RU2374264C1 - Method of producing carboxymethylated lignocarbohydrate material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical modification of lignocarbohydrate materials, which are used as sorbents. The method involves preliminary treatment of lignocarbohydrate material with formaldehyde in a propanol-2 medium in molar ratio formaldehyde: OH-group of the lignocarbohydrate material equal to (1-5):(1-90) in the presence of an acid catalyst and holding for 180 minutes at 40°C. Alkaline pre-treatment is carried out in molar ratio OH-group of the lignocarbohydrate material: NaOH equal to 1:1 at temperature 60°C for 120 minutes. Further, sodium monochloroacetate is added in molar ratio OH-group of the lignocarbohydrate material: ClCH₂COONa equal to 1:0.5, and is kept for 60 minutes at 60°C. The obtained product is washed with acidified mineral acid of ethanol and dried in air.

EFFECT: obtained product is characterised by high content of carboxylic groups, increased exchange capacity and is resistant to aqueous and non-aqueous media.

2 cl, 4 tbl, 12 ex

Description

The invention relates to chemical modification of ligno-carbohydrate materials (LUM) and is intended to produce carboxymethyl esters of ligno-carbohydrate materials, which can be used in various fields, for example, as sorbents.

Known methods of carboxymethylation of ligno-carbohydrate materials based on the reaction of hydroxyl groups of the main components of the ligno-carbohydrate material (cellulose, lignin, hemicellulose) with monochloracetic acid or sodium monochloracetate in an alkaline medium.

LUM (OH) _n + mClCH ₂ COOH + 2mNaOH → LUM (OH) _nm (OCH ₂ COONa) _m + mNaCl + 2mH ₂ O

So, in the patent [1], a carboxymethylation method is proposed, namely, that the initial ligno-carbohydrate material is treated with a solution of sodium hydroxide in isopropyl alcohol for 0.5-6.0 hours at 20-150 ° C, then with monochloracetic acid (MXYK) for 0.5-4.0 hours at 20-60 ° C. In this case, water-soluble products are formed (by 30-94%) with a content of carboxymethyl groups of 6.2-13.6%.

In the patent [2], it is proposed to mix ligno-carbohydrate material in the form of sawdust with solid sodium monochloracetate (Na-MHUK), NaOH and water (the hydraulic unit is ≈0.3). The mixture is subjected to intensive mechanical grinding at 20-80 ° C for 0.5-3 hours, resulting in the formation of water-soluble carboxymethylated products. The solubility in water of the obtained products is 87.9-96.0%, the relative alkaline solutions viscosity is 1.08-1.30.

In the patent [3], carboxymethylation of ligno-carbohydrate materials is carried out by the solid-phase method in the absence of water by mixing solid sawdust of ligno-carbohydrate material, Na-MCC, NaOH. The mixture is subjected to intensive mechanical grinding at 10 ° C for 5-30 minutes, resulting in the formation of water-soluble carboxymethylated products. Solubility in water - 61.0-99.0%, relative viscosity - 1.03-1.07.

Of the known technical solutions, the closest in purpose and technical essence to the claimed invention relates to a method of carboxymethylation of ligno-carbohydrate materials [4], adopted as a prototype, which includes preliminary removal of extractive and water-soluble substances from an air-dry ligno-carbohydrate material by a 3-stage sequential extraction with an alcohol-benzene mixture, cold and hot water. Then macromolecules are crosslinked by polycondensation of the extracted material with formaldehyde at a ratio of OH-group LUM: formaldehyde equal to 1: 3-5 in the presence of an alkaline catalyst. After that, the cross-linked ligno-carbohydrate material is washed and carboxymethylated with monochloroacetic acid (MCC) and alkali in the ratio of OH-group LUM: ClCH ₂ COOH: NaOH equal to 1: 3: 27, at 45-65 ° C for at least 3 hours, after which the carboxymethylated product is separated, treated with mineral acid to convert the carboxyl groups to the H-form, washed with water until the filtrate is neutral and dried. The invention allows to obtain a product characterized by a content of carboxyl groups of 0.8-2.5% and an increased exchange capacity, while being resistant to aqueous and non-aqueous media.

The disadvantages of the prototype include the following:

firstly, carboxymethylation of ligno-carbohydrate material is carried out in one stage, which leads to an increased consumption of reagents. While the step-by-step process allows to reduce the consumption of reagents and adjust the properties of the final product;

secondly, the production method proposed in the prototype, allows to obtain products with a low content of carboxyl groups (0.8-2.5%);

thirdly, the prototype uses an alkaline catalyst, and the use of an acid catalyst during crosslinking will avoid the swelling of cellulose fibers in the LUM;

fourthly, the method proposed in the prototype provides for the use of MCC as a carboxymethylating reagent, which is more hygroscopic than MCC, which reduces the manufacturability of the process.

