feasible, easy to control, and is a sustainable development of DHA in the long run.

Polyhydroxyalkanoate (PHA) is a natural polymer biomaterial that has a wide range of applications in medicine, packaging, materials, etc. It is one of the effective ways to use high value-added crude glycerol. ASHBY and other raw materials produced from biodiesel contain glycerin, soap salts and residual fatty acid methyl esters. Pseudomonasoleovorans is used to ferment PHB (polyhydroxybutyrate) and PHA, and biodiesel by-products are found to be coarse. Glycerol can be used to produce PHB and PHA, and the concentration of both products can be controlled by adjusting the growth environment of the strain. KOLLER and other high-permeability microbial fermentation hydrolyzed whey and biodiesel by-product crude glycerol were used as carbon source to produce PHA. It was found that the concentrations of PHA obtained by fermentation of two carbon sources were 5.5g/L and 16.2g/L, respectively. High efficiency in producing PHA. PHA is biodegradable, biocompatible, and has good thermal processing properties. It is a promising polymer, and the biosynthesis of PHA using crude glycerol as one of the raw materials will be one of the important ways to develop and utilize crude glycerol.

1.4 Other chemical products
In industrial microorganisms, glycerin can also be used as a carbon source to produce other valuable chemical products such as succinic acid, propionic acid, citric acid, lactic acid, acrolein, dyes and the like. Among them, acrolein is a multifunctional chemical intermediate that can be used to produce acrylates, superabsorbent polymers and detergents. Acryl aldehyde can be obtained by catalytic dehydration of glycerol by liquid phase or gas phase. The core of the technology is to select a suitable catalyst. OTT and the like use crude glycerol as raw material, subcritical or supercritical water as medium, and obtain acrylic acid by dehydration, but the product yield is not high; the yield of acrylic acid can be improved by adding inorganic acid or inorganic acid salt. In the experiment, The addition of zinc sulfate can achieve a conversion rate of up to 50% at 300-390 ° C and 25-34 MPa. This is mainly because the addition of zinc sulfate reduces the activation energy of the reaction. ZHOU et al. used microporous mesoporous molecular sieve HZSN-5 as a catalyst. The gas phase method catalyzed the dehydration of glycerol to acrolein. The reaction was carried out at 320 ° C. The conversion of glycerol was 98.27% and the selectivity of acrolein was 74.94%. Studies have shown that the use of glycerol to produce acrolein is an active field in the research and application of biodiesel by-product glycerol in recent years, and the core of its technology lies in the selective preparation of catalysts. It can be seen that crude glycerol is used as raw material or substrate, and various chemical products with high added value can be obtained by microbial technology or chemical catalytic hydrogenolysis, oxidation, hydrogenation and the like.

2 Crude glycerin is used to produce hydrogen
Hydrogen is a clean and efficient secondary energy source. With the continuous expansion of hydrogen application and the increasing emphasis on the world's energy and environmental issues, biological hydrogen production technology has received extensive attention. Among them, hydrogen production from crude glycerol is also an important comprehensive utilization of biodiesel by-products, and research in this area has received more and more attention. The main processes for the production of hydrogen from glycerol include steam reforming, partial oxidation, autothermal reforming, aqueous phase reforming and supercritical water reforming. The most widely used in the chemical industry is steam reforming. ADHIKARI et al [17] used hydrogen reforming process to prepare hydrogen, catalyzed high endothermic reaction of glycerol with water to produce hydrogen; investigated the catalytic reforming performance of Ni/MgO, Ni/TiO2 and Ni/CeO2 catalysts, and found Ni /MgO has the highest hydrogen production activity at a reforming temperature of 650 ° C, and the hydrogen yield can reach 56.5%. SLINN et al. investigated the feasibility of hydrogen production from biodiesel by-product glycerol steam reforming. Using Pt-Al2O3 as catalyst, it was found that the higher the reaction temperature, the higher the gas phase yield, the highest yield is close to 100%, and the selectivity is 70%. Under the optimal hydrogen production conditions of glycerol steam reforming, the carbon deposition of biodiesel by-product glycerol is slightly higher than that of pure glycerol, but the catalyst activities of the two are similar. BYRD and other supercritical water reforming processes use biodiesel by-product glycerol as raw material and Au/Al2O3 as catalyst to produce hydrogen. The reaction is carried out in a tubular fixed-bed reactor at a reaction temperature of 700-800 ° C. Glycerol in the feed. The concentration (mass fraction) was 40%, and the highest reaction yield was close to the theoretical yield, and 7 mol of hydrogen per 1 mol of glycerol was obtained. These processes all have certain requirements on the purity of glycerol, because the excess impurities in the crude glycerol will have certain influence on the activity and service life of the catalyst. Therefore, in order to accelerate the efficiency of hydrogen production from crude glycerol and reduce the production cost, it is necessary to develop environmental adaptation. A catalyst with high capacity, corrosion resistance and high activity.

