FR2730236A1 - Utilising sugar beet pulp after extn. of saccharose - Google Patents

Abstract

In utilisation of sugar beet pulp: (a) the pulp is used after extn. of the saccharose, (b) the pulp is treated with an acid soln. under mild temp. conditions, to solubilise selectively, the pectic fraction of the pulp, (c) the liq. pectic phase is sepd. from the de-pectinised residual solid, (d) the solid phase is treated with a basic soln. under mild temp. conditions, to solubilise the hemicellulose fraction, (e) the hemicellulose liq. phase is sepd. from the residual cellulose solid, and (f) the pectins from stage (c) and the hemicellulose from stage (e) are mixed, to give the required biodegradable prod.

Description

PROCESS FOR THE VALORIZATION OF BEET PULP, IN
SPECIAL FOR PREPARING GLUES, PRODUCTS
COATING OR REVERSIBLE ADHESIVE FILMS IN WATER
The invention relates to a process for the recovery of beet pulps which makes it possible to obtain a biodegradable substance which is soluble in water and which has good stickiness and which can be used in particular for preparing glues or coating products, or flexible films. adhesives. The invention extends to the applications of said biodegradable substance and to the preparation methods used in the context of these applications.

 After sucrose extraction, beet pulp is an extraction residue that is currently sold by the sugar industries to feed formulators or directly to farmers for incorporation into animal feed rations (mainly ruminants). ).

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

 Furthermore, the patent FR-2,213,962 proposes a process for the recovery of pectin-rich materials consisting of reacting said materials with a polyol in order to obtain a gel which is then subjected to a dehydration process in order to produce coating or packaging. This gel does not seem to have a sticky power. The beet pulp is, among others, cited in this patent as likely to be a raw material rich in pectins. The major disadvantage of this process lies in the fact that it requires the use of a polyol (which plays the role of plasticizer): the cost of such a compound and the addition operation renders the process profitable in the case of the valuation of beet pulp.

 The patent application EP-0,506,650 proposes a packaging material obtained by hot acid degradation of vegetable waste, the degraded mixture obtained being diluted, homogenized and then brought to a specific acidic pH (pH: 3) and treated with the oven to obtain leaves; Beet pulp is cited as an example of plant waste that can be used. Such a technique that uses all of the constituents of vegetable waste after acid degradation to make the new sheet material seems to constitute a possible solution to the problem of valorizing beet pulp. However, this document gives no indication of the qualities of flexibility and folding resistance of the materials obtained and, in the absence of additives, it is likely, in the case of beet pulps, that the materials made from said pulps are brittle, have poor performance in flexibility (due in particular to the presence of the cellulosic fraction) and, in any case, do not have tackiness: consequently, the applications of these materials obtained from beet pulp remain limited or require the addition of third parties body as in the previous case.

 US-4,831,127 proposes a process for manufacturing parenchymal cellulose (PCC) from, in particular, beet pulp. This patent describes two distinct treatment routes, either acid combined with intense mechanical treatment, or basic combined with intense mechanical treatment, to extract and purify celluloses. Hemicelluloses containing arabinogalactans and pectins are recovered as a by-product mixture and it is proposed to incorporate them in adhesive vegetable gums. However, the stickiness of this by-product is low or zero and can not be used alone as a tackifier: this by-product has a low added value and serves only as a rheological load.

 The present invention proposes to provide a new recovery method specifically adapted to beet pulps to make it possible to valorize, in a profitable way, all the pulps produced by the sugar industries.

 An object of 1 invention is in particular to provide a process for the recovery of beet pulps leading to a biodegradable substance that can be used in wide applications because, firstly, of its high tack, reversible to water, on the other hand, properties of flexibility and mechanical strength of the products that can be prepared therefrom.

 Another objective is to provide a process leading to a cellulosic coproduct that is itself valuable.

The beet pulp beneficiation method according to the invention for obtaining a water-soluble, biodegradable substance having tackiness is characterized in that
(a) beet pulp is used after extraction of the sucrose,
(b) said pulp is placed in the presence of an acid solution under mild temperature conditions suitable for selectively solubilizing the pectic fraction of said pulp,
(c) separating the pectic liquid phase from the residual solid phase, called the depectinated solid phase,
(d) the depected solid phase is placed in the presence of a basic solution under mild temperature conditions suitable for solubilizing the hemicellulose fraction,
(e) separating the hemicellulosic liquid phase from the residual solid phase, referred to as the cellulosic solid phase,
(f) a mixture of pectins and hemicelluloses is prepared from the pectic phase resulting from the operation (c) and from the hemicellulose phase resulting from the operation (e), said mixture constituting the desired biodegradable substance.

