Field of the invention

The present invention relates to a process for the production of alcohol from biomass comprising the steps of pretreatment biomass using NH4HSO3, treatment using SO2 and NH4OH, and fermentation.

Background of the invention and prior art

So called sulphite cooking has been done to produce cellulose and ethanol from wood products. However, the yield of these processes is low and therefore expensive to use for the production of ethanol.

Known sulphite processes focus on production of paper and not breakdown of biomass into lignosulfonate, hemicellulose and other chemicals such as sugars.

Sulphite cooking/hydrolysis is performed in for example the paper industry, whereby sulphite is used in a hydrolysis step in the process. The active components in a sulphite cooking process are H ⁺ , SO2 and HSOa". In a bisulphite cooking process, the active components are the same but the concentration of HSOa" is larger compared to a sulphite cooking. The buffer capacity of the cooking liquid in a bisulphite cooking is less compared to a sulphite cooking. The active components are responsible for the breakdown of lignin and hemicellulose as well as sulphonation of lignin. The cooking process can be controlled and steered towards a desired end-product by controlling the equilibrium between the active components H ⁺ , SO2 and HSOa’ in the cooking liquid. By measuring the partial SO2 pressure and measuring the amount of bonded SO2 in the cooking liquid, the amount of H ⁺ and HSOa" can be controlled at any temperature and pressure. For example, if the temperature increases, the partial SO2 pressure increases, whereby the concentration of H ⁺ decreases and hence the pH increases. By degassing the cooking liquid during hydrolysis, the partial SO2 pressure can be controlled.

Sulphite cooking liquid can be analyzed by measuring total SO2, free SO2 and bound SO2 by using an iodine- and sodium hydroxy- titration method (PAUL F., Mitt. Klosterneuburg, Rebeu. Wein, 1958, ser. A, 821., OIV-MA-AS323-04A : R2012) The amount of total SO2 is a sum of all sulphite compounds in the liquid, i.e. SO2, HSOa’ and SOa ^2- . Bound SO2 is defined as the amount of SOa ^2- in the liquid. The total free amount of SO2 is determined by total SO2 minus (2 x bound SO2).

For ethanol production from biomass, such as hardwoods and softwoods, hydrolysis is needed to free the sugars from the biomass. The hydrolysis must be mild, i.e. the conditions may not be too acidic, the pressure must be controlled and the temperatures may not be too high to prevent the sugars from decomposing or forming furfural and other toxins. Also, corrosion of equipment may be a problem.

Mild-acid hydrolysis has been used to free sugars from biomass prior to fermentation. During this process, toxins, such as furfural are produced as well as other fermentation inhibitors. Corrosion of equipment, for example by CaSC>4, necessitated to use of expensive corrosion- resistant equipment. The process uses a large amount of chemicals that cannot be recycled, which increases the costs of the process. The yield of this process may be as low as 0.34 to 0.35 kg sugar per ethanol or 50 to 60 wt% sugar. The energy consumption in this process is high, about 2.7 kWh/l ethanol.

W02020041855 discloses a process for processing lignocellulosic biomass that includes pretreating lignocellulosic biomass, wherein the lignocellulosic biomass is heated in a pretreatment liquor containing sulfur dioxide and bisulfite salt, at a temperature between 120°C and 150°C, for at least 30 minutes. The pH of the pretreatment liquor at 25°C is less than 1.3, the concentration of sulfur dioxide is greater than 9.4 wt% (on liquor), and the concentration of alkali is between 0 wt% and 0.42 wt% (expressed as hydroxide, on liquor).

W02019090414 discloses a process for producing a fuel from lignocellulosic biomass.. The process includes obtaining a feedstock comprising lignocellulosic biomass, feeding the feedstock and sulfur dioxide into a pretreatment reactor, wherein a total amount of sulfur dioxide in the pretreatment reactor is greater than 70 wt% based on dry weight lignocellulosic biomass, and heating the feedstock and sulfur dioxide in the pretreatment reactor at one or more temperatures between 110°C and 150°C for more than 60 minutes.

