HUP0900567A2 - Composition for heat treatment of wood and process for treatment of it - Google Patents

Description

Material mixture for heat treatment of wood and method for treating wood

The invention relates to a material mixture for the heat treatment of wood and to a method for treating wood.

Thermal treatment of wood has long been a known technique. During these treatments, the wood undergoes so-called thermal modification, as a result of which the products and elements made from it are more resistant to external influences and acquire various beneficial properties. Such a solution is described, for example, in Hungarian patent specification No. 199,088.

For prior art heat treatments and thermal modifications, the wood is usually surrounded by a gaseous or liquid medium. The disadvantage of this is that the weight of the wood is usually significantly reduced during the treatment, and the substances released from it (tar, volatile substances) require special material handling and environmental protection measures.

There are also known solutions in which the wood material to be heat-treated is surrounded by a solid granular material for thermal modification; such a solution is described in Hungarian patent specification No. P 08 00358. According to this solution, the wood material to be treated is covered with rock salt (NaCI) or a mixture containing at least 20% rock salt by weight, and the heat treatment is carried out while the wood material is covered. According to this solution, a minimum of 20% rock salt content is required in the material mixture for its beneficial properties to appear. The disadvantage of this solution is that rock salt, due to its high dissociation ability, releases a lot of free Cl’ into the environment, which is extremely aggressive in terms of its environmental effects; plants cannot utilize or process it. The electronegativity of ΟΓ is high (according to the Pauling scale: 3.16), and

-2 corrodes when dissolved in water, which causes significant corrosion problems during the treatment technology in the metal (iron) material of the equipment and tanks used for the process, as well as in the metal-containing elements of buildings and cars in the vicinity. The need for increased corrosion protection measures significantly increases the cost of heat treatment equipment. Another problem is that due to the cementation effect of the magnesium and calcium salts in rock salt, the salt turns into a shapeless block of salt after heat treatment. Grinding this requires significant additional work during recycling. Another disadvantage is that due to the relatively high specific gravity of rock salt, a reinforced supporting structure and a higher heat input are required in the solution.

The invention aims to eliminate the disadvantages of the prior art solutions. During the research work leading to the invention, I realized that a development direction opposite to the solution in the above-mentioned Hungarian patent application No. P 08 00358 is desirable. I realized that the NaCl content in the material mixture used for heat treatment, surrounding the wood material, should be minimized. During the experiments, I found that if the NaCl content in the material mixture does not exceed 10% by weight, the harmful effects of NaCl are negligible and do not occur. I also realized that the material mixture must contain at least 5% by weight of a caking inhibitor and at least 20% by weight of a water absorbing/releasing material in order to achieve an effectively manageable and functional solution. According to the invention, it also contains a thermally conductive filler in an amount necessary to achieve the desired volume of the material mixture and to ensure the thermal conductivity of the material mixture, but at least 5% by weight.

The object of the invention is achieved by the mixture of materials according to claim 1 and the method according to claim 8. Preferred embodiments of the invention are defined in the subclaims.

To create the invention, I examined the properties of the cells in wood based on diffusion and osmotic pressure. The woody wall of dead plant cells is permeable to certain solutions and ions present in solutions. According to my theory, with the material mixture according to the invention, the treatment

During -3, the moisture removed from the wood first comes into contact with the solid salts surrounding the wood, hydrolyzing them by breaking their ionic bonds. This creates the possibility for the various anions and cations to enter the cells through the wood cell wall through osmosis and diffusion processes. Here I am primarily thinking of the Na ⁺ , K ⁺ , Ca ⁺ , Mg ⁺ cations and the Cl', PO4 ² ', SO4 ² ' anions.

During the treatment, at a temperature of 80 °C, the moisture content in the wood begins to be removed into the surrounding materials, which hydrolyze with water, and the migration of ions through the cell wall also begins. When extracting water, it is important that it is done gently. Therefore, it is important that, in addition to the mineral salts, an additional water-absorbing/releasing material is also used in the material mixture, which first physically absorbs the water and then releases it as the temperature increases.

During the heat treatment process, water is first extracted from the wood by diffusion and osmosis using a water-absorbing/releasing (i.e. water-soluble, hygroscopic and/or water-binding) material. To effectively implement this process, the material mixture must contain at least 20% by weight of water-absorbing/releasing material.

