WO2010077172A1

WO2010077172A1 - Process for pretreatment of wood raw material for saccharification, system and product

Info

Publication number: WO2010077172A1
Application number: PCT/RU2009/000567
Authority: WO
Inventors: Evgeniy Rubenovich Davidov; Petr Sergeevich Kanygin; Oleg Anatolievich Frakin; Igor Vladimirovich Cheremnov
Original assignee: Limited Liability Company "Prof Business"
Priority date: 2008-12-29
Filing date: 2009-10-22
Publication date: 2010-07-08
Also published as: RU2008151902A; RU2405832C2

Abstract

The present invention relates to a process for pretreatment of wood raw material comprising two stage milling, wherein at the first stage a coarse milling is carried out, followed by an extraction of pitch and at the second stage a ultrafine milling is carried out, moreover the mechanoactivation of the obtained product takes place at the second stage, also the invention relates to a system for carrying out of the process and product obtained by the process.

Description

Process for pretreatment of wood raw material for saccharification, system and product

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an improved process for pretreatment of wood raw material for saccharification. Also the invention relates to a system for carrying out of the process and product obtained by the process.

BACKGROUND OF THE INVENTION

In dry wood cellulose fibers are embedded in a matrix of other structural biopolymers, primarily hemicelluloses and lignin. Crystallinity and presence of lignin in most of the natural celluloses are major impediments towards development of an economically viable process technology for enzymatic hydrolysis of cellulose. Most of β-glycosidic bonds in wood-base material are inaccessible to cellulose enzymes by virtue of the small size of the pores in the multicomponent biomass. The molecules of individual microfibrils in crystalline cellulose are packed so tightly that not only enzymes but even small molecules like water cannot enter the complex structure. Suitable pretreatment to remove these blocks is necessary to obtain hydrolysis rates for the process to be viable. Pretreatment is a process that converts the wood raw material from its native form, in which it is recalcitrant to enzyme systems, into a form for which enzymatic hydrolysis is effective (Ashok Pandey, Handbook of Plant-Based Biofuels, CRC Press, 2008, p. 122). Many different pretreatments have been attempted. Some have been demonstrated to be effective in disrupting lignin cellulose complex, while others are responsible for breaking down the highly ordered cellulose crystalline structure, which is prerequisite for enzyme action.

The known pretreatment techniques include physical, chemical, and biological methods that may be used separately or in combination.

Physical treatments such as grinding, milling, high temperature, radiation and steaming/steam explosion are aimed at size reduction and mechanical decrystallization.

JP55009758 discloses the pretreatment of scrap wood by grinding in a vibration ball mill.

JP63137693 discloses the pulverization of wood wherein roughly crushed wood powder compressed and pulverized under pressure of 50 kg/mm² and, if necessary, the pulverized material is disintegrated by a disintegrator. Further the obtained product should be classified to separate the fine particles. However these documents do not give due attention to quality of pulverized wood raw material, but finally this factor just defines high sugar yield. WO2008/073186 discloses a method of changing a molecular structure of a biomass feedstock comprising radiation in the form of an electron beam and/or sonication.

RU2088108 discloses a wood processing method by ionizing radiation providing absorbed ionizing radiation dose of 100-290 kGy and simultaneous drying, grinding and sorting of wood raw material at temperature of drying agent of 413-423K. Though radiation has superior penetrating power and ionization action, which breaks cellulose chains, the method is slow and expensive, sometimes this pretreatment results in oxidation, degradation of molecules, dehydration.

US2005069998 describes the pretreatment comprising stages of grinding the lignocellulosic biomass to a size of 15-30 mm, subjecting the product to steam explosion pretreatment at a temperature of 190-230 ⁰C for 1 to 10 minutes. The steam explosion does not always break down lignin completely and some of the compounds produced can be inhibitory to the subsequent fermentation.

Chemical methods can include pretreatment with dilute acid, alkaline, organic solvent, ammonia, sulfur dioxide, carbon dioxide, ionic liquid.

US4266981 discloses the process in which cellulosic raw material are hydrolyzed by dilute sulfuric acid to remove hemicellulose. Such process significantly increases cellulose hydrolysis, however acid consumption is n expensive part of the method; it requires expensive corrosion-resistant materials and disposal of solid waste generated is a problem.