Enzyme hydrolysis, where hydrolysis is followed by an enzymatic treatment, has been used to free sugars from biomass priorto fermentation. This process is complex, time consuming (72h) and expensive but uses less energy compared to mild-acid hydrolysis, about 1.96 kWh/l ethanol. Also, the yield is improved compared to mild-acid hydrolysis to 0.45 kg sugar per ethanol. Investment costs for this process are high, especially for large scale production of ethanol. Besides, the enzyme degenerates over time, which makes process conditions variable and harder to control. None of the known processes can be used in a continuous process.

Summary of the invention

It is an object of the present invention to at least partly overcome the above-mentioned problems and to provide an improved process for the production of alcohol from biomass.

This object is achieved by a process as defined in claim 1.

The fermentation process for the production of alcohol from biomass comprises or consists of the steps of

- Pretreatment of the biomass comprising or consisting of the steps of

1. steaming chips of biomass using water,

2. prehydrolysing the steamed biomass using NH4HSO3, a pH 3 to 7, a temperature 80 to 250°C, and an atmospheric pressure for 5 to 360 minutes, cleaning the prehydrolysed product,

- Treatment of the prehydrolysed product comprising or consisting of the steps of

8. hydrolysing the prehydrolysed product using SO2 at 1 to 15 wt% of dry mass, a temperature 125 to 350°C, a pressure of 0.5 to 4 MPa for 1 to 20 minutes, 9. afterhydrolysing the obtained the hydrolysed product using SO2 at 1 to 75 g/l and NH4OH, a pH 2 to 7, a temperature 90 to 250°C, a pressure of 0.1 to 2 MPa for 1 to 75 minutes, cleaning the hydrolysed product,

- Fermentation of the hydrolysed product comprising or consisting of the steps of

15. fermenting of hexose using yeast,

17. fermenting of pentose using yeast, and cleaning the fermented liquid to obtain a solution of 90 to 98 vol% ethanol.

In some aspects, the process is continuous.

In some aspects, biomass is herbaceous energy crops and/or short-rotation energy crops and any waste product thereof.

In some aspects, prehydrolysing the steamed biomass in step 2 is done using NH4HSO3, a pH of 3 to 7, a temperature of 100 to 200°C, and an atmospheric pressure for 10 to 240 minutes. The amount of NH4HSO3 depends on the partial SO2 pressure. At a pH of 3 to 7, or 4 to 5 during prehydrolysis, hemicellulose solubilizes and can be separated from the biomass.

In some aspects, hydrolysing the prehydrolysed product in step 8 is done using SO2 at 1 to 10 wt% of dry mass, a temperature of 150 to 300°C, and a pressure of 1 to 2.5 MPa for 1 to 15 minutes. In some aspects, SO2 is added in the form of gas. SO2 may be added as a mixture of air and SO2. The pH may be between 2 and 7, or 3 to 4.

In some aspects, afterhydrolysing the hydrolysed product in step 9 is done using SO2 at 1 to 50 g/l and NH4OH, a pH of 2 to 7, a temperature 100 to 200°C, a pressure of 0.1 to 1 MPa for 5 to 60 minutes. The amount of NH4HSO3 may be 150 to 500 mg/l.

The process of the invention has an improved yield compared to known mild acid hydrolysis processes or processes where hydrolysis is combined with enzymes. Mild acid hydrolysis processes have an average yield of 0.34-0.35 kg of sugar/ethanol and enzyme-hydrolysis may have a yield of 0.45 sugar /ethanol. The process of the invention has an estimated yield of 0.44 kg sugar/ethanol. The total amount of energy used in the process of the invention is estimated at 2.04 kWh/l ethanol, whereas mild acid hydrolysis uses 2.67 kWh/l ethanol. The investment costs are less compared to enzymatic processing.

The three-step process of the invention provides a stable process with improved controllability of the different steps, which also improves flexibility in the use of raw material. Any kind of starting material can be used, such as any herbaceous energy crops or shortrotation energy crops.