In the material mixture according to the invention, heat-transferring, heat-conducting materials should also be used to achieve the best possible heat treatment between the heat source and the cellulose-containing wood materials. These materials practically also act as fillers, i.e. they swell the material mixture to the amount and volume necessary to cover the wood material. The amount of this component is adjusted to the actual application and the volume to be used, but to achieve adequate heat transfer, it should be at least 5% by weight.

The material mixture according to the invention also contains an ingredient for preventing the caking of the powdered treatment material. According to my experiments, the material mixture should contain at least 5% by weight of an anti-caking agent in order to avoid caking.

In the heat treatment process with a mixture of materials according to the invention, the solid, i.e. granular or powdery material is covered with the material to be treated.

-4wood material, to block it from air and oxygen. During heat treatment, i.e. thermal modification, water is extracted from the cells through the cell wall, reducing its bound water content. This is made irreversible by subsequently heat treating the wood material at a higher temperature, preferably between 60 - 240 °C for a longer period of time, preferably 6-48 hours.

The water absorbing/releasing material as described above can be, for example, a water-soluble, hygroscopic and/or water-binding material. These are suitably hygroscopic salts, compounds, such as various chlorides, phosphates or carbonates. Magnesium sulfate, sodium sulfate, calcium sulfate, sodium carbonate, sodium acetate, potassium chloride, magnesium chloride, calcium chloride, zeolites, magnesium oxide, silica gel, or any mixture thereof, have proven to be particularly advantageous.

KCI is not hygroscopic, but it is highly soluble in water, so it has good water-binding properties. It does not have as aggressive an effect on the environment as NaCl (it can be processed by plants as a fertilizer), but its corrosive effect on metals is also significant.

MgCI ₂ , CaCfe materials are highly hygroscopic, soluble in water, and have good water-binding properties. They do not have such an aggressive effect on the environment as NaCl (plants can process it as fertilizer), but they also have a corrosive effect on metals. When using them, it should be taken into account that while MgCI ₂ behaves as a weak acid in water, CaCI ₂ is a weak base.

When preparing the mixture, compounds containing the ΟΓ ion should be handled with caution. For the reasons mentioned above, NaCl should be avoided as much as possible. Caution should also be exercised when using other similar compounds, and they should only be used in lower concentrations (5 - 20% by weight).

The thermally conductive filler in the material mixture according to the invention is preferably selected from the following group, or is a mixture of one or more members of the group: sodium sulfate, sodium acetate, calcium chloride, oxide ceramics, aluminum oxide, clinker minerals, talc. As a thermally conductive filler, preferably

-5a material must be used that is itself well soluble in water, possibly even capable of absorbing crystal water. In this way, the development of the water balance of the wood to be treated during heat treatment can also be controlled by the choice of the thermally conductive filler.

Therefore, salts of halides, as well as salts of the radicals SO4 ² ·, PO4 ² ', CO3', SiO ₃ ² ' are less suitable for use as heat transfer fillers. These are not hygroscopic in themselves (they do not bind the moisture content of the air). However, Na ₂ SO ₄ , or K ₂ SO ₄ , which dissociate similarly to sodium acetate, or CaSO ₄ , whose crystal lattice structure is similar to NaCl, are highly effective.

The anti-caking agent, acting on the surfaces, reduces the tendency of the individual particles of the material mixture to stick together and is preferably selected from the following group, or is formed by a mixture of one or more members of the group: oxide ceramics, aluminum oxide, clinker minerals (e.g. Al ₂ O ₃ , Fe ₂ O ₃ +CaO), zeolites, magnesium oxide, talc (ground soapstone), silica gel. In addition to the various aluminates, the above-mentioned silica gel and zeolites also have anti-caking properties.

The following main requirements and guidelines are set for the materials to be used in the material mixture according to the invention:

- The compounds and/or mixtures must be solid between -40°C and +300°C; they must not melt or decompose within this temperature range.

- When composing the material mixture, it must be taken into account whether an acidic, basic or neutral aqueous solution is required.

