CA1217765B - Method of rendering lignin separable from cellulose and hemicellulose in lignocellulosic material and the product so produced - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Lignocellulosic material is packed in particulate form in a pressure vessel, steam is passed into the pressure vessel at a pressure of at least 500 psi to bring the ligno-cellulosic material to a temperature in the range 185 to 240°C
(preferably in the range 200 to 238°C, more particularly 234°C) in less than 60 seconds (preferably less than 45 seconds) to plasticize the lignocellulosic material. As soon as the ma-terial is plasticized it is extruded through a die to atmo-sphere where abrasion in the die and explosive decompression forms a particulate material like potting soil that rapidly sinks in water and from which the cellulose content is large-ly utilizeable, e.g. as a feed for ruminants. During extru-sion the softened material is subjected to severe deformation and then severe mechanical shock thus fracturing the linkages between lignin, the hemicellulose and the cellulose. The temperature range and rapid rise thereto by the material substantially minimizes degradation of the fragile hemicellu-lose. The process according to the present invention con-verts lignocellulosic material into a substrate which is extremely easy to treat by enzymes, either as a feed for ruminant animals or for conversion to sugars and alcohols and for the solvent extraction of lignin.

Description

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This invention relates to a method of rendering lignin separable from cellulose and hemicellulose in ligno-cellulosic material and the product so produced.
In this specification, rendering lignin separable from hemicellulose and cellulose in lignocellulosic material means that the lignin is capable of being separated from the hemicellulose and cellulose by, e.g., organic solvent extraction.
In United States Patent Number 3,212,932, dated October 19, 1965, "Selective Hydrolysis of Lignocellulose Materials", R. ~7. Hess, A. M. Thomsen, F. Porter and J. ~J.
Anderson, there is described a two stage hydrolysis process for producing pentose sugars and hexose sugars in separate fractions from lignocellulosic materials so that each may be applied as desired in the formulation of stock feed or each may be applied separately to various other commercial uses to which pentose and hexose sugars are applicable. The lignocellulosic materials which may be employed in the selective hydrolysis process of Hess et al comprise those classes of lignocellulosic materials which stem from plant growth processes and are readily available as waste by-products of various industries. Thus they may comprise oat hulls, corn stalks and bagasse. In particular, however, they comprise the woods of various species of trees. The lignocellulosic material requires no special treatment preliminary to its use in the Hess et al process, although it should be reduced to a finely divided state if it already is not present in this 77~

condition. Thus wood may be employed to advantage in the form of sawdust, wood shavings, thin chip flakes, ar.d the like.
In the first stage hydrolysis of the Hess et al process the lignocellulosic material is heated with a first aqueous liquor of such a nature, and under such conditions, as to hydrolyze selectively the hemicellulose content of the lignocellulose, forming pentose sugars as the desired product.
The premixed lignocellulose and aqueous liquor are introduced into a suitable pressure vessel. This may be either a continuous or batch pressure reactor provided with means for heating the charge to the predetermined temperature at the predetermined pressure. As stated before, this may be accomplished by direct steam injection.
~ Jithin the reactor the pressure upon the change is increased as rapidly as possible to a value from 100-700 psi preferably from 250-600 psi, the temperature being increased contemporaneously to the corresponding levels for saturated steam. These conditions are maintained for a relatively brief period of time, sufficient only to convert substantially and selectively the hemicellulose content of the lignocellulose to pentose sugars. In the average case this requires but from 0.3-10 minutes, the time being in substantially inverse relation to the temperature applied. That is, the higher the temperature, the shorter the time, and vice versa.
As a result, there is formed a first liquor product containing a substantial proportion of pentose sugars, together with a small amount of volatile organic acids, such as acetic ~2~77~

acid, as well as the residual mineral acid if a mineral acid is included in the first instance. There also is formed a first solid residue which is substantially free from pentosans and contains predominantly undegraded lignin and undegraded cellulose.
The pressure next is reduced preliminary to sepa~ation of the liquor and solid residue products. ~Jhereas the time required for pressure reductiGn by prior art procedures has been very long, i.e. of the order of several hours, it is important for the success of the presently described process that it be kept at a very low value. Thus there is a substantially instantaneous reduction of pressure resulting in what is termed herein a "flash blowdown". ~Jhere a continuous reactor is employed, the blowdown time is but a few seconds. ~1here a large bath reaction is used, the blowdown time is but a few minutes.
Such a rapid reduction in pressure has several significant effects.
First, it rapidly stops the hydrolytic reaction.
This in turn minimizes the production of hexose sugars from degradation of the cellulose. It also minimizes production of lignin degradation products and prevents the decomposition of the desired sugar products.
Secondly, the flash blowdown evaporates some of the water which is present. The resultant steam then may be employed to advantage in a heat exchange with the material charged in the reactor.

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Third, the fla~h blcwdown flashes off acetic acid, formic acid, or other organic volatiles which may have been formed as by-pro~ucts of the reaction. There thus is provided a built-in operation for separation and removing impurities from the reaction products.
Fourth, the flash blowdown explodes the particles of the solid residue. This makes them porous opening them up for more efficient treatment in the second hydrolytic stage.
In the second stage hydrolysis of the Hess et al process the second stage reactor conditions are more strenuous than those prevailing in the first stage reactor. They have as their object the conversion of the cellulose to hexose sugars without inducing undue degradation of the lignin.
Accordingly the charging liquor to solids ratio is maintained within the broad range of from 1:1-5:1, preferably from 1:1-3:1. The mineral acid concentration of the liquor treating agent is maintained at a level of from 0.3-3.0% by weight.
The reactor is heated indirectly or preferably by the direct injection of steam, until a pressure of 150 to 900 psi preferably from 400-800 psi and corresponding temperatures for saturated steam, are reached.
The reactor is maintained under the foregoing conditions for a time which is substantially inverse relation to the temperature, i.e. the higher the temperature the shorter the time and vice versa. During this time, which is within the 77~

