Field

[0001] The invention relates to a hydrolysis process in which polysaccharides are broken down.

Background

[0002] Ethanol may be produced by breaking down cellulose in a hydrolysis reactor to produce glucose, which may then be further converted into ethanol in a fermentation process. Cost-efficient ethanol production aims at using high glucose concentrations in order to achieve an ethanol concentration of over 4% in the fermentation broth. Usually a glucose concentration of at least 8% is required to reach an ethanol concentration of at least 4% in fermentation. An ethanol concentration of less than 4% in the fermentation mixture increases distillation costs significantly. For a glucose content of 8% to be achieved, a pulp containing lignin cellulose must typically have a dry matter content of over 15% in an enzymatic hydrolysis.

[0003] Since an efficiently working hydrolysis process is aimed at, the pulp containing cellulose and enzyme is mixed in the hydrolysis reactor during the process.

[0004] However, there are problems involved in hydrolysis. Proper mixing is not achieved especially if the dry matter content and/or particle size is high. Mixing also consumes a lot of energy and a requirement of continuous mixing limits the hydrolysis options available. There is therefore a need for a novel hydrolysis process.

Brief description

[0005] It is an object of the invention to provide an improved hydrolysis process. This is achieved by a hydrolysis apparatus comprising a hydrolysis process part; an inlet connector structure for receiving pulp containing polysaccharide and a catalyst and/or pre-catalyst, which is arranged to produce a catalyst in the hydrolysis process part, and for transferring them to the hydrolysis process part; and the hydrolysis process part is arranged to keep the hydrolysis process of the pulp and catalyst mixture running by micromixing only for splitting the polysaccharide. [0006] The invention also relates to a method for carrying out hydrolysis. The method comprises receiving pulp containing polysaccharide and a catalyst and/or pre-catalyst, which produces a catalyst in the hydrolysis process part, by an inlet connector structure and transferring the pulp and the catalyst and/or pre-catalyst into the hydrolysis process part; keeping the hydrolysis process of the pulp and catalyst mixture running in the hydrolysis process part by micromixing for splitting the polysaccharide.

[0007] Preferred embodiments of the invention are disclosed in the dependent claims.

[0008] The method and performance measurement system of the invention provide several advantages. Poor mixing performance in a hydrolysis process can be avoided/which saves energy.

List of figures

[0009] The invention will now be described in greater detail with reference to preferred embodiments and the accompanying drawings, in which:

Figure 1 is a block diagram of a hydrolysis process apparatus;

Figure 2A illustrates the use of a chemical mixer in the hydrolysis process apparatus;

Figure 2B illustrates the use of a pump and/or a conveyor in the hydrolysis process apparatus;

Figure 3 illustrates mixing of a non-hydrolysed and/or a hydrolysed mixture in the hydrolysis process part;

Figure 4 illustrates separation of solids from a hydrolysed mixture;

Figure 5 illustrates additional hydrolysis processes after the actual hydrolysis;

Figure 6 illustrates additional hydrolysis of solids after the actual hydrolysis;

Figure 7 illustrates recycling of a catalyst;

Figure 8 shows glucose yield in hydrolysis processes, the mixture being mixed in one of them, whereas in another one it is not;

Figure 9 shows a tower reactor; and

Figure 10 is a flow chart of the method. Description of embodiments

[0010] In the following, different embodiments will be described with reference to the figures. The invention is not, however, restricted to the disclosed embodiments but the presented solutions are examples of feasible implementation manners. Features of various embodiments may also be combined if they are not specifically conflicting or alternative with regard to their technical implementation.

[0011] Figure 1 is a simple block diagram of a hydrolysis process apparatus. Hydrolysis is a chemical reaction in which a compound decomposes when reacting with water. Usually this takes place under the influence of a catalyst. The hydrolysis process apparatus comprises a hydrolysis process part 100 and an inlet connector structure 102 for receiving pulp 104 containing polysaccharide and a catalyst and/or pre-catalyst 106 (these are shown in Figure 2) and for transferring it to the hydrolysis process part 100.

