FR2600063A1 - Process and installation for the treatment of plant matter to produce especially furfural - Google Patents

Abstract

The installation essentially comprises a steam cracking unit A for thermomechanically separating insoluble materials, such as lignin and cellulose, and soluble materials, such as pentosans and pentoses, a location 8 for injecting acid into the materials leaving the steam cracking, a unit B which makes it possible to extract pentosans and pentoses with water and to separate them from a solid residue, this unit being connected to a unit C for converting pentoses to furfural, which unit is connected to a unit D for purifying the furfural leaving the unit C. The process and the installation of this invention make possible the combined production, with a high yield, of furfural and of cellulose food for cattle (livestock).

Description

 The main subject of the present invention is a process for treating plant materials of the lignocellulosic type, in particular for producing furfural.

 It also relates to an installation for the implementation of this process.

 We already know steam-cracking units of various plant materials such as wood, stalks and stalks of corn, bagasse and others - these units allowing the in situ production of furfural. However, this type of unit provides a yield of furfural product which remains relatively low.

 On the other hand, we know steam-cracking units of vegetable materials to make a pulp or pulp containing materials such as for example cellulose and pentosans, these materials allowing for example to make paper or food for the livestock.

 However, these units do not produce furfuraldehyde or produce very few.

 It has therefore become essential to propose a method and an installation which are capable of efficiently producing a combined material of furfural and cellulosic feeds for livestock, since no installation known today allows this purpose to be achieved.

 The object of the present invention is to fill this gap by proposing a process and an installation for processing plant materials which allow the combined production of furfural and animal feed with quite remarkable efficiency, yield and reliability.

 To this end, the subject of the invention is a process for the treatment of lignocellulosic plant materials in order to produce in particular furfural and of the type consisting in subjecting the plant materials to a steam-cracking ensuring in particular the digestion of these materials in order to obtain in particular a paste containing insoluble materials such as cellulose and lignin and soluble materials such as pentosanes and pentoses, characterized in that the materials leaving the steam cracking are washed with water to extract the pentosanes and pentoses, this washing being carried out after introduction of an acid into these materials in order to increase the solubility of the pentosans and pentoses, which are subsequently treated to produce furfural, while the residue of the washed insoluble materials is separated to constitute a nutritious food for the cattle.

 According to another characteristic of this process, the liquid containing the extracts of pentosans and pentoses is heated, and, in this liquid, a supplement of acid acting as catalyst for the transformation is introduced before and / or after heating thereof. pentosans in pentoses and pentoses in furfural, and the liquid thus obtained is introduced into a reaction chamber with several stages, at least one stage of which receives additional acid and all the stages of which are subjected to stripping by steam to entrain furfural gas in the enclosure as the pentoses are transformed into furfural, which furfural in vapor phase is then condensed.

 It will also be specified here that the heating of the liquid containing the extracts of pentosans and pentoses is carried out by heat exchange with the liquid effluents leaving the abovementioned reaction enclosure, for a time less than or equal to 10 seconds.

 According to yet another characteristic of this process, the introduction of the abovementioned acid consists in adding phosphoric or acetic acid according to approximately 0.5 to 5% by weight of the dry equivalent of the vapor-cracking materials. matter coming out of the steam cracking.

 It will also be specified here that the separation of the residue from the insoluble matter washed is carried out by filtration or other suitable means at a temperature of between approximately 300C and 800C.

 As for the above-mentioned acid supplement, it consists of sulfuric, phosphoric, nitric or hydrochloric acid at an acid concentration of between approximately 0.05 and 0.8 N.

 According to yet another characteristic of this process, the liquid containing the extracts of pentosans and pentoses is heated to a temperature of between approximately 150 and 2100C after having been compressed to a pressure of between approximately 10 and 25 bar absolute.

 It will also be specified here that the liquid in the reaction chamber remains there for a time of between 1 and 10 minutes and is heated by the entrainment steam to a temperature between about 170 and 230 C.

 The invention also relates to an installation for implementing the method meeting one or the other of the above characteristics, this installation being of the type comprising a steam cracking unit for thermo-mechanically separating materials insoluble such as lignin and cellulose, and soluble materials such as pentosanes and pentoses, and is characterized in that it successively comprises, downstream of said unit, an acid injection station in the materials leaving the steam cracking , a unit allowing the extraction by water of pentosanes and pentoses and their separation from a solid residue, this unit being connected to a reaction chamber with at least one stage ensuring the transformation of pentosanes into pentoses and pentoses into furfural , which unit is connected to a furfural condensation system.

