ITFI20090210A1 - PROCEDURE FOR THE TOTAL AND EFFICIENT CONVERSION OF ARUNDO DONAX TO GIVE FURALDEHYDE, LEVULIN ACID AND LIGNINIC DERIVATIVES - Google Patents

Description

PROCEDURE FOR THE TOTAL AND EFFICIENT CONVERSION OF ARUNDO

DONAX TO GIVE FURALDEHYDE, LEVULINIC ACID AND LIGNIN DERIVATIVES

DESCRIPTION

The present invention refers to a process of efficient and total acid-catalyzed chemical transformation of Arundo donax, a lignocellulosic biomass of high potential, to give with high furfural yields (also known as furaldehyde and indicated below with the acronym FA), levulinic acid (4-oxopentanoic acid) (also indicated below by the acronym LA) and a lignin residue that can be used for various application purposes, as well as under the reaction conditions used to carry out this conversion.

The increase in the cost of oil, its price fluctuations and less and less availability make the need to move from an economy based on fossil energy sources to renewable raw materials, to be used for energy uses and synthesis of chemicals. It is no coincidence that the European Community has established that by December 2020 20% of fuel for transport must come from biomass. The annual production of biomass is in the order of 2 x 10 <11> tons and their composition can be extremely variable. Generally speaking, the average composition of biomass can be indicated as about 35-50% of cellulose, 20-32% of hemicellulose and 15-25% of lignin. The use of biomass for the production of non-food substances has recently been rationalized in the vast concept of biorefinery, that is the integrated process that enhances biomass by transforming it into fuel, energy and chemical products.

The present process of simultaneous conversion of pentosans (contained in the hemicellulose) to give FA and of the hexoses (mainly contained in the cellulose) into levulinic acid, with the subsequent recovery by filtration of the ligninic component (Scheme 1), is placed in this context .

Scheme 1- Acid catalyzed conversion of biomass

The maximum theoretical weight yield in furfural obtainable starting from a pentosan is 72.72%, while the theoretical maximum weight yield in levulinic acid obtainable starting from cellulose is 71.5%. The formation of furfural starting from the raw lignocellulosic biomass involves acid-catalyzed hydrolysis: the polymer chains of the pentoses are hydrolyzed to monomeric pentoses and these are subsequently dehydrated to give FA.

Similarly, levulinic acid is obtained by acid hydrolysis of cellulose: the first reaction stage is represented by the hydration of the condensed cellulose polysaccharide to give the glucose monosaccharide, by hydrolysis of the b- (1-4) glycosidic bonds of the polysaccharides. Subsequently the glucose in a multistage mechanism hydrolyzes to give LA and formic acid.

When the process is not carried out under optimal reaction conditions, alongside these products there is also the formation of unwanted dark, soluble or, more often, solid and sticky by-products, called â € œumineâ €. Their formation, in addition to significantly lowering the yield of the process, creates considerable problems from the plant engineering point of view because they cause considerable fouling and even clogging of the reactor and separators, and furthermore their deposition on the walls makes heat exchange difficult. and therefore the control of the process temperature, a fundamental parameter for maximizing catalytic performances.

The process outlined above is particularly advantageous when the yields in the various products are high and the biomass used as raw material is economically and environmentally sustainable.

In this context, in recent years, in Italy and abroad, the changes imposed by the Community Agricultural Policy have favored the emergence of an idea of agriculture not intended solely for food uses, but also aimed at the production of raw materials. raw materials and industrial auxiliaries as an eco-sustainable alternative to products of chemical origin. Mainly, the research conducted up to now on lignocellulosic crops has been aimed at the use of annual species such as sorghum (Sorghum bicolor M.) and perennials such as miscanthus (Miscanthus x giganteus), common reed (Arundo donax L. ), thistle (Cynara cardunculus L.) and poplar Short Rotation Forestry (Populus deltoides Bart.) for the production of renewable energy through thermochemical or biological conversion processes.

The idea behind the present invention is instead that of enhancing the biomass of common cane (Arundo donax L.), a species chosen for many factors linked to productive, economic and environmental aspects, through the production of high added value by using only catalytic conversion reactions.

