FIELD

This disclosure relates to an organosolv biorefining process. This disclosure further relates to the lignins, uses, apparatus, and the like. BACKGROUND

For environmental, economic, and resource security reasons, there is an increasing desire to obtain energy and material products from bio-renewable resources and particularly from "waste" and/ or non-food biomass feedstocks. The various chemical components within typical biomass can be employed in a variety of ways. In particular, the cellulose and hemicellulose in plant matter may desirably be separated out and fermented into fuel grade alcohol. And the lignin component, which makes up a significant fraction of species such as trees and agricultural waste, has huge potential as a useful source of aromatic chemicals for numerous industrial applications. However, most separation techniques employed by industry today are not optimal for providing industrially useful chemicals. For example, the techniques may be too harsh and chemically alter the lignin component during separation to the point where it is no longer acceptable for use in many of these potential applications.

Organosolv extraction processes can be used to separate lignin and other useful materials from biomass. Such processes can be used to capitalize on the value from multiple components in the biomass. Organosolv extraction processes however typically involve extraction with a volatile solvent at higher temperatures and pressures than other industrial methods and thus are generally more complex and expensive. While large scale commercial viability had been demonstrated decades ago from a technical and operational perspective, organosolv extraction has not, to date, been widely adopted.

SUMMARY The present disclosure provides an organosolv biorefining process. The present process comprises treating a lignocellulosic biomass in the presence of a solvent and under certain conditions to separate at least a part of the lignin from the biomass.

As used herein, the term "biorefining" refers to the co-production of bio-based products (e.g. lignin derivatives), fuel (e.g. ethanol), and/ or energy from biomass. As used herein, the term "organosolv" refers to bio-refinery processes wherein the biomass is subject to an extraction step using solvent at an elevated temperature.

As used herein, the term "native lignin" refers to lignin in its natural state, in plant material.

As used herein, the terms "lignin derivatives" and "derivatives of native lignin" refer to lignin material extracted from lignocellulosic biomass. Usually, such material will typically be a mixture of chemical compounds that are generated during the extraction process.

This summary does not necessarily describe all features of the invention. Other aspects, features and advantages of the invention will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an example of a Lignol® lignin (Alcell®) organosolv process;

Figure 2 shows the dependence of lignin & glucose yields on solids content (L:W Ratio) at 2% acid on aspen wood, 50% EtOH in liquor, 120 min cooking time, 165 °C cooking temperature;

Figures 3, 4 and 5 shows the time-to-conversion target for various biomass samples.

DETAILED DESCRIPTION

The present disclosure provides an organosolv biorefining process. Organsolv processes are well known in the art. See, for example, US Patent 4,100,016; US Patent 4,764,596; US Patent 5,681,427; US Patent 7,465,791; US Patent Application 2009/0118477; US Patent Application 2009/0062516; US Patent Application 2009/00669550; or US Patent 7,649,086.

Four major "organosolv" pulping processes have been tested on a trial basis. The first method uses e hanol/ water pulping (aka the Lignol® (Alcell®) process); the second method uses alkaline sulphite anthraquinone methanol pulping (aka the "ASAM" process); the third process uses methanol pulping followed by methanol, NaOH, and anthraquinone pulping (aka the "Organocell" process); the fourth process uses acetic acid/hydrochloric acid or formic acid pulping (aka the "Acetosolv" and "Formacell" processes).

A description of the Lignol® Alcell® process can be found, for example, in US Patent 4,764,596 or Kendall Pye and Jairo H. Lora, The Alcell™ Process, Tappi Journal, March 1991, pp. 113-117 (the documents are herein incorporated by reference). The process generally comprises pulping or pre-treating a fibrous biomass feedstock with primarily an efhanol/water solvent solution under conditions that include: (a) 60% efhanol/40% water (W/W), (b) a temperature of about 180° C to about 210° C, and (c) pressure of about 20 atm to about 35 atm. Derivatives of native lignin are fractionated from the biomass into the pulping liquor which also receives solubilised hemicelluloses, other carbohydrates and other components such as resins, phytosterols, terpenes, organic acids, phenols, and tannins. Organosolv pulping liquors comprising the fractionated derivatives of native lignin and other components from the fibrous biomass feedstocks, are often called "black liquors". The organic acid and other components released by organosolv pulping significantly acidify the black liquors to pH levels of about 5 and lower. After separation from the pre-treated lignocellulosic biomass or pulps produced during the pre-treatment process (e.g. pulping process), the derivatives of native lignin are recovered from the black liquor by flashing followed by dilution with acidified cold water and/ or stallage which will cause most of the fractionated derivatives of native lignin to precipitate thereby enabling their recovery by standard solids/liquids separation processes. Various disclosures exemplified by US Patent No. 7,465,791 and PCT Patent Application Publication No. WO 2007/129921, describe modifications to the Lignol® Alcell® organosolv.

