FR2747125A1 - Processing beet pulp to give useful products - Google Patents

Abstract

Processing beet pulp to give useful products comprises (a) using beet pulp after extraction of the saccharose, (b) treating the beet pulp with (i) a basic solution with a molar concentration of 1-25 milliequivalents OH<-> per g dry pulp and (ii) H2O2 in an amount of less than 30 % H2O2 by weight on the dry pulp, at a temperature of 40-100 deg C for a time sufficient to solubilise the non-cellulosic polysaccharide (NCP) fraction of the pulp; (c) separating the liquid phase containing the NCP fraction from the solid phase consisting of a bleached cellulosic material which is especially useful as a rheological agent or filler, (d) precipitating the NCP fraction from the liquid phase and recovering the precipitated material as a biodegradable material having adhesive activity which is reversible with water, useful e.g. in the preparation of sizes and pastes, coating products and flexible adhesive films.

Description

PROCESS FOR VALUING BEET PULPS
TO OBTAIN PRODUCTS WITH HIGH ADDED VALUE
The invention relates to a process for upgrading beet pulps making it possible to obtain products with high added value, in particular a bleached cellulosic product, which can be used in particular as an additive or rheological filler, and a biodegradable substance having a sticky power that is reversible to water, which can be used in particular for preparing glues, coating products or flexible adhesive films. The invention extends to products prepared by carrying out the process.

After extraction of sucrose, beet pulps constitute an extraction residue which is currently sold by the sugar industries to animal feed formulators or directly to breeders with a view to being incorporated into animal feed rations (mainly ruminants ).

However, this market has been on the decline for several years and it is no longer possible to absorb all the production of beet pulp through this recovery route.

US Pat. No. 4,831,127 proposes a process for manufacturing parenchyma cellulose (PPC) from in particular beet pulp. This patent describes two distinct treatment routes, either acid combined with an intense mechanical treatment, or basic also combined with an intense mechanical treatment, with a view to extracting and purifying the celluloses. Hemicelluloses containing arabinogalactans and pectins are recovered in admixture as a by-product and it is proposed to incorporate them into adhesive vegetable gums. However, the tackiness of this by-product is low or zero and does not allow it to be used alone as a tackifier: this by-product has low added value and serves only as a rheological filler. The same is true for the recovered cellulose by-product, which is strongly colored and cannot be used directly. It should be emphasized that the temperature and pressure conditions of this process are severe (preferential temperatures between 1500 ° C. and 1800 ° C.) and lead to a significant degradation of the product and to mediocre recovery yields.

Patent application FR 95.01643 in the name of the applicant describes a process for upgrading beet pulps by implementing a combined acid and basic treatment. The present invention proposes to provide a new recovery process which makes it possible to simplify the process of this application and to increase the added value of the products obtained compared to those resulting from this process.

An objective of the invention is in particular to improve the quality of the polysaccharide sticky biodegradable substance obtained (whiteness, non-coloring character in aqueous solution).

Another object is to produce a bleached cellulose co-product constituting an additive or rheological filler, which does not require subsequent bleaching in most applications.

It should be noted that several types of bleaching treatments are known by means of chlorinated derivatives, hydrogen peroxide, or ozone and could be applied to the cellulosic product obtained at the end of the recovery treatment of the pulp described in application FR 95.01643 with a view to improving the quality of this cellulosic product. However, such a bleaching treatment is not suitable for the polysaccharide sticky substance, because it would lead to a significant degradation of the substance, resulting in a loss of its sticky power; moreover, with regard to cellulosic co-products which exhibit strong coloration, subsequent bleaching would require high proportions of reagents in order to obtain satisfactory whiteness, and its cost would be prohibitive.

The process according to the present invention for upgrading beet pulps and extracting high added value products therefrom is characterized in that
(a) beet pulp is used after extraction of the sucrose,
(b) said pulp is placed in the presence, on the one hand, of a basic solution of molar concentration substantially between 1 and 25 milliequivalents OH per gram of dry pulp, on the other hand, of hydrogen peroxide in weight proportion less than 30% H2O2 relative to the dry pulp, at a temperature between 400 C and 1000 C for a period suitable for solubilizing the non-cellulosic parietal polysaccharide fraction of the pulp, known as the PPNC fraction,
(c) the liquid phase containing the PPNC fraction is separated from the solid phase constituting a bleached cellulosic product, which can be used in particular as a rheological agent or filler,
(d) the PPNC fraction is precipitated from the liquid phase, and the precipitate obtained is extracted, constituting a biodegradable substance having a sticky power that is reversible with water, which can be used in particular for preparing adhesives or coating products or flexible films adhesives.

