A method for extracting alginate from brown algae through high-shear digestion

Abstract

The present application belongs to the technical field of seaweed chemical industry, and particularly relates to a method for extracting alginate from brown algae by high-shear digestion. The method comprises the following steps: 1) digestion: adding brown algae into a high-shear digestion reactor for alkali digestion, wherein the high-shear reactor is a disc mill type reactor; and 2) obtaining a product: obtaining alginate from the digestion solution. Preferably, the rotation speed of the grinding disc is 500-1500 r / min. The present application realizes the coupling of physical shearing and chemical digestion of mechanical elements, breaks the raw materials through physical shearing to promote the mixing of materials and improve the digestion rate, accelerates the disintegration of the raw materials through chemical digestion, and reduces the action intensity of the mechanical elements, so that the mechanical elements do not need to be frequently replaced, thereby providing convenience for production operation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of seaweed chemical industry, and particularly relates to a method for extracting alginate from brown algae by high-shear digestion, especially for high-viscosity alginate. BACKGROUND

[0002] Alginate is the general term for alginic acid and its salts, which is a plant polysaccharide existing in the cell wall and intercellular substance (mainly in the cell wall) of large multicellular brown algae. It has thickening, stabilizing, emulsifying, pseudoplastic, water-holding, film-forming and adhesive properties, and is widely used in food, textile printing and dyeing, medical and health, daily chemical, biotechnology and wastewater treatment fields. Due to the better thickening stability of high-viscosity alginate, it has more extensive application requirements and higher value. Improving the viscosity of alginate is one of the important ways for production enterprises to improve production efficiency.

[0003] In industry, the extraction of alginate from brown algae generally uses a stirred tank reactor to digest the brown algae by alkali method, that is, by using a weak acid and a strong alkali salt (industrially, sodium carbonate is generally used) to convert insoluble alginate salt in brown algae into soluble alginate salt, so as to leach the alginate into an aqueous solution. Since the industrial brown algae raw material is mainly dry algae, in order to facilitate the digestion reaction in the stirred tank, the traditional technology for extracting alginate from brown algae generally uses soaking and cutting as pretreatment for the digestion process, soaks the water into the algae in advance, and cuts the algae to reduce the size of the algae to facilitate the solid-liquid mixing in the digestion reactor.

[0004] For example, in the production of sodium alginate, the industrial production of brown algae glue generally uses "soaking-cutting (crushing)-digestion" process route, the soaking time is generally 3-6h, and the digestion time is 3-6h. The soaking and digestion time is as long as 6-12h, the production cycle is long; the yield of sodium alginate obtained is generally 20-30g / 100g, the yield of brown algae glue is only 50%-70%; the product viscosity of sodium alginate (1% sodium alginate aqueous solution) is generally 400-700mPa·s, and it is difficult to obtain brown algae glue with viscosity above 1000mPa·s. When using Lessonia with dense structure as raw material, the soaking time and digestion time need to be further prolonged. Zhang Yan (Zhang Yan et al., Process Engineering, 2016, 16(1): 144-150) soaked the stems of Lessonia trabeculata in 10 times dry algae weight of 2% formaldehyde solution at 35℃ (soaking and simultaneous color fixing) for 48h, then crushed to 1-3mm for digestion reaction. The optimal digestion conditions are: temperature 70℃, Na2CO3 concentration 1.67%, stirring speed 400r / min, solid-liquid mass ratio 1:15, and digestion time 8h. Under this condition, the yield of sodium alginate product is 34.80g / 100g, and the product viscosity is 2261.67mPa·s. As can be seen, although using Lessonia as raw material can obtain high viscosity brown algae glue, compared with traditional raw materials, the soaking time even increases by an order of magnitude, the digestion time almost doubles, and the production cycle is greatly prolonged. In addition, due to the dense structure and hard texture, the mechanical element wear in the crushing process is more serious, and the crushing element needs to be frequently replaced or adjusted.

[0005] An (An, Chuanfeng, Digestion process of extracting alginate from Laminariales sp., Master's thesis, 2017, University of Chinese Academy of Sciences) soaked Laminariales sp. stem for 48 h for simultaneous color fixing, using a twin-screw extruder as a digestion reactor, under the conditions of solid-liquid ratio of 1:15, investigated the effects of sodium carbonate concentration and digestion temperature on digestion efficiency: at 80℃, 13.8g / L Na2CO3(sodium carbonate dosage is 20.7% of the dry algal mass), solid-liquid ratio of 1:15, under the conditions of 25min digestion, the digestion yield of alginate was 35.31g / 100g raw material, the product yield of alginate was 30.41g / 100g raw material, and the product viscosity reached 1900mPa·s. However, the 48h soaking process before digestion undoubtedly becomes a bottleneck that limits production efficiency. In addition, the twin-screw extruder is a single-pass / flow channel along the screw axis material transmission mode, with low processing capacity and high equipment cost, which is difficult to be applied in the industrialization of alginate production. Patents ZL 201710042249.2 and ZL 201710042247.3 point out that the digestion efficiency can be improved by soaking in advance, and the alga is pretreated such as crushing before soaking, so that the soaking time of rhizome type brown algae is shortened to 8h, the digestion time is shortened to 6h, and the yield can reach 60%~90%. Patent ZL 201710041932.4 (CN108329401B) based on the fact that alginate exists in the cell wall and intercellular substance of brown algae, proposes a digestion process of crushing the brown algae to less than 1mm for digestion, which shortens the digestion time to 0.5~1h, significantly improving the digestion efficiency; however, in actual production, it is found that for hard rhizome type raw materials such as Laminariales stem, the blades of the crusher need to be replaced or adjusted every month (even less than a month) to meet the particle size requirements, which brings inconvenience to production.

[0006] In summary, the digestion efficiency of extracting alginate from Laminariales sp. stem with a twin-screw extruder as a reactor is significantly improved, but the soaking before digestion becomes a bottleneck that limits production efficiency, and the twin-screw extruder as a digestion reactor has the problems of low processing capacity and high equipment cost, which is difficult to be applied in industrialization. When using the current stirring tank reactor to digest brown algae to extract alginate, the raw material needs to be pretreated before digestion, which is complicated and time-consuming, and seriously limits the production efficiency. When using hard rhizome type brown algae as raw material, the mechanical elements such as blades in the crushing or cutting steps are prone to wear and tear, and need to be adjusted or replaced frequently, which brings inconvenience to production. SUMMARY

[0007] The present application aims to solve the problems of multiple pretreatment steps, long production cycle and easy wear of the crushing equipment of hard brown algae in the process of extracting alginate from brown algae, and provides a high-shear digestion method for industrialized digestion and extraction of alginate from brown algae without soaking or / and crushing.

