HK1189014A - A process and apparatus for modification of lignocellulosic materials and products of modified lignocellulosic materials obtained by the process - Google Patents

Description

Method and apparatus for modification of lignocellulosic material and modified lignocellulosic material product obtained by the method

Technical Field

The present invention relates to a method and apparatus for producing a modified lignocellulosic material by contacting and reacting a lignocellulosic material with a modifier comprising an anhydride and exfoliating the modified lignocellulosic material to remove excess modifier and by-products.

The terms "lignocellulosic" and "lignocellulosic material" are recognized by those skilled in the art of natural products and plant science. These terms refer to any of several closely related substances that make up an essential part of the woody cell wall of plants containing cellulose in close association with lignin and hemicellulose. Carbohydrate polymers of lignocellulose (cellulose and hemicellulose) are firmly bound to lignin by hydrogen and covalent bonds.

Examples of plant materials having great potential as a source of lignocellulosic materials are wood, including soft and hard wood, flax, hemp, jute, coconut shells, cereals and straw. These materials are characterized and known to be very rich in hydroxyl groups. Hydroxyl groups are reactive functional groups that are susceptible to chemical modification with such known chemicals that react with hydroxyl groups. The hydroxyl group is thus readily esterified with a mono-or dicarboxylic acid anhydride or a combination thereof, provided that the anhydride has ready access to the hydroxyl group.

In the description of the invention and in the claims, the pressure "kPag" given as gauge pressure is stated by the appended "table (gauge)" or "g" or by the "absolute" or suffix "a", for example "kPaa".

Technical Field

It is known to modify lignocellulosic materials by acetylation to improve the dimensional stability of the products obtained.

US4804384(Rowel et al) discloses a process for modifying lignocellulosic material by catalyst-free acetylation by the steps of: contacting lignocellulosic material in the form of plies, chips, flakes, fibers or particles with a liquid reactant of acetic anhydride and acetic acid; heating the reactant-contacted lignocellulosic material at a temperature of at most 120 ℃ for 1-5 hours; and removing unreacted acetic anhydride and acetic acid from the resulting acetylated lignocellulosic material. The liquid reactant consists essentially of acetic anhydride and 0 to 55 volume percent acetic acid, preferably 10 to 30 volume percent acetic acid. The contact with the liquid reactant is carried out by simple impregnation. Rowe1 does not teach avoiding contact with ambient moisture and oxygen. Unreacted acetic anhydride and acetic acid may be recovered and added back to the reactant bath until the acetic acid concentration exceeds about 30% by volume.

EP0650998(Nelson et al I) discloses a process for the acetylation of lignocellulosic fibres. Contacting the fiber with an acetylating agent comprising acetic anhydride at a temperature of 70-140 ℃. The acetylated fibers are then contacted with a superheated chemical agent comprising acetic acid and/or acetic anhydride at a temperature above 140 ℃ to remove residual acetic acid or acetic anhydride content to below 10 wt%.

The method includes compacting the fibers with a plug screw feeder to reduce the permeability of the fibers to the gas stream. After injection of preheated acetylating agent of 10wt% acetic acid and 90 wt% acetic anhydride, the compacted fibers were dispersed and fed to a first reactor purged with nitrogen. The first reactor was heated at 120 ℃ and maintained at this temperature during the exothermic acetylation, which was recovered and recycled with the gasification of the acetylating agent containing 70 wt% acetic anhydride.

The acetylated fibers formed from the first reactor contained about 40% by weight of liquid. The fiber was recompacted in another plug screw feeder and then dispersed and treated with superheated steam of acetic anhydride, optionally containing some acetic acid from the recycle stream, at about 190 ℃.

The thus treated fibers are entrained in a superheated vapor stream to a cyclic stripper where the chemicals adsorbed or entrained in the fibers are vaporized. The hot fibers entrained in the distillate from the stripper overhead are recovered in a cyclone. After further stripping in a stripper where any residual acetic anhydride in the fiber is hydrolyzed to acetic acid and the acetic acid is stripped off, the treated fiber is recovered from the overhead with a cyclone.

Based on experiments performed by the present inventors, it was found that fibres treated in a plug screw feeder as suggested in EP0650998(Nelson et al I) were reduced to an undesirably small particle size. The resulting staple fibers having an undesirably short length of about 1mm are thus filtered to produce fibers. Furthermore, the resulting fibers have a very unpleasant odor. Furthermore, the process is very complex and expensive for large scale commercial production.

WO9523168(Nelson et al II) discloses a similar process for acetylation of lignocellulosic material in a first stripper using heated inert gas. The residual amount of acetic acid is said to be 0.5 wt% or less.

WO9619526(Nelson et al III) discloses a further development of the two processes described above, using a superheated acetylating agent comprising at least 20 w/w acetic anhydride at a temperature of 140 ℃ and 220 ℃. The fibers were fed into a narrow chamber (chamber) with a star feeder where oxygen was displaced by purging with nitrogen, followed by spraying with acetic anhydride. To avoid reflux of acetic anhydride, the chamber was maintained at a pressure slightly below atmospheric pressure. The fibers are moved from the chamber to an acetylation reactor where the fibers are treated with superheated acetic anhydride. According to WO9619526(Nelson et al III) the reactor is also a steam jacketed circulation stripper, where adsorbed or entrained chemicals in the acetylated cellulose are evaporated. In the above mentioned process, the acetylated fibres are recovered in a cyclone and stripped once more with steam and recovered in a second cyclone. Several systems for recovering and recycling the acetylating agent are involved in the process, indicating that the agent will contain more than 5 wt% acetic acid in several locations.