According to the taxonomic classification, the common reed belongs to the Poaceae family. It is a species provided with rhizomatous roots from whose buds annually originate new stems that develop up to 5 meters in height and which are largely covered by the leaf sheath that expands into a long and wide leaf plate (alternate leaves, lanceolate and glaucous). On the terminal part of the culm a panicle is formed consisting of spikelets of flowers. The inflorescence is sterile and for this reason the reproduction can take place exclusively by vegetative way from rhizome or from cutting.

The first factor that has oriented the choice of substrate towards the common cane, and which assumes a role of fundamental importance, is the level of yield that characterizes this species, over 35 t ha <-1> of dry matter per year as an average of 15 years of planting, which make its production performances clearly superior to the other species so far proposed for the production of lignocellulosic biomass.

Furthermore, this species is widespread spontaneously in the Mediterranean area and therefore its inclusion in the current agricultural systems would not involve alterations in the balance of the ecosystems involved.

As far as the cultivation technique is concerned, it must be emphasized that the common reed is a perennial species which therefore requires planting operations of the crop, such as working the soil and transplanting the rhizomes, only in the year of planting while, over the years subsequent crop management can be limited to a fertilization intervention before the vegetative restart of the crop and to the collection of the biomass produced at the end of the growing season. The duration of the system can also be up to 15 years. In addition, it cannot be overlooked that this crop has little need for crop inputs: in fact, in environments characterized by good water availability, it can be grown in the absence of irrigation, it does not have high nutritional requirements thus allowing a reduction of contributions of fertilizers, it is very competitive with respect to the infesting flora and therefore the management of weeds can be limited to mechanical interventions in the year of planting and currently there are no pathogenic or harmful insects that attack this species in our environments. which should not resort to the use of pesticides.

This simplified crop management that characterizes the common cane has in turn positive repercussions on the farmer's income, reducing the cultivation costs that the latter will have to bear and on the environment both for the limited use of chemical substances such as fertilizers , herbicides and pesticides that can contribute to safeguarding the agro-ecosystem, improving the living conditions of agricultural operators and general citizens and both for increasing the energy efficiency of the system or the ratio between the outputs and the inputs. Still in relation to the environmental advantages, we must also remember how the reduction of tillage, limited to the year of planting only, can also determine a reduction in the risk of soil erosion, an increase in the carbon content in the soil, a increase in the biological activity of the soil and also an increase in the activity of numerous species, especially mammals and insects that can find a home in the crop and thus favor the maintenance of biodiversity.

It has never been reported in literature, scientific or patent, any process that uses Arundo donax as raw material for obtaining furfural and levulinic acid.

On the other hand, there are very few in the literature processes for the co-production in appreciable yields of FA and LA starting from biomass, as up to now generally biomass rich in hemicellulose (minimum content of pentosans 18-20%) have been used to furfural production alone, while other biomasses, rich in cellulose, were used for the production of levulinic acid, preferably using sulfuric acid as a homogeneous acid catalyst. In the processes proposed so far, the lignin residue does not find any other valorization, other than that of being dried and used as a fuel, generally to produce steam in the plant itself or to be transformed into activated carbon.

There are no synthetic processes for the industrial production of FA. The industrial processes of furfural production are all based on biomass hydrolysis and have recently been commented on in a review (A.S. Mamman et al., Furfural: Hemicellulose / xylose-derived biochemical, Biofuels, Bioprod. Bioref. 2008, 2, 438-454).

The most widely used catalyst is 3-5% by weight sulfuric acid (calculated as weight of acid / weight of biomass solution), working at temperatures of about 170-185 ° C in stirred or continuous batch reactors maintained under pressure with steam. . Furfural yields in industrial processes typically range between 0.06 and 0.1 g FA / gram of dry biomass.

A 1972 US patent mentions the conversion of different types of biomass (sugar cane, rice husk, ear of oats) to give furfural and levulinic acid in the presence of 1.5% by weight sulfuric acid as catalyst : no mention is made of the ligninic fraction or the possible formation of by-products: furfural with a yield of 7.2% by weight and levulinic acid with a yield of 11.65% by weight is obtained from the rice husk.

Recently M. Vazquez (Hydrolysis of sorghum straw using phosphoric acid: evaluation of furfural production, Biores. Tech. 2007, 98, 3053-3060) studied the hydrolysis of sorghum straw in the presence of 6% phosphoric acid: the maximum yield (0.13 g FA / g of dry biomass) was obtained by adopting a reaction temperature of 134 ° C for 300 minutes.

