OPTIMIZATION OF CHEMICAL CONSUMPTION IN BIOMASS DELIGNIFICATION

Abstract

In one example, a process includes providing a system with a first vessel and a second vessel; providing a biomass comprising lignin, hemicellulose and cellulose fibers into said first vessel; providing an aqueous acidic composition comprising an acid; providing a modifier component; providing a peroxide component; exposing said biomass to said sulfuric acid, modifier and peroxide components, creating a reaction mass; mixing said reaction mass; and allowing said sulfuric acid component and peroxide component to come into contact with said biomass for a period of time sufficient to a delignification reaction to occur and remove a pre-determined amount of said lignin from said biomass. The pre-determined amount may be assessed by determining a first remaining peroxide concentration in the reaction mass, with a suitable apparatus, when said first remaining peroxide concentration is reached, the biomass is transferred to said second vessel.

Claims

1. A process to perform a controlled exothermic delignification on a batch of lignocellulosic biomass, said process comprising: providing a system comprising at least a first vessel and a second vessel; providing said biomass comprising lignin, hemicellulose and cellulose fibers into said first vessel; providing an aqueous acidic composition comprising an acid selected from the group consisting of: sulfuric acid; an alkylsulfonic acid; an arylsulfonic acid and combinations thereof; providing a modifier component; providing a peroxide component; exposing said biomass to said said acidic composition, said peroxide component and said modifier component to create a reaction mass; mixing said reaction mass; allowing said said acidic composition and peroxide component to come into contact with said biomass for a period of time sufficient to a delignification reaction to occur and remove a pre-determined amount of said lignin from said biomass, wherein said pre-determined amount is assessed by determining a first remaining peroxide concentration in the reaction mass, with a suitable apparatus, when said first remaining peroxide concentration is reached, the biomass is transferred to said second vessel; allowing the temperature of the biomass mixture to increase during the residence time of said biomass in said second vessel; allowing said acidic composition, said modifier component and said peroxide component to continue said delignification reaction at said second temperature and remove a second pre-determined amount of said lignin from said biomass, wherein said second pre-determined amount is assessed by testing a second remaining peroxide concentration, with a suitable apparatus, in the reaction mass, when said second remaining peroxide concentration is reached, the biomass is removed from said second vessel; and optionally, a washing step is employed to separate a resulting liquid portion comprising said lignin and hemicellulose from the solid portion containing the cellulose extracted from the biomass.

2. The process according to claim 1, wherein said system comprises a third vessel where the biomass is sent to after being removed form said second vessel, and further comprising: allowing the temperature of the biomass mixture to increase during the residence time of said biomass in said second vessel; and allowing said acidic composition, said modifier component and said peroxide component to continue said delignification reaction at said second temperature and remove a third pre-determined amount of said lignin from said biomass, wherein said third pre-determined amount is assessed by testing a third remaining peroxide concentration, with a suitable apparatus, in the reaction mass, when said third remaining peroxide concentration in said reaction mass is reached, the biomass and the aqueous acid composition are removed from said third vessel.

3. The process according to claim 2, where said process requires temperature control at said first vessel, and said second vessel.

4. The process according to claim 3, where said temperature control comprises a heat exchanger, jacketed vessel and baffles.

5. The process according to claim 4, where said primary temperature control is a heat exchanger, secondary control is a jacketed tank and tertiary control is a baffle.

6. The process according to claim 5, where said system has an outlet which allows the separation of solids from liquids.

7. The process according to claim 6, where said mixing in said first vessel is performed by a recirculation of the reaction mass.

8. The process according to claim 7, where said mixing in said second vessel is performed by a paddle mixer.

9. The process according to claim 8, where said mixing in said third vessel is performed by a paddle mixer.

10. The process according to claim 1, where said said acidic composition, said modifier component and said peroxide component form a modified Caro's acid composition selected from the group consisting of composition A; composition B and Composition C; wherein said composition A comprises: sulfuric acid in an amount ranging from 20 to 70 wt % of the total weight of the composition; a modifier component comprising an amine moiety and a sulfonic acid moiety selected from the group consisting of taurine; taurine derivatives; and taurine-related compounds; and a peroxide; wherein said composition B comprises: an alkyl sulfonic acid; and a peroxide; wherein the acid is present in an amount ranging from 40 to 80 wt % of the total weight of the composition and where the peroxide is present in an amount ranging from 10 to 40 wt % of the total weight of the composition; wherein said composition C comprises: sulfuric acid; and a two-part modifier component comprising: a compound comprising an amine moiety; a compound comprising a sulfonic acid moiety; and a peroxide.