- The particle size of the compounds and/or mixtures should preferably be selected to be between 10 pm and 20 mm.

- The compounds and/or mixtures must have ideal moisture absorption and retention capacity for this process, so that by setting the appropriate treatment (technological) time, we can remove moisture through the cell walls without damaging them using osmotic pressure.

- The compounds and/or mixtures must be free of knots even after the moisture has been removed from the wood and absorbed and then released by them.

In the treatment process with the inventive material mixture, the wood pieces are surrounded by the material mixture, thus creating an oxygen-poor physical environment. The wood to be treated is preferably surrounded by the material mixture in a tray and pushed into the firebox of a furnace. By gradually increasing the temperature, the free moisture in the wood and the bound moisture in the wood cell structure are removed through the cell walls, avoiding their destruction. After this process is completed, the cell walls are closed by further increasing the temperature to prevent subsequent moisture absorption.

It is preferable to place a 2 - 3 mm thick plate with good thermal conductivity (e.g. aluminum) between the wooden materials placed in the tray, along the entire length of the material to be treated. This avoids local overheating and allows for a more even heat distribution. This solution also significantly improves the efficiency of energy use.

During the heat treatment, the temperature is preferably varied between 60 - 240 °C and the treatment is carried out for a period of 6-48 hours. The process can be batch or continuous.

In my experience, different mineral compounds (salts) and their mixtures have different effects on cellulose-based wood materials during treatment, depending on the temperature. While beech wood treated with a mixture containing predominantly NaCl was of relatively good quality, pine was treated only at an average value. The results were particularly poor with oak and acacia wood. At low temperatures (150-170 °C) with a sodium acetate-silica gel mixture, pine and oak wood showed good results, while the results of beech wood were worse. I achieved better results with beech wood when I added 30% by weight of aluminum oxide to the compounds described above, increased the proportion of silica gel, and increased the temperature.

-7The effect of a certain mixture of materials can be modified by spraying the surface of the mixture of materials covering the wood with a liquid (water). This mixture of materials forms a thin layer on the surface of the mixture with the salts (e.g. CaS04) under the influence of heat, which increases the isolation of the wood from the external environment, and thus reduces the loss of specific gravity of the wood.

Table 1 below contains exemplary materials that can be advantageously used in the material mixture according to the invention.

Thermal Conductive Filler Water absorbing/releasing material Anti-knotting agent Water-soluble substance Hygroscopic material Water-binding agent Magnesium sulfate X X X Sodium sulfate X X Calcium sulfate X X Sodium iodide X X X Sodium bromide X X X Sodium carbonate X X Sodium acetate X X X X Potassium sulfate X X Potassium chloride X Magnesium chloride X X Calcium chloride X X X Oxide ceramics X X Aluminum oxide X X Clinker minerals X X Zeolites X X Magnesium oxide X X Talcum X X Silica gel X X X

Table 1

It can be seen that Table 1 also contains a number of materials that have at least two of the properties of anti-caking, water absorbing/releasing and thermally conductive filler. Materials with these dual properties can be used particularly advantageously in the material mixture according to the invention.

-8I have prepared several advantageous mixtures of materials according to the invention from the materials listed in Table 1, which have been found to have better efficiency and more environmentally friendly properties compared to treatment with rock salt. In the development of advantageous mixtures, the following basic compounds can be used either alone or as a mixture:

- Sodium acetate, silica gel, talc, alumina, calcium sulfate,

magnesium sulfate, sodium carbonate, sodium sulfate.

- Halide salts, potassium chloride, calcium chloride, sodium bromide, sodium iodide.

Example 1 Sodium acetate 20 - 80% by weight Silica gel Talcum 10-40% by weight 10-50% by weight Sodium carbonate 5-20% by weight Example 2 Calcium sulfate 10-40% by weight Sodium carbonate 10-40% by weight Talcum 10-30% by weight Silica gel 20 - 40% by weight Example 3 Magnesium sulfate Aluminum oxide 30 - 50 wt% 10-50 wt% Silica gel 10-70% by weight Example 4 Sodium carbonate 10-40% by weight Magnesium sulfate Calcium sulfate 15-50% by weight 10-40% by weight Talcum 5-25% by weight Aluminum oxide 5-25% by weight

