EP3638803A1

EP3638803A1 - Process for obtaining cellulose from plant material

Info

Publication number: EP3638803A1
Application number: EP18749583.3A
Authority: EP
Inventors: Cornelis Adrianus Maria VAN LOON; Eduard Jan VAN ANTWERPEN; Johannes Izaak VAN KLINK; Ulrich Dreier; Manfred Steiner
Original assignee: Innovative Sustainable Technologies BV
Current assignee: Innovative Sustainable Technologies BV
Priority date: 2017-06-14
Filing date: 2018-06-12
Publication date: 2020-04-22
Also published as: WO2018231052A1; NL2019066B1

Abstract

The invention relates to a process for obtaining cellulose or a cellulose- containing substance from plant material, the process comprising - providing mashed plant material having a water content of at least 10 wt.% then - subjecting the plant material, when having a temperature of at least 40 °C, to a reduction in pressure by at least 0.1 bar by means of vacuum extrusion; then - fermenting the plant material to yield a fermentation broth comprising cellulose; then - isolating the cellulose or the cellulose-containing substance from the fermentation broth by one or more separation methods selected from the group of distillation, decantation, centrifugation, filtration, evaporation and washing with a fluid.

Description

Process for obtaining cellulose from plant material

The invention relates to a process for obtaining cellulose from plant material and to cellulose obtainable by such process.

Fueled by growing concerns about the environment and energy demands, there is an increasing interest to produce low-cost, biodegradable and environmentally friendly materials derived from renewable resources, such as agricultural waste or agro-industrial by-products.

Cellulose is one of the world's most useful and abundant natural materials. Essentially, they are chains of linked sugar molecules

(monosaccharides) that form the main component of cell walls in plant material. Since they are non-toxic, biodegradable and come from a renewable source, cellulose, and especially cellulose fibers, are an excellent component for the manufacture of a variety of consumer goods, such as textiles, paper and diapers, but also as a dietary fiber. In addition, due to their strength and durability, fibers of cellulose are increasingly being used as reinforcing materials in thermoset and thermoplastic polymeric matrices. Composite products reinforced by natural fibers can be used to replace those that are reinforced by synthetic fibers, for example in the automotive, packaging, and furniture manufacturing. Cellulose may also be used as an effective thermal isolator, for example as an aerogel in walls.

For many applications of cellulose (fibers), it is important that the cellulose is free of the other components that are naturally present in the plant from which the fibers are obtained, or at least that they are present in an amount that does not have a negative influence in the application of the cellulose. This concerns for example the presence of starch, hemi-cellulose, lignin,

(oligo)saccharides (such as sugar), proteins and salts. The incorporation of one or more of such components may lead to decreased product properties. For example, the presence of sugar or protein in paper or cardboard often causes an unpleasant odor. Also, the use of cellulose as a reinforcement fiber does not benefit from the presence of additional components such as lignin or

hemicellulose. It is this thus very important that other plant materials are partly or completely stripped from the cellulose during the isolation process. Isolating cellulose (or cellulose fibers) from plant material usually requires the destruction of the plant's cellular structure, including the disruption of the cells themselves. In conventional methods, this is often performed with extensive mechanical, chemical, and/or thermal treatments for disrupting the cell walls. Mechanical treatments to specifically break open the cellular structure include milling, shearing, grinding, crushing or squeezing. Other methods for disrupting cell walls include mechanical agitation, ultrasonic treatment, and electroporation. Typical chemical treatments are alkali treatments, bleaching treatments, acid treatments and oxidative treatments such as ozonolysis.

Processes that rely on a high temperature and/or a high pressure are, for example, torrefaction, hot water treatments, steam explosion, CO₂-explosion and the like.

Drawbacks of these conventional processes are that they generate high amounts of chemical waste and/or are energy intensive, which makes them unattractive to use from an environmental point of view. Moreover, they require high capital expenditures.

It is therefore an object of the present invention to provide a clean and effective process for obtaining cellulose (or cellulose fibers) from plant material. It is also an object to provide cellulose fibers that can replace conventional fibers in the reinforcement of materials.

It has now been found that one or more of these objects can be reached by making use of a particular sequence of treatments of the source plant material.

Accordingly, the present invention relates to a process for obtaining cellulose or a cellulose-containing substance from plant material, the process comprising

providing mashed plant material having a water content of at least 10 wt.%; subjecting the mashed plant material, when having a temperature of at least 40 °C, to a reduction in pressure by at least 0.1 bar by means of vacuum extrusion, to yield vacuum extruded plant material;

fermenting the vacuum extruded plant material to yield a fermentation broth comprising the cellulose or the cellulose-containing substance; isolating the cellulose or the cellulose-containing substance from the

fermentation broth mixture by one or more separation methods selected from the group of distilling, decanting, centrifuging, filtering, evaporating, and washing with a fluid (e.g. with water.)

For the purpose of the invention, by a polysaccharide is meant a polymer comprising two or more saccharide monomers joined by glycosidic bond. Polysaccharides that comprise up to ten saccharide monomers are usually termed oligosaccharides. Sugars include monosaccharides and oligosaccharides, in particular oligosaccharides of two, three or four saccharide monomers, for example sucrose, fructose, glucose, galactose, maltose, lactose, and mannose.