WO2008065433 discloses a process for the fermentative production of ethanol from solid lignocellulosic material comprising a step of treating the solid lignocellulosic material with alkaline solution in order to remove the lignin. All the lignin and part of hemicellulose are removed but this method is not able to disrupt the crystallinity of cellulose.

US2008227162 discloses the pretreatment of biomass by incubating the biomass in an ionic liquid for approximately from 5 minutes to 8 hours at 50 to 200 C.

Biological pretreatment can involve applying lignin-solubilizing microorganisms.

JP2008006372 discloses the wood-based biomass pretreatment method which comprises grinding processing using white-rot fungi having lignin-decomposing activity. The white-rot fungi are Trametes hirsute. Biological pretreatments appear to have the advantages of requiring no chemicals (if nutrient supplementation is not required) and low energy input. However, biological pretreatments are relatively slow processes, and most lignin-solubilizing microorganisms also solubilize or consume hemicellulose and cellulose (David M. Mousdale, Biofuels: biotechnology, chemistry and sustainable development, CRC Press, 2008, pp. 56-63). The shortcomings of the known methods are low enzymatic hydrolysis rate and low sugar yield. It should to be noted that because of the increased awareness of, and emphasis on, human health and environmental protection, effective pretreatment that use few or no (hazardous) chemicals are likely to gain research, development, and deployment momentum. This trend is believed to be crucial in guiding future research and development efforts (Handbook on Bioethanol: production and utilization, Edited by Charles E. Wyman, Applied Energy Technology series, p.194).

Therefore the efforts of inventors have been oriented to an improved pretreatment process which does not requre use of chemicals and provides high productivity of the enzymatic hydrolysis of wood-base material to soluble sugars.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a process for pretreatment of wood raw material comprising two stage milling, wherein at the first stage a coarse milling is carried out, followed by an extraction of pitch and at the second stage a ultrafine milling is carried out, moreover the mechanoactivation of the obtained product takes place at the second stage. In one embodiment the first stage is carried out at temperature no more than 130 ⁰C and during the mechanoactivation the material subjected to CO₂ action.

The present invention also relates to a system for carrying out of the process comprising a device for a coarse milling of wood raw material, an extractor, a device for an ultrafine milling and mechanoactivation. Additionally the device for an ultrafine milling and mechanoactivation comprises a device for CO₂ gas supply. The present invention also relates to products obtained by the claimed process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system for carrying out the claimed process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The wood raw material may be subjected to pretreatment with the aim of producing substrates that can be more rapidly and efficiently hydrolyzed to yield mixtures of fermentable sugars; in turn the valuable chemical compounds can be obtained through fermentation from the sugars.

It is known that milling can greatly increase the susceptibility to enzymic depolymerization of cellulose. However two stage milling (firstly a coarse milling to particles ranging in size from 1 mm to 2 mm and then ultraflne milling to particles 1-5 μm with mechanoactivation) has given rather surprising results.

We have discovered that in result of two-step mechanical activation of the wood-base material cellulose crystallinity index is decreased from 65-70% to 10%. Also the time of saccharifϊcation of such raw material at pH 5-6 and temperature of 50 ⁰C is only 12-13 hours, and in column process 3-7 hours. The sugars yield is 50% from the weight of wood raw material.

Mechanoactivation of wood-base material per se is known (Kuznetsova S.A., et al. Obtaining Arabinogalactan, Dihydroquercetin and Microcrystalline Cellulose Using Mechanochemical Activation, Chemistry for Sustainable Development 13 (2005) 261-268, Mikushina I.V., Changes in the Chemical Composition of Wood during Mechanochemical Treatment, Chemistry for Sustainable Development 10 (2002), 441-445), but these documents do not teach, disclose or suggest the possibility to use the mechanoactivation in the pretreatment process for saccharifϊcation.

It should to be noted that the ultrafine wood powder has specific properties; particularly it is watered rapidly and goes down immediately compared to conventional wood chips that float awash. It is clear that such properties give option to enzymes to contact efficiently with cellulose material. Also the saccharification process of such activated material takes less water, it is very important on an industrial scale. It gives option to improve the mixing with water, using ratio 1:6 (in case of untreated raw material 1:10). Such activated layers of the material surface have anomalously high chemical activity and sorption capacity but very low diffusion resistance. Large energy store accumulated in the disordered structure of the surface layers and low diffusion resistance may be used in low-temperature chemical reactions and define mechanochemical and mechanosorption processes. These factors results in increasing external surface that promotes the uniform dispersion of the fine powder in liquid during saccharification.