range of from 0.3 to 10 minutes, the cellulose content of the charge is converted substantially selectively to hexose sugars, leavin~ a solid residue containing predominantly unhydrolyzed lignin.
As in the first stage, it is hi~hly desirable to terminate the reaction abruptly in order to evaporate excess water, in order to flash off any organic volatiles which may be present, and in order physically to modify the lignin residue so that it may be filtered and handled more easily.
For these reasons the charge of the reactor is subjected to a flash blowdown as by passing it continuously to a blowdown cyclone apparatus. This reduces the pressure to atmospheric pressure in a matter of but a few seconds.
The steam from the blowdown apparatus is vented while the solid product is washed with water in a second stage extractor. The operation of this extractor results in separating the hexose sugar liquor from the cellulose containing lignin residue, which is recycled or passed to waste.
Thereafter the liquor is treated with a neutralizing agent such as calcium carbonate and any appropriate filter aid, more water is added if necessary and the mixture filtered.
llhile the EIess et al process is a useful contribution to the art the applicant has found that the hydrolysis, which renders the pentose sugars and hexose sugars separable from the lignin in lignocellulosic materials, does so at the expense of loss of useful hemicellulose substances present in lZ~7~

lignocellulosic materials from plant growth products. The acid action of the hydrolysis that is necessary to break down the lignocellulose, progressively destroys the fermentation value of the hemicellulose, so that an undesirably high proportion of the hemicellulose is rendered indigestible by ruminants in the period necessary for hydrolysis of the lignocellulose to have occurred.
There is a need to provide a method of increasing the accessibility of cellulose in lignocellulosic materials wherein the fermentation value of the hemicellulose is largely preserved.
In United States Patents Numbers 3,667,961, dated June 6, 1972, "Process for Improving Digestibility of Feed-stuffs for Ruminant Animals", J. ~J. Algeo and 3,817,786, dated June 18, 1974, "Equipment for Converting the Physical and Complex Molecular Bond Structures of Natural Feedstuffs for Ruminant Animals to Different and Less Complex Molecular Bond Structures Thereof", J. 1~. Algeo, equipment and a process are described for subjecting ruminant animal feedstuffs to high pressure steam in a pressure vessel and effecting explosive release thereof to the atmosphere through a central valve for collection and storage of sponge-like end products which are characterized by their capacity to take up water and digestive juices readily when ingested by a ruminant animal. For cellulosic feedstuffs such as all common roughages including hays, straws and the like, as well as for lignocellulosic feedstuffs such as cottonseed hulls, rice hulls, nut shells or ~Z~L'77~

coffee grounds the steam pressure in the pressure v~ssel is rapidly raised to 500 to 1,000 psi and the temperatures achievec3 therein approximate 470DF (243C) to 5~6~ (285C).
This process may be described as a thermo-mechanical process for treating lignocellulosic materials. It is also applicable to other substances such as grain feedstuffs which are not lignocellulosic and for these substances a temperature range for the steam of between 350F (177C) and 400F (204C) is used.
11hile the Algeo process is undoubtedly a useful contribution to the art is has been found by the applicant that raising the material to a temperature range of 470F (2~3C) to 546F (285C) taught by Algeo drastically reduces the fermentation value of the hemicellulose. As previously stated, a need exists for a method of rendering lignin separable from the cellulose and the hemicellulose contained in lignocellulosic materials of plant growth process, which will, for some uses of the product so produced, largely preserve the fermentation value of the hemicellulose therein and at the same time will increase the accessibility of the alphacellulose therein to enzymatic digestion.
In this specification plant growth species means a soft stemmed or hard stemmed organism wherein organic substances have been produced by photosynthesis. This material is commo~ly referred to as biomass.
Lignocellulosic materials of plant growth processes are created in nature as a three-dimensional composite in which lZ~7~

the cell~lose, hemicelluLose and the lignin polymers are intim~tely mixed in a complex structure which varies from one plant growth species to another ancl with age for a particular species. Lignin is an amorphous three-dimensional polymer, each macromolecule of w~ich is built up from several hundred phenyl propane units linked in various ways. The lignin, probably in compound with the hemicellulose, permeates the matrix of cellulose microfibrils in the cell walls and largely fills the spaces between the cells. X-ray crystallographic eviAence suggests that because the cellulose microfibrils constitute a separately crystalline phase, the lignin is more intimately cross-linked with the hemicellulose than with the alphacellulose.
Dry cellulose of plant growth has a softening or glassification temperature of 230C and because of its crystalline nature, this temperature is not much reduced by the presence of moisture. In contrast, the hemicellulose and lignin of plant growth soften at 120-180C and because these materials are non-crystalline, their softening temperatures vary with moisture and pressure. The polymers of plant growth are formed in definite morphological patterns and are interconnected by covalent bonds which can be likened to "spot welds" and it is these "spot welds" which produce the well-known and persistent association between lignin and the hemicelluloses of plant growth. In a spot welded composite of macromolecules of plant growth, the thermal softening is dominated by the behaviour of the cellulose component. Even -- ~3 --77~, when sorbed moisture lowers the transition temperature of the amorphous constituents, the material retains its rigidity up to temperatures near 230C (446F) because of the over-riding effect of the cellulose frame-work which is not plasticized by water molecules.
The lignocellulosic composite of plant growth represents a hindrance to an enzyme or rumen microflora trying to break down cellulose and hemicellulose to simple sugars.
Lignocellulosic materials vary in their degree of cross-linkage. In order to improve digestibility these lignin-carbohydrate bonds, chemical and/or physical need to be broken.
It is another object of some embodiments of the present invention to provide a thermo-mechanical process for rendering lignin separable from cellulose and hemicellulose in lignocellulosic material with negligible loss of the fermentation value of hemicellulose substances.
According to one aspect of the present invention there is provided a method of rendering lignin separable from cellulose and hemicellulose in lignocellulosic material, comprising:
a) packing the lignocellulosic material in a divided, e~posed, moist form in a pressure vessel having a valved outlet, b) with the valve closed, rapidly filling the pressure vessel with steam at a pressure of at least 500 psi to bring the lignocellulosic material to a temperature in the ~177~

range 185 to 240C in less than 60 seconds to thermally soften the lignocellulosic material into a plastic condition, and c) as soon as the said plastic condition has been attained, opening the valved outlet and instantly and explosively expelling the lignocellulosic material in the said plastic condition from the pressure vessel through the outlet to atmosphere so that the said material issues from the outlet in particulate form with lignin therein rendered into particles substantiall~ in the range 1 to 10 microns and separable from the cellulose and hemicellulose the particulate lignin and cellulose being together in disassociated form having the appearance of potting soil, a major portion of the lignin being soluble in methanol or ethanol and being thermoplastic, the cellulose being in the form of crystalline alpha cellulose microfibrils and suitable for digestion by microorganisms and enzymes.
Preferably the lignocellulosic material is extruded on to an impinging surface.
In preferred embodiments of the present invention the lignocellulosic material is brought to a temperature in the range 200 to 238C in less than 45 seconds.
In some embodiments of the present invention the process is repeated at least once more with the lignocellulosic material at a temperature no greater than that at which the 7~