In some aspects, the chips of biomass or wood used in step 1 are pieces of biomass or wood having a maximum length/diameter of 1000 to 0.5, or 150, 100, 50 or 10 mm. Biomass may be mechanically treated prior to the use of the material in the process of the invention.

This size allows the use of basically any type of raw material, such as any hard- or softwood. Sawdust and other left-over products can be used in the process of the invention. The size also minimized the time needed to process the material. This in turn reduces energy costs for the overall process. The size of the chips also reduces the amount of chemicals and water needed to process the biomass.

Steaming step 1 is important for opening the cells in the biomass. Steaming allows air bound in the biomass to be removed. Steaming therefore improves the effectiveness and efficiency of the hydrolysis in step 8. The use of the steaming step reduces water and energy consumption in the subsequent steps of the process, especially in hydrolysis steps 2, 8 and 9.

During prehydrolysis in step 2, lignin and hemicellulose are removed from the biomass. The cellulose fibers become exposed for fermentation. During hydrolysis, the negative charges or acidity increases inside the biomass, among others by sulphonated lignin that has not solubilized yet. This increase in acidity must be balanced by an increase in positive cations. The advantage of using NH4 ⁺ can be explained by the fact that ionic strength is affected by the squared ionic charge. This reduces the amount of thiosulfate ions, S2O2 ^-3 ' in solution, especially at low Kappa numbers.

The lower pH during hydrolysis allows for the removal of the hemicellulose from the biomass. The combination of prehydrolysis in step 2 at higher pH and hydrolysis in step 8 at lower pH improves selectivity of the treatment towards removal of lignosulfonate and hemicellulose from the biomass.

The mild conditions in this prehydrolysis step prevent the sugars in the biomass from being degenerated/decomposed. Therefore, the amount of sugar from biomass that can be used for fermentation increases, which increases the yield of the overall process. The use of NH4HSO3 further improves the release of sugars from the biomass. Prehydrolysis prevents or minimizes the forming of CaSC>4, thereby reducing corrosion. The prehydrolysis also improves the effectiveness and efficiency of the hydrolysis in step 8. Lignosulphonate is produced during the prehydrolysis step 2. This product has a high market value, thus the sales reduce the overall costs of the process. Furthermore, prehydrolysis reduces the formation of toxins during further processing of the biomass. Toxins inhibit fermentation and may reduce the yield of the process.

The fiber slurry that enters the hydrolysis step 8 comprises about 30 to 60 wt%, or 35 to 50 wt% dry mass. In step 8, hemicellulose and lignin are further removed from the biomass and sugars become dissolved in the liquid.

Afterhydrolysis step 9 is important for splitting poly— and di-saccharides into sugars. NH4OH used in the step 9 prevents the decomposition of the sugars. This increases the yield in the process. NH4OH also prevents the formation of toxins, such as furfural from pentose. These toxins can be formed when SO2 hydrates into H2SO4. Due to the presence of NH4OH in step 9, this reaction is almost completely prevented. This again improves the efficiency of the fermentation. Compared to an enzymatic hydrolysis in step 9, the afterhydrolysis is less time and energy consuming. It is also cheaper and requires less investment costs. Ammonium will bind to the fibers. It has been found that these ammonium bindings are used as a nitrogen source by the yeast and do not have any negative impact on the fermentation process.

Both ammonium, sulfites, sulfur and other chemicals can be recycled and reused.

In some aspects, cleaning the prehydrolysed product in the pretreatment step comprises or consists of the steps of

3. filtering lignin and lignosulfonate,

4. washing to remove sugar-containing liquid, and

5. washing the remaining biomass to remove toxins.

Lignin has a negative impact on the fermentation process and is preferably removed prior to fermenting the sugars from the biomass.

Sugars may have a negative impact on the efficiency of the hydrolysis step 8. It is thus preferred to remove sugars prior to hydrolysing the biomass. The sugars may be added to the process prior to fermentation, for example in steps 13 or 15.

Toxins prevent microorganisms (e.g. yeast) from growing and are preferably removed to prevent inhibition of fermentation. This will improve the yield of the process.