WO9409057(Rogers et al) discloses the reaction of lignocellulosic material with acetic anhydride vapor. The reaction is carried out without any co-solvent or added catalyst and without the need for distillation/rectification. The heated, partially dried or dried lignocellulosic material is treated with acetic anhydride vapor. The material is reacted and dried with or without a gas flow. Only acetic acid was removed and further treated with ketene for re-evaporation. The method does not describe essential technical features. Thus, WO9409057(Rogers et al), in particular, does not disclose a limitation on the amount of acetic acid that can be accepted in the anhydride vapor.

US7,413,662(Eriksen et al) discloses an improved sorptive lignocellulosic fibrous material, the hydroxyl groups on the lignocellulosic fibers being doubly modified by esterification with a combination of monocarboxylic and dicarboxylic ester groups. The esterification can be prepared with aliphatic monocarboxylic acid anhydrides and cyclic dicarboxylic acid anhydrides, for example with acetic anhydride and maleic anhydride. The adsorbent fibrous material is very effective for removing oils and other contaminants, including heavy metals, from fluids such as contaminated water by the combined adsorption of hydrophobic contaminants and ion exchange.

US7,413,662 to the applicant discloses the preparation of modified adsorbent lignocellulosic fibre materials on a laboratory scale using maleic acid in a solvent. In order to prepare the fibers on a commercial basis on a large scale, a suitable process needs to be found. Based on the above mentioned US4804384(Rowel et al) and further developments of nelson et al (EP0650998, WO9523168 and WO9619526), experiments performed in pilot plant (pilot) scale were unsuccessful due to several problems. Severe emissions of reactor feed occur. The pressure is out of control and rises to about 200kPag or higher (≈ 300kPaa (absolute) or more). The fibers are separated (defibrated) to an undesirably small particle size. The chemicals were not removed sufficiently and the resulting fibers had an unpleasant odor. Furthermore, the esterification is not efficient leaving most of the-OH groups in the unesterified lignocellulose.

There still appears to be a need for a suitable process and apparatus for the preparation of esterified lignocellulosic materials which meets the following requirements:

efficient and controlled esterification agent migration and its access to reactive-OH groups,

-an efficient and controlled esterification reaction,

efficient and controlled removal of excess esterification agent and by-products,

a commercially acceptable cost, and

-environmentally healthy.

Disclosure of Invention

One aspect of the invention is a process for preparing a modified lignocellulosic material by contacting and reacting a lignocellulosic material with a modifier comprising an anhydride, and exfoliating the modified lignocellulosic material to remove excess modifier and by-products, the process comprising the steps of:

a) introducing the lignocellulosic material into a first activator zone and treating the lignocellulosic material in the first activator zone having an atmosphere of a modifier in the form of a vapor in a gas at a gauge pressure of 0-50kPag and a temperature of 100-,

b) transferring the lignocellulosic material from the first activator zone to a second reactor zone and treating the lignocellulosic material in the second reactor zone with a gaseous atmosphere at a gauge pressure of 0-50kPag and a temperature of 120-,

c) transferring the lignocellulosic material from the second reactor zone to a stripper zone and stripping the lignocellulosic material in the stripper zone with steam or water.

d) Optionally transferred to further processing.

Preferably, the gas is an inert gas such as nitrogen (N)₂)。

In a particularly preferred embodiment, the lignocellulosic material comprises wood chips or larger woody material. It was surprisingly found that the use of wood chips (chips) in the process according to the invention gives particularly satisfactory results in terms of the degree of modification of the material. In other words, the adsorption of the material to the modifying agent is significantly improved compared to prior art processes that have used defibrated materials in the activation and reactor zones. Without wishing to be bound by theory, it is believed that the use of coarser materials, such as wood chips, improves the access of the modifier due to the increased porosity of the overall material. The final product obtained with the process of the invention is therefore characterized by a surprisingly high degree of modification of the lignocellulosic material.

Preferably, the lignocellulosic material comprises extra large wood chips, super thick wood chips, large qualified wood chips and/or small qualified wood chips.

In another embodiment, the lignocellulosic material consists of wood chips.

In another aspect, the present invention relates to a modified lignocellulosic material obtained with the process of the present invention.

Another aspect of the invention is an apparatus for carrying out the method, said apparatus comprising:

a) a closed first activator zone having a first active agent concentration,

means for introducing the virgin cellulosic material to the first activator zone,

means for introducing a modifying agent into the first activator zone,

means for introducing a gas into the first activator zone,

a heating device, and

an outlet for activated lignocellulosic material;

b) a closed second reactor zone in which the first reactor zone,

means for introducing activated lignocellulosic material into the second reactor zone,

means for introducing a gas into the second reactor zone,

a heating device, and

one or more outlets for removing treated (reacted) lignocellulosic material and by-products from the second reactor zone;

c) stripper zone

Means for introducing the reacted lignocellulosic material to the stripper zone,

apparatus for introducing water or steam into the stripper zone, and

one or more outlets for removing the modified lignocellulosic material and byproducts from the stripper zone.

The process of the present invention is more efficient than prior art processes, providing better access of the anhydride to reactive hydroxyl (-OH) groups located on the internal surfaces of pores and capillary channels in the lignocellulose. Furthermore, the required equipment is relatively simple. This makes the process and apparatus of the present invention suitable for cost effective production of modified lignocellulosic fibres on an industrial scale.