lignocellulosic material was treated for the first time in steps b) and c).
In some embodiments of the present invention the lignin is solvent extracted from the particulate material that has issued from the outlet, preferably by a solvent selected from the group consisting of ethanol, methanol and acetone.
~ Jet alcohol insolubles may be separated from the particulate material by alcohol prior to lignin extraction therefrom by acetone.
Uater solubles may be extracted from the particulate material by water before or after lignin has been solvent extracted therefrom.
The solvent extracted lignin may be in particulate form with particles substantially in the range 1 to 10 microns, have a purity of the order of 93 weight ~, be readily reactive chemically, be thermoplastic, and have an infrared spectrum approaching that of so-called native lignin.
Hemicellulose may be extracted from the lignocellu-losic material by hydrolysis with hot water prior to packing the lignocellulosic material in the pressure vessel.
Preferably when the lignocellulosic material is wood, the pressure vessel is rapidly filled with steam at a pressure in the range 600 to 700 psi to minimize hydrolysis.
More particularly when the lignocellulosic material is wood, the pressure vessel is preferably rapidly filled with steam at a pressure in the region 650 psi.

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Preferably when the lignocellulosic material is annual plant material, the pressure vessel is rapidly filled with a steam at a pressure in the range 500 to 600 psi, more particularly in the region 550 psi.
In some embodiments of the present invention, the lignocellulosic material in finely divided form is moist with water, in the region of fibre saturation, when packed in the pressure vessel.
In some embodiments of the present invention, when the lignocellulosic material :is annual plant substance, the pressure vessel is rapidly filled with steam at a pressure in the region of 550 psi, after approximately 40 seconds the steam pressure is rapidly increased to a higher pressure and the material is explosively expelled immediately upon achieving said higher pressures.
According to a second aspect of the present invention, there is provided the product in particulate form produced by the method according to the present invention.
The product according to the present invention has the desirable characteristics that a significant portion Gf the alphacellulose that was present in the lignocellulosic material is now accessible in a digestible form for microorganism digestion while minimal decrease in the fermentation value or content of hemicellulose that was present in the lignocellulosic material is found to have occurred. Thus the product is useful:
i) as a feed for ruminants, ~Z177~

ii) for the enzymatic production of sugars, iii) for the conversion to alcohol using microbiological or chemical or both means.
The product of the present invention also has the desirable characteristics that:
a) a major portion of the sugars of the hemicellulose are removable therefrom by, for example, hot water, and b) a major portion of the lignin is removable therefrom by solvent extraction, for example, using ethanol, methanol or acetone leaving a cellulose rich material for use, for example, as pulp in a cellulose derivative process or to be directly solubilized using an appropriate cellulose solvent.
In this specification "lignocellulosic material"
includes such plant growth materials as oat hulls, corn stalks, bagasse, wheat straw, rice straw, oat straw, barley straw, and woods of various species, particularly hardwoods.
In the accompanying drawings, Figure 1 is a sectional side view of a pressure vessel having an extrusion die outlet and which has been used to verify the present invention, Figure 2 is a graph showing the rate at which reducing sugar is released by hydrolysis from products produced by the extrusion process, Figure 3 is a graph of enzyme digestibility of reducing substances such as glucose produced by different temperatures at which the lignocellulosic material is extruded, Figure 4 is a graph of the enzyme digestibility of ~2~77~

the sugar content produced by different temperatures at which the lignocellulosic material is extruded, Figures 5 to 8 are scanning electron micrographs of products according to the present invention produced usi.ng the apparatus shown in Figure 1, Figure 9 is a flow diagram for solvent extraction of lignin from treated aspen wood, Figure 10 is a flow diagram for solvent extraction of lignin from treated barley straw, Figure 11 is a flow diagram for solvent extraction of lignin from treated aspen wood or barley straw using acetone as the solvent, and Figure 12 is a flow diagram of the acetone extraction of lignin from, for example, treated wood or straw.
In Figure 1 there is shown a pressure vessel 2 having a valved outlet which in the embodiment illustrated is a star-shaped extrusion die outlet 4, an extrusion die closure plug 6, a loading.end closure flap 8 and steam inlet orifices 10 to 12.
The pressure vessel 2 has a bottle neck portion 14 leading to the die 4 and entry ports 16 and 18 for temperature probes (not shown).
The front end of the pressure vessel 2 containing the die outlet 4 has a flange 20 to which is sealed a curved impinging tube 22 which gradually reduces in cross-section in a downstream direction. The curved impinging tube 22 has a spindle inlet sleeve 24 provided with a flange 26. A pneumatic f 7~

ram 28 is attached to the flange 26 and has a die closure plug 30 mounted on the spindle 32 of the ram 26.
The rear end of the pressure vessel 2 is sealed to the remainder by flanges 36 and 38 and has the loading end closure flap 8 hinged thereto by a hinge 40 and sealable therewith by a clamp 42.
In operation the loading end closure flap 8 is opened and the pressure vessel 2 is loaded with lignocellulosic material in a divided form with the die closure plug 30 closing the die outlet 4. A rod tnot shown) is used to pack the lignocellulosic material in the pressure vessel 2.
~ith the pressure vessel 2 completely filled with lignocellulosic material the die closure plug 30 is sealed by the pneumatic ram 28 and the closure plug 8 is sealed to the rear end 34 by the clamp 42 and then the pressure vessel is filled with steam at a pressure of at least 500 psi, preferably in the range 500 to 700 psi, and at a sufficient temperature to raise the temperature of the lignocellulosic material to a temperature in the range 185 to 240C, preferably 200 to 238C
and in particular 234C, in less than 60 seconds (preferably less than ~5 seconds), to plasticize the hemicellulose and the lignin in the lignocellulosic material so that the lignocellulosic material is thermally softened into an extrudable condition, by injecting steam into the steam inlet orifices 10 to 12 from a source (not shown). The temperature probes (not shown) in the ports 16 and 18 are used to monitor the temperature of the lignocellulosic material in the 7~