11. The process according to claim 1, where the temperature of the reaction mass is maintained at a temperature ranging from 25-45 C.

12. The process according to claim 1, wherein at least part of the resulting liquid portion obtained at the end of the reaction is used to treat at least one additional biomass batch.

13. The process according to claim 1, wherein at least part of the resulting liquid portion obtained at the end of the reaction is used to treat at least four additional biomass batches.

14. The process according claim 1, wherein at least part of the resulting liquid portion obtained at the end of the reaction is used to further treat additional biomass batches until the peroxide concentration reaches less than 1%.

15. A continuous digester adapted for use in the delignification of lignocellulosic biomass with a modified Caro's acid composition, where said continuous digester comprises: a cylindrical vessel comprising a first extremity and a second extremity; a diameter to length ratio of said vessel ranging from 0.08-0.2; a biomass wt % loading ranging from 3-15% relative to delignification blend in the digester; a gauge pressure to be 0-14 psi and a temperature to remain below 60 C.; an inlet, located at said first extremity, for loading said digester with said biomass component and said modified Caro's acid thus creating a reaction mixture; at least two zones for mixing a reaction mixture comprising said modified Caro's acid and said biomass component, said at least two zones being positioned sequentially within said cylindrical vessel, and each one of said at least two zones comprising: a temperature indicator/controller to monitor changes in a pre-determined temperature set point, to control heat exchanger setpoint, jet nozzles flow; a jet nozzle, located at a top section of said zone, to provide pumping mixing of the reaction mixture comprising said biomass component and said modified Caro's acid; an extraction screen, located proximate at a bottom section of said zone, to allow the extraction of said modified Caro's acid from the bottom section of said zone; a screen section on the vertical plane having perforations of a shape selected from the group consisting of: circle, rectangular, square etc. and where screen size openings ranging from to 6; a piping connected to said extraction screen and said jet nozzle to allow for recirculation of said modified Caro's acid from the bottom section of the zone to said top section of said zone; a chiller and heater feed loop, located outside of said zone, to allow for chilling/heating the modified Caro's acid solution to desired parameters; a Kappa number analyzer to allow the determination of the pulping percentage of the biomass; and a peroxide analyzer to allow the determination of the peroxide consumption; and a cone bottom adapted with an outlet, located at said second extremity, for discharging of the reaction mass.

16. The continuous digester according to claim 15, wherein said digester is positioned vertically with the inlet being located a top portion thereof and the outlet located at a bottom portion of said digester.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0165] Features and advantages of embodiments of the present application will become apparent from the following detailed description and the appended figures, in which:

[0166] FIG. 1 illustrates a system capable of implementing the process according to a preferred embodiment of the present invention;

[0167] FIG. 2 shows a scaled-up system capable of performing the process according to a preferred embodiment of the present invention; and

[0168] FIG. 3 shows a continuous digester capable of performing the process according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION

[0169] According to a preferred embodiment of the present invention, there is provided a process to perform a controlled exothermic delignification of biomass, said process comprising the steps of: [0170] providing a system comprising at least a first vessel and a second vessel; [0171] providing biomass comprising lignin, hemicellulose and cellulose fibers into said first vessel; [0172] providing a aqueous acidic composition comprising a sulfuric acid component; [0173] providing a peroxide component; [0174] exposing said biomass to said sulfuric acid component and peroxide component, creating a reaction mass (or mixture); [0175] mixing said reaction mass; [0176] allowing said sulfuric acid component and peroxide component to come into contact with said biomass for a period of time sufficient to a delignification reaction to occur and remove a pre-determined amount of said lignin from said biomass;
wherein said pre-determined amount is assessed by testing a first remaining peroxide concentration, with a suitable apparatus, in the reaction mixture, when said first remaining peroxide concentration is reached, the biomass is transferred to said second vessel; [0177] allowing the temperature of the biomass mixture to increase during the residence time of said biomass in said second vessel; [0178] allowing said sulfuric acid component and peroxide component to continue said delignification reaction at said second temperature and remove a second pre-determined amount of said lignin from said biomass;
wherein said second pre-determined amount is assessed by determining a second remaining peroxide concentration, with a suitable apparatus, in the reaction mixture, when said second remaining peroxide concentration is reached, the biomass is removed from said second vessel; [0179] optionally, a washing step is employed to separate the liquid portion containing said lignin and hemicellulose from the solid portion containing the cellulose extracted from the biomass.