 According to another characteristic of this installation, at least one acid injection pipe is provided to at least one stage of the reaction chamber, and at least one acid injection pipe in the pipe for conveying the liquid from the aforementioned extraction-separation unit, the latter leads to the level of the first stage of the reaction chamber.

 The installation of this invention is further characterized by a heat exchanger through which the flow of liquid leaving the reaction chamber and through the liquid from the extraction-separation unit of pentosans and pentoses.

 The installation of the invention is further characterized by a condenser traversed by the flow of furfural in the gas phase leaving the reaction chamber, by at least one furfural subcooling device, and by an associated heat recovery system. to the condenser and to the aforementioned sub-cooling apparatus.

However, other characteristics and advantages of the invention will appear better in the detailed description which follows and refers to the appended drawings, given solely by way of example, and in which:
FIG. 1 is a block diagram illustrating the main units of an installation in accordance with the principles of the invention, and
- Figure 2 is a schematic view illustrating in detail one of the units of the installation visible in the figure, and namely the unit ensuring the transformation of pentosans into pentoses and pentoses into furfural.

Referring to FIG. 1, it can be seen that an installation conforming to the principles of the installation essentially comprises a unit A of steam cracking, a unit B for extracting pentosans and pentoses with water and from which it is separated. a residue intended to constitute a nutrient for livestock, a unit
C for converting pentosans into pentoses and pentoses into furfural (this unit C being shown in detail in FIG. 2), and a unit D for purifying furfural by distillation.

 In the steam cracking unit A, which is of a type known per se, a vegetable material of agricultural or forestry origin and of the lignocellulosic type, that is to say comprising essentially lignin and cellulose, is introduced via line 1.

 This material is subjected to steam heating at a high temperature of between 160 and 2500C approximately and under a corresponding pressure of between 5 and 40 bars approximately. We have shown in 2 a water vapor supply line to unit A, and in 3 a line ensuring the rejection of steam to the atmosphere.

 The digestion products leaving the steam cracking unit A via line 4 are essentially cellulose, hemicellulose derivatives (pentosanes and pentoses), and lignin, it being understood that the composition obviously depends on the vegetable matter introduced into unit A.

 More precisely, the aforementioned products leaving via line 4 form two categories of products, namely, on the one hand, solid products which cannot be extracted with water (mainly cellulose and lignin), and products which are soluble in water (pentosans and pentoses essentially) which constitute the raw material allowing to manufacture furfural. These products constituting the pulp and forming a paste are sent via line 4 to unit B in particular to extract the pentosans and pentoses therefrom.

 In unit B, the pulp or paste is washed with water introduced through a line 5 to extract the pentosans and pentoses which are soluble products. This extraction is preferably carried out in several stages against the current so as to increase its efficiency, to reduce the consumption of water and to increase in the filtrate the content of pentosans extracted.

 In unit B, the pentosans and the pentoses sent to unit C via a line 6 are separated by filtration from a residue or cake intended to constitute a nutritious feed for livestock, which is evacuated through a line 7.

 A vacuum of about 800 to 200 mm of mercury in unit B is required, depending on the plant material being treated. Filtration is carried out at a temperature between 30 and 800 C, and preferably between 50 and 600 C to promote the extraction of the monomers that are pentoses, and oligomers that are pentosans. It will be emphasized here that unit B advantageously makes it possible simultaneously to obtain a filtrate of pentosans and pentoses which lends itself perfectly to the subsequent manufacture of furfural, and a solid residue forming a nutritious feed for livestock based on lignin and cellulose which has acquired excellent digestibility properties.

 It will be added that upstream of the unit B, an acid is introduced via a line 8 into the line 4 for transporting the pulp or paste leaving the steam-cracking unit A and sent to the unit B.

 This acid can be phosphoric or acetic acid which slightly acidifies the diluted pulp or paste passing through line 4. This acid can represent between 0.5 and 5% by weight of the dry matter, that is to say say the dry equivalent of the material leaving unit A of steam cracking.

 This injection of acid upstream of unit B surprisingly increases the solubility of the pentosans which will subsequently be treated to produce furfural.

 The phosphoric or acetic acid injected downstream of the steam cracking (A) and immediately upstream of the washing (B) acts in the manner of a catalyst for the following hydrolysis reaction (C5H804) n + n H20 H + n C5H1005.

 Other acids, such as for example sulfuric, hydrochloric or nitric acids can be used, but phosphoric or acetic acids have the advantage, at low concentration, of being edible and that is why they will be used as such. , preferred.

