WO2020049226A1

WO2020049226A1 - A porous formable material and a method for producing it

Info

Publication number: WO2020049226A1
Application number: PCT/FI2019/050642
Authority: WO
Inventors: Tuomo Hilli
Original assignee: Fifth Innovation Oy
Priority date: 2018-09-07
Filing date: 2019-09-09
Publication date: 2020-03-12
Also published as: FI129154B; EP3847129A1; FI20185748A1

Abstract

The invention relates to a porous formable material and to a method for producing it. Lignocellulose-based starting material in used in the method by forming a lignin- containing mixture from fractions obtained from biomass fractionation, which mixture is treated to form a porous object. In the method the material is foamed, formed, heat treated, carbonized and activated. The obtained carbonized and activated object is suitable to be used among other as a filler, filter and catalyst substrate.

Description

A POROUS FORMABLE MATERIAL AND A METHOD FOR PRODUCING IT

Field of the Invention

The present invention relates to porous formable biomaterial-based materials, their production and their use.

In particular, the invention concerns a method for producing a porous formable object according to the preamble of claim 1, and to a product obtained by such a method.

The invention also concerns a porous object according to claim 16 and its use.

Description of Related Art

The so-called porous i.e. foamed carbon can be used in a number of different applications, such as in thermal insulation (also at very high temperatures), various filters and in catalysis. In catalysis reactions porous carbonized materials are used particularly as carriers for catalysts because of their high specific surface area.

Conventionally, porous carbon materials are mainly produced by carbonizing synthetic resin foams, such as polyurethane and phenolic resin foams. Such materials are non- ecological and expensive to manufacture. Thus, the study aims at finding alternative materials for these synthetic materials. For example, use of lignin to replace phenols in polyurethane foam is known.

In the past, attempts have been made to produce a variety of bio-based foam products mainly from pure biomaterial-based starting materials, such as tannin, lignin and furfural alcohol, but the use of impure starting materials has also been studied.

Prior art in this respect is represented, for example, by publication US3894848 which discloses the preparation of a porous formable material from an aqueous solution of lignin. The method comprises foaming and heat treatment of the starting material in a mold, as well as carbonization of the porous material thus obtained.

The articles titled“Tannin based foams and its derived carbon foams” (Tondi, G. et al, 2010) and’’Chemistry, morphology, microtomography and activation of natural and carbonized tannin foams for different applications” (Pizzi, A., 2012) describe tannin foams of a 95 % purity as well as carbonization and optional activation thereof.

Publication W02005016818 describes a process for producing carbon foam from a metal salt of lignosulfonate. In the process, foaming and the carbonization of the starting material are carried out simultaneously in an oxygen-free atmosphere at a pressure above 100 psi and at a temperature above 250 °C.

It is also known to produce from carbon materials activated carbon, the function of which is based on adsorption, wherein the activated carbon acts as an adsorbent binding certain molecules of either gaseous or liquid material to its surface. Typically, some molecules are already trapped in the pores of a foamed carbon material simply because of their physical size, depending of course on the pore size and size of the molecules, whereby the porous material acts as a so-called sieve as such. A notable feature of activated carbon is its particularly porous structure which provides its large specific surface area while simultaneously improving the filtering properties of the activated carbon.

The size of the effective surface area of activated carbon varies greatly depending on the degree of the carbon activation and the raw material used to produce the activated carbon. The aim is to choose a raw material that provides the best properties for the coming use of the activated carbon. The most common activated carbon raw materials used are wood, sawdust, peat, coconut shells, coal and crude oil residues. Typically, the selected raw material is crushed and then carbonized at a temperature of about 800 to 1000 °C. During carbonization, most of the hydrocarbon and part of the carbon are removed, thereby increasing the surface area of the carbon.

Activation of carbon can improve the adsorption capacity of organic substances of carbon by increasing the pore size and diameter. During activation, different substances are removed from the pores of the carbon leaving voids in the structure i.e. increasing the volume of the pores. As a result of the activation, the removing substances also form completely new pores in the carbon. Activated carbon typically has a specific surface area of 500 to 1500 m²/g.