This process leads, in the first place, to a bleached cellulosic product, the whiteness of which is compatible with direct uses as an agent or rheological filler (ISO whiteness index of the order of 50%, this whiteness index being determined according to the standard. "Tappi test method T 452 om 92"); of course, this whiteness index could, where appropriate, for more demanding applications, be improved by a subsequent bleaching treatment.

The product also leads to a biodegradable substance having excellent tackiness: by simple mixing with a liquid (water or other), it gives either a reversible water-based glue which can be used in particular for gluing materials such as paper, wood, glass , synthetic material, metals, or induction products for the gluing of wallpapers (which can be easily removed by dissolving in water). This biodegradable substance also makes it possible to produce flexible adhesive films for protecting objects or surfaces or for making masks which can be removed by washing with water.

Said biodegradable substance has the following characteristics
- composition based on substantially non-degraded hemicelluloses and polygalacturonates,
- ISO whiteness index at least equal to 18% (according to the previously mentioned standard),
- non-coloring character in aqueous solution.

The obtaining of these products with high added value is explained by the combined action of the base and of the hydrogen peroxide, which solubilizes the PPNC fraction by blocking the formation of colored degradation products linked to the alkaline medium and heating.

It should be noted that the presence of H2O2 has no detrimental action on the yield of extraction of the wall compounds by the base. These actions of extraction, inhibition of secondary reactions of degradation and oxidation of chromophoric groups lead to products exhibiting remarkable whiteness qualities for very low H2O2 consumption. It should be noted that the ultimate effluent collected at the end of the process is itself very light in color and can be disposed of or recycled at low cost. In addition, there is an improvement in the stickiness of the biodegradable polysaccharide substance compared to that obtained by a simple basic treatment at comparable concentration: this is probably explained by the higher purity of the mixture obtained hemicelluloses / polygalacturonates (blocking of side reactions). .

It should be noted that these results are obtained with low basic concentrations and moderate temperatures (below 1000 ° C.), which is opposed to the teachings of the prior art (where the extractions are carried out under much more severe conditions. temperature and basicity).

The following preferential conditions appear to lead to the best results
- basic solution, in particular sodium hydroxide solution, with a molar concentration substantially between 2.5 and 6 milliequivalents OH per gram of dry pulp,
- hydrogen peroxide in a proportion by weight substantially between 4% and 15% H202 relative to the dry pulp,
- temperature substantially between 700 C and 900 C for a period substantially between 0.3 and 2 hours,
- liquid / solid dilution weight ratio (dry matter) substantially between 8 and 25.

According to a preferred embodiment, the treatment (b) is carried out by bringing the pulp into contact with the basic solution at the appropriate temperature, then by gradually introducing during the treatment the aforementioned quantity of hydrogen peroxide. This implementation leads to a significantly higher whiteness of the products, without this result being currently clearly explicable.

It is also possible to carry out the treatment (b) by mixing the basic solution with the appropriate amount of hydrogen peroxide, then bringing the pulp into contact with the mixture, and bringing the medium to the appropriate temperature.

Furthermore, additives such as sodium silicate advantageously combined with magnesium sulfate can be placed in the medium to carry out treatment (b). The silicate makes it possible to buffer the medium and to avoid a drop in pH; moreover, combined with magnesium sulphate, it forms a colloidal suspension which protects the hydrogen peroxide from a decomposing action due to the presence of transition metals in the medium (in particular iron, copper, manganese). Preferably, the magnesium sulphate and the sodium silicate are mixed beforehand with water, this mixture being used to prepare the basic solution with a view to the treatment (b), the proportion by weight of magnesium sulphate being adjusted to be substantially between 0.05% and 0.5% relative to the dry pulp, and the proportion by weight of sodium silicate to be substantially between 1% and 5% relative to the dry pulp.

In addition, the pulp is advantageously pretreated by means of a chelating agent in particular
EDTA (ethylenediamine tetraacetic), DTPA (diethylene triamine pentaacetic), or sodium salts of these two compounds; this agent is preferably brought into contact with the pulp prior to the treatment (b) in a proportion by weight substantially between 0.2% and 3% of chelating agent relative to the dry pulp. This agent allows the elimination of metals after complexation, which very effectively limits the parasitic decomposition of H202.

Furthermore, the solid cellulosic phase obtained at the end of step (c) is preferably washed with a dilute acid solution with a pH greater than or equal to 2.

This acid washing limits any subsequent coloring reactions due to the residual basicite of the product and stabilizes its whiteness; it can be combined conventionally with water washes.