Another biomass widely studied for the production of FA is rice husk, the raw material used in industrial processes currently underway in China: in this case 7% by weight sulfuric acid is the catalyst adopted . Recent work has shown how the engineering of the process and in particular the continuous extraction with supercritical CO2 of the produced AF allows to maximize its yield (W. Sangarunlert et al., Furfural production by acid hydrolysis and supercritical carbon dioxide extraction from rice husk, Korean J. Chem. Eng.

2007, 24, 936-941).

The new SupraYield® process also aims at optimizing process engineering to increase AF yields by improving separation and recovery stages.

As far as levulinic acid is concerned, the most common processes for its synthesis use a dilute mineral acid as catalyst (generally chosen from HCl, H2SO4, HBr or H3PO4) adopting high process temperatures. The raw materials used in this process are monosaccharides such as glucose and fructose, but also sucrose and biomass such as wood or wood processing waste, sawdust, starch, cotton, wheat and rice straw, virgin cellulose, tobacco ribs and other products. of agricultural waste. We will summarize below some of the most interesting results reported in the literature on this process.

A recent patent (W.A. Faraone, J.E. Cuzens, Method for production of levulinic acid and its derivatives (2000) US 6,054,611) reports the use as a raw material of newsprint with a cellulose content of 85%. This material is pre-hydrolyzed with 10% sulfuric acid so as to reach a weight concentration of cellulose of 25.5%, in order to achieve the decrystallization of the cellulose in 1.5 hours at 40 ° C. Subsequently the reaction mixture is heated up to 150 ° C and kept for 8 hours at this temperature. Levulinic acid yields of 10.9% by weight are obtained with respect to the raw material introduced, corresponding to 59.8% of the theoretical maximum yield obtainable calculated on the basis of the cellulosic content. It is evident from these data that the performances claimed in this patent show considerable weaknesses in the long overall reaction times required to achieve low yields, against a very high cellulose content of the starting material, which can hardly be defined as a cellulosic waste.

In 2002 the conversion of sorghum grains (starch content 74%) was reported (Q. Fang, M.A. Hanna, Experimental studies for levulinic acid production from whole kernel grain sorghum, Bioresource Technology 81 (2002) 187-192), in the presence of 8% sulfuric acid, carrying out the reaction at 200 ° C. In this experiment, sulfuric acid proved to be a better catalyst than hydrochloric acid. The maximum yields claimed by the authors are 32.6% by weight with respect to the starting raw material. Also in this case it must be emphasized that the quality of the raw material and the high concentration of acid used affect the economy of the process.

In 2007 a research work was reported (C. Chang, P. Cen, X. Ma, Levulinic acid production from wheat straw Bioresource Technology 98 (2007) 1448-1453) in which wheat straw is used as raw material ground, containing 40.4% cellulose. The optimal conditions identified are the following: initial biomass concentration equal to 6.4% by weight; 3.5% sulfuric acid; reaction temperature 209.3 ° C for 37.6 minutes. Under these conditions the authors claim a yield of 19.8% based on the weight of the raw material, corresponding to 68.8% of the theoretical maximum yield that can be obtained calculated on the basis of the cellulose content.

As regards continuous processes, much less extensively investigated than batches, a patent for the production of levulinic acid in which a reactive extrusion technology is adopted for the first time is worth mentioning (V.M Ghorpade, M.A. Hanna, Method and apparatus for production of levulinic acid via reactive extrusion (1999) US Patent 5,859,263). Starch, water and sulfuric acid are premixed and the resulting slurry is extruded at a temperature between 80-150 ° C using a twin screw extruder. With this type of process, weight yields of up to a maximum of 48% are claimed for wheat starch. The obvious limit of this process, which also gives rise to the formation of uminic by-products while using a precious raw material such as starch, is represented by the need to continuously use an expensive special steel extruder.

