Method for preparing xylose from bamboo processing excess materials

Abstract

The method for preparing xylose from bamboo processing excess materials comprises the following steps that the bamboo processing excess materials are smashed, and purified bamboo powder is obtained through sand setting, impurity removal and dilute acid pretreatment; mixing the purified bamboo powder with 1-2% of inorganic acid, hydrolyzing at 110-120 DEG C for 2.5-4 hours, and discharging hydrolysate; adding hot water into the hydrolysis residues for washing, and combining a washing solution with the hydrolysate in the step S2 to obtain a crude sugar solution; sequentially carrying out adsorption resin decoloration and electrodialysis treatment on the crude sugar solution to obtain a deacidified and desalted sugar solution; purifying the deacidified and desalted sugar solution by ion exchange resin, and concentrating to obtain a xylose product; wherein the adsorption resin is alkalescent anion exchange resin, the electric conductivity of the sugar liquid after electrodialysis treatment is smaller than or equal to 500 microseconds per centimeter, the use of activated carbon is avoided, meanwhile, a neutralizer is not introduced in the whole process, and through the neutralizer-free closed-loop deacidification process, the temperature-controlled hydrolysis process and the resin-membrane coupling purification process, the yield is remarkably increased, and the cost and pollution are reduced.

Description

TECHNICAL FIELD

[0001] The present application is a method for preparing xylose, in particular a method for preparing xylose from bamboo processing residues. BACKGROUND

[0002] As a main raw material for producing xylitol, xylose has been produced from bamboo processing residues such as bamboo chips. Some methods for preparing xylose from bamboo chips are given in documents such as CN104450830A, CN116676434A, CN117701782A, CN119286956A, CN119320811A, CN119320811A, etc.

[0003] However, the existing methods have the following problems: Active carbon is usually used for decolorization treatment, which has the risk of particle residue and high cost due to difficult treatment of active carbon waste.

[0004] When alkaline hydrogen peroxide is used for pretreatment, calcium carbonate needs to be used for neutralization, which is easy to produce new ion pollution.

[0005] The overall hydrolysis efficiency is low, so the xylose recovery rate is usually ≤80%.

[0006] Therefore, a process without active carbon, higher efficiency, lower cost, and lower pollution load is developed to utilize bamboo processing residues to prepare xylose. SUMMARY

[0007] To this end, the present application provides a method for preparing xylose from bamboo processing residues to solve the above technical problems.

[0008] A method for preparing xylose from bamboo processing residues, characterized in that it comprises the following steps: S1: crushing the bamboo processing residues to 60 mesh or more, removing impurities by sand settling, and pretreating with 0.05%-0.25% dilute acid to obtain purified bamboo powder; S2: mixing the purified bamboo powder with 1-2% inorganic acid, hydrolyzing at 110-120°C for 2.5-4 hours, and discharging the hydrolysis liquid; S3: adding hot water to the hydrolysis residue for washing, and combining the washing liquid with the hydrolysis liquid of step S2 to obtain a crude sugar liquid; S4: sequentially decolorizing the crude sugar liquid with adsorption resin and electrodialysis treatment to obtain a deacidification and desalination sugar liquid; S5: purifying the deacidification and desalination sugar liquid with ion exchange resin and then concentrating to obtain a xylose product; In step S4, the adsorption resin is a weakly basic anion exchange resin, the sugar liquid has an electrical conductivity of ≤500 μS / cm after electrodialysis treatment, and no neutralizing agent is introduced throughout the process.

[0009] In step S2, the process of mixing the purified bamboo powder with 1-2% inorganic acid is as follows: Bamboo powder feeding: The purified bamboo powder is fed into the hydrolysis tank, and the solid content is controlled to be 15-20%; Acid injection: 68-72% of inorganic acid is injected for the first time, and stirring is performed for 8-12 min at a stirring speed of 45-55 r / min; then, the remaining 28-32% of inorganic acid is added, and stirring is performed for 5-8 min at a stirring speed of 30-35 r / min.

[0010] When the pH in the hydrolysis tank is greater than 2.0, dilute sulfuric acid is added until the pH is 1.5-2.0.

