CC BY
17
74
AZ9RBAYCAN KIMYA JURNALI № 1 2016
UDC 661.21; 658.567; 669.054.8
STUDY OF ACTIVITY OF CATALYSTS SYNTHESIZED ON THE BASIS OF INDUSTRIAL WASTE IN THE REACTIONS OF REDUCING CH4/SO2 AND H2S/SO2
Y.B.Kahramanova, M.M.Ahmadov, S.T.Jafarova, A.I.Agayev
M.Nagiyev Institute of Catalysis and Inorganic Chemistry of NAS Azerbaijan
roma-fk@mail.ru Received 02.06.2015
In the paper the results of reduction (the Claus process) of sulfur dioxide with methane and hydrogen sulfide in the presence of new red mud bentonite (RMB) of synthesized catalyst are given. Optimal conditions of the process were determined: temperature of I reactor - 8500C, volume velocity - 1000 s-1; volume ratio of initial reagents CH4/SO2=0.5-0.6, temperature of II reactor - 2500C, volume velocity -500 s-1. Overall sulfur yield 95-97%.
Keywords: sulfur, catalyst, methane, sulfur dioxide, reduction, hydrogen sulfide.
Introduction
In non-ferrous metallurgy during pirome-tallurgical processing sulfide ores tonnes of sulfur dioxide are thrown into atmosphere that leads to pollution of ecology and destroys ecological balance in nature [1, 2]. Solution of utilization process of waste sulfur dioxide prevents the loss of valuable raw materials (elementary sulfur) and protects the environment.
As is known, production of elementary sulfur from waste sulfur dioxide is conducted in two main directions by using different reducers -high temperature (thermal) and low temperature (catalytic) methods [3, 4]. Thermal reduction of sulfur dioxide with methane is conducted at 1200-1300°C:
2SO2+CH4 =S2+CO2+2H2O. (1)
The Claus process - reduction of sulfur dioxide with hydrogen sulfide is conducted at 230-2500C:
2H2S+ SO2 =1.5S2+2H2O. (2)
In thermal reduction process of sulfur dioxide total yield of sulfur is not more than 7080% and several difficulties appear. Thus, stable construction materials are required for high temperature and aggresive medium, cooling and heating of gas mixture several times after reduction of SO2, obtaining of multiple additional products (COS, CS2, H2S), multi-stage process etc. Only from this point, conducting the reduction of SO2 with methane by using low temperature catalytic method is expedient.
By using active catalysts it is possible to
decrease the temperature of reduction process of sulfur dioxide with methane up to 750-8500C and to increase the yield of sulfur.
Active catalysts prepared on the basis of aluminium oxide, alumonickel, alumocobalt, natural zeolites (clinoptilolite, mordenite) are used in the production process of elementary sulfur from sulfurcontaining waste gases obtained in the processing of sulfide ores and these catalysts contain Fe, Ni, Co, Cr, Ti and other elements [5, 6].
During production of aluminium and processing of bauxite ore a great amount of ecologically hazardous red mud wastes are assembled. Considering that red mud contains empty rock and certain elements (Fe2O3 - 45.2, Al2O3 - 13.2, SiO2 - 10.8, TiO2 - 4.4, P2O5 -0.59, MgO - 0.73, Na2O - 6.0, K2O - 0.16%) it can be used as a catalyst.
For this purpose the catalysts have been prepared for both reduction of sulfur dioxide with methane from red mud and the Claus process.
