RU2493907C1 - Method of making carbon sorbent from vegetable stock - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to method of producing carbon sorbent. Proposed method comprises heating at the rate of 10-15°C/min of chemically processed vegetable stock to 300-400°C. Millet seed coats are used as vegetable stock. Stock is chemically treated by aqueous solution of ammonium tetrafluoroborate simultaneously with carbonisation and holding for 5 minutes.

EFFECT: simplified and accelerated process.

1 tbl

Description

The invention relates to methods for producing carbon sorbents and can be used in the chemical industry for wastewater treatment from liquid hydrocarbons, in the utilization of oil waste and in various sectors of the national economy to protect the environment.

A known method of producing sorbents based on plant materials, namely, polysaccharide-containing raw materials - waste microbiological industry and agriculture. The waste is crushed and treated with a mixture containing phosphoric acid, dimethylformamide and urea at a temperature of 150 ° C for 2-4 hours. (RF patent No. 2077541 publ. 04/20/1997)

The disadvantages of this method are the use of toxic products - phosphoric acid and dimethylformamide, which is a carcinogen, urea, and the need for grinding increases the cost of the product.

A known method of producing sorbents based on plant materials, shells of walnuts. The method consists in combining the operations of impregnation and processing of the shell with concentrated hydrochloric acid, then with a 33% alkali solution, followed by grinding and drying at 100 ° C. (RF patent No. 2172209 publ. 08/20/2001)

The disadvantages of the method are the use of aggressive, toxic compounds of acid and alkali, the presence of a pollutant in the composition of the sorbents - potassium chloride formed during the neutralization of hydrochloric acid with alkali, the need to grind waste plant materials, as well as equipment corrosion.

A known method of producing a sorbent by pyrolysis of woodworking waste in the environment of combined-cycle pyrolysis products. (RF patent No. 2160632 dated 12/15/1999)

The disadvantage of this method is the low sorption capacity, low buoyancy of the sorbent due to insufficient hydrophobicity, since pyrolysis is carried out in a medium that causes hydrophilic surface activation.

The closest technical solution, taken as a prototype, is a method for producing a carbon sorbent from sunflower husk.

A method of obtaining a carbon adsorbent from waste plant materials, namely, from sunflower husk, including chemical removal of ballast substances, washing with water and drying at 100-120 ° C. The removal of ballast substances is carried out in two stages: in the first chemical stage, the husk is treated at 90-100 ° C, with a suspension containing the following components, wt.%: Calcium hydroxide 6.2-8.5; carbamide 5.3-7.5; water 84.0-88.0; in the ratio suspension: sunflower husk, parts by weight, equal to 1: (0.06-0.10) for 0.5-1.0 hours, in the second stage, the processed sunflower husk is thermally carbonized, previously heated in a stream of nitrogen at atmospheric pressure at a rate of 10-15 ° C / min to a temperature of 300-400 ° C, followed by exposure for 0.25-0.5 hours, washing and drying is carried out before the second stage, and the washed husk is dried in a stream of nitrogen for 0 , 3-0.5 hours (RF Patent No. 2395336 of November 05, 2008)

The disadvantages of the prototype are: multi-stage process, the use of toxic products, increased overall process duration, the presence of wastewater requiring regeneration.

The objective of the invention is to reduce the number of stages of the process and its duration, eliminate toxic components, eliminate the regeneration of wastewater and thereby maintain a favorable ecological environment.

To achieve this technical result in a method for producing a carbon sorbent from plant material, which includes heating at a rate of 10-15 ° C / min chemically treated plant material to a temperature of 300-400 ° C. followed by a temporary exposure and its carbonization, the waste of threshing millet seeds - shells of millet seeds, the chemical treatment of which is carried out with an aqueous solution of ammonium tetrafluoroborate at a concentration of 25-35% in a ratio of 1: 1 at the same time as heating carbonization and temporary exposure for 5 minutes.

Thus, the difference of the proposed method from the prototype is: one-stage production of the sorbent by carbonization by heating from T = 300 ° C to 400 ° C with a speed of 10-15 ° C / min. chemically treated shells of millet with an aqueous solution of ammonium tetrafluoroborate concentration of 25-35% in a ratio of 1: 1 and exposure at 300 ° C-400 ° C for 5 minutes.

In this case, the stages are excluded: heating the suspension for chemical treatment of waste threshing seeds, grinding the waste and separating the fine fraction, chemical treatment for 0.5-1.0 hours, the washing and drying stages. The supply of toxic nitrogen is excluded, and the exposure after heating is reduced to 5 minutes. Treatment with ammonium tetrafluoroborate capable of catalyzing the processes of polysaccharide structuring provides, during carbonization, an increase in the sorbent yield from 52.63% of the mass of the prototype to 70% of the mass of the inventive method and the creation of the sorbent pore size necessary for absorption of oil and oil products.

The method is as follows:

An aqueous solution of ammonium tetrafluoroborate is prepared. Mix 100 g of millet shells and 100 g of the prepared solution, providing a ratio of 1: 1. The wet mixture is placed in a furnace with programmed control of the rate of temperature rise in the furnace. Carbonize upon reaching the set temperature from 300 ° C to 400 ° C with exposure for 5 minutes. The structural parameters of the shell were evaluated on a NOVA 1200 e instrument.