The essence of the method for producing a crosslinked carboxymethylated ligno-carbohydrate material is that the ligno-carbohydrate material (LUM) is crosslinked by polycondensation of the feedstock with formaldehyde in a molar ratio of formaldehyde: OH-group LUM equal to (1-5) :( 1-90), in the presence of acid catalyst at a temperature of 40 ° C, keeping for 180 min, then alkaline treatment is carried out in a molar ratio of OH-group LUM: NAOH equal to 1: 1, at a temperature of 60 ° C for 120 min, sodium monochloracetate is added in molar ootnoshenii OH groups LSM: ClCH ₂ COOONa, equal to 1: 0.5, and incubated for 60 min at 60 ° C, whereupon the product is washed with ethanol acidified with a mineral acid and dried in air.

After the stage of processing with formaldehyde for additional crosslinking of the ligno carbohydrate material, heat treatment is carried out at a temperature of 105 ° C and a duration of 15 to 90 minutes.

The present invention, a method for producing a cross-linked carboxymethylated ligno-carbohydrate material (LUM), allows to obtain a product characterized by a high content of carboxyl groups (COOH) and increased sorption ability with respect to heavy metal ions, while being resistant to the action of aqueous media. This is the technical result of the invention.

As an example of the initial LUM, pine wood or flax bonfire with a sawdust fraction of 0.63-0.315 mm with a moisture content of up to 5% is used. According to our data, the initial pine wood contains on average 48% cellulose, 27% lignin, and flax fire - 38% cellulose, 31% lignin.

Common to the prototype and the claimed invention is carboxymethylation of ligno-carbohydrate material, as well as crosslinking of LUM macromolecules with formaldehyde. LUM is used as a raw material for carboxymethylation without dividing them into separate hydroxyl-containing components.

This invention differs from the prototype:

1) preliminary crosslinking with formaldehyde in an acidic environment at a temperature of 40 ° C;

2) lower flow rates (for formaldehyde and sodium monochloracetate);

3) by heat treatment at 105 ° C for 15-90 minutes;

4) the subsequent carboxymethylation reaction in two stages, including alkali activation and interaction with sodium monochloracetate.

The method is illustrated by examples.

Example 1-5.

5 g of pine wood is treated with formaldehyde in a molar ratio of formaldehyde: OH-groups LUM equal to (1:30 - 5: 1) in an organic solvent (propanol-2 - 35 ml) in the presence of an acid catalyst (H ₂ SO ₄ , 17 ml 0.003 M) at 40 ° C and incubated for 180 minutes Then, alkaline treatment is carried out in a molar ratio of the OH group of LUM: NaOH equal to 1: 1 at a temperature of 60 ° C and a duration of 120 minutes. Next, sodium monochloracetate is added to the reaction vessel in a molar ratio of the OH group of LUM: ClCH ₂ COONa, equal to 1: 0.5, and incubated for 60 minutes at a temperature of 60 ° C. The resulting product is washed with acidified acetic acid with 70% ethanol and dried in air.

Example 6-8.

The method is carried out analogously to example 1, only as the original LUM use flax fire. The molar ratio of formaldehyde: OH-group LUM is equal to (1:90 - 1: 1).

Table 1 shows the properties of the products obtained at different molar ratios from different LUM (examples 1-8). The control sample was carboxymethylated pine wood, obtained under the same conditions as in examples 1-5, with the exception of pretreatment with formaldehyde.

Example 9-12 The method is carried out analogously to example 1 with a molar ratio of OH-group LUM: formaldehyde equal to 1: 1, and after the crosslinking step, heat treatment is carried out in an oven at a temperature of 105 ° C and a duration of 15-90 minutes Then, alkaline treatment and carboxymethylation are carried out as in Examples 1-5. The properties of the obtained products are shown in table 2.

All products are obtained in the H-form and are insoluble in water.

Carboxymethylated LUM obtained by carboxymethylation of LUM pretreated with formaldehyde have a higher content of carboxyl groups (Table 1). This is due to the fact that pretreatment with formaldehyde leads to the destruction of the supramolecular structure of the main components of LUM, which provides better accessibility of the reaction centers for the carboxymethylating reagent.

The heat treatment of carboxymethylated LUM leads to a decrease in the content of carboxymethyl groups, which indicates additional crosslinking and the formation of a three-dimensional structure, which lead to a decrease in the number of reaction centers available for sodium monochloracetate.

