EP3155114A1

EP3155114A1 - Method and plant for the conversion of mainly cellulosic material

Info

Publication number: EP3155114A1
Application number: EP15732434.4A
Authority: EP
Inventors: Cristian TORRI
Original assignee: Giacomelli Claudio; Universita di Bologna
Current assignee: Giacomelli Claudio; Universita di Bologna
Priority date: 2014-06-11
Filing date: 2015-06-10
Publication date: 2017-04-19
Also published as: WO2015189775A1

Abstract

A method for conversion of mainly cellulosic material, comprising the steps of predisposing a quantity (1) of mainly cellulosic material, predisposing an anaerobic bacterial population (2), predisposing a mixed aerobic bacterial population (3), decomposition of the quantity (1) of mainly cellulosic material into a liquid fraction (1a), a gaseous fraction (1b) and a solid fraction (1c) with a predetermined thermochemical treatment, fermentation of the liquid fraction (1a) and gaseous fraction (1b) inside a fermenter (12) by inoculating the anaerobic bacterial population (2) in the liquid fraction (1a) and gaseous fraction (1b), so as to produce a solution (VFA) containing volatile fatty acids, aerobic digestion of a first portion (VFA_a) of the solution (VFA) by action of the mixed aerobic bacterial population (3) for the production of an enriched bacterial population (4) producing polyhydroxyalkanoates, aerobic digestion of a second portion (VFA_b) of the solution (VFA) performed through an action of the enriched bacterial population (4) for obtaining products (5) rich in polyhydroxyalkanoates and separation of the products (5) into a usable fraction (5a') mainly composed of polyhydroxyalkanoates (PHA), and a residual fraction (5b, 5a"), at least partly composed of a cellular residue (5a").

Description

DESCRIPTION

METHOD AND PLANT FOR THE CONVERSION OF MAINLY CELLULOSIC MATERIAL.

Technical field

This invention relates to a method and a plant for the conversion of mainly cellulosic material.

This invention is thus applied in particular in the chain of recycling, and in particular in the exploiting of the waste of the printing or offset printing industry.

Background art

The prior art includes some methods allowing recovery of cellulosic waste and transforming it in substances of wide consumption and use, such as for example methane gas, other types of fuels or in recycled paper.

For example: US publication US2012/0073199 described a bio-treatment able to transform wood-cellulosic materials into methane or ethanol.

The process described therein consists of a succession of steps, which consists mainly in a first step of pyrolysis at low temperature and of long duration {Long Time-Low Temperature) followed by an anaerobic bio- treatment of digestion, or of fermentation with low oxygen content.

This document, centring mainly on the treatment of the wood, in particular stresses the need to limit the temperature of the pyrolysis to a range of between 175° C and 325° C so as to obviate the problems connected to toxicity, in anaerobic digestion, of the products of pyrolysis obtained at high temperature (>350° C), and therefore to the poor convertibility thereof obtained at high temperatures.

Downstream of the pyrolysis, the process illustrated in US2012/0073199 comprises inlet of the pyrolysis liquids (and preferably also of the pyro- gas) in an anaerobic fermenter, for obtaining ethanol, or in an anaerobic digester, for obtaining biogas (methane).

The described process can disadvantageously develop only a portion of the methane potential of the material, which makes it relatively not easily applicable and economically disadvantageous.

Moreover, the low value of the biogas, of the methane or the ethanol, fuels obtainable starting from an enormous quantity of materials and waste, makes it more difficult for the manufacturer to enter a market that, apart from being already saturated, offers considerable competition.

Further, the residence times necessary for methanogenesis and the dilutions required to reduce the toxicity of the products of pyrolysis towards the methanogenic microbic communities determine a need for large reaction volumes which increase the cost of the digestion system. Aim of the invention

An aim of the present invention is therefore to provide a method and a plant for the conversion of mainly cellulosic material, or for waste from the industry of the paper/offset printing, able to overcome the drawbacks of the prior art.

In particular, the aim of this invention is to provide a method and a plant for the conversion of mainly cellulosic material that is rapid and efficient. Further, an aim of this invention is to provide a method and a plant for the conversion of mainly cellulosic material able to produce bioplastic.

The aims are achieved by a method for the conversion of mainly cellulosic material according to or more of the claims from 1 to 13 and by a plant for the conversion of mainly cellulosic material according to or more of claims from 14 to 25.

In specifically, the aims are achieved by a method comprising steps of:

- predisposing a quantity of mainly cellulosic material;

- predisposing an anaerobic bacterial population;

- predisposing a mixed aerobic bacterial population; - decomposition of said quantity of mainly cellulosic material into a liquid fraction, a gaseous fraction and a solid fraction by means of a predetermined thermochemical treatment;

- fermentation of at least said liquid fraction and gaseous fraction inside a fermenter, by inoculating said anaerobic bacterial population in the liquid fraction and gaseous fraction, in order to produce a solution containing volatile fatty acids (beyond to other products of fermentation);

- aerobic digestion of a first portion of said solution by means of the action of said mixed aerobic bacterial population for producing a bacterial population enriched with polyhydroxyalkanoates;

- aerobic digestion of a second portion of said solution by means of the action of said enriched bacterial population for obtaining products rich in polyhydroxyalkanoates;

- separation of said products in a fraction useful, defined mainly by polyhydroxyalkanoates, and a residual fraction, defined mainly by a cellular residue.

Advantageously, in this way is possible to treat the waste of offset printing and transform it, by a continuous process (or substantially continuous) into bioplastic, by means of at least three macro-steps, as follow:

- thermochemical treatment at high temperature (and therefore rapid);

- digestion/anaerobic fermentation;

- aerobic reaction for accumulation of polyhydroxyalkanoates.