Experimental part
Reduction of sulfur dioxide with methane and Claus process were conducted in laboratorial equipment. Analyses were performed by classic -chemical methods. First we prepared 2*2 mm cylindrical granules from red mud, it was dried within 24 hours in an open air, then calcinated at 1100C temperature in a drying chamber. Mechanical hardness of obtained granules was not
satisfactory, so we prepared granules by adding bentonite clays at different ratios (4, 6, 8, 10%) as "hardening" materials and their hardness was checked. It was determined that granules prepared from 10% bentonite clay containing red mud (RMB) is sufficiently hard. After detecting hardness of red mud we synthesized catalysts modified with Co, Ni, Cr. Cu et all elements by using red mud as a carrier by absorption method [7]. Synthesized catalysts were dried within 24 hours in an open air, calcinated at 1100C temperature in a drying chamber. After these catalysts decomposed salts separately in nitrogen flow at 2003 000C, they were made red-hot at 8000C. One of the factors influencing on reduction of sulfur dioxide with methane is a temperature mode. That's why we first studied temperature dependence of sulfur dioxide output. Reduction process of sulfur dioxide was conducted at 800-9000C temperature range, 1000 s- volume velocity of gas mixture, 20% density of SO2, CH4/S02=0.5 volume ratio of initial reagents. The results of experiments are given in the Table 1. As is seen from the Table catalysts activities modified by red mud bentonite and red mud differ
very little. The yield of elementary sulfur is found to be 23-46% at 8000C. When the temperature increases to 500C, reaction of methane with sulfur dioxide is considerably accelerated and at 8500C the yield of elementary sulfur increases and it is found to be 80%. Thus, we may consider the optimal temperature of reduction process of sulfur dioxide with methane to be 850 C. Analyses of experimental results show that activity of RMB catalyst is not less than modified catalysts and even more than some of them. Therefore further experiments were conducted with the presence of RMB catalyst.
High conversion degree of sulfur dioxide dependes on storage duration of initial reagents in catalyst zone. In this connection we studied the dependence of volume velocity of gas mixture on reduction of sulfur dioxide with methane in the presence of RMB. Condition of experiment: temperature of the process - 8500C, volume ratio of initial reagents CH4/S02=0.5, volume velocity of gas mixture 500-2000 s-1. The results of dependence of yield of elementary sulfur and hydrogen sulfide on volume velocity of gas mixture are given in Fig. 1.
Table 1. Comparative results of reduction of sulfur dioxide with methane (volume ratios of initial reagents CH4/S02=0.5, volume velocity of gas mixture 1000 s-1). *RMB - red mud+10% bentonite catalyst_
Catalyst Temperature, 0C Distribution of sulfur in reaction products, %
S H2S SO2
800 22.9 3.6 73.6
s) RMB 850 76.1 7.3 16.6
900 70.2 11.5 18.3
800 32.3 3.5 64.2
RMB + 9%NiO 850 69.4 7.6 23.0
900 79.5 10.4 11.1
800 41.7 4.6 53.7
RMB + 9%CoO 850 78.1 11.6 10.3
900 80.5 12.9 6.6
800 46.1 5.5 48.4
RMB + 9%CuO 850 77.8 13.5 8.7
900 73.0 15.1 11.9
800 23.1 2.6 74.3
RMB + 9%Cr2O3 850 71.9 8.9 19.2
900 69.0 11.7 19.3
800 55.4 7.2 27.4
Y-AI2O3 850 75.7 8.2 16.1
900 74.1 9.5 16.4
.s 60
40
К
20 -
Figure 1. Dependence of yield of sulfur and hydrogen sulfide (a) on volume velocity of gas mixture (t -
8500C; CSo2 - 20%; CH4/S02=0.5;
catalyst - RMB).
500
1000
1500
2000
V, s1
As is seen from the figure when volume velocity increases, yield of sulfur and hydrogen sulfide decreases. If the yield of elementary sulfur is maximum 85% in 500 s-1 volume velocity of gas mixture, yield of sulfur in 2000 s-1 volume velocity is found to be 53%. Yield of hydrogen sulfide decreases from 16% to 3%. Considering the yield of elementary sulfur to be 85-76% in 500-1000 s-1 volume velocity of gas mixture, then this volume velocity interval may be accepted as optimum.