pressure vessel 2 to de~ermine when the lignocellulosic material has reached the chosen temperature.
As soon as the lignocellulosic material in the pressure vessel 2 reaches the desired temperature the pneumatic ram 28 is actuated to withdraw the closure plug 30 and more or less instantaneously open the die outlet 4 to atmosphere so that the lignocellulosic material is extruded through the die outlet 4 in the plasticized condition and at the extrusion pressure and is flashed to atmosphere preferably in milli-seconds along the curved impinging tube 22. This sudden release to atmosphere explosively expels the lignocellulosic material in the plasticized condition at the pressure preferably in the region of 500 to 700 lbs. per square inch and produces a particulate material having the appearance of potting soil which stains the fingers brown and has a high enough specific gravity to sink like a stone in water.
~ 1hile the curved impinging tube is not essential it has the advantage of utilizing some of the extrusion force to further comminute the lignocellulosic material in addition to the comminution obtained by extrusion.
A possible explanation of the present invention is that with the lignocellulosic material in the plasticized condition the lignin, hemicellulose and cellulose are softened and thereby structurally weakened so that during extrusion the softened material is subjected to severe mechanical shock which has the effect of fracturing the cross links between the lignin, the hemicellulose and the cellulose. As the weakened 7~

and fractured lignocellulosic material emerges from the die outlet 4 the instantaneous drop in pressure causes the weakened and fractured lignocellulosic material to explode, thereby degrading the hemicellulose to a low molecular weight and at the same time causing substantial degradation of the main fibre structure, which in turn exposes substantial areas of the alphacellulose microfibrils for, in some uses of the present invention, attack by the fermentation agent.
The basic crystalline structure of the cellulose microfibrils is retained. A very high degree of disassociation of the lignin is achieved. ~hen the process is carried out at a temperature above the upper temperature of 243C the xylose component decomposes, probably to furfural, and valuable digestible matter is lost from the substrate. Also, decomposition causes toxicity to microorganisms. One objective of this process is to make the alphacellulose highly accessible to the microorganism minimizing the effect of hydrolysis on the hemicellulose, thus it is important that the time to achieve temperature should not exceed 1 minute and better still, should be in the range of 30 to 50 seconds. Pressure is not critical except as it affects the time to achieve the optimum temperature of 220-230C. The process can be repeated at least once more at the same or lower temperatures and will produce a further increment or increments in improvement in the digestibility.

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Tests to verify the present invention were carried out using apparatus shown in Figure 1 having the following dimensions:
Internal diameter of major portion of the pressure vessel 2 = 7~ inches (190.5 mm), Smallest internal diameter of bottle-necked portion of the pressure vessel 2 = 31~ inches (82.5 mm), Length of the interior of the pressure vessel 2 =
45 inches (1.14 m), Bore of each steam inlet 10 and 12 = 1~ inch (19 mm), Bore of steam inlet 11 = 2 inches (50.8 mm), The orifice of the die outlet was star-shaped with five equally spaced points giving a cross-sectional area of 0.8 square inches (11.6 square mm).
In the following Tables I to V the temperature is the temperature of the material in the pressure vessel 2 when the closure plug 30 is removed, and the steam pressure is the steam pressure in the pressure vessel 2 at this moment. The time is the time in which temperature o~ the lignocellulosic material was raised to the temperature indicated and then extruded from the pressure vessel 2. The tables show the results of tests of products of the present invention compared with tests carried out at temperatures that are greater than those according to the present invention. In the tests digestibility was evaluated in two ways, _ vitro and in vivo testing with ruminant animal microflora, and secondly by treatment with a ~2~77~

cellulase enzyme and the results are given in Tables I to V
respectively.
In all of the tables the same lignocellulosic product tested is designated in the same manner, for example, in each test A designates the same lignocellulosic material and so on.

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_20 _ ~ 7~3 It will be seen from Table I that with material temperatures above about 240C there is a drastic drop in the alphacellulose digestibility and as this represents approximately 65% by weight of the total digestible carbo-hydrate present in the starting material it is necessary for this to be high.
Analysis shows (see Figure 4 where sugar content, arbitrary units, is plotted against temperature in C) that the alphacellulose has not been destroyed by this treatment, therefore the loss in digestibility in vitro by animal rumen is caused by some extraneous factor.

A CHEMICAL CHARACTERIZATION OF TREATED ~IOOD CHIPS
The main objective of the following study was to compare the effects of the process under different reaction conditions. The experiments conducted were of an exploratory nature and the samples used were those obtained in tests A to D, and also processed aspen and processed barley straw which were fed to sheep in a digestibility trial. These tests covered a broad range of reaction conditions. The results of the analysis are displayed in Tables~II to IV.
In general, the results of the study will be seen to indicate that these samples can be classified into two categories;
ood that has been treated according to the present invention at temperatures below 240C (A, B and C).

i~77~'!,j 2. ~ood that has been treated at temperatures above 240~C (D and IJood as Fed).
The samples in the first category appear to be a better source for carbohydrate material than the second category because the high temperatures required to produce the second group have resulted in the extensive decomposition of pentose sugars present in the wood.

METHODS
Sample Preparation The samples (A, B, C, D and llood as Fed) were dried at 105 overnight to a constant weight. Samples (10 g) were extracted with water using Soxhlet extractors for 18 hrs. The wood fibre was dried and the weight of extracted sùbstance was determined. The water extract was diluted to 250 ml and analyses were performed on aliquots of this extract.
Analytical Methods Used on Samples Total carbohydrate was determined by the phenol-sulfuric acid colorimetric method (M. Dubois et al, Anal.
Chem. 28 t3) 350, (1956)); reducing sugar was determined by the Somogyi micro copper titrimetric method (Methods in Carbohydrate Chemistry, Vol. I, page 380, 1962, Academic Press Inc.); and total sugars by gas chromatography were determined after hydrolysis using Tappi method T249 pm-75.