 By "mild temperature conditions" is meant a temperature below about 1000 C 1100 C.

 The biodegradable substance obtained by carrying out the process defined above is characterized in that it comprises a polysaccharide mixture of substantially undegraded pectins and substantially non-degraded hemicelluloses, in the substantial absence of celluloses. By "substantially undegraded pectins", or "substantially undegraded hemicelluloses" is meant a compound in which the optionally degraded fraction is less than 5% by weight. The proportion by weight of pectins is in particular between 25% and 50% in the polysaccharide mixture. Experiments have shown that such a substance has a high stickiness and that it makes it possible in particular to prepare, without additive, glues and coating products and flexible films biodegradable adhesives, translucent thin, reversible to the The glues obtained can be used to glue materials such as paper, dense wood, metal, synthetic materials, glass or to carry out reversible labeling, in particular labeling of returnable containers that can be distinguished by simple soaking. The coatings obtained can be used to glue wallpapers (which can be easily removed by water solubilization) or to coat porous substrates to increase their airtightness. The films obtained have mechanical characteristics which are adapted to enable them to be used as object or surface protection or as masking products that can be eliminated by washing with water.

 As shown by the examples provided below, the substance according to the invention has a high stickiness, remarkable when compared to substances of the same type known from the prior art, in particular to the by-product of the process described in U.S. Patent 4,831,127. This can be explained by the fact that in this US process, pectins or hemicelluloses are highly degraded (demethylation or hydrolysis) which reduces or cancels their stickiness. Indeed, if the "basic" pathway is chosen, the pectins are strongly degraded in the US process, whereas it is the hemicelluloses which are strongly degraded when the acid treatment is chosen under the conditions of use used. (In particular, a temperature of between 1400.degree. C. and 2000.degree. C.), the intense mechanical treatment contributing to this degradation. On the contrary, in the process of the invention, two successive gentle treatments are combined which make it possible to separate the pectins and the hemicelluloses without to degrade them appreciably: first, a mild acidic treatment, capable of selectively solubilizing the pectic fraction, (without degradation of the hemicellulosic fraction in view of the conditions), then a basic treatment which relates only to the depectinated fraction and therefore does not degrade pectins already extracted.

 It has been possible to demonstrate that the high tackiness of the substance obtained is related to the synergy of non-degraded pectins and non-degraded hemicelluloses that it contains. Each non-degraded compound has separately a stickiness significantly lower than that of the mixture (each degraded compound having virtually no stickiness as already indicated).

 According to a preferred embodiment, the mixture of pectins and hemicelluloses is prepared from the liquid pectic phase and the liquid hemicellulose phase, by mixing the two liquid phases, treating the resulting liquid mixture in such a way as to precipitate the compounds in solution, and extracting the precipitate obtained.

 This embodiment has the advantage of being very simple since it avoids extracting separately the pectic and hemicellulose compounds; in addition, the acidity of one of the solutions and the basicity of the other contribute to the neutralization of the mixture obtained before precipitation: if necessary a pH adjustment can be carried out so that it is substantially between 5 and 7.

 Preferably the liquid mixture is concentrated before precipitation, the latter being obtained by adding an alcohol, in particular ethanol.

According to another embodiment, it is possible to carry out the mixture of pectins and hemicelluloses:
by treating the pectic liquid phase so as to precipitate and extract the pectins,
by treating the hemicellulosic liquid phase so as to precipitate and extract the hemicelluloses,
and mixing the thus obtained extracts of pectins and hemicelluloses.

 It is necessary, in this case, to neutralize the hemicellulosic liquid phase before precipitation (pH brought to a value substantially between 5 and 7). Each liquid phase is preferably concentrated before precipitation, the latter being obtained, as in the first embodiment, by adding an alcohol, in particular ethanol. This mode of implementation, more complex, may in some cases make it possible to achieve with more flexibility different formulations of the pectin / hemicellulose mixture.