[0011] In step S2, the hydrolysis process includes: First-stage hydrolysis: The temperature is increased to 110±2°C at a rate of 2±0.2°C / min at room temperature, and the first-stage hydrolysis is maintained for 30±5 min; Second-stage hydrolysis: After the first-stage hydrolysis is completed, the temperature is increased to 120±2°C at a rate of 1±0.1°C / min, and the second-stage hydrolysis is maintained for 2.5-4.0 h; During the first-stage and second-stage hydrolysis, the pressure in the hydrolysis tank is maintained at 0.2-0.3 MPa.

[0012] In step S3, the hot water washing of the hydrolysis residue includes: injecting hot water, increasing the temperature to 110-120°C, maintaining and stirring for 25±5 min, and discharging the washing liquid, wherein the pressure during the washing process is 0.15-0.20 MPa, the water injection amount is 3-4 times the dry weight of the residue, and the stirring speed is 60±5 r / min.

[0013] In step S3, the hot water washing of the hydrolysis residue includes: First hot water washing: After the temperature of the hydrolysis residue is reduced to 85±5°C, 80±2°C hot water is injected, stirring is performed during the water injection process, the stirring time is 20±2 min, the temperature is maintained at 80±2°C, and then the first washing liquid of the first hot water washing is discharged; Second hot water washing: 60±2°C hot water is injected into the residue after the first hot water washing, stirring is performed during the water injection process, the stirring time is 15±1 min, and then the second washing liquid of the second hot water washing is discharged; The combined washing liquid and the hydrolysis liquid of step S2 include the first washing liquid, the second washing liquid, and the hydrolysis liquid of step S2.

[0014] The water injection amount in the first hot water washing is 3-4 times of the absolute dry weight of the residue, and the stirring speed is 40±2 r / min during the water injection process; the water injection amount in the second hot water washing is 3-4 times of the absolute dry weight of the residue; and the stirring speed is 30±1 r / min during the water injection process.

[0015] In step S4, the crude sugar solution is further subjected to decolorization by adsorption resin before the decolorization. The crude sugar solution is pre-filtered by a microfiltration bag.

[0016] The purification is performed by using a hollow fiber membrane microfiltration device, the hollow fiber membrane has a pore size of 0.1-0.2 μm, and the transmittance of the purified crude sugar solution is greater than or equal to 30%.

[0017] In step S4, during the electrodialysis treatment, dilute sulfuric acid with a concentration of 0.3-0.5% is recovered from the outlet of the concentrated water chamber and reused in step S1; the conductivity of the outlet of the dilute water chamber is less than or equal to 500 μS / cm, and the pH is 5-6.

[0018] In step S5, the deacidification and desalination of the sugar solution is purified by ion exchange resin, including: removing impurities, small molecule pigments and residual acid ash in the sugar solution by cation and anion exchange resin to obtain highly purified sugar solution, and reducing the conductivity of the sugar solution to less than or equal to 20 uS / cm, and the pH is 5.5-6.

[0019] In step S5, the concentration of the purified sugar solution is performed by the following method: first concentrated by nanofiltration membrane to greater than or equal to 20%, then concentrated by first effect evaporation to greater than or equal to 50%, then concentrated by second effect evaporation to greater than or equal to 80%, and finally concentrated by third effect evaporation to greater than or equal to 90%, and before the nanofiltration membrane concentration, the purified sugar solution is first filtered by a 1 μm safety filter.

[0020] Beneficial effects: the method for preparing xylose by using bamboo processing residues provided by the embodiment of the application comprises the following steps: S1: crushing the bamboo processing residues to more than 60 meshes, removing impurities by sand setting, and pretreating with 0.05%-0.25% dilute acid to obtain purified bamboo powder; S2: mixing the purified bamboo powder with 1-2% inorganic acid, hydrolyzing at 110-120°C for 2.5-4 hours, and discharging the hydrolysis liquid; S3: adding hot water to wash the hydrolysis residue, combining the washing liquid with the hydrolysis liquid of step S2 to obtain a crude sugar solution; S4: sequentially subjecting the crude sugar solution to decolorization by adsorption resin and electrodialysis treatment to obtain a deacidification and desalination sugar solution; and S5: concentrating the deacidification and desalination sugar solution after purification by ion exchange resin to obtain a xylose product; wherein the adsorption resin in step S4 is a weak alkaline anion exchange resin, the conductivity of the sugar solution after the electrodialysis treatment is less than or equal to 500 μS / cm, no activated carbon is used, and no neutralizing agent is introduced in the whole process, so that the yield is significantly improved, the cost is reduced, and the pollution is reduced by the processes of closed-loop deacidification without neutralizing agent, temperature-controlled hydrolysis, and resin-membrane coupled purification. Attached Figure Description

[0021] Figure 1 A flowchart of a method for preparing xylose using bamboo processing waste materials according to an embodiment of the present invention; Detailed Implementation

[0022] Please refer to Figure 1 This invention provides a method for preparing xylose using bamboo processing waste. S1: The bamboo processing waste is crushed to a fineness of 60 mesh or higher, and then pretreated with sand to remove impurities and 0.05% to 0.25% dilute acid to obtain purified bamboo powder.