In some aspects, the prehydrolysed product is further pretreated prior to hydrolysis in the treatment step comprising or consisting of the steps of

6. optionally adding lye from other hydrolysis processes,

7. optionally adding sulphite, and optionally heating the prehydrolysed product in a heat-exchanger.

Lye from other hydrolysis processes is often discarded or burned. This lye can however advantageous be used and added to the process in step 6. This improves the reuse of biomaterial and reduces the carbon footprint of the processes. This may also reduce the overall cost of the process.

Sulphite may be added in step 7 to prevent microorganisms from growing. Such unwanted microorganisms will reduce the effectiveness of the fermentation steps. This improves the yield of the process of the invention.

The heat generated in the different steps of the process may be used in the heat -exchanger. By pre-heating the prehydrolysed product, less time is needed for hydrolysis step 8, which reduces the overall time, cost and energy use in the process of the invention.

In some aspects, cleaning the hydrolysed product in the treatment step comprises or consists of the steps of

10. washing lye,

11. filtering lignin and lignosulfonate, and

12. washing to remove toxins from the liquid. Washing the lye in step 10 improves the overall yield of the process. In some aspects, washing includes removal or stripping SO2 from the liquid. Steam at low pressure, e.g. a pressure of 0.05 to 0.1 MPa and a temperature of 120 to 125°C, or a pressure of 0.3 to 0.45 MPa and a temperature of 135 to 165 °C, may be used to remove the SChfrom the liquid. Especially when rest-steam from other processes is used, the pressure may be 0.05 to 0.1 MPa and the temperature of 120 to 125°C.

Lignin has a negative impact on the fermentation process and is preferably removed prior to fermenting the sugars from the biomass.

As mentioned above, toxins have a negative impact on the fermentation process and are preferably removed. The pH may be adjusted in step 12 to about 7 to improve the tolerance of yeast for acetic acid.

In some aspects, the fermentation step comprises or consists of the steps of

15. fermenting of hexose using yeast,

16. filtering to remove the hexose yeast,

17. fermenting of pentose using yeast, and cleaning the fermented liquid to obtain a solution of 90 to 98 vol% ethanol.

In some aspects, the yeast is selected from the group comprising or consisting of Saccharomyces cerevisiae, Saccharomycesuvarum, Schizosaccharomyces pombe and Kluyveromyces. The yeast preferably tolerates high concentrations of ethanol. In some aspects, the amount of yeast is 5 to 15 g/l, or about 12 g/l.

In some aspects, hexose fermentation in step 15 is done for 24 hours, at pH 3.5 to 6, a temperature of 28 to 35°C (30°C). In some aspects, the yeast is Saccharomyces cerevisiae.

Filtering step 16 prevents contamination of hexose yeast with pentose yeast used in step 17. This improves the yield of the process of the invention.

In some aspects, pentose fermentation in step 17 is done for 48 hours, at pH 3.5 to 6, a temperature of 28 to 35°C.

In some aspects, the hydrolysed product is pretreated prior to fermentation in the fermentation step comprising or consisting of the steps of

13. adding sugar and other ingredients that improve fermentation, optionally using a heat-exchanger to reduce the temperature prior to fermentation, and

14. adding NaCI and ethanol.

To improve the effectiveness of the fermentation and the yield of the process, sugars may be added. In some aspects, sugars removed in step 4 are added in step 13.

By cooling the hydrolysed product, fermentation can start quicker, which reduces the overall time for the process of the invention. In some aspects, other ingredients are selected from the group comprising or consisting of NH3, vitamins, amino acids, minerals and sterols, such as cholesterol.

To improve the effectiveness of the fermentation and the yield of the process, ethanol may be added. Ethanol and NaCI also prevent grow of or reduce the viability of unwanted bacteria such as lactic acid or acetic acid bacteria, which negatively impact the fermentation process.

Glycerol and xylitol may be formed during fermentation. In some aspects, optionally melass is added in step 17. Melass may reduce xylitol production by 50 vol%. In some aspects, one or more microorganisms, such as ceftazidime resistant (TAZ-4) is added in step 17. Such organisms may reduce xylose formation by 75% and may improve the yield at a concentration of ethanol of 42 to 46 vol% to a yield of 90%.