When selecting the raw material, it is important to consider the desired particle size of the final product, the structure of the pores, the total surface area and the void between the components, and of course the cost of the raw material.

Typically, the activated carbon is provided either as a fine powder or in a granular form, but also foamed activated carbon has been produced.

It is also known to produce activated carbon from biomass. Such has been described for example in publications CN1070021486 and US4552863. Publication CN1070021486 discloses a method for producing activated carbon from biomass by foaming, calcining and finally activating the carbonized foam using gas. In the method according to publication US4552863, activated carbon is produced by using wood as a carbon source.

Heat-treated foams alone have often been found to be quite brittle. Carbonization and activation can also be used to improve, among other things, mechanical resistance of the porous material.

There is still room for improvements in the properties, and particularly in the formability, and in the used starting materials, of the porous materials. In particular, use of ecological starting materials should be enhanced and the utilization of industrial by-products further increased. None of the starting materials has been successfully optimized with respect to all its beneficial properties while simultaneously being environmentally friendly and inexpensive. The properties sought are relatively low density, mechanical strength and high thermal conductivity, which is generally the result of an at least partially organized crystal structure. Summary of the Invention

It is an object of the present invention to provide a new method for producing porous formable materials from bio-based starting materials. In particular, it is an object to provide a method for producing carbon foams by using inexpensive starting materials which nevertheless have the necessary physical and chemical properties for use.

In particular, it is an object of the invention to provide a method which can be used to produce carbon foams from lignocellulosic starting material.

It is also an object of the invention to provide a new kind of formable material.

The invention is based on the finding that by treating lignocellulosic starting material by the method of the invention, a bio-based porous formed object is provided, which object is carbonized and activated throughout.

In the method of the invention, a mixture comprising a liquid medium is formed from a lignin-containing fraction obtained from biomass fractionation, into which mixture is optionally also added other fractions resulting from biomass fractionation. The resulting mixture is foamed and formed in a mold into a pre-determined shape. The formed foam thus obtained is further subjected to a heat treatment, which after it is carbonized and finally activated.

In the described way, foamed biomass-based objects are provided, which objects can be used for example in a variety of purification applications, such as in purification of gases and liquids or in cleaners, as a filler or as a catalyst substrate.

More specifically, the invention is characterized by what is stated in the characterizing part of the independent claims.

Considerable advantages are achieved by the invention. Thus, the method provides self- standing monolithic, activated, porous structures. In particular, porous formed objects are provided, which objects are carbonized and activated throughout. The carbonized and activated porous object according to the invention has preferred properties, such as low electrical conductivity, low thermal conductivity and low density. These properties can also be diversely modified depending on the application. In the case of insulators, for example, low thermal conductivity may be sought by reducing the density, and electrical conductivity may be controlled, for example, by the addition of more electrically conductive metals to the foam. The electrical conductivity is also affected by the temperature used in the heat treatment, for example, high temperature heat treatment typically improves electrical conductivity. Thus, the formed object according to the invention has wide application possibilities.

Most suitably, the foaming according to the invention occurs at normal pressure and at room temperature. However, the foaming can also be performed under reduced pressure or overpressure, for example at an absolute pressure of 0.1 to 10 bar. When the mixture is foamed without external heating, foaming can be better controlled and foam objects of uniform quality are obtained.

A wide variety of lignocellulosic raw materials, such as various plants and parts thereof, side fractions of different fractionation processes, and digestate from peat and biogas plants and other partially biodegraded or processed materials, can be used as starting material for the invention. The bio-based raw materials used in the invention reduce the need for fossil raw materials and reduce the carbon footprint of the product. Thus, it is possible to utilize cheaper, unrefined starting materials or purified raw materials, or combine these, in the method of the invention. Thus, also the side fractions of the fractionation process can be utilized.