[0180] The process mentioned hereinabove can be accomplished by using a system as illustrated in FIG. 1. Said system according to a preferred embodiment of the present invention comprises a first vessel (110) operating at a first temperature, where said biomass (101) is added and subsequently mixed with a delignification composition (102) having an initial peroxide concentration for a pre-determined period of time or until the reaction mixture reaches a pre-determined first remaining peroxide concentration which is measured through the use of a sampling point (115). Preferably, once the reaction mixture reaches a pre-determined first remaining peroxide concentration the it is then transferred to a second vessel (120) where the delignification reaction occurs at a second temperature which can be set higher than said first temperature. Said reaction mixture having said first remaining peroxide concentration continues to be mixed with said delignification composition for a pre-determined period of time or until the reaction mixture reaches a pre-determined second remaining peroxide concentration which is measured through the use of a sampling point (125) associated with said second vessel (120). Preferably, once the biomass reaches said pre-determined second remaining peroxide concentration the reaction mixture is then transferred to a third vessel where the delignification reaction occurs at a third temperature which can be set higher than said second temperature. Said reaction mixture having said second remaining peroxide concentration continues to be mixed with said delignification composition for a pre-determined period of time or until the reaction mixture reaches a third remaining peroxide concentration which is measured through the use of a sampling point (135) associated with said third vessel (130). Preferably, once the biomass reaches said pre-determined fourth kappa number, the reaction mixture is then discharged and the solid portion is separated from the liquid portion and the liquid is recovered and re-inserted into the process by injecting it into the first vessel.

[0181] The system comprises a temperature Indicator/Controller (111) which is designed to monitor changes in temperature set point, to control Heat Exchanger (112) setpoint, jet nozzles (117). The jet nozzles (117) on the center main piping system are designed to provide pumping mixing of the reaction mixture comprising the biomass feedstock and delignification composition (chemical solution).

[0182] According to a preferred embodiment of the present invention, the system further comprises an extraction screen for the liquid chemical solution which is designed to extract chemical solution from the vessel to pump into the jet nozzle.

[0183] As seen in FIG. 1, the system comprises a heat/cooling jacket (118) which is designed to be a secondary temperature control method for chilling/heating. This can prove to be useful since the delignification reaction is exothermic and control of the temperature is desirable in order to ensure that the yield is maximized.

[0184] At the bottom of each of the vessels (110, 120, 130) is located an actuated discharge valve (116, 126 and 136 respectively) which is designed to discharge product slurry (biomass and delignification composition) into next stage.

[0185] The advanced process controls (146) (APC) tool is generally used for individual processes and connects to the and distributed control system (148) (DCS) which is generally in control of the entire process facility. APC is the developed system of integrating multi factors including DCS. The system components virtually communicate with each other and adjust parameters according the programmed inputs. It utilizes real time optimization, reading process variables and continuously adjust for the target rage it is programmed for.

[0186] According to the preferred embodiment illustrated, the system also comprises a chiller & heater feed loop (119) which is designed to be the primary method to chill/heat solution to desired parameters.

[0187] In the embodiment illustrated in FIG. 1, the system further comprises a central main piping system which is a piping system equipped with jet nozzles (117) designed to distribute the chemical solution to biomass. The system further comprises a peroxide concentration testing points (115, 125, and 135, respectively) at each stage to determine the pulping percentage.

[0188] According to a preferred embodiment of the present invention, the system further comprises at least one tank baffle which is designed to increase mixing efficiency. Each of the vessels (110, 120, 130) in the system further comprises a cone bottom (113, 123, 133, respectively) which is desirable for easier reaction mixture discharge from one vessel to the next vessel.