[0012] Polysaccharides are polymeric carbohydrates. Common natural polysaccharides include cellulose and starch, which may be presented by a general chemical formula (C ₆ HioO ₅ )n, where n may obtain a value from tens up to thousands. The pulp 104 containing polysaccharide may be woody, non-woody or both. The plants used for making the pulp may be cut or chopped into pieces of desired sizes, for example into chips or the like. In that case the particle size may be in the order of centimetres, i.e. fairly big for hydrolysis. The raw material may consist of biomass, such as grass-stemmed plants.

[0013] The term 'grass-stemmed plants' usually refers to non-woody polysaccharide sources. In addition or alternatively, different trees may be polysaccharide sources of biomass.

[0014] The pulp 104 containing polysaccharide may be pre-treated before being fed into the hydrolysis process. The pre-treatment may be carried out in the inlet connector structure 102, for example, and it may include a mechanical, thermal and/or chemical treatment. In the pre-treatment, hemicellulose and/or lignin, for example, may be either partly or at least almost totally removed from the pulp 104 before the catalyst and/or the pre-catalyst is received. The pulp containing polysaccharide may be fractioned chemically, possibly combined with a thermal treatment, using for example organic acid, such as formic acid and/or acetic acid. The remaining pulp fraction thus contains the cellulose and part of the hemicellulose of the raw material, whereas lignin and the rest of the hemicellulose dissolve in the acid. The acid and the substances dissolved therein may then be easily separated from the solid cellulose by allowing liquid substances to drain, for example. Draining of solids in the liquid may be prevented by mechanical filtering.

[0015] In addition, liquid may be supplied into the hydrolysis process for changing the distribution of the pulp 104 and the catalyst 106 or the pulp 104 and the pre-catalyst 106 in relation to one another, whereby also the solids content in the mixture of the pulp 104 and the catalyst and/or the pre-catalyst 106 changes. The liquid may comprise water, for example, without being, however, limited thereto.

[0016] The pre-catalyst received at the hydrolysis process may be a microbe producing the necessary catalyst in the hydrolysis process part 100. A microbe is a microscopic organism, an individual microbe being usually too small to be visible at least by the naked eye. Microbes may be bacteria, mould, yeast, fungi, algae, protists or viruses, although a virus is not a living organism. Usually microbes are unicellular, but they may also appear in groups. For example, when cellulose is split into glucose, a microbe may be fungus, such as Trichoderma reesei, which produces enzymes that split cellulose. Instead of or in addition to a microbe, the pre-catalyst may comprise a chemical compound that breaks down to produce the catalyst in the hydrolysis process. Moreover, the pre-catalyst may consist of two different substances which combine in the hydrolysis process and form the catalyst.

[0017] According to an embodiment, the catalyst 106 may be a biological catalyst, such as an enzyme. Enzymes are usually proteins. An enzyme may be e.g. cellulase, such as exoglucanase, endoglucanase or the like. An example of a starch-splitting enzyme is amylase. In addition to or alternatively, a chemical catalyst is conceivable. The catalyst 106 may be a combination of one or more catalysing substances.

[0018] The catalyst and/or pre-catalyst may be fed into the hydrolysis process part 100 in a liquid form or, if the catalyst and/or pre- catalyst is dry, mixed into a liquid.

[0019] The hydrolysis process part 100 keeps the hydrolysis process of the mixture 108 containing the pulp 104 comprising polysaccharide and the catalyst 106 running by micromixing only for splitting the polysaccharide. Micromixing refers to the diffusion of the catalyst 106 into the pulp 108. Diffusion, in turn, may be based on random mixing of substances with each other due to a thermal movement and on the inherent tendency of concentrations to become equalized. The hydrolysis process part 100 thus maintains the hydrolysis without subjecting the mixture 108 to a mechanical force mixing the pulp 104. In other words, the hydrolysis process part 100 does not subject the mixture 108 to a force, such as a shearing force, breaking the structure of the pulp 104. Consequently 108, no part of the hydrolysis process part 100 directs force and no part penetrates into the mixture 108 in a deforming manner. The hydrolysis process part 100 is thus capable of maintaining the mixture 108 in an internally unchanged or nearly unchanged state in a macroscopic sense without mechanical mixing. External changes may occur, because the mixture may be transferred from one location to another, for example. According to an embodiment, non-mixing of the mixture 108 may also mean that the mixture 108 is not subjected to particle radiation, electromagnetic radiation or acoustic radiation.