The production method of the invention has the additional benefit of being environmentally friendly, involving simple technology and having low energy consumption. Energy consumption can be reduced by harnessing the energy of the gas streams used in the various process steps by recovering it and utilizing for example in pre-heating. In addition, the volatile components used for foaming can be recycled by condensation and reuse. The volatile fractions generated during the carbonization step can also be utilized as an energy source or heat can be recovered from those by condensation, whereby also these liquid fractions can be utilized in other processes. Non-condensable gases can be burned and the energy thus produced can be utilized for example in the process, in heating or in power generation.

The porous material of the invention also has the benefit of being capable of recycling and reuse. The prepared porous material can be directly regenerated by heating or alternatively crushing, which after it can be used as a raw material of new foam. Finally, carbonized material can be used as a soil improver, allowing the carbon (C0₂ negative) contained in it to be stored in the soil for a long term, or alternatively it can be burned to produce green energy.

Preferred embodiments of the invention will now be discussed in more detail with reference to the attached drawing. The drawing shows a simplified diagram of the method steps according to one embodiment.

Drawings

Figure l is a block diagram showing the steps of the method according to one embodiment.

Embodiments

The present invention relates to a porous formable material and a method producing the same.

The products to be produced will in the following be referred as“object” and“foam object” as being synonyms with each other. It is a three-dimensional object that is porous. After foaming, the porous material comprises mainly macropores. Typically, the smallest dimension of the pores is at least 0.01 mm. Activation results in a large number of micropores and mesopores in the object.

Most suitably the object is porous throughout, which means that the porous structure extends from the inside of the object to its surface. Most suitably, the porous object i.e. the foam object is permeable to gases.

The objects are“monolithic” which in the present context means that their body structure consists of the same material throughout, i.e. the object is“one substance”.

The objects are typically mechanically strong and the present material can be used to produce self-standing objects.“Self-standing” means that those can be used to form products, such as filters and the like, which do not require a separate body layer or structure.

The method according to one embodiment is presented in figure 1.

At the first step of the method (reference 2 of figure 1), a mixture comprising liquid medium is formed from a lignin-containing fraction obtained from the biomass fractionation 1.

Typically, the lignin-containing fraction is derived from biomass, such as wood or annual or perennial plants. The fraction is obtained for example by extracting the biomass with an aqueous solution, for example by hot water extraction or pressurized hot water extraction or traditional chemical pulp cooking. Most suitably, the aqueous solutions contain lignin- solubilizing components, such as alkali, for example alkali metal or alkaline earth metal hydroxides, carbonates, sulfides, or mixtures thereof. The extraction solutions can also contain peroxides and organic compounds, such as performic acid or Caron^'s salt. The extraction can also be carried out with organic or ionic solvents.

The liquid medium contained in the mixture acts as a foaming agent in the mixture.

According to one embodiment the liquid medium is water. According to another embodiment the liquid medium can be for example an organic solution, such as alcohol, or ionic solution. The liquid medium can also be a mixture of several liquids. By using liquid medium having a low boiling point, the amount of energy needed for drying of the foam can be reduced. According to one embodiment the liquid medium used for foaming can be recovered and recycled to be reused.

The lignin can be either untreated or treated or as a mixture thereof. Thus, the lignin can be in any form, such as an alkaline lignin, in a thiol-form or as a metal salt of lignosulfonate.

According to one embodiment, also other fractions obtained from the biomass fractionation 1 are added to the lignin-containing mixture. These fractions may or may not contain lignin. Typically, the fractions to be added contain for example organic components, such as extracts, furfural or tannin, or monomeric, oligomeric or polymeric saccharides, which are derived from cellulose or hemicellulose.

In addition, the fractions to be added can be pure or unrefined. The proportion of each of such fraction can be for example about 0.1 to 25 weight-% of the solids of the mixture to be foamed.

Thus, various side fractions of the fractionation process can be effectively utilized in the present invention.

According to one embodiment the mixture formed of the biomass fractions contains at least 1 weight-% lignin, preferably at least 5 weight-% lignin, more preferably 10 to 80 weight- % lignin, for example 20 to 50 weight-% lignin, calculated from the dry weight of the mixture.