In addition, according to a preferred embodiment, (d) the PPNC fraction is precipitated from the liquid phase, by concentrating said liquid phase, by adjusting, if necessary, its pH to a value substantially between 5 and 7, and by adding an alcohol.

The process of the invention gives the best results when the residual sucrose content of the pulps used is low and in practice less than 2% by weight. In general in the sugar industries, the residual rate of beet pulps is of the order of 2% so that the process of the invention can be carried out directly after the extraction of the sucrose without specific prior preparation.

The examples which follow illustrate the process of the invention and the characteristics of the products obtained.

The raw material used in these examples is beet pulp originating from sugar beets harvested in the region of Nassandres (France), after extraction of the sucrose (residual sucrose content (2%).

EXAMPLE 1: Implementation of the method
The treatment is applied to 100 g of dry matter of dehydrated pulp.

The solution intended for the extraction combined with the simultaneous bleaching is prepared by dissolving 0.1 g of magnesium sulphate (i.e. 0.1% of the dry matter of the pulp) in 1.5 l of demineralized water, then addition of Ig of sodium silicate (ie 1% of the dry matter of the pulp). 15 g of sodium hydroxide are then added at room temperature (ie 15% of the dry matter of the pulp). The pH of the solution is 13.7.

When the solution has reached a temperature of 900 ° C., the aforementioned quantity of pulp is added. The consistency of the medium is such that the ratio
L / S is 15. The reaction medium is then stirred for a period of one hour. After a few minutes of reaction, (5 to 15 min) 26.6 g of a 30% hydrogen peroxide solution (i.e. 8% peroxide relative to the dry mass of the pulp) are added gradually and in a fractional manner, so as to minimize the formation of significant foams which appear in the event of a rapid and radical introduction. Good agitation allowing a homogeneous distribution of the peroxide is then necessary.

After one hour of reaction, a solid liquid separation is carried out either by filtration through a filter cloth with a porosity of 1 to 10 μm, or by centrifugation.

The solid cellulose fraction is then subjected to one or more washes with water, then is neutralized by washing with an acid solution (HCl, pH = 2-3) in order to stabilize the whiteness. It is then dried.

The liquid phase is concentrated by removing 50% of water, by evaporation under reduced pressure (20 mm of Hg at 400 ° C.). The polysaccharide fraction is then obtained after neutralization of the medium with HCl to a pH of 6.5 and precipitation by adding 3 volumes of ethanol per volume of concentrate. After a standing time of at least 4 hours at 40 ° C., the mixture of polysaccharides is recovered either by centrifugation (3500 rpm for 30 min), or by filtration through a cloth with a porosity of 1 to 10 μm, then the mixture is dried in a ventilated oven at 400 C and crushed. This mixture represents a precipitate yield of 35% of the starting dry matter. It is characterized by an ISO whiteness index of 18% (it should be noted that no pretreatment is carried out in this example).

By way of comparison, a simple alkaline extraction without bleaching is carried out on 100 g of dry pulp. 15 g of sodium hydroxide are dissolved in 1.5 l of demineralized water, the solution is brought to 900 C. The pulp is then introduced and placed under stirring for 1 hour.

After liquid / solid separation, the treatment is the same as that described above. It leads to the precipitation of the polysaccharides in a yield of 36% of the starting dry matter, which have an ISO whiteness index of only 6%.

EXAMPLE 2: Process with chelating pretreatment
The treatment is applied to 100 g of dry matter of dehydrated pulp.

An assay of the metal cations contained in the beet pulp is carried out by atomic absorption after calcination at 5500 C for 3 hours and recovery of the ashes in 1 concentrated HCl. The metallic entities, iron, copper, manganese, cations essentially responsible for the decomposition of peroxide, are initially present in the pulp at a rate of 210 ppm of iron, 6.7 ppm of copper, 112 ppm of manganese, relative to the dry matter of pulp.

The chelating solution is obtained by dissolving 0.5 g of Ethylene Diamine Tetraacetic
Acid (EDTA) in 1.5 1 of demineralized water. The pH is if necessary adjusted to 4.5 by adding HCl. The aforementioned quantity of pulp is added when the temperature of the medium is 700 C. The reaction time is 30 minutes. The pulp thus treated is filtered or centrifuged and then subjected to one or more washes with water. The pulp thus obtained is approximately 20% dry matter.

The concentrations of the metals previously assayed were lowered to 35 ppm of iron, 1.5 ppm of copper, 2 ppm of manganese relative to the dry matter of the pulp.