[0023] Specifically, the bamboo processing waste can be bamboo shavings discharged from the washing machine process of bamboo pulping enterprises, powdered bamboo shavings generated from the cutting process of bamboo profile processing plants, bamboo powder processed by other special crushing equipment, or bamboo shavings or bamboo powder generated from bamboo processing in other stages. In addition, it is understood that the bamboo processing waste is not limited to the material of bamboo. Generally, bamboo such as Cizhu bamboo, Moso bamboo, wood bamboo, green bamboo, and Nan bamboo are all feasible.

[0024] Bamboo processing waste can be pulverized to a mesh size of 60 or higher using a hammer mill to pass through a 60-mesh sieve. In some embodiments, secondary or multiple pulverization processes can also be performed to obtain raw materials of 60 mesh or higher. 60 mesh refers to 60 sieve holes per inch. Specifically, the sieve hole diameter of the 60-mesh sieve is approximately 0.3 mm. At the same time, when pulverizing bamboo processing waste to a mesh size of 60 or higher, the proportion of the pulverized bamboo processing waste with a particle size of less than or equal to 0.3 mm should be greater than or equal to 95%.

[0025] The aforementioned sand settling process is used to remove heavy impurities such as mud and metal fragments, as well as floating light impurities from bamboo shavings. Specifically, in one embodiment, this can be achieved through the following steps: S11: Slurry preparation: Mix the crushed bamboo powder and water in a mass ratio of 1:8±0.2 in a thickening tank, stirring at 50 r / min to form a uniform suspension.

[0026] S12: Grit Removal: The suspension is pumped into a trapezoidal grit chamber. In this embodiment, the structural parameters of the trapezoidal grit chamber can be an aspect ratio of 4:1, an inclination angle of 30±1°, and a flow velocity control of 0.1±0.02m / s. Heavy impurities are removed using: Bottom sand and gravel: discharged via pneumatic sand discharge valve, with a discharge volume ≤ 5% of the total volume; Metal fragments: Magnetic rods are placed in the pool, and the fragments are manually removed after being attracted.

[0027] S13: Separation of light impurities: Install a 30-40 mesh inclined screen at the outlet of the sedimentation tank to intercept floating impurities such as bark and plastic; floating objects on the water surface are removed by a scraper.

[0028] In addition, the dilute acid pretreatment is used to dissolve ash, gum and part of hemicellulose in the bamboo powder, and improve the subsequent hydrolysis efficiency. Specifically, the bamboo powder can be soaked in 0.05%-0.25% (mass ratio) dilute acid for 1-4 hours at a soaking temperature of 30-80°C. Preferably, the dilute acid has a concentration of 0.1%.

[0029] Further, the solid-liquid ratio is 1:5 (dry weight of bamboo powder: volume of acid liquid) during the treatment process.

[0030] Further, the ash content of the purified bamboo powder after the pretreatment is ≤0.5%, and the iron ion content is ≤50 ppm.

[0031] S2: The purified bamboo powder is mixed with 1-2% (mass ratio) inorganic acid, and hydrolysis is performed at 110-120°C for 2.5-4 hours, and the hydrolysis liquid is discharged.

[0032] The inorganic acid can be hydrochloric acid or sulfuric acid, and preferably, the inorganic acid is sulfuric acid.

[0033] Specifically, the purified bamboo powder can be mixed with 1-2% inorganic acid and hydrolysis can be performed in the following manner.

[0034] S201: Bamboo powder feeding: The purified bamboo is fed into the hydrolysis tank, and the solid content is controlled to be 15-20% (mass fraction); S202: Acid liquid injection: 68-72% inorganic acid is injected for the first time, and stirring is performed for 8-12 minutes at a stirring speed of 45-55 r / min; then, the remaining 28-32% inorganic acid is added, and stirring is performed for 5-8 minutes at a stirring speed of 30-35 r / min, and preferably, the inorganic acid has a concentration of 1.5%.