This method is preferably actuated by a plant, also according to this invention, comprising:

- heating means provided with at least a chamber and designed to superheat the material contained in said chamber so as to break it down into a liquid fraction, a gaseous fraction and a solid fraction; said chamber being provided with at least an infeed, for allowing entry of a predetermined quantity of mainly cellulosic material, and at least an outfeed, for allowing said liquid fraction and said gaseous fraction to exit the chamber; - an anaerobic digester or fermenter operatively positioned downstream of said heating means, set up to receive said liquid fraction and gaseous fraction and designed to convert the fractions into a solution containing volatile fatty acids by means of the action of an anaerobic bacterial population;

- a first aerobic reactor, operatively positioned downstream of said anaerobic digester, set up to receive a first portion of said solution and designed to convert it, by means of the action of a mixed aerobic bacterial population, into a bacterial population enriched with polyhydroxyalkanoates;

- a second aerobic reactor provided with at least a first infeed and a second infeed respectively predisposed to receive a second portion of solution from said anaerobic digester and the enriched bacterial population from said first aerobic reactor; said second aerobic reactor being configured so as to make said second portion of the solution react with said enriched bacterial population for obtaining products rich in polyhydroxyalkanoates;

- separating means located operatively downstream of said second aerobic reactor and configured so as to split said products into a useful fraction, defined mainly by polyhydroxyalkanoates, and a residual fraction, defined mainly by a cellular residue.

Brief description of the drawings

These and further features and advantages of the present invention will become more apparent from the non-limiting description which follows of a preferred, non-limiting embodiment of a method and a plant for converting mainly cellulosic material as illustrated in the accompanying drawings, in which:

- figure 1 schematically illustrates a plant for the conversion of mainly cellulosic material according to the invention, in a first embodiment thereof; - figure 2 schematically illustrates a plant for the conversion of mainly cellulosic material according to the invention, in a second embodiment thereof;

- figure 3 schematically illustrates a plant for the conversion of mainly cellulosic material according to the invention, in a third embodiment thereof;

- figure 4 is a detail of figure 3.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, reference numeral 100 denotes a plant for recycling of mainly cellulosic material according to the invention, which plant 100 is preferably designed for implementing the conversion method of mainly cellulosic material, also described in the following and object of the present invention.

Note that the expression "mainly cellulosic material" is intended to define those materials wherein the percentage of lignin is very much lower than that of the cellulose, such as for example paper or cardboard.

Although wood is also to be considered a mainly cellulosic material (it is composed of cellulose up to approximately 40-50%), it has a high lignin content (25-30%), which makes not ideally suitable for the treatment using the method and plant according to the present invention.

In other words, the expression "mainly cellulosic material" will hereinafter be used, preferably, for those materials having a cellulosic content of above 40% and a lignin content of less than 20% (more preferably less than 15%, such as for example waste in the printing or offset printing industry.

More precisely, the expression "mainly cellulosic material" is used in this text to define a material with high cellulosic content (greater than 40%) and a carbon/nitrogen ratio of greater than 50 (C/N>50).

The method according to the present invention thus entails predisposing a predetermined quantity 1 of mainly cellulosic material to be treated. This quantity may be defined and discrete, or fed continuously to the plant 100.

In quantitative terms, the flow rate of mainly cellulosic material is preferably between 3000 and 5000 tonnes/year, more preferably approximately 4000 tonnes/year.

Also contemplated is the preparation of at least an anaerobic bacterial population 2 and at least a mixed aerobic bacterial population 3, which are used for the treatment of the mainly cellulosic material using the method according to the invention, which is described fully and in detail in the following.

Operatively, the method according to this invention comprises subjecting the quantity 1 of material to a succession of steps consisting mainly of a thermochemical treatment, followed by a fermentation or anaerobic digestion and by an aerobic digestion so as to obtain a production of polyhydroxyalkanoates (PHA), or of bioplastic.

More precisely, the method comprises a first step of decomposition of the quantity 1 of mainly cellulosic material into a liquid fraction 1 a, a gaseous fraction 1 b and a solid fraction 1 c.

The liquid fraction 1 a is defined as bio-oil (or tar); the gaseous fraction 1 b is known as syngas and the solid fraction is known as b o-char.

In particular, the liquid fraction 1 a comprises substances such as for example acetic aid, propionic acid, hydroxy acetaldehyde, hydroxy acetic acid, oligosaccharides, methanol, phenols.

The gaseous fraction 1 b on the other hand comprises portions of methane, carbon monoxide, carbon dioxide, hydrogen and other gaseous substances.

The solid portion 1 c is instead mainly defined by a carbon-rich residue (char) with a certain ash content.

This decomposition is performed using a predetermined thermochemical treatment. In other words, the step of decomposition is defined by a overheating of the quantity 1 of mainly cellulosic material performed to a preset temperature for a predetermined interval of time.

The thermochemical treatment is preferably carried out by superheating the quantity 1 of mainly cellulosic material in a high temperature environment, between 350 and 800 °C, preferably between 400° and 500°C.

Note that the above-mentioned thermochemical treatment is preferably defined by one of the following processes:

- pyrolysis;

- gasification;

- hydro-thermal liquefaction;

- thermal treatment at pressure.

In the first listed actuation, the pyrolysis is performed at high temperature and with a brief duration. In this embodiment, the liquid fraction 1 a is defined as pyrolysis oil (or tar); the gaseous fraction 1 b is known as syngas and the solid fraction is known as b o-char.

More precisely, the pyrolysis is performed by superheating the quantity 1 of material to a temperature of between 400° C and 550° C, preferably using the action of a current of inert gas (nitrogen, carbon dioxide or super-heated water vapour).

In this way it is advantageously possible to obtain the decomposition of the quantity in short times suited to a continuous process, facilitating also obtaining of bio-char.

In the embodiment which comprises performing a gasification, this treatment is performed at a temperature of between 650° C and 800° C and in the presence of a reactive gas (carbon dioxide, super-heated water vapour, oxygen or air in reduced quantity relative to the stoichiometry of combustion).

This process advantageously enables reducing the energetic requirements, and reducing the production of char, increasing the efficiency of the process. In the embodiment that comprises a hydrothermal liquefaction, on the other hand, this treatment is performed at a temperature of between 250° C and 400° C.

Advantageously, the hydrothermal liquefaction does not comprise the passage of state (volatilization) of the products, and may thus be performed on a moist or watery substrate (having a water content of up to

95% in weight) with acceptable costs consumption.

