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10Journal of Siberian Federal University. Chemistry 2 (2010 3) 104-109
УДК 542.97; 665.612.2; 546.264-31
Carbon Dioxide Conversion of Real Associated Gases in Presence of Water Over the KMR-8 Catalyst
Sholpan S. Itkulova and Gaukhar D. Zakumbaeva*
D. V. Sokolsky Institute of Organic Catalysis & Electrochemistry 142 Kunaev st., Almaty, 050010 Republic Kazakhstan 1
Received 4.06.2010, received in revised form 11.06.2010, accepted 18.06.2010
The new supported zeolite-containing catalyst has been investigated in the reaction of interaction between carbon dioxide and real associated petroleum gases (APG) in presence of water steam at varying experiment temperature within a range of300-900 °C and space velocity from 1000 to 6000 hr-1. It has been shown that the catalyst performs the high activity in reforming of APG. At 800 °C, the complete conversion of C2+ hydrocarbon fraction is occurred, degree of methane conversion gets 92.2 and carbon dioxide conversion - 93.4 %.The main product of reaction is synthesis-gas (mix of carbon oxide and hydrogen) with a ratio of H2/CO=1.4 at 800 °C. Also water and traces of oxygenates (basically acetic acid) are produced at T < 600 °C. The catalyst works with practically the same activity at increasing space velocity by 4 times. The advantages of the synthesized catalyst are its activity, selectivity, stability, ability to work in water presence, and resistance to coke formation.
Keywords: carbon dioxide conversion, associated gases, synthesis-gas.
Introduction
Associated petroleum gas (APG) is still burned in Kazakhstan. Kazakhstan ranks the fifth place on amount of burned APG (Russian Federation is in the lead). Information on total amount of burned gases in Kazakhstan is not complete and has an inconsistent character. In 2008 according to the official data the gross output was 33.5 bln. m3 at that volume of burned associated gases was decreased to 1.8 bln. m3 [1].
From 25 to 1000 m3 of associated gases is extracted at producing 1 ton of oil at the Kazakhstan's oil and oil-gas condensate fields. In a best case they are squeezed into oil reservoir. This approach does not solve the problem of
* Corresponding author E-mail address: itkulova@nursat.kz
1 © Siberian Federal University. All rights reserved
utilization of associated gases. Moreover as a rule it leads to raising the gas amount at the following oil extraction and increase in cost for re-squeezing.
At APG combustion, the high value hydrocarbon raw material is aimlessly burned that is accompanied with carbon dioxide and hazardous sulfur and nitrogen oxides formation. Carbon dioxide among these anthropogenic gases is a main greenhouse gas. The amount of carbon dioxide formed exceeds twice the amount of burned fuel.
Obviously that burning of APG is unacceptable from a point of view of environment protection and resource-saving. One of decisions
of this problem is creation of infrastructure for APG collection, their transportation, purification, separation, and squeezing into main pipe line that requires the huge investments [2].
Other way is processing of APG into motor fuel, methanol, and other high value products directly at the oil fields [2-4]. The light hydrocarbons in composition of APG can be converted into liquid products by so called GTL process (Gas-To-Liquid) [4], and also they can be a source for hydrogen production [5]. The GTL process has been considered as a clean and alternative process in an environmental respect.
Light hydrocarbons can be converted into syngas. Syngas, a mixture of H2 and CO is a major feedstock for methanol, ammonia and Fischer-Tropsch (F-T) synthesis. There are three main catalytic ways for syngas production from hydrocarbon feed with involving: 1) water -steam reforming (equationl), 2) half oxygen -partial oxidation (equation2); and 3) carbon dioxide - dry reforming (equation 3). The last one attracts interest because of allows utilizing greenhouse gases - methane and carbon dioxide with producing syngas with a ratio of H2/CO = 1 [6-10].