The patents on which the Biofine technology is based (S.W. Fitzpatrick Production of levulinic acid from carbohydrate-containing materials US Patent 4,897,497 (1990) and US Patent 5,608,105 (1997)) describe a continuous process starting from raw materials such as waste paper with 80% cellulose content, wood and other lignocellulosic raw materials. The raw material, premixed with 2-7% sulfuric acid, is continuously fed to two reactors placed in cascade. In the first reactor, operating at 210-220 ° C, the carbohydrates undergo a preliminary hydrolysis with a residence time of 12-25 seconds. In this unstirred tubular reactor, raw material depolymerization and pre-hydrolysis of pentoses to furfural and hexoses to 5-hydroxymethylfuraldehyde should occur. The flow leaving this reactor is continuously fed to a second stirred reactor operating at a lower temperature (190-200 ° C) but with a much longer residence time (20 minutes), where the hydrolysis with levulinic acid is completed. The solid by-products are then removed with a filter press and the purified levulinic acid by distillation. The author claims a yield of up to 62% by weight in levulinic acid using as raw material a waste paper containing 80% of cellulose, a raw material with a high cellulosic content that cannot be defined as waste from the process paper mill. Furthermore, the use of two different reactors built in special materials, given the corrosiveness of the reaction environment, certainly makes the management of the process complex and burdensome. The same author also reports the possibility of obtaining both furfural and levulinic acid from hardwood, and in this case the authors claim that the addition of 100 ppm of sodium sulphite to the reaction mixture, containing sulfuric acid at 3.7 % by weight, it should be able to prevent clogging of the reactor by by-products. No explanation is provided for this effect, also because the authors, despite using a biomass containing 13% of ash and 24% of lignin, in this patent do not mention the solid residues or by-products that are certainly present.

Finally, a process has recently been patented (A.M. Raspolli Galletti et al., It. Pat. Appl. CE 2008A000002) in which the conversion of waste biomass, such as tobacco ribs and paper mill waste, was optimized by operating in the presence of hydrochloric acid and inorganic salts. In the conversion of the tobacco ribs, a levulinic acid yield of 60% was reached with respect to the cellulose introduced, or 83.9% of the theoretically obtainable maximum yield. In this patent, only the enhancement of the cellulosic fraction was pursued.

All the processes described so far for the synthesis of FA and LA show the use as catalysts of strong inorganic acids used in the homogeneous phase mainly for the conversion of aqueous solutions or suspensions. However, it must be remembered that various works are also reported in the literature which use, for the conversion of aqueous solutions of xylose, glucose, fructose or sucrose, heterogeneous catalysts such as zeolites or acid ion exchange resins (K. Lourvanij, G.L. Rorrer, Dehydration of Glucose to Organic-Acids in Microporous Pillared Clays Catalyst, Applied Catal. A: General 1994, 109, 147-165; A.S. Dias et al, Modified versions of sulfated zirconia as catalyst for the conversion of xylose to furfural, Cat. Lett. 2007, 114, 151-160). However, this approach is inapplicable when the starting raw material is in turn insoluble in water and also has the considerable limitations associated with the high cost and the easy deactivation, due to thermal phenomena or a dirty surface, of the heterogeneous catalysts. Alternatively, the approach has been proposed of combining a first stage of homogeneous acid hydrolysis of the raw biomass to give xylose or glucose, followed by the dehydration in heterogeneous acid catalysis of the latter carbohydrates. However, this much more complex methodology does not avoid the use of homogeneous acid and still maintains the aforementioned limitations connected with heterogeneous acids.

It is therefore an object of the present invention to provide a simple and efficient catalytic process for the total conversion of biomass to give furfural, levulinic acid and a reactive ligninic residue with high yields, minimizing the formation of by-products, in particular of the uminic type.

A particular object of the present invention is to set up a catalytic process of the aforementioned type without fouling or clogging of the reactor.

In the process according to the present invention arundo donax in aqueous suspension is used as biomass and protic acids or combinations thereof, at high temperatures, are used as conversion catalyst. Protic acids suitable for use in the process according to the present invention are hydrochloric, phosphoric, hydrobromic, formic, acetic and oxalic acids. Preferably low concentration hydrochloric acid is used (1-5% by weight and preferably 1.5-3%).