[0189] According to a preferred embodiment of the present invention, the system further comprises a top mount agitator (127, 137) which is designed to provide the desired agitation to the reaction mixture in the said second vessel (120) and third vessel (130). In some cases, the mixing in the first vessel (110) is done by a paddle mixer in other cases it may be done by recirculation of the reaction mixture through a pump and jet nozzle. In other cases, there can be a combination of mixing effected by a paddle stirrer and pumping mixture recirculation.

[0190] According to a preferred embodiment of the present invention, the system further comprises a top mount agitator (127, 137) which is designed to provide the desired agitation to the reaction mixture in the said second vessel (120) and third vessel (130). Mixing in the first vessel (110) is done by recirculation of the reaction mixture through a pump and jet nozzle.

[0191] According to a preferred embodiment of the present invention, the process comprises a step of blending where the liquid containing a proprietary blend is routed to the reactor vessel. Subsequently, the mixer agitates the blend in the reactor during chemical addition, biomass addition, and reaction. To increase mixing, the circulation pump is used to circulate material from the mesh back to the top. The biomass is added to the reactor through the top entry port.

[0192] The delignification reaction takes place and creates an exothermic environment within the reaction vessel. The level & temperature in the reactor is monitored. When the first stage of the reaction is completed (based on the determined remaining peroxide concentration), an actuated valve is opened, and the reaction mixture is moved to the second vessel to being the second stage of the delignification process. The process is repeated for stages 2 & 3 (i.e. when there is a second and a third vessel).

[0193] Preferably, the heating of the mixture is carried out by using a glycol-water mixture heated by a boiler. The heat exchanger fluid travels through the reactor(vessel) heat exchanger & tank jacket, bypassing the chiller, to heat the reaction mixture to the desired reaction starting temperature. During biomass addition and reaction, the glycol water mixture is cooled by the chiller. The heat exchanger fluid travels through the external reactor heat exchanger & cooling jacket to maintain the desired reaction temperature.

[0194] According to a preferred embodiment of the present invention, the system further comprises an emergency shutdown procedure where if the reaction temperature increases above a certain set temperature, for example in some cases it may be set at 50 C., a control valve opens and the reactor is flooded with water thereby stopping the reaction. When such a shutdown occurs, the contents of the reactor are rerouted to the overflow tank via the circulation pump.

[0195] According to a preferred embodiment of the present invention, the system is set up to have the initial reaction temperature of the process be in the range of 20-30 C. and increase as the reaction progresses. The temperature transmitter submerged in the reactor sends this value to the temperature control system. As the temperature increases to 50 C., the Temperature Controller sends a signal to the control valve on the water outlet line to open by 25%. According to a preferred embodiment of the present invention, the system will, with every 1 C. increase registered by the Temperature Transmitter starting at 50 C., send a signal to the control valve to open by 25% more until fully opens at 53 C., stopping the reaction completely. Preferably, the temperature control is performed by using jet nozzle sprays which can spray uniformly the surface of the chemical-biomass mixture. The water sprayed is then mixed in with the mixture in the presence of agitators or by re-circulation of the reaction mixture (i.e. without a conventional agitator).

[0196] As illustrated in FIG. 2, a system according to a preferred embodiment of the present invention comprises a first vessel (210) operating at a first temperature, where said biomass (201) and a delignification composition (202) (having an initial peroxide concentration) are combined to produce a reaction mixture. The reaction mixture is mixed for a pre-determined period of time or until the reaction mixture reaches a first remaining peroxide concentration in the reaction mass. Said first remaining peroxide concentration in the reaction mass being determined by removing a portion of the delignification composition and testing for the peroxide concentration at a testing point (215). Preferably, once the biomass reaches a pre-determined first remaining peroxide concentration in the reaction mass the reaction mixture is then transferred to a second vessel (220) where the delignification reaction occurs at a second temperature which can be set higher than said first temperature. Said biomass having said first remaining peroxide concentration in the reaction mass continues to be mixed with said delignification composition for a pre-determined period of time or until the biomass reaches a pre-determined a second remaining peroxide concentration in the reaction mass. Said second remaining peroxide concentration in the reaction mass being determined by removing a portion of the delignification composition and testing for the peroxide concentration at a testing point (225) associated with said second vessel (220). Preferably, once the reaction mixture reaches said pre-determined second remaining peroxide concentration, the reaction mixture is then transferred to a third vessel where the delignification reaction occurs at a third temperature which can be set higher than said second temperature. Said reaction mixture having said second remaining peroxide concentration in the reaction mass continues to be mixed with said delignification composition for a pre-determined period of time or until the biomass reaches a pre-determined third remaining peroxide concentration in the reaction mass. Said third remaining peroxide concentration in the reaction mass being determined by removing a portion of the delignification composition and testing for the peroxide concentration at a testing point (235) associated with said third vessel (230). Preferably, once the reaction mixture reaches said pre-determined third remaining peroxide concentration, the reaction mixture is then discharged through the discharge (242) and the solid portion is separated from the liquid portion and the liquid is recovered and re-inserted into the process by injecting it into the first vessel. The cellulose comprising the solid portion is subjected to other post-delignification treatment steps depending on the ultimate use thereof.