Crude glycerol can also be converted to hydrogen by the form of microbial catalytic conversion. GUILLAUME et al. [20] used photosynthetic bacteria Rhodopseudomonaspalustris to ferment crude glycerol to hydrogen. The yield of this process is high, producing 6 mol of hydrogen per 1 mol of glycerol (75% of the theoretical value, theoretically producing 8 mol of hydrogen per 1 mol of glycerol). The impurities in the biodiesel by-product crude glycerol have no inhibitory or toxic effects on the entire fermentation process. Through the above analysis, using biodiesel by-product crude glycerol as raw material, hydrogen can be produced through various chemical catalytic process technologies or microbial conversion technologies, and the hydrogen production efficiency is high. The process has the advantages of renewable raw materials, cleanliness and no pollution. It is one of the efficient ways to produce hydrogen and has a good space for development.

3 Crude glycerin is used as a fuel additive
Glyceryl alkyl ether is a good fuel additive that improves fuel performance, increases cetane number, increases flow properties, reduces the composition and content of harmful substances in the combustion exhaust, and is used as an additive for diesel and biodiesel. The use of crude glycerin in this technique allows the use of biodiesel by-product glycerin as well as high value-added glyceryl alkyl ether fuel additives.

Among them, glyceryl tert-butyl ether obtained by reacting glycerol with isobutylene or tert-butanol is a promising additive. Adding it to diesel fuel can significantly reduce the content of particulate matter, hydrocarbons and carbon monoxide in the exhaust gas. . KARINEN et al. investigated the etherification reaction of crude glycerol with isobutylene in the liquid phase with acidic ion exchange resin as catalyst. The main reaction of the whole process was etherification reaction. The main products were five ethers and the side reaction was isobutylene. The oligomerization reaction produces C8~C16 hydrocarbons; the molar ratio of isobutylene to glycerol is 3:1, the reaction temperature is 80 °C, the selectivity of the reaction is the best, and the composition of the ether products can be controlled by changing the reaction conditions. And the extent of the etherification reaction. KIATKITTIPONG and other fluidized bed catalytic cracking (FCC) gasoline and glycerol were used as reactants. Amberlyst16, Amberlyst15 and β-molecular sieves were used as catalysts to investigate the effect of etherification reaction on the performance of FCC gasoline. The results showed that compared with the original FCC gasoline. The olefin content of the etherified gasoline product is significantly decreased, and the octane number is increased. When β-molecular sieve and Amberlyst 16 catalyst were used, β-molecular sieve was found to have good catalytic effect, and it is more suitable as a catalyst for etherification reaction.

Glycerol can also be catalytically converted into a fuel additive by acetylation, acetalization, and the like. In its review article, RAHMAT et al. studied the reaction process and specific characteristics of glycerol converted into fuel additives by etherification, acetylation and acetalization, and applied it to gasoline, biodiesel and diesel. The effect of the additives obtained in each reaction. PRADIMA et al. also react different processes of glycerol conversion to biofuel additives (esterification, etherification, acetylation and condensation)

Analysis of the market price trend of refined glycerin in 2018

Despite the US anti-dumping policy on biodiesel in Argentina and Indonesia, the EU has lowered the tariff on biodiesel for Agenyan and Indonesia. The biodiesel has collided with the news, and the output of biodiesel has not increased significantly. As crude oil goes up, there is room for profit in biodiesel production, and market participants expect more supply of crude glycerin. The price of crude glycerin began to loosen, and the price of crude glycerin in the market may continue to decline.

The United States still has anti-dumping against biodiesel in Argentina and Indonesia, but the EU has adjusted the high tax rate for biodiesel in Argentina and Indonesia, and lowered the tariff on biodiesel in Argentina and Indonesia. The long and short news between Argentina and Indonesia is intertwined, but due to the low price of crude oil in the previous period, the operating rate of biodiesel has not increased significantly.

Nowadays, international crude oil is rising at a low level and breaking through the mark of US$60/barrel. Under this background, market participants believe that the production of biodiesel will be profitable in the later period, and the supply of crude glycerin will increase. At the same time, crude glycerin has been curbing demand in China at the price of US$500/ton CIF China. The demand in China is slow and heavy, which has led to an increase in crude glycerin shipment pressure.

