RU2459204C1 - Method for diagnosing state of sorbent - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: degree of refinement and determination of remaining life of a chemical sorbent - mercerised wood - is carried out by monitoring change in colour thereof from white and brown shades to black in proportion to saturation of the absorbent with acidic compounds depending on content of the absorbed component in the sorbent, equal to 0-45 wt %, with degree of refinement of the sorbent from 0-100%, wherein the wood fibre is a colour indicator.

EFFECT: simple and efficient monitoring of the state of a sorbent, from the visual appearance of which the criteria of its refinement and degree of saturation with an adsorbate can be determined.

4 cl, 1 ex, 3 tbl, 4 dwg

Description

The invention relates to inorganic chemistry and, in particular, to technologies for diagnosing materials in the chemical and nuclear industry.

Solid chemicals are often used as sorbents for trapping gaseous compounds. Sorbents can be salts (fluorides, carbonates, metal sulfates, etc.), oxides (aluminum, silicon, calcium, magnesium, etc.), hydroxides (calcium, magnesium, iron, etc.), which are usually white in bulk. color, as well as organic substances (ion exchangers, coal, wood, etc.) [Baskin Z.L. Industrial environmental control. Chromatographic methods for the analysis of fluorine and its compounds. - M .: Energoatomizdat, 2008, p.31-34].

As a rule, when gases are absorbed by sorbents, the system visually does not undergo any changes [N. Galkin and others. Capture and processing of fluorine-containing gases. - M .: Atomizdat, 1975, p. 83-86, 142-148]. For example, in the process of absorption of gaseous substances of an acidic nature, for example, HF, UF ₆ , etc., on sorbents based on alkali or alkaline-earth fluorides, the color of the final substances (NaHF ₂ , LiHF ₂ , Na ₂ UF ₈ , BaUF ₈ , etc. ) is unchanged, i.e. stays white. By the type of substance obtained, it is impossible to determine the degree of saturation of the absorbed component. These characteristics can be calculated in two ways: 1) chemical analysis of the material for the content of the absorbed component and 2) the content of the absorbed component in the gas behind the sorbent layer above a given breakthrough value. In both cases, a sufficiently long time is required to assess the degree of saturation of the sorbent and make a decision on its regeneration or replacement. A similar picture is observed when cleaning air, for example, from sulfur or carbon dioxide using hydroxides or oxides. In appearance, it is impossible to determine the degree of sorbent mining, since the color of the initial and saturated sorbent is the same.

However, it is known that the interaction of chemical compounds in many cases changes the color of the system during the transition from the starting reagents to the reaction products. So, for example, a solution of potassium permanganate, which has a purple color, when restored to potassium manganate acquires a green color. Or, under the action of hydrofluoric acid on solutions of uranyl salts having a lemon yellow color, a dark green uranium tetrafluoride is formed. Similar examples can be given almost endlessly.

It is also known that in the titrimetric determination of one or another ion in solution, two or three drops of an indicator are added to the titrated solution to fix the equivalence point, usually representing an organic compound that changes color when the pH of the solution changes [Gillebrand B. F. et al. A Practical Guide to Inorganic Analysis. Per. from English Ed. Yu.Yu. Lurie. - M .: GNTIHL, 1957, p. 183, 196]. For example, when determining acidity, an indicator, colorless phenolphthalein, is added to an aliquot. During titration with an alkali solution, the color of the solution changes to raspberry at the equivalence point, which means complete neutralization of hydrogen ions in the initial solution, i.e. their practical disappearance and the appearance in the solution of excess hydroxyl ions. In the case of the reverse process, i.e. determine the alkalinity of the solution using phenolphthalein, the color of the titrant changes from raspberry to colorless.

Thus, the color change of the system in the above examples is used as a criterion for diagnosing the end of a process or, in other words, a change in the color of the system signals the exhaustion of one of the starting compounds, which is, in turn, a criterion for terminating the process.

Sorbents obtained by processing wood with alkali solutions according to the methods [SU No. 710601; SU No. 1255175; RU No. 2283175; RU No. 2283176, IPC B01J 20/24], contain NaOH in their composition. After the wood is aged in an alkali solution and dried, the material has a color from light beige to light brown, depending on the type of source wood with a white coating of adsorbed dry alkali.

Figures 1 and 2 show mercerized wood.

In Fig. 1: In Fig. 2: The NaOH content is 36-40% (wt.). The NaOH content of 46-48% (wt.). The content of H ₂ O 10-12% (wt.). The content of H ₂ O 9-11% (wt.).

The technical result of the present invention is to find a simple and effective way to control the state of the sorbent, the visual appearance of which can determine the criteria for its development and the degree of saturation of the adsorbate.

The technical result of the invention is achieved in that the degree of development and determination of the residual resource of the chemical sorbent — mercerized wood — is carried out by controlling its color change from white and shades of brown to black as the absorber is saturated with acidic compounds, depending on the content of the absorbed component in the sorbent, equal to 0 to 45% (wt.) With the degree of sorbent development from 0 to 100%, while wood fiber is a color indicator.

When the content of the absorbed compound is up to 30 wt.%, The color of the sorbent changes from shades of brown to uniform gray with a working degree of 80-85%.

When the content of the absorbed compound is in the range of 30-39% (wt.), The material consists of approximately equal amounts of gray and black particles, and the degree of its development is 85-95%.

When the content of the absorbed compound is more than 40% (wt.), The color of the sorbent becomes predominantly black at a degree of development approaching 100%.

The criterion for the development of the sorbent is the content of the absorbed component, equal to 31-35% (wt.), And the material consists mainly of gray particles with black inclusions.