[0020] The hydrolysis process part 100 may be a kind of an open or closed container in which the mixture 108 is fed and where the mixture 108 remains for the duration of the hydrolysis. The material of the hydrolysis process part 100 may be metal or plastic, for example. The hydrolysis process part 100 may be a batch reactor or a continuous reactor. The hydrolysis process part 100 may be a tower or a drum reactor, for example, the mixing operation of which is interrupted for the duration of the hydrolysis. The duration of the hydrolysis may be some hours up to some days, depending on the quality and quantity of the mixture.

[0021] The hydrolysis process part 100 keeps the hydrolysis process running for producing monosaccharide, disaccharide, oligosaccharide and/or a shorter polysaccharide than the original saccharide chain. Hydrolysis may be used for converting cellulose to glucose, for example, by means of a catalyst.

[0022] Figure 2A illustrates an embodiment in which the inlet connector structure 102 comprises a pump and/or a conveyor 202 receiving pulp 104 that contains polysaccharide. The pump pumps and/or the conveyor carries the pulp 104 to a chemical mixer 200, where also the catalyst and/or pre-catalyst 106 are fed. The chemical mixer 200 may produce a turbulent mixing zone axially, linearly and/or horizontally. The chemical mixer 200 may comprise e.g. a paddle wheel, a propeller or a blade that may be rotated by a motor. The chemical mixer 200 may be located for example in a tube, through which the pulp 104 flows. The chemical mixer 200 mixes the pulp 104, the catalyst and/or pre-catalyst 106 together before the hydrolysis and feeds the mixture 108 to the hydrolysis process part 100. Mixing in the chemical mixer 200 may take less than a minute, for example, and this time, or retention, is so short that it is not conceivable that hydrolysis would start during that time.

[0023] Figure 2B illustrates an embodiment in which the inlet connector structure 102 comprises a pump and/or a conveyor 202 receiving both pulp 104 that contains polysaccharide and the catalyst and/or pre-catalyst 106. The pump pumps and/or the conveyor carries the mixture 108 of the pulp 104, the catalyst and/or the pre-catalyst 106 to the hydrolysis process part 100 for hydrolysis. The pump 202 may a so-called MC (Medium Consistency) pump, for example, which is used when bleaching pulp at a solids content of more than 8%, for example. In this example the pump 202 mixes the pulp 104, the catalyst and/or the pre-catalyst 106 during the pumping. The mixing in the pump and/or the conveyor 202 is so short that it is not conceivable that hydrolysis would start during that time.

[0024] Figure 3 illustrates an embodiment in which the inlet connector structure 102 comprises a pulp inlet connector 110 for receiving the pulp 104 containing polysaccharide and for transferring it to the hydrolysis process part 100, and a separate catalyst inlet connector 112 for receiving the catalyst and/or pre-catalyst 106 and for transferring it to the hydrolysis process part 100.