In some aspects, a weight ratio of glucose to xylose is 1:3 to 7, or 1:5. This ratio improves fermentation and reduces the formation of glycerol and xylitol during fermentation.

In some aspects, cleaning the fermented product in the fermentation step comprises or consists of the steps of

18. distilling the obtained liquid in one or two steps, and

19. cleaning the distilled liquid.

In some aspects, distilling is done in two steps. In step 18-1 distilling may be done at a pressure of 0.02 to 0.06, or 0.04 MPa. This may increase the ethanol concentration to 50 vol%. In step 18-2 distilling may be done at a pressure of 0.100 to 0.15, or 0.25 MPa. This may increase the ethanol concentration to 94 vol%.

In step 19, a molecule filter may be used to remove all non-ethanol molecules. An example of a molecule filter is a micropolar gel particle used for absorbing non-ethanol molecules.

In some aspects, the yeast used in the fermentation step is recycled by reacting the yeast in an aerobic environment with the addition of a nitrogen source, such as COfNH?)? or NH4CI, preferably recycled from other processes on the plant, an oxygen source (e.g. from hydrogen gas production on plant) and glucose (e.g. from melass) for about 20 to 50, or 30 minutes at room temperature.

This recycling process allows yeast to grow. The recycling process reduces the cost of the use of yeast.

The invention also relates to a system for performing the process as defined anywhere herein comprising or consisting of

- a steaming tank I for steaming chips of biomass using water in step 1,

- a prehydrolysis tank II for prehydrolysing the steamed biomass in step 2,

- one or more cleaning tanks lll-V for cleaning the prehydrolysed product,

- optionally mixing tanks VI and/or VII for adding lye and sulphite and the like,

- a hydrolysis tank VIII for hydrolysing the prehydrolysed product in step 8, - an afterhydrolysis tank IX for afterhydrolysing the hydrolysed product in step 9,

- one or more cleaning tanks X-XII for cleaning the hydrolysed product,

- optionally mixing tanks XII and/or XIV for adding sugar, NaCI, ethanol and/or other ingredients,

- a first fermentation tank XV for fermenting of hexose in step 15,

Optionally tank XVI for filtering the liquid,

- a second fermentation tank XVII for fermenting of hexose in step 17, and

- one or more cleaning tanks XVI I l-XIX for cleaning the fermented product, and

Optionally burning tank XX for burning the remaining/residual biomass for production of energy that can be used in processes of the system or for production of biofuels.

Brief description of the drawings

The invention will now be explained more closely by the description of different embodiments of the invention and with reference to the appended figures.

Fig. 1 shows an overview of the process of the invention.

Fig. 2 shows an overview of the pretreatment steps.

Fig. 3 shows an overview of the treatment steps.

Fig. 4 shows an overview of the fermentation steps.

Fig. 5 shows an overview of the process including all cleaning steps and all optional steps marked in dotted lines.

Detailed description of various embodiments of the invention

Definitions

Wt% as used herein are weight percentages of the total weight of the dry material/mass.

Vol% as used herein are volume percentages of the total volume of the liquid/solution.

As used herein "biomass" means herbaceous energy crops and/or short-rotation energy crops and any waste product thereof.

As used herein "herbaceous energy crops" means plants with no or little woody tissue and grown for the production of food or feed. Examples may be grasses, sugarcanes, corn, soybeans, wheat, barley, sunflower, rapeseed, and the like.

As used herein "short-rotation energy crops" means fast growing softwoods, such as pine, spruce, birch and cedar or hardwoods, such as aspen, cotton woods, poplar, willow and eucalyptus.

As used herein "atmospheric pressure" means a pressure of about 0.101325 MPa.

As used herein "tank" means any container, basin or reactor that can hold a liquid or hold a pressurized liquid. The invention relates to a fermentation process for the production of ethanol from biomass. Biomass may be defined as short-rotation energy crops, such as wood products.