[0197] As seen in FIG. 2, each vessel (210, 220, 230) comprises their own paddle stirrer (217, 227, 237, respectively), heat exchanger (212, 222, 232 respectively), composition sampling or testing points (215, 225, 235, respectively) while the system operates with an advanced process control (246) and a distributed control system (248). According to a preferred embodiment of the present invention, there are no internal baffles in the digester.

[0198] Preferably, the third remaining peroxide concentration in the reaction mass is near zero as the presence of peroxide at the point of discharge of the delignified biomass is undesirable for further treatment of the liquid discharge. Moreover, unreacted peroxide at the point of discharge is considered to be waste. Since the peroxide is the main consumed reactant during the delignification of lignocellulosic biomass it is desirable to optimize the reaction parameter to make use of it.

Biomass Loading

[0199] According to a preferred embodiment of the present invention, the biomass loading in the vessel for the delignification reaction can go up to 20 wt. %. According to a preferred embodiment of the present invention, the biomass loading in the vessel for the delignification reaction can go up to 15 wt. %. According to a preferred embodiment of the present invention, the biomass loading in the vessel for the delignification reaction can go up to 10 wt. %. Preferably, the biomass loading in the vessel for the delignification reaction can go up to 8 wt. %. More preferably, the biomass loading in the vessel for the delignification reaction can go up to 7 wt. %. According to a preferred embodiment of the present invention, the biomass loading in the vessel for the delignification reaction ranges from 4 to 6 wt. %.

Temperature

[0200] According to a preferred embodiment of the present invention, the initial temperature in the vessel where the delignification occurs can be as low as 25 C. and still provide substantial delignification within a reasonable period of time. Preferably, the initial temperature in the vessel where the delignification occurs is 27 C. More preferably, the initial temperature in the vessel where the delignification occurs is 30 C. According to a preferred embodiment of the present invention, the initial temperature in the vessel where the delignification occurs ranges from 30 to 45 C. According to a preferred embodiment of the present invention, the initial temperature in the vessel where the delignification occurs ranges from 32 to 40 C.

Time

[0201] According to a preferred embodiment of the present invention, the duration of the delignification reaction can last up to 24 hours. Preferably, the duration of the delignification reaction can last up to 12 hours. Preferably, the duration of the delignification reaction can last up to 6 hours. Preferably, the duration of the delignification reaction can last up to 4 hours. According to a preferred embodiment of the present invention, the duration of the delignification reaction takes about 3 hours. In some preferred embodiments, the duration of the delignification reaction may take as little as 1.5 hours.

[0202] According to a preferred embodiment of the present invention, the chemicals used in a delignification reaction may be reused in a subsequent delignification and still maintain good delignification power. According to a preferred embodiment of the present invention, the chemicals used in a delignification reaction may be reused in a subsequent delignification by adding some of the peroxide component (referred to as topping up) and still maintain good delignification power. The recycling of the chemicals used in the delignification provides several advantages with one of the most obvious one being eliminating the discharge of spent (or used) chemicals). According to a preferred embodiment of the present invention, the chemicals used in a delignification reaction may be reused several times by topping up with peroxide between each reaction.

[0203] According to a preferred embodiment of the present invention when employing a batch method to delignify biomass, a valuable approach to optimize the hydrogen peroxide (H.sub.2O.sub.2) consumption is the recycling of the reaction blend after each reaction and removal of the solid cellulose by solid liquid separation methods. This is performed and is highly advantageous to do so since only 20% of the hydrogen peroxide (H.sub.2O.sub.2) added to the blend is consumed. Hence, in such an instance, recycling the acid blend (modified Caro's acid), having a high quantity of unreacted peroxide component after the separation of the resulting cellulose substantially reduces the overall peroxide (H.sub.2O.sub.2) consumption.