Figure 1 displays a schematic representation of the process of the invention.

Figures 2 and 3 display the breaking length of paper as a function of the beet pulp content when the paper is manufactured manually.

Figures 4 and 5 display the breaking length of paper as a function of the beet pulp content when the paper is manufactured with a paper machine.

The application of vacuum extrusion on plant material followed by a fermentation appears to be a mild and effective method to destroy the plant's cellular structure and at the same time to provide a first product stream of cellulose (or a cellulose-containing substance) and a second product stream of fermentation product(s), i.e. products resulting from the fermentation of mono- or

oligosaccharides, for example sugar.

The vacuum extrusion as well as the fermentation are performed under relatively mild conditions and can easily be integrated into one process. It was found that the obtained cellulose is substantially free of sugar, and has a reduced content of hemicellulose, pectin and lignin as compared to the cellulose originally present and also as compared to the cellulose obtained via conventional processes. The particular properties of the obtained cellulose make it suitable for use as e.g. a reinforcement material or an isolation material.

In the process of the invention, the vacuum extrusion to disrupt the cells is in fact an extrusion of the plant material into a decompression chamber. This comprises feeding the plant material from an inlet through a small opening into a vacuum chamber that is at a pressure below atmospheric pressure. Typically, prior to the feeding into the chamber, the plant material is at atmospheric pressure or at a pressure in the range of 1 .0-2.5 bar. The vacuum chamber is at a dynamic vacuum during operation, and is therefore connected to a vacuum pump. Since the inlet is typically at atmospheric pressure or above atmospheric pressure, there is a pressure difference between both sides of the opening. The entrance in the chamber occurs through a relatively small opening, so that the pressure difference is maintained and the flow of plant material into the vacuum chamber is not too high. In this way, an explosion-like evaporation of water occurs, as a result of which the cellular structure is disrupted. It is understood that the capacity of the vacuum pump and an eventual condenser associated thereto, as well as the dimensions of the vacuum chamber also play a role in here, since a strong pump and a large vacuum chamber may allow for a bigger opening without

compromising the result of the vacuum extrusion (the size of the opening can usually be set, for example by means of a pump). Moreover, the size of the vacuum chamber is important for its capacity of separating water from cellulose- containing plant material.

The temperature of the stream of mashed plant material at the entrance of the vacuum chamber is at least 40 °C. It is typically in the range of 40-80 °C, for example in the range of 45-70 °C or in the range of 50-60 °C. In particular, when sugar beet is used as a plant material, a temperature in the range of 60-70 °C is preferred.

In general, the higher the temperature of the plant material just before the entrance of the vacuum chamber, the more efficient the vacuum extrusion step is (more plant cells are broken open in less time and/or larger sized pieces of plant material can be used). Further, heating of the plant material prior to the vacuum extrusion also helps to reduce the number of micro-organism contaminants. In some embodiments, the plant material can be heated to a temperature as high as about 120 °C. In most cases, however, a lower temperature is sufficient for an efficient vacuum extrusion. Generally, temperature is less than 100 °C.

Part of the water that is present in the stream of mashed plant material evaporates upon entry into the vacuum chamber, which is therefore often provided with a condenser. As a result, the temperature of the plant material drops and the water vapor condenses in the vacuum chamber. The water may be collected on the bottom of the vacuum chamber and fed upstream to the mashed plant material. In general, the higher the initial temperature of the mashed plant material prior to the decompression is, the higher the temperature of the vacuum extruded material is after the decompression. In the event that mashed plant material of sugar beet is used at a temperature in the range of 70-90° C before the

decompression, it drops to a temperature in the range of 30-50 °C in the vacuum chamber, which is a suitable temperature for the fermentation of the vacuum extruded product. Further heating of the fermentation broth is then usually not necessary. When an active condenser is present, then the capacity thereof influences the drop in temperature. For example, with a high capacity, more water is condensed, which results in a lower temperature of the vacuum extruded product.

It has been found that the vacuum extrusion not only destroys the plant material's cellular structure, but also other living cells present, such as

micro-organisms originating e.g. from the soil in which the plant was grown or that became associated with the plant material during storage. Thus, the vacuum extrusion also has the effect of reducing the number of micro-organisms present in the plant material feedstock. Usually, this effect plays a significant role when the temperature of the mashed plant material at the entrance of the vacuum chamber is at least 85 °C. This is especially advantageous in view of the subsequent fermentation, because micro-organisms often disturb the fermentation, especially when present in high amounts. It is therefore an advantage of the process of the invention that with the disruption of the plant material's cellular structure, also the number of micro-organisms is reduced. This may reduce the need for extensive cleaning of the raw plant material.

Without wishing to be bound to any theory, the rapid decompression during vacuum extrusion is believed to result in an explosion of the cell wall of the plant material, resulting in the destruction of the cell. Any micro-organisms present on the plant material {e.g. from the soil in which the plant was grown or that became associated with the plant material during storage), will likely also be killed during the vacuum extruding process.