The increase in shipment pressure may increase the supply of crude glycerin in the later period, resulting in a high stagflation of crude glycerol and a downward trend. The price of 80% crude glycerin was high, and the Asian crude glycerin market fell by US$10/ton, down 3% from the previous period. The CIF China main port price closed at US$490-505/ton.

Market participants are expected to be short-selling in the later stage of crude glycerol, and they believe that the price of crude glycerin may continue to decline. On the one hand, due to the weakening of the implementation of the anti-dumping policy, it is still unclear whether the output of Argentina and Indonesia in 2018 can be as low as in 2017, but market participants expect that the production of biogas in Argentina and Indonesia will be 2018 compared with 2017. The increase will also drive the increase in crude glycerin production, and the market buying is weakening.

On the other hand, China's acceptance of high-priced crude glycerol is low. The price of 80% crude glycerin has risen to the level of US$520/ton CIF China. China's refined glycerin producers have strong risk aversion and the downstream acceptance of high-priced refined glycerin has also weakened. The market has changed from the buyer's market to the seller's market. The main contradiction has shifted from supply to downstream demand. The weakening of demand will drag down the price of crude glycerin.

Supply has increased expectations, downstream demand has declined for high price acceptance, and the market has shipping pressure. Zhuo Chuang expects 80% crude glycerin to slow down from a high level in 2018, and the market pressure of refined glycerin will turn into downstream demand.

Application of Polyglycerol

Polyglycerol has higher viscosity and boiling point than glycerol, less volatility and hygroscopicity, good moisturizing property, and has the characteristics of improving emulsification stability. It has the following applications:

(1) Cosmetic raw materials (using their hygroscopicity and moisture retention)

Polyglycerol is used to make cream and emulsion. It can be used as thickener for paste in toothpaste. Polyglycerol propylene oxide adduct is the raw material of high-quality hair cosmetics. It can replace petroleum chemicals (aliphatic alcohol ether, shampoo and hair conditioner; benzophenone derivatives for ultraviolet absorption; dibasic esters or salts for emulsifiers and detergents) in areas requiring higher safety. )

Textile industry

The surface softness and hydrophilicity of hydrophobic fibers can be improved by immersing fibers in aqueous solutions of polyglycerol and other compounds, and they can also be used as dyeing auxiliaries for water insoluble dyes.

Plastics industry

It can be used as nylon plasticizer, hydroxypropyl cellulose plasticizer and polyurethane plasticizer. In addition, it is expected to be used as plasticizer for PVA, gelatin and semi-permeable membranes.

In addition, polyglycerol is used as antistatic agent and stabilizer in synthetic resin, polyglycerol is added to water-soluble binders such as dextrin, calcium chloride and gelatin, and polyglycerol borate is added to starch paste to adjust curing time and improve storage stability. It is also expected to be used as a hot-melt binder. Polyglycerol epoxy propane adduct can be used as defoamer for oil recovery, raw material for ethyl carbamate (polyurethane), slurry agent for diazo copying paper and image accelerator, as well as as as as polyformaldehyde stabilizer and stationary liquid for gas chromatography analysis. It can be added to electroless plating bath to improve plating quality, prevent cracking and shorten curing time in cement.

Polysiloxane modified by branched-chain polyglycerol not only has the inherent characteristics of low irritation, yellowing and viscosity, but also has high hydrophilicity, lubricity and ductility. It also has good wettability and Adsorbability to various substrates. It is widely used in cosmetics and fiber treatment.

Castor oil and polyglycerol can synthesize a defoamer used in fermentation process, which has a good effect on defoaming and antifoaming of fermentation broth.

Oligomeric glycerol can be used as the main grinding aids to increase production and reduce energy consumption. It can also be used as one of the components of multi-functional composite concrete slag admixtures to improve the compactness of concrete and have anti-freeze-thaw destructive properties.

It can also be used as an integral part of latex paint, ballpoint pen ink, oral health products, etc.

Analysis on the Quality of Glycerol Products

The quality problems of glycerol products are mainly manifested in coke taste, yellow color, unsatisfactory saponification equivalent, excessive acrolein and reducing substances, excessive chloride, ash and carbide-prone substances, etc. The reasons for these problems are as follows:

1.Oils and fats: Low-grade oils and fats generally refer to the oxidative deterioration of organic components caused by improper storage of sour and deteriorating oils or oils with more impurities, as well as various kinds of recovered oils and fats, because they contain many oxidized fatty acids, low-carbon fatty acids and impurities such as aldehydes, ketones and proteins, or because of improper processing of saponification waste liquor, long storage time, and unclean containers. These substances are dissolved in saponification waste liquor and are not easily removed in the treatment process. As a result, the crude glycerol is dark and heavy, and the distilled essential glycerol has odor and yellowing color. Therefore, in the operation of distillation, it is necessary to avoid excessive residence time, excessive liquid level, excessive fluctuation of liquid level and too low vacuum. Low-grade grease should be properly pretreated or separately treated.