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TABLE III
ANALYSIS OF HOT WATER EXTRACTABLES

SAMPLE TOTAL % BY WEIGHTl % BY WEIGHT OF2 TOTAL ~ BY WEIGHT

CHROMATOGRAPHY

A 56.7~ 27.7% 36.6%
B 47.5% 25.8% 40.4%
C 44.5% 27.4% 36.1%
D 24.2% 23.6% 15.8%
Wood as 9.1% 9.0% 12.4%
fed 1 Total carbohydrate determined by Phenol-Sulfuric acid colorimetric method using glucose as a reference sugar.
2 Reducing sugar determined by Somogyi Micro Copper Method.
3 Total sugar determined after hydrolysis by gas chromatography using Tappi method T249 pm-75.

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DISCUSSION
The p~l values of the samples ranged from 3.6 to 4.1.
This range is considered normal for samples from wood substance treated with high pressure ste~n (600 psi). Under the reaction conditions listed in the introduction the acetyl groups present in the wood would be expected to undergo hydrolysis releasing acetic acid which would decrease the pEI (i.e. increase the acidity). This acidity would assist in hydrolyzing the lignocellulosic material and increasing the water extractable material in the wood.
The processes are shown to have solubilized 18 to 34~
of the wood substance (Table II). 1700d is normally composed of 2 to 3% water solubles. The samples in catégory l (A, B and C) have water extractables ranging from 29.0 to 34.7~ whereas samples in category 2 tD and llood as Fed) have only 18.1 to 21.6~. The lower percentages of extractables in category 2 have resultea from the decomposition of carbohydrate material (pentose sugars) because of the high reaction temperature.
For samples in category 1, the reducing sugar content of the extract is approximately half of the total carbohydrate content (Table III). This indicates that the carbohydrate material present has an average degree of pol~nerization of 2.
For samples in category 2, the reducing sugar content of the extract is nearly equal to the total carbohydrate content.
This indicates that all the solubilized carbohydrate material has been converted to monomers.

~"f 7~

The gas chromatographic analysis of sugars present in the water extractables is tabulated in Table IV. All samples tested have approximately the same quantity of hexose sugars (mannose, galactose, glucose) but samples D and ~700d as Fed have much lower pentose sugar contents (arabinose and xylose) than the other samples which were treated at lower temperatures. These results indicate that at a temperature between 238C and 246C there exists a transition point (range) for the destruction of pentose sugars. Above this temperature pentose sugars are destroyed by decomposition to furfural.
Thus, wood fibre treated above this transition temperature has a lower fraction of water soluble extractables than samples treated below this transition point because the furfural produced by the decomposition of pentose sugar is "flashed off"
during the explosion process. The decomposition of hexose sugars does not appear to be a problem at the temperatures tested mainly because of their higher stability to thermal decomposition.
Destruction of pentose sugars above the transition temperature reduces the quantity of sugars available for digestion by approximately 10% based on treated wood weight.
Analysis of the water soluble extractives shows that above the transition temperature only 2 to 3% of fibre weight is composed of solubilized carbohydrate (e.g. D and ~700d as Fed) but below the transition temperature 10 to 14% of fibre weight is composed of solubilized carbohydrate (e.g. A; B and C). This weight (sugar) loss was caused by the destruction of xylose and 7~

arabinose. This loss of 10% of wood weight carbohydrate material is supportea by further studies, ~lood as Fed (treated at 246C) was found to have a final reducing sugar value of 33.8~ after digestion for 2~ hrs with Maxazyme (a commercial Trichoderma viride cellulase) whereas all other wood samples (treated below 238C~ had reducing values hetween 42.8% and 47.4~. Sample D was not tested in this manner.
Treated wood samples were hydrolyzed with 2N
H2So4 at 100C to determine if a chemical method could be used to correlate digestibility with the rate of carbohydrate release on hydrolysis. The results of this study are shown in Figure 2 where the ~ by weight reducing sugar by weight of dry product (RS) is plotted against the digestibility time in minutes (TM).
In Figure 2 the graphs designate:
x x is sample A in Table IV
~ is sample B in Table IV
0 - - - 0 is sample C in Table IV
+ + is sample D in Table IV, and ~ ~ is wood was fed (Aspen) in Table IV.
Samples, D and ~700d as Fed, have reducing values slightly lower than the other three samples probably because the pentose sugars in these two samples have been decomposed and are not available for hydrolysis. The difference in final ; reducing value (2 hrs) and the rate of sugar release indicate that approximately the same amount of cellulose is exposed in the wood fibre of each sample (i.e. the accessibility of each i~7 7~g fibre to acid is the same for all samples). Since the accessibility of the cellulose is the same, it may be expected that the digestibility of the fibre will be the same but this may not necessarily be true since the approach of a cellulose enzyme to a cellulose fibril may be much more restricted than an acid.

CONCLUSIONS
1. The treatment of wood chips with high pressure steam results in hydrolysis of acetyl groups and degradation of hemicellulose present in wood, releasing acetic and uronic acid.
2. Treatment of hardwood chips by the extrusion process renders 18 to 34% by weiqht of the wood substance hot water extractable.
3. Solubilized carbohydrate material appears to exist in the form of monomers and dimers.

4. The Applicant's temperature of approximately 240C appears to be the transition point, above which substantial decomposition of the pentose sugars takes place.

5. Destruction of pentose sugars above this transition point reduces the quantity of sugars available for digestion by approximately 10% of the treated wood weight.

6. The portion of "exposed" cellulose on the surface of the exploded fibre appears to be roughly the same in all samples tested.

~Z~7~

An enzyme digestibility characterization of treated wood chips The following Table V gives the results of measurements of enzymatic digestibility by Trichoderma viride cellulase of an aqueous suspension of the product.