Structurally, with the aim of performing this step of decomposition, the plant 100 is equipped with heating means 1 1 provided with at least a chamber 16 for containing the quantity 1 of material to be broken down.

The heating means 1 1 are thus configured for superheating the material 1 contained in the chamber 16 with the aim of decomposing it into the liquid fraction 1 a, the gaseous fraction 1 b and the solid fraction 1 c.

In this regard, the chamber 16 is thus provided with at least an inlet 16a, designed to allow access of the predetermined quantity 1 of mainly cellulosic material, and of at least an outlet 16b, designed to allow the release of the liquid fraction 1 a and the gaseous fraction 1 b.

The chamber 16 preferably also comprises a second outlet 16c designed to enable exit of the solid fraction 1 c.

In the preferred embodiments, the heating means 1 1 preferably comprise a pyrolyser 29 or a gasifier.

The pyrolyser 29 is preferably configured for superheating the chamber 16 (by action of an inert gas, previously super-heated, or using another carrier) to a temperature of between 350° C and 800° C, preferably between 400° C and 600° C, even more preferably between 400° C and

500°C.

In the embodiment equipped with a gasifier (not illustrated): the gasifier is configured so as to perform the decomposition of the quantity 1 of material at high temperatures, higher than 650° C, in the presence of a gasifying action (carbon dioxide, water vapour, oxygen or air in sub-stoichiometric quantities). At the end of the decomposition step, the quantity 1 of mainly cellulosic material is broken down into three distinct fractions 1 a, 1 b, 1 c.

According to the invention, at least the liquid fraction 1 a and gaseous fraction 1 b are then subjected to a fermentation inside a fermenter (or digester) 12.

This fermentation is performed by introduction of the liquid fraction 1 a and gaseous fraction 1 b into an anaerobic environment (at very low or zero quantity of oxygen) and inoculated with an anaerobic bacterial population 2.

Therefore, the plant 100 comprises an anaerobic digester 12 or fermenter operatively positioned downstream of the heating means 1 1 , predisposed for receiving the liquid fraction 1 a and gaseous fraction 1 b. Consequently, the anaerobic digester 12 has an inlet 12a in fluid connection with the first outlet 16b of the chamber 16.

The anaerobic digester 12 is configured for converting the liquid fraction 1 a and gaseous fraction 1 b into the VFA solution containing volatile fatty acids by the action of an anaerobic bacterial population 2.

More precisely, the anaerobic bacterial population 2 is designed, in anaerobic conditions, such as to convert the liquid fraction 1 a and gaseous fraction 1 b into a VFA solution containing volatile fatty acids.

The expression "volatile fatty acids" is taken to define those acids having a carbon-rich skeleton with a number of less than six.

These acids are for example acetic acid, propionic acid and butyric acid. Therefore the VFA solution obtained with the fermentation step defines a substrate rich in these acids.

The anaerobic bacterial population 2 is preferably accumulated in a specific medium and is defined by the capacity thereof of converting the pyrolysis gas (gaseous fraction 1 b) and the pyrolysis liquid (liquid fraction 1 a) in a solution 4 enriched with volatile fatty acids (VFA).

Preferably, in order to speed up the conversion of the gaseous fraction 1 b and of the liquid fraction 1 a into VFA solution, the digester 12 is added to by a predetermined quantity of solid fraction 1 c (or of vegetable carbon otherwise obtained).

Therefore, and preferably, the anaerobic digester 12 is in connection (functional and structural) with the second outlet 16c of the chamber 16. In the preferred embodiment (as well as illustrated), the method also comprises a mixing step performed operatively upstream of the fermentation step, wherein the gaseous fraction 1 b is struck by a nebulized portion 2a of the anaerobic bacterial population 2.

The mixing also preferably occurs by Venturi effect.

To enable mixing, the plant 100 preferably comprises an absorption column 17 operatively interposed between the heating means 1 1 and the anaerobic digester 12.

It should be noted that the nebulized portion 2a is aspirated from the digester 12 by special means.

Therefore, the absorption column 17 is equipped with suction means 17a

(e.g. a hydraulic pump) for aspirating a portion 2a of the anaerobic bacterial population 2 from the anaerobic digester 12, striking at least the portion gaseous fraction 1 b with this nebulized portion 2a.

Advantageously, in this way the exchange between the gaseous fraction 1 b, in outlet from the heating means 1 1 , and the anaerobic bacterial population 2 is increased.

This also enables speeding up the action of the subsequent anaerobic digester 12, allowing a continuous operation of the plant (that is, a continuous carrying out of the method).

The absorption column 17 preferably comprises at least a Venturi tube 17b

(i.e. a "choked" or tapered tube) in which the gaseous fraction 1 b and the portion 2a of anaerobic bacterial population 2 are mixed (specially nebulised).

In other words, in the preferred embodiment, the absorption column 17 is defined by a Venturi Scrubber. Therefore, the absorption column comprises the Venturi tube 17b, into which the gaseous fraction 1 b and the nebulized portion 2a of the anaerobic bacterial population 2 are introduced, and a filling column (not illustrated), in which the gaseous fraction 1 b, when rising along the column, is freed from a liquid part, which goes to mix with the liquid fraction 1 a in inlet to the anaerobic digester 12.

In other words, the gaseous fraction 1 b is introduced together with the nebulized portion 2a through the Venturi tube 17b; in proximity of the choke in the pipe 17b there is a reduction in cross-section of the pipe and therefore an increase of the speed through it; this increase of the speed generates load losses in the flow, which generate turbulences that are aimed at facilitating the absorption action of the nebulized portion 2a.

The anaerobic digester 12 thus provides, at a relative outlet 12b, the VFA solution containing volatile fatty acids, defining a substrate for the subsequent steps of the method.

In a preferred embodiment, the presence of a device selector 32 is provided operatively downstream of the digester 12, which selector 32 is configured for decomposing the VFA solution in such a way as to separate the compounds of interest (the volatile fatty acids VFA proper) from other compounds of the solution, such as for example anhydro sugars, sugars, phenols or primary products of cellulose pyrolysis.