Further experiments were devoted to studying the impact of CH4/S02 volume ratio of initial reagents on reduction of sulfur dioxide with methane. The dependence of yield of sulfur and hydrogen sulfide on volume ratio of initial reagents was studied at 8500C, V - 1000 s-1
volume velocity of gas mixture, CH/S02=0.4-0.8 volume ratio of reagents. The results are given in Fig. 2. As is seen from the figure in CH4/S02=0.4 volume ratio of gas mixture reagents the yield of elementary sulfur is less than 40%. When the amount of a reducer in gas mixture increases, the yield of sulfur in reaction solutions considerably rises and when volume velocity is CH4/S02= 0.5-0.6, the yield of sulfur is found to be 76-80% correspondingly.
Further increase in reducer causes decreasing the amount of sulfur in reaction solution and rises the yield of hydrogen sulfide. According to the results from Fig. 2 we may state that optimum volume ratio of initial reagents in reduction process of sulfur dioxide with methane is found to be CH4/S02=0.5-0.6.
80
^ 60
и 40
Д
и
e" 20
0.4
0.5
0.6 0.7 CH4/SO2
0.8
Figure. 2. Dependence of the yield of sulfur and hydrogen sulfide (a) on volume ratio of CH4/SO2 (t - 8500C; Cso2 - 20%; V - 1000 s-1; catalyst -RMB).
The results of experiments show that in the reduction of sulfur dioxide with methane the yield of elementary sulfur at high volume velocity of gas mixture is not satisfactory. The reason is that hydrogen sulfide prevents production of elementary sulfur in one stage. On the other hand, due to the partial conversion sulfur dioxide which did not undergo the reaction, remains in reaction solutions. That's why production process of elementary sulfur from sulfur dioxide must be conducted in two stages. At the first stage obtaining of sulfur, hydrogen sulfide and sulfur dioxide, at the second stage production of sulfur after condensing and then separating obtained sulfur by Claus process. At the second stage (Claus process) to achieve maximum sulfur output, volume ratio of H2S/SO2 in reaction solutions at the first stage must be 2. When investigating the reduction of sulfur dioxide we studied volume ratios of initial reagents and results are given in Figure 2. As is seen from the figure H2S:SO2 = 2:1 stoichiometric amount is achieved in 0.650.70 limit of CH4/SO2 ratio.
The Claus process was studied in detail and widely used in industry. In this process the catalysts which were mofidied with bauxite, alumocement, aluminium oxide and transition elements, were used.
In the work we studed the activity of red mud bentonite and modified catalysts (in the Claus process). Experiments were conducted at 2500C temperature, 1000 s- volume velocity of
gas mixture, CH/SO2=0.65-0.70 volume ratio of initial reagents and 20% density of sulfur dioxide. Results of experiments are given in Table 2. As is seen from the table activity of catalysts modified on the basis of red mud bentonite and Co, Ni, Cr, Cu elements, differs very lightly. Overall output of elementary sulfur is 86.5-90.5%. according to experiments we may state that by using red mud as a carrier there will be no need to prepare catalysts which were modified by above mentioned metals, because since overall output of sulfur for RMB is 90.5%, it is found to be 86.590.0% for the rest. For this reason, further experiments have been conducted in the presence of RMB catalyst.
In Claus process we studied the impact of volume velocity of gas mixture on overall output of sulfur. Experiments were performed at 2500C temperatue of reactor, CH4/SO2=0.65-0.70 ratio of initial reagents, 500-2000 s-1 volume velocity of gas mixture.
Analyses of experimental results show that at 500 s-1 volume velocity of gas mixture conversion of sulfur dioxide goes fully and causes the increase of amount of hydrogen sulfide and overall output of sulfur is found to be 95.0-97.0%. 2000 s-1 volume velocity of gas mixture causes the increase of amount of sulfur diocide and hydrogen sulfide in reaction solutions and overall yield of sulfur decreases up to 74.0-75.0%, and amount of hydrogen sulfide increases up to 4.0-5.0%.