The term "reactive hydroxyl group" as used in the present specification and claims means a hydroxyl group that can be esterified by reaction with an acid anhydride.

The term wood chips as used herein is Scan-CM40 as in 2001(Scandinavian pulp, paper and board test committee): 01 classification method as defined in. In this method, a sample of wood chips is placed on the top screen of a stack of 5 sieve trays and one fine particle tray (fines tray). The screen has holes or slots of a specified size and holds the stack in reciprocating motion. After a predetermined time, the screening was stopped, and the obtained six grades were weighed. The size of each grade is its mass, expressed as a percentage of the total weight of all six grades. The term wood chips thus includes extra large wood chips, super thick wood chips, large acceptable wood chips, small acceptable wood chips and small wood chips (pin chips). Fines do not fall within the definition of wood chips as used herein.

Larger wooden objects used here are wooden objects with a size exceeding that of wood chips, such as wood veneers (veneer).

The scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description, the drawings, and the specific examples are included merely for purposes of illustrating preferred embodiments and that various changes and modifications within the scope of protection will be apparent to those skilled in the art based upon the detailed description.

Drawings

The invention is described in detail below with reference to the attached drawing figures, wherein

FIG. 1 is a schematic representation of the process and apparatus of the present invention for preparing a modified lignocellulosic material for Medium Density Fiberboard (MDF), fiber for filtration, oriented structural chipboard (OSB) or chipboard, and

fig. 2 is a schematic diagram of the process and apparatus of the present invention for preparing modified lignocellulosic material for modified plies, sheets or mats.

The following abbreviations are used in FIGS. 1 and 2

LC lignocellulosic materials

ZONE first activator ZONE

MA modifier

ZONE second reactor ZONE

STRIP stripper or stripper zone

H₂O steam or water

Detailed Description

Referring now to fig. 1, which illustrates the general principle of the method and apparatus of the present invention, fig. 1 shows the modification of lignocellulosic material prior to processing into Medium Density Fiberboard (MDF), fiber for filtration, oriented structural chipboard (OSB), or chipboard. Flakes and/or chips of lignocellulosic material LC are fed from a container 1, such as a hopper or batch tank (batch tank), to a first activator zone 3 with a feeding device 2, such as a rotary valve or similar feeding device. Modifier MA in liquid form is fed from a container 4 to the first activator zone 3 by a dosing device 5, such as a sprayer, in controlled doses and at a controlled temperature.

The first activator zone 3 is provided with heating means (not shown) to maintain the temperature of the first activator zone at 100-160 ℃. The first activator zone 3 is purged with a gaseous atmosphere, such as nitrogen, introduced through conduit 6 by nitrogen source 7 to remove oxygen and moisture from the zone. After removal of oxygen and moisture, the introduction of the gas atmosphere is continued to maintain the pressure in the first activator zone at atmospheric pressure or slightly above ambient atmospheric pressure, e.g., 0-50kPa above ambient atmospheric pressure (absolute 100-150 kPa. apprxeq.0-50 kPa).

The dosage of the modifier MA is controlled such that the desired ratio between the reactive-OH groups of the lignocellulosic material LC and the modifier MA is ensured. Further, the temperature of the introduced modifier MA is controlled to ensure that vapor of the modifier is generated in the first activator zone 3. Thus, when equilibrium is obtained, the free space of the first activator zone 3 contains a gaseous atmosphere with a certain content of modifier vapour (MA-vapour).

The lignocellulosic material LC is introduced into the first activator zone from ambient conditions at ambient temperature. The MA-vapour provided in the first activator zone will therefore easily condense on and/or adsorb in the lignocellulosic material LC. Preferably, the temperature of the incoming lignocellulosic material should be close to or preferably below the dew point temperature of the MA-vapour. This promotes condensation and adsorption on the outer and inner surfaces of the porous lignocellulosic material by contact between MA-vapor and the lignocellulosic material. At the bottom of the first activator zone 3 is a drain 8.

After treatment with the modifier MA in the first activator zone, the lignocellulosic material LC is conveyed to the second reactor zone 9. The second reactor zone 9 is provided with heating means (not shown) for heating the temperature to 120 ℃ and 190 ℃ and maintaining the pressure in the second reactor zone at or slightly above ambient atmospheric pressure in a gas atmosphere, for example on the scale of 0-50 kPa. In practice, the two zones 3 and 9 are connected so that the purge gas atmosphere from the source 7 flows through the first and second zones 3 to the second reactor zone 9 via conduit 10 and is returned to the source 7 after removal of oxygen, water and by-products in scrubber 12 via conduit 11. If desired, make-up gas may be introduced directly into the second reactor zone 9 from source 7 via conduit 13. Other ways are possible, but it is important that especially the gaseous atmosphere in the first activator zone is kept substantially free of water, oxygen and hydrated acids. At the bottom of the second reactor zone 9 is a discharge 14.

The first and second zones 3 and 9 are heated by a heating device (not shown). The heating device may be any conventional heating device such as an oil heater or an electric heating mantle. Microwave heating is also contemplated.

After treatment in the second reactor zone 9, the lignocellulosic material LC is conveyed to a stripper zone 15 where it is treated with steam or water H₂O peeling it off. The bottom of stripper zone 15 is connected to a condenser 16 having a drain 17.

After stripping, chips and/or flakes (flake) of the modified lignocellulosic material are transported from the stripper zone 15 to an advanced process 18.