[0008] The technical solution of the present application is: adding brown algae and sodium carbonate into a disc mill type high shear reactor for direct digestion. The advantages are: (1) rapid dispersion and mixing of materials is achieved through high shear, for example, for dry algae, rapid liquid-solid mixing is achieved, eliminating the soaking step and the pretreatment of crushing or cutting vegetables; (2) through the combined action of physical shear and chemical digestion during the digestion process, the structure of the raw material is destroyed, the internal mass transfer efficiency is improved, the mixing between substances is promoted, and the digestion rate is improved, so that the raw material does not need to be soaked and crushed for pretreatment operation by physical methods such as physical destruction, and rapid and efficient digestion can also be achieved; (3) through the coupling of physical shear and chemical digestion, the mechanical strength of the material is reduced, the action strength on the mechanical elements is reduced, and frequent replacement of the mechanical elements is avoided.

[0009] The specific embodiments of the present application are as follows:

[0010] The method for extracting alginate from brown algae by high shear digestion of the present application comprises the following steps:

[0011] 1) Alkali digestion: adding brown algae into a high shear digestion reactor for alkali digestion to obtain a digestion solution; the high shear reactor is a disc mill type reactor, and the disc mill type reactor has a crushing ratio of brown algae (the ratio of the particle size of brown algae before treatment by the disc mill type reactor to the particle size of brown algae after treatment by the disc mill type reactor) of 3 or more;

[0012] 2) Obtaining a product: treating the digestion solution to obtain alginate.

[0013] Wherein, the meaning of "high shear" is that the mechanical shear action of brown algae material in the disc mill type reactor is much higher than that in a traditional stirred tank digestion reactor. In a traditional stirred tank digestion reactor, the stirring paddle can only increase the spatial distribution uniformity of particles in the mixture, which is non-dispersive mixing (also called distribution mixing or simple mixing). Because the shear of the stirred tank digestion reactor is low, it cannot reduce the particle size, and the shear is lower than the allowable stress of the solid. Therefore, the traditional digestion needs to cut or crush the brown algae before digestion. The disc mill type reactor of the present application has a crushing ratio of brown algae of 3 or more, which can reduce the size of solid particles to achieve dispersive mixing and achieve a shear greater than the allowable stress of the solid phase. The disc mill type reactor of the present application has a shear significantly higher than that of the traditional stirred tank digestion reactor, which is different from the traditional digestion. Therefore, the digestion method of the present application is called "high shear digestion".

[0014] According to the method of the present application, preferably, the number of grooves distributed circumferentially on the grinding disc of the disc mill type reactor is not less than 5, and the grooves have 1-5 weirs along the radial direction.

[0015] According to the method of the present application, preferably, the disc mill reactor comprises one disc mill alone used in single disc mill, double disc mill or triple disc mill; or the disc mill reactor comprises at least two disc mills above used in series in single disc mill, double disc mill and triple disc mill.

[0016] The gap between the grinding discs of the disc mill reactor is 0.5-5 mm.

[0017] Specifically, the single disc mill (1 moving disc, 1 fixed disc), double disc mill (2 moving discs) or triple disc mill (1 moving disc, 2 fixed discs) in the high-shear digestion reactor can be used alone or in series. Further preferably, the disc mill reactor is a single disc mill and a triple disc mill used in series in three stages, the gap between the grinding discs of the single disc mill in the first stage is 2-4 mm, the gap between the grinding discs of the triple disc mill in the second stage is 1.5-3 mm, and the gap between the grinding discs of the triple disc mill in the third stage is 1-2 mm.

[0018] According to the method of the present application, preferably, the rotating speed of the grinding discs of the high-shear digestion reactor is 500-1500 r / min.

[0019] According to the method of the present application, preferably, the crushing ratio of the high-shear digestion reactor to dry brown algae is above 5, and the crushing ratio to fresh brown algae is above 3.

[0020] According to the method of the present application, preferably, the tooth shape of the high-shear digestion reactor is narrow at the top and wide at the bottom (the root of the grinding teeth connected to the grinding disc is wide, and the top of the grinding teeth away from the grinding disc is narrow), the root width of the grinding teeth is 4-12 mm, and the ratio of the top width of the grinding teeth to the root width of the grinding teeth is 0.4-0.8.

[0021] According to the method of the present application, preferably, in the step 1) of alkali digestion, the water amount is 8-20 times the weight of the brown algae, the sodium carbonate amount is 10%-20% of the weight of the brown algae, the digestion temperature is 25-90℃, and the digestion time is 3-30 min, wherein the weight of the brown algae is the weight of the dry algae with a water content of 15%, and the same applies hereinafter.

[0022] According to the method of the present application, as a preferred, the brown algae include but not limited to one or more of the following: Laminaria, Sargassum, Ascophyllum, Macrocystis, Ecklonia, Tinocladia and Lessonia. Preferably, one or more of the following: Laminaria japonica, Sargassum pallidum, Sargassum horneri and Hizikia fusifarme of Sargassum, Ascophyllum nodosum of Ascophyllum, Macrocystis pyrifera of Macrocystis, Ecklonia maxima of Ecklonia, Tinocladia crassa (Sur.) Kuck. of Tinocladia, and Lessonia trabeculata and Lessonia nigrescens of Lessonia.

[0023] Further preferably, when the brown algae is one or more of the following: Lessonia trabeculata, Lessonia nigrescens stem, Laminaria hyperborea, the digestion temperature in the alkali digestion is 60-90°C, the amount of sodium carbonate is 15%-20% of the weight of the brown algae, and the digestion time is 10-30 min.

[0024] Alternatively, when the brown algae is one or more of the following: Laminaria japonica, Ascophyllum nodosum, Sargassum pallidum, Sargassum horneri, Hizikia fusifarme, Macrocystis pyrifera, Tinocladia crassa (Sur.) Kuck., Lessonia nigrescens stem, and Ecklonia maxima, the digestion temperature in the alkali digestion is 30-70°C, the amount of sodium carbonate is 10%-15% of the weight of the brown algae, and the digestion time is 3-15 min.

[0025] In the step 1) alkaline digestion, when the moisture content of the kelp added into the high-shear reactor is less than 70%, sodium carbonate is added in the form of sodium carbonate aqueous solution; when the moisture content of the kelp added into the high-shear reactor is not less than 70%, sodium carbonate can be added in the form of solid or sodium carbonate aqueous solution. Sodium carbonate can be added at one time or by flow addition or segmented addition. Water can be added at one time or by flow addition or segmented addition.