This device is preferably a pertraction device 32a.

Thus, preferably this device comprises a first 33 and a successive second stage 34.

In the first stage 33, the VFA solution is mixed with a non-water-soluble dilutant (biodiesel, diesel oil, vegetable oil) and a non-soluble amine.

The presence of the amine is such that the VFAs separate from the other compounds, solubilising in the non-water-soluble dilutant.

This step is preferably, performed in a CSTR reactor 33a in order to maximise the effect. Following this step, and still in the first step 33, a sedimenter 33b is located where the aqueous phase (containing anhydro sugars, sugars and phenols), is separated from the non-water-soluble dilutant (containing the salt formed by amine and the VFAs)

At this point, the aqueous phase is reintroduced upstream of the digester 12 and the mixture formed by the non-hydrosoluble dilutant, amine and VFA enters the second stage 34.

The second step 34 has two inlets, one for the mixture and the other for receiving a strongly alkaline liquid solution 5b (preferably with PH>=9). It should be noted that, similarly to the preceding stage 33, the second stage 34 also includes a CSTR reactor 34a for maximising the efficiency of the reaction.

In the second step 34, the alkalinity of the liquid solution 5b is such that the VFA acids separate from the oil and combine with the liquid solution 5b.

Therefore, in outlet from the second step 34 (preferably passing through a further sedimenter 34b) the non-hydrosoluble dilutant and amine mixture in the original form is re-obtained, at the same time producing a watery solution containing VFA acids and moderately alkaline.

Note that the mixture of non-water-soluble dilutant and amine is then sent back to the first step 33 so as to newly react with further VFA solution in arrival from the digester 12.

In this way it is advantageously possible to separate the fermentation products of interest from the reagents in continuous mode, enabling the conversion of substances with different degradation times (e.g. sugars and phenols) thus maximizing the efficiency of conversion.

This device enables in effect retaining the anhydro sugars generated from the pyrolysis of the paper (which are deleterious for conversion) and transfer the acidic compounds generated by the conversion (VFA). Therefore, the step implemented by the device 32 is a step of pertraction, performed in two stages of mixing, sedimentation and successive separation (as already described in the foregoing).

For descriptive simplicity, in the following the VFA solution will be termed in the same way both in a case where it has crossed the selector device 32 and in embodiments where the device is not present.

Following the step of fermentation and, where included, following the pertraction, the method comprises dividing the VFA solution into a first portion (VFA_a) and a second portion (VFA_b).

In a first embodiment (figure 1 ), this sub-division occurs downstream of the digester 12, which therefore has single outlet 12b.

In a second embodiment (figure 2), the division occurs internally of the digester 12, which therefore has an outlet 12b and a further outlet 12c. The flow of volatile acids dissolved in the first portion (VFA_a) is preferably comprised between 100 and 140 kg/h, more preferably about 120 kg/h. Similarly, the flow rate of acids volatile dissolved in the second portion (VFA_b) is between 120 and 170 kg/h, more preferably approximately 150 kg/h.

The first portion (VFA_a) is subjected to a respective step of aerobic digestion, performed by the action of a mixed aerobic bacterial population 3, with the aim of producing an enriched bacterial population 4 of polyhydroxyalkanoates (PHA).

The mixed aerobic bacterial population 3 is preferably accumulated in a specific terrain and is defined by a set of aerobic micro-organisms able to convert the VFA solution obtained starting from the fermentation of the liquid fraction 1 a and gaseous fraction 1 b.

In particular, the mixed anaerobic bacterial population 3 comprise mixed bacterial cultures, for example bacteria of the following phyla: Proteobacteria, Bacteroidetes, Firmucutes and Actinobacteria.

Note that the expression "polyhydroxyalkanoate-enriched bacterial population" is used to define, with no distinction: - a bacterial colony having a high polyhydroxyalkanoate content, or

- a bacterial culture containing a quantity, even a small quantity, of polyhydroxyalkanoates (PHA) but able to synthesise them in a subsequent accumulating step of (i.e. in a further step of aerobic reaction).

In other words, the enriched bacterial population 4 comprises a plurality of micro-organisms suitable for production polyhydroxyalkanoates (PHA). Structurally, therefore, the plant 100 comprises at least a first aerobic reactor 13, operatively located downstream of the anaerobic digester 12 (associated to the outlet 12b).

This first aerobic reactor 13 is predisposed to receive the first portion

(VFA_a) of the VFA solution and is configured to convert it, by the action of the mixed aerobic bacterial population 3, into the enriched bacterial population 4 of polyhydroxyalkanoates.

The enriched bacterial population 4, in outlet from the first aerobic digester 13, is preferably composed of a moist part (sludge) and a dry part.

From the point of view of quantity, the moist part has a flow rate of between 0.5 and 1 .5 m³/h, preferably approximately 1 m³/h.

The dry part, on the other hand, has a flow rate of between 40 and 60 kg/h, preferably approximately 50 kg/h.

In the preferred embodiment, the aerobic reaction for obtaining the enriched bacterial population 4 is made according to the feast & famine principle.

In other words, the obtaining of this enriched bacterial population 4 is achieved by a precise separation into two sub-steps, temporal or spatial, of the step of aerobic digestion of the first portion (VFA_a), and in particular into:

- a first step (temporal or spatial) of supplying the substrate (the substrate of the first portion (VFA_a) inoculated with the mixed aerobic bacterial population 3; - a second step (temporal or spatial) wherein the substrate supplied in the first undergoes the bacterial action without addition of further substrate. Thus, the plant 100 can be realised in at least two substantially equivalent embodiments, one with "time separation" and the other with "spatial separation", which differ simply for the fact that the second step in one case is temporally distinct with respect to the first and in the other is spatially distinct in relation to the first.