[0204] According to a preferred embodiment of the present invention, good control of the reaction temperature is one of the factors in driving the delignification reaction forward which indicates that the reaction is kinetically driven. Other experiments demonstrate that a delignification reaction time of 3 hours is achieved. Those experiments carried out in a temperature ranging from 30 to 45 C. show that the desired delignification is achieved without impacting the hydrogen peroxide (H.sub.2O.sub.2) consumption and the resulting cellulose's kappa number.

[0205] As illustrated in FIG. 3, a continuous digester system according to a preferred embodiment of the present invention comprises a vessel divided into distinct zones (310, 320 and 330). Said first zone (310) operating at a first temperature, where said biomass (301) is continuously added at wt % loading of 3-6 wt %, or 7-10 wt %, or 10-15 wt % relative to liquid volume in the digester and a delignification composition (302) (having an initial peroxide concentration (ranging from 5 to 15%)) are combined to produce a reaction mixture. The reaction mixture is mixed using an internal close loop system by pumping liquid from screen (355) to input nozzle (315) for a pre-determined period of time to reach a residence time of 1-4 hrs or until the reaction mixture reaches a first remaining peroxide concentration in the reaction mass. Said first remaining peroxide concentration in the reaction mass being determined by performing an inline testing for the peroxide concentration at a testing point (319). Preferably, once the reaction mixture reaches a pre-determined first remaining peroxide concentration, the biomass slurry is then moved on to a second zone (320) by controlling the flow rates of the internal circulation in distinct zones where the delignification reaction occurs at a second temperature which can be set higher than said first temperature. Said reaction mixture having said first remaining peroxide concentration continues to be mixed with said delignification composition for a pre-determined period of time or until the reaction mixture reaches a pre-determined a second remaining peroxide concentration. Said second remaining peroxide concentration in the reaction mixture being determined by by performing an inline testing for the peroxide concentration at a testing point (329) associated with said second zone (320). Preferably, once the reaction mixture reaches said pre-determined second remaining peroxide concentration, the reaction mixture is then moved on to a third zone (330) where the delignification reaction occurs at a third temperature which can be set higher than said second temperature. Said reaction mixture having said second remaining peroxide concentration continues to be mixed with said delignification composition for a pre-determined period of time or until the reaction mixture reaches a pre-determined third remaining peroxide concentration. Said third remaining peroxide concentration in the reaction mixture being determined by performing an inline testing for the peroxide concentration at a testing point (339) associated with said third zone (330). Preferably, once the reaction mixture reaches said pre-determined third remaining peroxide concentration, the reaction mixture is then discharged through the discharge (342) of the digester and the solid portion is separated from the liquid portion and the liquid is recovered and re-inserted into the process by injecting it back into the digester. The cellulose comprising the solid portion is subjected to other post-delignification treatment steps depending on the ultimate use thereof.

[0206] As seen in FIG. 3, each zone (310, 320, 330) comprises their own mixing through the use of jet nozzles (317, 327, 337, respectively), as well as heat exchanger (318, 318) represent the tubing for the circulation of the heating/cooling liquid for the first zone), composition sampling or testing points (315, 325, 335, respectively) while the system operates with an advanced process control (346) and a distributed control system (348). Further, each zone comprises an extraction screen (355, 365, 375 respectively) to allow for the removal of a portion of the liquid chemical solution from the zone to pump back into their respective zone and as such provide mixing within the zone as well as to heat or cool the solution.

Batch Experiments

[0207] A series of experiments carrying out delignification using a modified Caro's acid were carried out to evaluate the feasibility of recycling the reacted modified Caro's acid composition for continuous batch processing. This was studied to evaluate the behavior of the peroxide component in terms of efficiency in delignification and in order to determine how often it can be recycled in a batch process.

[0208] It was hypothesized that, under controlled conditions, continuous batch processing could be used to approximate a similar approach applied to continuous digestion (or delignification) of lignocellulosic biomass.