Organosolv processes, particularly the Lignol® Alcell® process, can be used to separate highly purified lignin derivatives and other useful materials from biomass. Such processes may therefore be used to exploit the potential value of the various components making up the biomass.

Organosolv extraction processes however typically involve extraction with a volatile solvent at higher temperatures and pressures compared to other industrial processes and thus are generally considered to be more complex and expensive. For example, when the processes are run at higher pressures (~25-30 bar) capital costs can increase due to the necessity of using more robust equipment. In addition, the necessity of heating the biomass to high temperatures requires extra expense in terms of energy input leading to increased operating costs.

Moreover, organosolv extraction processes can result in the production of self- precipitated lignins or lignins with poor solubility in the cooking liquor (SPLs), particularly when using softwood biomass but also when other types of biomass is used. SPLs can attach to metal surfaces causing equipment to be fouled and are difficult to remove.

In order to improve the commercial viability of organosolv processes it is desirable to keep capital and operating costs low while maximizing the potential revenue streams. For example, the cost of the enzymes used to convert the cellulose-rich pulp to mono- and/or oligosaccharides which can then be fermented into biofuels such as ethanol and n-butanol or bio-based chemicals such as xylitol and other sugar-alcohols, succinic acid and other organic acids, etc represents a significant operating cost and, therefore, it would be advantageous to reduce the amount of enzymes needed. Also, recovered lignin derivatives represent a source of high-value chemicals and, therefore, it would be advantageous to increase the yield of such substances.

Surprisingly, it has been found that organosolv processes operated within relatively narrow ranges of process conditions offer significant advantages in terms of, for example, glucose yield and/ or lignin derivative yield.

The present disclosure offers an organosolv process which operates at significantly lower temperature and pressure than typical for organosolv biorefining allowing, for example, savings in capital, operating, and/ or energy expenditure.

Embodiments of the present process demonstrate significantly less equipment fouling than seen in prior art organosolv processes. For example, when the present process utilizes softwood feedstock there is a marked reduction in the amount of SPLs seen. A reduction in the amount of SPLs can result in lower equipment fouling. This offers the possibility of an improved commercial scale organosolv plant that has the ability to process softwood and other types of biomass that suffer from problems with SPLs.

Typical organosolv processes, such as LignoPs® Alcell® process, generally recover around 60% of the theoretical maximum Ugnin. The remaining Hgnin content is generally degraded and ends up as a waste residue. This non-recovered fraction can be toxic to microorganisms and can contaminate certain of the product streams reducing their processability by microorganisms and/ or value.

Embodiments of the present disclosure offer surprisingly high lignin yields which increases the value derivable from the lignin stream of a particular process and may also reduce the amount of non-recovered lignin contaminating product streams from the process.

Embodiments of the present disclosure offer pretreated solids ("pulps") with surprisingly good enzymatic hydrolability. This characteristic increases the pulps reactivity to enzymes and, hence, reduces the amount of enzyme needed for converting the pulp to sugars and subsequendy to ethanol or other chemicals.

Embodiments of the present disclosure offer surprisingly high yields of glucose.

The present invention provides an organosolv process, said process comprising:

(a) pretreating (e.g. pulping) a lignocellulosic biomass with an organic solvent to form a pulp comprising cellulose and an extraction liquor comprising lignin derivatives;

(b) separating the cellulosic pulp from the extraction liquor; and

(c) recovering at least a portion of the extracted compounds from the extraction liquor. At least a portion of the cellulosic pulp may be converted into carbohydrates, ethanol, or other chemicals.