Consequently, in the "temporal separation" embodiment, the step of aerobic digestion of the first portion (VFA_a) of the VFA solution is sub- divided into:

- a first period, (corresponding to the first step) with a predetermined duration, in which the first portion (VFA_a) of the VFA solution is introduced into an aerobic digester 13 containing the mixed aerobic bacterial population 3;

- a second period, (corresponding to the second step) with a duration that is at least double that of the first period, in which the supply of the VFA solution to the aerobic digester 13 is stopped, in order to promote the accumulation of polyhydroxyalkanoates (PHA).

It should be noted that to facilitate the substantial continuity of the process, the first and the second periods are repeated cyclically in succession.

In this embodiment, the first aerobic reactor 13 preferably comprises at least a continuous flow stirred-tank reactor (CSTR) 27.

This reactor is constituted by a tank 27a supplied by a flow of material (VFA solution and mixed aerobic bacterial population 3) and equipped with a stirring system 27b.

This type of reactor advantageously enables an excellent mixing of the substrate, which is therefore homogeneous.

In this embodiment, the plant 100 preferably comprises feed means 18 associated with said first aerobic reactor 13 and designed to supply it with said first portion (VFA_a) of the VFA solution intermittently, at predetermined time intervals.

In this regard it should be mentioned that in order to facilitate the coupling between the anaerobic digester 12, operating continuously, and the first aerobic reactor 13, operating intermittently, in this embodiment the plant 100 comprises at least an anaerobic storage tank 19 located downstream of the anaerobic digester 12.

The storage tank 19 is equipped with an inlet 19c connected to the anaerobic digester 12 (that is to the outlet 12b) and at least a first outlet 19a connected to the first aerobic reactor 13. The feed means 18 are therefore associated to this first outlet 19a.

This enables the plant 100 of have at least a buffer that can enable the heating means 1 1 , the anaerobic digester and the first aerobic reactor 13 to be operative independently for at least a transient emergency.

In the "spatial separation" embodiment, this digestion is sub-divided into: - a sub-step of introducing the first portion (VFA_a) of VFA solution into a first aerobic space (13a), having a predetermined size, containing the mixed aerobic bacterial population 3;

- a sub-step of accumulating polyhydroxyalkanoates (PHA) in a second aerobic space 13b, with predetermined size and operatively positioned downstream of said first aerobic space 13a so as to obtain said bacterial population 4 enriched with polyhydroxyalkanoates;

- a sub-step of extracting said bacterial population 4 enriched with polyhydroxyalkanoates from said second aerobic space 13b.

Note that the second space 13b is positioned in succession to the first space 13a.

Advantageously, in this way, the step of aerobic digestion of the first portion (VFA_a) of the VFA solution is also temporally continuous, avoiding the need for introducing storage tanks to interrupt the feeding of substrate to the first reactor 13.

In this embodiment the first aerobic reactor 13 is preferably of the plug- flow type, which comprises at least a piston flow reactor (PFR) 26. In this type of reactor, the biochemical reaction (i.e. the conversion of the first portion (VFAa) of the VFA solution into the enriched bacterial population 4) occurs inside the reactor and the concentration of products increases, and then decreases, with the spatial variable.

Alternatively, the single piston flow reactor (PFR) 26 could be substituted by a plurality of continuous flow stirred-tank reactors (CSTR) located in series.

In both the embodiments described above (temporal separation and spatial separation), the step of aerobic digestion of the first portion (VFA_a) is stabilised by addition of inorganic nutrient products 7.

The expression "inorganic nutrient products" is intended to define one or more of the following substances:

- nitrogen;

- phosphorus;

- ammonia content;

- nitrates;

- nitrites;

- phosphates;

- sulphur

- mineral salts in general;

- metals and other micronutrients in traces.

In this regard, the plant 100 preferably comprises at least a tank 21 (hopper) containing these inorganic nutrient products 7 and configured for providing the products 7 to the first aerobic reactor 13 for increasing the stability of the reaction.

Note that the plant 100 could be equipped with as many tanks as there are nutrients or with a single tank containing all the nutrients used.

Also, the tank 21 is preferably operatively connected to the heating means 1 1 so as at least in part to receive the solid fraction 1 c of the quantity 1 of mainly cellulosic material.

In fact, the solid fraction 1 c of the quantity 1 of prevalently cellulosic material obtained following the decomposition step is rich in some inorganic nutrients 7.

Therefore, the method preferably also comprises a step of accumulating at least a part of the solid fraction 1 c of the quantity 1 of mainly cellulosic material in outlet from the heating means 1 1 .

This accumulated part is stored in the tank 21 or directly inoculated inside the first aerobic reactor 13 with the function of a nutrient.

According to one of the main aspects of the invention, the method includes a (further) step of aerobic digestion of a second portion (VFAb) of the VFA solution carried out by the action of the enriched bacterial population 4 for obtaining products 5 rich in polyhydroxyalkanoates.

In other words, the step of aerobic digestion of the second portion (VFAb) is a step of accumulating polyhydroxyalkanoates (PHA).

Advantageously, in this way it is possible to convert print waste (or the mainly cellulosic material) into bioplastic or into products having a high bioplastic content.

This (further) step of aerobic digestion is preferably performed in a second aerobic reactor 14 provided with at least a first 14a and a second inlet 14b respectively set up to receive respectively:

- the second portion (VFAb) of VFA solution from the anaerobic digester

12, and

- the enriched bacterial population 4 from the first aerobic reactor 13.

This second aerobic reactor 14 is thus configured so as to make the second portion (VFAb) of the VFA solution react with the enriched bacterial population 4 to obtain products 5 rich in polyhydroxyalkanoates.

The products 5 in outlet from the second aerobic digester 14 are preferably composed of an aqueous part and a dry part.

From the point of view of quantity, the dry part has a flow rate of between 15 and 30 kg/h, preferably approximately 23 kg/h.

The second aerobic reactor 14 preferably, comprises an aerated tank into which the enriched bacterial population 4 is inoculated (through the second inlet 14b).

In the preferred embodiment, the second aerobic reactor 14 is a continuous flow stirred-tank reactor CSTR 28 (structurally alike the one described above).

Note that the first inlet 14a might be in direct connection with the anaerobic digester 12, in particular with a further outlet 12c thereof (figure 2) or through the storage tank 19 (figure 1 ).