In one embodiment, where applicable to wood chips and/or flakes for use in making MDF or filter fibers, the material is stripped with steam at a temperature of about 100 ℃, e.g., 100 ℃ to 110 ℃. Stripper zone 15 is also a defibrator in this embodiment. The stripper/defibrator thus removes excess modifier and by-products from the material and simultaneously defibrates the material. The conventional preparation process of MDF starts with the decomposition and defibration of lignocellulosic material. Thus, the defibered material exiting stripper zone 15 can be further processed in a conventional manner to obtain MDF. See, for example, WO 2008/030172 (MetsoPanel-board AB).

The modified fiber material exiting the stripper/defibrator zone 15 may also be subjected to a pH adjustment treatment to produce carboxylate anions on pendant groups (pendant groups) formed by modification with dicarboxylic acid anhydrides. This treatment is described in example 6 of US7,413,662(Er iksen et al) and modified fibres are available which can be used as adsorption substrates in devices such as loose mats, filter cartridges, adsorption grids, filtration units etc. where the fibres are active adsorbents for oil or other organic contaminants in water, or as ion exchange materials or as combined cation exchangers and oil adsorbents.

In the case of lignocellulosic material for the production of MDF or filter fibres, the starting material is typically wood chips of a size of 1-4cm x 1-2cm x 0.2-1cm or flakes of a size of 5-10cm x 1-2cm x 0.5-1 or 2 mm. After defibration, the obtained fibers typically have a length of about 4mm and a thickness (diameter) of 0.02-0.04 mm. All these values are mean values.

In another embodiment, the material is stripped with steam in a stripper without a fiber separation device. After optional drying, the material can be further processed in a conventional manner to produce oriented structural chipboard (OSB) or chipboard.

For the preparation of particle board, the average size of the wood chips may vary above or below the above values depending on the source.

The transport of the lignocellulosic material through the first and second zones should be carried out in a closed transport system, suitably selected in view of the physical form of the lignocellulosic material using conventional transport means. Useful conveying devices include screw conveyors, belt conveyors, and conveyor rolls.

Another embodiment of the method and apparatus of the present invention suitable for making modified plies, sheets or laminae is illustrated in fig. 2. The wood veneer, sheet or veneer 101 is moved by a conveying device 123, such as a belt conveyor or a conveyor roll, through a gate or damper 119 into the first activator zone 103, then through a gate or damper 120 into the second reactor zone 109, then through a gate or damper 121 into the stripper 115 zone and finally out of the gate or damper 122.

Similar to the embodiment shown in fig. 1, modifier MA in liquid form is fed with a dosing device 105, such as a nebulizer, from a vessel 104 into the first activator zone 103 at a controlled dose and at a controlled temperature. It is contemplated that the modifying agent is introduced from several sprayers, for example from both sides of the material to be modified in the first activator zone 103 and/or from several locations along the material.

Similar to fig. 1, the first activator zone 103 is provided with heating means (not shown) to maintain the temperature at 100 and 160 ℃. A gas atmosphere, such as nitrogen, is introduced from nitrogen source 107 through conduit 106 to remove any oxygen and moisture and maintain the pressure at or slightly above ambient atmospheric pressure, such as on the scale of 0-50 kPa. The dosage and temperature of the modifier MA are controlled so as to ensure the desired ratio between the reactive-OH groups and MA-vapor generated by MA. The plies, sheets or laminae of lignocellulosic material are introduced into the first activator zone from ambient conditions at ambient temperature, preferably at a temperature below the dew point temperature of the MA-vapor in the first activator zone. The MP-vapor condenses and/or is adsorbed on the outer and inner surfaces of the pores in the plies, sheets or laminae of lignocellulosic material. At the bottom of the first activator zone 103 is a drain 108.

The plies, sheets or sheets from the first activator zone 103 are transported to the second reactor zone 109 through a gate or damper 120. The second reactor zone 109 is provided with heating means (not shown) to heat at a temperature of 120 ℃. 190 ℃ and the pressure of the second reactor zone is maintained at or slightly above ambient atmospheric pressure in a gas atmosphere, for example on the scale of 0-50 kPa. Some gas may be entrained through a lock or damper, but it is generally necessary to introduce make-up gas from the source 107 directly into the second reactor zone 109 through conduit 113. The gas exits the second reactor zone 109 and flows back to the source 107 after removing oxygen, water and byproducts in a scrubber 112 via conduit 111. At the bottom of the second reactor zone 109 is a discharge port 114.

The first and second zones 103 and 109 are heated by a heating device (not shown). The heating device may be any conventional heating device such as an oil heater or an electric heating mantle. Microwave heating is also contemplated.

The veneer, sheet or sheet is transported from the second reactor zone 109 through a lock or damper 121 to a stripper zone 115 where steam or water H is used₂O peeling it off. At the bottom of the stripper zone 115 is connected to a condenser 116 having a drain 117.

After stripping, the plies, sheets or sheets are removed from the stripper zone 115 through a gate or airlock 122 for further processing in conventional equipment 118 for preparing the ply, sheet or sheet product.

The conveying device 123 may be any suitable conveyor, preferably a belt conveyor or a conveyor roller. Preferably, the conveyor is designed to minimize the obstruction of MA-vapor access to both surfaces of the laminate, sheet or lamina. The belt of the belt conveyor may thus be open or may be in the form of a net. In the case of a conveying roller, a sufficient space between adjacent rollers is required.

