CN108484545B - Method and system for continuously synthesizing furan dicarboxylic acid - Google Patents

Abstract

The invention discloses a method for continuously synthesizing furan dicarboxylic acid, which comprises the following steps: (1) dissolving saccharide in organic solvent to obtain 5-50 wt% saccharide solution, and reacting at 60-140 deg.c for 0.5-12 hr under the action of solid acid dewatering catalyst; (2) adding an alkaline aqueous solution and an oxidant into the effluent liquid of the step (1), and reacting for 2-12 hours at the temperature of 60-110 ℃ and under the pressure of 0.1-1MPa under the action of a supported oxidation catalyst; (3) evaporating the effluent liquid of the step (2) to remove the solvent, adding an acidifying agent, adjusting the pH to be less than 2, and precipitating a crude furandicarboxylic acid product; filtering, washing and recrystallizing to obtain the furandicarboxylic acid. The invention also discloses a system for continuously synthesizing furan dicarboxylic acid. The method does not need to separate and purify the intermediate 5-hydroxymethylfurfural, can synthesize the furandicarboxylic acid with high yield under mild conditions, can be operated continuously, and has important application prospect.

Description

Method and system for continuously synthesizing furan dicarboxylic acid

Technical Field

The invention relates to the field of synthesis of furandicarboxylic acid, in particular to a method and a system for continuously synthesizing furandicarboxylic acid.

Background

Chemical industries that use fossil resources as a base material are not sustainable because of the non-renewable nature of fossil resources such as petroleum and coal. The method is based on renewable biomass resources, obtains bio-based chemicals and energy with important application prospects through efficient biological and chemical conversion, can seek a reasonable and effective way for the replacement of petrochemical products, and is an effective measure for solving the problem that the current fossil resources cannot be sustained.

2,5-Furandicarboxylic acid (FDCA) is a novel important bio-based monomer with a wide application prospect, and is similar to the traditional petroleum-based monomer terephthalic acid in structure and chemical properties, so that the FDCA can be used for replacing terephthalic acid to manufacture new polymer materials such as polyester, polyamide and the like. For example, as a bio-based alternative to polyethylene terephthalate (PET) in annual yields of over 6000 million tons, polyethylene furan dicarboxylate (PEF) has not only better sustainability, but also significant advantages in performance, including higher heat resistance, mechanical strength, and gas barrier properties that are about an order of magnitude higher. The price of PEF depends greatly on the price of FDCA, and as the technology of FDCA synthesis matures, the production cost of PEF will further decrease.

The synthetic technical route of FDCA mainly comprises a 5-Hydroxymethylfurfural (HMF) route, a adipic acid route, a furfural route and a diglycolic acid route, wherein the HMF route is most important, has made remarkable progress, and is a method expected to realize industrial production first.

The HMF route is generally divided into a two-step process, i.e. first a HMF solution is obtained from the dehydration of sugars, which HMF is separated, purified and then used for the oxidative synthesis of FDCA, and a one-pot process. The separation and purification processes of the HMF are relatively complicated, the operation cost is high, and the HMF is unstable in the environment, easy to absorb water and decompose and difficult to store in large quantities. The one-pot method is to obtain HMF solution through saccharide dehydration, and HMF is directly oxidized in the solution without separation to obtain the target product FDCA. The method avoids the separation and purification process of HMF, so that the cost of FDCA synthesis is greatly reduced. However, the one-pot synthesis of FDCA still has some problems to be solved. Firstly, a great deal of research shows that efficient saccharide dehydration mainly occurs in an organic solvent or an ionic liquid, and the HMF oxidation process mainly achieves better effect in an alkaline aqueous solution, so that it is very important to design a solvent system suitable for two-step reaction. Secondly, the synthesis of FDCA directly from carbohydrates involves the risk that the carbohydrates are oxidized by the direct oxidation catalyst without dehydration, which needs to be solved by isolating the two catalysts, dehydration and oxidation.

