A METHOD OF PRODUCING BIOMASS DEGRADATION PRODUCTS

Abstract

A method of producing biomass degradation products from soft biomass is disclosed, the method comprising the steps of—providing a soft biomass, pretreating the soft biomass in a pretreatment step at a pressure below 2 bar by heating the soft biomass to at a pretreatment temperature between 65 and 100 degrees Celsius to obtain a pretreated biomass, hydrolyzing the pretreated biomass in a first hydrolyzation step to obtain a biomass hydrolysate, and posttreating the biomass hydrolysate in a pressurized posttreatment step by heating the biomass hydrolysate to a posttreatment temperature above 150 degrees Celsius to obtain a posttreated biomass, hydrolyzing the posttreated biomass in a second hydrolyzation step, wherein biogas is obtained from at least the first hydrolyzation step or the second hydrolyzation step.

Claims

1. A method of producing biomass degradation products from soft biomass, the method comprising the steps of: providing a soft biomass, pretreating the soft biomass in a pretreatment step at a pressure below 2 bar by heating the soft biomass to at a pretreatment temperature between 65 and 100 degrees Celsius to obtain a pretreated biomass, hydrolyzing the pretreated biomass in a first hydrolyzation step to obtain a biomass hydrolysate, and posttreating the biomass hydrolysate in a pressurized posttreatment step by heating the biomass hydrolysate to a posttreatment temperature above 150 degrees Celsius to obtain a posttreated biomass, hydrolyzing the posttreated biomass in a second hydrolyzation step, wherein biogas is obtained from at least the first hydrolyzation step or the second hydrolyzation step.

2. The method according to claim 1, wherein the pretreatment step is non-pressurized.

3. The method according to claim 1, wherein the method further comprises separating the biomass hydrolysate in a first separation step into a solid fraction and a liquid fraction.

4. The method according to claim 1, wherein the method further comprises separating the posttreated biomass in a second separation step into a solid fraction and a liquid fraction.

5. The method according to claim 1, wherein the method further comprises recirculation of at least a part of a liquid fraction from any separation step to any hydrolyzation step and/or the pretreatment step.

6. The method according to claim 1, wherein biogas is obtained from both the first hydrolyzation step and from the second hydrolyzation step.

7. (canceled)

8. (canceled)

9. The method according to claim 1, wherein the amount of hemicellulose in the biomass hydrolysate is less than 40% by weight of the amount of hemicellulose in the soft biomass.

10. The method according to claim 1, wherein the amount of cellulose in the biomass after the second hydrolyzation step is less than 40% by weight of the amount of cellulose in the posttreated biomass.

11. The method according to claim 1, wherein furfural and 5-HMF and 2-furioc acid are generated in a combined amount of less than 5% by weight.

12. (canceled)

13. The method according to claim 1, wherein lignin is obtained from the second hydrolyzation step in a purity of more than 30%.

14. The method according to claim 1, wherein the pretreatment temperature is between 65 and 90 degrees Celsius.

15. The method according to claim 1, wherein the posttreatment temperature is between 150 and 230 degrees Celsius.

16. The method according to claim 1, wherein the pretreatment step is performed for 2 hours or less.

17. The method according to claim 1, wherein the first hydrolyzation step is performed for less than 20 days.

18. The method according to claim 1, wherein the posttreatment step is performed for less than 1 hour.

19. The method according to claim 1, wherein the second hydrolyzation step is performed for less than 30 days.

20. (canceled)

21. The method according to claim 1, wherein the second hydrolysis step is performed by bacteria, enzymes and/or fungi.

22. (canceled)

23. (canceled)

24. The method according to claim 1, wherein acid and/or food waste is added to the soft biomass.

25. The method according to claim 1, wherein the acid is a weak acid.

26. (canceled)

27. The method according to claim 1, wherein the pH in the pretreatment step is between 2 and 11.

28. (canceled)

Description

THE FIGURES

[0115] The invention will now be described with reference to the figures where

[0116] FIG. 1 illustrates a general method of producing biomass degradation products, such as biogas, from soft biomass according to an embodiment of the invention.

[0117] FIG. 2 illustrates a further method of producing biomass degradation products, such as biogas, from soft biomass according to an embodiment of the invention.