If medicinal grade glycerol and explosive glycerol are produced, the variety and quality of oil and fat must be selected and controlled. Experience has proved that besides the saponification waste liquor of castor oil, fish oil, Litsea cubeba seed oil and silkworm chrysalis oil, rice bran oil and cottonseed oil should also be used cautiously.

2.Low Molecular Fatty Acids (LMFAs): When saponified waste liquor or or sweet water is purified, low molecular fatty acids (salts) enter the purified water and then into crude glycerol. During distillation, organic salts are decomposed and free fatty acids are esterified by glycerol vapor in the gas phase, resulting in an increase in the ester content of essential glycerol. Therefore, the alkalinity of crude glycerol can be controlled appropriately (0.1% - 0.2%) during distillation. Conversely, it also shows that when purifying saponification waste liquor or or sweet water, the fatty acid can be removed as much as possible.

3.Operating conditions, low vacuum and high temperature or local overheating under vacuum can increase the amount of propanal, overflow the liquid level, too large vacuum fluctuation, entrainment of mist into the condenser due to imperfect gas separation device, resulting in unqualified indicators such as chloride of essential glycerol, ash, carbide and so on. In addition, leakage of equipment should be prevented during operation.

4.The steamed glycerol from roasted feet is dark in color and strong in smell. It should be separated from the normal steamed glycerol and should be re-steamed with crude glycerol.

The difference between the non-distillation glycerin refining process and the current distillation glycerin refining process

There are only two refined glycerin products in the global glycerin market: food-grade glycerin and industrial grade glycerin. The same is true for the domestic glycerin market: only the two kinds of refined glycerin products, namely, Gan Gan and Gong Gan.
The raw material for producing refined glycerin is crude glycerin. Raw crude glycerol has three sources:

(1) renewable new energy biodiesel production;
(2) fat decomposition of oleochemicals;
(3) crude glycerol produced by soap production.
Crude glycerol contains too much organic and inorganic impurities. Crude glycerin must be purified to make refined glycerin before it can be used as a raw material for other industries.
More than 99% of the world's refined glycerin is produced by the traditional ultra-high vacuum distillation process. The boiling point of glycerol is 290 °C. The physical properties of glycerol high boiling point, despite the use of ultra-high vacuum distillation, glycerol distillation still consumes a lot of energy.
A simple distillation process with a low degree of vacuum is commonly used in China. The process reduces the vacuum by increasing the glycerol distillation temperature, thereby greatly reducing the simplified distillation of plant equipment investment.
There are three shortcomings of this simple distillation method:

1. High energy consumption, large sewage discharge, and no perfect equipment for recycling impurities;


2. The product quality is low, can only produce industrial grade glycerin products. Can not produce high-purity food-grade refined glycerin;


3. Batch operation and manual operation. High labor costs.

The glycerin non-distillation process will be fully automated. According to the crude glycerin raw material index, each process data can be automatically adjusted by selecting the required product specifications in the console, and different types of refined glycerin products are produced. The new process uses advanced room temperature processing, which greatly reduces energy consumption and greatly reduces production costs. The new process is equipped with thermal energy and gas-liquid recovery devices, which not only greatly reduces emissions, but also increases the output value through the value of recycled materials.
The specific advantages are described in detail below.
Second, the advantages of non-distillation glycerin refining process
1, non-distillation glycerin refining process energy saving
(1) Deep energy saving.
The new process purifies crude glycerin at normal temperature or at a lower temperature. Compared with glycerin distillation, energy saving is more than 60%.
Glycerin has a very high boiling point: 290 ° C. Ultra-high vacuum distillation is to heat the crude glycerin to above 170 ° C and to carry out distillation under extreme vacuum conditions; the simple distillation method is to heat the crude glycerin to above 220 ° C and to carry out distillation under general industrial vacuum.
(2) Deep reduction.
a. Saving energy, directly or indirectly reduce sewage.
b. The new process recycles all recoverable substances (heat, fatty acids, salt, methanol, process water, etc.), in addition to reducing costs and increasing revenue, it also greatly reduces emissions.