[0035] In this way, the purified bamboo powder is uniformly mixed with the inorganic acid.

[0036] In addition, when the pH in the hydrolysis tank is >2.0, dilute sulfuric acid should be added to the pH=1.5-2.0. Specifically, the dilute sulfuric acid has a concentration of 0.08%-0.25%, and preferably, the dilute sulfuric acid has a concentration of 0.1%.

[0037] The hydrolysis process includes the following processes: S211: First-stage hydrolysis: The temperature is increased to 110±2°C at a rate of 2±0.2°C / min under room temperature, and the first-stage hydrolysis is performed for 30±5 minutes. S212: Second-stage hydrolysis: After the first-stage hydrolysis is completed, the temperature is increased to 120±2°C at a rate of 1±0.1°C / min, and the second-stage hydrolysis is performed for 2.5-4.0 hours.

[0038] Further, the pressure in the hydrolysis tank is kept at 0.2-0.3 MPa during the one-stage and two-stage holding processes.

[0039] Further, the stirring speed is controlled at 50±3 r / min during the temperature rising processes of the one-stage and two-stage hydrolysis processes to break the fiber lumps, and the stirring speed is controlled at 30±2 r / min during the holding processes of the one-stage and two-stage hydrolysis processes to reduce the steam disturbance and promote the hydrolysis.

[0040] It can be understood that, during the one-stage holding process, the hemicellulose is dissolved to make the xylose oligosaccharide account for ≥40%, and during the two-stage holding process, the xylan is deeply hydrolyzed to make the xylose conversion rate >80%.

[0041] S3: hot water is added to the hydrolysis residue for washing, and the washing liquid is combined with the hydrolysis liquid of step S2 to obtain a crude sugar liquid.

[0042] Specifically, the hot water is added to the hydrolysis residue for washing by single pressure washing or atmospheric low-temperature multiple washing.

[0043] The single pressure washing step is: hot water is injected, heated to 110-120°C, and held for 25±5 min with stirring, and the washing liquid is discharged, wherein the pressure during the washing process is 0.15-0.20 MPa, the water injection amount is 3-4 times the absolute dry weight of the residue, and the stirring speed is 60±5 r / min.

[0044] The atmospheric low-temperature multiple washing can be performed twice, and the washing liquids of the two hot water washings are combined with the hydrolysis liquid of step S2 to recover as much xylose as possible.

[0045] S31: one hot water washing.

[0046] After the temperature of the hydrolysis residue is reduced to 85±5°C, hot water at 80±2°C is injected, preferably, the hot water is softened water; the water injection amount is 3-4 times (by mass ratio) the absolute dry weight of the residue, the water injection mode can be a tank bottom perforated distributor, and the stirring is performed at a speed of 40±2 r / min during the water injection process, and the stirring time is 20±2 min, and at the same time, the temperature is maintained at 80±2°C, and then the one washing liquid of the one hot water washing is discharged.

[0047] Further, the sugar concentration of the one washing liquid is 8-12%, and the pH is 2.2-2.5.

[0048] S32: two hot water washings.

[0049] The residual slag after once hot water washing is injected with 60±2℃ hot water, and the water injection amount is 3-4 times (in mass ratio) of the absolute dry weight of the residual slag; during the water injection process, stirring is carried out at a speed of 30±1 r / min, and the stirring time is 15±1 min, and then the secondary washing liquid of the secondary hot water washing is discharged.

[0050] The hydrolysis liquid, the first washing liquid and the second washing liquid are combined to obtain a crude sugar liquid, and at the same time, the crude sugar liquid has a pH of 1.5-2, a solid content of 3-4%, and an electrical conductivity of 3-10 mS / cm.

[0051] Further, when the hydrolysis liquid, the first washing liquid and the second washing liquid are combined to obtain a crude sugar liquid, the following method is adopted: first, the hydrolysis liquid is added to the mixing tank, and then the first washing liquid and the second washing liquid are added in sequence, and during the adding and mixing process, the stirring speed is 60±3 r / min, and the mixing time is 30±5 min.

