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UDC 661.21; 658.567; 669.054.8
DEVELOPMENT AND STUDY OF PROPERTIES OF CONTACT MASSES
ON THE BASIS OF RED MUD
S.T.Jafarova, E.B.Gahramanova, A.I.Agayev, M.M.Ahmadov
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS ofAzerbaijan
[email protected] Reseived 19.05.2016
The prospects of using wastes of alumina industry - red mud as contact masses for utilization of sulphur containing gases have been studied. The properties of contact masses prepared on the basis of red mud and layered montmorillonite - bentonite (natural) have been researched. Primary material has been studied using physico-chemical methods of analysis. Optimum composition of contact mass, conditions of their thermal processing have been determined. It was established that clay leads to considerable increase of mechanical characteristics of contact masses comparing to pure red mud. Granulated samples have been tested in reduction processes of sulphur dioxide with methane and hydrogen sulphide and their high activity has been shown.
Keywords: red mud, bentonite, sulfur dioxide.
Presently human activity has been quite developed that involves a considerable amount of industrial wastes [1]. Obtaining of alumina is involved in the formation and accumulation of large amount of by-product - red mud (RM). During production of alumina by Bayer process 1 ton of RM are formed from 1 ton of primary raw material (bauxite). Growth rate of production of aluminum causes the increase in the formation of a waste. According to WBMS world's consumption of aluminum has risen up to 6.7% in 2015. Inthematerials of International Aluminum Institute it is stated that production of initial aluminum in the world for the first quarter of 2016 made up 13.778 million tons. This leads to the increase of formation of byproduct - RM and present the problem of its utilization more sharply. Analysis of scientific literature data shows that the data on processing of RM in the amount comparable with of their yield is practically absent, that is related to difficult complex of their physico-chemical properties. The solution of this problem promotes expansion of utilization of products obtained on the basis of it.
Researches show prospects of using RM in construction industry, agriculture and metallurgy [2-4]. The use of it as catalyst forming mass for different processes is also prospective. Thus on the basis of RM the effective catalysts are prepared for thermal catalytic decomposition of carbon monoxide [5], conversion of
carbon monoxide and methane [6].
It is known that RM contains a considerable amount of iron oxides (up to 55%) which is comparable to iron oxide in iron ores of average quality. Besides, there are significant amount of titanium oxides, a lot of aluminum Al203. That's why the preparation of catalyst for contact masses on the basis of it is technically expedient for purification of sulphur containing exhaust gases, since the composition of RM is comparable to the composition of effective industrial adsorbents and catalysts for these processes.
The aim of present work is to create contact masses on the basis of RM and study of their properties. For achieving this aim we studied the influence of component composition on physico-mechanical properties of obtained masses, as well as catalytic properties of contact masses with optimum composition were studied in reduction reactions of sulphur dioxide with methane and hydrogen sulfide.
Experimental part
Materials. In the work we used: RM -waste of aluminum complex DETAL (Azerbaijan, Ganja), bentonite (B) of the plant "Azer-bentonite".
Devices. Mineralogical composition of primary materials was determined on diffract-tometer "D2 Phaser" "Bruker" (Germany) (CuXa-irradiation, X=1.54 Á, nickel filter).
Thermo stability of samples was studied on de-rivatograph STA 449 F3 Jupiter of company NETZSCH (Germany).
Activity. Catalytic activity of catalysts samples was studied on laboratory installation, the scheme of which is presented in Figure 1. During the reduction process of sulphur dioxide
Results and discussion
Performance of deep researche sof primary wastes with the aim of selecting optimum method of the irpreparation is necessary for creation of high-efficiency catalysts on the basis of industrial wastes.
It is known that chemical composition of bauxites varies in wide ranges both in different deposits and in the range of one deposit as well as their compositions and properties may change from year to year and influence on the content of waste - RM.
In this connection for preparation of catalyst for ming masses we used samples of current and 20 years of production. Accordingly [5], minerals containing iron, titanium oxide, carbonates basically concentrated in samples of RM of current production in small fractions (0.01 mm), focused on larger classes.
Chemical composition on basic components of used samples is given in Table 1.