[0026] According to the method of the present application, preferably, the kelp is fixed by adding a fixing agent before or during the step 1) alkaline digestion. Preferably, the fixing agent is used in an amount of 5% to 15% of the weight of the kelp.

[0027] According to the method of the present application, preferably, a step of washing or removing impurities is added before the step 1) alkaline digestion.

[0028] According to the method of the present application, preferably, a step of pressing the kelp is added before the step 1) alkaline digestion, so as to reduce the mechanical strength of the kelp rhizome raw material.

[0029] According to the method of the present application, the subsequent treatment of the obtained digestion solution can refer to the production of corresponding alginate products according to the existing process, such as separating the residue liquid to obtain a clear liquid, precipitating calcium alginate from the clear liquid by calcium precipitation method, obtaining alginic acid by hydrochloric acid decalcification, and obtaining target alginate by neutralization and conversion, or the subsequent process can be improved and adjusted according to actual needs and product requirements.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] In the present application, the kelp is directly added into a high-shear digestion reactor for digestion. For large-scale production of alginate using dry kelp as raw material, the traditional process route of “soaking - cutting (cutting or wet kelp crushing) - digestion” is shortened to the process route of “one-step digestion”, which can omit the soaking, cutting or crushing processes, shorten the digestion time to within 0.5 h, and the yield of alginate can reach 30-42 g / 100 g of kelp (calculated based on the weight of dry kelp with a moisture content of 15%, the same below), the yield of alginate reaches 70%-95%, and the viscosity of 1% sodium alginate aqueous solution can reach 1500 mPa·s or more. For traditional raw materials (kelp, sargassum, bladderwrack, giant kelp), the soaking process can be omitted and the digestion time can be shortened by 1-5 hours; for the structure-dense leison kelp raw material, the soaking process which takes 48 h can be omitted and the digestion time can be shortened by 6-7 hours; by reducing the process steps and shortening the production time, the production cycle of alginate is greatly shortened, the production efficiency is improved, the loss in the operation link is reduced, and the labor and production cost are saved.

[0032] On the other hand, for dense rhizomatous brown algae raw materials, the shearing elements of the high-shear reactor do not need to be replaced frequently. They can maintain a certain pulverization ratio even after a year of continuous use. If there is slight wear, the required pulverization ratio can be achieved by adjusting the grinding disc spacing.

[0033] The high-shear digestion of this invention couples the physical shearing of mechanical components with chemical digestion. By using high physical shear stress to break down the raw materials, it promotes the mixing of substances and increases the digestion rate. This eliminates the need for pretreatment operations such as soaking and crushing of the raw materials before digestion, and also achieves rapid and efficient digestion. Chemical digestion reduces the structural substances (mainly insoluble alginate) that make up brown algae, accelerates the disintegration of the raw materials, reduces the stress on the mechanical components, and eliminates the need for frequent replacement of mechanical components, thus facilitating production operations.

[0034] Furthermore, due to the thickening properties of alginate, the viscosity of the digestate increases significantly with increasing alginate concentration as digestion proceeds. In traditional stirred tank digesters, a large amount of water needs to be added to reduce the alginate concentration and thus lower the viscosity of the digestate, achieving good mixing of substances in the bulk phase outside the particles, in order to achieve good flow of the digestate. However, alkali concentration is an important factor affecting the digestion reaction rate; with higher water usage, the amount of sodium carbonate also needs to be increased to maintain a higher alkali concentration. This invention is based on the fact that the digestate is a shear-thinned fluid (…). Figure 1 The discovery that the apparent viscosity of the digestate decreases with increasing shear rate, combined with experimental observations, shows that even at high alginate concentrations, the digestate maintains good fluidity under the high shear rate of a high-shear reactor. Therefore, this invention ensures a high sodium carbonate concentration by reducing the water usage in the digestion step. Through the combined effect of reduced water usage and high-shear enhanced mixing, the alkali usage of this invention can be reduced by more than 30% compared to traditional stirred tank digesters. Attached Figure Description

[0035] Figure 1 The viscosity of the digestive fluid of *Pinus massoniana* stems in Example 8 at different shear rates at 60°C;

[0036] Figure 2(a) is a photomicrograph of a section of *Pinus thunbergii* stem magnified 400 times using an optical microscope (DM1000, LEICA).

[0037] Figure 2(b) is a photomicrograph of a brown algae median section obtained by adding the stem of *Pinus thunbergii* and red ink solution to a high-shear reactor at 25°C for 13 seconds, magnified 400 times using an optical microscope (DM1000, LEICA).

[0038] Figure 3To adopt the method of ZL201710042249.2, the Lessonia trabeculata was crushed to d 50 =3mm, soaked for 6h, the micrograph of the median section of the brown algae before digestion at 400 times magnification;

[0039] Figure 4 To adopt the method of ZL201710042249.2, the Lessonia trabeculata was crushed to d 50 =3mm, soaked for 6h, the micrograph of the median section of the brown algae after digestion for 15min at 400 times magnification;

[0040] Figure 5 To adopt the method of ZL201710042249.2, the Lessonia trabeculata was crushed to d 50 =3mm, soaked for 6h, the micrograph of the median section of the brown algae after digestion for 90min at 400 times magnification;

[0041] Figure 6 To adopt the method of ZL201710042249.2, the Lessonia trabeculata was crushed to d 50 =3mm, soaked for 6h, the micrograph of the median section of the brown algae after digestion for 5h at 400 times magnification;

[0042] Figure 7 To adopt the method of ZL201710042249.2, the Lessonia trabeculata was crushed to d 50 =3mm, soaked for 6h, the micrograph of the median section of the brown algae after digestion for 5h at 1000 times magnification. DETAILED DESCRIPTION

[0043] The application will be further described below in combination with examples.

[0044] Example 1

[0045] The brown algae gel was extracted by the digestion process route of the application, and the raw material was dry Lessonia trabeculata. The diameter of the Lessonia trabeculata stem was about 5-20mm, the water content was 15%, and the Lessonia trabeculata was purchased from Runlininvestment co., LTD.