CH4 + H2O ^ CO + 3H2 CH4+1/2O2 ^ CO + 2H2
(eq.1)
(eq.2)
CH4 + CO2 ^ 2CO + 2H2 (eq. 3)
Also the combination of these methods is possible. For example, combined steam and carbon dioxide reforming of methane is a suitable process for the direct control of the H2/CO ratio by regulating the H2O/CO2 feed ratio [11]. This process allows using the real petroleum gases
containing water and carbon dioxide without their extraction and drying.
The aim of this study was the development and test of the new catalyst - KMR-8 for converting the real associated gases by involving into the process carbon dioxide in presence of water (carbon dioxide - steam reforming or bi-reforming).
Experimental
The catalyst - KMR-8 with total metal content - 5 weight % supported on alumina promoted with zeolite has been synthesized and tested in conversion of real associated gases (APG) from one of the Kazakhstan's oil field. The reforming of APG by carbon dioxide at presence of water (bi-reforming process) was carried out in a flow quartz reactor at atmospheric pressure and varying experiment temperature from 300 to 900 °C and space velocity from 1000 to 6000 hr1. The catalyst loading was 10-30 mL. Ratio of CO2:APG:H2O was constant - 1:1:0.1.
The composition of associated gases extracted from one of oil wells of the West Kazakhstan is presented in Table 1.
The set was combined with gas chromatographs (GC) equipped with thermal conductivity detector for on-line analysis of H2, Ar, CO, CH4, 02, C02 (columns: molecular sieves and activated coal) and flame-ionization detector (FID) for on-line analysis of hydrocarbons (column: modified alumina). Liquid phase was collected in a special cooled trap (separator) and then analyzed by GC equipped with FID on columns: Carbowax/Carbopak and Poropak N, as well as by IR-spectroscopy. The carbon formation was controlled by thermogravimetric
Table 1. Hydrocarbon composition of real associated gas extracted from one of oil well of the West Kazakhstan
Hydrocarbons C1 C2 C3 C4 C5 C6 C7
Content, vol. % 52.1 20.1 14.0 8.1 4.4 1.1 0.2
100
80
c o w
(D >
c o
O
60
40
20
0
200 300 400 500 600 700 Temperature, oC
-♦—K(CH4) K(C2H6) K(C3H8) K(C4H10) K(C5H12) K(C6H14) K(C7H16) -K(C02)
800 900
Fig. 1. Effect of temperature on conversion degree of hydrocarbons and CO2 at bi-reforming of associated gases over the KMR-8 catalyst
analysis (TGA), thermo-programmed reduction (TPR) and electron microscopy.
The catalyst was studied with using BET, IR-spectroscopy and electron microscopy.
Results and disscussion
The hydrocarbons are converted with noticeable activity in carbon dioxide - steam reforming (bi-reforming) over the KMR-8 catalyst already at T=300 °C. Under these conditions, the C7 hydrocarbons (heptanes) are completely converted, the conversion degree for C6 (hexane) is 96.7, C5 (pentane) - 94.5, C4 (butane) - 66.7, C3 (propane) - 36.5, C2 (ethane) - 3.5, Q (methane) -9.2 and carbon dioxide - 17.1 %. Increase in temperature is accompanied with raising conversion degree of all initial components as it shown in Fig. 1. The hydrocarbons with higher molecular weight are converted first. For example, if the 100 % conversion of pentane is occurred at 550 °C, ethane is completely converted at 800 °C (Fig. 1).
Methane and carbon dioxide are not completely converted within temperature region of 300 - 800 °C. With temperature increase the
conversion degrees of CH4 and CO2 are increased from 9.2 to 92.2 and from 17.1 to 93.4 % respectively (Table 2).
The main product of APG conversion by carbon dioxide is syngas. The formation of hydrogen is occurred at 300 °C while carbon oxide is produced at higher temperature - 400 °C. The total yields of hydrogen and carbon oxide are constantly grown with increase in conversion of hydrocarbons. At lower temperature -400 °C syngas is reached with hydrogen. In temperature region of 450-600 °C the yield of hydrogen and carbon oxide becomes relatively equal and ratio of H2/C0=0.9-1. At higher process temperatures 650-800 °C, the hydrogen production is prevailed and maximum ratio of H2/CO=1.4 is observed at 800 °C.