The pulp thus pretreated is then subjected to the process described in Example 1. The polysaccharide substance resulting from this treatment, with a yield of 34.5% of the starting dry matter, has a lighter color than that of Example 1. It is characterized by an ISO whiteness index of 26%. At the same time, the co-produced cellulosic fiber exhibits higher whiteness, with an ISO index of the order of 50 t.

The polysaccharides are then used for the preparation of a biodegradable and water-reversible glue, by dissolving 15 g of dry polysaccharides in 85 ml of water with stirring at room temperature. The dry extract determined according to the NFT 76 101 standard by drying the adhesive at 1050 ° C. for 3 hours is therefore 15%.

The properties of the glue solution are evaluated by shear resistance tests of joints glued by stress to rupture according to standard NFT 76 107.

The assemblies tested are: paper
Kraft / Kraft paper, Kraft paper / aluminum, paper
Kraft / cardboard, aluminum foil / aluminum foil, aluminum foil / cardboard, Kraft paper / cardboard, Kraft paper / glass, and all lead to the cohesive failure of any of the backings. In the case of assemblies of wooden specimens (4 to 5 mm thick), the breaking force of the glue joint is of the order of 400N. The glue does not leave traces on the wood.

EXAMPLE 3: Comparison of the process with separate extraction and bleaching
By way of comparison, the mixture of polysaccharides as well as the cellulose co-product, resulting from the alkaline extraction alone described in Example 1, are subjected separately to bleaching with 8% hydrogen peroxide relative to the mass of dry product. treaty.

Thus, a chelating pretreatment followed by the process described in Example 2 is applied to the cellulose co-product obtained from Example 1. The fiber thus obtained is more colored than that of Example 2.

At the same time, 35 g of dry polysaccharides obtained from Example 1 are dissolved in 170 ml of a 0.85% sodium hydroxide solution supplemented with 0.036 g of magnesium sulfate and 0.36 g of sodium silicate. The pH of the solution is 13.2. 10.52 g of a 30% hydrogen peroxide solution are then added and the medium is then heated at 90 ° C. for 1 hour 15 minutes. After cooling, the bleached polysaccharides are precipitated with 3 volumes of ethanol, then treated. according to the process described in Example 1. The overall yield of dry polysaccharides is 28% of the initial dry pulp. Their ISO whiteness index is only 17%.

A 15% dry extract glue solution prepared and tested according to the procedure described in Example 2 leads, in the case of wooden specimens, to a breaking force of the glue joint of less than 150 N.

The glue obtained has thus lost its adhesive power and furthermore stains the wood. Splitting the extraction and bleaching into separate stages does not appear to be a good alternative.

EXAMPLE 4: Another Mode of Implementation of the Process with Chelating Pretreatment
The procedure differs from Example 2 in the mode of introduction of the peroxide.

The solution intended for the simultaneous extraction / bleaching is prepared by dissolving 0.1 g of magnesium sulfate, 1 g of sodium silicate and 15 g of sodium hydroxide. 26.6 g of a 30% hydrogen peroxide solution are then added to the extracting solution at room temperature.

100 g of dry matter of dehydrated pulp which has undergone the chelating treatment are then introduced into the mixture placed under stirring for 1 hour 30 minutes and brought to a temperature of 90 ° C. The procedure is then identical to that of Example 1.

The products of a mixture of polysaccharides (precipitated with a yield of 31.4% of the starting dry matter) and cellulosic co-product, exhibit whiteness characteristics similar to those of Example 2.

The tackiness of a solution of polysaccharides at 15% of dry extract, prepared and tested according to the procedure described in Example 2, is characterized by a breaking force of the glue joint for wooden specimens of the order of 500 N. The other types of assemblies described in Example 2 also lead in this example to the cohesive failure of one of the supports.

EXAMPLE 5 Variation in the level of peroxide during the process with chelating pretreatment
The procedure is identical to that described in Example 2. The quantity of added hydrogen peroxide in this case represents 15% of the dry matter of the pulp after treatment with EDTA. The cellulose fiber thus obtained is better bleached than in Example 2. The polysaccharides precipitated with a yield of 30% relative to the starting dry pulp have a better ISO whiteness index than in Example 2: 43%.

A 15% dry extract glue solution prepared according to the protocol given in Example 2 leads to a breaking force of the glue joint with respect to shear of the order of 500 N (wood / wood joints).

The other types of assemblies lead in all cases to the cohesive rupture of one of the supports.

The increase in the level of peroxide consequently makes it possible to increase the whiteness of the products, without reducing the tackiness of the solutions of polysaccharides.