Table 1. ^ Chemical composition of samples of RM, weight %
№ samples Fe2O3 Al2O3 SiO2 TiO2 P2O5 MgO zr2O
Na2O K2O
1 45.2 13.2 10.8 4.4 0.59 0.73 6.0 0.16
2 45.82 24.6 5.8 4.82 - - 3.1
Table 1 shows that on basic components RM consists of iron and aluminum and oxides of waste rock (SiO2, TiO2 and others). It should be noted that oxides of alkali and alkali earth
with methane we used a part of installation, which is marked in the scheme by the field I. The other field II in the scheme conforms to obtaining process of sulphur with full technological scheme including one stage of Claus process. Activity of samples was determined by the yield of elementary sulphur.
Fig. 1. Installation chart for studying catalytic properties of samples: 1 - balloons, 2 - needle valves, 3 - rheometers, 4 - mixer, 5 - furnace, 6 - reactors, 7 -sulphur condenser, 8 - potentiometer, 9 - thermo couple, 10 - trap with solution NaOH.
metals, as well as SiO2 in RM can correct the properties of contact masses in the process of preparation.
Mineralogical composition of RM is very complex like processed bauxites, however the value of minerals has the following minerals: hematite, boehmite, diaspora, caolinite and others. Results of X-ray phase analysis of RM samples are given in Figure 2.
The influence of temperature change on RM samples is given in the Figure 3.
Interpretation of results of derivato-graphic studies shows that in the range of 140-2800C we observed mass loss of 6.70% which is conditioned by dehydration. Endothermic effect with maximum at 2320C conforms to it.
Thus, the study of the RM samples shows that on basic components its composition varies within the permissible limits. Besides, it was established that considerable effects in heating process of the samples is not observed. Correspondingly, adsorbents and catalysts with optimum properties can be prepared on the basis of it.
For preparation of catalyst samples we selected a method which differs with simpli city and availability of devices. Since characteristic property of RM is extreme dispersity then for obtaining of catalyst samples we used a method of mechanical "dry" mixing of all components of catalysts [7].
Fig. 2. X-ray phase analysis of RM samples: 1 - Fe2O3 (Hematite), 2 -Na6CaAl6Si6(CO3)O24^2H2O (Can-crinite), 3 - Fe2TiO5 (Pseudobro-okite), 4 - SiO2 (Tridymite), 5 -SiO2 (Quartz), 6 - FeSiO3 (Ferro-silite), 7 - AI2O3 P-AI2O3 (Aluminium oxide).
ТГ/% ДТА /(мкБ/мг)
Те мператураГС
Fig. 3. Results of derivatogra-phic studies of RM samples.
This method is based on mixing dry components with simultaneous humidifying of a mixture. Both water and different acids like sulphuric, nitric and other acids can be used as humidifying substances. To add contact mass a number of specific properties we used drying product of fine grinding of bentonite clay (natural) - nanoclay (product of the plant "Azerbentonite"). It should be noted that this plant uses natural clay from Dash-Salahly deposit (Azerbaijan), which has large industrial reserves - 86 million tons.
To prepare catalytic mass with optimum properties, ratio of primary materials: RM and bentonite, porophore were varied in a wide range.
To prepare the samples of catalysts using additional components they were put into burden during mixing for the formation of granules. As a porophore we used activated charcoal. Catalytic mass was formed using extrusion technique by pressing the mass. 2-5 mm granules were obtained. To increase estability and final formation of the structure of catalyst granules we used
thermal processing. Piercing mode was the following: it was dried at room temperature for 24 hours, then at 1100С in drying board for 3 hours, after that it was pierced in muffle furnace at different temperatures up to 6500С with gradual increase of temperature with delay at each temperature for 2 hours. Properties of prepared samples are given in Table 2.
Analysis of mechanical properties of contact masses showed that just introduction of small amount of clay (2%) increases already density up to 10.8 MPa. Growth of density, probably, is related to good dispersability of a small amount of clay between fine dispersed particles of RM. The most preferred sample is this sample with 10 mass% bentonite (18.7 MPa) piercing of which exceeds the density up to 23.7 MPa, probably, due to the interaction of components. Such density remain almost son the same level (24.2 MPa) till the content of 20 mas.% of clay. Thus, the annealed samples, with amount of bentonite of samples show the best properties which containing 10 and 20 mas.% of bentonite.