By the term vacuum chamber is meant a chamber (e.g. a container or vessel) that is at a reduced pressure, i.e. a pressure lower than atmospheric pressure. The pressure in the vacuum chamber during operation of the process may in principle be at any value between 0 and 1 bar. Since the vacuum chamber receives a continuous feed of wet plant material, the pressure in the vacuum chamber during operation of the process of the invention is not actually a high vacuum, so that in practice it is typically at least 0.005 bar. For example, it is in the range of 0.01-0.9 bar, in the range of 0.05-0.5 bar, or in the range of 0.1-0.25 bar. The reduction in pressure is usually a reduction in the range of 0.2-5 bar, in particular in the range of 0.25-2.5 bar, more in particular in the range of 0.3-1 .3 bar, even more in particular in the range of 0.5-0.9 bar. Accordingly, the pressure before entrance into the vacuum chamber may be 4 bar or less, 3 bar or less,

2 bar or less, 1 .5 bar or less or 1 .2 bar or less. In principle, the pressure is one bar or higher. Preferably, the pressure before entrance into the vacuum chamber is in the range of 1-2 bar, more preferably in the range of 1 .0-1 .5 bar.

In particular, when sugar beet is used as a plant material, the pressure before entrance into the vacuum chamber is in the range of 1.0-2.0 bar and drops to a pressure in the range of 0.05-0.25 bar in the vacuum chamber. The temperature in the vacuum chamber may then be in the range of 25-45 °C, in particular in the range of 30-40 °C.

In many conventional processes for the extraction of valuable products from plant material, the plant material is sliced or cut into smaller pieces (such as cossettes) and then boiled to form an aqueous extract with the desired

components. This is for example the treatment on which the isolation of sucrose from sugar beets conventionally relies. The residue that remains after the separation of the extract contains cellular material, which is for a large part cellulose. However, the cellulose obtained in this way is usually not suitable for use in consumer products, such as card board or, on the high-end, for use as a reinforcement fiber. It is therefore commonly used as a fertilizer or fed to a fermenter for the production of biogas.

The plant material in a process of the invention, on the other hand, needs to be mashed or crushed prior to the vacuum extruding and have a water content of at least 10 wt.% so that an effective disruption occurs during the vacuum extrusion. Usually, it is at least 25%, preferably it is at least 50%. It may be in the range of 10-90 wt.%, in particular in the range of 50-80 wt.%. The mashing ensures that the original shape and structure of the plant material as formed during its growth are essentially lost, so that the mashed plant material essentially has become a fluid. This is important because the transport of the plant material through the opening to the vacuum chamber should not be discontinued due to the presence of lumps of material that may only pass a whole. In addition, it is important that the plant material is not too viscous and can easily flow through the pipes in the system wherein the process is performed {e.g. through the heat exchanger and through the pipes that feed the inlet of the vacuum chamber). The skilled person will be able to find the appropriate process conditions for a specific plant material, such as the water content (and thus the viscosity) of the mashed plant material, the temperature at the entrance of the vacuum chamber and the pressure at which the vacuum chamber is operated, by routine experimentation and without exerting an inventive effort.

Preferably, the flow of plant material to the vacuum chamber in such system is accomplished without exerting high pressures, because this would put additional requirements to the equipment and is not energy-efficient. In case the mashed plant material as such does not easily flow in the system, extra water may be added. For example, a sugar beet has a water content of approximately 75 wt.%. For a good processability of the mashed beet, the flow properties may be improved by the addition of water. For example, water is added to yield a total water content of up to 80 wt.%, up to 85 wt.% or up to 90 wt.%.

Apart from these considerations with respect to the processability, it is preferred, however, that the water content in a process of the invention is as low as possible. This is because in subsequent process steps any water that is present also has to be removed from the cellulose fibers. When this is performed by evaporation (or distillation), this requires undesired amounts of energy, and when this is performed by a filtration or decanting, there is a stream of aqueous waste that is relatively diluted, which is also undesired. Therefore, the water content is usually 90 wt.% or less, preferably it is 80 wt.% or less, more preferably it is 70 wt.% or less.

Harvested plant material often comprises the dirt that is typically present in an agricultural field, such as sand, soil, organic material not belonging to the harvested crop, micro-organisms (such as yeasts and bacteria), fertilizer or manure. Such contaminations may interfere with the process, and negatively affect it. Yeasts and bacteria present on the plant material may be particularly disturbing during the fermentation and can then give undesired products. Therefore, the plant material in a process of the invention is usually cleaned before it is used in the process. This may be performed by washing it with water, preferably by making use of a high speed water spray.

Generally, the term "plant material" refers to a relatively unprocessed plant material, having intact plant cells. The plant material may in principle be any plant material. Usually, it is derived from a plant selected from the group consisting of a grain, a root, a vegetable, a fruit, a legume, and a grass. When mashed, a stream of such plant material may be obtained that is suitable for being processed in a process of the invention.