The operational characteristics of the sorbent - the effectiveness of the sorbent - oil absorption, water absorption, buoyancy were determined according to TU 214-10942238-03-95. In tests, Grozny oil and motor oil were used.

In more detail the essence of the claimed invention is described by the following examples, table 1.

Example 1

A 25% aqueous solution of ammonium tetrafluoroborate is prepared (250 g of ammonium tetrafluoroborate is introduced into 750 g of water). Raise the temperature in the oven at a rate of 10 ° C / min. to 300 ° C and incubated for 5 minutes. The sorbent has a specific surface area of 17 m ² / g, pore volume 0.07 cm ³ / g, pore radius 15 A, water absorption 20%, sorbent yield is 70%.

Example 2

The method is carried out as in example 1.

A 30% aqueous solution of ammonium tetrafluoroborate is prepared.

Raise the temperature in the oven to 350 ° C. at a rate of 10 ° C / min.

The sorbent yield is 65%, water absorption 5%. Structural indicators: specific surface area of the sorbent - 77 m ² / g, pore volume - 0.74 cm ³ / g, pore radius - 80 A.

Example 3

The method is carried out as in example 1.

A 30% aqueous solution of ammonium tetrafluoroborate is prepared.

Raise the temperature in the oven at a rate of 15 ° C / min. up to 350 ° C.

The sorbent yield is 60%, water absorption 10%. Structural indicators: specific surface area 25 m ² / g, pore volume - 0.54 cm ³ / g, pore radius - 25 A.

Example 4

The method is carried out as in example 1. Prepare a 35% aqueous solution of ammonium tetrafluoroborate. Raise the temperature in the oven at a rate of 12 ° C / min. up to 400 ° C. The sorbent yield is 60%, water absorption - 12%. Structural indicators: specific surface area of the sorbent - 21 m ² / g., Pore volume - 0.52 cm ³ / g, pore radius - 60 A.

The choice of exposure time during carbonization is due to the fact that with exposure less than 5 minutes does not occur carbonization of the entire mass of the sorbent, and it turns out to be heterogeneous. When the exposure time is more than 5 minutes, the carbonized structure is destroyed, the pores necessary for sorption are destroyed. Thus, the optimum exposure time is 5 minutes.

The choice of carbonization temperature is associated with the peculiarity of chemical processes in cellulose-containing polymers during heating.

During the thermal decomposition of polysaccharides, as a result of the breaking of oxygen-carbon bonds, three main processes occur: dehydration, depolymerization, and then deep destruction. As a result of dehydration, conjugated unsaturated structures are formed, which form a carbonized residue during pyrolysis. Ammonium tetrafluoroborate due to the presence of fluorine and boron atoms in it, refers to a compound that catalyzes the dehydration process, while ensuring the yield behavior of carbon structures up to 60%, and at the same time, ammonium tetrafluoroborate completely decomposes during carbonization in the temperature range 300-330 ° C . Water vapor and gases released during the decomposition of ammonium tetrafluoroborate destroy the structure of the millet shell, contributing to an increase in porosity and the creation of the necessary specific surface and pore radius of the sorbent.

The experiment found that a temperature increase at a rate above 15 ° C / min increases the rate of decomposition of the millet shell, ammonium tetrafluoroborate and water evaporation and leads to intensification of the release of volatile products, which stimulates an increase in the pore radius to 8000 nm, and also reduces the mechanical strength of the sorbent, increases water absorption.

With slow heating of 5–9 deg / min, the duration of the process increases and the number of pores capable of absorbing sufficiently large oil molecules (A) decreases, which leads to a decrease in oil intensity. The duration of thermal exposure is 5 minutes so that the creation of an optimal sorbent structure is ensured. At the end of the heat treatment in isothermal conditions, the temperature drops to 60 ° C.

Thus, the use of the proposed method allows you to:

- reduce the number of technological operations from 5 to 2;

- reduce the time of thermal exposure by 5 times;

- reduce the overall duration of the process.

The listed advantages lead to a reduction in the cost of raw materials and energy, to an increase in the environmental safety of the production of sorbents due to the absence of a washing stage and, accordingly, the absence of wastewater and their regeneration process. The energy intensity of the process is reduced by eliminating the stage of the drying process and reducing the heat treatment time by 5 times.

Table 1 No. Prime
ra Process parameters Main characteristics Temp. ° C Conc.% Oil specific gravity, g / g The effectiveness of water purification from oil,% Specific oil absorption, g / g Buoyancy,% one 300 25 5.85 98.65 5.65 95.50 2 350 thirty 6.3 99.75 6.15 100.00 3 350 thirty 6.14 99.55 6.10 99.90 four 400 35 6.00 99.01 5.93 99.75 Proto
type of 400 16 5.80 98.45 5.69 99.32

Claims (1)

A method of producing a carbon sorbent from plant materials, including heating chemically treated plant materials to a temperature of 300-400 ° C at a rate of 10-15 ° C / min, followed by a temporary exposure and its carbonization, characterized in that millet seed shells are used as plant materials chemical treatment of which is carried out with an aqueous solution of ammonium tetrafluoroborate of a concentration of 25-35% in a ratio of 1: 1 simultaneously with carbonization, heating and temporary exposure for 5 minutes.