7~

h O
, 0 0 U~
00 ~ 0~ 0 ,1 ~_~

~ ~ ~ 3 a~
H . ,~
~ o ~ ~ O
~Ll ~ ~ Q ~_) E~ ~ N
a --a tn U~
~ a) I
C..) Q r~ ~
O ~ ~) 1~; 0 3--`
4 ~1 0 Q a o ~ ~
O
~ ~-- U~
P ~ tJl N O U~ .--I ~ ~D U~ U') H ~ ~ ~ O
W ~-:1 ~ (1) 0 ~:1 1-l a~ m ~¢ ~1 ~a h U~

U~

~ ~ I
c~ 0 ~ s~
æ a~
,~E~ .
~ a o aJ
u~ ~lE-~ 3~1 a ~ ~1 0 r-l O
u~ ~0 ~ ~ 1_ ~ ~ ~ ~ ~ ~r ~I ~ ~ ~ ~ ~ ~ ~ a~
h (11 a ~ o o o o u~ o o In I
E~O _ _ _ _ _ _ _ -- -- a 0 *
~ m c~
E~
E

u~ a) U~ ~ 0 ~: ~ a) 3 3'~J S
Q- O ~ h h h IL~
U~ O
3 m u~

~2~77~

Enzymic digestion conditions: 1% by volume of aqueous suspension Pulp consistency: 0.5~ by volume of aqueous suspension pEI of aqueous suspension: 5.0 Temperature of aqueous suspension: 30C
Incubation: continuous mixing Time: 24 hrs, (1 hr) Figure 3 is based on the results shown in Table V and shows the % by weight of dry product of reducing substances (RS%) derived such as, for example, glucose, plotted against the temperature (TEMPC) at which the lignocellulosic material was extruded.
In Figure 3 the graphs designate:
after digestion by digestion only before digestion.
Figure 4 is based on the results shown in Table V and shows the sugar contents in arbitrary units (SC) after enzymic digestion plotted against the temperature (TEMPC) at which the lignocellulosic material was extruded.
In Figure 4 the graphs designate:
- hexoses - pentoses.
The Figures 3 and 4 show that the yield of hexoses remains unaffected by the temperature at which the lignocellulosic material is extruded while the yield of ,. .~

lZl~'`7~g pentoses starts dropping rapidly towards zero at temperatures greater than 240C. These results compare very well with the results given in the previous tests.
In Table V, Test F was double processed at both temperatures shown and this further improved the digestibility.
Tests have shown that a die having an orifice cross-sectional area of 0.8 square inches works well. However, any valved outlet that is sufficiently narrow in diameter to permit an explosive discharge and mechanical working of the plasticized lignocellulosic mass during discharge adequate to produce the product described may be used. The shape of the die orifice is not important but a star-shaped orifice has been found to give a large boundary to cross-sectional area so that a large amount of mechanical deformation occurs with good fracturing of the cross-links between the lignin, the hemicellulose and the cellulose.
A preferred temperature range is 200 to 234C, particularly 234C.
The following rnorphological analyses were conducted on treated aspen wood and barley straw:
- Freeze-drying, to determine the moisture content of the samples while maintaining their structure.
- Optic microscopic observation of the freeze-dried products.
- Boiling water extraction for 24 hours.

i;~l771~

- Stereotypic diffraction by X-rays of the ori~inal products, of the freeze-dried product, and of the extraction residue.
- Observation of the freeze-dried result by a scanning electron microscope.
l. Freeze-Drying -SAMPLE MOISTURE CONTENT
Aspen llood 48.8% by weight Barley Straw 45.3% by weight After freeze-drying, the dark brown colour of each of the two samples brightens and reveals grayish reflections.
The strong and acidic odor is characteristic of carbonized sugars and carbohydrates.
2. Optic Microscopic Observations of Freeze-Dried Samples The fibrillar structure of cellulose is recognizable, but the fibres are distinctly slashed. It appears that the fibres have been striated or split during treatment; their characteristic features (lumen, punctuations) are still visible. To recognize the leafy nature of wood used, by the presence of wood vessels, is possible.

3. Extraction with H 0, 100C, 24 hrs This extraction is done with the help of a soxhlet tube, under water reflux at 100C for 24 hours. In fact after 24 hours, the extraction appears total since the extracted solution in the last cycles is limpid.
Aspen llood 30.0% extracted Barley Straw 26.8% extracted ~ Z~77~ ~

Note: The sample's characteristic odor has lessened in the extracted residues, but t~e colour seems identical. The carbohydrates and the weak chains of lignin have passed into solution, but the residue contains much more lignin, insoluble in water at lOO~C. In brief:
Residue = cellulose + long chains of hemicellulose + lignin Extract = carbohydrates from hemicellulose hydrolysis + already carbonized sugars ~ a few traces of lignin.
The cold extracted solution is coloured, but also contains a large percentage of non-dissolved matter.
4. X-Ray Analysis Cellulose is found in crystalline form in the crude products, the freeze-dried products and the extracted residues.
This confirms the presence of long cellulose chains (in the form of more or less slashed fibers after sustained treatments).
There was no significant difference between samples of processed Aspen ~700d and Barley Staw.
5. Scanning Electron Microscope In Figures 5 to 8 there are shown electron micrographs of the freeze-dried products of Table V and they represent: ~700d as Fed (x 1,350), ~lood as Fed (x 2,640), Straw as Fed (x 6,380) and Straw as Fed (x 2,760), respectively.
These micrographs demonstrate the high accessibility of the alphacellulose microfibrils, as well as the degree of lignin separation, demonstrated by the spheres of lignin spread throughout the material.

77~

From the Figures 5 to ~ of each of the freeze-dried samples, it will be observed that lengthwise torn fiber fragments are visible. The spherical particles, probably lignin, have been expelled from the fibers and have been ejected as small droplets, during processing.
Conclusions from the Morphological Analyses The greater accessibility of fibers due to "tears"
and cleavages of the secondary wall explains the increased enzymatic accessibility which occurs in the processed material.
In fact, the specific surface area of fibers distinctly increases (wall cleavage).
This cleavage seems to be due to the bursting of the middle lamella; the lignin is then expelled, and thereby disassociated from the walls.
~ n the other hand, at the microfibrillar level, the cellulose crystallinity is preserved as deduced from X-ray diffraction analysis.