EXAMPLE 6 Variation of the level of peroxide according to another embodiment of the method with chelating pretreatment
The procedure is identical to that described in Example 4. The quantity of hydrogen peroxide required for the bleaching represents 15% of the mass of dry pulp resulting from the chelating treatment.

The cellulose fiber is whiter than in the case of Example 4. The polysaccharides are precipitated in a yield of 35% of the starting dry pulp mass and have an ISO whiteness index of around 45%.

Claims (16)

1 / - Process for upgrading beet pulps making it possible to obtain products with high added value, characterized in that (a) beet pulp is used after extraction of the sucrose, (b) said pulp is placed in the presence, on the one hand, of a basic solution of molar concentration substantially between 1 and 25 milliequivalents OH per gram of dry pulp, on the other hand, of hydrogen peroxide in weight proportion less than 30% H2O2 relative to the dry pulp, at a temperature between 400 C and 1000 C for a period suitable for dissolving the non-cellulosic parietal polysaccharide fraction of the pulp, known as the PPNC fraction, (c) the liquid phase containing the PPNC fraction is separated from the solid phase constituting a bleached cellulosic product, which can be used in particular as a rheological agent or filler, (d) the PPNC fraction is precipitated from the liquid phase, and the precipitate obtained is extracted, constituting a biodegradable substance having a tackiness which is reversible with water, which can be used in particular for preparing adhesives or coating products or flexible films adhesives. 2 / - Method according to claim 1, characterized in that (b) the pulp is placed in the presence of a basic solution of molar concentration substantially between 2.5 and 6 milliequivalents OH per gram of dry pulp, and peroxide of hydrogen in a proportion by weight substantially between 4% and 15% H202 relative to the dry pulp. 3 / - Method according to one of claims 1 or 2, characterized in that the treatment (b) is carried out by contacting the pulp with the basic solution at the appropriate temperature, then gradually introducing during the treatment the aforementioned amount of hydrogen peroxide. 4 / - Method according to one of claims 1 or 2, characterized in that the treatment (b) is carried out by mixing the basic solution with the appropriate amount of hydrogen peroxide, then by contacting the pulp with the mixture , and bringing the medium to the appropriate temperature. 5 / - Method according to one of claims 1, 2, 3 or 4, characterized in that (b) the medium is placed in the presence of sodium silicate. 6 / - Method according to claim 5, characterized in that (b) the medium is placed in the presence of magnesium sulfate. 7 / - Method according to claim 6, characterized in that the magnesium sulfate and sodium silicate are mixed beforehand with water, this mixture being used to prepare the basic solution for the treatment (b) so that the proportion by weight of magnesium sulphate is substantially between 0.05% and 0.5% relative to the dry pulp and that the proportion by weight of sodium silicate is substantially between 1% and 5% relative to the dry pulp . 8 / - Method according to one of claims 1, 2, 3, 4, 5, 6 or 7, characterized in that (b) the medium is placed in the presence of a chelating agent, in particular EDTA (ethylene diamine tetraacetic ), DTPA (diethylene triamine pentaacetic), or sodium salts of these two compounds. 9 / - Method according to claim 8, characterized in that the chelating agent is brought into contact with the pulp prior to the treatment (b) in a proportion by weight substantially between 0.2% and 3% of chelating agent relative to the pulp dried. 10 / - Method according to one of the preceding claims, characterized in that the treatment (b) is carried out at a temperature substantially between 700 C and 900 C for a period substantially between 0.3 and 2 hours. 11 / - Method according to one of the preceding claims, wherein the sodium hydroxide is used for the treatment (b). 12 / - Method according to one of the preceding claims, wherein the treatment (b) is carried out with a liquid / solid dilution weight ratio (dry matter) substantially between 8 and 30. 13 / - Method according to one of the preceding claims, characterized in that the solid cellulose phase obtained at the end of step (c) is washed with a dilute acid solution of pH greater than or equal to 2. 14 / - Method according to one of the preceding claims, characterized in that (d) the PPNC fraction is precipitated from the liquid phase, by concentrating said liquid phase, by adjusting, if necessary, its pH to a value substantially between 5 and 7, and adding an alcohol. 15 / - Method according to one of the preceding claims, wherein (a) using a beet pulp containing less than 2% by weight of residual sucrose. 16 / - Biodegradable substance capable of being obtained by carrying out the process according to one of claims 1 to 15, characterized in that it comprises substantially non-degraded hemicelluloses and polygalacturonates, and in that it has a sticky power reversible with water, a whiteness index ISO at least equal to 18% and a non-coloring character in aqueous solution.