More in particular, the plant material may be derived from a plant selected from the group consisting of sorghum (milo), sweet sorghum, oats, barley, wheat, rye, millet, berry, grape, rye, maize, rice, potato, sweet potato, cassava, sugar beet, sugar cane, pineapple, grasses, and vegetables and parts thereof like stamps and leaves.

The process of the invention works particularly effective with plant material wherein there is a moderate degree of lignification of the cellulose.

Lignification of a material is known as the result of the deposition of lignin in the extracellular polysaccharidic matrix (cellulose), making that material hard, like wood. A softer plant material usually has a lower degree of lignification and is more prone to delignification by a process of the invention. A plant material that that is particularly suitable as a feed in the process of the invention is a plant material that originates from sugar beet crop (Beta vulgaris, in particular Beta vulgaris subspecies vulgaris), in particular the root of this crop.

This species appeared to be a particularly suitable substrate plant material to feed to the process of the invention and so let it undergo the vacuum extrusion to destruct the cell walls and convert these into cellulose (or a cellulose- containing substance) of a high grade. It seems that the stripping of lignin, pectin and hemicellulose from the cellulose is performed particularly well with this species. Another advantage of using sugar beet is that it yields a first product stream of fermented sugar products and a second product stream of cellulose (or a cellulose-containing substance). Without wishing to be bound to theory, it is contemplated that the advantages obtained with the use of sugar beet rely on the features of the cellulose fibers (appropriate dimensions, no too long, not too much lignified) in combination with the presence of an appropriate amount sugar. There appears to be a synergy between the two in that the consumption of sugar leads to an improved disengagement of the cellulose.

On the other hand, it is preferred not to use plant material derived from wood, because this material is usually too much lignified (i.e. too hard and too solid) for vacuum extrusion.

Usually, the plant material is plant material that has been mashed after its harvesting and which has not yet undergone any treatments wherein some of its contents were removed (such as extraction). It is however possible that the plant material that is used in a process of the invention has indeed already been subjected to any such treatments, for example to a sugar extraction treatment in the case of sugar beets. The cellulose waste product produced by the

conventional processing of sugar beets (to produce sugar) may act as the source plant material in a process of the invention. This waste material usually comprises slices and/or chunks of sugar beet that still have their original shape, but which are well suited to transform into cellulose fibers via a process of the invention.

By fermentation is meant the process of transforming an organic molecule into another molecule using a micro-organism. It can for example refer to the aerobic transformation of sugars or other molecules from extruded plant material to produce one or more products selected from the group of alcohols (e.g. ethanol, methanol, butanol), organic acids (e.g., citric acid, acetic acid, itaconic acid, lactic acid, gluconic acid), ketones (e.g., acetone), amino acids (e.g. glutamic acid), gases (e.g. H₂ and CO₂), antibiotics (e.g. penicillin and tetracycline), enzymes, vitamins (e.g. riboflavin, Bi₂, beta-carotene), and hormones.

Fermentation can include fermentations used in the consumable alcohol industry (e.g. beer and wine), dairy industry (e.g., fermented dairy products), leather industry, and tobacco industry. Thus, fermentation includes alcohol fermentation. Fermentation also includes anaerobic fermentations, for example, for the

production of biogas.

The fermentation serves two main purposes. First, it converts part of the plant's constituents, in particular sugars, into valuable products such as fuels or starting materials for various chemical processes. Second, many plant

constituents that naturally surround the cellulose in the plant material, are removed from the cellulose during the fermentation (lignin, pectin, hemicellulose). In this way, cellulose can be obtained that is substantially free of such constituents, or contains substantially smaller amounts of them. In this way, the invention accomplishes that the plant material is converted into two valuable product streams by applying one single, integrated, process, viz. a first stream of cellulose (or a cellulose-containing substance) and a second stream of fermentation product(s). Moreover, this process is robust and straightforward.

The fermenting step usually comprises the preparation of the fermentation mixture. This may be performed by mixing the extruded plant material with water and yeast. It may be advantageous to add water to the vacuum extrusion product prior to the fermentation, to lower the viscosity and facilitate the transport in the pipes that feed the vacuum chamber, circumventing for example the use of high pressure to achieve the transport.

In some embodiments, the preparation of the fermentation mixture comprises the addition of an enzyme, which converts the polysaccharides in the fermentation mixture into fermentable sugars and/or further breaks down plant cell walls. The amount of enzyme may be in the range of 1-200 g of enzyme per hectoliter of fermentation mixture, in particular in the range of 100-150 g. It may also be in the range of 5-50 g or in the range of 10-20 g of enzyme per hectoliter of fermentation mixture. The fermentation mixture may also be prepared without the addition of an enzyme. A stabilizer may be added in order to create better conditions for the fermentation, for example one or more compounds selected from the group of SO2, antibiotics and potassium metabisulfite (K2S2O5).

The fermentation is usually carried out by incubating the fermentation mixture to a temperature in the range of 10-80 °C. Depending on the type of yeast, a particular temperature may be applied. For example, the temperature may be in the range of 15-50 °C, in the range of 20-40 °C, or in the range of 30-35 °C. It may also be in the range of 30-75 °C, in the range of 40-60 °C or in the range of 45-55 °C. Fermentations to yield ethanol are usually carried out at a temperature in the range of 10-40 °C, for example at a temperature in the range of 32-34 °C.