The process comprises or consists of the steps of pretreatment, treatment and fermentation as shown in figures 1 and 5. The process may be performed in a system as described below. The system comprises tanks as shown in figure 2 to 4. The number of the tank corresponds to the number of the step performed in a tank.

Pretreatment

During pretreatment, the biomass is prepared for the release of sugars, hemicellulose and lignin. Pretreatment starts with step 1 of steaming chips of biomass using water in tank (I). The chips of biomass may have a size of about 100, 50, 25, 15, 10, 5 or 1 cm or less. The temperature may be between 80 to 120, or 90 to 110°C. Steaming may be done for 1 to 30, or 1 to 20, or 1 to 15, or 1 to 10, or 1 to 5 minutes. The pressure may be atmospheric (0.1 MPa). A washing or filtering step may be done prior to steaming.

In step 2, the steamed biomass is prehydrolyses using NH4HSO3 in tank (II). The prehydrolysis may be done at a pH of 2 to 8, or 3 to 7. The temperature may be 80 to 250°C,or 90 to 225°C, or 100 to 200°C. The pressure may be 0.09 to 0.11 MPa or atmospheric. Prehydrolysis may be done for 5 to 360 minutes, or 10 to 240 minutes.

Subsequently, the prehydrolysed biomass is cleaned. The cleaning may comprise or consist of steps 3 to 5. In step 3, the biomass is filtered to remove lignin and lignosulfonate in tank (III). In step 4, the liquid is washed in tank (IV) to remove the sugars present in the liquid. In step 5, the biomass is washed in tank (V). This wash further cleans the biomass from e.g. toxins, prior to entering the treatment step.

Treatment

The cleaned prehydrolysed biomass may be further pretreated prior to hydrolysis in the treatment step. In an optional step 6, lye from other hydrolysis processes may be added in tank (VI). In an optional step 7, sulphite may be added in tank (VI) or (VII). Steps 6 and 7 may be done in tank (VII) or (VIII).

A heat-exchanger (H-E 1) may be used to increase the temperature of the prehydrolysed biomass prior to entering tank (VIII) for hydrolysis.

In the treatment step, the prehydrolysed biomass is hydrolysed under "hard" conditions and subsequently afterhydrolysed under "milder" conditions.

In step 8, hydrolysis is performed using SO2 in tank (VIII). SO2 may be in gas form. The SO2 used may be pure SO2 or a mixture of SO2 and air, such as 25 vol% SO2 gas mixed with 75 vol% air. The amount SO2 used during hydrolysis may be 0.5 to 25 wt%, or 1 to 15 wt% of dry mass. The temperature may be 110 to 325°C, or 130 to 310°C, or 150 to 300°C. The pressure in tank (VIII) may be 0.5 to 4 MPa, or 0.75 to 3 MPa, or 1 to 2.5 MPa. Hydrolysis may be done for 0.5 to 25 minutes, 1 to 20 minutes, 1 to 15 minutes.

In step 9, an afterhydrolysing is performed using SO2 and NH4OH in tank (IX). The SO2 used may be pure SO2 or a mixture of SO2 and air, such as 25 vol% SO2 gas mixed with 75 vol% air. The amount of SO? used in step 9 may be 0.5 to 75 g/l or 1 to 60 g/l or 1 to 50 g/l hydrolysate. The amount of NH4OH may be 150 to 500mg/l, or 200 to 400 mg/l, or 250 to 350 mg/l, with 15 to 40 vol%, or 20 to 30 vol% ammonia. The pH may be 1 to 8, or 2 to 7. The temperature may be 80 to 275°C, or 90 to 250°C, or 100 to 200°C. The pressure in tank (IX) may be 0.09 to 2 MPa, or 0.1 to 2 MPa, or 0.1 to 1 MPa. Afterhydrolysis may be done for 1 to 75 minutes, or 1 to 60 minutes, or 5 to 60 minutes.

The yield may be 70 to 98 wt% sugar. Subsequently, the hydrolysed biomass is cleaned. The cleaning may comprise or consist of steps 10 to 12. In step 10, the lye is washed in tank (X). Steam at a low pressure may be used to remove SO? from the liquid prior to fermentation. The removed SO? can preferably be recycled in the process of the invention. Especially when rest-steam from other processes is used, the pressure may be 0.05 to 0.1 MPa and the temperature of 120 to 125°C.