[0046] (1)alkali digestion: the gap of the millstone of the single disc mill (the diameter of the millstone is 300 mm, the number of the circumferential distributed grooves on the millstone is 5, and the number of the dam of each groove is 1) is adjusted to 5 mm, the crushing ratio of the dry L. trabeculata is 3, the single disc mill is started, the rotating speed is 500 r / min, 30 kg of dry L. trabeculata is added into the feeding hopper through the screw conveyor, 240 L of sodium carbonate aqueous solution with a concentration of 12.5 g / L and a temperature of 25±5 ℃ is pumped into the feeding hopper, the discharge is pumped into the feeding hopper of the single disc mill again, and the circulation operation is carried out. The digestion time is 3 min, the treatment time is 3 min, and the treatment capacity is 600 kg / h of dry L. trabeculata.

[0047] (2)the subsequent treatment of the obtained digestion liquor is carried out according to the existing process for producing sodium alginate product, and the specific process is as follows: tap water with a dry algal weight of 160 times is added into the digestion liquor for dilution, a 18-mesh filter is started for rough filtration, the filtrate is injected into a floating tank for floating for 3 h, the gel liquid after floating is refined through a 120-200 mesh screen to obtain clear gel liquid; after the clear gel liquid is adjusted to pH=6.5, a calcium chloride solution with a mass concentration of 12% is added, so that the calcium ion concentration in the calcification tank is between 0.045% and 0.050%, and calcium alginate is obtained by calcium precipitation; the calcium alginate is put into a decalcification tank, water is added to immerse the calcium alginate, hydrochloric acid with a mass fraction of 31% is added to pH=2, and the decalcification is carried out for about 2 h to obtain alginate acid; after the alginate acid is dehydrated to a water content of less than 70% by using a screw press, the alginate acid is crushed and added into a neutralization tank together with alcohol with a concentration of 90% at a proportion of 1:1, the pH is maintained at about 8 by adding a sodium hydroxide solution with a mass concentration of 40% while stirring, and the pH is not changed until the end; after the solid-liquid separation, the sodium alginate is dried to a water content of less than 15% to obtain 4.71 kg of sodium alginate, the yield is 15.7 g / 100 g of brown algae (calculated according to the weight of dry algae with a water content of 15%, the same below), and the viscosity of 1% sodium alginate aqueous solution is 1076 mPa·s.

[0048] Example 2

[0049] The raw material for extracting alginate according to the digestion process route of the present application is dry L. trabeculata, the diameter of the L. trabeculata stem ranges from 5 mm to 20 mm, the water content is 15%, and the L. trabeculata is produced in Chile and purchased from Runlininvestment co., LTD.

[0050] (1) Alkaline digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams in each groove 2, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width 0.6, and pulverization ratio of *Pterocarya stenoptera* 3) to 4mm, turn on the single-disc mill, and rotate at 500r / min. Add 100kg of dry *Pterocarya stenoptera* var. *stenoptera* to the feeding hopper via a screw conveyor. Pump 400L of sodium carbonate aqueous solution with a concentration of 37.5g / L and a temperature of 60±5℃ into the feeding hopper. The material from the first stage is pumped into a two-stage double-disc mill (450mm diameter, 100 grooves, 2 dams, 5mm root width, and 3mm top width of the grinding teeth) with a 3mm gap between the grinding discs and 400L hot water, at a rotation speed of 500 rpm. The output from the second-stage double-disc mill is then pumped into a third-stage double-disc mill (450mm diameter, 100 grooves, 2 dams, 5mm root width, and 3mm top width of the grinding teeth), with a 2mm gap between the grinding discs, at a rotation speed of 500 rpm. The digestion time is 18 minutes, the processing time is 18 minutes, and the processing capacity (based on dry thread-worn *Pinus massoniana*) is 333 kg / h, which can meet general industrial production needs.

[0051] (2) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: 160 times the weight of the dry algae is added to the digestion liquid to dilute it with tap water, and an 18-mesh filter is turned on for coarse filtration. The filtrate is injected into a flotation tank and floated for 3 hours. The floated gel is then finely filtered through a 120-200 mesh sieve to obtain a clear gel. The clear gel is adjusted to pH=6.5, and a 12% (w / w) calcium chloride solution is added to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%. Calcium alginate is obtained through calcium precipitation. The calcium alginate is placed in a decalcification tank, and after being submerged in water, a (w / w) calcium chloride solution is added. 31% hydrochloric acid was used to bring the pH to 2, and decalcification was carried out for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then crushed and added to a neutralization tank with 90% alcohol in a 1:1 ratio. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 30.1 kg of sodium alginate, with a yield of 30.1 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 1476 mPa·s.

[0052] Example 3

[0053] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonia trabeculata, with a stem diameter ranging from approximately 5 to 20 mm and a moisture content of 15%. It was produced in Chile and purchased from Runlininvestment co.,LTD.

[0054] (1) Alkali digestion: The grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams 2, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width of 0.6, and pulverization ratio of *Pterocarya stenoptera* 3) is adjusted to 4mm. The single-disc mill is turned on at a speed of 1000r / min. 100kg of dry *Pterocarya stenoptera* var. *stenoptera* is added to the feeding hopper through a screw conveyor. 400L of sodium carbonate aqueous solution with a concentration of 37.5g / L and a temperature of 60±5℃ is pumped into the feeding hopper. The discharge of the single-disc mill is pumped into the mill with a grinding disc gap of 3mm. A two-stage double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, 5mm root width of grinding teeth, 3mm top width of grinding teeth, and a grinding ratio of 3 for *Raphatherum sp.*) is used at a speed of 1000 r / min. The output from the two-stage double-disc mill is then pumped into a three-stage double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, 5mm root width of grinding teeth, 3mm top width of grinding teeth, and a grinding ratio of 3 for *Raphatherum sp.*) with a disc gap of 2mm, at a speed of 1000 r / min. The digestion time is 8 min, the processing time is 8 min, and the processing capacity (based on dry *Raphatherum sp.*) is 750 kg / h, which can meet general industrial production needs.

[0055] (2) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: 160 times the weight of the dry algae is added to the digestion liquid to dilute it with tap water, and an 18-mesh filter is turned on for coarse filtration. The filtrate is injected into a flotation tank and floated for 3 hours. The floated gel is then finely filtered through a 120-200 mesh sieve to obtain a clear gel. The clear gel is adjusted to pH=6.5, and a 12% (w / w) calcium chloride solution is added to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%. Calcium alginate is obtained through calcium precipitation. The calcium alginate is placed in a decalcification tank, and after being submerged in water, a (w / w) calcium chloride solution is added. 31% hydrochloric acid was added to pH=2 and decalcified for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then pulverized and added to a neutralization tank in a 1:1 ratio with 90% alcohol. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 25.3 kg of sodium alginate, with a yield of 25.3 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 1307 mPa·s.