Table 2. Main physico-chemical characteristics of samples of catalysts depending on different factors
No samples Form of binding substance Saturated density, g/cm3 Temperature of thermal processing, 0C Amount of binding substance, mas. % Amount of porophore, mas. % Limit of density, MPa Pore volume, 3 / * cm /g LOSS, on calcination %*
1 - 1.18 600 - - 3.4 - 3.23
2 bentonite 1.027 110 2 - 10.82 - -
3 bentonite 1.032 110 6 - 17.9 - -
4 bentonite 1.064 110 8 - 17.07 - -
5 bentonite 1.093 110 10 - 18.75 - 3.17
6 bentonite 1.10 450 10 - 23.75 0.407 3.11
7 bentonite 1.12 600 20 - 24.2 0.397 3,02
8 bentonite 1.14 650 10 1.5 21.25 0.358 4.63
9 bentonite 1.13 650 10 3 17.5 0.382 3.79
10 bentonite 1.045 650 10 7 16.25 0.385 4.25
11 bentonite 1.012 650 10 12 15 0.442 4.69
12 Na2Si039H20 1.04 600 10 - 5 0.285 3.98
* dash means that these parameters have not been determined.
Addition of layered montmorillonite -clay to the composition of samples also promotes preservation of the structure of samples during heating, since addition of nanoclay acts as a barrier for volatile product, for example, aqueous steams, which are formed during heating. For investigation of effect of binding substance we used synthetic material -sodium silicate. This is a sample 12.As it is seen this sample has low density (5 MPa), unlike the samples containing bentonite. Thus, results of these investigations showed that properties of contact masses and their structure depend on intra phase interactions on the border of phase interface. Addition of activated charcoal into the samples leads to decrease of density due to the growth of pore volume. Such tendency is observed in parameters of density in samples when the amount of clay in them increases. This has an important value when using catalysts directly in the processes.
Obtained results show that the samples of contact masses prepared on the basis the RM with additions of nanoclay differ from primary RM with essential improvement of a number of indictors.
Catalytic properties of prepared samples of RM - bentonite (RMB) were studied in reduction reaction of sulphur dioxide with methane and hydrogen sulphide for obtaining elementary sulphur as a valuable product. Optimum conditions for these reactions using
RM - bentonite sample as a catalyst were investigated by us earlier and presented in the works [8, 9]. Earlier we investigated the properties of RMB in these reactions, but systematical researches on development of optimum structural-mechanical properties of the catalyst as well as influence of several factors on the activity in processes have not been performed. Optimum conditions for reduction of sulphur dioxide are the followings: with methane - temperature 8500C, CHVS02=0.5-0.6; with hydrogen sulphide - temperature 2500C, CH4/S02=0.65-0.70.
In this work we presented the results of effect of concentration of sulphur dioxide on temperature dependence of sulphur distribution in products of the reaction during reduction of sulphur dioxide with methane (Figure 4), as well as thein fluence of gas load on the catalyst during obtaining of sulphur by full technological scheme including one stage of Claus (Figure 5).
Concentration of sulphur dioxide in the composition of exhaust gases varies depending on sulphuric gases sourcein to atmosphere, as well as during input on catalyst in a certain limit from one source. As Figure 4 shows increase in concentration of sulphur dioxide in initial gas promotes growth of yield of sulphur that is explained by Le Chatelier principle and decrease of yield of by-products.
Fig.4. Temperature dependence of sulphur yields at volume rate of gas mixture w=1000 h-1 and CH4/S02=0.5; 1,2,3 - concentration of S02=30-32%, 1',2',3'=20-24% in products of reaction; in primary gas: 1,1' - S, 2,2' - H2S, 3,3' -S02; R2 - coefficient of reliability of approximation
During studying the properties of catalysts the effect of piercing temperature of catalyst samples on the activity is of an important value. In the present work in found optimum conditions in [8] for reduction of sulphur dioxide with methane we investigated the dependence of activity of the sample No 6 on temperature of its piercing. For studying this influence this sample of RMB was pierced at different temperatures: 450, 600 (at air stream) and 9000C (in muffle furnace) and studied in reduction process of sulphur dioxide with methane at temperatures 850-9000C and CH4/S02=0.5. First two samples showed identical activity in reduction reaction of sulphur dioxide with methane (72-75%), while the samples pierced at 9000C for 4 hours and after 4 hours of processing in stream of reaction medium showed activity 3-5% lower, that is, probably, explained by slight sintering of a catalyst under these conditions.
