CS240621B1 - Method for preparing energy feed from hardly digestible lignocellulosic materials - Google Patents

Abstract

The method of transporting energy feed from lignocellulosic materials by acid hydrolysis consists in that the hydrolysis is carried out at a temperature of 5 to 130 C with a mixture of hydrochloric and phosphoric acids in a ratio of 1:0.2 to 5, with the total mass concentration of acids in the aqueous medium ranging from 0.5 to 5% and the mass ratio of the aqueous solution of acids to the dry matter of the lignocellulosic material being 2 to 10:1.

Description

(54) Method for preparing energy feed from indigestible lignocellulosic materials

The method of transporting energy feed from lignocellulosic materials by acid hydrolysis consists in that the hydrolysis is carried out at a temperature of 5 to 130 C with a mixture of hydrochloric and phosphoric acids in a ratio of 1:0.2 to 5, with the total mass concentration of acids in the aqueous medium ranging from 0.5 to 5% and the mass ratio of the aqueous solution of acids to the dry matter of the lignocellulosic material being 2 to 10:1.

The invention relates to a method for preparing energy feed and difficult-to-digest lignocellulosic materials, e.g. straw, cereals, corn cobs and sawdust of deciduous trees, e.g. beech, poplar, oak, aspen, birch.

The most important energy component of livestock nutrition is simple carbohydrates, which are either formed in the digestive tract of livestock from polysaccharide feeds (cereals, roughage) or are intentionally added to feeds (e.g. molasses). While cereals are dominated by easily digestible polysaccharides of the type of various starches, in roughage polysaccharides are mainly represented in the form of various hemicelluloses and cellulose. In addition to the two polysaccharide components mentioned, a polymeric component with an aromatic character, so-called lignin, is also present in varying amounts. The ratio of individual components, their mutual interconnection and the so-called supramolecular structure of the components are largely determining for the digestibility of natural lignocellulose complexes, i.e. various grasses and herbs, straw, various parts of useful plants and, last but not least, comminuted woody plants. The examples given below document the qualitative similarity of the composition of various natural lignocellulose materials and their significantly different digestibility.

Component Ingredient content in % dry matter in woods grasses Cellulose 41 to. 45 26 to 35 Hemicelluloses 23 to 30 43 to 50 Lignin 19 to 33 7 to 10 Material Cellulose content Lignin in % of su- Digestibility and hemicelluloses Sine % in % dry matter Dried fenugreek 67 7 54 Wheat straw 75 13 38 PRO-STEM ^a/Z 67 13 60 Bagasse 81 13 28 PR0-CANE ^b/ 71 12 60 Poplar 79 19 21 Oak 68 26 15 Pine trees 67 31 4 Aspen 69 15 21 PRO-CELL ^c/ 50 13 58

The values in the table were taken from the material on the STAKE 11 process by Compagnie Prancaise d'Etudes et de Construction Technique, Paris la Dáfense, France, presented at the Symposium on Biomass Steam Cracking Applications in Moscow in February 1983.

a/ straw treated by steam cracking in the STAKE 11 process ^b// bagasse treated by steam cracking in the STAKE II process hardwood (aspen) treated by steam cracking in the STAKE II process.

During the digestion of lignocellulosic feeds, the lignocellulosic complex is disrupted, the depth of which determines digestibility, i.e. the usability of carbohydrate components for the construction and function of the entire animal organism. Some plants or parts of plants, almost generally this applies to woody plants, have a structure that resists the chemical and biochemical effects of the digestive tract, and are therefore unusable for the nutrition of the organism.

The limited extent of agricultural land or its limited fertility in various countries gives rise to efforts and even the necessity of complete utilization of agricultural phytomass, or. partial narrowing of dendromass. This fact is reflected in various chemical or biochemical treatments of straw, or. similar agricultural waste, and in the treatments of wood waste for feed purposes, which have in common the disruption of individual components (hemicelluloses and cellulose).

Biochemical pathways involve breaking down the indigestible structure by the action of enzymes, which are most often the product of certain types of fungi. Since the invention does not concern this method of treatment, the aforementioned biochemical pathway is not discussed further.

Chemical routes can be roughly divided into hydrothermal treatments, alkaline treatments, partial delignification with alkali to partial alkaline hydrolysis and treatments based on the principle of acid hydrolysis of the polysaccharide portion of the lignocellulosic material (partial or complete hydrolysis of the polysaccharide portion).