The pretreatment step (a) of the present process can be operated at pressures of about 18 bar or less. For example, about 7 bar or less, about 6 bar or less, about 15 bar or less.

The biomass/ solvent mixture of pretreatment step (a) of the present process may be heated to a temperature of from about 130°C or greater, about 132°C or greater, about 134°C or greater, about 136°C or greater, about 138°C or greater, about 140°C or greater, about 142°C or greater, about 144°C or greater, about 146°C or greater, about 148°C or greater, about 150°C or greater, about 152°C or greater, about 154°C or greater.

The biomass/solvent mixture of pretreatment step (a) of the present process may be heated to a temperature of from about 70°C or less, about 168°C or less, about 166°C or less, about 165°C or less.

For example, the biomass/solvent mixture of pretreatment step (a) of the present process may be heated to a temperature of from about 155°C to about 165°C.

The biomass/solvent mixture of pretreatment step (a) of the present process may be kept at the elevated temperature for about 45 minutes or more, about 50 minutes or more, about 55 minutes or more, about 60 minutes or more, about 65 minutes or more, about 70 minutes or more, about 75 minutes or more, about 80 minutes or more, about 95 minutes or more, about 100 minutes or more, about 105 minutes or more, about 110 minutes or more, about 115 minutes or more, about 120 minutes or more.

The biomass/solvent mixture of pretreatment step (a) of the present process may be kept at the elevated temperature for about 200 minutes or less, about 195 minutes or less, about 190 minutes or less, about 185 minutes or less, about 180 minutes or less.

For example, the biomass/solvent mixture of pretreatment step (a) of the present process may be kept at the elevated temperature for about 120 to about 80 rninutes.

The solvent mixture of pretreatment step (a) of the present process may comprise about 40% or more, about 42% or more, about 44% or more, about 46% or more, about 48% or more, about 50% or more, organic solvent such as ethanol.

The solvent mixture of pretreatment step (a) of the present process may comprise about 70% or less, about 68% or less, about 66% or less, about 64% or less, about 62% or less, about 60% or less, about 58% or less, about 56% or less, organic solvent such as ethanol.

For example, the solvent mixture of pretreatment step (a) of the present process may comprise about 45% to about 60%, about 50% to about 55%, organic solvent such as ethanol. The solvent mixture of pretreatment step (a) of the present process may have a pH of from about 1.5 or greater, about 1.6 or greater, about 1.7 or greater. The solvent mixture of pretreatment step (a) of the present process may have a pH of from about 2.5 or lower, about 2.4 or lower, about 2.3 or lower. For example, the solvent mixture of pretreatment step (a) of the present process may have a pH of from about 1.5 to about 2.5. For example, from about 1.6 to about 2.3.

From about 1.5% or greater, about 1.7% or greater, about 1.9% or greater, about 2% or greater, by weight, of acid (based on dry weight wood) may be added to the biomass. From about 3% or lower, about 2.7% or lower, about 2.5% or lower, by weight, of acid (based on dry weight wood) may be added to the biomass.

The weight ratio of liquor to biomass in the pretreatment step (a) may be from about

10:1 to about 4:1, about 9:1 to about 5:1, about 8:1 to about 6:1.

The pretreatment step (a) of the present process may generate pretreated biomass solids with Time-to-Conversion-Target (TCT) equal to about 120 h or less, about 110 h or less, about 100 h or less, about 90 h or less, about 80 h or less, about 75 h or less, about 60 h or less, about

40 h or less. The pretreatment step (a) may generate pretreated biomass solids with an Overall

Glucose Conversion (OGC) of about 50% or higher, about 65% or higher, about 70% or higher, about 75% or higher, about 80% or higher, about 85% or higher.

The present organic solvent may be selected from any suitable solvent. For example, aromatic alcohols such as phenol, catechol, and combinations thereof; short chain primary and secondary alcohols, such as methanol, ethanol, propanol, and combinations thereof. For example, the solvent may be a mix of ethanol & water.

The present process may utilize any suitable lignocellulosic feedstock including hardwoods, softwoods, annual fibres, energy crops, municipal waste, and combinations thereof.