After the first stage of reduction gas mixture enter the second stage of reduction,
where Claus reaction takes place, i.e. interaction reaction between H2S+C0S and S02. The composition of gas, entering to Claus knot is the following: hydrogen sulphide - 13.16-13.8, sulphur dioxide 6.58-6.6, carbon oxysulphide -0.9-0.11, hydrogen - 0.90-1.2, carbon monoxide - 1.94-2.3. The ratio (H2S+C0S)/S02 was equal to 2.1. Effect of gas load on the property of a catalyst was studied. Results of investigations are given in the Figure 5.
Increase of gas load on catalyst from 500 to 2000 h-1 during reduction of sulphur dioxide by full technological scheme including one stage of Claus considerably decreases the yield of end product. 0ptimum gas load can be considered 500-1000 h-1.
0btained results shows that samples of catalyst RMB show high activity during reduction of sulphur dioxide, yield of sulphur during reduction by full technological scheme makes 96.8-89.6% at 500 and 1000 h-1, correspondingly.
Figure 5. Dependence of yield of sulphur on volume rate of gas mixture: A - CH4, o - H2S.
Results of investigations showed that samples of catalyst with optimum physical-chemical properties can be obtained from the waste of aluminum production - RM and layered montmorillonite - bentonite using mechanical "dry" mixing with humidifying and following formation and thermal processing. This preparation technique is easily realized and does not require expensive materials.
Thus, analysis of experimental materials shows that red mud can be successfully used for obtaining catalytic masses which can be widely applied as catalysts and adsorbents for certain processes.
References
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8. Kahramanova Y.B., Ahmadov M.M, Jafarova S.T, Agayev A.I. Study of catalysts synthesized on the basis of industrial wastes in CH4/SO2 and H2S/SO2 reactions// Azarb. kimya jurnali. 2016. № 1. S. 74-78.
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QIRMIZI §LAM OSASINDA KONTAKT KÜTLOLORiN ͧLONMOSÍ VO ONLARIN
XASSOLORÍNÍN TODQÍQÍ
S.T.Cafarova, Y.B.Qahramanova , A.I.Agayev, M.M.Ohmadov
Qil-torpaq istehsalinin tullantisi olan qirmizi ¡jlamin kontakt kütlalar kimi kükürd tarkibli qazlann utilizasiya proseslarinda istifada olunmaginin perspektivliyi nazardan kegirilmi§dir. Qirmizi §lam va layli montmorillonit- bentonit (tabii) asasinda hazirlanmi§ kontakt kütlalarin xassalarinin tadqiqi apanlmi§dir. Xammal fiziki-kimyavi üsullarla tadqiq edilmi§dir. Kontakt kütlalarin optimal tarkibi va onlann termiki i§lama §artlari müayyan edilmi§dir. Malum olunmu§dur ki, kontakt kütlalarintarkibinda gilin olmasi kontaktlann mexaniki xüsusiyyatlarini tamiz qirmizi §lamla müqayisada xeyli artmasina gatirib gixanr. Granul §aklinda formala§dinlmi§ nümunalar kükürd dioksidin métanla va hidrogen sulfidla reduksiya proseslarinda sinaqdan kegirilmi§ va yüksak aktivliya malik olmalan müayyan edilmi§dir.
Agar sözlar: qirmizi §lam, bentonit, kükürd qazi, kükürd.
РАЗРАБОТКА И ИССЛЕДОВАНИЕ СВОЙСТВ КОНТАКТНЫХ МАСС НА ОСНОВЕ
КРАСНОГО ШЛАМА
С.Т.Джафарова, Е.Б.Гахраманова, А.И.Агаев, М.М.Ахмедов
Рассмотрены перспективы использования отходов глиноземного производства - красного шлама в качестве контактных масс для процессов утилизации серосодержащих газов. Исследованы свойства контактных масс, изготовленных на основе красного шлама и слоистого монтмориллонита - бентонита (природного). Исходный материал исследован физико-химическими методами анализа. Определен оптимальный состав контактной массы, условия его термической обработки. Установлено, что наличие глины приводит к значительному возрастанию механических характеристик контактных масс по сравнению с чистым красным шламом. Гранулированные образцы испытаны в процессах восстановления диоксида серы метаном и сероводородом и показана их высокая активность.
Ключевые слова: красный шлам, бентонит, сернистый газ, сера.