Currently, few research reports on the synthesis of FDCA by a saccharide one-pot method are reported, and the synthesis can be divided into two types according to the design of a catalyst. First, there is a one-pot synthesis of FDCA using isolation of both dehydration and oxidation catalysts. Kroger et al (Topics in Catalysis, 2000, 13 (3): 237-. The fructose is catalyzed by solid acid in the water phase, the generated HMF is diffused to the MIBK phase through a PTFE membrane, and finally, the FDCA is generated through catalysis of Pt-Bi/C. However, since the HMF generation stage is carried out in the aqueous phase, a large amount of by-products are generated, and the final FDCA yield is only 25%. Yi et al (Chemuschem, 2015, 8 (7): 1151-5.) designed a three-phase system: TEAB or water (phase I)MIBK (phase II) -water (phase III). Fructose is catalytically dehydrated in phase I by Amberlyst-15 to HMF, which is transferred to phase III by extraction and purification in phase II, in Au₈Pd₂The further oxidation is carried out to FDCA under the action of the HT catalyst, and the total yield of the FDCA reaches 78 percent. Wang et al (Acs Sustainable Chemistry)&Engineering, 2015, 3 (3): 406-412.) a one-pot synthesis of FDCA was achieved by catalyst replacement in a single solvent system. First using Fe having magnetism₃O₄@SiO₂-SO₃Dehydrating fructose in a DMSO (dimethyl sulfoxide) solvent by using an H acid catalyst to synthesize HMF (HMF), separating the catalyst by using an external magnetic field, and adding a new catalyst nano-Fe into a reaction system₃O₄CoOx and the oxidant t-BuOOH, reaction for 15h gave an FDCA yield of 60%. The use of two magnetic catalysts makes the recovery of the catalyst extremely convenient. However, the FDCA yield still remains to be improved and only the specific oxidant t-BuOOH can be used.

A bifunctional catalyst containing two catalysts is also designed and prepared by people, and the one-pot synthesis of FDCA is realized. Ribeiro et al (Catalysis Communications, 2003, 4 (2): 83-86.) with Co (acac)₃/SiO₂Is a catalyst, in which the acidic carrier SiO₂And Co (acac)₃The dehydration and oxidation effects are respectively realized, the one-pot method for preparing the FDCA by the fructose is realized in the MIBK-aqueous solution, the fructose conversion rate is 72 percent, and the FDCA selectivity is 99 percent. However, the reaction conditions are relatively severe (165 ℃ C., 20bar air).

In summary, the yield of the target product in the current one-pot method is low, and the design of the catalyst is mainly focused on. From a solvent perspective, a more rational and efficient solvent system design is also necessary.

Disclosure of Invention

In the traditional technology for preparing furan dicarboxylic acid by two steps, the solvents and catalysts adopted in the first step and the second step are different, so that the target product FDCA is difficult to obtain by directly oxidizing HMF in a solution without separation. Aiming at the defects of the prior art, the invention provides a method and a system for continuously synthesizing furandicarboxylic acid, firstly proposes the use of a mixed solvent to realize one-pot method for preparing the furandicarboxylic acid, is simpler and more convenient compared with the traditional method, and can effectively reduce the equipment cost, material loss and energy consumption.

The technical scheme adopted by the invention is as follows:

1. a process for the continuous synthesis of furandicarboxylic acid comprising the steps of:

(1) dissolving sugar in an organic solvent to prepare a sugar solution with the mass concentration of 5-50%, and reacting the sugar solution at 60-140 ℃ for 0.5-12 hours under the action of a solid acid dehydration catalyst to obtain a 5-hydroxymethylfurfural solution;

(2) adding an alkaline aqueous solution and an oxidant into the effluent liquid of the step (1), and reacting for 2-12 hours under the conditions of 60-110 ℃ and 0.1-1MPa under the action of a supported oxidation catalyst to obtain a furan dicarboxylate solution;

(3) evaporating the effluent liquid of the step (2) to remove the solvent, adding an acidifying agent, adjusting the pH to be less than 2, and precipitating a crude furandicarboxylic acid product; filtering, washing and recrystallizing to obtain the furandicarboxylic acid.

The saccharide is one or more of fructose, glucose, sucrose and inulin.

Preferably, the sugar solution has a mass concentration of 5% to 20% within which both production economy (higher raw material content per unit solvent) and higher yield (significantly lower raw material concentration) are ensured.

The organic solvent is one or more of dimethyl sulfoxide, N-dimethylformamide, 1, 4-dioxane, isopropanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, acetone, tert-butyl alcohol, tetrahydrofuran and methanol.