A further test was conducted to investigate the feasibility of leaching of lignin from treated aspen wood and barley straw using ethyl alcohol, and to measure the lignin yields of such extractions.
As shown in Figure 9, treated wet aspen wood (55% by weight moisture), designated ~AP, was equally divided into two portions. Each portion was extracted three times with 95~
ethanol at room temperature (methanol may also be used as well as other related solvents). The mixture was stirred ~77~

continuously in a plastic container with an air operated impeller. The extraction duration and volume of ethanol used were as follows:
1st Extraction: 12 liters, 0.5 hr 2nd Extraction: 12 liters, 2 hrs 3rd Extraction: 7 liters, 2 hrs.
The dark alcohol extract (fraction No. 1), designated Fl was in the form of wet alcohol solubles and was filtered, centrifuged in a centrifuge designated C, and then concentrated down to a thick black solution. Sediments from the centrifuge bottles were washed with fresh ethanol and extracted with about 500 ml of benzene in a separatory funnel. A green fat (fraction No. 6), designated F6, was obtained from the benzene layer and a gray powder (fraction No. 7), designated F7, was obtained from the water layer upon concentration.
About 3 liters of acetone was slowly added to the concentrated alcohol extract swirled in a flask. The mixture was let stand overnight and then filtered to obtain a damp acetone insoluble precipitate (fraction No. 2), designated F2. The acetone filtrate was concentrated down to about 1 leter and slowly added to 14 liters of water and stirred in a plastic container. The water insoluble precipitate (fraction No. 3), designated F3, was filtered off and extracted twice with a total of 5 liters of petroleum ether to yield a small wax (fraction No. 8), designated F8. The water solution was evaporated to about 1.5 liters and extracted twice with 2 liters of ethyl acetate to obtain the ethyl acetate soluble ~2~7~

fraction (fraction No. 5) designated F5, and the fraction remaining in water (fraction Mo. 4), designated F4.
Initially, the wet weight of the wet aspen wood product (~1AP) was 3,252 g and the oven dry weight was 1,463 g.
The following Table VI gives comments on each fraction obtained from the process described with refe~-ence to Figure 9.
TABLE VI
.
~Jeight % of total Oven dry oven dry weight exploded Fractiong wood Comments .
Fl884.0 60.4 carbohydrate rich F2 94 5 6.5 carbohydrate rich F3272.5 18.6 lignin rich F4115.3 7.9 carbohydrate rich F5 81.3 5.6 lignin rich F6 14.6 1.0 F7 0.6 0.04 F8 0.9 0.06 .

A similar leaching procedure was carried out for treated wet barley straw, designated ~TBSP in Figure 10.
In Figure 10, the same fractions are designated by the same references as those in Figure 9 and the previous description is generally relied upon to describe them and how they were obtained.

12~ ~76~

The initial wet weight of the wet barley product was 173.4 g and the oven dry weight was 88.97 g.
The initial extraction was in two stages using 1000 ml of 95% ethanol in each stage.
The concentrated alcohol extract of fraction No. 1 (Fl) was concentrated to almost dryness and acetone was added for fraction No. 2 (F2).
The acetone filtrate of fraction No. 2 (F2) was concentrated to about 120 ml precipated and was added to 1.8 litres of water.
The ethyl acetate soluble fraction Mo. 5 (Fs) was extracted twice with ethyl acetate.
The following Table VII gives comments on each fraction obtained with the process described with reference to Figure 10.
TABLE VII
. .
~leight %
Oven dry of total weight oven dry Fraction g UBSP Comments _ Fl 55.76 65.9% carbohydrate rich F2 7.67 9.1% carbohydrate rich F3 11.53 13.6% lignin rich (93%
pure) F4 5.32 6.3% carbohydrate rich F5 4.32 5.1% lignin rich 12177~

Lignin was probably present in very small amounts in ~ractions l, 2 and 4. Infrared spectra of these fractions had absorption characteristics of carbohydrate rich materials.
Fractions 3 and 4 were rich in lignin. The Klason lignin contents of fraction 3 for barley straw was 92.9~ by weight, and for ~1AP was 93.1%. These fractions had the infrared absorption characteristics of native lignin. It may be concluded that a very large fraction of the lignin content of the exploded materials can be easily extracted with ethyl alcohol. Disassociation of the lignin from the cellulose and hemicellulose was probably caused by the method of depolymerizing lignin according to the present invention.
Since ethanol and acetone can be readily recovered in this simple extraction, it provides a very efficient method to obtain lignin.
Lignin is disassociated from the lignin carbohydrate complex (LCC) after the treatment of, for example, wood and straw by the process. A further test was made to show that most of this native lignin can be readily extracted with acetone.
In this test, 70.5 g of treated, wet aspen wood (55.4% moisture, oven dry weight 31.44 g) designated A~ was extracted three times with acetone in a 500 ml beaker. About 250 ml of acetone was used in each extraction. The mixture was stirred with a glass rod for about 5 min and then filtered.
The third extract was clear and light in colour. The extracts were combined and concentrated to about 150 ml in a rotary ~12~i7~

evaporator. Thus acetone insolubles (AI) were obtained and acetone solubles ~AS) in fraction 1 (Fl). Near the end of the evaporation care was taken to avoid overheating the solution which would cause the lignin suspension to coagulate and form a sticky mass. The concentrated extract was slowly poured into 1 litre of cold water (10C) and stirred in a container. The lignin water mixture was then filtered through a slow flow filter paper and dried at room temperature and 6.55 g of dry lignin rich powder of water insoluble precipitate (~7IP) was obtained in fraction 2 (F2). This represented 20.8% of the total dry material leaving a fraction 3 (F3) remaining in water as water soluble (~lS).
Similar extraction was carried out with the treated barley straw designated BS. 97.0 g of wet exploded BS (50.0%
moisture, 48.5 g oven dry weight) was extracted three times with a total of 1050 ml. The extract was concentrated down to about 200 ml and slowly poured into litre of cold water. 7.2 g of dry lignin rich powder was obtained, which was about 14.8 of the total dry material.
The ratio of solvent volume t,o material weight was arbitrarily chosen so that the mixture was not too thick to stir. A concentration of about 12 g DM/100 ml liquid mixture was probably thin enough for stirring with a glass rod. Since the extracted lignin was quite soluble in acetone and the leaching was fast, one would expect a very large stage efficiency. ~owever, the equilibrium data for the acetone extraction is needed to determine the requirement of solvent ~2~771~

quantity and the number of stages. Because of the presence of water in the exploded material, some low molecular weight hemicellulose was also leached out. Other much smaller amounts of wax, phenolics and extractives were also extracted. The wax (in A~ only) stayed with the lignin rich fraction and represented less than 1~ of the total material. Figure 11 shows the leaching sequences of A~J and BS.
The following Table VIII gives the amounts of each fraction and comments upon them.

