WO1998027830A1

WO1998027830A1 - Controlled release urea product, method for its production and use of said product as feed supplement

Info

Publication number: WO1998027830A1
Application number: PCT/NO1997/000347
Authority: WO
Inventors: Fernando Basile De Castro
Original assignee: Norsk Hydro Asa
Priority date: 1996-12-20
Filing date: 1997-12-18
Publication date: 1998-07-02
Also published as: GB9626608D0; GB2320410A; EP0957689A1; AU7870098A; BR9714154A; PL334299A1; CA2275031A1; ZA9711463B

Abstract

The present invention relates to a controlled release urea product which primarily consists of urea entrapped or bonded in a lignin matrix forming a lignin-urea (LU) product, a method for preparation of said LU product and use of said LU product as a slow release urea feed supplement in ruminant feed. The ruminant feed comprises 0.5-5 weight % diet urea as a lignin-urea (LU) product. The preferred ratio lignin:urea in the LU product is 75-15:25-85. Said LU product may contain additives such as rosin, starch, lanolin, polyethylene glycol, glycine which can be mixed with both urea and lignin as well as have coating agent, e.g. lanolin or rosin. The controlled release urea product can be prepared by mixing lignin with melted urea at 155-170 °C and at a retention time of 10-0.5 minutes. The resulting lignin-urea product can be particulated by prilling, granulation, crushing or milling to desired size.

Description

Controlled release urea product, method for its production and use of said product as feed supplement

The present invention relates to controlled release urea product which can be applied as a slow release urea feed supplement. The invention also comprises a method for preparing said urea product.

Controlled release or slow release urea products can be applied for several purposes like fertilisers and in feeds like ruminant feeds. The slow release effect of the urea can be obtained by application of coatings, usually large amounts of coating will be necessary, various types of chemical bonding of the urea, etc. If the final use of the urea product is as a feed supplement, the components used for obtaining the slow release effect must meet the requirements for feed.

Urea is a non-protein nitrogen rich chemical and widely used as a feed supplement for ruminants. Ideally urea N is converted into microbial protein thereby supplying additional protein to the host animal. However, an imbalance in the rate of N supply and the supply of fermentable carbohydrates to the rumen can result in excessive NH₃ generation and high ammonia concentration. Too low ammonia levels will reduce efficiency of rumen fermentation i.e. microbial growth and fibre degradation, whereas too high ammonia levels will reduce N-utilisation and in severe cases cause NH₃-toxicity. As unprotected urea is rapidly solubilized in the rumen its use can result in high ammonia concentrations shortly after ingestion. As the rate of ammonia production from urea can exceed (by up to four times) that of ammonia absorption by the rumen bacteria, there is a limit to the amount of unprotected urea that should be used. Accordingly, the urea should be released slowly to get a more even ammonia-nitrogen concentration during the first eight hours after feeding in order to give the rumen the ability to utilise the urea efficiently.

Several attempts have been made to develop feeds comprising urea which is slowly released, but most of these have failed for different reasons such as high cost, unacceptable additives and inefficiency with regard to release rate of urea .

Preparation of a slow release urea product for application as ruminant feed supplement is described in US-Patent No. 4.089.980. A cellulose-containing commodity, urea and a dilute mineral acid like hydrochloric acid are mixed together and heated to 50-120°C for several hours to cause chemical bonding of urea to a level of at least 40% of theoretical of the monosaccharide potential of said cellulose containing commodity based on a 1 :1 molar ratio of binding of urea to monosaccharide. The pH of the obtained mixture is adjusted to between 3-7. The slow release effect observed in such product is due to formation of chemical bonds between urea and carbohydrate fraction of said cellulose commodity.