Preferably, the organic solvent is dimethyl sulfoxide, N-dimethylformamide or 1, 4-dioxane, and the yield of HMF in the solvent is high.

The solid acid dehydration catalyst is one or more of sulfonic acid group ion exchange resin, metal oxide sulfate catalyst, sulfonic acid group carbon-containing catalyst, sulfonic acid group metal organic frame catalyst and sulfonic acid group mesoporous catalyst.

Preferably, the solid acid dehydration catalyst is sulfonic acid group ion exchange resin, the catalyst has the best catalytic effect, and the HMF yield is high.

The dosage of the solid acid dehydration catalyst is 5-100% of the mass of the saccharides.

Preferably, in step (1), the reaction temperature is 90-120 ℃ and the reaction time is 0.5-2 hours, and the yield of HMF is higher in the temperature and time range.

The alkaline aqueous solution is Na₂CO₃Aqueous solution, NaHCO₃Aqueous solution, K₂CO₃Aqueous solution, KHCO₃One or more of an aqueous solution, an aqueous NaOH solution and an aqueous KOH solution; preferably, the alkaline aqueous solution is Na₂CO₃Aqueous solutions or K₂CO₃The aqueous solution has good effect by using the additive, and the yield of the FDCA is high.

The concentration of the alkaline aqueous solution is 0.01-1mol/L, and the dosage of the alkaline aqueous solution is 100-500% of the mass of the organic solvent in the system.

Preferably, the dosage of the alkaline aqueous solution is 200-300% of the mass of the organic solvent in the system, the oxidation reaction is easy to efficiently proceed in the range, and the yield of FDCA is high.

The supported oxidation catalyst is Au/C, Au/CeO₂、Au/TiO₂、Pt/C、Pt/Al₂O₃、Pt/CeO₂、Pt/RGO、Pd/C、Pd/Al₂O₃、Ru/C、Ru/Al₂O₃And Ru/CeO₂The dosage of the supported oxidation catalyst is 20-500% of the adding mass of the saccharides.

The oxidant is O₂Air, H₂O₂t-BuOOH and CH₃One or more of COOOH; preferably, the oxidant is O₂。

The acidifying agent is HCl or H₂SO₄、HNO₃And H₃PO₄One or more of (a).

The invention also provides a system for continuously synthesizing furan dicarboxylic acid, which comprises a raw material liquid preparation tank, a first reactor, a mixer, a second reactor, an evaporator, an acidifier, a filtering washer, a crystallizer, a filter and a product tank;

dissolving sugar in an organic solvent in a raw material solution preparation tank, inputting the obtained sugar solution into a first reactor filled with a solid acid dehydration catalyst for reaction to obtain a 5-hydroxymethylfurfural solution;

directly outputting the obtained 5-hydroxymethylfurfural solution to a mixer, adding an alkaline aqueous solution, uniformly mixing, inputting the mixture to a second reactor filled with a supported oxidation catalyst, and introducing an oxidant into the second reactor for reaction to obtain a furan dicarboxylate solution;

inputting the obtained furan dicarboxylic acid salt solution into an evaporator to evaporate the solvent, inputting the solution into an acidifier, adding an acidifier into the acidifier, adjusting the pH value to be less than 2, and precipitating a furan dicarboxylic acid crude product;

the furan dicarboxylic acid crude product is separated by a filtering washer and then input into a crystallizer, recrystallized in the crystallizer and then input into a filter for filtering to obtain the furan dicarboxylic acid product, and the furan dicarboxylic acid product is output into a product tank.

Preferably, the solvent distilled off from the evaporator is recovered, mixed with a fresh organic solvent, and then introduced into the raw material liquid preparation tank.

Compared with the prior art, the invention has the beneficial effects that:

(1) the method abandons the traditional complex methods of synthesizing HMF by saccharide dehydration, separating and purifying HMF and synthesizing FDCA by HMF oxidation, and directly uses the solution in the oxidation step to synthesize FDCA without HMF separation and purification after saccharide dehydration to obtain HMF solution.

(2) The preparation method provided by the invention has the advantages of short reaction time and high efficiency. The reaction time in the carbohydrate dehydration stage is only 0.5-12 hours, and the yield of HMF reaches 97.1 percent; in the HMF oxidation stage, the reaction time is only 2-12 hours, and the yield of the FDCA is as high as 91%; the total yield of the furan dicarboxylic acid directly synthesized from the saccharides is up to 88.4 percent, which is far higher than the highest yield of the furan dicarboxylic acid synthesized from the saccharides reported at present by 78 percent. When the continuous operation is carried out, the total yield of the FDCA is also as high as 85 percent.