[0056] Example 4

[0057] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonia trabeculata, with a stem diameter ranging from approximately 5 to 20 mm and a moisture content of 15%. It was produced in Chile and purchased from Runlininvestment co.,LTD.

[0058] (1) Alkaline digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams 2, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width of 0.6, and pulverization ratio of *Pterocarya stenoptera* 3) to 4mm, turn on the single-disc mill, and rotate at 1500r / min. Add 100kg of dry *Pterocarya stenoptera* var. *stenoptera* to the feeding hopper via a screw conveyor. Add 5kg of color-fixing agent to 400L of sodium carbonate aqueous solution with a concentration of 37.5g / L at a temperature of 60±5℃ and pump it into the feeding hopper. Pump the discharge from the single-disc mill into a two-disc mill with a grinding disc gap of 3mm. A first-stage double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, 5mm tooth root width, 3mm tooth tip width, and a pulverization ratio of 3 for *Raphatherum sp.*) is used, rotating at 1500 rpm. The output from the second-stage double-disc mill, along with 400L of hot water at 60±5℃, is then pumped into a third-stage double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, 5mm tooth root width, 3mm tooth tip width, and a pulverization ratio of 3 for *Raphatherum sp.*), with a disc gap of 2mm, rotating at 1500 rpm. The digestion time is approximately 5 minutes, the processing time is 5 minutes, and the processing capacity (based on dry *Raphatherum sp.*) is 1200 kg / h, which can meet general industrial production needs.

[0059] (2) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: 160 times the weight of the dry algae is added to the digestion liquid to dilute it with tap water, and an 18-mesh filter is turned on for coarse filtration. The filtrate is injected into a flotation tank and floated for 3 hours. The floated gel is then finely filtered through a 120-200 mesh sieve to obtain a clear gel. The clear gel is adjusted to pH=6.5, and a 12% (w / w) calcium chloride solution is added to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%. Calcium alginate is obtained through calcium precipitation. The calcium alginate is placed in a decalcification tank, and after being submerged in water, a (w / w) calcium chloride solution is added. 31% hydrochloric acid was used to bring the pH to 2, and decalcification was carried out for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then crushed and added to a neutralization tank with 90% alcohol in a 1:1 ratio. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 23.9 kg of sodium alginate, with a yield of 23.9 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 1731 mPa·s.

[0060] Example 5

[0061] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonia trabeculata, with a stem diameter ranging from approximately 5 to 20 mm and a moisture content of 15%. It was produced in Chile and purchased from Runlininvestment co.,LTD.

[0062] (1) Fixing color: Fix 100kg of thread-shaped algae with 5kg of fixing agent;

[0063] (2) Alkaline digestion: The grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams 2, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width 0.6) is adjusted to 3mm. The pulverization ratio of *Zingiber officinale* is 4. The single-disc mill is turned on and the rotation speed is 500r / min. The color-fixed *Zingiber officinale* is added to the feeding hopper through a screw conveyor. 400L of sodium carbonate aqueous solution with a concentration of 37.5g / L at a temperature of 60±5℃ and 5kg of color-fixing agent are pumped into the feeding hopper. The discharge from the single-disc mill is pumped into a secondary mill with a grinding disc gap of 2mm. A double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, 5mm tooth root width, 3mm tooth tip width, and a pulverization ratio of 3 for *Raphatherum sp.*) is used, rotating at 500 rpm. The output from the second-stage double-disc mill, along with 400L of hot water at 60±5℃, is then pumped into a third-stage double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, 5mm tooth root width, 3mm tooth tip width, and a pulverization ratio of 3 for *Raphatherum sp.*), with a disc gap of 1mm, rotating at 500 rpm. The digestion time is approximately 25 minutes, the processing time is 25 minutes, and the processing capacity (based on dry *Raphatherum sp.*) is 300 kg / h, which can meet general industrial production needs.

[0064] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: Add 160 times the weight of dry algae to the digestion liquid with tap water, turn on the 18-mesh filter for coarse filtration, inject the filtrate into the flotation tank for 3 hours, and then filter the flotation liquid through a 120-200 mesh screen to obtain a clear liquid; adjust the pH of the clear liquid to 6.5, add 12% calcium chloride solution to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%, and obtain calcium alginate by calcium precipitation; put the calcium alginate into the decalcification tank, add water to submerge the calcium alginate, and then add a mass fraction of 31% hydrochloric acid was used to bring the pH to 2, and decalcification was carried out for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then pulverized and added to a neutralization tank in a 1:1 ratio with 90% alcohol. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 39.1 kg of sodium alginate, with a yield of 39.1 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 2061 mPa·s.

[0065] Example 6

[0066] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonia trabeculata, with a stem diameter ranging from approximately 5 to 20 mm and a moisture content of 15%. It was produced in Chile and purchased from Runlininvestment co.,LTD.

[0067] (1) Rolling: The threaded pine needle algae is pressed to a compression ratio of about 1.2 to 5 by a double roll crusher.

[0068] (2) Alkaline digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams in each groove 2, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width 0.6, and pulverization ratio of *Pterocarya stenoptera* 3) to 4mm, turn on the single-disc mill at a speed of 500r / min, add 100kg of dry *Pterocarya stenoptera* granules to the feeding hopper via a screw conveyor, and pump 400L of 37.5g / L sodium carbonate aqueous solution at 60±5℃ into the feeding hopper; the single-disc mill... The material is pumped into a two-stage double-disc mill (450mm diameter, 100 grooves, 2 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth) with a 3mm gap between the discharge and the 400L hot water, at a rotation speed of 500 rpm. The discharge from the two-stage double-disc mill is then pumped into a three-stage double-disc mill (450mm diameter, 100 grooves, 2 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth), with a 2mm gap, at a rotation speed of 500 rpm. The digestion time is 18 minutes, the processing time is 18 minutes, and the processing capacity (based on dry thread-worn *Pinus massoniana*) is 333 kg / h, which can meet general industrial production needs.

[0069] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: Add 160 times the weight of dry algae to the digestion liquid with tap water, turn on the 18-mesh filter for coarse filtration, inject the filtrate into the flotation tank for 3 hours, and then filter the flotation liquid through a 120-200 mesh screen to obtain a clear liquid; adjust the pH of the clear liquid to 6.5, add 12% calcium chloride solution to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%, and obtain calcium alginate by calcium precipitation; put the calcium alginate into the decalcification tank, add water to submerge the calcium alginate, and then add a mass fraction of 31% hydrochloric acid was added to pH=2 and decalcified for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then pulverized and added to a neutralization tank in a 1:1 ratio with 90% alcohol. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 35.3 kg of sodium alginate, with a yield of 35.3 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 1621 mPa·s.