According to one embodiment the mixture formed of the fractions of the biomass contains at least 1 weight-% lignin, preferably at least 5 weight-% lignin, more preferably 10 to 75 weight-% lignin, for example 30 to 50 weight-% lignin, calculated from the total weight of the mixture.

According to one embodiment the formed mixture contains a liquid medium of 0.1 to 70 weight-%, preferably 1 to 50 weight-%, more preferably 5 to 30 weight-%, for example about 10 weight-%, calculated from the total weight of the mixture. Components modifying the properties of the final product according to the application can also be added to the mixture.

According to one embodiment these components are added prior to foaming. According to another embodiment these components can also be added in any other method step, such as prior to drying or carbonizing, or in several different steps.

In one embodiment, a substance or substances belonging to one or more of the following groups are added to the mixture:

a substance modifying mechanical properties of the produced objects (in particular those increasing their strength),

a substance modifying the fire and rot resistance properties of the produced objects, catalyst, or a substance functioning as an insecticide in the produced objects.

Further, various fillers, wetting agents and stabilizing agents can also be added to the mixture.

The amounts of the above described substances and components are typically about 0.01 to 25 weight-%, in particular 0.1 to 10 weight-% of the dry weight of the starting material.

In the next step 3 of the method, the formed mixture is foamed and molded into a predetermined shape.

According to one embodiment the mixture formed from the fractions resulting from the biomass fractionation is foamed prior to being fed in the mold, wherein the mold can be carefully filled and the foamed object becomes precisely mold-shaped. According to another embodiment the mixture is not foamed until in a mold. The mold can be heated to promote foam solidification, as described below.

The mixture can be foamed by any of the well-known foaming methods, such as heating, mechanical mixing, blowing gas process or saline process. Preferably, the mixture is foamed by mechanically mixing or chemically. In chemical foaming a use can be made for example of sodium carbonate or potassium carbonate, which upon decomposition produce carbon dioxide and, alkaline part of which simultaneously serves as an activating additive. The foaming can be performed for example in a mixing tank.

In order to promote the foaming, a foaming agent, such as surface-active agent, such as polysorbate, can be added to the mixture for example about 0.1 to 10 weight-% of the dry matter of the mixture.

According to preferred embodiment the foaming is carried out at normal pressure or under a slight overpressure, for example at an absolute pressure of 1.1 to 10 bar. The foaming temperature is preferably above 20 °C but below 100 °C. The reaction is exothermic i.e. without heating the foaming is better controllable and the shaping of the object is easier.

The molded foamed product has a clear, three-dimensional shape that is by no means limited. It can be for example a cube, a cone, a cylinder or a ball. According to a preferred embodiment the mold is closable. However, the mold can also be open.

The formed porous material produced as described above is subjected to a heat treatment 4.

The formed porous material is heat treated 4 at a mild temperature to consolidate the foam. In a preferred embodiment the heat treatment is carried out while the foam is still in the mold.

However, the heat treatment can also be carried out in a separate oven.

The heat treatment is carried out by heating the foamed mixture to a suitable temperature and by holding it at this temperature for a sufficient time, such as for 0.1 to 24 hours, for example 0.5 to 12 hours, always according to the composition of the formed mixture.

Preferably, the heat treatment is carried out at temperature below 250 °C, for example below about 200 °C, most suitably at about 101 to 195 °C. Usually, the heat treatment is carried out at normal air pressure (about at a pressure of 1 bar) but of course it is also possible to be carried out at an elevated pressure, for example at an absolute pressure of about 1.1 to 10 bar. The foam temperature should be raised at a low enough speed so that the material warms up evenly. According to one embodiment, a suitable heating rate is about 1 to 120

°C/minute, in particular the temperature is raised in the heat treatment vessel at a rate of about 5 to 50 °C/minute, for example about 10 to 30 °C/minute.