 The process of the invention leads, at the end of the separation operation (e), to a cellulosic solid phase which can itself be valorized by known methods of pressing (thermopressing or cold pressing), where appropriate after resuspension. For example, it is possible to manufacture with this co-product, biodegradable objects that are generally made from peat or wood cellulose, such as pots or transplanting buckets, divided media crop above ground, trays packaging fragile products , disposable trays ..... Such a covalorization increases the profitability of the process of the invention. Of course, the cellulosic fraction obtained may, if appropriate, be used in other applications.

 The acid treatment operation (b) which makes it possible to selectively solubilize the pectic fraction takes place under mild temperature conditions, in particular by means of an aqueous solution of strong acid, brought to a temperature substantially between 500 ° C. and The pH of the bath is advantageously adjusted to a value substantially between 1 and 2, the treatment duration being provided to solubilize at least 70% of the pectins present. Preferably, the weight ratio of liquid / solid dilution (dry matter) is adjusted to a value of between 8 and 30 during the acid treatment.

Such an implementation benefits from good selectivity and solubilizes pectins without appreciable hydrolysis of hemicelluloses (less than 5% degraded hemicelluloses).

 The basic treatment operation (d) is also performed under mild conditions. The depectinated solid phase may in particular be placed in the presence of a solution of sodium hydroxide or potassium hydroxide such that the number of milli-OH equivalents per gram of solids is between 4 and 38 g-1, the weight ratio of dilution liquid / solid preferably being between 8 and 30. The temperature of this basic treatment is advantageously adjusted to a value between 400 C and 900 C. In practice, the basic treatment will be continued for a period allowing solubilization at least 70% hemicelluloses present.

 The method of the invention gives good results when the residual sucrose content of the pulps used is low and in practice less than 3% by weight. In general in the sugar industries, the residual rate of beet pulp is of the order of 2%, so that the process of the invention can be carried out directly after the extraction of sucrose without specific prior preparation.

 The aforementioned separating operations of the liquid and solid phases can be carried out conventionally by decantation and pressing, filtration under pressure, spinning, or by any other known method.

 The substance obtained by carrying out the process of the invention can be used in all applications where the following properties are sought: high tack, water repellency, biodegradability, water solubility, film-forming character.

 In particular, this substance makes it possible to manufacture either glues, in particular by adjusting the weight hydration rate of the mixture (water / dry matter) to a value substantially between 14 and 25 to obtain an appropriate viscosity solution, that is coating, in particular by adjusting the degree of hydration by weight to a value substantially between 4 and 15 to obtain a pasty composition.

 The substance according to the invention also makes it possible to manufacture flexible, adhesive films, in particular by adjusting the degree of weight hydration of the mixture obtained (water / dry matter) substantially to a value of between 4 and 25, by spreading the product obtained on a surface to form a layer and performing a partial drying of said layer to a weight hydration level substantially between 0.1 and 0.2.

The invention is illustrated by the following implementation examples
EXAMPLE 1: PRODUCTION OF A SUBSTANCE
BIODEGRADABLE BY MIXING OF PECTINS AND HEMICELLULOSES
In this example, the raw material used is beet pulp obtained after extraction of sucrose (residual sucrose content <2%) and dehydration. The pectins, then the hemicelluloses are successively extracted and isolated according to the following protocol
- Obtaining the Pectines:
68 g of dry matter of dehydrated beet pulp are introduced into a reactor containing 1.5 liter of water and 4.6 g of sulfuric acid (pH 1.5). The whole is stirred at 700 C for 2 hours. The liquid phase and the solid phase are then separated by filtration. The pectic liquid phase is concentrated by removing 50% of water, by evaporation under reduced pressure (20 mm Hg) at 400 ° C. The pectins contained in the concentrate are then precipitated by adding 3 volumes of ethanol per volume of concentrate. After a rest period of 12 hours at 40 ° C., the pectic cake separated from the liquid phase by filtration is dried in an oven ventilated at 400 ° C. and milled.

 According to this method, the yield of pectic powder is 13.5% relative to the dry matter of beet pulp.