[0070] Example 7

[0071] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonia trabeculata, with a stem diameter ranging from approximately 5 to 20 mm and a moisture content of 15%. It was produced in Chile and purchased from Runlininvestment co.,LTD.

[0072] (1) Rolling: The threaded pine needle algae is pressed to a compression ratio of about 1.2 to 5 by a double roll crusher.

[0073] (2) Alkaline digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams in each groove 3, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width 0.6, and pulverization ratio of *Pterocarya stenoptera* 3) to 4mm, turn on the single-disc mill at a speed of 500r / min, add 100kg of dry *Pterocarya stenoptera* var. *stenoptera* to the feeding hopper via a screw conveyor, and pump 400L of 37.5g / L sodium carbonate aqueous solution at 80±5℃ into the feeding hopper; mix the output of the single-disc mill with the 4 Hot water at 80±5℃ was pumped into a two-stage double-disc mill (disc diameter 450mm, 100 grooves, 4 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth) with a disc gap of 3mm, at a rotation speed of 500r / min. The output from the two-stage double-disc mill was then pumped into a three-stage double-disc mill (disc diameter 450mm, 100 grooves, 5 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth) with a disc gap of 1mm, at a rotation speed of 500r / min. The digestion time was 30min, the processing time was 30min, and the processing capacity (based on dry thread-shelled pine needle algae) was 200kg / h.

[0074] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: Add 160 times the weight of dry algae to the digestion liquid with tap water, turn on the 18-mesh filter for coarse filtration, inject the filtrate into the flotation tank for 3 hours, and then filter the flotation liquid through a 120-200 mesh screen to obtain a clear liquid; adjust the pH of the clear liquid to 6.5, add 12% calcium chloride solution to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%, and obtain calcium alginate by calcium precipitation; put the calcium alginate into the decalcification tank, add water to submerge the calcium alginate, and then add a mass fraction of 31% hydrochloric acid was used to bring the pH to 2, and decalcification was carried out for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then crushed and added to a neutralization tank with 90% alcohol in a 1:1 ratio. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 40.5 kg of sodium alginate, with a yield of 40.5 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 935 mPa·s.

[0075] Example 8

[0076] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonia trabeculata, with a stem diameter ranging from approximately 5 to 20 mm and a moisture content of 15%. It was produced in Chile and purchased from Runlininvestment co.,LTD.

[0077] (1) Pressing: 100 kg of threaded pine needle algae is pressed to a compression ratio of about 1.2 to 5 by a double roll crusher.

[0078] (2) Fixing: Fix the rolled threaded pine needle algae with 5 kg of fixing agent;

[0079] (3) Alkaline digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams per groove 3, root width of grinding teeth 5mm, ratio of grinding tooth top width to grinding tooth root width 0.6, and pulverization ratio of *Pterocarya stenoptera* 3) to 4mm, turn on the single-disc mill at a speed of 500r / min, add 100kg of dry *Pterocarya stenoptera* granules to the feeding hopper through a screw conveyor, and pump 400L of 50g / L sodium carbonate aqueous solution at 80±5℃ into the feeding hopper; mix the output of the single-disc mill with 40... Hot water at 80±5℃ (L) was pumped into a two-stage double-disc mill (disc diameter 450mm, 100 grooves, 3 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth) with a disc gap of 3mm, at a rotation speed of 500r / min. The output from the two-stage double-disc mill was then pumped into a three-stage double-disc mill (disc diameter 450mm, 100 grooves, 5 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth) with a disc gap of 1mm, at a rotation speed of 500r / min. The digestion time was 30min, the processing time was 30min, and the processing capacity (based on dry thread-like algae) was 200kg / h.

[0080] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: Add 160 times the weight of dry algae to the digestion liquid with tap water, turn on the 18-mesh filter for coarse filtration, inject the filtrate into the flotation tank for 3 hours, and then filter the flotation liquid through a 120-200 mesh screen to obtain a clear liquid; adjust the pH of the clear liquid to 6.5, add 12% calcium chloride solution to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%, and obtain calcium alginate by calcium precipitation; put the calcium alginate into the decalcification tank, add water to submerge the calcium alginate, and then add a mass fraction of 31% hydrochloric acid was added to pH=2 and decalcified for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then pulverized and added to a neutralization tank with 90% alcohol in a 1:1 ratio. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 42.1 kg of sodium alginate, with a yield of 42.1 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 2135 mPa·s.

[0081] Example 9

[0082] The digestion process of this invention was used to extract alginate. The raw material was the stem of Lessonianigrescens, with a moisture content of 15%, produced in Chile and purchased from Runlin Investment Co., Ltd.

[0083] (1) Digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams in each groove 2, width of the grinding tooth root 5mm, and ratio of the width of the grinding tooth top to the width of the grinding tooth root 0.6) to 3mm, the pulverization ratio of blackening pine algae is 5, start the single-disc mill, the rotation speed is 500r / min, add 100kg of dried blackening pine algae to the feeding hopper through a screw conveyor, and pump 400L of 37.5g / L sodium carbonate aqueous solution at 60±5℃ into the feeding hopper; the output of the single-disc mill... The feed material was pumped into a two-stage double-disc mill (450mm diameter, 100 grooves, 2 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth) with a 3mm gap between the grinding discs and 400L of hot water, at a rotation speed of 500 rpm. The output from the two-stage double-disc mill was then pumped into a three-stage double-disc mill (450mm diameter, 100 grooves, 2 dams, 5mm root width of the grinding teeth, and 3mm top width of the grinding teeth), with a 2mm gap between the grinding discs, at a rotation speed of 500 rpm. The digestion time was 15 minutes, and the processing time was 15 minutes. The processing capacity, based on dried black pine algae, was 400 kg / h, which can meet general industrial production needs.

[0084] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: Add 160 times the weight of dry algae to the digestion liquid with tap water, turn on the 18-mesh filter for coarse filtration, inject the filtrate into the flotation tank for 3 hours, and then filter the flotation liquid through a 120-200 mesh screen to obtain a clear liquid; adjust the pH of the clear liquid to 6.5, add 12% calcium chloride solution to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%, and obtain calcium alginate by calcium precipitation; put the calcium alginate into the decalcification tank, add water to submerge the calcium alginate, and then add a mass fraction of 31% hydrochloric acid was used to bring the pH to 2, and decalcification was carried out for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then crushed and added to a neutralization tank with 90% alcohol in a 1:1 ratio. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 32.7 kg of sodium alginate, with a yield of 32.7 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 3217 mPa·s.