Several important features have been found for successful modification of lignocellulosic materials. Reactive lignocellulosic hydroxyl (-OH) groups are located on the interior surfaces of pores and capillary channels in lignocellulose. For successful modification, the modifier needs to migrate into these pores and channels, react with the hydroxyl groups so that-in the case of monocarboxylic acid anhydrides-a part is bound to the lignocellulose molecule via the oxygen of the hydroxyl group, another part bound with the hydrogen from the hydroxyl group is released as a by-product and eventually the by-product needs to migrate out of the modified lignocellulose. In the case of cyclic dicarboxylic acid anhydrides, only the excess modifier which has not reacted is released.

When the modifier is a monocarboxylic acid anhydride such as acetic anhydride, the hydroxyl groups of the lignocellulose are acetylated to form acetic acid as a by-product:

lignocellulose-OH + CH₃-CO-O-CO-CH₃→ lignocellulose-O-CO-CH₃+CH₃-COOH

When the modifier is a dicarboxylic anhydride, such as maleic anhydride, after ring opening of the maleic anhydride, the hydroxyl group-O-H in the lignocellulose-O-H leaves its hydrogen atom to form a pendant (pending) carboxyl group, while the carbon atom in the other carbonyl group of the maleic anhydride combines with the-O-group in the lignocellulose-O-to form an ester. The reaction therefore does not release any by-products:

lignocellulosic materials such as wood typically have a water content of 16 to 20 wt%. To ensure efficient migration of the modifier into the pores and channels, it is preferred to remove a substantial portion of the water content prior to introduction into the first activator zone. Thus, the lignocellulosic material may be dried to a water content of 2-10wt%, preferably 3-7 wt%, more preferably 4-6 wt%, for example about 5 wt%. Drying to a moisture content of less than 2 wt.% can lead to structural deterioration, while a moisture content of greater than 10 wt.% can hinder the migration of the modifier.

The ratio between the lignocellulosic material and the modifier is an important feature. When the purpose of the modification is to improve dimensional stability and resistance to bioerosion (attack), a sufficient portion of the reactive hydroxyl groups should be modified. According to general experience, in the case of acetylation, the degree of modification required corresponds to a weight gain of at least 16wt%, based on the dry lignocellulosic material having a water content of 5 wt%.

In most cases, the preferred weight gain is 17 to 25 wt.%, more preferably 19 to 22 wt.%.

It has been found that suitable results are obtained when a modifying agent, such as acetic anhydride, is added to the first activator zone in close to or slightly greater than stoichiometric amounts relative to the reactive hydroxyl groups to be modified. Assuming that only one of the acetic acid moieties is bound to the lignocellulosic molecule, while the others are released as acetic acid, a weight gain of about 20 wt% requires about 40 wt% of acetic anhydride stoichiometrically, i.e. 40g of acetic acid per 100g of lignocellulosic material. The optimal amount can be easily estimated by a person skilled in the art by simple trial and error experiments. The optimum amount is presently considered to be 0.9 to 2.0, preferably 0.95 to 1.5, more preferably 1.0 to 1.3 or 1.05 to 1.2, for example about 1.1, of the amount of the chemical dose. In this way the total amount of unreacted acetic anhydride and liberated acetic acid in excess is kept at the desired minimum.

In the case of the modifier being a dicarboxylic anhydride, the stoichiometric calculation is made as an addition for the pure. Thus a 20% weight gain requires 20g of dicarboxylic anhydride per 100g of lignocellulosic material. Also in the case of dicarboxylic anhydrides, the optimum amount can be easily estimated by the person skilled in the art by simple trial and error tests. In the same way, it is considered that the optimum amount is from 0.9 to 2.0, preferably from 0.95 to 1.5, more preferably from 1.0 to 1.3 or from 1.05 to 1.2, for example about 1.1, of the stoichiometric amount. In this way the excess of unreacted dicarboxylic anhydride is kept at the desired minimum.

As mentioned above, the exact dosage ratio between the lignocellulosic material and the modifier is believed to be very important for successful results, especially when working on an industrial scale. In the examples below, laboratory scale conditions were designed to fit as much as possible to an industrial scale. The stoichiometric amount of acetic anhydride was 1.25 in examples 1, 2 and 5, and the stoichiometric amount of maleic anhydride was 1.5 in examples 3 and 5. It is believed that closer to stoichiometric amounts would be more desirable on an industrial scale.

Another very important feature is the conditions prevailing in the first activator zone when introducing cold lignocellulosic material into the MA-vapour atmosphere in the gas.

The MA-vapor is provided by feeding the modifier in liquid form to the first activator zone where it evaporates almost immediately. Preferably, the amount of MA-vapour (its partial pressure) should be sufficient to bring the dew point of the vapour in the gas atmosphere close to or below the temperature of the externally introduced lignocellulosic material. In this way, MA-vapour will condense to MA-dew and/or be easily adsorbed on the outer and inner surfaces of the lignocellulosic material. This is believed to ensure effective access of the modifier to the reactive hydroxyl groups.

In the case of acetic anhydride, which is liquid at ambient temperature (15-25 ℃), heating of the acetic anhydride at the start of the process in the first activator zone is not required. Obviously, it is possible to generate acetic anhydride vapor or mist to ensure proper contact between the lignocellulosic material and its hydroxyl groups and acetic anhydride. However, particularly when the process is carried out continuously, the temperature within the first activator zone is maintained at 100 ℃ and 160 ℃. Under such conditions, acetic anhydride vapor above ambient temperature should be readily established.

In the case where the melting point of maleic anhydride is 52.8 c, it is heated to at least about 80 c before it can be fed to the first activator zone to provide a vapor, which can condense on and/or be adsorbed by the lignocellulosic material.