According to one embodiment, the temperature of the heat treated porous material is preferably lowered to a temperature of about 50 to 100 °C. The lowering of the temperature is most suitably carried out at such a slow rate that no fractures due to thermal stress occur in the carbon foam. A suitable cooling rate is about 1 to 120 °C/minute, in particular the temperature is lowered in a heat treatment vessel at a rate of about 5 to 50 °C/minute, for example about 10 to 30 °C/minute. This is typically done when the formed porous object is removed from the mold at this point and the next method steps are carried out without the mold. Typically, the porous object is held in the mold also during the carbonization and activation if the mold is such that the gases released during the carbonization and activation are free to pass it.

In another preferred embodiment, the heat treated porous material is directly introduced to the next process step without substantially reducing its temperature, in which process step it is carbonized and activated.

According to a preferred embodiment, the carbonization 5 after the heat treatment takes place in an inert gas phase at a temperature above 500 °C, such as 500 to 1500 °C, preferably about 800 to 1000 °C. The temperature of the foam is slowly raised to the carbonization temperature. A suitable heating rate is about 1 to 120 °C/minute, in particular the temperature is raised in a heat treatment vessel at a rate of about 5 to 50 °C/minute, for example about 10 to 30 °C/minute.

The inert gas phase used in the carbonization can contain any gases which are essentially inert under the carbonization conditions. As an example of such gases a mention can be made of nitrogen, helium, carbon dioxide and argon and mixtures thereof.

The carbonization can be carried out in a closable reactor or in an oven. Typically, such reactor or oven operates close to the atmospheric pressure or at a slight overpressure.

According to one embodiment, also after the carbonization the temperature of the object should be lowered at a slow enough rate to prevent fractures in the object. A suitable cooling rate is about 5 to 50 °C/minute.

In another preferred embodiment the carbonized porous material is directly introduced to the next optional process step without essentially reducing its temperature, in which process step it is being activated.

According to a preferred embodiment the carbonized object is activated in order to further increase its specific surface area. With the help of the present method the material is first carbonized and then activated uniformly throughout. The carbonization and activation steps also increase the mechanical resistance of the porous material.

According to one embodiment the object is chemically activated. Preferably, the chemical activation is carried out by heating the material treated with activation chemicals to a temperature of 400 to 800 °C. The activation chemicals are used to remove moisture from the material. As activation chemicals a use can be made for example of alkali salts, phosphoric acid, zinc chloride or sulfuric acid or a mixture thereof.

According to another embodiment the object is physically activated, wherein the carbon is activated by gas at a temperature of about 800 to 1100 °C. The used gas can be for example water vapor, carbon dioxide or a mixture thereof. Due to the exothermic reactions of the activation, hydrogen, carbon monoxide and carbon dioxide are removed from the material.

According to a preferred embodiment the object is activated with water vapor. The external adsorption surface area of the activated material then becomes large and the structure has small pores, wherein the foam comprises mainly micropores (pores below 2 nm) and mesopores (pores of 2 to 50 nm), respectively.

According to a preferred embodiment the specific surface area of the object after the activation is over 500 m²/g which corresponds to the minimum requirement for the surface area of activated carbon. More preferably, the specific surface area of the object after activation is over 600 m²/g, for example 750 to 2500 m²/g.

According to a preferred embodiment the pore volume of the object after the activation is over 0.3 cmVg. More preferably the pore volume of the object after the activation is over 0.4 cm³/g, for example 0.5 to 0.7 cmVg.

According to one embodiment the carbonized porous object can further be graphitized prior to the activation of the object by heating the object to an even higher temperature of over 1500 °C. The graphitization can be used to further modify the properties of the carbon foam.

According to one embodiment, the temperature of the object should be lowered at a slow enough speed also after the activation to prevent fractions in the object. A suitable cooling rate is about 5 to 50 °C/minute.

According to one embodiment the porous carbonized object produced by the method can be washed in order to reduce possible inorganic materials. The washing can be carried out for example with water, aqueous acid, alkali or with some other solution, in particular with aqueous solution. After this, the object can be optionally dried by generally known drying methods.