(3) In the present invention, the HMF oxidation step can be carried out under mild conditions (reaction temperature not exceeding 100 ℃, reaction pressure being atmospheric). The low temperature effectively inhibits the side reaction of HMF, the low pressure condition has low requirement on experimental equipment, the cost is saved, and the economic benefit is improved.

(4) In the invention, a proper amount of alkaline aqueous solution (100-500% of the mass of the organic solvent) is added in the HMF oxidation step, so that the oxidation of HMF can be effectively promoted, the reaction time is shortened, and the selectivity of FDCA can be improved.

(5) In the preparation method provided by the invention, the solid catalyst is easy to recycle and has long service life; the continuous method does not need to separate the catalyst, can continuously operate for a long time under normal pressure, and has high production efficiency.

Drawings

FIG. 1 is a HPLC chromatogram of a product solution of HMF prepared by dehydration of fructose according to example 13 of the present invention;

FIG. 2 is an HPLC chromatogram of an oxidation product of HMF of example 21 of the present invention;

FIG. 3 is a diagram showing FDCA as a reaction product in example 21 of the present invention¹H nuclear magnetic spectrum;

FIG. 4 is a schematic diagram of a system for continuously synthesizing furandicarboxylic acid according to the present invention.

Detailed Description

Specific examples of the present invention are given below. The specific examples are only intended to illustrate the invention in further detail and do not limit the scope of protection of the claims of the present application.

In order to conveniently describe the influence of the reaction conditions on the two-step reactions of preparing HMF by dehydrating saccharides and preparing FDCA by oxidizing HMF, respectively, the two-step reactions are separately described in the examples.

Examples 1 to 4:

preparation of HMF by dehydration of saccharides

4g fructose, 16g DMSO and 1g Amberlyst-15 catalyst were added to a 50mL three-necked flask, and N was introduced₂And (3) emptying, heating to the temperature shown in the table 1, fully stirring, and reacting for 90min to obtain the HMF solution. High performance liquid chromatography for HMF content in product liquidThe amount was analyzed to obtain the yield of HMF, see table 1.

TABLE 1 yield of HMF by dehydration of fructose at different temperatures

The HMF yield calculation method comprises the following steps:

examples 5 to 7

The other process conditions and experimental procedures were the same as in example 4, but different reaction times were used in the stage of preparing HMF by dehydration of fructose, and the reaction conditions and results are shown in Table 2.

TABLE 2 yield of HMF from dehydration of fructose at different reaction times

As can be seen from table 2, the HMF yield substantially increases with the increase of the reaction time in the early stage, and reaches the maximum value after the reaction time reaches 90min, and as the reaction time continues to increase, the HMF undergoes side reactions and begins to decrease in yield.

Examples 8 to 9

The other process conditions and experimental procedures were the same as in example 4, but different solvents were used in the stage of preparing HMF by dehydration of fructose, and the reaction results are shown in Table 3 below.

TABLE 3 yields of HMF prepared by dehydration of fructose in different solvents

Examples 10 to 11

The other process conditions and experimental procedures were the same as in example 4, but different catalysts were used in the stage of preparing HMF by fructose dehydration, and the reaction results are shown in Table 4 below.

TABLE 4 yield of HMF by dehydration of fructose over different catalysts

Examples 12 to 13

The other process conditions and experimental procedures were the same as in example 4, but different starting concentrations of the starting materials were used in the stage of fructose dehydration to produce HMF, and the results are shown in Table 5 below.

TABLE 5 yield of HMF by dehydration of fructose at different starting concentrations

The HPLC results of example 13 dehydration product HMF are shown in fig. 1, where the test conditions are: a sample pump (Waters 1524), a separation column of C18 column (Lichrospher 5), a column temperature of 20 ℃, an ultraviolet detector (Waters 2489), a mobile phase of acetonitrile: 0.1 wt% acetic acid aqueous solution (1:9v/v), flow rates of 0.05mL/min and 0.45mL/min, respectively, and a sample volume of 20. mu.L.