[0052] It can be understood that when it is necessary to reduce the time and improve the efficiency, single pressure washing can be selected, and when it is necessary to improve the yield of crude sugar or reduce the demand for pressure tank, multiple normal pressure low temperature washing can be selected. In the normal pressure low temperature washing, through the combination of one high temperature hot water washing and two low temperature washings, the yield of the crude sugar liquid can reach more than 91%, which is higher than the yield of less than 80% in the prior art. At the same time, due to the increase of lignin dissolution efficiency under high temperature and high pressure in single pressure washing, the yield of crude sugar through the above washing process can also reach 90%.

[0053] S4: The crude sugar liquid is sequentially subjected to decolorization by adsorption resin and electrodialysis treatment to obtain a deacidification and desalination sugar liquid; In step S4, the adsorption resin is a weakly basic anion exchange resin, and the electrical conductivity of the sugar liquid after the electrodialysis treatment is ≤500 μS / cm, and no neutralizing agent is introduced in the whole process.

[0054] Specifically, the decolorization by adsorption resin can adopt the following steps: S411: The crude sugar liquid is pre-filtered by a microfiltration bag.

[0055] The microfiltration bag can be a 5 μm microfiltration bag, which is used to remove particulate matter with a particle size of >20 μm.

[0056] S412: Purification and concentration of deacidification and desalination.

[0057] The hollow fiber membrane microfiltration device is used for purification, the pore size of the hollow fiber membrane is 0.1-0.2 μm, and after purification, the transmittance of the crude sugar liquid should reach 30%.

[0058] Further, about 90% of the colorants are removed by using a special decolorization resin.

[0059] Further, the decoloring treatment uses three groups of stainless steel columns connected in series, filled with D301 weakly basic anion exchange resin, the resin pore size range is 5-20 nm, the loading amount is 1 / 10 of the sugar liquid volume. It can be understood that the resin needs to be activated before use: cycle washing with 4% NaOH solution for 2 hours, and then washing with pure water until pH=7±0.5.

[0060] The crude sugar liquid passes through the resin column at a flow rate of 0.5 BV / h, the temperature is constant at 50±2°C, and when the outlet sugar liquid transmittance≥85% (wavelength 550 nm), the decolorized liquid is collected.

[0061] The resin adsorption capacity is controlled to be≤0.5g pigment / g resin (calculated by pigment absorbance 420nm), and the decolorization rate is≥90%.

[0062] It can be understood that the above treatment process avoids the problem of residual activated carbon micro-particles, and the decolorization efficiency is improved by more than 10% compared with the traditional method.

[0063] Specifically, the electrodialysis treatment can use the following steps: S421: The sugar liquid after decolorization is refined, wherein a 1 μm safety filter is used for refining.

[0064] S422: The refined sugar liquid is treated by an electrodialysis membrane stack system.

[0065] The electrodialysis membrane stack system is configured with at least two groups of parallel homogeneous ion exchange membrane stacks, wherein the effective area of a single stack is 50㎡, the distance between the anion and cation membranes is 0.8mm, during the electrodialysis treatment: voltage 12-15V, current density 30±2mA / cm², sugar liquid flow rate 0.8-1.0m / s, temperature 45±2℃, during the electrodialysis treatment process, the concentration of the concentrated sulfuric acid recovered from the outlet of the concentrated water chamber is 0.2-0.5%, which can be reused in the pretreatment process of step S1; the conductivity of the outlet of the dilute water chamber is reduced to≤500μS / cm, and the pH is stable at 5-6, without introducing any neutralizing agent throughout the process, wherein the concentrated water chamber refers to the acid recovery compartment in the electrodialysis membrane stack system, and the dilute water chamber refers to the sugar liquid desalination compartment.

[0066] Further, the calcium ion in the sugar liquid after pretreatment is controlled to be≤10ppm, and 0.1mmol / L EDTA is added to the extreme water to chelate residual metal ions. If there are signs of pollution such as membrane stack pressure difference>0.15MPa, start 1% citric acid solution (50°C) cycle cleaning for 1 hour, the flux recovery rate can reach more than 95% to ensure long-term operation of the system.