- Obtaining hemicelluloses
41 g of dry matter of beet pulp depectinées, according to the protocol defined above, are introduced into a reactor containing 0.9 liter of a 5% sodium hydroxide solution. The whole is stirred at 700 C for 2 hours. The liquid phase and the solid phase are then separated by filtration. The hemicellulosic liquid phase is concentrated by removing 50% of water, by evaporation under reduced pressure (20 mm Hg) at 400 ° C. The pH of the concentrate is then adjusted to 6.5 by adding concentrated acetic acid. The hemicelluloses contained in the concentrate are then precipitated by adding 3 volumes of ethanol per volume of concentrate. After a rest period of 12 hours at 40 ° C., the hemicellulose cake separated from the liquid phase by filtration is dried in an oven ventilated at 400 ° C. and milled.

 According to this method, the yield of hemicellulosic powder is 11% relative to the dry matter of beet pulp initially introduced.

- Manufacture of biodegradable and reversible glue
3.3 g of peptic powder and 6.6 g of hemicellulose powder are dissolved in 90 ml of water and heated with stirring at 500 ° C. for 1 hour 30 minutes. The solution obtained can be used directly as a biodegradable and reversible glue. 'water. The following assemblies were made: kraft / kraft paper kraft paper / aluminum foil; craft paper / glass; kraft paper / cardboard; aluminum foil / aluminum foil; aluminum foil / cardboard; cardboard / cardboard; glass / glass; Kraft paper / polyethylene.

The shear strength tests of joints bonded by tensile stress to failure, according to the NFT 76-107 standard, lead to the following results
Assemblies Strength of bonded bond (N) kraft paper / kraft paper> that of kraft paper / aluminum foil> that of kraft paper / paperboard> that of aluminum foil / aluminum foil> that of aluminum foil cardboard> to cardboard / cardboard material 308
EXAMPLE 2 COMPARISON OF GLUE
EXAMPLE 1 WITH GLUES CONSTITUTED BY EXTRACTS FROM
PECTINES ON THE ONE HAND, AND HEMICELLULOSES ON THE OTHER.

 In this example, the raw material and the conditions for obtaining pectic powders and hemicellulose powders are identical to those of Example 1.

The manufacture of biodegradable and reversible adhesives with water, according to the same protocol as that described in Example 1, is conducted, on the one hand, with the pectic powder alone and, on the other hand, with the hemicellulose powder alone. . The same assemblies as in Example 1 are made. The shear strength tests of joints bonded by tensile stress to failure, according to the NFT 76-107 standard, lead to the following results
a) for the pectic powder-based glue
Assemblies Strength of bonded bond (N) kraft paper / kraft paper> that of kraft paper / aluminum foil> that of kraft paper / paperboard> that of aluminum foil / aluminum foil> that of aluminum foil cardboard> to cardboard / cardboard material 213
b) for hemicellulose powder glue
Assemblies Strength of bonded bond (N) kraft paper / kraft paper> that of kraft paper / aluminum foil> that of kraft paper / paperboard> that of aluminum foil / aluminum foil> that of aluminum foil cardboard> to cardboard / cardboard material 240
These results illustrate that in the case of tensile-resistant materials, the glue based on the mixture of pectins and hemicellulose described in Example 1 leads to better results than glues based on pectins alone or based on hemicelluloses alone.

EXAMPLE 3 COMPARISON WITH GLUE
EXAMPLE 1 A GLUE MADE BY TREATMENT
EXTRACTION ALKALINE
In this example, the raw material used is identical to that of Example 1.

 68 g of dry matter of dehydrated beet pulp are introduced into a reactor containing 1.5 liter of water and 75 g of sodium hydroxide. The whole is stirred at 700 C for 2 hours. The liquid phase and the solid phase are then separated by filtration. The polysaccharide liquid phase is concentrated by removing 50% of water, by evaporation under reduced pressure (20 mm Hg) at 400 ° C., and the pH of the concentrate is adjusted to 6.5 by addition of concentrated sulfuric acid. The polysaccharides contained in the concentrate are then precipitated by adding 3 volumes of ethanol per volume of concentrate. After a rest period of 12 hours at 40 ° C., the polysaccharide cake separated from the liquid phase by filtration is dried in an oven ventilated at 400 ° C. and milled.

 According to this method, the yield of polysaccharide powder is 34% relative to the dry matter of beet pulp.