The conversion of the biomass to furfural is preferably carried out by subjecting the aqueous suspension of the biomass with the addition of acid, to a preheating stage at a temperature between 70 and 180 ° C and preferably between 90 and 160 ° C under nitrogen pressure and / or steam for a time between 15 minutes and 2 hours and preferably between 15 and 60 minutes. This stage allows the conversion of the pentosans present in the hemicellulose to give FA, which is removed from the reaction environment by selective extraction with solvent, or by resorting to other separative techniques such as extraction with supercritical CO2 or distillation in steam current. The process is then continued on the residual acidic aqueous suspension, subjecting it to a subsequent stage of conversion of the cellulosic component to give levulinic acid. This second hydrolysis stage is carried out at a higher temperature, between 150 and 250 ° C, and preferably between 180 and 220 ° C, operating under nitrogen and / or steam pressure for a time between 15 minutes and 2 hours and preferably between 15 and 90 minutes and possibly increasing the acidity of the reaction medium with respect to the previous stage.

The two stages of acid hydrolysis, which lead to FA and LA respectively, can be advantageously carried out in a single reactor or in two sequential reactors.

At the end of the second stage of acid hydrolysis, the solid residue is removed by filtration and characterized by various analytical techniques, including thermogravimetry in a nitrogen and air atmosphere (Mettler TA 4000 equipped with a TG50 / M3 thermobalance) and a Py-GC system / MS (Agilent GC System 6890N Gas Chromatograph with Agilent MS 5973-Network Quadrupole Mass Spectrometry Detector, equipped with a CDS Pyroprobe 5000 pyrolyzer). Thanks to these techniques, in a rapid and quantitative way, it was possible to evaluate the degree of conversion of cellulose and hemicellulose at the temperatures adopted for the catalytic conversion reactions. The Py-GC / MS allows to evaluate the evolution of the lignin fraction at the end of the two stages of catalytic conversion. In particular, the formation of compounds with a lower molecular weight corresponding to the monomer units constituting the lignin has been demonstrated, through the splitting of bonds following the heat treatments undergone by the material. This factor gives the recovered lignin residue a certainly more polar nature as during the conversion reaction the lignin undergoes a sort of depolymerization which leads to the formation of units rich in free phenolic groups. This means that the solid residue of the acid hydrolysis process (containing the ashes present in the biomass and all the lignin in partially depolymerized form) can be advantageously used for numerous application purposes, including the synthesis of polymers such as polyesters and polyurethanes, of composites and as an antioxidant additive.

The process for obtaining FA and LA starting from arundo donax according to the present invention allows, with respect to the known technique, to enhance the hemicellulosic and cellulosic fraction of the biomass itself with a high quantitative yield, providing a simple and efficient approach to the integral enhancement of a highly competitive as the arundo donax. The proposed process also makes it possible to avoid the use of sulfuric acid which causes the precipitation of insoluble sulphates. Of course, the proposed process can also be used to obtain only Fa or only LA by operating at the respective conversion temperatures and discarding unwanted by-products.

Advantageously, the process according to the present invention avoids the formation of solid uminic by-products which would lower yields and make the management of the industrial process much more complex and burdensome.

The process according to the present invention can be carried out both in a stirred batch reactor and in a continuous reactor without the type of process adopted modifying the performances achieved. In any case, the reactor does not present problems of encrustations due to solid uminic or inorganic by-products. The acid catalyst used can be recycled after removal of FA and LA from the reaction environment, thus limiting the consumption of acid and its environmental impact.

The catalytic conversion of biomass can be carried out either by traditional heating or by microwave irradiation of the aqueous suspension. This methodology allows significant energy savings (up to 85 times compared to traditional heating) and significant shortening of reaction times (D. Dallinger et al., Microwave-assisted synthesis in water as solvent, Chem. Rev. 2007, 107, 2563 ) and is particularly interesting, from the point of view of a sustainable process, when operating in an aqueous reaction medium.

The furfural obtained according to the present invention finds vast applications: as an additive for fuels, as a selective solvent also in large-scale petrochemical processes, and as an intermediate for the synthesis of furan derivatives with high added value. In particular, the furfural hydrogenation product, furfuryl alcohol, is the starting raw material for the synthesis of furan biopolymers.

The levulinic acid obtained according to the present invention is useful in numerous applications such as, for example, plasticizer, anti-freeze, solvent, flavoring for food, starting raw material for the production of fine chemicals. In fact, the industrial applications of AL derivatives are extremely numerous.

From the chemical point of view, levulinic acid behaves like any other molecule which has a carboxylic group and a ketone group in its structure.