[0067] It can be understood that the weak alkaline resin adsorbs the bamboo lignin pigment with high specificity by the coupling treatment of decolorization and electrodialysis, and the adsorption capacity is more than 30% higher than that of activated carbon; meanwhile, the direct deacidification by electrodialysis cancels neutralization, avoids ion exchange resin calcium poisoning, and greatly prolongs the service life of the system. In addition, through the neutralizer-free closed loop design: the recovery rate of dilute acid recovered from the concentrated water chamber is more than 80%, the consumption of sulfuric acid is reduced by 25%; and the conductivity is controlled to be less than or equal to 500 μS / cm, which can guarantee the subsequent ion exchange efficiency. In addition, by canceling the neutralization process, more ash enters the hydrolyzate, and the resin decolorization process used in the decolorization process eliminates the risk of small particles entering the electrodialysis during the activated carbon decolorization process. At the same time, the adsorption resin can be regenerated and reused, reducing the decolorization cost and the problems of operating dust and waste carbon treatment. In addition, the resin decolorization-electrodialysis deacidification and desalination is easy to integrate and control, and the conductivity of the sugar solution can be controlled at a low level, which can greatly reduce the load and cost of the subsequent anion and cation exchange resins.

[0068] S5: The deacidification and desalination sugar solution is concentrated after being purified by ion exchange resin to obtain a xylose product.

[0069] Specifically, the xylose product can be obtained by the following steps.

[0070] S51: The deacidification and desalination sugar solution is purified by cation and anion exchange resins to remove impurities, small molecule pigments and residual acid ash in the sugar solution, to obtain a purified sugar solution, and to reduce the conductivity of the sugar solution to less than or equal to 20 uS / cm and the pH to 5.5-6.

[0071] Further, the purified sugar solution can be further purified by a three-stage series ion exchange system, which comprises a cation column, an anion column and a mixed ion column. The sugar solution flows through the system at a flow rate of 2 BV / h, and the temperature is controlled at 45±2℃ to prevent resin denaturation, wherein the cation column is filled with 001×7 strong acid resin, the anion column is filled with 201×7 strong base resin, and the mixed ion column is filled with D001+201 mixed resin.

[0072] S52: The purified sugar solution is concentrated and thickened.

[0073] The first evaporation is used to concentrate the sugar solution to ≥20%, and then the first evaporation is used to concentrate the sugar solution to ≥50%, and then the second evaporation is used to concentrate the sugar solution to ≥80%, and finally the third evaporation is used to concentrate the sugar solution to ≥90%.

[0074] Further, the purified sugar solution can be further purified by a three-stage series ion exchange system, which comprises a cation column, an anion column and a mixed ion column. The sugar solution flows through the system at a flow rate of 2 BV / h, and the temperature is controlled at 45±2℃ to prevent resin denaturation, wherein the cation column is filled with 001×7 strong acid resin, the anion column is filled with 201×7 strong base resin, and the mixed ion column is filled with D001+201 mixed resin.

[0075] S53: Sugar powder preparation.

[0076] Further, the sugar powder can be prepared by spray drying.

[0077] Further, the product xylose content is ≥98.5%, meeting the xylose quality requirements. Embodiment

[0078] S601: Crush the bamboo processing waste to 60 mesh or more, remove impurities by sand settling, and pretreat with 0.05%-0.25% dilute acid to obtain purified bamboo powder.

[0079] The bamboo processing waste is Dendrocalamopsis oldhami processing waste with a moisture content of 12%, and is crushed to 60 mesh, of which the particle size ≤0.3mm accounts for 96%.

[0080] Sand settling and impurity removal: Slurry preparation: Mix the bamboo powder with water at a ratio of 1:8, stir at 50 r / min, and the solid content is 12.5%.

[0081] Sand settling and heavy impurity removal: trapezoidal sand settling tank with length-width ratio of 4:1 and inclination angle of 30°, flow rate of 0.1 m / s, and magnetic bar adsorption of metal fragments.

[0082] Light impurity separation: 35 mesh inclined screen mesh intercepts bark / plastic.

[0083] Dilute acid treatment: 0.1% sulfuric acid, solid-liquid ratio 1:5, 60°C soaking for 3 hours, to obtain purified bamboo powder with ash content of 0.42% and iron ion of 38 ppm.

[0084] S602: Mix the purified bamboo powder with 1.5% sulfuric acid, hydrolyze, and discharge the hydrolysis liquid.

[0085] The solid concentration of the purified bamboo powder is 18%.

[0086] Mixing process: Firstly, inject 70% sulfuric acid (concentration 1.5%, total amount 1.8%), stir at 50 r / min for 10 min; Add the remaining 30% sulfuric acid, and stir at 32 r / min for 7 min.