Comparative examples 1 to 2: oxidation of pure HMF to FDCA

In a 50ml three-neck flask preheated to 75 ℃, 0.126g of reagent grade pure HMF is added, DMSO solvent and K with different masses and concentration of 0.014mol/L are added₂CO₃The total amount of the aqueous solution was 20g, the mass ratio of DMSO to the aqueous solution is shown in Table 6, 0.2g of a Pt/C (Pt molar content: 5%) catalyst was added, and oxygen was introduced at a rate of 30 mL/min. The resulting solution was heated for 6 hours with sufficient stirring at the above temperature, and the contents of HMF, FDCA, 5-hydroxymethyl-2-furoic acid (HMFCA) and 5-formyl-2-furoic acid (FFCA) in the resulting solution were analyzed by high performance liquid chromatography, and the results of the reaction are shown in Table 6 below.

TABLE 6 HMF Oxidation results at varying aqueous alkaline solution dosages

Examples 14 to 15: oxidation of pure HMF to FDCA

Other process conditions and experimental procedures were the same as those of comparative examples 1-2, except that the mass ratio of DMSO to the aqueous alkaline solution was different, and the reaction results were as shown in Table 7 below.

TABLE 7 HMF Oxidation results at different amounts of aqueous alkaline solution

As is clear from the reaction results of comparative examples 1-2 and examples 14-15, HMF (purity) was used as it is>99%) as raw material, in pure DMSO solvent, the conversion rate of HMF is extremely low, and no FDCA is generated. Adding 30% of K₂CO₃In the quality of aqueous alkaline solutions, the conversion of HMF can be partial, but the yield of FDCA is still low; when K is₂CO₃When the dosage of the alkaline aqueous solution is higher than 100%, the yield of the FDCA is obviously improved; when K is₂CO₃When the dosage of the alkaline aqueous solution reaches 300 percent, the yield of the FDCA reaches 89.4 percent. The presence of a suitable amount of aqueous alkaline solution promotes the conversion of HMF and the selective formation of FDCA.

Wherein, the calculation method of the HMF conversion rate, the yield of FDCA and important intermediate products FFCA and HMFCA is as follows:

example 16: oxidation preparation of FDCA from fructose dehydration product HMF solution

The oxidation experiments were carried out directly using the fructose dehydration product HMF solution as starting material. In a 50mL three-necked flask preheated to 75 ℃, 5g of the HMF solution obtained by dehydration of fructose in example 13 and 0.14mol/L K were charged₂CO₃15g of aqueous solution and 0.2g of Pt/C (5 mol% Pt) catalyst, oxygen was introduced at a rate of 30 mL/min. Heating at 75 deg.C for 12 hr under stirring, and analyzing the product liquid by high performance liquid chromatography to obtain HMF conversion rate of 100%, FDCA yield of 91.1%, and FFCA yield of 0.3%.

Examples 17 to 18

Other process conditions and experimental procedures were the same as in example 16, and different types of bases were added at the stage of preparing FDCA by HMF oxidation, and the reaction results are shown in table 8 below.

TABLE 8 oxidation results of HMF solutions with different base additions

Example 19

Other Process conditions and Experimental procedures As in example 16, different concentrations of K were used during the preparation of FDCA by oxidation of HMF₂CO₃Aqueous solution, the reaction results are shown in table 9 below.

TABLE 9 different concentrations K₂CO₃Oxidation results of aqueous HMF solution

Examples 20 to 21

The other process conditions and experimental procedures were the same as in example 16, but different temperatures were used in the stage of preparing FDCA by oxidation of HMF for 10 hours, and the reaction results are shown in Table 10 below.

TABLE 10 oxidation results of HMF solutions at different temperatures

As can be seen from Table 10, the yield of FDCA reached a higher level at a reaction temperature not exceeding 100 ℃. HPLC results of the oxidized product solution of HMF in example 21,¹The H nuclear magnetic results are shown in FIG. 2 and FIG. 3, respectively.