Hardwood feedstocks include Acacia; Afzelia; Synsepalum duloijicum; Albizia; Alder (e.g.

Alnus glutinosa, Alnus rubra); Applewood; Arbutus; Ash (e.g. F. nigra, F. quadrangulata, F. excelsior, F. pennsylvanica lanceolata, F. latifolia, F. profunda, F. americand); Aspen (e.g. P. grandidentata, P. tremula, P. tremuloides); Australian Red Cedar Toona ciliatd); Ayna Distemonanthus benthamianus ; Balsa (Ochroma pyramidak); Basswood (e.g. T. amemana, T. heteropbylld); Beech (e.g. F. sylvatica, F. grandifolid); Birch; (e.g. Betula populijo ^' lia, B. nigra, B. p pyrifera, B. lenta, B. alleghaniensis/B. lutea, B. pendula, B. pubescens);

Blackbean; Blackwood; Bocote; Boxelder; Boxwood; Brazilwood; Bubinga; Buckeye (e.g. Aesculus hippocastanum, Aesculus glabra, Aesculus java I Aesculus octandrd); Butternut; Catalpa; Cherry (e.g.

Primus serotina, Prunus pennsylvanica, Prunus avium); Crabwood; Chestnut; Coachwood; Cocobolo;

Corkwood; Cottonwood (e.g. Populus balsamijera, Populus deltoides, Populus sargentii, Populus heterophylla); Cucumbertree; Dogwood (e.g. Cortius florida, Cornus nuttallii); Ebony (e.g. Diospyros kur^ii, Diospyros melanida, Diospyros crassiflord); Elm (e.g. Ulmus americana, Ulmus procera, Ulmus thomasii, Ulmus rubra, Ulmus glabra); Eucalyptus; Greenheart; Grenadilla; Gum (e.g. Nyssa sylvatica, Eucalyptus globulus, Eiquidambar syt raciflua, Nyssa aquatica); Hickory (e.g. Carya alba, Carya glabra, Carya ovata, Carya laciniosd); Hornbeam; Hophornbeam; Ipe; Iroko; Ironwood (e.g. Bangkirai, Carpinus Carolinian a, Casuarina equisetifolia, Choricbangarpia sub argent e a, Copaifera spp., Eusideroxylon Guajacum officinale, Guajacum sanctum, Hopea odorata, Ipe, Krugiodendron ferreum, Eyonothamnus lyomi (L. floribundus), Mesua je ^' rrea, Olea spp., Olneya tesota, Ostrya virgi iana, Parrotia persica, Tabebuia serratifolid); Jacaranda; Jotoba; Lacewood; Laurel; Limba; Lignum vitae; Locust (e.g. Robinia pseudacacia, Gleditsia (riacantbos); Mahogany; Maple (e.g. Acer saccharum, Acer nigrum, Acer negundo, Acer rubrum, Acer saccharinum, Acer pseudoplatanus); Meranti; Mpingo; Oak (e.g. Quercus macrocarpa, Quercus alba, Quercus stellata, Quercus bicolor, Quercus virginiana, Quercus michauxii, Quercus prinus, Quercus muhlenbergii, Quercus chrysolepis, Quercus y l rata, Quercus robur, Quercus petraea, Quercus rubra, Quercus velutina, Quercus launfolia, Quercus falcata, Quercus nigra, Quercus phellos, Quercus texand); Obeche; Okoume; Oregon Myrde; California Bay Laurel; Pear; Poplar (e.g. P. balsamifera, P. nigra, Hybrid Poplar {Populus x canadensis)); Ramin; Red cedar; Rosewood; Sal; Sandalwood; Sassafras; Satinwood; Silky Oak; Silver Wattle; Snakewood; Sourwood; Spanish cedar; American sycamore; Teak; Walnut (e.g. Juglans nigra, Juglans regi ); Willow (e.g. Salix nigra, Salix alba); Yellow poplar [Uriodendrvn tulipiferd); Bamboo; Palmwood; and combinations /hybrids thereof.