[0085] Example 10

[0086] The digestion process of this invention was used to extract alginate. The raw material was dried Lessonianigrescens leaves with a moisture content of 15%, produced in Chile and purchased from Runlin Investment Co., Ltd.

[0087] (1) Alkaline digestion: Adjust the grinding disc gap of the single-disc mill (grind disc diameter is 595mm, number of grooves is 144, number of dams in each groove is 2, width of the grinding tooth root is 5mm, and the ratio of the width of the grinding tooth top to the width of the grinding tooth root is 0.6) to 2mm, the pulverization ratio of blackened pine algae leaves is 8, turn on the single-disc mill, and the rotation speed is 500r / min. 100 kg of dried blackened *Pinus massoniana* was added to the feeding hopper via a screw conveyor. 5 kg of color-fixing agent was added to 400 L of 37.5 g / L sodium carbonate aqueous solution at 25 ± 5 °C and pumped into the feeding hopper. The output from the single-disc mill and 400 L of hot water were pumped into a two-stage double-disc mill (disc diameter 450 mm, 100 grooves, 2 dams, 5 mm root width of the grinding teeth, and 3 mm top width of the grinding teeth) with a disc gap of 1 mm and a rotation speed of 500 r / min. The output from the two-stage double-disc mill was then pumped into a three-stage double-disc mill (disc diameter 450 mm, 100 grooves, 2 dams, 5 mm root width of the grinding teeth, and 3 mm top width of the grinding teeth) with a disc gap of 1 mm and a rotation speed of 500 r / min. The digestion time is 7 minutes, the processing time is 7 minutes, and the processing capacity based on dried black pine algae is 857 kg / h, which can meet the needs of general industrial production.

[0088] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: 160 times the weight of the dry algae is added to the digestion liquid to dilute it with tap water, and an 18-mesh filter is turned on for coarse filtration. The filtrate is injected into a flotation tank and floated for 3 hours. The floated gel is then finely filtered through a 120-200 mesh sieve to obtain a clear gel. The clear gel is adjusted to pH=6.5, and a 12% (w / w) calcium chloride solution is added to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%. Calcium alginate is obtained through calcium precipitation. The calcium alginate is placed in a decalcification tank, and after being submerged in water, a 3% (w / w) calcium chloride solution is added. 1% hydrochloric acid was added to pH=2 and decalcified for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then pulverized and added to a neutralization tank in a 1:1 ratio with 90% alcohol. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 36.96 kg of sodium alginate, with a yield of 36.96 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 4013 mPa·s.

[0089] Example 11

[0090] The digestion process of this invention is used to extract alginate. The raw material is fresh kelp (Laminaria japonica) with a water content of 88%, produced in Rongcheng, Shandong.

[0091] (1) Alkaline digestion: The grinding disc gap of the single-disc mill (grind disc diameter 595mm, number of grooves 144, number of dams in each groove 2, width of the grinding tooth root 5mm, and ratio of the width of the grinding tooth top to the width of the grinding tooth root 0.6) is adjusted to 3mm. The crushing ratio of fresh kelp is 6. The single-disc mill is turned on at a speed of 1500r / min. 700kg of fresh kelp and 10kg of sodium carbonate are added to the feeding hopper through a screw conveyor. The output of the single-disc mill and 400L of hot water are pumped into a secondary double-disc mill (grind disc diameter 450mm, grinding disc...) with a grinding disc gap of 3mm. The first stage of the double-disc mill has 100 grooves, 2 dams, a tooth root width of 5mm, and a tooth top width of 3mm, and operates at a speed of 1500 r / min. The output of the second-stage double-disc mill is then pumped into a third-stage double-disc mill (disc diameter 450mm, 100 grooves, 2 dams, tooth root width of 5mm, and tooth top width of 3mm) with a disc gap of 2mm, operating at a speed of 1500 r / min, a digestion time of 5 min, and a processing time of 5 min. The processing capacity based on fresh kelp is 8.4 t / h, which can meet the needs of general industrial production.

[0092] (3) The subsequent processing of the obtained digestion liquid is carried out in accordance with the existing process for the production of sodium alginate, as follows: Add 160 times the weight of dry algae to the digestion liquid with tap water, turn on the 18-mesh filter for coarse filtration, inject the filtrate into the flotation tank for 3 hours, and then filter the flotation liquid through a 120-200 mesh screen to obtain a clear liquid; adjust the pH of the clear liquid to 6.5, add 12% calcium chloride solution to make the calcium ion concentration in the calcification tank between 0.045% and 0.050%, and obtain calcium alginate by calcium precipitation; put the calcium alginate into the decalcification tank, add water to submerge the calcium alginate, and then add a mass fraction of 31% hydrochloric acid was added to pH=2 and decalcified for about 2 hours to obtain alginic acid. The alginic acid was dehydrated using a screw press until the water content was less than 70%, then pulverized and added to a neutralization tank in a 1:1 ratio with 90% alcohol. While stirring, a 40% sodium hydroxide solution was added to maintain the pH at around 8 until the pH remained constant. After solid-liquid separation, the sodium alginate was dried until the water content was less than 15%, yielding 29.1 kg of sodium alginate, with a yield of 29.1 g / 100 g of brown algae (converted to the weight of dry algae with a water content of 15%, the same below). The viscosity of a 1% sodium alginate aqueous solution was 4017 mPa·s.

[0093] The technical solution of this invention is based on the following:

[0094] The inventors discovered that adding unsoaked dried brown algae and sodium carbonate aqueous solution to the high-shear digestion reactor (disc mill reactor) described in this invention significantly improves digestion efficiency compared to traditional simmering-stirring digestion, where the brown algae is pre-crushed and then added to the stirred tank digestion reactor, or crushed and soaked before being added to the stirred tank digestion reactor.