The manufacture of biodegradable glues and reversible with water is conducted according to the same protocol as that described in Example 1. The same assemblies as in Example 1 are made. The shear strength tests of joints bonded by tensile stress to failure, according to the NFT 76-107 standard, lead to the following results
Assemblies Strength of bonded bond (N) kraft paper / kraft paper> that of kraft paper / aluminum foil> that of kraft paper / paperboard> that of aluminum foil / aluminum foil> that of aluminum foil cardboard> to that of cardboard / cardboard material 117
In this case, the results show that the polysaccharides extracted in one step, under alkaline conditions, lead to lower bonding performance than those obtained with, on the one hand, the glue based on pectins not substantially degraded (example 2) and the adhesive based on the mixture of pectins and hemicelluloses not significantly degraded (Example 1).

EXAMPLE 4 COMPARISON WITH GLUE
EXAMPLE 1 OF A GLUE BASED ON DEGRADED PECTINS
In this example, the raw material and the conditions for obtaining the pectic powder are identical to those of Example 1.

 10 g of pectic powder are placed in a stirred reactor, containing 1.5 liters of water and 75 g of sodium hydroxide at 700 ° C. for 2 hours. The liquid phase is then concentrated by removing 50% of water, by evaporation under reduced pressure (20 mm Hg) at 400 C. The polysaccharides contained in the concentrate are then precipitated by adding 3 volumes of ethanol per volume of concentrate. . After a rest period of 12 hours at 40 ° C., the cake separated from the liquid phase by filtration is dried in a ventilated oven at 400 ° C. and milled.

 According to this method, the yield of polysaccharide powder is 6.7% relative to the dry matter introduced.

 Under the same conditions of manufacture and implementation of adhesives as those described in Example 1, no bonding efficiency could be observed, except for the assembly paper kraft / kraft paper, including shear strength the seal bonded by tensile stress to failure (NFT 76-107 standard) is 49 N.

 This result illustrates the fact that the pectins degraded under alkaline treatment conditions, identical to those of the extraction used in Example 3, no longer exhibit interesting tacky properties.

EXAMPLE 5: PRODUCTION OF A SUBSTANCE
BIODEGRADABLE COLLANT BY SIMULTANEOUS PRECIPITATION OF
PECTINES AND HEMICELLULOSES
In this example, the raw material and the extraction conditions of pectins and hemicelluloses are identical to those of Example 1.

 The pectic and hemicellulosic liquid phases obtained after separation of the liquid and solid phases are mixed in a stirred reactor, the pH is adjusted to 5.7 by addition of concentrated acetic acid. The mixture obtained is concentrated by evaporation of 50% of the water at 400 ° C. under reduced pressure (20 mm Hg).

 The pectins and hemicelluloses contained in the concentrate are then precipitated by adding 3 volumes of ethanol. After a rest period of 12 hours at 40 ° C., the precipitate of not significantly degraded pectins and hemicelluloses not significantly degraded is separated from the liquid phase by filtration and then dried in a ventilated oven at 400 ° C. and milled.

 According to this process, the yield of pectic and hemicellulosic powder is 33% relative to the dry matter of the beet pulp.

 The properties of the biodegradable and reversible adhesive with water obtained are identical to those of Example 1.

EXAMPLE 6: PROCESS VARIANT
MANUFACTURING
In this example, the raw material used and the extraction conditions of the pectins are identical to those of Example 1, except that 1.5 g of 35% concentrated hydrochloric acid are used. instead of 4.6 g of sulfuric acid.

 According to this method, the pectic powder yield is 12% relative to the dry matter of the beet pulp.

 The adhesive obtained according to the same protocol as that described in Example 1 can be used directly to make the assemblies.

 The results of the bonding tests and the mechanical tests carried out are identical to those obtained in Example 1.