[0087] Hydrolysis process: Stage 1: increase temperature to 110°C at 2°C / min, keep for 60 min, pressure 0.22 MPa, stirring at 50 r / min; Stage 2: increase temperature to 120°C at 1°C / min, keep for 3.5 h, pressure 0.25 MPa, stirring at 30 r / min, xylose conversion rate 83.1%.

[0088] S603: Add hot water to the hydrolysis residue for washing, combine the washing liquid with the hydrolysis liquid of step S2 to obtain a crude sugar liquid.

[0089] First washing: the residue is cooled to 85℃, 80℃ softened water is added, the water amount is 3.6 times of the absolute dry weight of the residue, 40r / min stirring for 20min, the first washing liquid is discharged, the sugar concentration is 10.5%, pH=2.3.

[0090] Second washing: 60℃ hot water is added, the water amount is 3.2 times of the absolute dry weight of the residue, 30r / min stirring for 15min, the second washing liquid is discharged.

[0091] The hydrolysis liquid, the first washing liquid and the second washing liquid are combined to obtain a crude sugar liquid, pH=1.9, solid content 3.6%, conductivity 8.2mS / cm, yield 92.3%.

[0092] S604: the crude sugar liquid is sequentially subjected to decolorization by adsorption resin and electrodialysis treatment to obtain a deacidification and desalination sugar liquid.

[0093] Decolorization process: Pre-filtration: first filtered through a 5μm microfiltration bag, and then filtered through a 0.15μm hollow fiber membrane, and the light transmittance is 35%.

[0094] Resin decolorization: D301 weak basic resin column (50℃, 0.5BV / h), decolorization rate 93.2%.

[0095] Electrodialysis treatment process: Fine filtration: filtered through a 1μm security filter.

[0096] Electrodialysis membrane stack: homogeneous ion exchange membrane, negative membrane AMV / positive membrane CMV, voltage 14V, 45℃, sugar liquid outlet conductivity 460μS / cm, pH=5.7; 0.42% dilute sulfuric acid is recovered in the concentrated water chamber and reused for the dilute acid pretreatment in step S601, reuse rate 82%.

[0097] S605: the deacidification and desalination sugar liquid is purified by ion exchange resin and then concentrated to obtain a xylose product.

[0098] Ion exchange treatment: three-stage series connection (001×7 positive column→201×7 negative column→D001+201 mixed bed), conductivity is reduced to 18μS / cm, pH=5.6.

[0099] Concentration: nanofiltration membrane→three-effect evaporation to 90% concentration.

[0100] Spray drying: inlet air temperature 180℃, xylose powder is obtained, xylose content 98.7%. Example

[0101] In step S603, hot water is injected into the hydrolysis residue, the temperature is raised to 115 DEG C, and the temperature is kept for 30 min with stirring, and the washing liquid is discharged, wherein the pressure during the washing process is 0.18 MPa, the water injection amount is 1.5 times the absolute dry weight of the residue, the stirring speed is 60 r / min, and the washing liquid is discharged after two times of pressure relief.

[0102] In Comparative Example 1, xylose was prepared by the method of CN116676434A.

[0103] The comparison results of Example 1 and Comparative Example 1 are as follows: From the above comparison, compared with Comparative Example 1, the method provided in Example 1 has an increase of 11.5% in xylose conversion rate, an increase of 16.5% in crude sugar liquid yield, and a decrease of more than 85.7% in ash content of the final product, and the method provided in Example 2 has an increase of 10.8% in xylose conversion rate, an increase of 15.5% in crude sugar liquid yield, and a decrease of more than 85.7% in ash content of the final product.

[0104] The above is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation obtained by utilizing the content of the specification and drawings of the present application, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing xylose using bamboo processing waste material, characterized by, The method comprises the following steps: S1: crushing bamboo processing waste to 60 mesh or more, removing impurities by sand setting, and pretreating with 0.05%-0.25% dilute acid to obtain purified bamboo powder; S2: mixing the purified bamboo powder with 1-2% inorganic acid, hydrolyzing at 110-120°C for 2.5-4 hours, and discharging the hydrolysis liquid; S3: washing the hydrolysis residue with hot water, and combining the washing liquid with the hydrolysis liquid of step S2 to obtain a crude sugar liquid; S4: sequentially decolorizing the crude sugar liquid with an adsorption resin and treating by electrodialysis to obtain a deacidified and desalted sugar liquid; S5: purifying the deacidified and desalted sugar liquid with an ion exchange resin, and then concentrating to obtain a xylose product; In step S4, the adsorption resin is a weakly basic anion exchange resin, the conductivity of the sugar liquid after the electrodialysis treatment is ≤500 μS / cm, and no neutralizing agent is introduced in the whole process.