[0095] For example, but not limited to, according to the inventor's research, adding dried *Raphatherum sp.* and water to a high-shear reactor (disc mill reactor) with a grinding ratio of approximately 3 (*Raphatherum sp.* with a particle size of approximately 10 mm is ground to approximately 3 mm), with a residence time of 13 s, the water absorption rate of *Raphatherum sp.* at 30°C is 216%. This is comparable to the water absorption rate (average sieve particle size d) obtained by soaking ZL201710042249.2 and ZL201710042247.3 for 2.5 h. 50 When the thickness is 5 mm, the water absorption rate of *Raphatherum sp.* stems after soaking for 2.5 hours is over 210%, and the water absorption rate after soaking for 6 hours is 240%. At 80℃, the water absorption rate of *Raphatherum sp.* can reach approximately 360% after a residence time of 13 seconds in a high-shear reactor, which is far higher than the water absorption rates of ZL201710042249.2 and ZL201710042247.3 after soaking for 8 hours. Figure 2(a) is a micrograph of a dried *Raphatherum sp.* stem section; the cells are shriveled and the cell walls are thin. Figure 2(b) is an optical microscope image of a median section of *Raphatherum sp.* stems after treatment with red ink and *Raphatherum sp.* stems in a high-shear digestion reactor. The optical microscope shows that the median section of the treated *Raphatherum sp.* stems turns red, and the intercellular spaces are filled with water, indicating that water can fully saturate the *Raphatherum sp.* (Figure 2(b)). Therefore, the inventors proposed a high-shear digestion method that omits the soaking step and directly adds dried brown algae and sodium carbonate aqueous solution to a high-shear reactor (disc mill reactor) for digestion.

[0096] On the other hand, during the digestion of brown algae using the method of ZL201710042249.2, the inventors discovered that as the digestion process progressed, the mechanical strength of the brown algae decreased, from initially being unbreakable to being easily crushed; microscopic observation revealed that during digestion, the cell walls shrank, the boundaries between cells gradually disappeared, and the complete cell structure ceased to exist; the flow of liquid could also be observed when a finger pressed on the slide. Figures 3-7 Therefore, it can be concluded that the transformation of alginate from insoluble to soluble substances helps to break down the raw materials. If the shearing action is coupled with chemical digestion, the intensity of the mechanical components will be reduced. This can reduce the energy consumption for physical disintegration (crushing) of the raw materials by means of chemical digestion, and can also avoid the phenomenon of frequent replacement of mechanical components caused by the wear of materials on mechanical components during the pretreatment process such as crushing before digestion in the existing technology when using dense rhizomatous brown algae as raw materials.

[0097] Using a disc mill as a high-shear reactor, multiple channels can be connected in parallel through the gaps between the mill discs and the grooves distributed circumferentially on the discs. Compared with twin-screw extruders that transport materials axially, it can achieve a larger throughput with lower energy consumption (for example, a twin-screw extruder with a screw diameter of about 130-133 mm, a main power of 600-800 kW, a throughput of about 100-250 kg / h based on dry screw thread *Pinus massoniana*, and a price of about 750,000 yuan; a single-disc mill with a mill disc diameter of 595 mm, ...). The main unit requires only 90kW of power, and the processing capacity of dry thread pine algae can reach 300-1000kg / h, with a price of approximately 90,000 yuan. In the disc mill, the material passes from the inside to the outside and undergoes multiple shearing processes along the radial direction, resulting in better crushing of solids. Furthermore, by setting different grinding tooth structures along the radial direction, multiple stages of shearing with different intensities can be formed in series, which can achieve the required crushing ratio while reducing the wear of the grinding teeth. By setting dams in the grooves on the grinding disc of the disc mill, liquids or fluids can be blocked, thereby enhancing liquid-solid mixing.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for high-shear digestion of brown algae to extract alginate, comprising the following steps: 1) alkali digestion: adding brown algae into a high-shear digestion reactor for alkali digestion to obtain a digestion solution; the high-shear reactor is a disc mill reactor, and the disc mill reactor has a crushing ratio of brown algae of 3 or more; 2) obtaining a product: processing the digestion solution to obtain alginate; the disc mill reactor comprises one disc mill alone used in single disc mill, double disc mill or triple disc mill; or the disc mill reactor comprises at least two or more disc mills used in series; the disc mill reactor has a disc mill gap of 0.5-5 mm; the high-shear digestion reactor has a tooth type of narrow top and wide bottom, a tooth root width of 4-12 mm, and a ratio of a tooth top width to a tooth root width of 0.4-0.

8.

2. The method of claim 1, wherein, The disc mill reactor has a number of grooves distributed circumferentially on the disc mill of not less than 5, and the grooves have 1-5 weirs along the radial direction.

3. The method of claim 1, wherein, The disc mill reactor is used in three stages in series with single disc mill and triple disc mill, the disc mill gap of the single disc mill in the first stage is 2-4 mm, the disc mill gap of the triple disc mill in the second stage is 1.5-3 mm, and the disc mill gap of the triple disc mill in the third stage is 1-2 mm.

4. The method according to any of claims 1 to 3, characterized in that, The disc mill rotates at a speed of 500-1500 r / min; the high-shear digestion reactor has a crushing ratio of dry brown algae of 5 or more and a crushing ratio of fresh brown algae of 3 or more.

5. The method of claim 1, wherein, In the alkali digestion of step 1), the water is used in an amount of 8-30 times the weight of the brown algae, the sodium carbonate is used in an amount of 10%-20% of the weight of the brown algae, the digestion temperature is 25-90℃, and the digestion time is 3-30 min, wherein the weight of the brown algae is the weight of the dry algae with a water content of 15%.

6. The method of claim 1, wherein, The brown algae include one or more of algae in the genus Laminaria, Sargassum, Codiurn, Durvillaea, Ecklonia, Agarum and Lessonia.

7. The method of claim 6, wherein, The brown algae include one or more of Laminaria hyperborea, Laminaria hyperborea stem, Laminaria hyperborea, and Laminaria hyperborea; in the alkali digestion, the digestion temperature is 60-90℃, the digestion time is 10-30 min, and the amount of sodium carbonate is 15%-20% of the weight of the brown algae. Alternatively, the brown algae include one or more of Laminaria japonica, Codiurn fragile, Sargassum thunbergii, Sargassum horneri, Sargassum fusiforme, Durvillaea potatorum, Agarum gmelini, Lessonia nigrescens, and Himanthalia elongata; in the alkali digestion, the digestion temperature is 30-70℃, the digestion time is 3-15 min, and the amount of sodium carbonate is 10%-15% of the weight of the brown algae.

8. The method of claim 1, wherein, Before or during the alkali digestion of step 1), a color fixing agent is added to fix the color of the brown algae; and / or, Before the alkali digestion of step 1), a washing or impurity removal step is added; and / or, before the alkali digestion of step 1), a step of pressing the brown algae is added.

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