Furthermore, the amount of carboxylic acid, e.g. acetic acid, in hydrated form should be kept at a low level, preferably well below 5 wt%, in the modifier added to the first activator zone, as exemplified in WO 96/19526 (Nelson et al III). The boiling points of acetic anhydride and acetic acid are 139.8 ℃ and 118.1 ℃ respectively. This indicates that the acid to anhydride ratio in the condensed dew and/or adsorbed species will be greater than in the vapor. The amount of hydrated acid should therefore be kept as close to zero as possible.

Thus, preferably the modifier introduced into the first activator zone has a hydrated acid content of less than 5 wt%, more preferably less than 3 wt% or 2 wt%, even more preferably less than 1 wt% and indeed most preferably as low as possible, for example 0 wt%.

During activation of the first zone, the main process is believed to be the migration of the anhydride to the site of the reactive hydroxyl groups through the pores and channels. Contrary to the teachings of the prior art, it is believed that the hydrated carboxylic acid should be considered to have a role as a by-product, which, along with any residual water, is a barrier or resistance to migration to hydroxyl groups.

According to the inventors' experience, when the lignocellulosic material is treated under the above mentioned conditions, using about stoichiometric amounts of anhydride substantially free of hydrated acids, under a nitrogen purge, at about atmospheric pressure or slightly above atmospheric pressure and at 120 ℃ for a period of time of 10-20 minutes, for example 15 minutes, ensures effective modification even when the lignocellulosic material is a wood board having a thickness of at most 30 or 50 mm.

Nitrogen pressure is maintained in the second reactor zone and the temperature is raised to 120-190 ℃ preferably at least 145 ℃ in the case of acetylation and at least 165 ℃ in the case of maleic acylation. When other modifiers are used, the optimum temperature can be estimated by simple experimentation. The main processes considered in the reactor zone are the esterification reaction between hydroxyl groups and the modifying agent already located close to the hydroxyl group sites, and the subsequent migration of by-products from this site out of the lignocellulosic material through channels and pores.

In contrast to the prior art, neither anhydride nor hydrated acid is added at this stage. This may also be a barrier or resistance to migration without increasing the degree of esterification as a result.

As with the activation in the first zone, the reaction time in the second zone is relatively short. For example, the reaction may be carried out under the above conditions for 10 to 20 minutes, for example, 15 minutes.

To remove residual excess modifier and byproducts, the modified lignocellulosic material is stripped with steam in a stripper. The temperature of the steam is not critical. Typically 100-. In fact, it is believed that washing in water can adequately remove residual chemicals with unpleasant odors. Of course, such washing with water takes more time. The use of steam in the stripper may be required in cases where some by-products form entrained solids, such as maleic acid formed by hydration of excess maleic anhydride.

The process appears to be faster, more efficient and free of the bad smell found in the products treated according to the prior art compared to the prior art processes. Such products are typically treated over a longer period of time and use an excess of anhydride resulting in a large amount of hydrated acid. As already mentioned above, the inventors have experimented with prior art methods and found that the modification is not effective, probably because the modifier does not reach the position of the hydroxyl group and may be washed out again by peeling. This is not the case by the process of the present invention, by which the modifying groups resist effective steam stripping.

Furthermore, the present method and apparatus are simpler and the method is easier to control, as long as the relevant parameters, as indicated above, are kept within the appropriate ranges, either mentioned in the present application or easily found by routine experimentation.

The modified lignocellulosic material exiting the stripper is in conditions for further processing depending on the intended end use of the product. Possible end products include fiber boards, such as MDF (medium density fiberboard) and OSB (oriented strand board) and similar board standards, filter fibers such as the adsorbent fiber material disclosed in the above-mentioned US7,413,662(Eriksen et al), ply products, and other products based on lignocellulosic materials in the form of fibers, chips, plies, boards or veneers.

In general, the modifier may be selected from any mono-and dicarboxylic acid anhydrides and mixtures thereof which may be introduced into the first activator zone under vapor formation in a gaseous atmosphere. From the vapor, the agent can readily condense on and/or be adsorbed by the lignocellulosic material. Preferably, the dew point of the vapor is below the temperature of the incoming lignocellulosic material, in effect keeping it at ambient temperature prior to treatment.

Suitable anhydrides include, but are not limited to, monocarboxylic acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride, and dicarboxylic acid anhydrides such as maleic anhydride, succinic anhydride, and phthalic anhydride.

As can be seen from the above disclosure, it is important to maintain and control the conditions in the first activator zone under the process of the present invention. The basic atmosphere may be maintained as an inert atmosphere, which requires the continuous introduction of an inert gas such as nitrogen. This will result in a slightly elevated pressure, but to avoid escape of contaminating and/or malodorous compounds, the pressure should be kept as close to ambient pressure as possible. In practice this level is between 0 and 50 kPag.

Furthermore, the introduction and temperature of the modifying agent should be controlled in such a way that a suitable vapour is generated, which vapour should tend to easily condense on and/or be adsorbed by the lignocellulosic material. In each case, the optimum temperature and concentration of the vapor depends on the modifier chosen and can be estimated by simple trial and error tests.

Finally, the introduction of the lignocellulosic material to be modified should be controlled to obtain a suitable ratio between the lignocellulosic material and the modifying agent, which ratio should be such as described above, that the dose of modifying agent introduced into the first activator zone is 0.9-2.0 of the stoichiometric amount of modifying agent calculated on the basis of the reactive hydroxyl groups to be modified in the lignocellulosic material.