According to one embodiment, impregnates i.e. additives can be added to the starting material, which impregnates further improve for example adsorption of certain substances to the material during use. The amount of such substances is typically about 0.1 to 10 weight-% of dry weight of the starting material.

Based on the above, the method according to the invention comprises in the first embodiment 1) biomass fractionation and formation of a liquid medium-containing mixture from fractions, at least some of which contains lignin, 2) subjecting the mixture in a closed mold, 3) foaming of the mixture, 4) heat treatment of the porous material in order to consolidate the foam, 5) carbonization of the consolidated foam and 6) finally activation of the carbonized object.

In another embodiment the method according to the invention comprises 1) biomass fractionation and formation of a liquid medium-containing mixture from fractions, at least some of which contains lignin, 2) foaming of the mixture, 3) subjecting the porous material in a closed mold, 4) heat treatment of the porous material in order to consolidate the foam, 5) carbonization of the consolidated foam and 6) finally activation of the carbonized object.

According to one embodiment an efficient energy use can be combined to the method according to the invention when the energy of the gas streams used at different process steps are utilized. Such process diagram is presented in figure 1.

According to one embodiment, the volatile fractions resulting from the carbonization step of the method according to the invention are condensed, wherein the heat energy can be recovered from those. At the same time liquid fractions are formed, which fractions can be utilized in other processes. The liquid fractions can be recovered or burned.

According to another embodiment, which can also be combined to the previous one, the volatile fractions resulting from the carbonization step and the possible non-condensable gases of the previous embodiment are burned to generate energy. The generated energy can be utilized for example in the process, heating or power generation.

According to one embodiment the recovered heat energy can be utilized in the internal heating of the process i.e. for example in the heating of the raw materials or the building. According to another embodiment the heat energy can be sold to third parties.

The carbon content of the porous object according to the present invention depends on the used starting material and temperature used in the carbonization and graphitization.

According to one embodiment the carbon content of finished porous object is 50 to 100 weight-%, preferably 75 to 100 weight-%, for example 80 to 98 weight-% of the weight of the finished product. According to one embodiment the density of the porous object according to the invention is 20 to 950 g/dm³, preferably 50 to 500 g/dm³ and compressive strength is about 0.07 to 7 MPa, preferably about 0.1 to 1.0 MPa.

The present invention also relates to a porous object which is produced by the method of the present invention.

In addition, the present invention generally relates to a porous, monolithic, self-standing and formed object prepared from a starting material containing lignocellulose-based lignin, which object is carbonized and activated throughout.

Examples Example 1 First, 150 g of water, 200 g of furfuryl alcohol and 25 g of surfactant (polysorbate) were mixed until they formed a homogeneous mixture. Thereafter, 200 g of lignin powder and 200 g of tannin acid were added to the mixture, which after the mixture was vigorously mixed for several minutes. In the third step of the mixture formation, 50 g of volatile compound (n-pentane) was added. Finally, 100 g of acid catalyst (para-toluene sulfonic acid) was added, which started a reaction and the foaming started as a result of the chemical reaction.

After the foaming was stabilized, the mixture was placed in a mold and transferred to an oven for consolidation of the foam. The foam was kept in the oven for 1200 minutes at a temperature of 110 °C. After the consolidation, the carbonization was carried out in an inert gas phase by raising the foam temperature to 550 °C. After the carbonization, the object was activated at a temperature of 800 °C by using water vapor as an activation gas. After the activation, the object temperature was lowered to room temperature and the finished porous object was removed from the mold. Industrial Applicability

The method according to the invention can be utilized for production of various porous formable materials and the material produced by the method can be widely used for various industrial applications. The material can be used as such or it can be utilized as a starting material in other processes.

The produced activated porous material can be utilized among other in various purification applications, such as in purification of gases and liquids, and in cleaners and filters, such as in automotive fresh air filters.

Other applications for the material according to the invention are for example use as filler, catalyst substrate, for storing of gases and as a porous electrode.