Table 2. Comparative results of activities of catalysts prepared on the basis of red mud in Claus process (CH4/SO2= 0.65-0.70; H2S:SO2=2, volume velocity of starting gas mixture F=1000 s-1)_
After I reactor After II reactor
Tempe- Distribution of S in Tempe- Distribution of S in
Catalyst rature, reaction products, % Catalyst rature , reaction products, %
0C S H2S SO2 0C S H2S SO2
850 79.6 13.8 6.6 RMB 250 90.5 6.5 3.0
850 80.7 13.5 5.8 RMB+9%CuO 250 89.0 7.3 3.7
RMB 850 80.0 15.5 4.5 RMB+9%Cr2O3 250 90.0 8.0 2.0
850 77.0 14.5 8.5 RMB+9%CoO 250 86.5 8.2 5.3
850 80.6 12.9 6.5 RMB+9%NiO 250 89.7 4.9 5.4
Results
1. Thus, according to the results we synthesized high catalytically active RMB catalyst from red mud which was obtained in the production of easily obtained and cheap aluminium and tested in both stages (I - temperature -8500C, CH4/SO2; II - H2S/SO2 Claus process) of sulfur production and it was determined that it has a sufficient high activity
2. We have developed an optimum condition for reduction process of sulfur dioxide with the methane in the presence of red mud bentonite catalyst: temperature - 8500C; volume velocity - 1000 s-1; volume ratio of initial reagents CH4/S02=0.5-0.6; after I reactor output of sulfur is found to be 76.0-80%.
3. We determined an optimum condition for Claus process in the presence of red mud bentonite catalyst: temperature - 2500C; volume velocity - 500 s-1; volume ratio of initial reagents CH4/S02=0.65-0.7; overall yield of sulfur is found to be 95-97%.
References
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SONAYE TULLANTISI OSASINDA SlNTEZ OLUNMUÇ KATALlZATORUN CH4/SO2 va H2S/SO2 REDUKSIyASI REAKSIyALARINDA AKTlVLlYlNlN TODQlQl
Y.B.Qahramanova, M.M.Ohmadov, S.T.Cafarova, A.l.Agayev
Sintez etdiyimiz katalizatorun yeni qirmizi çlam bentonit (Q§B) içtiraki ils kükürd dioksidin metan va hidrogen sulfidla reduksiya (Klaus proses) proseslarinin naticalari verilmiçdir. Prosesin optimal çaraiti müayyanla¡jdirmi¡jdir: I reaktorun temperaturu - 8500C, hacmi sürati - 1000 s-1; ilkin reagentlarin hacm nisbati CH4/SO2=0.5-0.6; II reaktorun temperaturu - 2500C, hacmi sürati - 500 s-1. Ümumi kükürdün çiximi 95-97% taçkil etmiçdir.
Açar sözlar: kükürd, katalizator, metan, kükürd qazi, reduksiya, hidrogen sufid.
ИССЛЕДОВАНИЕ АКТИВНОСТИ КАТАЛИЗАТОРА, СИНТЕЗИРОВАННОГО НА ОСНОВЕ ОТХОДА ПРОИЗВОДСТВА В РЕАКЦИЯХ ВОССТАНОВЛЕНИЯ CH4/SO2 и H2S/SO2
Е.Б.Гахраманова, М.М.Ахмедов, С.Т.Джафарова, А.И.Агаев
Приведены результаты экспериментальных исследований процесса восстановления диоксида серы сероводородом и метаном (процесс Клауса) на синтезированном нами новом катализаторе - красный шлам бентонит (КШБ). Найдены оптимальные условия данного процесса: температура реактора I - 8500С, объемная скорость -1000 ч-1, соотношение исходных компонентов - 0.5-0.б; температура реактора II - 2500С, объемная скорость -500 ч-1. Общий выход серы составил 95-97%.
Ключевые слова: сера, катализатор, метан, сернистый газ, восстановление, сероводород.