In this further embodiment (figure 1 ), the storage tank 19 is in effect also provided with a second outlet 19b connected to the second aerobic reactor 14 (i.e. to the first inlet 14a thereof).

In this way the separation of the VFA solution into the first portion (VFA_a) and the second portion (VFAb) advantageously takes place inside the storage tank 19.

Following the aerobic digestion of the second portion (VFAb) products 5 rich in polyhydroxyalkanoates (PHA) are thus obtained.

To obtain the bioplastic, i.e. the dried polyhydroxyalkanoates (PHA), the method comprises a final step of separation of the products 5 into a useful fraction 5a', defined mainly by polyhydroxyalkanoates (PHA), and a residual fraction 5b, 5a", defined mainly by a cellular residue.

In the light of this, the plant comprises separating means 15 operatively positioned downstream of the second aerobic reactor 14 and configured so as to split the products 5 into a usable fraction 5a', mainly made up of polyhydroxyalkanoates (PHA), and a residual fraction 5b, 5a", at least partly made up of a cellular residue 5a".

The step of separating preferably comprises a sub-step of filtering, in which the products are divided into a solid portion 5a and a liquid portion 5b.

It should be noted that the liquid portion 5b is strongly alkaline; in the light of this, in the embodiment of figure 3 the liquid portion 5b is collected and introduced into the second stage 34 of the selector device 32 (that is of the pertraction device 32a).

The filtration sub-step is preferably performed using mechanical separating means 30, such as for example a centrifuge, a decanter or a filtration apparatus.

Further, the separating step also comprises a sub-step of extraction, subsequent to the step of filtering, in which the useful fraction 5a' is extracted from the solid portion 5a, leaving a cellular residue 5a", performed by suitable extractor organs 31 .

Therefore, the residual fraction is defined by the liquid portion 5b and the cellular residue 5a".

The liquid portion 5b (or clarified solution) is preferably re-introduced in the process internally of the anaerobic digester 12.

This advantageously enables eliminating a possible waste and reaching the dilution level necessary for an effective digestion of the pyrolysis oil. Further, in the preferred embodiment, the cellular residue 5a" is reintroduced into the process during the step of decomposition (that is, internally of the heating means).

Thus, at least part of the residual fraction is re-introduced before or during the thermochemical treatment.

This advantageously enables increasing the performance of the method, and therefore of the plant 100.

In this regard, the plant 100 comprises recirculating means 20 associated with the separating means (in particular the extractor organs 31 ) configured so as to:

- collect at least part of the residual fraction (in particular the cellular residue) of the products 5 rich in polyhydroxyalkanoates from the separating means 15;

- transport said part of the residual fraction (in particular of the cellular residue 5a") towards the heating means 1 1 ;

- introduce the part of the residual fraction (in particular the cellular residue 5a") into the heating means 1 1 so as to increase the plant 10 output.

Structurally, these recirculation means 20 can be defined by a conveyor belt, by a screw conveyor or by vehicles controlled by an operator, as well as automated.

The plant 100 preferably also has a system of actuators and sensors which enables dynamic control of the reactions.

This advantageously enables maximising the yield of the plant 100, optimising the quality of the bioplastic and reducing waste.

More precisely, the plant 100 comprises a plurality of actuator means18, 22, 23, a plurality of sensor means 24 and a control unit 25 associated thereto and configured such as to control the actuator means 18, 22, 23 as a function of respective signals received by the sensor means 24.

In particular, the plant comprises first actuator means 18 (corresponding to the previously-described feed means) operatively interposed between the anaerobic digester 12 and the first aerobic reactor 13.

The first actuator means 18 are configured for collecting the first portion

(VFA_a) of the VFA solution and sending it to the first aerobic reactor 13.

They are preferably located at the first outlet 19a of the storage tank 19. Further, the plant comprises second actuator means 22 operatively interposed between the anaerobic digester 12 and the second aerobic reactor 14.

The second actuator means 22 are configured to collect said second portion (VFAb) of the VFA solution and send it to the second aerobic reactor 14.

The second actuator means 22 are preferably located at the second outlet

19b of the storage tank 19 (where present).

Further, in the embodiments provided with the tank 21 , the plant also comprises third actuator means 23 operatively interposed between the tank 21 and the first aerobic reactor 13.

The third actuator means 23 are configured for collecting the inorganic nutrient products 7 and sending them to the first aerobic reactor 13.

Other actuators are present in the plant, such as for example the hydraulic suction pump of the portion 2a of anaerobic bacterial population. However, in the majority of cases these actuators not are piloted by the dynamic control system.

The sensor means 24 are associated with the anaerobic digester 12, with the first aerobic reactor 13 and with the second aerobic reactor 14 for detecting a plurality of parameters representative respectively of said anaerobic digestion and said aerobic reactions.

More precisely, the sensor means 24 comprise at least a first sensor group 24a associated with the anaerobic digester 12 and configured for detecting one or more of the following parameters:

- pH;

- redox;

- temperature;

- quantity of ammonium;

- quantity of dissolved oxygen or redox potential (V);

- quantity of phosphates.

Moreover, the means sensors 24 comprise at least a second group sensor 24b associated to the first aerobic reactor 13 and configured for detecting one or more of the following parameters:

- pH;

- temperature;

- quantity of dissolved oxygen or redox potential (V);

- quantity of ammonium;

- quantity of phosphates;

- turbidity or concentration of biomass (g S.S. ¹);

- electrical conductivity or salinity (S).

Preferably, the sensor means 24 comprise at least a third sensor group 24c associated to the second aerobic reactor 14 and configured for detecting one or more of the following parameters: -pH;

- quantity of dissolved oxygen or redox potential (V);

- quantity of ammonium;

- quantity of phosphates;

- turbidity or concentration of biomass (g S.S. ¹);

- conductivity or salinity (S).

In the preferred embodiments, the sensor means 24 comprise at least a first sensor group 24d associated to the anaerobic digester 15 and configured for detecting one or more of the following parameters:

- density of the products 5;

- measurement of the purity of the polyhydroxyalkanoates;

- mass flow.