[0025] As shown in Figure 3, although not restricted to Figure 3, the hydrolysis process part 100 may also comprise a mixer 300 configured to mix the pulp 104, the catalyst and/or pre-catalyst 106 arrived at the hydrolysis process part 100 for mixing the catalyst and/or pre-catalyst 106 into the pulp 104 before hydrolysis is started. The mixing in the mixer 300 may take less than a minute, for example, the time being so short that it is not conceivable that hydrolysis would start during that time. The mixer 300 may be a propeller mixer, a paddle mixer or a turbine mixer, for example. The mixer 300 may also be incorporated into the hydrolysis process part 100, which may be of a free fall type, for example. A free fall type reactor may be a cylinder rotating about its longitudinal axis, for example, a rotation causing protrusions inside the cylinder to lifting up the mixture until the mixture on a protrusion that has risen up falls down to the bottom of the cylinder. [0026] The inlet connector structure 102 and the hydrolysis process part 100 may treat a mixture 108 that may have a solids content of over 20% at the start of the hydrolysis. In addition, the inlet connector structure 102 may receive other liquid to such an extent that the solids content of the resulting mixture 108 consisting of the liquid, pulp 104, catalyst and/or pre-catalyst 106 is (at least) 1 % lower than the original solids content of the pulp 104. However, the decrease in the solids content is not restricted to a specific value but may also be less or more than 1 %. Added liquid allows the catalyst and/or pre- catalyst 106 to be spread efficiently into the pulp 104.

[0027] Figure 4 illustrates an embodiment in which the hydrolysis process apparatus comprises a separator 400 that may receive a hydrolysed product 402 coming from the hydrolysis and separate solids 404 and other material 406 therefrom. The product 402 coming from the hydrolysis may be an end product of the hydrolysis. The separator 400 may be a sieve, such as a web made of a non-woven fabric. The separator 400 may also be a device separating solids from the rest of the material by gravitation (settling) or a centrifugal force (centrifugation). The other material 406 in the product 402 coming from the hydrolysis comprises split polysaccharide, which may be glucose, for example. The solids 404 may consist of cellulose that has not been split, for example. The solids 404 may also contain litter and/or other material non-degradable in a hydrolysis process. Split polysaccharide separated by the separator 400 may be transferred to fermentation, for example, for making alcohol of the split polysaccharide.

[0028] According to an embodiment, the split polysaccharide does not need to be transferred to a separate fermentation reactor, but the fermentation may be performed in the hydrolysis process part 100.

[0029] Figure 5 illustrates an embodiment in which the hydrolysis process part 100 may feed the product 402 coming from the hydrolysis to at least one additional hydrolysis process part 500, 502 for continued hydrolysis. In this example the product 402 consists of hydrolysed pulp whose viscosity has dropped below a predetermined threshold value. From each additional hydrolysis process part 500, 502 the split polysaccharide may be transferred to fermentation, for example, for making alcohol of the split polysaccharide.

[0030] According to an embodiment the catalyst and/or pre-catalyst 106 may be added to the product 402 before the additional hydrolysis process part 500, 502 (depicted by a broken line). [0031] Although in Figure 5 the additional hydrolysis process parts 500, 502 are side by side, it is also possible that the additional hydrolysis process parts 500, 502 are successively.

[0032] In said at least one additional hydrolysis process part 500, 502 the product 402, with the (pre-)catalyst or without the (pre-)catalyst, may be mechanically mixed during the additional hydrolysis, or left unmixed. The mixing may be carried out by a separate mixer. When a hydrolysed product is being transferred, the mixing may be carried out by a pump and/or a conveyor.

[0033] An already at least partly hydrolysed mixture is much easier to mix than the original pulp having a high solids content, because the hydrolysis reduces the solids content in the hydrolysed mixture and, correspondingly, the amount of liquid medium increases. Physical mixing aims at generating mechanical forces in the pulp that disintegrate fibres that still remain by tearing and twisting and thus detach them from one another, increasing at the same time the surface area exposed to enzyme activity. In addition, the mixing is thought to accomplish the following: a close contact for a water soluble enzyme and insoluble cellulose; restriction or prevention of locally accumulated high cellobiose concentrations (as cellobiose inhibits cellulase enzymes and thus slows down the progress of an enzymatic hydrolysis); a contact between a Cellulose binding domain (CBD) and cellulose-containing fibre and transfer of CBD on the cellulose fibre from one location to another or transfer to another fibre; enhanced transfer of material and heat.