In case sugar beet crop is used in the process of the invention, the process is usually performed 1 ) with mashed sugar beet crop that comprises an additional amount of water in the range of 0-25%; 2) at a temperature that is in the range of 25-40 °C; 3) with a pH that is in the range of 1 .0-10.0, in particular in the range of 2.0-9.0, more in particular in the range of 2.5 to 8.0. In such process, it is preferred that 1 ) the mashed plant material comprises an additional amount of water in the range of 0-20%; 2) the temperature is in the range of 28-32 °C;

and 3) the pH is in the range of 3.0-7.0, more preferably in the range of 3.5-6.0. It is further preferred that the fermentation mixture is stirred at regular intervals.

The fermentation may be performed batch-wise or in a continuous manner. When batch-wise, the period during which the fermentation takes place is usually in the range of 4-200 hours, in particular in the range of 5-120 hours, more in particular in the range of 10-72 hours and even more in particular in the range of 35-48 hours.

For the purpose of the present invention, the mixture of products that is formed during the fermentation of the plant material is named the fermentation broth. This mixture contains the cellulose and/or the cellulose-containing substance as well as the products into which polysaccharide materials (in particular the sugars) of the plant material are converted.

In an embodiment, the fermentation comprises

adding water and yeast to the vacuum extruded plant material to form a fermentation mixture;

maintaining the fermentation mixture at a temperature in the range of 30- 35 °C during a time period in the range of 5-120 hours.

The fermentation is usually performed by a fungal organism (e.g., yeast or filamentous fungi). The yeast may in principle be any yeast that is capable of converting constituents of the plant material into the desired product. Usually, the yeast is capable of producing ethanol. The yeast can include strains from a Pichia or Saccharomyces species. The yeast species may for example be

Saccharomyces cerevisiae. It is also possible that the fermentation is performed by bacteria. For example by Clostridium acetobutylicum (which produces butanol) and

Corynebacterium glutamicum (which produces monosodium glutamate (MSG)).

The micro-organism that is used in the fermentation (e.g. yeast or bacteria) can be a genetically modified micro-organism.

The pH of the mixture during the fermentation also depends on the type of yeast. Usually, however, the pH is in the range of 3.0-6.6, in particular in the range of 5-6, more in particular in the range of 5.0-6.0.

The fermentation results in the formation of the fermentation product mixture, the fermentation broth. This is an aqueous mixture comprising the products produced by the yeasts and the products resulting from the further destruction of the cellular materials, such as cellulose or a cellulose-containing substance, the latter being a composite of cellulose with e.g. hemicellulose, pectin and/or lignin.

The cellulose product (and/or the cellulose-containing product) needs to be isolated from the fermentation broth. This comprises a purification method, which is typically a solid-liquid separation, since the cellulose is not dissolved. This purification or separation may be performed by techniques known in the art, in particular by a method selected from the group of distilling, decanting, centrifuging, and filtering. In particular, a solid-solid separation may be required to remove solid residues of the fermentation broth (e.g. remnants of the yeasts) from the cellulose. In case the products produced by the yeasts have a suitable boiling point, for example ethanol, then these can be removed by distillation. In such case, a further solid-solid separation may in particular be needed because residues from the fermentation broth are still present after distillation. The (residual) fermentation product containing the cellulose may then be washed to remove dissolved byproducts such as salts and other water-soluble components that originate from the treated plant material or are formed during the process of the invention. Use may e.g. be made of filtration and/or sedimentation followed by decantation.

Techniques for solid-solid separation that are known in the art may also be applied, in particular to remove non-cellulosic material that is not dissolved, from the cellulose or the cellulose-containing substance. In an embodiment, the isolation of the cellulose or cellulose-containing substance comprises heating the fermentation broth to remove ethanol, followed by washing the cellulose with water, or a water-containing fluid.

Usually, the purification method comprises, or is followed by, the removal of water so that a substantially dry product is obtained. This may be performed by centrifugation or by the evaporation of water, in particular by drying under reduced pressure (usually at a pressure lower than atmospheric pressure). For example, the water content in the isolated cellulose or the cellulose-containing substance is 5 wt.% or less, 4 wt.% or less, 3 wt.% or less, 2 wt.% or less, 1 wt.% or less, 0.5 wt.% or less, 0.2 wt.% or less, 0.1 wt.% or less or 0.05 wt.% or less.

Figure 1 displays an embodiment of process (1 ) of the invention, wherein the subsequent process steps are identified. First, mashed plant material (1 1 ) is provided, which undergoes the vacuum extrusion to yield the vacuum extruded plant material (12). Thereafter, this is fermented to yield fermentation broth (13). The fermentation broth is then separated into different

components (14). The cellulose or the cellulose containing substance is separated as the first product stream (14a), which is typically a substantially dry product. The product(s) resulting from the fermentation of sugar (typically ethanol obtained by distillation) form(s) the second product stream (14b). The matter that remains after the separation of (14a) and (14b) from the fermentation broth is residue (14c).