2. The method of claim 1, wherein, In step S2, the process of mixing the purified bamboo powder with 1-2% inorganic acid is as follows: Bamboo powder feeding: the purified bamboo powder is fed into a hydrolysis tank, and the solid content is controlled to be 15-20%; Acid injection: 68-72% inorganic acid is first injected, and stirring is performed for 8-12 min at a stirring speed of 45-55 r / min; then, the remaining 28-32% inorganic acid is added, and stirring is performed for 5-8 min at a stirring speed of 30-35 r / min.

3. The method of claim 2, wherein, When the pH in the hydrolysis tank is greater than 2.0, dilute sulfuric acid is added until the pH is 1.5-2.

0.

4. The method of claim 2, wherein, In step S2, the hydrolysis process comprises: First-stage hydrolysis: the temperature is increased to 110±2°C at a rate of 2±0.2°C / min under room temperature, and first-stage preservation is performed for 30±5 min; Second-stage hydrolysis: after the first-stage preservation is completed, the temperature is increased to 120±2°C at a rate of 1±0.1°C / min, and second-stage preservation is performed for 2.5-4.0 h; In the first-stage and second-stage preservation processes, the pressure in the hydrolysis tank is maintained at 0.2-0.3 MPa.

5. The method of claim 4, wherein, In step S3, the hot water washing of the hydrolysis residue comprises: injecting hot water, increasing the temperature to 110-120°C, and preserving and stirring for 25±5 min, and discharging the washing liquid, wherein the pressure during the washing process is 0.15-0.20 MPa, the water injection amount is 3-4 times the absolute dry weight of the residue, and the stirring speed is 60±5 r / min.

6. The method of claim 4, wherein, In step S3, the hot water washing of the hydrolysis residue comprises: First hot water washing: after the temperature of the hydrolysis residue is reduced to 85±5°C, 80±2°C hot water is injected, stirring is performed during the water injection process, the stirring time is 20±2 min, the temperature is maintained at 80±2°C, and then the first washing liquid of the first hot water washing is discharged; Second hot water washing: 60±2°C hot water is injected into the residue after the first hot water washing, stirring is performed during the water injection process, the stirring time is 15±1 min, and then the second washing liquid of the second hot water washing is discharged; The combining of the washing liquid and the hydrolysis liquid of step S2 comprises combining the first washing liquid, the second washing liquid, and the hydrolysis liquid of step S2; The water injection amount in the first hot water washing is 3-4 times of the absolute dry weight of the residue, and the stirring speed is 40±2 r / min during the water injection process; the water injection amount in the second hot water washing is 3-4 times of the absolute dry weight of the residue, and the stirring speed is 30±1 r / min during the water injection process.

7. The method of claim 5 or claim 6, wherein, In step S4, the crude sugar solution is further subjected to decolorization by adsorption resin before purification. The crude sugar solution is pre-filtered by a microfiltration bag. The hollow fiber membrane microfiltration device is used for purification, the pore size of the hollow fiber membrane is 0.1-0.2 μm, and the transmittance of the purified crude sugar solution is ≥30%.

8. The method of claim 7, wherein, In step S4, during the electrodialysis process, the concentrated water chamber outlet recovers dilute sulfuric acid with a concentration of 0.3-0.5%, which is recycled to step S1; the conductivity of the fresh water chamber outlet is ≤500 μS / cm, and the pH is 5-6.

9. The method of claim 7, wherein, In step S5, the deacidification and desalination sugar solution is purified by ion exchange resin, which includes: the deacidification and desalination sugar solution is treated by anion and cation exchange resin to remove impurities, small molecule pigments and residual acid ash in the sugar solution, to obtain highly purified sugar solution, and to reduce the conductivity to below 20 uS / cm, and the pH is 5.5-6.

10. The method of claim 9, wherein, In step S5, the concentration of the purified sugar solution is increased by the following method: first, the purified sugar solution is concentrated to ≥20% by nanofiltration membrane, then concentrated to ≥50% by the first effect evaporation, then concentrated to ≥80% by the second effect evaporation, and finally concentrated to ≥90% by the third effect evaporation, and before the nanofiltration membrane concentration, the purified sugar solution is first filtered by a 1 μm safety filter.

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