One slow release technology applicable for pesticides is described in the patent application GB. 2.109.687 A. According to this application kraft lignin can be applied as a main inert material. The raw materials are mixed and subjected to high shear forces and at temperatures below the melting point of the active ingredient. When proper blending between the active ingredient and lignin is not achieved, it is suggested use of a processing aid such as rosin (colophony) or urea. From EP 0 716.056 A1 there is known a method for producing slow-release nitrogenous organic fertilizer from biomass. Ligno-cellulosic materials and starchy materials selected from the group consisting of agricultural waste, forestry waste, municipal waste, wood, grasses etc. are subjected to pyrolysis and the products thereof are chemically combined with a nitrogen compound containing NH₂ (amino) groups, such as urea, aqueous solutions of urea, ammonia, amine and ammonium salts. Though this fertilizer product may give some slow release effect when applied in the soil, it is not known to be used in rumen feed. A somewhat similar product is known from EP 0 007.136 A1. This application describes a cattle fodder from partially hydrolysed ligno-cellulosic material and urea. The fodder is prepared by hydrolysing, straw, bagasse or other ligno-cellulosic by-products with diluted acid, and subsequently condensing said prehydrolysed material with urea. The total nitrogen content of the raw product indicated that it contained nearly 100% of the urea added at the start. Of this urea, 67% was shown to be slow release urea while 33% was present as free urea. The ligno-cellulosic material is treated to hydrolyse at least a major part of the hemicellulosic portion thereof into reducing saccharides prior to its contact with a urea solution before the mixture is heated to bind the urea. The prehydrolysis takes about 2-4 hours at 90-130°C and the heating to effect the condensation with urea 2-5 hours at 70-100°C. The process is rather expensive and the amount of urea in the product, as slow release urea, is low making the product, on a urea basis, expensive. It is important to highlight that, in both inventions described in the above EP-applications, urea undergoes major chemical changes and it becomes chemically bound to the fibre.

From GB-Patent 1.502.441 there is known a process for obtaining slow release of biologically active materials, especially pesticides. A composition comprising an intimate mixture of an organic polymer and a biologically active component. Thus it is obtained a gradual release of the pesticide to the environment which said composition is exposed to. The polymer is selected from thermoplastic polyamides, kraft lignin, asphaltic resins, polyvinylacetate and natural occurring polymers.

Another method of obtaining slow release of a biologically active material is described in US-Patent No. 3.929.453. According to this patent the active agent is either entrapped by a lignin macromolecular matrix or held by physical-chemical forces of van der Waal^'s hydrogen bonding or ion association types. This method does not apply heat in order to achieve chemical bonding between the lignin and the active agent. Instead, chemical reactions in the liquid state are described.

The main objective of the invention was to arrive at an improved controlled release urea product, primarily for application as a feed supplement. Said urea product should release the urea in the rumen slowly and gradually such that undesired high ammonia concentrations in the rumen could be avoided.

Another objective was to arrive at an efficient economic method for preparation of a controlled release urea product.

A further objective was to produce rumen feed comprising feed supplement that could endure the process condition used for preparation of complete feed comprising compounds having nitrogen to carbon ratios such as hay, straw etc.

In his search for finding a solution to the above stated problem the inventor evaluated previous attempts to make slow release urea, both within the fertilizer field and the rumen feed field. The main problem was to select a material that could encapsulate or bind urea in such a way that urea would be released slowly and gradually. Among all such materials previously tested some were obviously unacceptable as feed components. Another problem was to select a material that was readily available at a reasonable price and which would not cause any adverse effects during processing and use. One possible useful material was lignin which is available from various sources. According to the above referred GB-Patent No. 1.502.441 one type of lignin, kraft lignin, could be used to make products containing biologically active agents as pesticides which then would be released slowly during application of said products. The question was then whether lignin could react with urea in manner which would encapsulate relatively large amounts of urea which subsequently could be slowly released , for instance in the rumen. Urea itself is not a biologically active agent. Urea will only be biologically active when it is degraded. In order to test this idea of making a controlled release lignin-urea (LU) product, preparation of such products were started. During the initial tests kraft lignin was used as the lignin source. However, other types of lignin were also considered to be useful. It was found that urea was somehow bonded to the lignin when the two components were mixed together at high temperatures. The LU products for the present tests were prepared at 158°C or 170°C and atmospheric pressure. However, the preparation of useful LU products could also be obtained at other temperature and pressure conditions.

Various types of lignin coming from different sources could be applied. Thus the lignin could be obtained from straw, sugar cane bagasse or eucalyptus, the native lignin source could be subjected to auto hydrolysis at temperatures above 170°C and subsequently washed with water and subjected to alkaline treatment. The resulting lignin extract could be precipitated with acid and centrifuged and had a typical analysis of more than 90% lignin content. The contaminants will mainly be ash, sugar and some cellulose. When this lignin was mixed together with melted urea at for instance 158°C, a rather viscous homogenous LU product would be obtained. The LU product hardened as it was cooled at ambient temperature. The hard LU product was crushed or milled and desired particle size was obtained by sieving. Further tests showed that LU products with different lignin:urea ratios in fact gave a marked reduced release of urea in rumen.