Currently, acid hydrolysis of lignocellulosic materials is not used for direct feed preparation. Hydrolysis plants in the USSR, in more than 40 plants processing several hundred kilos of wood and lignocellulosic agricultural waste, prepare diluted carbohydrate solutions by so-called percolation hydrolysis (J. J. Korolov: Perkolyatsionyj gidroliz rastitělnovo syrja, Izdatelstvo Lesnaja promyshlenost Moscow 1968) at higher temperatures of 130 to 190 °C and pressures of 1.6 to 1.8 MPa, which serve as raw materials for fermentation processing into yeast biomass (Ctobul), or into ethanol.

Hydrolysis is carried out in relatively complex acid-resistant tower reactors, which are followed by a system of heat exchangers, or a distillation column for removing furan. The insoluble residue of approximately 50% of the dry matter of the starting lignocellulosic material is waste, which is burned, or used as fertilizer or has a number of different smaller volume uses. Only half of the lignocellulosic material is used for the feed industry, and even then indirectly after fermentation processing.

The acid hydrolysis catalyst - sulfuric acid, which is used in an amount of up to 0.09 t/t of raw material, is removed from the reaction mixture in the form of CaSO^, which requires special filters (filter presses) or filter centrifuges. In addition to the above separation problems, this is a very energy-intensive process. The energy consumption per 1 t of sanharides in the form of a 3% solution is 27 OJ.

Another industrially implemented process of acid hydrolysis of lignocellulosic materials with saturated hydrochloric acid (41 ž&) does not directly prepare feed, but a concentrated solution of sugars, which can also be fed directly. The by-product is about 30% lignin, a waste that can be used as an energy source. For 1 t of dry starting material, about 1.5 t of hydrogen chloride is needed, i.e. about 3.5 t of 41½ hydrochloric acid. The process gives high yields of carbohydrates, higher than 90% of theory, but is complicated by a highly corrosive environment and the need to regenerate the hydrochloric acid used in a costly and complex manner. (Ullmans Encyclopedia of Technical Chemistry, volume 23, page 581, Verlag Chemie Weinheim 1980).

Hydrolysis procedures with diluted acids of 0.5 to 2% HgSO^, or 0.5 to 0.2% HC1 at lower temperatures of 100 to 130 °C were mostly used for the so-called pre-hydrolysis of wood, mostly before the actual hydrolysis of the cellulose component of lignocellulosic material. Again, in these cases, the diluted acidic solution of carbohydrates is usually separated, after neutralization it is processed by fermentation on torula, from the insoluble residue, which is intended for further processing, but not direct feeding.

The above disadvantages are eliminated by the hydrolysis process according to the invention, which consists in

That the lignocellulosic material is treated at a temperature of 5 to 130 °C with a mixture of hydrochloric and phosphoric acid in a ratio of 1:0.2 to 5, with the total mass concentration of acids in the aqueous medium ranging from 0.5 to 5% and the mass ratio of the aqueous acid solution to the dry matter of the lignocellulosic material being 2 to 10:1.

During the period of contact of lignocellulosic material with an aqueous solution of acids, there is a gradual increase in the degree of disruption of the lignocellulosic complex and the decomposition of polysaccharide components, which is manifested both by an increasing content of water-soluble substances and by an increasing content of reducing carbohydrates. Not only the content of soluble substances contributes to the increase in digestibility, but also, for example, 1 insoluble cellulose released from the lignocellulosic complex.

After the selected time of action of the selected mineral acid solution on the lignocellulosic substrates, the acids present can be neutralized, preferably with hydroxides or carbonates of cations that are physiologically desirable or harmless. Most often, these are sodium hydroxide and hydroxide or calcium carbonate. Preferably, an amount of sodium hydroxide is added to the mixture that is equivalent to the amount of hydrochloric acid introduced, after which enough hydroxide or calcium carbonate is added to achieve the selected pH value, usually 4.5 to 5.0.

The product obtained in this way can be used directly as an ingredient in feed mixtures without further treatment, so this entire simple treatment process is actually a waste-free technology in the truest sense of the word.

The production is waste-free and all components of the reaction mixture, including chemicals for neutralization, remain in the product and contribute to the nutritional value of the product.

The digestibility of the treated material will be increased by increasing the degree of utilization of carbohydrates due to the disruption of the lignocellulose complex, and by easier and faster absorption in the digestive tract of water-soluble carbohydrates and other organic substances.