In the presence of an alcohol and an acid catalyst LA rapidly forms the corresponding ester derivative. These esters, in particular ethyl levulinate, find application as plasticizers, in the perfume industry and, above all, as an oxygenated additive for diesel fuel (E.S. Olson, M. R. Kjelden, A. J. Schlag, R. K. Sharma Levulinate esters from biomass wastes, ACS Symposium Series 2001, 784, 51-63). Levulinic acid esters can also replace kerosene as a fuel for gas turbines.

Gamma-valerolactone, the hydrogenation product of levulinic acid, has recently been proposed as a sustainable additive for fuels and as a more advantageous alternative to bioethanol (I.T. Horváth et al., G-Valerolactone-a sustainable liquid for energy and carbon-based chemicals, Green Chem. 2008, 10, 238-242).

From the foregoing the advantages that the method according to the present invention allows to obtain are evident. The invention will be described in the following by means of the demonstrative examples numbered from 1 to 8 without however being limited to them, but it is understood that the quantities and percentages of the described reagents can be varied, as well as the type of reactors used while remaining within the scope of the present invention.

Example 1

A suspension consisting of 35 ml of water, 1.4 ml of 37% and 2.5 HCl is introduced into a 100 ml autoclave equipped with a thermocouple for reading the internal temperature, magnetic stirring and taps for filling gases. g of pulverized biomass obtained by grinding the stem and leaves of Arundo donax. The autoclave is pressurized with nitrogen and / or steam and introduced into a thermostated oil bath previously brought to the chosen reaction temperature.

The autoclave is kept at 150 ° C for 30 minutes. At the end of the reaction the autoclave is rapidly cooled, discharged and the suspension obtained, filtered and analyzed.

A furfural yield of 9.6% by weight is observed with respect to the introduced dry biomass.

Example 2

The test described in example 1 is repeated in the same way as reported, using 2.5 grams of pulverized Arundo donax as substrate, with the exception that at the end of the reaction the furfural is removed by solvent extraction and the residual aqueous suspension heated for a further 60 minutes at 200 ° C. At the end of the reaction there is no deposition of uminic products. The autoclave is rapidly cooled, discharged and the suspension obtained is filtered and analyzed. The analysis shows a levulinic acid yield of 20.1% by weight with respect to the introduced dry biomass. A solid, easily filterable, containing ash and lignin fraction is also separated by filtration (yield in residual solid 29% by weight with respect to the dry biomass introduced). Upon Py-GC / MS analysis and thermal analysis, this solid appears to contain partially depolymerized lignin rich in free phenolic groups and residual ash, which is about 4% by weight with respect to the dry biomass introduced.

Example 3

The test described in example 2 is repeated using 3.6 grams of pulverized stems of arundo donax as substrate, containing 29.2% of hemicellulose and 36.6% of cellulose, in suspension of 50 ml of water and 2 ml of 37% HCl. At the end of the first conversion stage, the furfural yield is 10.3% by weight with respect to the dry biomass introduced, corresponding to a yield equal to 48.5% of the maximum yield theoretically obtainable from the hemicellulose present in the biomass. After extraction of the furfural, the residual suspension was subjected to the subsequent hydrolysis stage at 200 ° C: a yield in LA of 21.4% by weight is obtained with respect to the dry biomass introduced, or 81.7% of the yield maximum theoretically achievable by cellulose present in biomass. A solid, easily filterable, containing ash (3.7%) and lignin derivatives is also separated by filtration. The yield in this solid product is 27% by weight with respect to the dry biomass introduced.

Example 4

The test described in example 3 is repeated using 3.6 grams of pulverized leaves of arundo donax as substrate, containing 26.03% of hemicellulose and 32.8% of cellulose, in suspension of 50 ml of water and 2 ml of 37% HCl. At the end of the first conversion stage, the furfural yield is 7.3% by weight with respect to the dry biomass introduced, corresponding to a yield equal to 38.5% of the maximum yield theoretically obtainable from the hemicellulose present in the biomass. After extraction of the furfural, the residual suspension was subjected to the subsequent hydrolysis stage at 200 ° C: an LA yield of 15.7% by weight is obtained with respect to the dry biomass introduced, i.e. 66.9% of the theoretically achievable maximum yield. from the cellulose present in the biomass.