As mentioned above, there are several types of lignin having somewhat different properties. In order to obtain the best LU- products some lignin types were further investigated as useful carriers for slow release urea.

Hydrolytic lignin

Source: softwood, hardwood, cereal straw and sugarcane bagasse.

The lignin is extracted from a ligno-cellulosic material by steam treatment at high temperatures (t>185°C and P>13atm.) for 5-20 minutes. The water-soluble residue is removed from the steam-treated fibre. The remaining residue is treated with either acetone or ethanol to dissolve the lignin fraction. Lignin is precipitated by decreasing the pH to about 2 with either sulphuric- or hydrochloric acid. The precipitate is oven-dried after several washes to remove excess chemicals.

Kraft lignin

Source: softwood and hardwood.

This alkali lignin is extracted from the kraft or black liquor which is produced during the Kraft pulping process. Such a process uses sodium hydroxide and sodium sulphide as the main chemicals. Kraft lignin can be extracted from the kraft liquor by precipitation as described above.

Organosolv lignin

Source: A mixture of maple-, birch- and poplar wood. Method of extraction: The lignin is a by-product of the organosolv pulping process. The process of lignin extraction is similar to a standard organosolv process (for instance as described in patent application EP-569.526A1 ), in which fibrous material, namely hardwood, softwood or cereal straws, is soaked in organic solvent, e.g. ethanol, is kept under pressure and high temperature for a period of time. The lignin is solubilized under such conditions and later separated off by filtration.

The properties of these various types of lignin are given in the following table 1.

Table 1

expressed as ferulic acid equivalent.

Evaluation of the various properties of lignin with respect to obtaining a slow release of urea showed that lignin solubilization in aqueous solutions is quite important. From table 1 it can be seen that organosolv lignin has relatively low water-solubility. Urea was subjected to heat treatment in absence and in presence of lignin to monitor degradation products. Presence of lignin did not increase urea degradation. The following conditions were found to have low impact on urea degradation, and thereby suitable for practical use.

Temperatures: 150-170°C . Retention time: 10-1 minutes.

Application of additives, defined as chemical substances other than urea and lignin in the product formulations, at levels lower than the lignin content, were also investigated and found to result in greater control over the rate of urea release. Lanolin was shown to have such effect, especially when applied as a coating. Provided that the lignin coating can endure the conditions for producing feed containing such coated LU feed supplements, this will be a useful procedure for obtaining the desired slow release urea containing feed. Rosin (chemically unmodified pine resin) which is generally known as a coating agent from Spanish patent No 536.567, was found to be a useful additive also for LU-products for reducing the release of urea. When used as a coating material rosin protected even further the LU-product.

The controlled release urea product, primarily being urea entrapped or bonded in a lignin matrix forming a lignin-urea (LU) product was developed. This LU product according to the invention can be applied as a feed supplement in compound feed and premixes, but also together with hay, straw etc. The LU product may contain additives, such as starch, rosin, lanolin, glycine, paraffin and/or polyethyleneglycol (peg), to improve the performance of the product in the rumen.

The ratio lignin:urea in the LU product will preferably be 75-15:25-85.

The LU product may comprise rosin either as an additive or a coating. The preparation of the controlled release urea product can be performed by mixing lignin with melted urea at temperatures of 155-170°C, pressures of 1-10 bar and at retention times of 0.5-10 minutes. The resulting LU product can be particulated by prilling or granulation and can also be milled or crushed to desired size. The lignin applied for the preparation of the LU product can be produced from native lignin by various methods as described previously, i.e. steam-treatment, kraft and organosolv pulping.

The most preferred type of lignin was found to be organosolv lignin.

Use of additives, e.g. rosin, starch, polyethylene glycol, which become part of the LU matrix, improves urea protection. In order to further improve the slow release properties a coating can be applied on the LU product. Lanolin or rosin were found to be the most suitable coating materials.

A ruminant feed according to the invention comprises 0.5-5 weight% diet urea as lignin-urea (LU) product, based on the total feed dry matter.