Static exchange capacity (SOE) was determined with respect to Fe (III) and Cr (IV) ions. For this, a weighed portion (0.5 g) of the sorbent (crosslinked carboxymethylated LUM) is poured into 25 ml of a solution containing Fe (III) and Cr (IV) ions of a given concentration and kept for 4 h until equilibrium is established. Then it is filtered off and the residual (equilibrium) concentration of the studied ion is determined in the filtrate. SOE is calculated by the known formula

SOE = (C ₀ -C _equal ) · V / m,

where SOE - static exchange capacity, g / g; m is the mass of dry sorbent, g; V is the volume of the test solution, l; С ₀ - element concentration in the initial solution, g / l; C _equ - residual concentration of the recoverable element in the solution, g / l.

The research results are presented in tables 3 and 4.

From the presented data it follows that the proposed method allows to obtain cross-linked carboxymethylated LUM with a higher content of carboxyl groups. The resulting crosslinked carboxymethylated LUMs can quite efficiently recover heavy metal ions (Fe (III) and Cr (IV)), which allows them to be used as sorbents.

Bibliographic list

1. Patent No. 2130947 (Russia). The method of carboxymethylation of ligno-carbohydrate materials / Galochkin A.I., Markin V.I., Bazarnova N.G., Zastavenko N.V., Krestyannikova N.S. / Public. 1999.05.27. Bull. No. 15.

2. Patent No. 2131884 (Russia). The method of carboxymethylation of ligno-carbohydrate materials / Bazarnova N.G., Markin V.I., Galochkin A.I., Tokareva I.V. / Public. 1999.06.20. Bull. Number 17.

3. Patent No. 2135517 (Russia). The method of carboxymethylation of ligno-carbohydrate materials / Bazarnova N.G., Tokareva I.V., Galochkin A.I., Markin V.I. / Public. 1999.08.27. Bull. Number 24

4. Patent No. 2252941 (Russia). The method of carboxymethylation of ligno-carbohydrate materials / Brovarova O.V., Belyaev V.Yu., Kocheva L.S., Karmanov A.P. / Public. 2005.05.27. Bull. Number 15

Table 1 Properties of LUM carboxymethylation products pre-crosslinked with formaldehyde Example LUM

Ratio

The content of COOH groups,% Control sample Pine - 5.7 one Pine 1:30 12.9 2 Pine 1:10 17,2 3 Pine 1: 1 15.8 four Pine 5: 1 12.6 5 Pine 5:90 14.2 6 flax bonfire 1:90 7.7 7 flax bonfire 1:30 10.1 8 flax bonfire 1: 1 10.8

table 2

.Effect of the duration of heat treatment at 105 ° C on the properties of LUM carboxymethylation products pre-crosslinked with formaldehyde

. Example The duration of the heat treatment, min The content of COOH groups,% 9 fifteen 9.5 10 thirty 11,4 eleven 60 9.1 12 90 3.3

Table 3 Static exchange capacity (SOE) of crosslinked carboxymethylated wood derivatives at different initial concentrations of Fe (III) Example The concentration of the stock solution, g / l COE · 10 ³ , g / g Control sample 0.015 0.2 Control sample 0.6 5,4 3 0.015 0.37 3 0.6 10.6 12 0.015 0.39 12 0.6 9.3

Table 4 Static exchange capacity (SOE) of crosslinked carboxymethylated wood derivatives at different initial concentrations of Cr (IV) Example The concentration of the stock solution, g / l COE10 ³ mg / g Control sample 0,0008 0,031 Control sample 0.1 7.8 3 0,0008 0,033 3 0.1 8.4 12 0,0008 0,026 12 0.1 8.7

Claims (2)

1. A method of obtaining a cross-linked carboxymethylated ligno-carbohydrate material, comprising pretreatment with formaldehyde in propanol-2 medium of air-dried sawdust of ligno-carbohydrate material (LUM), characterized in that formaldehyde and LUM are used in a molar ratio of formaldehyde: OH-group LUM equal to (1) 5) :( 1-90), while the treatment is carried out in the presence of an acid catalyst at 40 ° C with holding for 180 minutes, then alkaline treatment is carried out in a molar ratio of the OH group of LUM: NaOH equal to 1: 1 at a temperature of 60 ° C and will continue lnosti 120 minutes, sodium monochloroacetate is added in a molar ratio of OH groups LSM: ClCH ₂ COONa, equal to 1: 0.5, and incubated for 60 min at 60 ° C, whereupon the product is washed with acidified with mineral acid with ethanol and dried in air . 2. The method according to claim 1, characterized in that after processing with formaldehyde, heat treatment is carried out at a temperature of 105 ° C and a duration of 15-90 minutes