Furthermore, the sensory and organoleptic properties of the prepared feed are significantly improved compared to the starting material. In addition, up to 50% of the original lignocellulosic material is converted into water-soluble organic substances, and of the soluble substances, approximately half is made up of reducing carbohydrates.

The presence of acids - hydrochloric and phosphoric, which can both be neutralized directly in the reaction mixture after hydrolysis to physiologically harmless salts, on the contrary contribute to improving the quality of the prepared feed. This means that after hydrolytic treatment, complex and difficult separation operations are eliminated and the entire process is simplified. The device used in the process according to the invention is also simple, which is an acid-resistant boiler, e.g. enameled or a container made of polypropylene or corobon, equipped with a heating jacket, heating coil or other heating element, or a stirrer. No special emphasis is placed on the quality of the starting feed, moisture content, ash content. Both the hydrolysis medium and the hydrolyzed raw material are introduced into the reactor, after a certain period of heating, the mixture is neutralized in the same device and after draining the mixture is ready for feeding or can be mixed with other feed components.

In the case of crushed modified corn fuels (corn cobs), or other materials, only the amount needed for a one-day or several-day feed ration (fresh mixture) can be prepared from the stock, as starting up and shutting down a simple device is not a problem.

The preparation and properties of the products obtained are illustrated by the examples.

Example 1

120 kg of meal prepared from corn cobs (de-kerned corn cobs) and with an average moisture content of 20% by weight is added to a mixture of 110 kg of an aqueous solution of 2% hydrochloric acid and 330 kg of an aqueous solution of 2% phosphoric acid. While stirring, the said mixture is heated to boiling in an enameled kettle and stirred at a boiling temperature of 100 °C for another four hours.

The initially heterogeneous mixture acquires a mushy consistency and after cooling to approximately 60 °C, 2.41 kg of NaOH is gradually added in the form of a 25% aqueous solution. After the entire amount of NaOH has been introduced, a total of 5.00 kg of calcium hydroxide is gradually added, the pH of the reaction mixture after neutralization is 4.6.

The dry matter of corn cobs produces 49.0% water-soluble substances, of which 28% are reducing substances. The mixture prepared in this way contains 8.63% water-soluble organic substances, of which 4.9% are reducing substances, and the mixture also contains 0.62% NaCl and 1.6% CaHPO ₄ .

Example 2 kg of corn cobs (50 kg of dry matter) are mixed in an enamel pressure vessel (in a steamer) with 165 kg of 2% aqueous phosphoric acid and 55 kg of 2% hydrochloric acid. After closing the pressure vessel and heating to 110 °C, this temperature is maintained for another 3 hours. After cooling to approximately 50 °C, the mixture is discharged into a mixing tank containing a solution of 1.2 kg of NeOH and 2.5 kg of calcium hydroxide in 25 liters of water.

The neutralized and homogenized mixture contains 8.8% soluble organic substances, of which 4.8% are reducing substances.

Example 3

125 kg of crushed corn cobs with an average moisture content of 20% by weight were mixed in an enameled duplicator kettle with 100 kg of 0.5% HCl and 300 kg of 0.5% HjPO^.

The mixture was heated to boiling (100 °C) for 8 hours with stirring. During heating, the mixture gradually acquired a mushy consistency. After cooling to 60 °C, 0.55 kg of NaOH in the form of a 25% aqueous solution and 1.1 kg of calcium hydroxide were gradually added with stirring in approximately five portions so that the pH of the resulting reaction mixture was around 4.5.

From the dry matter of the starting material, 44% of water-soluble substances were formed, of which 25% were reducing substances. The mixture prepared in this way contains 0.80 kg NaCl and 2.1 kg Ca(HPO^), kg of soluble organic substances, mainly of a saccharide nature, i.e. approx. 0.15% Nad,

0.4% Ca(HPO4) and 8.3% soluble mono- and oligosaccharides. The composition of the prepared feed, calculated on the dry matter, is as follows: 42.76% mono- and oligosaccharides soluble in water, 0.78% NaCl, 2.04% Ca( _HPO4 ).