[0118] FIG. 3 illustrates an even further method of producing biomass degradation products, such as biogas, from soft biomass according to an embodiment of the invention.

[0119] FIG. 4 illustrates methane yield for raw wheat straw and heated wheat straw as a function of time according to an embodiment of the invention.

[0120] FIG. 5 illustrates the effect on hemicellulose concentration and inhibitor formation as result of time of heating to 70 degrees Celsius according to an embodiment of the invention.

[0121] FIG. 6 illustrates the effect on hemicellulose conversion as result of time of digestion according to an embodiment of the invention.

[0122] FIG. 7 illustrates the effect of temperature and pH in the pretreatment step according to an embodiment of the invention. The first number is temperature (° C.) and second is pH in the pretreatment.

[0123] FIG. 8 illustrates the effect of both pretreatment and posttreatment on the methane yield according to an embodiment of the invention.

[0124] FIG. 9 illustrates the impact on biochemical methane potential (BMP) of different hydrothermal treatments (HT) on the pretreated wheat straw over 21 days.

[0125] FIG. 10 illustrates BMP comparison of the hydrothermal treated samples, after 21 days.

[0126] FIG. 11 illustrates the impact on BMP of different pH treatments on wheat straw, with and without hydrothermal treatment.

[0127] FIG. 12 illustrates biomethane potential of different pH pretreatments on wheat straw, with and without hydrothermal treatment. Further, it illustrates the amount of inhibitors w/w % relative to TS.

DETAILED DESCRIPTION

[0128] Referring to FIG. 1, a schematic view of a process according to an embodiment of the invention is shown.

[0129] Further embodiments are illustrated in FIGS. 2-3, and all of these embodiments may be understood in the light of FIG. 1 and the discussion thereof below.

[0130] Returning to FIG. 1, a soft biomass, which may advantageously be acidic, is provided and subjected to heating in a non-pressurized pretreatment step at a pretreatment temperature PT between 65 and 100 degrees Celsius at ambient pressure. The heating may for example be performed in a tank or container with or without stirring. The retention time in the pretreatment step is usually short, such as less than one hour or less than 30 minutes, but it may also be longer if this may be convenient. The pretreated biomass (PB) may then be conveyed into a further tank to be hydrolyzed in a first hydrolyzation step or it may in principle also be hydrolyzed in the same container as it was pretreated. The hydrolyzation may be performed without any further additives, where any acid already present may catalyze the hydrolyzation, or it may be performed for example by the addition of bacteria or fungi. The first hydrolyzation is usually performed at a pH around neutral, such as for example between pH 6-8. It may also be lower for example in the case of an acid catalyzed hydrolyzation. In the first hydrolyzation step both hemicellulose and cellulose are hydrolyzed, however relatively more hemicellulose than cellulose is hydrolyzed. The hydrolyzation products may for example be C5 sugars from hemicellulose and C6 sugars from cellulose, which may be further degraded. An important degradation product, which may be obtained from the first hydrolyzation step is biogas, comprising methane and/or carbon dioxide.

[0131] The resulting biomass hydrolysate (BH) is then posttreated in a pressurized posttreatment step, where the temperature is above 150 degrees Celsius and the pressure is above ambient, such as for example between 5 and 25 bar. The posttreatment may be performed in a closed container or tank. Subsequent to the posttreatment step, the posttreated biomass may then be subjected to a second hydrolyzation step. Biogas may advantageously be obtained from the first and/or second hydrolyzation step. The biogas from the second hydrolyzation step may be further purified and may be combined with the biogas produced in the first hydrolyzation step.

[0132] Referring to FIG. 2, an embodiment of the invention is shown, where the process of FIG. 2 includes, further to the steps of the embodiment of FIG. 1, a separation step after the first hydrolyzation step. The separation step, may be called a first separation step. The separation step separates the biomass hydrolysate into a solid fraction and a liquid fraction. The solid fraction is then subjected to a pressurized posttreatment step and the resulting posttreated biomass is subjected to a second hydrolyzation and thereafter it may be subjected to a second separation step leading to a liquid fraction and a solid fraction.

[0133] Referring to FIG. 3, an embodiment of the invention is shown, where the process of FIG. 3 includes, further to the steps of the embodiment of FIG. 1 or 2, that any liquid fraction LIF from any of the separation steps may be recycled into the non-pressurized pretreatment step and/or the second hydrolyzation step.