More precisely, the fourth group sensor 24d is divided into a first sensor 24d' associated to mechanical separating means 30 and a second sensor 24d" associated to the extractor means 31 .

The control unit 24 is operatively associated with the first 18, second 22 and third 23 actuator means and with the sensor means 24 and:

- predisposed to receive signals correlated with the representative parameters of the anaerobic digestion and the aerobic reactions, - programmed to process the signals for the efficiency of the aerobic reactors 13, 14 in the conversion of the VFA solution into the enriched bacterial population 4 and products 5 rich in polyhydroxyalkanoates;

- configured such as to control the first 18, second 22 and third 23 actuators depending on the signals, for maintaining a high level of adaptation of the enriched population 4.

The invention achieves the preset aims and provides major advantages. In effect, with the method and the plant of the present invention it is possible to obtain bioplastic starting from print waste, thus considerably increasing the use of these materials and achieving excellent yield.

With the use of this method the production of bioplastic effectively represents the most attractive economic aim for the exploitation of offset printing waste, previously reusable in the recycling chain, for the production of energy or electric carriers, with a modest economical yield. Moreover, technical details such as the pre-mixing of the syngas with the anaerobic bacterial population (in the Venturi Scrubber) enable considerably increasing the productivity of the plant, which can operate in continuous mode.

Further, the use of bio-char as nutrient and additive in anaerobic digestion increases the stability of the reactions, thus considerably limiting the waste material from the plant.

Also, this re-utilisation, in the thermochemical treatment of cellular residue following extraction, newly enables increasing the of the plant yield, thus minimising waste products.

Claims

1 . A method for conversion of mainly cellulosic material, characterised in that it comprises following steps:

- predisposing a quantity (1 ) of mainly cellulosic material with a carbon/nitrogen ratio of greater than 50;

- predisposing an anaerobic bacterial population (2);

- predisposing a mixed aerobic bacterial population (3);

- decomposition of said quantity (1 ) of mainly cellulosic material into a liquid fraction (1 a), a gaseous fraction (1 b) and a solid fraction (1 c) by means of a predetermined thermochemical treatment;

- fermentation of at least said liquid fraction (1 a) and gaseous fraction (1 b) in a fermenter (12), by inoculating said anaerobic bacterial population (2) in the liquid fraction (1 a) and the gaseous fraction (1 b), for producing a solution (VFA) containing volatile fatty acids;

- aerobic digestion of a first portion (VFA_a) of said solution (VFA) by means of the action of said mixed aerobic bacterial population (3) for producing a bacterial population (4) enriched with polyhydroxyalkanoates;

- aerobic digestion of a second portion (VFAb) of said solution (VFA) by means of the action of said enriched bacterial population (4) for obtaining products (5) rich in polyhydroxyalkanoates;

- separation of said products (5) into a usable fraction (5a'), mainly composed of polyhydroxyalkanoates (PHA), and a residual fraction (5b, 5a"), at least partly composed of a cellular residue (5a").

2. The method according to claim 1 , characterised in that said predetermined thermochemical treatment is defined by pyrolysis or gasification or hydrothermal liquefaction or thermal treatment under pressure.

3. The method according to claim 1 or 2, characterised in that said thermochemical treatment is carried out by superheating said quantity (1 ) of mainly cellulosic material in a high temperature environment, between 350 and 800 °C, preferably between 400° and 500°C.

4. The method according to claim 3, characterised in that, during said fermentation step, said quantity of solid fraction (1 c) or of vegetable charcoal is added to speed up the conversion into the solution (VFA) containing volatile fatty acids of said gaseous fraction (1 b) and said liquid fraction (1 a) which were obtained following said high temperature thermochemical treatment.

5. The method according to any one of the preceding claims, characterised in that it comprises a mixing step operatively carried out upstream of said fermentation step, wherein said gaseous fraction (1 b) is struck by a nebulised portion (2a) of said anaerobic bacterial population (2).

6. The method according to claim 5, characterised in that said mixing step is carried out using the Venturi effect.

7. The method according to any one of the preceding claims, characterised in that it comprises following steps:

- predisposing inorganic nutrient products (7);

- adding said inorganic nutrient products (7) during said step of aerobic digestion of the first portion (VFA_a) of the solution (VFA) so as to stabilise the reaction.

8. The method according to claim 7, characterised in that said step of predisposing inorganic nutrient products (7) comprises a sub-step of accumulating at least part of said solid fraction (1 c) of the quantity (1 ) of mainly cellulosic material.

9. The method according to any one of the preceding claims, characterised in that the aerobic digestion of the first portion (VFA_a) of said solution (VFA) is divided into:

- a first period, with predetermined duration, in which the first portion

(VFA_a) of solution (VFA) is introduced into an aerobic digester (13) containing said mixed aerobic bacterial population (3);

- a second period, with a duration at least double that of said first period, in which the supply of said solution (VFA) to the aerobic digester (13) is stopped, to promote the accumulation of polyhydroxyalkanoates (PHA).

10. The method according to claim 9, characterised in that said first and second periods are cyclically repeated one after another.

1 1 . The method according to any one of the preceding claims, characterised in that the aerobic digestion of the first portion (VFA_a) of said solution (VFA) is divided into:

- a sub-step of introducing said first portion (VFA_a) of solution (VFA) into a first aerobic space (13a), with predetermined size, containing said mixed aerobic bacterial population (3);

- a sub-step of accumulating polyhydroxyalkanoates (PHA) in a second aerobic space (13b), with predetermined size and operatively positioned downstream of said first aerobic space (13a) so as to obtain said bacterial population (4) enriched with polyhydroxyalkanoates;

- a sub-step of extracting said bacterial population (4) enriched with polyhydroxyalkanoates from said second aerobic space (13b).

12. The method according to claim 1 1 , wherein said second space (13b) is positioned in sequence after said first space (13a).

13. The method according to any one of the preceding claims, characterised in that said decomposition step comprises introduction, before or during said thermochemical treatment, of said residual fraction (5b), obtained during the step of separation of said products (5) rich in polyhydroxyalkanoates.