For example, hardwood feedstocks for the present invention may be selected from

Acacia, Aspen, Beech, Eucalyptus, Maple, Birch, Gum, Oak, Poplar, and combinations /hybrids thereof. The hardwood feedstocks for the present invention may be selected from Populus spp. (e.g. Populus tre uloides), Eucaylptus spp. (e.g. Eucaylptus globulus), Acacia spp. (e.g. Acacia dealbata), and combinations/hybrids thereof.

Softwood feedstocks include Araucaria (e.g. A. cunninghamii, A. angustifolia, A. araucand); softwood Cedar (e.g. Juniperus rginiana, Thuja plicata, Thuja occidentalis, Chamaecyparis thyoides Callitropsis nootkatensis); Cypress (e.g. Chamaeyparis, Cupressus Taxodium, Cupressus ari^onica, Taxodium distichum, Chamaecyparis obtusa, Chamaecyparis lawsoniana, Cupressus semperviren); Rocky Mountain Douglas fir; European Yew; Fir (e.g. Abies balsa ea, Abies alba, Abies procera, Abies amabilis); Hemlock (e.g. Tsuga canadensis, Tsuga mertensiana, Tsuga heterophylla); Kauri; Kaya; Larch (e.g. Larix decidua, Larix kaempferi, Larix laricina, Larix occidentalis); Pine (e.g. Pinus nigra, Pinus banksiana, Pinus contorta, Pinus radiata, Pinus ponderosa, Pinus resinosa, Pinus sylvestris, Pinus strobus, Pinus monticola, Pinus lambertiana, Pinus taeda, Pinus palustris, Pinus rigida, Pinus echinatd); Redwood; Rimu; Spruce (e.g. Picea abies, Picea mariana, Picea mbens, Picea sitchensis, Picea glaucd); Sugi; and combinations /hybrids thereof.

For example, softwood feedstocks which may be used herein include cedar; fir; pine; spruce; and combinations /hybrids thereof. The softwood feedstocks for the present invention may be selected from loblolly pine (Pinus taed ), radiata pine, jack pine, spruce (e.g., white, interior, black), Douglas fir, Pinus silvestris, Picea abies, and combinations /hybrids thereof. The softwood feedstocks for the present invention may be selected from pine (e.g. Pinus radiata, Pinus taeda); spruce; and combinations/hybrids thereof.

Annual fibre feedstocks include biomass derived from annual plants, plants which complete their growth in one growing season and therefore must be planted yearly. Examples of annual fibres include: flax, cereal straw (wheat, barley, oats), sugarcane bagasse, rice straw, corn stover, corn cobs, hemp, fruit pulp, alfalfa grass, esparto grass, switchgrass, and combinations /hybrids thereof. Industrial residues like corn cobs, fruit peals, seeds, etc. may also be considered annual fibres since they are commonly derived from annual fibre biomass such as edible crops and fruits. For example, the annual fibre feedstock may be selected from wheat straw, corn stover, corn cobs, sugar cane bagasse, and combinations/hybrids thereof.

It is contemplated that any embodiment discussed in this specification can be implemented or combined with respect to any other embodiment, method, composition or aspect of the invention, and vice versa.

All citations are herein incorporated by reference, as if each individual publication was specifically and individually indicated to be incorporated by reference herein and as though it were fully set forth herein. Citation of references herein is not to be construed nor considered as an admission that such references are prior art to the present invention.

The invention includes all embodiments, modifications and variations substantially as hereinbefore described and with reference to the examples and figures. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. Examples of such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way.

The present invention will be further illustrated in the following examples. However it is to be understood that these examples are for illustrative purposes only, and should not be used to limit the scope of the present invention in any manner. EXAMPLES

The following examples are intended to be exemplary of the invention and are not intended to be limiting.

Example 1:

All the modeling work was performed with the help of two software packages: Microsoft

Excel 2007 & MatLab Version 7.7.0.471 (R2008b) with Model-Based Calibration Toolbox Version 3.5 & the CAGE Optimization Module (The MathWorks, Inc., MA, USA).

The aspen chips used for the optimization were produced by Econotech after debarking and splitting logs sourced from a local BC forest. Validation of the found optimal region was performed with aspen chips supplied from Slave Lake, Alberta and screened at Lignol by Pilot Plant Operations.