EXAMPLES

Example 1: The Effect of Pretreating a Biomass Before a Biogas Process in a Hydrolyzation Step

[0134] This example describes the effects of pretreating a biomass by heating the biomass prior a biogas process in a hydrolyzation step. A fixed amount of raw wheat straw has been heated for one hour together with food waste prior the biogas process.

[0135] Materials and Methods:

[0136] Biomass mix: [0137] 3.51 g of wheat straw with a dry matter of 86% [0138] 23.12 g of food waste with a dry matter of 13.8% [0139] 57.41 g of water (no dry matter)

[0140] The solution has been stirred for 5 min. Upon stirring, the solution with at pH of 4.5 was heated to 70° C. for one hour and then cooled down to 50° C. 315.9 g of inoculum was added to the solution and the biogas process was started using the APTMS-II system from BiogasSystems.

[0141] The biogas process was conducted in 30 days at a pH of 8.5 and a temperature of 50° C.

[0142] As controls, three samples with pure inoculum were digested as well as two samples with food waste and inoculum and one sample with raw wheat straw, i.e. six control digestions in total, see Table 1.

TABLE-US-00001 TABLE 1 Samples for the first example. Sample Contents Mass (g) 3 x Blank Inoculum 400 2 x Food waste control Inoculum 400 Food waste 58.5 1 x Wheat straw control Inoculum 284.7 Wheat straw 6.3 Water 108.9 1 x Heat treated wheat straw Inoculum 316.0 and food waste Food waste 23.1 Wheat straw 3.5 Water 57.4

[0143] Results

[0144] Soft biomass, in this case wheat straw, will, if not pretreated, tend to create floating layers in an otherwise wet solution, inhibiting the biogas process. Heating the wheat straw together with food waste allows the biomass to be diluted in the solution, instead of floating on top of the biomass mix, allowing a more efficient anaerobic digestion process afterwards.

[0145] To quantify the effect of heating the wheat straw together with the food waste, total methane production was measured from the mix, upon which, the contribution to the methane production from the inoculum and the food waste were subtracted, taking into account the results from controls. A large increase of 20% on the methane yield was observed compared to the raw wheat straw sample, see FIG. 4. The corresponding numbers of FIG. 4 are listed in Table 2.

TABLE-US-00002 TABLE 2 Methane yield versus time Methane yield (m.sup.3 CH.sub.4/ton) Time (days) Raw wheat straw Heated wheat straw 0 0 0 1 10 94 2 42 148 3 66 217 4 89 214 5 111 211 6 140 237 7 159 271 8 172 281 9 184 288 10 193 294 11 201 295 12 210 294 13 214 295 14 216 303 15 218 311 16 219 317 17 220 322 18 220 325 19 220 328 20 220 328 21 221 331 22 222 332 23 223 333 24 225 335 25 219 329 26 221 329 27 223 330 28 224 329 29 224 328 30 226 329

Example 2: Hemicellulose Conversion

[0146] Heating wheat straw in a pretreatment step damages the structure of the biomass and makes the hemicellulose more accessible without producing a large concentration of inhibitors such as furfural and 5-HMF which a pretreatment at higher temperatures does. This example describes the effect on hemicellulose conversion during the pretreatment step and the first hydrolyzation step.

[0147] Materials and Methods:

[0148] Four samples are prepared with wheat straw, citric acid and water and stirred for 5 min. The solutions are heated for 0 min, 15 min, 30 min, 45 min or 1 hour, respectively, at 70° C., and the hemicellulose concentration and the inhibitor concentration are measured at the different time points.

[0149] Five new samples are prepared with wheat straw, citric acid and water and stirred for 5 min, heated for 1 hour at 70° C. and cooled down to 50° C. The solutions are adjusted to a pH of 8 with NaOH and afterwards mixed with inoculum and a first hydrolyzation step comprising an anaerobic digestion process is started. The first hydrolyzation, here a biogas process, is stopped after 12 days, and the hemicellulose concentrations and the inhibitor concentrations are measured in each of the samples.

[0150] The hemicellulose and inhibitor concentrations are also measured in samples with pure inoculum and with raw wheat straw and inoculum.