Claims (16)

 1 / - Process for the recovery of beet pulps enabling a biodegradable substance having a sticky power to be obtained, which can be used in particular for preparing adhesives or coating products or flexible adhesive films, which are reversible with water, characterized in that than  (a) beet pulp is used after extraction of the sucrose,  (b) said pulp is placed in the presence of an acid solution under mild temperature conditions suitable for selectively solubilizing the pectic fraction of said pulp,  (c) separating the pectic liquid phase from the residual solid phase, called the depectinated solid phase,  (d) the depected solid phase is placed in the presence of a basic solution under mild temperature conditions suitable for solubilizing the hemicellulose fraction,  (e) separating the hemicellulosic liquid phase from the residual solid phase, referred to as the cellulosic solid phase,  (f) a mixture of pectins and hemicelluloses is prepared from the pectic phase resulting from the operation (c) and from the hemicellulose phase resulting from the operation (e), said mixture constituting the desired biodegradable substance.  2 / - Process according to claim 1, characterized in that (f) the mixing is carried out  by performing a liquid mixture of the pectic liquid solution and the hemicellulosic liquid solution,  treating said liquid mixture to precipitate the compounds in solution,  and extracting the precipitate obtained.  3 / - The method of claim 2, wherein the treatment of the liquid mixture is carried out by adjusting, if necessary, the pH to a value substantially between 5 and 7, concentrating said liquid mixture and adding an alcohol.  4 / - Process according to claim 1, characterized in that (f) the mixing is carried out  by treating the pectic liquid phase so as to precipitate and extract the pectins,  by treating the hemicellulosic liquid phase so as to precipitate and extract the hemicelluloses,  and mixing the pectin and hemicellulose extracts.  5 / - The method of claim 4, wherein  the treatment of the pectic liquid phase is carried out by concentrating said phase and adding an alcohol,  the treatment of the hemicellulosic liquid phase is carried out by neutralizing said phase to obtain a pH substantially between 5 and 7, concentrating said phase and adding an alcohol.  6 / - Method according to one of claims 1, 2 or 3, 4 or 5, wherein (a) beet pulp is used containing less than 2% by weight of residual sucrose.  7 / - Method according to one of claims 1, 2, 3 or 4, 5 or 6, wherein (b) the beet pulp is placed in the presence of an aqueous solution of strong mineral acid so as to adjust the pH of the bath to a value substantially between 1 and 2 and the bath is heated to a temperature substantially between 500 C and 900 C for a time to solubiliser at least 70% of the pectins present.  8 / - The method of claim 7, wherein (b) the acid treatment is carried out so that the weight ratio of liquid / solid dilution (dry matter) is between 8 and 30.  9 / - Method according to one of the preceding claims, wherein (d) the solid phase is portreated in the presence of a sodium hydroxide solution or potash so that the number of milli-equivalents OH molar per gram of solids is between 4 and 38 g 1 and the bath is heated to a temperature substantially between 400 C and 900 C for a time to solubiliser at least 70% of hemicelluloses present.  10 / - The method of claim 9, wherein (d) the basic treatment is carried out so that the weight ratio of liquid / solid dilution is between 8 and 30.  11 / - recovery process according to one of claims 1 to 10, wherein the cellulosic solid phase obtained at the end of the separation operation (e) is pressed, optionally after resuspension, for the Obtaining biodegradable objects such as pots or transplanting buckets, divided media for growing above ground, packaging trays, disposable trays.  12 / - Process for preparing a reversible glue with water, from a substance manufactured by carrying out the method according to one of claims 1 to 10, wherein the weight of hydration is adjusted the mixture obtained (water / dry matter) to a value substantially between 4 and 25, to obtain a viscous solution suitable for bonding materials such as paper, dense wood, metal, synthetic materials, glass.  13 / - Process for preparing a coating product, from a substance manufactured by carrying out the method according to one of claims 1 to 10, wherein the weight hydration rate of the precipitate is adjusted. obtained at a value substantially between 4 and 15, in order to obtain a paste suitable for effecting the coating of a surface.  14 / - Process for preparing a flexible biodegradable adhesive film from a substance manufactured by carrying out the process according to one of claims 1 to 10, wherein the weight of hydration of the mixture obtained is adjusted (water / dry matter) substantially to a value of between 4 and 25, the product obtained is spread on a surface to form a layer and partial drying of said layer is carried out to a substantially inclusive hydration rate between 0.1 and 0.2.  15 / - Biodegradable substance obtainable by carrying out the method according to one of claims 1 to 10, characterized in that it comprises a polysaccharide mixture of substantially undegraded pectins and substantially undegraded hemicelluloses.  16 / - biodegradable substance according to claim 15, characterized in that the polysaccharide mixture contains a relative weight proportion of pectins of between 25% and 50%.