Enzymatic hydrolysis was run at 50 g scale at 16% solids, 120 h, 150 rpm, pH 5.0, CellicCTec2 loaded at 12 mg/g glucan. Samples were taken after 24 h hydrolysis but here for simplicity we will report only yields after 120 h hydrolysis. This experimental design has proven to be representative of what one can see at larger scale (4-L & 20-L fermentor scale).

Thirty eight sets of five process variables (Table 1) were selected to run the optimization experiments and the results were used to build the models (Table 3).

The produced models showed that one can find pretreatment conditions for Aspen biomass where the Lignin Yield is higher than 80% and the Glucose Yield is higher than 85%). In all studied conditions the operating pressure was around 16 bar or lower.

The optimum conditions for aspen lignin yield and glucose yield (~80% or higher theoretical yields) lies between 155 and 165 °C, ~50-55% EtOH, 120-180 min cooking time, 2.0- 2.5% acid at a fixed L:W ratio of 8:1 to 7:1. Any combination of these conditions yields operating pressures around or below 16 bar. Decrease of L:W ratio (increase of % solids) is beneficial and leads to increase glucose and lignin yields under certain conditions such as the ones described in Figure 2.

Table 1 Sets of process variables selected to run the optimization experiments

Acid Time Temperature Ethanol Solids L:W

#

% wt. min °C % wt. % :1

1* 2.00 105 148 55 15.0 5.7

2* 2.50 143 139 48 12.5 7.0

3* 1 .50 68 156 63 17.5 4.7

4* 1 .38 133 158 53 10.6 8.4

5* 1.63 114 145 42 1 1.9 7.4

6* 2.06 166 144 63 10.3 8.7 7* 1.69 175 151 50 17.2 4.8

8* 2.44 82 155 62 10.9 8.1

9* 2.00 112 152 55 13.1 6.6

10* 1.41 168 152 57 12.7 6.9

11* 2.50 145 143 48 1 1.6 7.6

12* 2.28 140 150 63 12.0 7.3

13* 1.50 78 161 63 14.6 5.8

14* 1.78 103 159 55 14.5 5.9

15* 2.53 121 137 59 10.8 8.3

16* 1.97 145 149 43 10.5 8.6

17* 2.75 128 139 66 13.9 6.2

18* 1.75 62 157 51 10.9 8.2

19* 1.59 98 143 53 11.1 8.0

20* 1.25 95 148 59 15.4 5.5

21* 1.34 79 164 41 12.3 7.1

22* 2.83 92 139 63 13.8 6.2

23* 2.25 161 166 44 12.4 7.1

24* 1.58 111 152 67 10.1 8.9

25* 2.08 73 161 59 12.6 7.0

26* 1 .88 170 136 61 15.0 5.7

27* 1.20 45 159 69 12.0 7.4

28* 2.45 176 137 65 13.2 6.6

29* 2.88 103 154 46 12.0 7.4

30* 1 .52 162 140 60 15.4 5.5

31* 2.27 69 144 49 1 1 .6 7.6

32* 2.38 70 145 68 13.5 6.4

33* 2.89 153 134 51 1 1 .0 8.1

34* 1.89 78 151 66 16.0 5.2

35* 2.14 172 155 47 12.3 7.2

36* 1.38 136 163 53 10.5 8.5

37* 1.64 59 164 55 14.8 5.8

38* 2.89 176 166 69 17.5 4.7

Table 2 Output boundaries of dependent process variables

Lignin Yield Glucose Yield Washed Pulp Yield

% % % bd wood

Min 51.5 70.2 42.8

Max 85.1 87.5 55.8 Table 3 Lignin Yield, Glucose Yield, and Washed Pulp Yields Models

Lignin Yield (%) = -146.0292+27.99547*Solids+0.03120071 ^* Temp ^* EtOH-

0.1121524*Temp*Solids+0.0015453*Time*Time+0.003185002*Tim e ^* EtOH+0.03481116 ^* Time*Acid- 0.04457228*Time*Solids-0.03969131 ^* EtOH ^* EtOH-0.07047815 ^* EtOH ^* Solids (^=0.705)