 During the washing in unit B, a large part of the acid, up to approximately 75 to 90% of the initial amount, passes into the filtrate 6 which constitutes the feed to the unit C for producing furfural . This acid washing process makes it possible to extract approximately 85 to 95% of the pentosans and pentoses, the amount of pentosans and pentoses being increased by approximately 3 to 5% by virtue of the addition of acid being understood, as explained above, that the acid supply in no way affects the digestibility and the organoleptic qualities of the nutritive matter leaving via line 7 of unit B.

 In unit C which will now be described in detail with reference to FIG. 2, the pentosans will be transformed into pentoses and the pentoses into furfural which will leave unit C via line 9 to be sent to distillation D.

 More specifically, the filtrate 6 is pumped by a pump P at a pressure between about 10 and 25 bars and, after preheating in an exchanger 13 at a temperature between 150 and 2100C, is sent through a pipe 14 at the head of a reaction chamber 15 which, according to an exemplary embodiment, is a column with plates 16.

An additional acid, which can be sulfuric, phosphoric, nitric or hydrochloric acid at an acid concentration of between approximately 0.05 and 0.8
N, is introduced into unit C via a pipe 11. More precisely and as can be seen in FIG. 2, this additional acid is introduced, by means of a pump 17 on the pipe 11 into the enclosure or column 15 by a duct 18 which is preferably divided into a plurality of portions of ducts 18a with valves 19, each opening out above a plate 16 of the enclosure 15.

 We can take a sample of this additional acid to send it to the filtrate passing through line 6, 14 and arriving at the top of the enclosure 15. For this purpose, we can provide a portion of line 20 with valve 20a connecting the acid transport pipe 18 to the pipe 14 located downstream of the exchanger 13 and conveying the filtrate to the column 15. A portion of pipe 21 can also be provided connecting the pipe 18 to the pipe 6 for transporting the filtrate located upstream of the exchanger 13. One and / or the other line 20, 21 can be used in unit C.

 At the bottom of column 15, water vapor is sent through a line 12 and, as can be seen in FIG. 2, the liquid effluents leaving column 15 leave this column through line 22, and undergo an exchange heat, in the exchanger 13, with the filtrate 6 passing through the column 15, to be finally evacuated via the pipe 10.

 At the top of the column or enclosure 15, thanks to continuous steam stripping, furfural in the vapor phase is produced as the pentoses are transformed into furfural, and is evacuated via a line 23.

 It will be noted here that the liquid in the reaction chamber 15 stays there for a time of between 1 and 10 minutes and is heated by the entrainment steam to a temperature between about 170 and 2300C.

 It is important to emphasize that the injection of acid into column 15, the residence time of the liquid in this column and the continuous stripping with steam will advantageously allow a complete hydrolysis reaction of the pentosans to be carried out. in pentoses and to obtain an excellent yield of furfural production leaving at the head of the enclosure 15 via the conduit 23.

The vapors of furfural and water passing through line 23 are condensed in a train of exchangers 24, 25 and 26 to finally produce a final liquid leaving through line 9 to go to the distillation
D, as can be seen in Figures 1 and 2.

 Demineralized and suitably treated water is sent to the unit via line 27. This water is preheated by passage through the exchanger 25, mixed at 28 with condensates recirculated by a pump 29 from a boiler tank 30, and partially vaporized in the exchanger 24. The mixture of steam and condensate leaving via line 31 at a pressure of between approximately 3 and 5 bar absolute, is separated in the balloon 30 to form a vapor phase discharged through the line 32 and a liquid phase sent to the pump 29 via the line 33.

 At the outlet of the exchanger 25, a sub-cooling of the aqueous furfural solution is carried out in the exchanger 26 crossed by a path 34 of cooling water.

 It will be noted here that the quantity of low pressure steam passing through the pipe 32 can represent from 60 to 90% of the high pressure steam used in the enclosure or entrainment column 15.

This constitutes a considerable advantage of the process in that the low pressure steam can be used for example in the unit D for purifying furfural.

 Returning to FIG. 1, it can be seen that the furfural solution 9 leaving unit C which has just been described in detail, is mixed with water vapor condensates rich in furfural which are conveyed by a line 35 connecting unit A in line 9 at point 36. The furfural solution is then routed through line 37 to unit D to be purified. This furfural purification unit is of a type known per se and uses, for example, azeotropic distillation, decantation, vacuum dehydration and then final purification by distillation of furfural.

 The various fluids leaving unit D have been shown diagrammatically in FIG. 1, namely the flow of purified furfural 38, the flow of heavy residues and acid solutions 39, and the flow 40 of light solvents such as methanol and acetone.