7~
_ , ..... . .. .

s ,~ s ~ ~ s O ~ h ~ h O h O ~1 h ~
O ~ ~ h ~ ,1 ~1 :~ h :>~ h ~ h :~ h ~: ~ S s~ S S ~ S
~ ~) O -~ O O -1 0 E ~ Q ~ Q ~ ~ Q
E~ h h t~' h h t~ h O ~ (1~
C_) ~ ~ C V ~ C.) ____ ,. . _~.__ , a O
a) ~ 0,o 0~o 0~o 0~o 0~ 0~
:~ h ~ ~ oo o o ~4 h ~) -,j O ~ h ~ o ~ r N
~1 0 ~C) N ~1 ~ r~ N
o~ ~ O ~J
a) S OS
.~ .~
H 3 3 _ _ __ . __ '3 o ~ o er 1~ ~ O N O
h ~ o ~D ~r O 1-- ~1 ~rs N ~ ~1 O

t:~ ~I N tr) _I N t'') 1~

3 m a) _ _ _ _ . , , _ 43-~2~77~

Klason lignin determinations of the lignin rich fractions indicated that the lignin rich fraction contained about 93% lignin. Therefore a minimum of 906 lignin yield can be expected from the leaching of wood and straw, processed according to the present invention, with acetone. The solvent can be readily recovered with little heat required, which makes the process even more attractive. Another advantage is that the material which has been extracted with acetone is almost free of lignin, therefore its value as a fermentation substrate or feed stock is increased. Figure 12 shows a simplified schematic diagram of the acetone extraction of lignin from, for example, treated wood and straw.
In Figure 12, treated material M is fed to extractors ES and fresh acetone (ethanol or methanol) FA is fed to a tanX
T. Acetone from the tank T is continuously fed to the extractors ES and overflows therefrom to a first evaporator EV1 while an underflow from the extractors ES flows to a first filter Fl. The filtrate from the first filter Fl is passed to the first evaporator EV1 while the residue from the first filter Fl is dried in a drier D to yield a carbohydrate rich solid Sl. Recovered acetone from the first evaporator EVl and the drier D is returned to the tank T. The residue from the first evaporator EVl is mixed with water ~ in a precipitator P.
The mixture from the precipitator P is passed to a second filter F3 from which filtered lignin FL of >90% purity is obtained. Residue from the second filter F2 is passed to a second evaporator EV2 where a carbohydrate rich solution S2 is ~Z177~P~

obtained while the evaporated products therefrom are passed to a distillation unit DU from which water 1~2 is separated from acetone and the acetone returned to the tank T.
The lignin produced in accordance with the present invention by solvent extraction from the treated material can be thermally plasticized and extruded as lignin filaments, and the lignin filaments can be carbonized in the presence of heat to form carbon fibers. Carbon filaments produced in this manner may be used in, for example, air or water filtration.

Claims (16)

1. A method of rendering lignin separable from cellulose and hemicellulose in lignocellulosic material, comprising:
a) packing the lignocellulosic material in a divided, exposed, moist form in a pressure vessel having a valved outlet, b) with the valve closed, rapidly filling the pressure vessel with steam at a pressure of at least 500 psi to bring, by means of the pressurized steam, substantially, all of the lignocellulosic material to a temperature in the range 185 to 240°C in less than 60 seconds to thermally soften the lignocellulosic material into a plastic condition, and c) as soon as the said plastic condition has been attained, opening the valved outlet and instantly and explosively expelling the lignocellulosic material, in the said plastic condition, from the pressure vessel through the outlet to atmosphere so that the said material issues from the outlet in particulate form with lignin therein rendered into particles substantially in the range 1 to 10 microns and separable from the cellulose and hemicellulose, the particulate lignin and cellulose being together in disassociated form having the appearance of potting soil, a major portion of the lignin being soluble in methanol or ethanol and being thermoplastic, the cellulose being in the form of crystalline alpha cellulose microfibrils and suitable for digestion by microorganisms and enzymes.

2. A method according to claim 1, wherein the outlet is configured and dimensioned to afford substantial mechanical working of the material as it is explosively discharged through the outlet.

3. A method according to claim 1 or 2, wherein the lignocellulosic material is extruded on to an impinging surface.

4. A method according to claim 1 or 2, wherein the pressure vessel is rapidly filled with steam to bring the lignocellulosic material to a temperature in the range 200 to 238°C in less than 45 seconds.

5. A method according to claim 1 or 2, wherein the pressure vessel is rapidly filled with steam to bring the lignocellulosic material to a temperature of 234°C in less than 45 seconds.

6. A method according to claim 1 or 2, wherein the steps a) to c) are repeated at least once more with the lignocellulosic material at a temperature no greater than that at which the lignocellulosic was treated for the first time in steps b) and c).

7. A method according to claim 1 or 2, wherein the extruding of the lignocellulosic material to atmosphere is accomplished in milli-seconds.

8. A method according to claim 1 or 2, wherein lignin in native form, having a purity of the order of 93 weight %, is solvent extracted from the particulate material by a solvent selected from the group consisting of ethanol and methanol and the lignin so extracted is readily reactive chemically, is thermoplastic, and has an infrared spectrum approaching that of so called native lignin.

9. A method according to claim 1 or 2, wherein the lignocellulosic material is wood and the pressure vessel is rapidly filled with steam at a pressure in the range 600 to 700 psi.

10. A method according to claim 1 or 2, wherein the lignocellulosic material is hardwood.

11. A method according to claim 1 or 2, wherein the lignocellulosic material is annual plant material and the pressure vessel is rapidly filled with steam at a pressure in the range 500 to 600 psi.

12. A method according to claim 1 or 2, wherein the lignocellulosic material is an annual biomass and the pressure vessel is rapidly filled with steam at a pressure in the region 550 psi.

13. A method according to claim 1 or 2, wherein the lignocellulosic material in finely divided form is moist with water in the region of fibre saturation when packed in the pressure vessel.

14. A method according to claim 1 or 2, wherein the lignocellulosic material is an annual plant substance, the pressure vessel is rapidly filled with steam at a pressure in the region of 550 psi, after approximately 40 seconds the steam pressure is rapidly increased to a higher pressure and the material is explosively expelled immediately upon achieving said higher pressure.

15. A method according to claim 1 or 2, wherein the lignocellulosic material is wood, the pressure vessel is rapidly filled with steam at a pressure in the region of 650 psi, after approximately 40 seconds the steam pressure is rapidly increased to a higher pressure and the material is explosively expelled immediately upon achieving said higher pressure.

16. The product in particulate form when produced by the method claimed in claim 1 or 2.