Example 4

125 kg of crushed de-kerned corn cobs (corn spindles) with an average moisture content of 20% by weight were moistened in an enameled autoclave with 200 kg of an acid mixture prepared by mixing 100 kg, 1.0% HCl and 100 kg 1.0% Η^ΡΟ ₄ . The mixture was heated to 130 °C within 30 minutes and maintained at this temperature for another 90 minutes. After cooling to 80 °C, 4 kg of a 25% NaOH solution and 0.75 kg of CaηOH? were gradually mixed into the thick slurry mixture. After all the CaηOHJg had been added, the mixture was stirred for another 20 minutes and a pH of 4.8 was reached. According to the analysis, the dry matter of the prepared feed contained 54.6% water-soluble mono- and oligosaccharides, 1.55% NaCl and 1.35% CaH(HPO) ₄

Example 5

62.5 kg of crushed blackened corn cobs with an average moisture content of 20% by weight were stirred and heated to reflux for 5 hours with 200 kg of 2% HCl and 300 kg of 2% H^PO ₄ · After cooling the relatively thin slurry mixture to 60 °C, 17.5 kg of 25% NaOH solution and 6.2 kg of finely ground limestone were added, the pH of the mixture was 4.3.

55% by weight of the dry matter of corn cobs passed into the solution, of which 32% represented reducing carbohydrates.

C

The mixture contains 4.89% of water-soluble organic substances, of which 2.84% are reducing carbohydrates, and also contains 1.13% NaCl and 1.48% CaHP0 ₄ ·

In the dry matter of the prepared feed, this corresponds to 42.5% mono- and oligosaccharides, 9.9%

NaCl and 12.85% CaHP0 ₄ .

Example 6

62.5 kg of crushed de-kerned corn cobs (corn cobs) were mixed with 250 kg of an aqueous solution of phosphoric acid and hydrochloric acid containing 0.84% by weight.

HCl and 4.16% ^H 3 ^PO 4 (ratio HCl : H^PO ₄ = 1 : 5). The mixture was heated to boiling (100 °C) for 5 hours and after cooling to 80 °C with stirring neutralized 9.2 kg 2516 sodium hydroxide solution and 7.86 kg Ca(OH) ₂ , respectively. 10.5 kg CaCO-j to pH 4.5.

From the dry matter of corn cobs, 52% by weight passed into the solution, of which 27% are reducing carbohydrates. The composition of the dry matter of the prepared feed is then as follows: 36.35% organic substances dissolved in water (mainly mono- and oligosaccharides), 4.95% NaCl, 21.25% CaHPO ₄ , the rest up to 100% is the water-insoluble part of the disrupted lignocellulose complex.

Example 7

62.5 crushed de-kerned corn cobs with an average moisture content of 20% by weight were mixed with 300 kg of an aqueous acid solution containing 0.65% _H2PO4 and 3.25% HCl ( ^{the ratio of HCl: H2PO4 is} approximately 1:0.2). The mixture was heated to boiling (i.e. to 100 °C) under reflux in an enameled kettle for 4 hours.

After the specified heating time, 57% of the dry matter was converted into a water-soluble form. Of this proportion, 32% are reducing substances. After spontaneous cooling to 80 °C, the reaction mixture is neutralized with 10.7 kg of NaOH (42.8 kg of 25% sodium hydroxide solution is added) and 1.5 kg of powdered Ca(OH) ₂ , optionally in the form of a thin aqueous suspension. After neutralization, the pH of the reaction mixture is 4.8.

The reaction mixture contains 16.8% dry matter, with the dry matter composition being 22.9% NaCl, 3.95% CaHPO ₄ and 41.71% water-soluble organic substances, mainly mono- and oligosaccharides.

Example 8

Crushed corn cobs (1 part by weight) are mixed with 2 parts by weight or 4 parts by weight of aqueous solutions of hydrochloric and phosphoric acids, respectively. The acid content in the aqueous solution is 2.56 wt. and the weight ratio of Η^Ρ0 ₄ : HC1 is 3 : 1. In both cases, the added aqueous solution is practically absorbed into the treated material. The mixture is stored at ambient temperature (12 to 16 °C) in a polyethylene container (or it can be stored in a silage pit lined with polyethylene or polypropylene foil) for six, nine, twelve to fifteen weeks.

The acids present prevent fermentation processes and fungal attack and disrupt the lignocellulose complex. The resin treatment increases the content of water-soluble organic substances and reducing substances as follows:

Weight ratio of 0 grains to aqueous acid solution 1:2 1 A (56) : 4 B (56) A (56) B (%) Duration of action 6 weeks 8.5 1.2 13.1 0.9 9 weeks 11.2 1.1 16.9 1.8 12 weeks 16.1 1.3 17.0 1.9 15 weeks 17.2 1 .4 17.8 1.9

A - soluble substances calculated on dry corn cobs

B - reducing substances calculated on dried corn cobs

The silage prepared in this way can be mixed with feed as an ingredient, thereby reducing acidity, or after being suspended in water, it can be neutralized with a solution of sodium hydroxide and milk of lime or calcium carbonate.