To ensure proper control of the process to continue with the lignocellulosic material continuously moving through the zone, the pressure and temperature will be maintained at selected levels, and thus the rate of introduction of the lignocellulosic material, the feed rate, and the temperature of the modifying agent are all controlled using conventional computer systems. In a batch process, similar calculations are required.

In the case of maleic anhydride, the modifier dose introduced into the first activator zone is typically 15 to 25 grams per 100 grams of lignocellulosic material. In the case of acetic anhydride, it is generally from 30 to 50g per 100g of lignocellulosic material.

The temperature in the first activator zone is typically chosen to be 100-160 c, preferably 110-150 c, depending on the actual modifier. Thus, in the case of acetic anhydride, it is preferably 110-. In the case of maleic anhydride (melting point 52.8 ℃), it is preferably 130-150 ℃ and more preferably 135-145 ℃. In case the modifier has a higher melting point, higher temperatures, such as 180 ℃ or even higher, may be suitable.

In the second reactor zone, the base pressure should be maintained at atmospheric pressure, which again requires continuous introduction of gas to obtain a slight increase in pressure. Likewise, the pressure should be kept as close to ambient pressure as possible to avoid escape of contaminating and/or malodorous compounds.

The temperature selected for the second reactor zone should be sufficient to support the reaction and on the other hand low temperatures lead to deterioration of the lignocellulosic material.

The temperature in the second reactor zone is typically chosen to be, depending on the actual modifier, 120-190 c, preferably 130-180 c. Therefore, in the case of acetic anhydride, it is preferably 130-150 ℃ and more preferably 135-145 ℃. In the case of maleic anhydride, it is preferably 140 ℃ and 185 ℃, more preferably 145 ℃ and 170 ℃.

Examples

Example 1

Laboratory experiments were performed to simulate activation in the first activator zone.

5g of acetic anhydride was added to a 500ml spinner flask with a heating mantle. 10g of cold (ambient temperature) lignocellulose fibers (average: about 4mm in length and 0.02-0.04mm in thickness (diameter)) are then added to the flask, and the sample is rapidly heated to about 120 ℃ and maintained at this temperature for 20-25 minutes with moderate rotation.

The sample was stripped conventionally with isopropyl alcohol (IPA) and dried in an oven overnight. The weight gain from 5 test runs was 8-12 wt%, with an average of 10 wt%. About 50% of the modifier (acetic anhydride) reacts with the hydroxyl groups of the lignocellulose, while the acetic acid formed as a by-product and unreacted acetic anhydride are removed by IPA-stripping.

The test was repeated with wood chips for MDF (average: 1-4 cm. times.1-2 cm. times.0.2-1 cm) with a weight gain of 8-12 wt.%.

Similar results were obtained in a 10L flask using 125g of acetic anhydride and 250g of flakes (5-10 cm. times.1-2 cm. times.0.5-2 mm).

Example 2

This example is illustrated by a laboratory experiment showing the two-step process of the present invention incorporating activation in the first activator zone and subsequent reaction as the second reactor zone in a 135-145 ℃ oven.

In the same manner as in example 1, 5g of acetic anhydride was added to a 500ml rotary flask with a heating mantle. Then 10g of cold (ambient) lignocellulosic fibres are added and rapidly heated to about 120 ℃ and the temperature is maintained for 20-25 minutes under moderate rotation.

The sample was transferred to a pre-heated and vented oven and heated at 135-145 ℃ for 20-25 minutes.

The reacted sample was stripped conventionally with isopropyl alcohol (IPA) and dried in an oven overnight. The weight gain from 5 test runs was 18-22 wt%, with an average of 20 wt%. The two-step modification thus appears to be very efficient since almost all of the modifier (acetic anhydride) reacts with the lignocellulosic hydroxyl groups. Thus, acetic anhydride present in the capillary channels and pores, but not reacted at the end of the first activator step, reacts with hydroxyl groups during the second reactor step and is not removed by stripping.

The experiment was repeated with wood chips for MDF with a weight gain of 18-22 wt% and an average of 20 wt%.

In this way, about 4.5kg of flakes for the OSB preparation experiment were obtained with an average weight gain of 19.5 wt%.

Example 3

This example illustrates modification with a dicarboxylic acid anhydride. The maleic anhydride was heated to a temperature of 52 c above its melting point prior to activation.

3g of maleic anhydride was added to a 500ml rotary flask with a heating mantle and heated to 80 ℃ under rotation. 10g of cold (ambient) lignocellulosic fiber was then added to the flask and the sample was heated to about 140 ℃ for about 20-25 minutes under continuous rotation.

The sample was transferred to a preheated and vented oven and heated at 145-165 ℃ for 20-25 minutes.

The reacted sample was stripped conventionally with isopropyl alcohol (IPA) and dried in an oven overnight. The weight gain from 5 test runs was 18-22 wt%, with an average of 20 wt%. This example illustrates that when the modifier is a dicarboxylic anhydride, effective modification is also obtained with the two-step process of the present invention because almost all of the modifier (maleic anhydride) reacts with the lignocellulosic hydroxyl groups.

Similar results were obtained with wood chips used for MDF products, with weight gain of 18-22 wt%, averaging 20%.

Example 4

This example illustrates the double modification using mono-and di-carboxylic acid anhydrides for making absorbent fibers as disclosed in US7,413,662(Eriksen et al).