The invention will be further envisaged and explained in the following examples:

Example 1

This example shows the release rate of urea from LU formulations as a function of particle size and lignin:urea ratio.

Three LU formulations containing different ratios of urea and lignin were prepared at both 158°C and 170°C. The LU formulations and analysis of end products are shown in table 2. Table 2

Each formulation was then separated into different physical sizes and tested for urea release characteristics over 48 hours using artificial saliva incubation tests. The release of urea from LU was assessed by incubating a series of flasks with 0.2 g LU and 100 ml artificial saliva at 39°C in a cradle with gentle stirring. Flasks were analysed throughout the incubation time chosen for the study. The artificial saliva buffer was prepared according to McDougal ( E.I. Biochemical Journal, 43, 99-109, 1948).

The particle sizes of the LU products were:

Pellet equivalent to an average size of 3x3 mm Ground capable of passing through a 250 μm sieve Small pellet* equivalent to an average size of 3x3 mm Medium pellet^* equivalent to an average size of 4x4 mm Large pellet* equivalent to an average size of 5x5 mm

products prepared from Sample No. 7 in table 2. Urea release data from each LU formulation obtained using the artificial saliva test, as urea released as % of potential as function of incubation time in hours, are shown in table 3.

Table 3

Samples Nos. 1-7 relate to Samples Nos. 1-7in table 2.

Table 3 shows that the release rate is high for all LU formulations when the LU products are ground. For large pellets the release rate is low and increasingly slower the first four hours. It is further shown that the release rate decreases significantly with increasing content of lignin in the LU formulations. Example 2

This example shows comparison of urea release from LU formulations with varying urea:starch:lignin ratios. Four LU formulations containing different ratios of urea, starch and lignin were prepared at 170°C and this is shown in table 4.

Table 4

Each LU formulation was then tested for urea release characteristic over 48 hours (incubation time) by the use of the artificial saliva procedure. The results are shown in table 5. Urea released are given as % of potential maximum.

Table 5

These results shows that there is little effect of substituting lignin with starch and that the content of lignin has the greatest effect on urea release. Further tests showed that coating of the LU particles with lanolin substantially reduced the urea release rate.

Example 3

This example shows the effect on ammonia nitrogen levels in rumen of sheep fed with diets containing 2% urea present as urea or LU comprising 65% lignin. The effect on rumen pH was also recorded. The effect on rumen pH was however, negligible which is a positive indication that nitrogen was not being released as ammonia in high, i. e. toxic, amounts. The dietary regimes were:

a) General purpose (GP) diet only (i.e. no added urea or LU) fed orally. b) GP diet plus 2% urea (urea control diet) fed orally. c) GP diet plus 2% urea present as LU product fed orally. d) GP diet plus 2% urea present as LU product with the GP fed orally and the LU component poured directly into the rumen.

Inclusion of treatment d) was to minimize any effect of chewing which could affect LU particle size.

Three sheep were used, each was fed the GP diet in the first rotation to get background data and then the three treatments with added urea were applied to the sheep using a Latin square experimental protocol. The average rumen ammonia-nitrogen levels (mg/l) for each dietary regime over the 8 hours period (time zero being immediately prior to feeding) are given in table 6 and shown graphically in figure 1. Table 6

As can be seen from table 6 and fig. 1 rumen ammonia-nitrogen concentration reached a peak value about 650 mg/ml after 2 hours when standard feed urea was used. Contrary to this, feeds containing the new LU product gave a far more gradual release of urea. Furthermore, both LU treatment exhibited similar urea release characteristics with peak urea concentrations, in the rumen being almost half the peak values of the feed containing unprotected urea. The LU products have accordingly potential to protect against ammonia toxicity.

Example 4

This example shows the effect of using different types of lignin in the LU-products on NH₃ release in vitro (mg/litre) The controlled release LU formulations were produced at 155°C and a retention time of 5 minutes. The incubation time in hours are shown in table 7 as function of type of lignin and Lignin: Urea ratio. Table 7

Incubation time, hours.

From table 7 it can be seen that organosolv lignin and hydrolytic lignin give about the same effect and that the LU-products have a substantially lower ammonia release in vitro than that of urea.

Example 5

This example shows the effect of applying Rosin in the LU-product, either as an additive or a coating in the ammonia release in vitro in mg/litre. Both organosolv lignin and hydrolytic lignin were used as lignin component in the LU-product.