Glucose Yield (%) = -62.07805+2.045008 ^* Time-186.731 ^* Acid+32.86724 ^* Solids- 0.007077812*Tempn ^" ime+0.02055919*Temp*EtOH+0.7270062*Temp*Acid-0.1413414 *Temp*Solids- 0.005416981 *Time ^* EtOH-0.05171966 ^* Time ^* Solids+0.4617057 ^* EtOH ^* Acid- 0.2913332*EtOH*Solids+8.300157*Acid*Acid+1.758393*Acid*Solid s+0.3140979 ^* Solids*Solids

(1^=0.858)

Washed Pulp Yield (%) = -15.8281 +0.621621 ^* EtOH- 5.53252*Acid+15.7276 ^* Solids+0.00179991 ^* Temp ^* Temp- 0.0821519*Temp*Solids+0.00062543*Time*Time-0.00132139*Time*E tOH+0.0230202 ^* Time*Acid- 0.01 18592*Time*Solids-0.0444829 ^* EtOH ^* Solids (1^=0.901)

Example 2:

Reactivity of biomass samples

"Time-to-Conversion-Target" (TCT, h) is a metric which characterizes biomass reactivity and it is defined as the time in hours required to enzymatically convert 85% of the total glucan in a pretreated biomass sample to monomelic glucose under the following reaction conditions:

12 mg protein/g glucan of the state-of-the-art enzyme CellicCTec2 (Novozymes North America Inc., Franklinton, NC, USA). The protein content in the preparation is determined by the

Pierce ^® Micro BCA Protein Assay Kit (Thermo Fisher Scientific Inc., Waltham, MA, USA) in absence of interfering compounds or the enzyme protein content value is supplied by the enzyme manufacturer;

50 g total reaction weight;

16% total pretreated biomass solids in reaction;

pH 5.0, 0.1 M sodium citric buffer prepared in deionized water;

0.50 ppm antibiotic Lactrol ^® ;

50 °C;

150 rpm mixing rate in an air incubator;

Five Zr beads per flask (Cat. No. 08-412-15C, Grinding Media for Ball Mills (Zirconia), O.D. x H 13x13 mm);

250-mL total volume of a sterilized by autoclaving glass Erlenmeyer reaction flask

The flask must be plugged with a foam plug cover by an aluminum foil to avoid evaporation or equivalent. The glucose released is measured chromatographically. Table 4: Comparison of biomass reactivity (TCT, h) between three differently pretreated aspen samples

The pretreated biomass sample SI 0005636 15(1) shows the highest reactivity with the shortest time (117.5 h) required to achieve the target (85% glucan-to-glucose conversion) while the sample S10005865 28(1) shows the lowest reactivity with a 168.6 h TCT. The TCT values are calculated by extra- or intrapolation using the experimental hyperbolic functions Glucan-to- Glucose Conversion (%) vs. Time (h) (figures 3-5). These hyperbolic functions are typical of enzymatic hydrolysis reactions.

"Overall Glucose Conversion" (OGC, % total glucose in raw biomass) is a metric which provides the total glucose recovered from the pretreated solids in fermentable monomelic form and it integrates both the glucose recovery yield after biomass pretreatment (PGY — Pretreatment Glucose Yield) and the glucose hydrolysis yield after enzymatic hydrolysis (HGY— Hydrolysis Glucose Yield). The OGC is calculated as follows:

OGC (%) = Recovered_Glucose_After_Pretreatment_per_100g

Pretteated_Raw_Material (g)*HGY(%) Table 5: Overall Glucose Conversion (OGC, % total glucose in raw biomass) yields of three differendy pretreated aspen samples

"Maximum Operating Pressure" (P _max , bar) is defined as the maximum operating pressure reached during the biomass pretreatment stage. In the case of the present invention this value is around 16 bar or lower. "Best Pretreated Biomass" (BPB) is defined as the pretreated biomass produced under P _max around or lower than 6 bar which shows the lowest TCT and the highest OGC with the highest lignin yield. The lignin yield must be considered for economic reasons but it does not necessarily impacts biomass reactivity.

In the case of the three compared pretreated aspen samples the BPB is the sample SI 0005636 15(1) since it showed the highest OGC and the lowest TCT while the maximum operating pressure (11 bar) was kept well below the allowed maximum of 16 bar.