The process of absorption of acid gases on such sorbents is as follows. A gaseous compound, for example HP, initially interacts with alkali adsorbed on the surface of the sorbent

HF + NaOH = NaF + H ₂ O

After the adsorbed alkali is exhausted, HF begins to react with the alkali chemically bound to cellulose (the basis of wood fiber)

R _cell OH NaOH + HF = R _cell OH Na + NaF + H ₂ O

Due to the friability of the formed sodium fluoride layer and the presence of water, HF finally begins to interact with cellulose, which is a polyhydric alcohol with a slightly alkaline character

R _cell OH + HF = R _cell F + H ₂ O

As shown by our studies, in the process of HF absorption, the color of the material changes significantly only at the last stage of the sorbent from the initial one, i.e. white and light brown, to gray and black, depending on the degree of saturation with neutralization reaction products (Table 1). Wood fiber is a color indicator of sorbent development.

Figures 3 and 4 show wood material containing various amounts of fluorine.

Fig. 3 - A sample of CP-MD containing 12.5% (wt.) Fluorine:

Fig. 4 - Used absorber:

Dark particles (frontal layer) contain 38-42% (wt.) Fluorine.

Light particles (output layer) contain from 0 to 1.8% (wt.) Fluorine.

Table 1 Physico-chemical condition of spent wood Sample Number Layer Mass change,% (wt.) Content,% (wt.) Appearance (color) NaOH F Ref. all 0 30.6 0 Cream one frontal 0 27.9 Gray average +26.7 22.8 3.0 Original with gray patches output 27.7 0.1 Source 2 frontal 0 33,2 Gray black average +46.0 0 30.7 Gray with black spots output 15.0 6.2 Original with individual gray particles 3 frontal 0 42.8 Black, wet mass, formalin odor average +110.0 0 46.6 Also output 0 36.3 Gray-black mass (~ 50% × 50%), formalin odor

Thus, by changing the color of wood exposed to acidic compounds, it is possible to determine the degree of development or the degree of residual resource of the sorbent. In this case, wood is an indicator, the color of which determines the degree of saturation of the sorbent with the adsorbate.

As a result of our studies on the saturation of chemical sorbents, on (in) the wood base of which solid sodium hydroxide was deposited (introduced) with hydrogen fluoride under dynamic conditions, the following data were obtained.

After mercerization of wood with a 25% NaOH solution, it contains 30-48% (wt.) Alkali (depending on the process time and type of wood), both adsorbed on the surface and chemically bonded to the wood fiber. The maximum possible absorbed fluorine content was equal to 57% (wt.). Physical state - volgla (wet) mass of black color. In this fully used state, the sorbent, or rather, what it has turned into, is a secondary source of harmful chemicals, in particular, a sharp smell of formaldehyde was felt, which was also confirmed by a qualitative chemical analysis. Formaldehyde begins to stand out from the mass of the absorber with a fluorine content of 45-47% (wt.). Thus, if we assume that the full degree of development of the absorber is achieved when the fluorine content in it reaches 45% (wt.), I.e. the beginning of the allocation of secondary water chemistry, the degree of mining can be determined from the data presented in table.2.

table 2 Determining the degree of mining No pp The fluorine content,% (wt.) The content of NaOH,% (wt.) Color The degree of development,% one 0 40-45 Light brown 0 2 25-30 3-5 Gray 80-90 3 31-35 0 Gray and black particles 90-95 four > 40 0 Mostly black one hundred

Thus, based on the data in Table 2, a material consisting of approximately equal amounts of gray and black particles and containing not more than 35% (wt.) Fluorine should be considered a spent chemical sorbent based on mercerized wood. This fluorine content is limiting and the sorbent in this case requires immediate replacement, since its further operation is fraught with secondary contamination of the gas purified from volatile halides with harmful chemicals, in particular formaldehyde.

Example

A gas mixture containing up to 9 vol.% HF in air was passed through four successive layers of sorbent with a thickness of each 20 cm, placed in a vertical column. After the column, the presence of HF in the exhaust air was not detected during the entire experiment. The absorber fulfills the resource in layers. The degree of development of successive layers is presented in table.3.

Table 3 The degree of development of the sorbent in dynamic conditions Layer number Layer color The fluorine content,% (wt.) The degree of development,% Source Light brown 0 - 1 layer The black 42,4 ~ 100 2 layer Gray with black particles 31.7 86 3 layer Gray 23.1 55 4 layer Light brown 1,5 ~ 10

As follows from the data in Table 3, of course, the 1st layer and, probably, the 2nd layer are subject to replacement in connection with an almost complete worked out resource.

Therefore, the criteria for working out the sorbent are the fluorine content at the level of 30-32% (wt.) And the color change to gray with black inclusions.

Claims (4)

1. A method for diagnosing the state of a sorbent based on mercerized wood in the process of saturation with acidic gaseous compounds, characterized in that they control the color change of the sorbent from white and shades of brown to black depending on the content of the absorbed component in the sorbent, equal to from 0 to 45 wt.% , with the degree of sorbent working out from 0 to 100%, while the wood fiber is a color indicator that changes color when the alkaline environment of the system goes into acidic. 2. The method according to claim 1, characterized in that when the content of the absorbed compound is up to 30 wt.%, The color of the sorbent changes from shades of brown to uniform gray with a working level of 80-85%. 3. The method according to claim 1, characterized in that when the content of the absorbed compound is in the range of 30-39 wt.%, The material consists of approximately equal amounts of gray and black particles, and the degree of development is 85-95%. 4. The method according to claim 1, characterized in that when the content of the absorbed compound is more than 40 wt.%, The color of the sorbent is predominantly black with a working degree approaching 100%.

Images