Table 8

Incubation time, hours.

From table 8 it can be seen that when rosin is used as a coating or additive, the slow release effect is significantly improved. It further seems that organosolv lignin gives a better slow release LU-product than hydrolytic lignin.

Example 6

This example shows degradation, expressed as urea loss, after heat treatment at different temperatures and reaction times of urea and LU-products in which organosolv lignin constitutes the lignin component. The ratio lignin:urea in the tested LU-products were 50:50. In table 9 urea% in heated urea is shown as function of temperature and reaction times in minutes.

Table 9

From table 9 it can be seen that urea degradation is markedly increased when harsher conditions are used. Accordingly milder conditions should be used. Example 7

This example shows application of LU products together with hay compared to different sources of urea. Comparative effects on ammonia-nitrogen concentration in rumen liquor incubated in vitro with hay and the various urea sources are given. Furthermore, the positive effect of an additive, lanolin, coated onto the LU product, is shown. Treatments used to ascertain the effect of different presentations of urea on the ammonia-nitrogen concentration in rumen liquor were:

1 Hay only

2 Hay + pure urea.

3 Hay + LU as used in feeding trials (example 1 )

4 Hay + LU with 25% urea

5 Hay + LU with 25% urea coated with lanolin.

The average in vitro ammonia-nitrogen concentrations (mg/l) for each treatment are given in table 9. The incubation time in hours varies from 1 -24 hours.

Table 10

values subtracted the control data (treatment 1 ). This example shows that hay plus pure urea gave far higher initial ammonia values than any of the LU treatments. Furthermore this example confirms the ammonia- nitrogen suppressing ability of the LU products is greater when the lignin content is greater (treatment 3 versus treatment 4) and that the lanolin coating is an effective method of enhancing the LU effect (treatment 4 versus treatment 5).

Further experiments showed that the functional specific gravity of the LU products can be an important factor in determining the utility of the products. It is essential that the urea containing feed stays in the rumen for a minimum time and this can be influenced by adjusting the specific gravity of the LU product. Firstly, higher specific gravity can be obtained during the production of the LU product itself by operating at conditions reducing the void fraction. Secondly, various gravity increasing/decreasing components can be incorporated in the LU product.

From the above experiments it can be seen that the inventor has succeeded in arriving at a new feed supplement containing urea which is slowly released in the rumen. The new LU product can be incorporated in compound feed/concentrates for ruminants or used as a feed supplement together with hay, straw etc.

The known ability of lignin to protect protein from microbial degradation, (Kawamoto, H; Nakatsubo, F; Murakami, K ,1992), Proteinadsorbing capacities of lignin samples. Mukusai Gakkaishi. 38:81-84, has also been retained by the LU products according to the invention.

Application of the new products can reduce substantially the risk of ammonia toxicity of ruminants fed urea containing feed.

Claims

1. Controlled release urea product, characterized in that said product primarily consists of urea entrapped or bonded in a lignin matrix forming a lignin-urea (LU) product.

2. Urea product according to claim 1 , characterized in that the ratio lignin : urea in the LU product is 75-15 : 25-85.

3. Urea product according to claim 1 , characterized in that the LU product is coated.

4. Urea product according to claim 1 , characterized in that the LU product comprises rosin either as an additive or a coating.

5. Method for preparation of a controlled release urea product, characterized in that lignin is mixed with melted urea at temperatures of 155-170┬░C and at pressures of 1-10 bar and that the retention time is 10-0.5 minutes, and that the resulting lignin-urea (LU) product is particulated by prilling, granulation, crushing or milling to desired size.

6. Method according to claim 5, characterized in that kraft lignin is applied as the lignin source in making the LU product.

7. Method according to claim 5, characterized in that the lignin applied is made from raw lignin subjected to auto hydrolysis at temperatures above 170┬░C, washing, alkaline treatment and acidification and that the resulting purified lignin is precipitated and separated as a product containing more than 90 weight% lignin, the rest being ash, sugar and some cellulose.

8. Method according to claim 5, characterized in that organosolv lignin is applied as the lignin source in making the LU-product.

9. Use of LU-products according to claims 1-4 as slow release urea supplement in ruminant feed in amounts of 0.5-5 weight% urea of the total feed dry matter.