The coarse milling of the lignocellulosic material is carried out in mills, preferably in ball-mills to particles ranging in size from 1 mm to 2 mm with simultaneous drying by hot air blowing with temperature of 120-130 ⁰C. The process gives option to dry the raw material and prepare it for the ultrafine milling.

The ultrafine milling is carried out in vibro energy, colloid or jet mill that provides the shearing force, the ultrafine milling is carried out to particles ranging in size from 1 μm to 4 μm. During ultrafine milling of wood raw material the destruction occurs mainly by "flaking off" (fatigue failure) because of surface fracture of milling particles. Therefore the ultrafϊne milling is carried out by high frequency action into the material with relatively light shocks. The ultrafine milling process relies on the discrete character of the process through time (alternation of stress field and its relaxation) and the local character of the mechanical action into substance. It is important that the stress field arises only on the contact of one particle with another particle or a working element.

In result of such ultrafine milling the destruction of the fibrillar nature is accompanied by a mechanical rupture of the cellulose chain molecules, an increase in the moisture adsorption (resulting in better watering).

Mechanoactivation process is accompanied by the saturation of CO₂ at supercritical pressure, resulting in producing of carbonic acid that blocks conglomeration of particles and secondary crystal formation.

When naturally-occurring wood extractives (pitch and volatile organic compounds) are found in both resin canals within the structure of the wood, as well as within the parenchyma cells of the wood, the removal of pitch is preferable before the ultrafine milling. More particularly, wood chips are subjected to a solvent extraction process, preferably with acetone, and ethanol (ratio 1 :7 - 1 : 10) for pitch removal.

The process may be more easily understood with reference to FIG.l, where the schematic view of the system for carrying out of the claimed process is shown. The pretreated wood raw material (wood chips with the natural moisture of 28-37% and size of 2-200 mm), e.g. wood scrap 1 or off grade wood 2 are processed in a device for a coarse milling 3, which can be a ball-mill. Then 1-2 mm particles of wood chips from the device 3 are charged to an extractor 4 to remove pitch. The extracted particles are subjected to the ultrafine milling in a device for fine milling and mechanoactivation 5, which can be vibro energy, colloid or jet mill.

The invention may be further understood by the following non-limiting examples.

Example 1

Coniferous wood chips are milled in the ball mill (e.g. AS-2M, Novosibirsk) to size of 1 - 2 mm and are dried on hot air to humidity no more than 10%. The operating time of this process is 1 second. Then the obtained wood chips are extracted (e.g. using ultrasound-assisted extraction) with acetone or ethanol; the ratio of solvent to wood chips is in the range of from about 7:1 to about 10:1. The extracted wood chips are milled in the activation mill (AC-2C, Novosibirsk) to the size of l-5μm. The total operating time is 3 seconds. The obtained product is mechanoactivated ultrafine powder with the particle size distribution given in the Table 1.

Table 1 Particle size distribution of the ultrafine powder

Therefore the claimed pretreatment process, system and product have got the following advantages: the pretreatment of the raw material does not requre use of chemicals, it results in high productivity of the enzymatic hydrolysis of wood material to soluble sugars.

Claims

1. A process for pretreatment of wood raw material comprising two stage milling, wherein at the first stage a coarse milling is carried out, followed by an extraction of pitch and at the second stage a ultrafine milling is carried out, moreover the mechanoactivation of the obtained product takes place at the second stage.

2. The process of claim 1 wherein the coarse milling is carried out with simultaneous drying by hot air blowing with temperature of 120-130 ⁰C.

3. The process of claim 1 wherein during the mechanoactivation the material subjected to CO₂ action.

4. System for carrying out of the process of claims 1-3 comprising a device for a coarse milling of wood material, an extractor, a device for an ultrafine milling and mechanoactivation.

5. System of claim 17 wherein the device for an ultrafine milling and mechanoactivation comprises a device for CO₂ gas supply.

6. Product obtained by the process of claims 1-5.