[0151] Results

[0152] Hemicellulose was not decomposed during the heat/acid treatment as illustrated in FIG. 5. The corresponding numbers of FIG. 5 are listed in Table 3.

TABLE-US-00003 TABLE 3 Minutes Hemicellulose Inhibitor 0 100% 9% 15 114% 9% 30  96% 5% 45  96% 0% 60 103% 7%

[0153] The inhibitors shown in Table 3, are shown as percentage of total hemicellulose in the sample.

[0154] The acid/heat treatment did open the wheat straw structure. 23% of the hemicellulose is converted for the heat/acid treated sample where only 8% of the hemicellulose was converted for the not treated sample, see FIG. 6. The corresponding numbers of FIG. 6 are listed in Table 4. The inhibitor concentration was below the detection limit (0.1 g/kg).

TABLE-US-00004 TABLE 4 Hemicellulose concentration Acid treated wheat Blank Water treated wheat Time (days) straw Acid (water) straw 1 100.0% 100% 100% 100% 12 76.8%  95%  92%  92%

Example 3: Effect of Pretreatment Severity in the Pretreatment Step on the Biogas Yield

[0155] This example describes the effect of pretreatment severity on the biogas yield (here methane). The pretreatment severity is described by temperature, pH and time. This example evaluates the effect of pH and temperature. The temperature is varied from 80° C. to 100° C. and the pH from 2 to 9.5. The experiment is done using a statistic experimental design.

[0156] Materials and Methods

[0157] 12 samples are prepared with wheat straw, Phosphorbuffer and stirred for 5 min. The solutions are heated for 1 hour. In total, eight combinations of temperature and pH are tested, in which two combinations are triplicated, see Table. All samples are cooled down after heat treatment, adjusted to a pH of 8 and then mixed with inoculum. Upon this, a biogas process is conducted for 12 days for each sample. The methane yields are measured.

TABLE-US-00005 TABLE 5 Experimental setup with different combinations of pH and temperature. Sample no. Temperature (° C.) pH 1 100 2 2, 3, 4, 80 4.5 5 100 7 6, 7, 8 80 9.5

[0158] Results

[0159] All the treated samples showed increase in biogas yield compared to the control, see FIG. 7. The corresponding numbers of FIG. 7 are listed in Table 6 below.

TABLE-US-00006 TABLE 6 m.sup.3 CH.sub.4/ton VS Sample Temp (° C.) pH Day 1 Day 13 1 100 2 47 231 2 80 4.5 48 231 3 80 4.5 46 224 4 80 4.5 49 224 5 100 7 45 226 6 80 9.5 48 235 7 80 9.5 47 230 8 80 9.5 47 230 Control 38 202

Example 4: The Effect of Pretreatment Severity in the Second Hydrolyzation Step on the Biogas Yield

[0160] This example describes the effect of pretreatment severity on the second hydrolyzation step on the biogas, in this case methane, yield. The pretreatment severity is described by temperature, pH and time. This example evaluates the effect of pH and temperature. The temperature is varied from 130° C. to 210° C. and the pH from 2 to 12. The experiment was conducted using a statistic experimental design.

[0161] Materials and Methods

[0162] 12 samples were prepared with wheat straw, citric buffer pH 4.5 and stirred for 5 min. The solutions were heated for 1 hour to 70° C., then cooled to 50° C., upon which inoculum were added. A second hydrolyzation step, comprising a biogas process, was conducted for 14 days for each of the samples. The samples were separated into a liquid fraction and a fiber fraction. The liquid fraction was transferred back to the biogas reactors. The fiber fractions were adjusted with phosphor buffer to reach the pH and heated for 15 min at 140, 170 or 200° C., see Table.

TABLE-US-00007 Flask no. Temperature (° C.) pH 1 140 12 2 170 12 3 200 12 4 140 7.5 5 170 7.5 6 200 7.5 7 140 3 8 170 3 9 200 3 12 Control, no treatment

[0163] Table 7: Experimental setup with different combinations of pH and temperature. Afterwards, the samples are cooled down, the pH was adjusted to pH 8 and mixed with inoculum and a biogas process in a second hydrolyzation step is conducted for 20 days for each sample. As it did take 3 days to heat all the solid fiber fraction samples the biogas process was conducted for 3 days without fibers.