 A process and an installation were therefore carried out according to the invention in which the pentosans originating from a steam-cracking unit are first treated by injection of acid and then by washing with water and filtration so as to obtain a nutritious feed for cattle and a pentose filtrate which is subsequently mice to a continuous steam stripping so as to.

produce furfural according to a high yield.

 We therefore understand all the interest represented by such a process and such an installation which allow the combined production of furfural and cellulosic feed for livestock.

 Of course, the invention is in no way limited to the embodiment described and illustrated, which has been given only by way of example.

 Thus, instead of the reaction chamber or column with plates 15, it is perfectly possible to use a series of reactors agitated and connected in series, without thereby departing from the scope of the invention.

 Consequently, the invention includes all the technical equivalents of the means described, as well as their combinations if these are carried out according to the spirit.

Claims (12)

 1. Process for the treatment of lignocellulosic plant materials to produce in particular furfural and of the type consisting in subjecting the plant materials to a steam cracking ensuring in particular the digestion of these materials in order to obtain in particular a pulp or paste containing insoluble materials such as cellulose and lignin and soluble materials such as pentosanes and pentoses, characterized in that the materials leaving the steam cracking are washed with water to extract the pentosanes and pentoses, this washing being carried out after introduction of an acid into these materials in order to increase the solubility of the pentosans which are subsequently treated to produce furfural, while the residue of the washed insoluble materials is separated to constitute a nutritious food for the cattle.  2. Method according to claim 1, characterized in that the liquid containing the extracts of pentosans and pentoses is heated, and in this liquid, an acid supplement acting as catalyst is introduced before and / or after heating thereof. for the transformation of pentosans into pentoses and pentoses into furfural, and the liquid thus obtained is introduced into a reaction enclosure with several stages, at least one stage of which receives additional acid and all the stages of which are subjected to stripping by steam for gas phase entrainment in the enclosure furfural as the pentoses are transformed into furfural, which furfural in vapor phase is then condensed.  3. Method according to claim 2, characterized in that the heating of the liquid containing the extracts of pentosans and pentoses is carried out by heat exchange with the liquid effluents leaving the aforementioned reaction enclosure, for a time less than or equal to 10 seconds.  4. Method according to claim 1, characterized in that the introduction of the abovementioned acid consists in adding phosphoric or acetic acid according to approximately 0.5 to 5% by weight of the substances leaving the steam cracking dry equivalent of the material leaving the steam cracking.  5. Method according to claim 1, characterized in that the separation of the aforementioned residue is carried out by filtration or other suitable means at a temperature between about 300C and 800C.  6. Method according to claim 2, characterized in that the aforementioned additional acid consists of sulfuric, phosphoric, nitric or hydrochloric acid at an acid concentration between about 0.05 and 0.8 N.  7. Method according to claim 2 or 3, characterized in that the liquid containing the extracts of pentosans and pentoses is heated to a temperature between about 150 and 2100C after being compressed to a pressure between 10 and 25 bar absolute.  8. Method according to claim 2, characterized in that the liquid in the reaction chamber remains there for a time between 1 and 10 minutes, and is heated by entrainment steam to a temperature between about 170 and 2300C.  9. Installation for implementing the method according to one of claims 1 to 8, and of the type comprising a steam-cracking unit (A) for thermo-mechanical separation of insoluble materials such as lignin and cellulose, and soluble materials such as pentosans and pentoses, characterized in that it successively comprises downstream of said unit, a station (8) for injecting acid into the materials leaving steam-cracking, a unit (B) allowing the extraction by water of pentosanes and pentoses and their separation from a solid residue, this unit being connected to a reaction chamber (15) with at least one stage ensuring the transformation of pentosanes into pentoses and pentoses into furfural, which unit is connected to a furfural condensation system (24, 25, 26).  10. Installation according to claim 9, characterized by at least one conduit (8) for injecting acid to at least one stage (16) of the reaction chamber (15) and by at least one conduit (20, 21) for injecting acid into the conduit (6, 14) for conveying the liquid coming from the abovementioned extraction-separation unit (B), which conduit (14) opens at the first stage of the reaction chamber (15).  11. Installation according to claim 9 or 10, characterized by a heat exchanger (13) through which the flow of liquid (22) leaving the reaction chamber (15) and by the liquid (6) coming from the extraction-separation unit (B).  12. Installation according to one of claims 9 to 11, characterized by a condenser (24, 25) traversed by the flow of furfural in a gas physic (23) leaving the reaction chamber (15), by at least one device (26) for sub-cooling the furfural, and by a system (27 to 33) for heat recovery associated with the condenser and the aforementioned sub-cooling device.