[0034] As an alternative to the solution of Figure 5, it is also possible that said at least one additional hydrolysis process part 500, 502 is not physically provided, but the original hydrolysis process part 100 carries out the continued hydrolysis by starting the mixing of the hydrolysed mixture.

[0035] Figure 6 illustrates an embodiment in which the hydrolysis process apparatus comprises a hydrolysis process part 100, a separator 400, at least one additional hydrolysis process part 500 and possibly an additional separator 600, which may receive the hydrolysed product 504 from the at least one additional hydrolysis process part 500 and separate solids 404 and the rest of the material 406 from the product 504. Also in this example the solids 404 may consist of cellulose that has not been split, for example. Split polysaccharide separated by the additional separator 600 may be transferred to fermentation, for example, for making alcohol of the split polysaccharide. [0036] In the examples of Figure 5 and Figure 6 the additional hydrolysis process part 500, 502 may mix the product 402 obtained from the hydrolysis 100 mechanically.

[0037] Figure 7 shows an embodiment according to which the catalyst is circulated. The catalyst may be circulated because it does not change in the hydrolysis reaction even though it is indispensable for hydrolysis to take place and/or for significantly accelerating it. In that case the hydrolysis process apparatus may comprise the hydrolysis part 100, the separator 400 and a recovery unit 700. The separator 400 is not necessarily needed, however. When the hydrolysis process part 100 has caused the viscosity of the hydrolysed product 402 coming from the hydrolysis to drop below the predetermined threshold value, the product 402 may be fed into the separator 400, which separates the solids 404 from the product 402. The separator 400 feeds the catalyst 106 and the rest of the material 406, which comprises the split polysaccharide, to the recovery unit 700, which separates the catalyst 106 from the rest of the material 406. The recovery may be carried out with film filters, a membrane or chromatographically, for example. It is also possible to allow the catalyst to attach to solids particles, for example, and to collect then the particles and the catalysts from the rest of the material 406 by mechanical filtering, for example. After this, the catalyst may be freed of the particles. The recovered catalyst 106 is fed back to the hydrolysis process part 100. The split polysaccharide may be fed from the recovery unit 700 to fermentation, for example.

[0038] Figure 8 illustrates the behaviour of a test hydrolysis process with mixing and without mixing. In the hydrolysis cellulose has been converted to glucose. The vertical axis represents glucose yield in percentage and the horizontal axis time in days. Lignin and hemicelluloses were separated from the biomass by the method disclosed in patent application PCT/FI08/50639. The cellulose fraction obtained by the separation was used as raw material in the hydrolysis. Curve 800 shows glucose yield when no mixing takes place in the hydrolysis process part 100 during the hydrolysis process. Curve 802 shows glucose yield when mechanical mixing is used in the hydrolysis process part 100 during the entire hydrolysis process. As shown by Figure 8, contrary to the common and established understanding of skilled professionals, mixing does not increase glucose yield but may in some cases even impair it. Mixing can thus be disposed of from a hydrolysis process. [0039] The hydrolysis process part 100 used in hydrolysis may be a tower reactor 900, depicted in Figure 9. The cellulose fraction serving as the pulp to be fed may be dried with a screw press, for example. The pulp consistency may be set at 30 to 40%, for example. Catalyst and/or pre-catalyst present in a liquid solution may be absorbed into the pulp by spraying, for example. The liquid may be water, for example. The spraying may be directed to a pulp in a flat form. Pulp thus treated may be fed to an upper part 902 of the tower reactor 900 through the inlet connector structure 102. According to an embodiment, a screw conveyor 904 transfers the high consistency pulp containing the catalyst and/or pre-catalyst to the upper part 902 of the tower reactor. During feeding of the pulp into the tower reactor 900, hydrolysis is not considered to have actually started yet.