[0164] The methane yields are measured after the biogas process.

[0165] Results

[0166] The result can be seen in FIG. 8. Both temperature and pH have an effect. Surprisingly the data show that the treatment at neutral pH gave the highest biogas production, the reason for that may possible be due to formation of inhibitors at low and high pH, since the process is performed batch-wise and not continuous. The corresponding numbers of FIG. 8 are listed in Table 8 below.

TABLE-US-00008 TABLE 8 Temp m.sup.3 CH.sub.4/ton VS Sample pH (° C.) Day 1 Day 36 12 140  12 140 28 281 12 200  12 200 48 289 7.5 140.sup.  7.5 140 59 309 7.5 200.sup.  7.5 200 46 317 3 140 3 140 48 262 3 170 3 170 47 262 3 200 3 200 50 257 Control 39 248

Example 5: Biomethane Potential (BMP) Test

[0167] This example describes the effect of pretreatment and hydrothermal treatment (HT).

[0168] Materials and Methods:

[0169] 5 samples were divided into; raw wheat straw, HT wheat straw and three acidic washed wheat straw, at pH 4.5 for 60 min. The raw wheat straw, the HT wheat straw and one sample of acidic washed wheat straw sample were run for the whole period of BMP test. The two other acidic washed samples were digested for 7 days and then hydrothermal treated before used in the BMP test again. One of the samples was hydrothermal treated with all the sample from the BMP test (fibers and inoculum), and then mixed with new inoculum before BMP test continued. The other sample had the fibers separated, which were hydrothermal treated, and then mixed into the same inoculum again. The samples were analyzed after HI for the inhibitors furfural and 5-HMF. The detection limit for the inhibitors was 0.06 w/w-% of total IS in the sample.

TABLE-US-00009 TABLE 9 Pretreatments Hydrothermal Samples Description Acidic wash treatment Raw Wheat Wheat Straw without any No No Straw pretreatment HT Wheat Wheat straw with HT before No Yes Straw BMP 4.5 pH Acidic pretreated wheat straw Yes No before BMP 4.5 pH w/ Acidic pretreated wheat straw Yes Yes HT of full before BMP and HT of full BMP sample sample after 7 days of BMP 4.5 pH w/ Acidic pretreated wheat straw Yes Yes HT of fibers before BMP and HT of fibers after 7 days of BMP

[0170] Results:

[0171] The results can be seen in FIG. 9 and FIG. 10. The results show that the acidic washed samples have a higher BMP than raw wheat straw. This tendency was observed after 3 days, and the difference increased until the end of the BMP test. The BMP of the HT wheat straw stopped producing gas after day 5, which could be due to inhibitors. The two HT acidic washed samples increased significantly after day 7, where the HT was implemented. The acidic sample which had HT on the separated fibers, had the best potential. The BMP of this sample is near the sample of cellulose, which would be the maximum BMP potential possible. The decrease in BMP of the acidic sample, with all sample hydrothermal treated, was due to this sample had lower gas production than pure inoculum samples.

TABLE-US-00010 TABLE 10 Pretreatments BMP Hydrothermal [m.sup.3 CH.sub.4/ton Samples Acidic wash treatment VS] Raw Wheat Straw No No 219 HT Wheat Straw No Yes 122 pH 4.5 Yes No 276 pH 4.5 w/HT of full Yes Yes 286 sample pH 4.5 w/HT of fibers Yes Yes 340

[0172] The results from FIG. 9 and FIG. 10, and shown at Table 10 above, show that the separation of fibers before HI was the best method to increase the BMP. This was replicated with the same pH of 4.5, but also with a much lower pH at 1.5 and a higher pH at 10. These samples were treated the same way, with washing at their respective pH for 60 min before used in BMP test. These samples are shown in Table 11. The inhibitors, furfural and 5-HMF, were measured on all samples after HI. Besides the pH samples, replicates of raw wheat straw and HI wheat straw were used in the BMP test. The results of this BMP was used in an average, with the samples replicates from the first BMP. The BMP results are shown in FIG. 11 and FIG. 12.