The cellulose product that is produced by the process of the invention is cellulose or a cellulose-containing substance. Depending on the purity, it is obtained as a dry powder or a more tight or stiff solid substance. It may be a white, off-white, yellow or even brownish substance. In an embodiment, the cellulose or cellulose-containing substance was isolated as cellulose fibers.

The obtained cellulose product may be used in a subsequent process, in particular a process wherein a certain product is made from the cellulose product. The obtained cellulose product may be modified, for example into an aerogel. It may also be incorporated into another material such as paper or polymer. The obtained cellulose product may also be converted into other products or compounds, for example a keto acid such as levulinic acid.

The cellulose-containing substance formed in the process of the invention usually contains at least 20 wt.% of cellulose. It may also contain 30 wt.% or more, 40 wt.% or more, 50 wt.% or more, 60 wt.% or more, 70 wt.% or more, 75 wt.% or more, 80 wt.% or more, 85 wt.% or more, 90 wt.% or more, 95 wt.% or more, 97 wt.% or more, 98 wt.% or more, 99 wt.% or more or 99.5 wt.% or more. Typically, the cellulose content is in the range of 65-99.8 wt.%, or in the range of 80-98.5 wt.%. Other components in the cellulose-containing substance are usually one or more compounds selected from the group of hemicellulose, pectin, proteins and saponins.

Accordingly, the invention further relates to cellulose (in particular cellulose fibers) or a cellulose-containing substance obtainable by the process of the invention. Preferably, the cellulose is derived from sugar beet {Beta vulgaris subsp. vulgaris).

The invention further relates to an object comprising cellulose or a cellulose-containing substance obtainable by the process of the invention, in particular cellulose fibers obtainable by the process of the invention. The cellulose in such object is preferably derived from sugar beet {Beta vulgaris, in particular Beta vulgaris subspecies vulgaris).

The cellulose in the object of the invention may act as a fire retardant. It may also provide (fiber) reinforcement to the object.

The invention therefore further relates to an object, in particular a plastic object, that is reinforced with cellulose or a cellulose-containing substance obtainable by the process of the invention, in particular with cellulose fibers obtainable by the process of the invention.

The cellulose and/or the cellulose-containing substance (in particular wherein the cellulose is present as fibers) obtainable by the process of the invention may be used for the manufacture of paper or cardboard. It is then preferably used to replace a part of the cellulose in conventional paper or cardboard.

The invention therefore further relates to a paper or cardboard comprising the cellulose or the cellulose-containing substance obtainable by the process of the invention. Preferably, the plant material in the process is sugar beet, so that the cellulose in the paper or cardboard is then derived from sugar beet {Beta vulgaris, in particular Beta vulgaris subspecies vulgaris). Usually, the cellulose that is formed with the process of the invention then constitutes 90 wt.% or less of the total cellulose amount in the paper or cardboard, in particular in the range of 2-75 wt.%, more in particular in the range of 5-50 wt.%. It may also comprise 80 wt.% or less, 70 wt.% or less, 60 wt.% or less, 50 wt.% or less, 40 wt.% or less, 30 wt.% or less, 25 wt.% or less, 20 wt.% or less, 15 wt.% or less, 10 wt.% or less, or 5 wt.% or less.

When the cellulose-containing substance is used for the manufacture of the paper or cardboard, then the dry matter (i.e. the weight of the substance that remains after the complete evaporation of the water from the substance) of this substance usually constitutes 90 wt.% or less of the dry weight of the final paper or cardboard, in particular in the range of 2-75 wt.%, more in particular in the range of 5-50 wt.%. It may also comprise 80 wt.% or less, 70 wt.% or less, 60 wt.% or less, 50 wt.% or less, 40 wt.% or less, 30 wt.% or less, 25 wt.% or less, 20 wt.% or less, 15 wt.% or less, 10 wt.% or less, or 5 wt.% or less. In these cases, the level of cellulose in the cellulose-containing substance may be in the range of 10-75 wt.%.

The dry matter of the substance usually constitutes at least 1 wt.% of the dry weight of the final paper or cardboard. It may also constitute at least 2 wt.%, at least 3 wt.%, at least 5 wt.%, at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, or at least 80 wt.%.

The invention further relates to a process for the manufacture of paper or cardboard, comprising the use of cellulose, preferably cellulose derived from Beta vulgaris, more preferably from Beta vulgaris subspecies vulgaris,

wherein that cellulose is obtained by

providing mashed plant material, preferably originating from Beta vulgaris, more preferably from Beta vulgaris subspecies vulgaris, having a water content of at least 10 wt.%; then

subjecting the mashed plant material, when having a temperature of at least 40 °C, to a reduction in pressure by at least 0.1 bar by means of vacuum extrusion; then

fermenting the vacuum extruded plant material to yield a fermentation broth comprising cellulose; thereafter subjecting the fermentation broth to one or more separation methods selected from the group of distillation, decantation, centrifugation, filtration, evaporation and washing with a fluid.