[0040] After the catalyst/pre-catalyst has been added, the consistency of the cellulose fraction in the upper part 902 of the reactor is usually about 15 to 25%. In the tower reactor 900 the pulp to be hydrolysed, which contains the catalyst fed or formed of pre-catalyst, flows downward as a tube current by gravitational force. As the hydrolysis proceeds, the consistency decreases and by adjusting the rate of the tube current in the tower reactor 900 and the catalyst and/or pre-catalyst dose in the initial stage, a desired consistency profile may be achieved in the height direction of the tower reactor 900. Pulp liquefied in hydrolysis flows easier than non-hydrolysed pulp. The pulp, and the non-hydrolysed pulp in particular, are not mixed separately during the flow in the tower reactor 900 by any passive or active device. When the pulp has been hydrolysed and flown down, the pulp, totally or partly liquefied as a result of the hydrolysis, may be pumped from the lower part 906 of the reactor 900 to subsequent process steps by means of a centrifugal pump or an MC (Medium Consistency) pump 908, for example, the pumping being possible for example because the consistency of the liquefied cellulose fraction of the pulp is now significantly lower than at the upper part 902 of the tower reactor. In addition, hydrolysed pulp, whose consistency has dropped from that of non-hydrolysed pulp, each easy to mix.

[0041] The consistency of the pulp to be fed to the tower reactor 900 may be over 10%. According to an embodiment, the consistency of the pulp to be fed to the tower reactor 900 is over 15%. This allows a high post- hydrolysis glucose concentration to be achieved, the glucose concentration being possibly over 100 g/kg, for example. The high consistency of the pulp to be fed into the tower reactor 900 reduces the size of the currents to be treated and thus enables smaller reactors to be used and hence smaller investments to be made.

[0042] According to an embodiment, it is desirable that the hydrolysis continues until it reaches a predetermined level of viscosity. An example of the viscosity level in question is a viscosity of less than 500 cP (centipoise), which corresponds to a maximum pulp viscosity of about (less than) 4%. Pulp of this viscosity may be efficiently pumped by common centrifugal pumps to a subsequent process step, such as a low-consistency hydrolysis reactor or an STR fermentor (Stirred Tank Reactor) or to a combined hydrolysis and fermentation reactor.

[0043] According to an embodiment, the hydrolysis is to continue to a predetermined viscosity level of less than 800 cP. This corresponds to the viscosity of pulp having a consistency of 8 to 14%. Also this type of pulp may be efficiently pumped by common screw pumps (MC pumps).

[0044] A mixture of a pulp fraction and catalyst and/or pre-catalyst having a thick initial consistency (of over 15%) is difficult or impossible to pump, but after an at least partial liquefaction and effective consistency change, pumping and mixing are easier to carry out by advantageous devices, such as an MC (Middle Consistency) mixer. When desired, catalyst and/or pre-catalyst may be added to the hydrolysed pulp and the pulp may be further mixed in connection with the devices in question and/or by the devices before transfer to the next process step. The next step may be for example a low- consistency hydrolysis reactor or fermenter (STR) or a combined hydrolysis and fermentation reactor.

[0045] Use of additives is not necessary in the disclosed solutions. A cellulose fraction produced by the formicobio process technology disclosed above typically contains only small amounts of lignin (1 to 3%, depending on the raw material), therefore additives for preventing absorption of lignin and enzymes are not needed, neither does their use provide significant technical or economic benefit. Additives preventing absorption of lignin and enzymes are observed to be advantageous only in cases where the cellulose fraction contains large amounts of lignin, typically over 10%.

[0046] Figure 10 is a flow chart of the method. In step 1000 pulp 104 containing polysaccharide and a catalyst and/or pre-catalyst 106, which produces a catalyst in the hydrolysis process part 100, is received by the inlet connector structure 102 and from the inlet connector structure 102 the pulp 104 and the catalyst and/or pre-catalyst 106 to be transferred to the hydrolysis process part 100. In step 1002 the hydrolysis process of the mixture 108 of the pulp 104 and the catalyst 106 carried out in the hydrolysis process part 100 is kept running by micromixing only for splitting the polysaccharide.

[0047] Even though the invention is described above with reference to the examples of the attached drawings, it is clear that the invention is not restricted thereto, but it may be modified in a variety of ways within the scope of the accompanying claims.