TABLE-US-00011 TABLE 11 Pretreatments Acidic/ Alkaline wash Hydrothermal Samples Description [pH] treatment Raw Wheat Straw Wheat Straw without any No No pretreatment HT Wheat Straw Wheat straw with HT No Yes pH 1.5 Acidic pretreated straw 1.5 No pH 1.5 w/HT Acidic pretreated straw with HT of 1.5 Yes fibers after 7 days of BMP pH 4.5 Acidic pretreated straw 4.5 No pH 4.5 w/HT Acidic pretreated straw with HT of 4.5 Yes fibers after 7 days of BMP pH 10 Acidic pretreated straw 10 No pH 10 w/HT Acidic pretreated straw with HT of 10 Yes fibers after 7 days of BMP

[0173] The results seen from FIG. 11 and FIG. 12 confirmed that acidic pretreatment at pH 4.5 for 60 min, with HI of the fibers, gives the best BMP—as seen in table 12.

TABLE-US-00012 TABLE 12 Pretreatments BMP Acidic/Alkaline Hydrothermal [m.sup.3 CH.sub.4/ton Samples wash [pH] treatment VS] Raw Wheat Straw No No 223 HT Wheat Straw No Yes 116 pH 1.5 1.5 No 196 pH 1.5 w/HT 1.5 Yes 236 pH 4.5 4.5 No 270 pH 4.5 w/HT 4.5 Yes 344 pH 10 10 No 259 pH 10 w/HT 10 Yes 317

[0174] It also confirmed the concern of the HI wheat straw to be inhibited by furfural and 5-HMF, as analyses had shown contents of 1.1% furfural and 0.32% 5-HMF, shown as percentage of total IS (w/w-%), which inhibited the production of gas. The samples with pretreated wheat straw showed no content of inhibitors after the HI. Regarding the pretreatment, it showed that pH 1.5 produced the lowest BMP, which was below raw wheat straw, and just above raw wheat straw if HI was included. The results also showed that pretreatment at pH 10 with HI gave nearly as good results of 317 m.sup.3 CH.sub.4/ton VS, as pH 4.5 with HI at 344 m.sup.3 CH.sub.4/ton VS. Furthermore, it was observed that for the pretreated straw samples, with HT after 7 days of BMP, it was not possible to detect inhibitors. This indicates that the pretreatment prevents the formation of the inhibitors, and increases the BMP.

[0175] Example of Biogas Production

[0176] Wheat straw, food waste and water is conveyed into a pretreatment tank, where it is heated at a temperature of around 70 degrees Celsius at ambient pressure for about 30 minutes. The pH of the soft biomass in the pretreatment tank is about 3.5. The pretreated biomass is then fed into a first hydrolysis tank, and bacteria in process water are added. The pH of the biomass in the first hydrolysis tank is about neutral and the retention time around 8 days. In the first hydrolysis tank biogas, such as methane and carbon dioxide is produced. The biogas may subsequently be further purified and utilized. The hydrolyzed biomass is drawn from the first hydrolysis tank and fed into a separator to obtain a liquid fraction and a solid fraction. The solid fraction is fed into a pressurized posttreatment tank where a posttreatment step is performed by heating the content to at around 170 degrees Celsius. After the posttreatment step the posttreated biomass may be separated by a separator, such as for example decantor and screw press, to obtain a liquid fraction and a solid fraction. At least a part of the liquid fraction or the entire liquid fraction may be recycled into the pretreatment tank or the first hydrolysis tank for reuse. The solid fraction is then subjected to a second hydrolysis step in a second hydrolysis tank by adding bacteria or enzymes or fungi. The retention time in the second hydrolyzation step is around 20 days. The biogas may be isolated and may be further purified and may be combined with the biogas produced in the first hydrolyzation step.

FIGURE REFERENCES

[0177] SB. Soft biomass [0178] NPS. Non-pressurized pretreatment step [0179] PT. Pretreatment temperature [0180] PB. Pretreated biomass [0181] FHS. First hydrolyzation step [0182] BH. Biomass hydrolysate [0183] PPS. Pressurized posttreatment step [0184] POT. Posttreatment temperature [0185] POB. Posttreated biomass [0186] SHS. Second hydrolyzation step [0187] BG. Biogas [0188] FSS. First separation step [0189] SSS. Second separation step