The separation method(s) in the last step may also be performed during the actual process of paper or cardboard making. For example, the fermentation broth as such may also be used as a cellulose pulp ('beet pulp') that is part of the starting material in paper or cardboard manufacture. To this end, the beet pulp is typically mixed with a conventional cellulose comprising pulp (for example one originating from old/recycled paper). The resulting pulp is then processed according to known procedures in the paper or cardboard manufacturing, which typically comprise a dewatering step where use is made of decantation or filtration. Such dewatering step is then a separation method as required in the process of the present invention.

It was surprisingly found that the mechanical properties of paper and/or cardboard obtained in this way were superior to those of recycled paper and to those of paper made of virgin cell material (i.e. non-recycled paper). For example, the breaking length of the paper and/or cardboard according to the invention appears to be higher than that of conventional paper. This is further described in Example 1 , and illustrated in Figures 2-5.

The invention further relates to a paper or cardboard comprising cellulose derived from sugar beet (Beta vulgaris, in particular Beta vulgaris subsp. vulgaris). Usually, the cellulose then constitutes 90 wt.% or less of the total cellulose amount in the paper or cardboard, in particular in the range of 2- 75 wt.%, more in particular in the range of 5-50 wt.%. It may also constitute 80 wt.% or less, 70 wt.% or less, 60 wt.% or less, 50 wt.% or less, 40 wt.% or less, 30 wt.% or less, 25 wt.% or less, 20 wt.% or less, 15 wt.% or less, 10 wt.% or less, or 5 wt.% or less. It may also constitute at least 2 wt.%, at least 3 wt.%, at least 5 wt.%, at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, or at least 80 wt.%.

In a process of the invention, there is in principle no need to add a further chemical such as liquid ammonia or potassium hydroxide for treating the plant material prior to the vacuum extrusion, or at any later stage of the process. Since the vacuum extrusion is performed under relatively mild conditions, such as low temperatures (e.g. 40-60 °C) and pressures around atmospheric pressure {e.g. 0.1-1 .1 bar), the process is energy-efficient and saves energy as compared to conventional processes. The mildness also manifests in that the vacuum extrusion does not produce toxic derivatives which can inhibit the subsequent fermentation step, such as furaldehyde, 5-hydroxymethyl-2- furaldehyde, and phenolic compounds resulting from lignin depolymerization. The formation of such inhibitors often occurs with harsh methods such as steam explosion - this then requires a washing step with e.g. water to remove the inhibitors prior to the fermentation.

The use of sugar beet as a plant material proved particularly advantageous, since a high quality cellulose can be isolated, or at least a cellulose-containing material with beneficial properties, by the process of the invention. The stripping of lignin, pectin and hemicellulose from the cellulose in this species occurs particularly effective with a method of the invention. In parallel to this, the process of the invention also yields a useful fermentation product

(ethanol).

An advantage of the process of the invention is that no further chemicals (for example ammonia or potassium/sodium hydroxide) are needed for the treatment of the plant material. In addition, no high pressures need to be applied, which results in a simple, energy-efficient and cost-effective process as compared to those known in the art. This is because the lower pressures require less energy and less robust equipment.

The invention further relates to the use of vacuum extrusion and fermentation for the isolation of cellulose or a cellulose containing substance from plant material, in particular isolation in a dry form, wherein the vacuum extrusion comprises subjecting the plant material, when having a temperature of at least 40 °C, to a reduction in pressure by at least 0.1 bars, and wherein the vacuum extrusion is followed by the fermentation. EXAMPLE

Formation of beet pulp and its use in the manufacture of paper. Sugar beets (Beta vulgaris subsp. vulgaris) were grown and harvested.

After the removal of sand and stones, the beets were mashed/crushed to yield a pumpable pulp. When necessary for sufficient pumpability, extra water was added. The beet material was then brought at a temperature of 68 °C and fed into the vacuum chamber through a small opening. This vacuum chamber was kept at a pressure of 0.20 bars; the speed of feeding through the small opening was chosen such that this pressure could be maintained. The temperature after decompression in the vacuum chamber was then in the range of 30-35 °C. The resulting vacuum extruded product was then fermented at 32 °C using bakers' yeast, followed by distillation at 100-1 10 °C to remove the ethanol. The resulting residue after fermentation ('beet pulp') was then mixed either with recycled paper or with virgin cellulose (i.e. cellulose that is not the result of the recycling of paper but freshly obtained from plant material, in this case a mixture of ground short fibers from Eucalyptus and long fibers from Celesta), resulting in a production pulp that forms the source pulp for the paper production. The amount of beet pulp in the

production pulp was varied in different paper production runs. A first set of production runs was performed manually on laboratory scale, wherein the paper was prepared from production pulp comprising 0%, 25%, 50% or 75% of beet pulp. A second set of production runs was performed with a conventional paper manufacturing machine, wherein the paper was prepared from production pulp comprising 0%, 10%, 20% or 30% of beet pulp. All these percentages are weight percentages based on the dry matter of the beet pulp, the recycled paper and the virgin cellulose. In both sets of productions runs, the beet pulp was either ground or used as such (unground). The paper was manufactured from the production pulp according to procedures known in the art and by using additives known in the art. In the process of paper making, the production pulp (i.e. including the beet pulp) was dewatered on a sieve. This was either a laboratory sieve wherein the production pulp dewaters stationary and in a vertical manner; or a sieve in a paper manufacturing machine wherein the pulp flows over the sieve. The length at breaking (the breaking length) of all obtained papers was determined. For the papers manufactured with the paper machine, the breaking length was determined in two perpendicular directions: in the machine direction (MD; the direction of the flow over the sieve) and the cross-direction (CD;

perpendicular to the machine direction). The breaking length (BL; in meters) was calculated according to the formula (I)