The invention is not intended to be limited to the exemplary embodiments set forth above, on the contrary, it is intended to be broadly construed within the scope defined by the following claims.

Reference numbers

1 biomass fractionation

2 mixing

3. foaming and forming

4. heat treatment

5. carbonization and activation

Citation List

Patent Literature

US 3894878 A

WO 2005016818 Al CN 1070021486 A

CN 106587001 A

US 4552863

WO 2018085918 Al

Non-Patent Literature

Tondi, G., Pizzi, A., Celzard, A. (2010) Tannin based foams and its derived carbon foams. Processing Technologies for the Forest and Biobased Products Industries, Kuchl/ Austria.

Pizzi, A., Celzard, V., Tondi, G. (2012) Chemistry, morphology, mi crotomography and activation of natural and carbonized tannin foams for different applications. Special Issue: Functional Polymeric Materials and Composites, Volume 313-314: 1, 100-111.

Claims

1. A method for producing porous objects from a lignocellulose-based starting material, according to which method

- a mixture containing liquid medium is formed from lignin-containing fraction obtained from biomass fractionation,

- other fractions obtained from the biomass fractionation are optionally added to the mixture,

- the mixture is foamed and brought to a predetermined form by means of a mold, and

- the thus obtained formed mixture is subjected to a heat treatment, which after it is carbonized,

characterized in that

- the carbonized object is activated in order to increase its specific surface area.

2. The method according to claim 1, characterized in that the mixture is foamed prior to feeding into the mold.

3. The method according to claim 1 or 2, characterized in that the liquid medium is water, organic solution or ionic solution or any mixture thereof.

4. The method according to any of the preceding claims, characterized in that the mixture is foamed by mechanically mixing or chemically.

5. The method according to any of the preceding claims, characterized in that the mixture is foamed at an absolute pressure of 0.1 to 10 bar and at a temperature below 100 °C , preferably at normal pressure and at room temperature.

6. The method according to any of the preceding claims, characterized in that an open or closable mold is used in the method, in which mold the foamed product is formed into a three-dimensional object which is for example a cube, a cone, a cylinder, or a ball.

7. The method according to any of the preceding claims, characterized in that the porous material is heat treated below 250 °C, preferably under 200 °C, more preferably at 75 to 150 °C, in order to consolidate the foam.

8. The method according to any of the preceding claims, characterized in that the heat treatment is carried out in the mold, in particular the heat treatment is carried out in the mold where the foam object is formed, without removing the object from the mold.

9. The method according to any of the preceding claims, characterized in that the foam object is carbonized in an inert gas phase at a temperature of over 500 °C, preferably at a temperature of 600 to 1200 °C.

10. The method according to any of the preceding claims, characterized in that the foam object is activated with water vapor, wherein its specific surface area is preferably over 500 m²/g and/or pore volume of micropores and mesopores is preferably over 0.3 cm³/g.

11. The method according to any of the preceding claims, characterized in that the mixture contains at least 1 weight-% of lignin, preferably at least 5 weight-% of lignin, more preferably 10 to 80 weight-% of lignin, for example 20 to 50 weight-% of lignin, calculated form the dry weight of the mixture.

12. The method according to any of the preceding claims, characterized in that the lignin-containing fraction is obtained by treating biomass, such as wood, annual or perennial plants, with aqueous solution containing lignin dissolution promoting agents, such as alkali, or organic or ionic solvent.

13. The method according to any of the preceding claims, characterized in that strength enhancer agents, such as anti-mold agents, flame retardants, catalysts or mixtures thereof, of the foam object is added to the mixture prior to the foaming of the mixture.

14. The method according to any of the preceding claims, characterized in that volatile fractions formed in the carbonization step are condensed or burned.

15. A porous object which is produced by the method according to any of the preceding claim.

16. A porous, monolithic, self-standing and formed object produced from a starting material containing lignocellulose-based lignin, which object is carbonized and activated throughout.

17. Use of the porous object according to claim 15 or 16 in purification applications or cleaners, as filler or catalyst substrate.