Example 9

500 kg of crushed de-kerned corn cobs (corn cobs) with an average moisture content of 20% by weight were placed in an earth pit (earth pit) lined with polypropylene foil.

The material was stored in several layers and each layer was always moistened with an aqueous solution of hydrochloric and phosphoric acids. A total of 1,600 liters of aqueous acid solution were used, this amount is practically absorbed into the silage material. The aqueous acid solution contained 0.5 * wt. HCl and 1.5 wt. H ₃ PO ₄ · The silage was slightly compacted, covered with polypropylene film and analyzed after 4 months (November to February). The pH of the silage mixture was 1.8. The high pH prevents fermentation processes and fungal attack. By analyzing a number of samples from different parts of the silage, the average proportion of the dry matter weight that was converted to water-soluble substances was found to be 15.7%, of which 1.7% were reducing substances.

Silage prepared in this way can be mixed with feed, which will reduce acidity, or it can be neutralized with NaOH and Ca(OH) ₂ .

Example 10

100 kg of silage from example 9 is mixed with 100 kg of aqueous solution of hydrochloric and phosphoric acids in an enameled boiler. The acid content is 0.5 wt. % HCl and 1.5 wt. % HCI.

H^PO^. 2a stirring, the mixture is boiled for 4 hours (at 100 °C) and after spontaneous cooling to 80 °C, 0.965 kg of NaOH and 2.00 kg of Ca(OH) ₂ are neutralized.

The feed prepared in this way contains 8.9% soluble organic substances, of which 4.7% are reducing substances, 0.27% NaCl and 0.7% CaHPO^. In terms of dry matter of the prepared feed, the composition is as follows: 54.6% water-soluble substances (mainly mono·» and oligosaccharides), 1.6½ NaCl and 4.2% CaHPO^, the rest up to 100% are water-insoluble cellulose fibers and lignin.

The importance of the procedures according to examples 9 and 10 lies primarily in the fact that corn cobs (de-kerned corn cobs), whose occurrence is seasonal, can be preserved practically all year round in the form of Silage (see example 9); from which the material for processing into a single feed ration is gradually removed. The mixture of acids for preservation and hydrolysis is preferably the same.

Preservation of crushed corn cobs in the form of the above silage (example 9) is often more advantageous than preservation by drying, which can be energy-intensive. Without drying or ensiling, the moist crushed corn cobs are easily attacked by mold, which degrades the raw material and can also reduce the quality of the prepared energy feed.

For example, 11 kg of beech sawdust are mixed with 11 kg of 2% hydrochloric acid solution and 33 kg of 2% phosphoric acid solution. The mixture is heated to boiling in an enameled reactor for 4 hours and neutralized with 244 kg of NaOH. It is further neutralized to pH 4.8 with a suspension of calcium hydroxide. This gives a mixture containing 3.6% of soluble organic substances, of which 2.1% are reducing carbohydrates. The dry matter of beech sawdust has passed into the solution in the form of soluble substances

19.5% by mass. Under these conditions, no more than 0.10% of the dry matter was converted to 2-furancarbaldehyde.

Example 12 kg of wheat straw is mixed with 1.1 kg of a 2% hydrochloric acid solution and 3.3 kg of 2% phosphoric acid. The aqueous acid solution is more or less absorbed into the straw. The mixture is heated to boiling for 4 hours and analyzed after this time. After the specified reaction time, 12.7% of the organic substances, based on the dry matter of the straw, pass into the aqueous solution. Of this, 8.8% are reducing carbohydrates and 0.47% is 2-furancarbaldehyde (furfural), which is approximately four times more than in the case of corn cobs or beech sawdust.

Claims (2)

SUBJECT OF THE INVENTION Process for the preparation of energy feed from difficult to digest lignocellulosic materials by acid hydrolysis, characterized in that the lignocellulosic material is treated at a temperature of 5 to 130 ° C with a mixture of hydrochloric acid and phosphoric acid in a ratio of 1: 0.2 to 5, the concentration of acids in the aqueous medium is in the range of 0.5 to 5% and the weight ratio of the aqueous acid solution to the dry matter of the lignocellulosic material is 2 to 10: 1. 2. Process according to claim 1, characterized in that the acid mixture obtained is neutralized to a pH of 4.5 to 5 after 2 to 8 hours in the reactor or after 5 to 15 weeks by silage treatment.