BL = 102 x (tensile strength / grammage) (I) The breaking length of the papers obtained under laboratory conditions is displayed as a function of the % beet pulp in the production pulp in Figure 2 (beet pulp with recycled paper) and Figure 3 (beet pulp with virgin cellulose). Both figures display two measurements for each % beet pulp in the production pulp. These concern papers produced with (right bars) or without (left bars) grinding the beet pulp.

The breaking length of the papers obtained with the paper machine is displayed as a function of the % beet pulp in the production pulp in Figure 4 (beet pulp with recycled paper) and Figure 5 (beet pulp with virgin cellulose). Both figures display four measurements for each % beet pulp in the production pulp. These concern papers produced with or without grinding the beet pulp; and each paper has been measured in either the machine direction (MD) or the cross direction (CD).

From these results, it can be concluded that the presence of beet pulp (cellulose derived from sugar beet) significantly adds to the strength of the paper. The smaller increase for papers manufactured on the paper machine (as compared to the manual production) is probably due to the fact that the cellulose fibers are given the possibility to orient themselves during their flow over the sieve in the paper machine. This orientation results in a better packing of the fibers and a stronger interaction between them. This however partly masks the surprising finding that the presence of beet pulp makes the paper significantly stronger.

Claims

1 . A process for obtaining cellulose or a cellulose-containing substance from

plant material, the process comprising

- providing mashed plant material having a water content of at least 10 wt.%; then

- subjecting the plant material, when having a temperature of at least 40 °C, to a reduction in pressure by at least 0.1 bar by means of vacuum

extrusion; then

- fermenting the plant material to yield a fermentation broth comprising

cellulose; then

- isolating the cellulose or the cellulose-containing substance from the

fermentation broth by one or more separation methods selected from the group of distillation, decantation, centrifugation, filtration, evaporation and washing with a fluid.

2. Process according to claim 1 , wherein the plant material is derived from a

plant selected from the group consisting of a grain, a root, a vegetable, a fruit, a legume, and a grass.

3. Process according to claim 1 or 2, wherein the plant material is derived from a plant selected from the group consisting of sorghum (milo), sweet sorghum, oats, barley, wheat, rye, millet, berry, grape, rye, maize, rice, potato, sweet potato, cassava, sugar beet, sugar cane, pineapple, grasses, and vegetables and parts thereof like stamps and leaves.

4. Process according to any of claims 1-3, wherein the plant material is derived from sugar beet {Beta vulgaris subsp. vulgaris).

5. Process according to any of claims 1-4, wherein the water content of the

mashed plant material is in the range of 10-90 wt.%, in particular in the range of 50-80 wt.%.

6. Process according to any of claims 1-5, wherein the vacuum extrusion is performed at a pressure in the range of 0.05 and 0.5 bar.

7. Process according to any of claims 1-6, wherein the reduction in pressure is a reduction in the range of 0.2-1 .1 bar, in particular in the range of 0.3-1 .0 bar, more in particular in the range of 0.5-0.9 bar.

8. Process according to any of claims 1-7, wherein the plant material is at a

temperature in the range of 45-70 °C when it is subjected to the reduction in pressure in the vacuum extrusion, in particular at a temperature in the range of 50-60 °C.

9. Process according to any of claims 1-8, wherein the fermentation comprises

- adding water and yeast to the vacuum extruded plant material to form a fermentation mixture;

- maintaining the fermentation mixture at a temperature in the range of 30- 35 °C during a time period of at least 5 hours, in particular in the range of 5-120 hours.

10. Process according to any of claims 1-9, wherein the isolation of the cellulose or cellulose-containing substance comprises heating the fermentation broth to remove ethanol, followed by washing the cellulose or cellulose-containing substance with a fluid, in particular water.

1 1 . Process according to any of claims 1-10, wherein the cellulose or cellulose- containing substance is isolated as fibers.

12. Process according to any of claims 1-1 1 , wherein water is removed during the isolation, so that the cellulose or cellulose-containing substance is isolated as a substantially dry product, preferably with a water content of 1 wt.% or less.

13. Process according to any of claims 1-12, followed by converting the obtained cellulose into levulinic acid.

14. Cellulose or cellulose-containing substance obtainable by the process of any of claims 1-12.

15. Paper or cardboard comprising the cellulose or cellulose-containing substance according to claim 14, wherein the cellulose is derived from Beta vulgaris, in particular from Beta vulgaris subsp. vulgaris.