2. Low cost.
Compared with existing products, the cost is about 40-50% of the cost of existing processing. It saves about 50-60% of the cost. Thereby increasing product profit.
Take industrial grade refined glycerin as an example: the cost is about 200-300 yuan / ton (RMB, the same below). At present, the domestic production cost is about 600-1200 yuan / ton, and the foreign cost is about 1800-2250 yuan / ton.
The new process has a greater cost advantage in producing food and drug grade products.
The new process has an absolute cost advantage in the production of new glycerin products.
3, the equipment costs are low
Equipment costs are low. The basic equipment with an annual output of 10,000 tons is less than 2 million yuan (excluding raw materials and finished products storage tanks, boilers, plant walls, flowers and plants, beautification lighting, fire safety, sewage pipelines, special anti-leakage loading and unloading site construction and other expenses).
The price of the equipment varies according to the manufacturer's qualifications. The price of low-end equipment manufacturers differs greatly from that of mid- to high-end equipment manufacturers and foreign equipment manufacturers.
4. Production of new glycerin products
The new process has a unique feature. This feature is not present in existing glycerin refining processes worldwide (so there are only two specifications in the world: glycerin: industrial grade and food and pharmaceutical grade). It can produce user-friendly glycerin products according to the needs of the task. It is also a new product that is not available on the market and does not exist. Of course, the production of standard industrial grade and food and pharmaceutical grade glycerol is a must. The products produced by the new process will be divided into several grades, and each grade will be subdivided into several sub-levels. For example, food and pharmaceutical grade glycerin can be subdivided into food grade, pharmaceutical grade, chemical grade (reagent grade); and industrial grade glycerin, can be further subdivided into A, B, C, D and other secondary. The A grade is the best Gong Gan (high-end user), the B grade is slightly lower than the current Gong Gan (middle and high-end users), and the C grade is given to the middle and low end users (such as plastic, rubber, antifreeze, paint, sticky). Glue, steel, etc.), work D grade to low-end users (such as ink, road de-icing, etc.). In addition, glycerin products customized according to the indicators provided by users are classified as “user level”, such as ECH grade, methanol grade and other green chemical users.
Third, the cooperation mode
This can be used by the Ministry of Science and Technology of China to collect the notice of the 2014 Sino-British Sustainable Advanced Manufacturing Industry Cooperation Project.
The two parties submitted application materials to the Ministry of Commerce and the UK Strategy Committee respectively. If the efforts are passed, the Chinese side supports 3 million yuan (the government and enterprises match), and the British side supports 50-80 pounds (equivalent to 5-8 million yuan). The funds supported by the respective countries may support the enterprises of their respective countries, but no matter what. More peace of mind and advantages than not through government cooperation.
Domestic enterprises undertaking national scientific research projects will bring intangible assets that enhance the qualifications of enterprises.
Foreign patents were obtained in March last year. Now we only need to cooperate with partner manufacturers to establish a small pilot plant (such as 100-200L/hour) to collect process data for industrial production and complete the entire industrialization process of system optimization, system integration, system simulation and system automation. This process takes about 1-2 years and is completed in about a year.
After the completion of the Chinese phase, it is possible to enter large-scale industrialization and build an industrialized large-scale glycerin refinery using new processes. And strive to set up branch factories in different regions of the country, and will promote the industry upgrade to the whole country.
Because of its great cost advantage, the company can make the company bigger and stronger through its own efforts. Enterprises can also take advantage of the advantages to open up new markets internationally.
The application deadline for the China-UK Sustainable and Advanced Manufacturing Industry Cooperation Program in the Ministry of Commerce of China is March 26, 2014, and the UK deadline is March 19. Therefore, there is not much time. In addition to being fully prepared as soon as possible, it is necessary to consult with the foreign parties and jointly develop the project implementation plan.
In addition to the support of national projects, if the company has the strength, it can also directly cooperate with foreign owners to carry out industrialization.
The process of industrialization, that is, collecting process processing information, is a process of system integration and automation step by step. The reason why there has been no preference for industrialization in China is that the foreign side is worried that it is not easy to do well in terms of confidentiality. It is difficult to design the production line and the entire factory in line with international regulations. As a result, the authorization or transfer to international users in the later stage will cause the enterprise to suffer huge losses that should not occur.
Fourth, the future of glycerin products
Glycerol is used in a wide variety of applications, and more than 1,500 glycerols are known for use. Glycerin is the most important raw material for renewable green chemical products in the world. However, the first thing to do, and what must be done, is glycerin refining, which is not suitable as a raw material for the production of green chemical products.
The use of glycerin will become more and more widespread and the dosage will be larger and larger. Glycerol refining will be of great use.