In step 11, the lignin, including lignosulfonate is filtered in tank (XI). In step 12, the liquid is washed to remove toxins from the liquid in tank (XII). For the removal of toxins, filters or separation using gravity may be used. Alternatively, extraction may be used.

Fermentation

The cleaned hydrolysed biomass may be pretreated prior to fermentation in the fermentation step. In an optional step 13, sugar or glucose may be added to the liquid in tank (XIII). In optional step 14, sodium chloride and/or ethanol may be added to the liquid in tank (XIV).

Although separate tanks XIII and XIV may be used, the additions in steps 13 and 14 can be directly done in fermentation tank (XV) or tank (XII).

The amount of NH4 and SO? may need to be adjusted prior to fermentation and/or during fermentation. Other ingredients, such as NH3, vitamins, amino acids, minerals, and sterols, such as cholesterol, may be added to optimize the fermentation. The fermentation can be optimized by monitoring and adapting the concentrations of the different ingredients prior to and during fermentation. Inhibition by overdosing must be prevented.

A second heat exchanger (H-E-2) may be used after step 13 or 14 to reduce the temperature of the liquid prior to fermentation.

Fermentation of the hydrolysed product may be done in one or more steps, using one or more different or the same yeasts. In one step 15, fermentation may be done using a yeast that ferments hexose from the liquid in tank (XV). Step 15 may be done for 12 to 36 hours, at pH 2 to 7, or 3.5 to 6 and a temperature of 25 to 40°C, or 28 to 35°C, or 30°C. The amount of yeast may be 6 to 20 g/l, or 8 to 15 g/l , or about 12 g/l liquid.

The yeast may be any yeast suitable to ferment hexose into ethanol. The yeast may be selected from the group comprising or consisting of Saccharomyces cerevisiae, Saccaromycesuvarum, Schizosaccharomyces pombe and Kluyveromyces. The yeast preferably tolerates high concentrations of ethanol. The yeast may be Saccharomyces cerevisiae. After fermentation step 15, the liquid may be filtered in filtering step 16 in tank (XVI) to prevent contamination of hexose yeast with pentose yeast used in step 17 in tank (XVII). Other products may be filtered from the liquid, such as glycerol or xylitol.

Prior to pentose fermentation step 17, sugar (glucose) may be added to the liquid to improve the yield of the process. Melass may also be added to the liquid prior to fermentation step 17.

Glycerol and xylitol may be formed during fermentation. Melass and/or ceftazidime resistant (TAZ-4) may be added prior to or in step 17. During pentose fermentation, a weight ratio of glucose to xylose may be controlled to reduce the formation of glycerol and xylitol during fermentation. The ratio may be 1: 2 to 8, or about 1:5.

The pentose fermentation in step 17 may be done for 12 to 36 hours, at pH 2 to 7, or 3.5 to 6 and a temperature of 25 to 40°C, or 28 to 35°C, or 30°C. The amount of yeast may be 6 to 20 g/l, or 8 to 15 g/l , or about 12 g/l liquid.

The yeast may be any yeast suitable to ferment pentose into ethanol. The yeast may be selected from the group comprising or consisting of Saccharomyces cerevisiae, Saccharomycesuvarum, Schizosaccharomyces pombe and Kluyveromyces. The yeast preferably tolerates high concentrations of ethanol. The yeast may be Saccharomyces cerevisiae.

Subsequently, the hydrolysed biomass is cleaned. The cleaning may comprise or consist of steps 18 and 19 to obtain a liquid/solution of 90 to 98 vol% ethanol. In step 18, the fermented liquid is distilled in one or more steps in tank (XVI 11 -1, XVI 11-2, etc).