[0209] Accordingly, several batches of lignocellulosic biomass were delignified using a modified Caro's acid having the following characteristics as listed in Table 1.

TABLE-US-00001 TABLE 1 Composition of the modified Caro's acid used in the batch experiments Component Molar Ratio Mass % H2O 56 38.53 H2O2 10 14.46 H2SO4 10 41.69 Taurine 1 5.32

[0210] A first batch of biomass was mixed with the above-mentioned modified Caro's acid kept at a temperature ranging from 32 to 37 C. for a duration of 20 hours. The initial peroxide concentration was determined to be 14.03%. The remaining peroxide concentration measured after the reaction was completed was determined to be 11.32%. The kappa number of the resulting cellulose at the end of the reaction was measured and determined to be below 5.

[0211] The resulting modified Caro's acid, where the content of peroxide determined to be 11.32%, was mixed with a second batch of biomass to provide a second treatment batch. The second treatment batch was kept at a temperature ranging from 32 to 37 C. for a duration of 20 hours. The remaining peroxide concentration measured after the reaction was completed was determined to be 8.44%. The kappa number of the resulting cellulose at the end of the reaction was measured and determined to be below 5.

[0212] The resulting modified Caro's acid, where the content of peroxide determined to be 8.44%, was mixed with a third batch of biomass to provide a third treatment batch. The third treatment batch was kept at a temperature ranging from 32 to 37 C. for a duration of 20 hours. The remaining peroxide concentration measured after the reaction was completed was determined to be 5.94%. The kappa number of the resulting cellulose at the end of the reaction was measured and determined to be below 5.

[0213] The resulting modified Caro's acid, where the content of peroxide determined to be 5.94%, was mixed with a fourth batch of biomass to provide a second treatment batch. The fourth treatment batch was kept at a temperature ranging from 32 to 37 C. for a duration of 20 hours. The remaining peroxide concentration measured after the reaction was completed was determined to be 3.83%. The kappa number of the resulting cellulose at the end of the reaction was measured and determined to be below 5.

[0214] The resulting modified Caro's acid, where the content of peroxide determined to be 3.83%, was mixed with a fifth batch of biomass to provide a second treatment batch. The fifth treatment batch was kept at a temperature ranging from 32 to 37 C. for a duration of 20 hours. The remaining peroxide concentration measured after the reaction was completed was determined to be 2.34%. The kappa number of the resulting cellulose at the end of the reaction was measured and determined to be below 5.

[0215] In order to use up the remaining peroxide in the modified Caro's acid composition resulting from the fifth delignification reaction, it has been determined that in the above experiments, the modified Caro's acid could be reused for at least another biomass delignification treatment.

[0216] On the basis of the above batch experiments, it has been determined that continuous batch treatments could be carried out to optimize delignification efficiency has well as residence time of biomass through various steps.

Continuous Experiments

[0217] The objective of the first experiment was to validate that a peroxide gradient exists between the digester zones. In this experiment, biomass was continuously added at 15 min to 1 hr interval into zone 320 till 6% loading was obtained and was mixed with table 2.1 above-mentioned modified Caro's acid kept at a temperature ranging from 25 to 35 C. for a duration of 60 hours (in a continuous mode for each batch addition lasting approximately 12 hours). The residence time was controlled through the flow of liquid from screen The initial peroxide concentration was determined to be 5% in section 320. As biomass was intermittently added (at 15 minute intervals), the peroxide concentration in zone 320 measured 3.8%, 3.7%, 3.2%, 2.8%, 1.7% at 12 hr intervals while in zone 330 the peroxide concentration remained relatively unchanged ranging between 4.6-5%, confirming that a peroxide gradient does exist. The kappa number of the resulting cellulose from the bottom discharge at 12 hr intervals was determined to be below 2.

TABLE-US-00002 TABLE 2.1 Composition of the modified Caro's acid used in the contious expirements Component Molar Ratio Mass % H2O 18 45.98 H2O2 10 12.71 H2SO4 10 36.64 Taurine 1 4.68

TABLE-US-00003 TABLE 2.2 Composition of the modified Caro's acid used in the contious experiments Component Molar Ratio Mass % H2O 18 39.63 H2O2 6 8.61 H2SO4 10 41.40 TEOA 1 6.30 MSA 1 4.06

[0218] To further validate that a peroxide gradient is achieved through controlling internal mixing, biomass loading and residence time, experiments were repeated using a modified Caros's acid composition as set out in Table 2.2 modified Caros's acid. The peroxide concentration in zone 330 vs 320 had the following values (7.03%/4.12%), (6.00%/2.97%) and (6.95%/5.7%) each experiment having been separately performed.

