The present invention relates to a method of disrupting fibrous biomass, wherein the biomass without addition of water is treated with an easily liquefiable gas or carbon dioxide under pressure in order to make it absorb the gas in liquid form, and wherein the biomass thus treated is depressurized quickly in order to make the gas evaporate rapidly.

EP-0077287-A2 discloses a method of increasing the chemical and biological reactivity of cellulose- containing materials in order to improve their usability, e.g. as animal feedstuff and as starting material in the fermentation industry. By this known method the cellulose material is treated with a volatile chemical compound, preferably liquid ammonia, at ambient temperature in a pressure vessel, agitation of the mixture of cellulose material and ammonia being performed for e.g. 1/2 h during the treatment. In the course of this treatment, the ammonia penetrates into the cellulose material. By a subsequent rapid depressurization instantaneous evaporation of the ammonia contained in the cellulose material takes place, causing the cellulose material to explode and consequently disrupt. In addition, the ammonia influences the crystallinity of the cellulose material, which additionally contributes to making it more easily accessible by e.g. enzymes, and increases its digestibility.

The known method, wherein a batchwise treatment of the cellulose material is performed, is unsuited for commercial operation, and it is the object of the invention to provide a method of the kind stated in the

preamble which allows continuous preparation of disrupted fibrous biomass.

This object is achieved by the method according to the invention, which method is characterized in that the fibrous biomass through a pressure-tight inlet device is fed into one end of an oblong pressure vessel having means for supply of easily liquefiable gas or carbon dioxide, that the biomass under pressure is advanced from the inlet device to the other end of the pressure vessel where a pressure-tight discharge device is provided, and that upon discharge through the discharge device it is depressurized rapidly under supply of heat.

By using the method according to the invention and by adapting the speed of movement of the fibrous biomass through the pressure vessel to the amount and kind of the biomass and to the amount of gas it is possible to have the biomass sufficiently saturated with said gas when it reaches the discharge device. Consequently, it can, without delay, be discharged from the pressure vessel and depressurized.

Examples of fibrous biomasses, which advantageously can be treated by the method according to the invention, are straw, grass, e.g. in the form of grass pellets or grass meal, alfalfa, e.g. in the form of alfalfa pellets or alfalfa meal, and other products from the green-crop drying industry, and residues formed by extracting oils from plant material, such as rapeseed cakes and crushings.

When grass is used as biomass, it is preferably in the form of chopped, dried grass.

The expression "easily liquefiable gas" is used herein to designate a gas which is liquefiable at 20 °C under a pressure not exceeding 2.5 MPa.

As easily liquefiable gas use is preferably made of ammonia, which boils at -34 °C, and which at 20 °C has a steam pressure of 0.86 MPa. Another example of an easily liquefiable gas is carbon dioxide.

The oblong reactor used in the method according to the invention is preferably a tubular reactor in which one or more helical conveyors are mounted. An apparatus being especially suited for carrying out the method according to the invention, and which is intended for e.g. steam treatment of bagasse in order to extract hemicellulose, lignin and cellulose, is sold under the name The StakeTech System (Stake Technology Limited, Ontario,

Canada) . This apparatus comprises a first tubular reactor with built-in helical conveyor, the tubular reactor at one end being connected with a feed bin, and at the other end with one end of a second tubular reactor which is positioned perpendicularly to the first tubular reactor, and which also has a built-in helical conveyor. A discharge device in the form of a helical conveyor encased in a discharge pipe which extends perpendicularly to the second tubular reactor is provided at the other end of the second tubular reactor. A feed pipe for easily liquefiable gas or carbon dioxide under high pressure, which pipe is equipped with a valve, is provided at the transition between the first and the second tubular reactor.

The starting material is conveyed from the feed bin into the first tubular reactor in which it is compressed by the helical conveyor so as to form a dense plug which is passed towards the site where the gas is introduced at a

high pressure. Here the material is caught by the helical conveyor in the second tubular reactor and passed continuously towards the outlet end thereof, the material being under the influence by the gas under pressure during this advancing movement.

Fibrous biomasses in the form of cellulose-containing materials, generally, contain three main components, viz. cellulose, hemicellulose and lignin, the mutual amounts varying dependent upon the origin of the material. The cellulose is embedded in a matrix of lignin and hemicellulose. By treating the cellulose-containing biomass with volatile, reactive chemical compound, the matrix is weakened or decomposed, and by the succeeding depressurization, which occurs instantaneously when the base-containing material is discharged through the discharge pipe at the other end of the second tubular reactor, a complete or partial disruption of the biomass takes place.

When using ammonia as easily liquefiable gas in the method according to the invention, preferably an internal pressure of 1-4 MPa is established in the reactor, and the apparatus is preferably operated in such a way that the retention time of the fibrous biomass in the reactor is 1-15 min.

In the following the invention is described in more detail, reference being made to the drawing which schematically illustrates an apparatus for carrying out the method according to the invention.

In the drawing, 1 is a feed bin for fibrous cellulose-containing biomass 2. The feed bin 1 is connected with one end of a feed pipe 3 via a dosing pipe 4 in which a helical conveyor 5 is mounted. The other end of the feed pipe 3 communicates with a tubular reactor 6

in which, similarly, a helical conveyor 7 is mounted. The flow of material from the feed pipe 3 to the tubular reactor 6 is controllable by means of a cone 8, the tip of which faces the outlet end of the feed pipe 3. The cone 8, which by means of drive means, not shown, is axially offsettable towards or away from the outlet end of the feed pipe 3, contributes to maintaining a gas impermeable material plug in the feed pipe 3. The tubular reactor 6, which extends perpendicularly to the feed pipe 3, is provided with a supply boss 9 having a valve for supply of ammonia under pressure, as well as a manometer 11.

The helical conveyor 7, which is driven by drive means, not shown, conveys biomass towards the discharge end 12 of the tubular reactor. A discharge pipe 13 is provided at this site, which pipe extends perpendicularly to the tubular reactor 6 and encases a helical conveyor 14, which via a shaft 15 is driven by drive means, not shown. The discharge pipe 13 has a ball valve 16 at its free end.

The mode of operation of the apparatus shown is as follows:

The fibrous, cellulose-containing biomass 2 is conveyed by the helical conveyor 5 into the feed pipe 3, in which it is compressed so as to form a dense plug by suitable adjustment of the cone 8. The formation of such a plug prevents ammonia, which at a pressure of e.g. 2 MPa is introduced into the tubular reactor 6 through the supply boss 9 and the valve 10, from escaping from the reactor 6, and thus can influence the biomass while the latter is conveyed through the tubular reactor 6 towards its discharge end 12. By i.a. controlling the speed of rotation of the helical conveyor 7, the retention time of

the biomass in the tubular reactor 6 can be adjusted according to need, and it is thus obtainable that the biomass, when withdrawn through the discharge pipe 13, is soaked with ammonia.

In the course of the discharge through the ball valve 16, during which the pressure is instantaneously reduced to atmospheric pressure, the ammonia undergoes an explosion-like increase of volume, which causes a disruption of the cellulose-containing parts of the biomass.

Examination of the enzyme solubility of the organic matter by the so-called EFOS method, has, as regards chopped alfalfa and grass powder, demonstrated a solubility increase of more than 10 %, as compared to untreated biomass.