Example 5

The test described in example 3 is repeated in the same way as described, using 3.6 grams of pulverized stems of arundo donax as substrate, with the difference that instead of in a traditionally heated autoclave, it is conducted in a reactor microwave (CEM Discover S-class system reactor) stirred magnetically, adopting the reaction temperatures set for the two stages, 150 and 200 ° C, with an irradiation time of 15 minutes for each stage and performing the intermediate extraction of the furaldehyde formed. At the end of the first stage of catalytic conversion, the yield in isolated furfural is 10.6% by weight with respect to the dry biomass introduced, corresponding to a yield equal to 50% of the maximum yield theoretically obtainable from the hemicellulose present in the biomass. At the end of the second stage of catalytic conversion, the yield in levulinic acid is 24.6% by weight with respect to the dry biomass introduced, corresponding to a yield equal to 94% of the maximum yield theoretically obtainable from the cellulose present in the biomass. A solid, easily filterable product containing ashes and lignin derivatives is also separated by filtration. The yield in this solid product is 26.3% by weight with respect to the dry biomass introduced.

Example 6

The test described in example 5 was replicated under completely identical reaction conditions, except for the fact that this time a temperature of 190 ° C is adopted for the second irradiation stage. The furfural yield obviously remains identical to that claimed in example 5 (10.6% by weight), while the yield in levulinic acid is 21.9% by weight with respect to the dry biomass introduced. The residual lignin solid product yield is 27.2% by weight with respect to the introduced dry biomass.

Example 7

The test described in example 5 was replicated under completely identical reaction conditions, except for the fact that this time 2.5 g of pulverized biomass obtained from the grinding of stem and leaves of Arundo donax were used as substrate. There is a furfural yield of 9.9% and a levulinic acid yield of 20.5% by weight with respect to the introduced dry biomass. The residual lignin solid product yield is 29.2% by weight with respect to the introduced dry biomass.

Example 8

The test described in example 7 was replicated under completely identical reaction conditions, except that this time 0.8 ml of 37% HCl and 0.5 ml of 85% H3PO4 were used as catalyst. There is a furfural yield of 10% and a levulinic acid yield of 20.7% by weight with respect to the introduced dry biomass. The residual lignin solid product yield is 30% by weight with respect to the introduced dry biomass.

Claims (12)

CLAIMS 1. Process for the catalytic conversion of biomass to give furfural, levulinic acid and a reactive ligninic residue characterized by the fact that arundo donax in aqueous suspension is used as biomass and a protic acid or a combination of high temperature protic acids as catalyst. 2. Process according to claim 1, characterized in that the catalytic conversion of the biomass is carried out in two stages: a first stage in which the suspension is heated to 70-180 ° C to produce furfural, which is separated by chemical means or physical, and a second stage in which the suspension is further heated to 150-250 ° C to produce levulinic acid which is separated from the solid lignin residue by filtration. 3. Process according to claim 2, wherein the first step of converting the biomass to furfural is carried out at a temperature between 90 and 160 ° C under nitrogen and / or steam pressure for a time between 15 minutes and 2 hours and preferably between 15 and 60 minutes. 4. Process according to claim 2, in which the second stage of converting the biomass to levulinic acid is carried out at a temperature between 180 and 220 ° C, operating under nitrogen and / or steam pressure for a time between 15 minutes and 2 hours and preferably between 15 and 90 minutes. Process according to any one of the preceding claims, in which the arundo donax biomass is used as such or stems and leaves of arundo donax are used separately. 6. Process according to any one of the preceding claims, wherein said protic acid is selected from hydrochloric, phosphoric, hydrobromic, formic, acetic, oxalic acid and their combinations. 7. Process according to any one of the preceding claims, wherein said protic acid is hydrochloric acid. 8. Process according to any one of the preceding claims, in which the acid is used in a concentration between 1 and 7% by weight and preferably between 1.5 and 3%. 9. Process according to any one of the preceding claims, wherein the biomass concentration in the aqueous suspension is preferably comprised between 5 and 35% by weight. 10. Process according to any one of the preceding claims, wherein the conversion reaction is carried out in a stirred batch reactor. 11. Process according to any one of claims 1 to 9, wherein the conversion reaction is carried out in a continuous reactor. Process according to any one of the preceding claims, wherein the heating of the aqueous suspension of biomass is obtained by microwave irradiation.