5g of acetic anhydride and 3g of maleic anhydride were added to a 500ml rotary flask with heating mantle and heated to 80 ℃ under rotation. 10g of cold (ambient temperature) lignocellulosic fiber was then added to the flask and the sample was heated at about 140 ℃ for 20-25 minutes under continuous rotation.

The sample was transferred to a pre-heated and vented oven and heated at 145-165 ℃ for 20-25 minutes and finally stripped as in the previous examples. The weight gain was 3.6g =36 wt% based on total acetylation and maleylation.

Similar results were obtained using wood chips.

Example 5

The test run according to examples 1-4 was repeated using vapor stripping instead of IPA-stripping. Steam at about 100 ℃ was generated in the kettle and transferred through a tube into the reaction flask. After stripping for a few seconds, the condensed water was removed by filtration and the sample was dried overnight in an air-vented oven and weighed. The vapor stripping and IPA-stripping are equally effective.

Similar results were obtained using warm or cold water stripping using acetic anhydride as the modifier, however, with large excess of maleic anhydride, maleic acid crystallization may occur.

The above description of the invention shows that it can be varied in a number of ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims (19)

1. A method of preparing a modified lignocellulosic material by contacting and reacting a lignocellulosic material with a modifier comprising an anhydride, and stripping the modified lignocellulosic material to remove excess modifier and by-products, the method comprising the steps of:

a) introducing the lignocellulosic material into a first activator zone (3) and treating the lignocellulosic material in the first activator zone having an atmosphere of a modifier in the form of a vapor in a gas at a gauge pressure of 0-50kPag and a temperature of 100 ℃ -,

b) transferring the lignocellulosic material from the first activator zone to a second reactor zone (9) and treating the lignocellulosic material in the second reactor zone with a gaseous atmosphere at a gauge pressure of 0-50kPag and a temperature of 120-,

c) transferring said lignocellulosic material from the second reactor zone to a stripper zone (15) and stripping said lignocellulosic material in the stripper zone with steam or water.

d) Optionally transferred to further processing.

2. The method according to claim 1, wherein the lignocellulosic material comprises wood chips.

3. A process according to claim 1 or 2, wherein the lignocellulosic material consists of wood chips.

4. Process according to any one of the preceding claims, wherein the modifier atmosphere in the gas in vapour form comprising one or more anhydrides at a gauge pressure of from 0 to 50kPag and a temperature of from 100 ℃ to 160 ℃ in the first activator zone is maintained by controlling the heating means, introducing the gas and quantitatively introducing the modifier.

5. The process according to any one of the preceding claims, wherein the dosage of the modifier introduced into the first activator zone is 0.9 to 2.0 of the stoichiometric amount of the modifier calculated on the basis of the reactive hydroxyl groups to be modified in the lignocellulosic material.

6. A process according to any one of the preceding claims wherein the modifier introduced into the first activator zone has a hydrated acid content of less than 3 wt%.

7. A process according to any one of the preceding claims wherein the vapour of the modifying agent is generated by spraying the modifying agent in liquid form into the first activator zone.

8. The process according to any one of the preceding claims, wherein the temperature of the lignocellulosic material prior to introduction to the first activator zone is below the dew point of the vapor of the modifying agent.

9. The process according to any one of the preceding claims, wherein the lignocellulosic material introduced to the first zone has been dried to a water content below 7 wt%.

10. A process according to any one of the preceding claims wherein the lignocellulosic material is treated in the first activator zone for 5 to 30 minutes.

11. A process according to any one of the preceding claims wherein the lignocellulosic material is treated in the second reactor zone for 5 to 30 minutes.

12. The process according to any one of the preceding claims, wherein the process is continuous and wherein the lignocellulosic material is passed continuously through the first activator zone, the second reactor zone and the stripper zone.

13. A process according to any of the preceding claims 1-9, wherein the lignocellulosic material is intermittently passed into the first activator zone, then into the second reactor zone and finally into the stripper zone.

14. The process according to any of the preceding claims, wherein the lignocellulosic material in step c) is stripped with steam at a temperature of 100-150 ℃.

15. The process according to any one of the preceding claims, wherein the resulting modified lignocellulosic material has a weight increase of 16-22% compared to the initial, dried lignocellulosic material introduced into the first activator zone.

16. A method according to any one of the preceding claims, wherein the lignocellulosic material comprises wood chips or larger woody material.

17. A modified lignocellulosic material obtainable by the process of any one of the preceding claims.

18. Apparatus for carrying out the method according to any one of claims 1 to 16, said apparatus comprising:

a)

a closed first activator zone (3),

means for introducing lignocellulosic material (1) into the first activator zone,

means for introducing a modifying agent (4) into the first activator zone,

means (6) for introducing a gas into the first activator zone,

a heating device, and

an outlet for activated lignocellulosic material;

b)

a closed second reactor zone (9),

means for introducing activated lignocellulosic material into the second reactor zone,

means (7) for introducing a gas into the second reactor zone,

a heating device, and

one or more outlets for removing treated (reacted) lignocellulosic material and by-products from the second reactor zone;

c)

stripper zone (15)

Means for introducing the reacted lignocellulosic material to the stripper zone,

an apparatus for introducing water or steam into the stripper zone, and

one or more outlets for removing modified lignocellulosic material and by-products from the stripper zone.

19. The device of claim 18, wherein the first activator zone further comprises:

means for adjusting the gauge pressure to 0-50kPag,

a device for adjusting the temperature to 100-140 ℃,

an apparatus for regulating the introduction of the modifying agent,

an apparatus for regulating the introduction of lignocellulosic material, and

a device for mutually adjusting all the above-mentioned devices.