Example -95

Potassium chloride 40 - 80% by weight Aluminum oxide 25 - 45% by weight Magnesium chloride 2-15% by weight Example 6 Sodium acetate 20 - 50% by weight Silica gel Aluminum oxide 20 - 30% by weight 20 - 30% by weight Potassium chloride 5-20% by weight

The mixture of materials according to the following example has proven to be extremely advantageous for all the intended purposes of the invention:

Example 7 Aluminum oxide Sodium acetate Silica gel Calcium sulfate Sodium sulfate

10-20% by weight 25 - 30% by weight 20 - 30% by weight

5-10% by weight

- 30% by weight

The specific gravity of the material mixture according to this latter example is 686.25 kg/m ³ , which is essentially half the specific gravity of NaCl, 1,259.63 kg/m ³ , thus requiring a lower cost support and movement structure and lower heat input.

Regarding the compounds in the examples above, I should note that most of them are non-toxic, and in fact, they are used as additives in quite a few foods. In terms of their environmental impact, they are not dangerous in small quantities.

To achieve the material treatment goals, the optimal material mixture must be selected depending on the type of wood, the intensity of the treatment, the moisture content, and the future properties of the treated wood.

-10The invention is of course not limited to the preferred embodiments described in detail above, but further material mixtures and processes are also possible within the scope of protection defined by the claims. For example, additives and heat distribution-improving components used in a known manner in the field of thermal modification can be added to the material mixture.

Claims (10)

1. A material mixture for heat treatment of wood, for surrounding the wood with the material mixture during heat treatment, which material mixture is in a solid state, characterized in that the material mixture - at least 5% by weight of an anti-caking agent, - at least 20% by weight of water absorbing/releasing material, and - contains a thermally conductive filler in an amount necessary to achieve the desired volume of the material mixture and to ensure the thermal conductivity of the material mixture, but at least 5% by weight, and - the NaCl content of the mixture of substances is maximum 10% by weight. 2. The material mixture according to claim 1, characterized in that it also contains a material that has at least two of the following properties: anti-caking, water absorbing/releasing and thermally conductive filler. 3. A mixture of materials according to claim 1 or 2, characterized in that the water-absorbing/releasing material is a water-soluble, hygroscopic and/or water-binding material. 4. The mixture of materials according to claim 3, characterized in that the water absorbing/releasing material is selected from the following group, or is a mixture of one or more members of the group: magnesium sulfate, sodium sulfate, calcium sulfate, sodium iodide, sodium bromide, sodium carbonate, sodium acetate, potassium sulfate, potassium chloride, magnesium chloride, calcium chloride, zeolites, magnesium oxide, silica gel. 5. The mixture of materials according to claim 1 or 2, characterized in that the anti-caking material is selected from the following group or is a mixture of one or more members of the group: oxide ceramics, alumina, clinker minerals, zeolites, magnesium oxide, talc, silica gel. 6. The material mixture according to claim 1 or 2, characterized in that the thermally conductive filler is selected from the following group, or the group -12 is a mixture of one or more of the following: sodium sulfate, calcium sulfate, sodium acetate, calcium chloride, oxide ceramics, alumina, clinker minerals, talc. 7. The mixture of materials according to claim 2, characterized in that - 10-20% by weight of aluminum oxide as a thermally conductive filler and anti-caking agent, - 25 - 30% by weight of sodium acetate as a thermally conductive filler and water absorbing/releasing agent, - 20 - 30% by weight of silica gel as a water-absorbing/releasing agent and anti-caking agent, - 5-10% by weight of calcium sulfate as a water absorbing/releasing agent, and - contains 20 - 30% by weight of sodium sulfate as a thermally conductive filler and water absorbing/releasing agent. 8. A method for treating wood, in which the wood is covered with a mixture of materials and the covered wood is heat-treated, characterized in that the mixture of materials according to any one of claims 1-7 is used during the method. 9. The method according to claim 8, characterized in that after covering the wood with the material mixture, the surface of the material mixture is sprayed with a liquid, preferably water. 10. The method according to claim 8 or 9, characterized in that the heat treatment is carried out at 60 - 240 °C for a period of 6-48 hours.