Example 22

As shown in fig. 4, this example provides a method for continuously synthesizing furan dicarboxylic acid from fructose:

in a raw material solution preparation tank, 0.05kg of fructose was dissolved in 1kg of DMSO to obtain a fructose solution having a concentration of 5 wt%. The fructose solution was pumped at a rate of 0.3mL/min into a first reactor (effective volume 63mL) filled with 20g Amberlyst-15 catalyst, the temperature of the first reactor being 120 ℃. The solution flowing out of the first reactor enters a mixer and is mixed with K with the concentration of 0.13mol/L and the flow rate of 0.9mL/min₂CO₃The aqueous solution was thoroughly mixed and introduced into a second reactor (effective volume 126mL) packed with 30g of Pt/C (5% Pt by mole) catalyst, into which 0.1MPa of oxygen was introduced at an oxygen flow rate of 30mL/min and a temperature of 100 ℃. The content of the product liquid discharged from the second reactor was analyzed by high performance liquid chromatography, and the yield of FDCA was 85.0%. And (3) inputting the product liquid flowing out of the second reactor into an evaporator, evaporating to remove the solvent, inputting into an acidifier, adding hydrochloric acid for acidification, and precipitating to obtain a crude product of FDCA. After the product liquid containing the crude FDCA passes through a filter washer, the crude FDCA obtained by separation is input into a crystallizer, and 500g H is added into the crystallizer₂Mixing O, heating to nearly boiling (about 95 ℃), quickly cooling, recrystallizing to obtain FDCA product, inputting to a filter, separating, and outputting to a product tank.

Claims (2)

1. A method for continuously synthesizing furan dicarboxylic acid, which is characterized by comprising the following steps:

(1) dissolving sugar in an organic solvent to prepare a sugar solution with the mass concentration of 5-20%, and reacting the sugar solution at 90-140 ℃ for 0.5-2 hours under the action of a sulfonic acid group ion exchange resin catalyst to obtain a 5-hydroxymethylfurfural solution;

(2) adding an alkaline aqueous solution with the concentration of 0.01-1mol/L and an oxidant into the effluent liquid of the step (1), and reacting for 2-12 hours under the conditions of 60-110 ℃ and 0.1-1MPa under the action of a supported oxidation catalyst to obtain a furan dicarboxylate solution;

(3) evaporating the effluent liquid of the step (2) to remove the solvent, adding an acidifying agent, adjusting the pH to be less than 2, and precipitating a crude furandicarboxylic acid product; filtering, washing and recrystallizing to obtain furandicarboxylic acid;

the organic solvent is dimethyl sulfoxide;

the sulfonic ion exchange resin catalyst is Amberlyst-15;

the alkaline aqueous solution is Na₂CO₃Aqueous solution, K₂CO₃One of an aqueous solution or an aqueous NaOH solution;

the dosage of the alkaline aqueous solution is 300-500% of the mass of the organic solvent in the system;

the supported oxidation catalyst is Pt/C, and the dosage of the supported oxidation catalyst is 20-500% of the adding mass of the saccharides;

the oxidant is O₂One or more of air;

the saccharide is fructose;

the method also relates to a system for continuously synthesizing furan dicarboxylic acid, which comprises a raw material liquid preparation tank, a first reactor, a mixer, a second reactor, an evaporator, an acidifier, a filtering washer, a crystallizer, a filter and a product tank; dissolving sugar in an organic solvent in a raw material solution preparation tank, inputting the obtained sugar solution into a first reactor filled with a sulfonic acid group ion exchange resin catalyst for reaction to obtain a 5-hydroxymethylfurfural solution;

directly outputting the obtained 5-hydroxymethylfurfural solution to a mixer, adding an alkaline aqueous solution, uniformly mixing, inputting the mixture to a second reactor filled with a supported oxidation catalyst, and introducing an oxidant into the second reactor for reaction to obtain a furan dicarboxylate solution;

inputting the obtained furan dicarboxylic acid salt solution into an evaporator to evaporate the solvent, inputting the solution into an acidifier, adding an acidifier into the acidifier, adjusting the pH value to be less than 2, and precipitating a furan dicarboxylic acid crude product;

the furan dicarboxylic acid crude product is separated by a filtering washer and then input into a crystallizer, recrystallized in the crystallizer and then input into a filter for filtering to obtain the furan dicarboxylic acid product, and the furan dicarboxylic acid product is output into a product tank.

2. The method for continuously synthesizing furandicarboxylic acid according to claim 1, wherein the sulfonic acid group ion exchange resin catalyst is used in an amount of 5 to 100% by mass of the saccharides.

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