In step 18-1, the fermented liquid may be distilled at a pressure of 0.02 to 0.06, or 0.04 MPa to increase the ethanol concentration to 50 vol%. In a step 18-2, the distilled liquid may be distilled again at a pressure of 0.100 to 0.15, or 0.25 MPa to increase the ethanol concentration to 90 to 99 vol% or 92 to 96 vol%, or about 94 vol%. Depending on the starting liquid, three or more distilling steps may be used, wherein the pressure in each step may be increased.

In step 19, a molecule filter may be used to remove all non-ethanol molecules in tank (XIX). An example of a molecule filter is a micropolar gel particle used for absorbing non-ethanol molecules.

The final liquid/solution may have a concentration of ethanol of 90 to 98 vol% ethanol.

The process of the invention may be continuous. The process of the invention is modular. The process of the invention is scalable.

All waste material from any of the steps can be used for recycling or for further processing. For example, the waste from fermentation can be used for the production of proteins. Alternatively, all solid waste can be burned to produce the energy needed in the different processes.

Figure 5 shows the process including all optional steps (dotted lines).

Recycling yeast The yeast used in the fermentation step(s) may be recycled. Recycling may be done by exposing the yeast to oxygen with the addition of a nitrogen source (CO(NHz)2 or NH4CI) and glucose for about 20 to 50, or about 30 minutes at room temperature.

System

The process of the invention may be performed in a system comprising tanks and connections between the tanks with valves to transport the mass and liquids between the tanks, and to remove gases and lye and liquids. Most of the mass, liquids and gases are preferably reused or recycled. The mass remaining at the end of the processes may be burned in a HTC or HTL tank (XX) to generate energy for performing the process of the invention. Alternatively, biofuel may be made from the residual biomass.

The system may comprise or consist of

- a steaming tank (I) for steaming chips of biomass using water in step 1,

- a prehydrolysis tank (II) for prehydrolysing the steamed biomass in step 2,

- cleaning tank (III) for filtering lignin and lignosulfonate from the prehydrolysed product in step 3,

- cleaning tank (IV) for washing and removing sugar-containing liquid in step 4,

- cleaning tank (V) for washing the remaining biomass to remove toxins in step 5,

- tank (VI) for optionally adding lye from other hydrolysis processes in step 6,

- tank (VII) for optionally adding sulphite in step 7,

- a hydrolysis tank (VIII) for hydrolysing the prehydrolysed product in step 8,

- an afterhydrolysis tank (IX) for afterhydrolysing the hydrolysed product in step 9,

- cleaning tank (X) for washing the lye in step 10,

- cleaning tank (XI) for filtering lignin and lignosulfonate in step 11,

- cleaning tank (XII) for washing and removing toxins in step 12,

- tank (XIII) for optionally adding sugar and possibly other ingredients in step 13,

- tank (XIV) for optionally adding NaCI and ethanol in step 14,

- a first fermentation tank (XV) for fermenting of hexose in step 15,

-a filtering tank (XVI) for filtering the fermented liquid in step 16,

- a second fermentation tank (XVII) for fermenting of hexose in step 17, and

- a distillation tank (XI 11-1) for distilling the fermented liquid in step 18-1,

- a distillation tank (XI 11-2) for distilling the fermented liquid in step 18-2,

- a cleaning tank (XIX) for molecule-filtering the distilled liquid in step 19,

- a burning tank (XX), which may be a hydrothermal carbonization (HTC) tank or a hydrothermal liquefaction (HTL) tank. The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims. Although the word tank is used to describe the stations where the different steps of the process may take place, a skilled artisan will understand that other equipment than tanks may be used in some of the steps, such as for example filters in step 16. The tanks used in the system may be reactors adapted to perform specific reaction steps. A tank may be adapted for a temperature and pressurized hydrolysis or for fermentation. Air-lift reactors may be used.

The amounts of ingredients mentioned in the different processes are adjustable depending on starting materials, and sizes of tanks used. Through monitoring the parameters, the chemicals, and ingredients during the processes, especially during continuous processes, the parameters amounts and ratios, etc. can be adapted to optimize the processes. A skilled artisan will understand that temperatures, pressures and amounts of different chemicals may vary depending on the type of starting material used, the size of the tanks used, the temperature of the environment, etc. .