[0219] The kappa number of the resulting cellulose from the bottom discharge at 12 hr intervals was determined to be below 2. This data indicates that the residence time of the biomass could be further shortened down to 8 hours and even more preferably, down to 4 hours.

[0220] An experiment was conducted using the modified Caros's acid composition set out in Table 2.1 to validate an overall decreasing peroxide can be obtained in the continuous digester.

[0221] Biomass was continuously added at 15 min to 1 hour intervals into zone 320 until 5% loading was achieved with a starting peroxide concentration of 5%. Zone circulation was performed to circulate in zone 330 using screen (375) resulting in the biomass travelling down the digester. Peroxide concentration was measured and determined to be 3.9% in zone B, and 3.7% in zone A, highlighting the presence of an overall peroxide gradient of 0.2%. Given the cellulose exiting zone 330 had a kappa number less than 2, this highlights the robustness and the reliability of the peroxide concentration measurements.

[0222] According to a preferred embodiment of the present invention, there is provided a new system and method conceived to modify the existing continuous digester used in energy-intensive delignification processes such as in the kraft process. Preferably, this continuous digester differs from existing pulp digesters as follows: [0223] the vessel is preferably made of stainless steel so as to withstand the modified Caro's acid which is used in the delignification process; [0224] the operating conditions are low, typically less than 14 gauge psi and 50 C.; [0225] monitoring of the extent of reaction output through a combination of peroxide analyzers and/or kappa number.

[0226] Preferably, the continuous digester utilizes the low energy intensive process of chemical impregnation of biomass with a chemical blend (preferably, a modified Caro's acid). According to a preferred embodiment of the present invention, the digester consists of a number of zones, each zone comprising a number of elements and providing a unique residence time for the reaction mixture determined by kappa analyzers and/or the peroxide concentration in the reaction mixture. Residence time is controlled through several factors such as biomass loading, biomass size, rate of circulation of each zone Careful monitoring of either one or both of those features ensures that the delignification reaction is carried out until the desired product is achieved. Preferably, this is meant to be understood that the kappa number of the resulting cellulose will be less than 10, more preferably, the kappa number will be less than 5, even more preferably, the kappa number will be less than 3, and yet even more preferably, the kappa number will be less than 2. According to a preferred embodiment, the remaining peroxide concentration in the final output from the continuous digester will be less than 4%, more preferably less than 3%, even more preferably less than 2% and yet even more preferably less than 1%.

[0227] According to a preferred embodiment of the present invention, the continuous digester delignifies the input biomass feedstock in a continuous process reactor. Preferably, the presence of a temperature Indicator/Controller allows operators to monitor changes in temperature set point, to control heat exchanger setpoint, jet nozzles flow. Preferably, the presence of jet nozzles on each zone provides pumping mixing of the biomass and chemical solution. Preferably, the presence of extraction screen for the liquid chemical solution allows the extraction of the chemical solution from the vessel to pump into zones as well as to heat or cool the solution. Preferably, the chiller and heater Feed Loop are the primary method to chill/heat solution to desired paraments. According to a preferred embodiment of the present invention, there are Kappa analyzers at each stage to allow the determination of the pulping percentage. According to a preferred embodiment of the present invention, there are peroxide analyzers at each stage which allow the operators to determine peroxide consumption. Preferably, the continuous digester has a cone bottom to allow for optimal output discharge.

[0228] According to a preferred embodiment of the present invention, the reaction temperature is in the range of 30 to 45 C. since it not only provides consistent remaining peroxide concentration in the final output from the continuous digester, it also provides a consistent lignin-hemicellulose-depolymerized-organic (LHDO) mixture. It also preserves the LHDO from potential oxidation by the hydrogen peroxide (H.sub.2O.sub.2). Preferably, the produced LHDO is separated from cellulose. This provides a unique organic stream that can be easily upgraded to a high value renewable fuel.

[0229] While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by those skilled in the relevant arts, once they have been made familiar with this disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims.