THE RESEARCH OF SORBENT PROPERTIES OF MODIFIED PEAT OF TOMSK REGION

THE RESEARCH OF SORBENT PROPERTIES OF MODIFIED PEAT OF TOMSK REGION

Research article

Martyniuk A.T.¹, Chuhareva N.V.²

^{1, 2} Tomsk Polytechnic University, Tomsk, Russia

Abstract

Extraction of different components (bitumen) from thermoprocessed up to 200-300°С peat puts the task of searching new alternative decisions of using the obtained remains. They can be used as cheap sorbent materials.

The aim of this research is to estimate sorbent properties of peat remains after the extraction bitumen from them.

Key words: peat, active coals, remains, burning degree, semicoking, thermoprocessed.

Experiments

The research was done on a sample of peat which features are given in Table 1.

Table 1.

The features of the sample (peat – transitional, pushitsevo-sphagnous, Bolshoe Pivovarovskoe Deposit, rate of decay (R)-25%).

Technical analysis of peat			Elemental analysis of peat, % per organic mass
Wa,%	Ad,%	Vdaf,%	C	H	N	O+S
6,71	6,59	69,40	52,94	5,17	2,05	38,48

Note: W^a – analytic humidity;  A^d – ash content per dry fuel; V^daf – output volatile components on fuel mass.

The peat was dried till air and dry condition. It was crushed for sifting0,25 mm. A peat of the sample was extracted using benzine BR-2 (remains 1-initial). The other part was preliminary heated up to the temperatures of 100, 150, 200 and 300°С in nitrogen. Further increasing the temperature for thermoprocessed peat according to [1] results in decreasing its sorbent properties. The speed of peat heating is 5 degrees/min. Component composition of thermoprocessed peat was found by using technique [2]. The results are in Table 2. While extracting with benzine BR-2, we obtained the remains 2-100, 2-150, 2-200, 2-250 and 2-300.

Table 2.

Component composition of the initial and thermoprocessed peat in nitrogen.

A sample of peat		The output of components, % per organic mass of the initial peat
		bitumen	WSS+EHS	HA	FA	C+NHR
The initial		3,4	35,9	33,7	11,1	15,2
Thermoprocessed up to the T, °С	100 150 200 250 300	3,9 4,0 4,2 4,6 3,2	35,5 62,8 60,0 48,7 17,5	33,0 32,1 29,8 27,7 10,8	10,5 10,4 9,8 9,2 5,9	16,3 17,0 17,1 17,7 43,5

Note: WSS - water-soluable substances, EHS - easy hydrolyzing substances, HA -humic acids, FA - fulvic acids, C - cellulose, NHR - not hydrolyzed remains.

Then we defined the density of the remains after the extraction: we measured the volume of exactly weighted samples according to the volume of the rock displaced by them at 20°С and we estimated the density on the basis of obtained data.

Active coals (AC) were obtained from the initial peat, remains 1, 2-100 – 2-300 using carbonization up to 600°С. To increase porosity of obtained particles of carbonic material, the studied AC samples were subject to activation by CO₂. According to [3], the range of 850-900°С was chosen as optimal temperature.

The carbonization of peat was done on the unit consisting of a chamber, an electric furnace, a graphite glass, a thermocouple contact, a water jacket, a trap, a refrigerator, a millivoltmeter. Activation of carbonized peat and remains was done on the unit consisting of a tank with CO₂, a tank with CaCl₂, a tank with silicagel, a rheometer, an electric furnace, 2 thermocouple contacts, a potentiometer, a reaction tube and gasometer.

Then the peat, the remains and the resulting active coals were studied to find adsorbent activity comparing with iodine according to State Standart 6217-74. Defining of specific surface was done using the technique of thermal desorption.

The results

The obtained experimental data about the output group components per organic mass of the initial peat within the temperatures 100-300°С are shown in Table 2.

The dependence of changes in the output of bitumen on the temperature of thermoprocessing the peat in nitrogen is as follows: while increasing the temperature of peat heating up to 250°С, the output of bitumen rises at 35,29% regarding the initial peat. It can be explained by a relative thermal stability of compositions which are contained in them and the decay of other peat components, confirmed by the figures about loss of its organic mass. Another reason for increasing the output of bitumen according to [4] can be the formation of groups of new substances – pyrobitumen which exist in a small temperature range and decay while forming liquid, solid and gaseous products. Further peat heating leads to reducing their output.

We can notice the same character of increasing the output of water-soluble substances within the temperatures of thermoprocessing the peat. Maximum value is for the peat heated up to 250°С.

Reverse dependence  is registered for the output easy hydrolyzing substances, humic acids and fulvic acids: increasing in temperature of heating peat in nitrogen up to 250°С results in reducing the content of these components comparing with the initial peat. Further temperature rise of preliminary heated raw materials up to 300°С results in spasmodic reducing the above mentioned components.

The obtained results of technical  analysis of the samples (Table3) show a deeper influence on the peat composition of preliminary heating in combination with extraction comparing with the remains 1-initial.

Table 3.

Technical analysis of the peat and the remains after extraction

An object of research	Wa,%	Ad,%	Vdaf,%
Remains 1-initial Ramains 2-100 Remains 2-150 Remains 2-200 Remains 2-250 Remains 2-300	7,87 5,66 5,39 5,02 4,90 4,16	8,18 9,59 10,00 10,12 10,10 10,69	69,53 68,12 65,41 63,00 61,00 59,40

The research of density of the peat samples remains after being extracted by benzine BR-2 showed the density of the 1-initial remain is 1,14g/cm³, while being within 0,42 g/cm³ for the initial peat. It corresponds to increasing the density 2,7 times having quite small change of sample masses.

Thermal modification of the peat from 100 till 300°С and its further extraction led to increasing the density to 3,5 times comparing with the initial sample. Further rise of temperature of peat heating doesn’t affect the change of density.

These results can be explained that the combination of methods of preliminary thermoprocessing the peat in nitrogen and further extraction of wax from it leads to significant compacting of the initial substance.

Adsorbent activity of the initial peat and the remains to iodine after extraction is within the range from 15,9 to 27,8%.

These differences in data don’t allow to make a specific conclusion about the effect of the temperature of thermal peat modification in combination with further extraction on adsorbent activity of the remains. Nevertheless, these results show significant changes of density and composition of the initial substance. It allows to use the remains after extraction as well as the initial peat as cheap natural sorbents of single use.

If we compare the results of adsorbent activity the initial peat and its remains to iodine with industrial active coals like decolorizing, we will obtain the average figure for them much higher being about 60%. Further carbonization and activation of all the samples allow to improve their adsorbent properties.

It is necessary to note a positive influence of thermal modification of the peat in nitrogen on dynamics of change AC properties from the remains comparing with AC from the initial material. Preliminary heating of the peat before extraction leads to increasing the adsorbent activity and specific surface of AC.

Preliminary thermoprocessing of the peat in nitrogen before semicoking leads to significant compacting  of the remains with a small loss of the peat mass. While further semicoking, as we can see, in these compact particles a large quantity of zonules appears activating  in micropores of AC. It is known that energy of adsorption in them is much higher than in macropores and transitional pores. It means that there is an adsorbent field in the total volume of macropores which defines their main role in adsorption of the peat AC. Formation of macrozones, probably, is connected with the extraction of wax which, in principle, is similar to famous popular processes of obtaining porous glass while lixiviating.

Conclusions

1. The initial peats and the remains of the peat after extraction with benzine BR-2 have small  adsorbent activity and can be use as cheap natural sorbents of single use.

2. The combination of preliminary thermal modification of raw materials from 100 to 300°С with step of heating 50°С and the speed of heating 5degrees/min in nitrogen and further extraction of raw wax from it improve the quality of obtained AC.

3. Maximum positive results of the rates of adsorbent activity and specific surface for AC obtained from thermalprocessed peat up to 250 and 300°С are obtained at burning degree 69%.

References

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