14. A plant for the conversion of mainly cellulosic material with a carbon/nitrogen ratio of greater than 50, characterised in that it comprises: - heating means (1 1 ) provided with at least a chamber (16) and designed to superheat the material (1 ) contained in said chamber (16) so as to break it down into a liquid fraction (1 a), a gaseous fraction (1 b) and a solid fraction (1 c); said chamber (16) being provided with at least an infeed (1 1 a), for allowing entry of a predetermined quantity (1 ) of mainly cellulosic material, and at least an outfeed (1 1 b), for allowing said liquid fraction (1 a) and said gaseous fraction (1 b) to exit the chamber;

- an anaerobic digester (12) or fermenter operatively positioned downstream of said heating means (1 1 ), predisposed to receive said liquid fraction (1 a) and gaseous fraction (1 b) and designed to convert the fractions into a solution (VFA) containing volatile fatty acids by means of the action of an anaerobic bacterial population (2);

- a first aerobic reactor (13), operatively positioned downstream of said anaerobic digester (12), set up to receive a first portion (VFA_a) of said solution (VFA) and designed to convert it, by means of the action of a mixed aerobic bacterial population (3), into a bacterial population (4) enriched with polyhydroxyalkanoates;

- a second aerobic reactor (14) provided with at least a first infeed (14a) and a second infeed (14b) respectively predisposed to receive a second portion (VFAb) of solution (VFA) from said anaerobic digester (12) and the enriched bacterial population (4) from said first aerobic reactor (13); said second aerobic reactor (14) being configured so as to make said second portion (VFAb) of the solution (VFA) react with said enriched bacterial population (4) for obtaining products (5) rich in polyhydroxyalkanoates; - separating means (15) operatively positioned downstream of said second aerobic reactor (14) and configured so as to split said products (5) into a usable fraction (5a'), mainly made up of polyhydroxyalkanoates (PHA), and a residual fraction (5b, 5a"), at least partly made up of a cellular residue.

15. The plant according to claim 14, characterised in that said heating means (1 1 ) comprise at least a pyrolyser (29) and/or a gasifier designed to superheat said chamber to a temperature of between 350°C and 800°C, preferably between 400°C and 500°C.

16. The plant according to claim 14 or 15, characterised in that it comprises an absorption column (17) operatively interposed between the heating means (1 1 ) and the anaerobic digester (12) and provided with extractor means (17a) for extracting a portion (2a) of said anaerobic bacterial population (2) from the anaerobic digester (12) so as to increase the exchange between said gaseous fraction (1 b), exiting from the heating means (1 1 ), and said anaerobic bacterial population (2), speeding up the action of the subsequent anaerobic digester (12).

17. The plant according to claim 16, characterised in that said absorption column (17) comprises at least a Venturi tube (17b) in which the gaseous fraction (1 b) and the portion (2a) of anaerobic bacterial population (2) are mixed.

18. The plant according to any one of claims from 14 to 17, characterised in that it comprises feed means (18) associated with said first aerobic reactor (13) and designed to supply it with said first portion (VFA_a) of the VFA solution intermittently, at predetermined time intervals.

19. The plant according to claim 18, characterised in that it comprises at least an anaerobic storage tank (19) positioned downstream of said anaerobic digester (12) and provided with at least a first outfeed (19a) and a second outfeed (19b) which are respectively connected to the first aerobic reactor (13) and to the second aerobic reactor (14); said feed means (18) being associated with said first outfeed (19a).

20. The plant according to any one of claims 14 to 19, characterised in that said second aerobic reactor (14) is a continuous flow stirred-tank reactor CSTR.

21 . The plant according to any one of claims 14 to 20, characterised in that said first aerobic reactor (13) is a continuous plug flow reactor PFR, or two or more continuous flow stirred-tank reactors CSTR positioned in series.

22. The plant according to any one of claims 14 to 21 , characterised in that it comprises recirculating means (20) configured such as to:

- collect the residual fraction (5a) of said products (5) rich in polyhydroxyalkanoates from the separating means (15);

- transport said residual fraction (5a) towards the heating means (1 1 ); - introduce said residual fraction (5a) into the heating means (1 1 ) to increase the plant (10) output.

23. The plant according to any one of claims 14 to 22, characterised in that it comprises at least at least a tank (21 ) containing inorganic nutrient products (7) configured so as to supply said inorganic nutrient products (7) to said first aerobic reactor (13) in order to increase the stability of the reaction.

24. The plant according to claim 23, characterised in that said tank (21 ) is operatively connected to said heating means (1 1 ) for receiving at least part of said solid fraction (1 c) of the quantity (1 ) of mainly cellulosic material.

25. The plant according to claim 23 or 24, characterised in that it comprises:

- first actuator means (18) operatively interposed between said anaerobic digester (12) and said first aerobic reactor (13) and configured so as to pick up said first portion (VFA_a) of the solution (VFA) and send it to the first aerobic reactor (13);

- second actuator means (22) operatively interposed between said anaerobic digester (12) and said second aerobic reactor (14) and designed to pick up said second portion (VFAb) of the solution (VFA) and send it to the second aerobic reactor (14);

- third actuator means (23) operatively interposed between said tank (21 ) and said first aerobic reactor (13) and designed to pick up said inorganic nutrient products (7) and send them to the first aerobic reactor (13);

- sensor means (24) associated with the anaerobic digester (12), with the first aerobic reactor (13) and with the second aerobic reactor (14) for detecting a plurality of parameters representative respectively of said anaerobic digestion and said aerobic reactions;

- a control unit (25) operatively associated with said first (18), second (22) and third (23) actuator means and with said sensor means (24) and:

- predisposed to receive signals correlated with the representative parameters of the anaerobic digestion and the aerobic reactions,

- programmed to process said signals for the efficiency of the aerobic reactors (13, 14) in the conversion of the solution (VFA) into said enriched bacterial population (4) and products (5) rich in polyhydroxyalkanoates;

- configured such as to control said first (18), second (22) and third (23) actuators depending on said signals, for maintaining a high level of adaptation of said enriched population (4).