Except synthesis-gas traces of oxygenates are formed over the KMR-8 catalyst at bi-reforming of APG at T< 600 °C. Acetic acid is prevailed among them. There is no oxygenates at higher temperature - 800 °C (Table 3).
The effect of space velocity on the process of APG conversion has been studied. The conversion degree of methane is slightly decreased from 98.9
Table 2. Effect of temperature on bi-reforming of associated gases over the KMR-8 catalyst (APG /C02 / H20=1/1/0.1, P= 1 atm, space velocity - 1500 hr1)
T, °C Degree of conversion (K), % H2/C0
KCi KC2+ KC02
300 9.2 3.5 17.1 *
400 37.7 30.4 28.9 3.8
450 27.9 70.8 30.4 1.0
500 36.3 99.6 36.3 1.0
550 37.4 99.0 38.4 0.9
600 48.4 98.6 44.3 1.0
650 66.8 98.7 57.4 1.1
700 75.0 97.9 73.8 1.2
750 84.8 99.3 86.9 1.3
800 92.2 100 93.4 1.4
* CO is not produced at this temperature
Table 3. Composition of products formed at conversion of associated gases (P=1 atm, S.V=1500 hr-1)
T,0 C
Degree of conversion, %
CH4
C2-
CO2
H2/CO
Yield of oxygenates, %
600 800
48.4 92.2
> 98 100
44.3
93.4
1.0 1.4
traces
not observed
Table 4. Effect of space velocity on bi-reforming of associated gases over the KMR-8 catalyst (APG/C02/ H20=1/1/0.1, P=1 atm, T=885 °C)
S.V.*, hr-1 KcH4,% Kc2-C7,% Kc02,% Selectivity on syngas production, % H2/C0
1500 98.9 100 95.1 100 1.3
2250 98.7 100 95.0 100 1.2
3600 98.7 100 94.3 100 1.2
4500 97.7 100 93.4 100 1.2
6000 96.7 100 93.1 100 1.2
* S.V. - space velocity
to 96.7 % with increasing space velocity by 4 times (from 1500 to 6000 hr1) at T=885 °C. C2-C7 hydrocarbons are completely (100 %) converted under these conditions. The C02 conversion degree is not significantly decreased too: from 95.1 to 93.1 % (850 °C). At increasing space velocity, the contact time is shorted but it did not cause any substantial decreasing the activity of
the catalyst. The yield of syngas is not changed too. Ratio of H2/CO is also constant 1.2. By other words, the KMR-8 catalyst performs the high productivity.
The catalyst demonstrates the high resistance to coke formation. We consider that water positively effects on suppression of coke formation over the catalyst. By electron microscope it was
shown that the catalyst keeps its high dispersed state after reaction. The catalyst worked with the stable activity during all period of its exploitation (more than 50 hours).
Conclusions
Te KMR-8 catalyst performs the high activity (Xch4 = 92-98 % and Xco2 ~ 93 %) and productivity: up to ~ 12,000 L of syngas can be produced from 3,000 L of APG by 1 L of the catalyst per hour. Syngas produced has an appropriate ratio for Fisher-Tropsch synthesis -H2/CO=1.2-1.4. The advantages of the synthesized catalyst also are stability and resistance to coke
formation. Ability to work in water presence allows to use the real APG and to avoid the additional stages of their drying that reduces the investment costs.
The catalyst can be recommended for the industrial application to produce syngas from APG. In whole, the introduction of the technology of APG utilization into practice will promote also the mitigation of carbon dioxide emissions.
Acknowledgement
The special thanks to the Laboratory of physico-chemical study of catalysts of IOCE for carrying out the catalysts investigation.
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Углекислотная конверсия
реальных попутных газов в присутствии
воды на катализаторе КМР-8
Ш.С. Иткулова, Г.Д. Закумбаева
Институт органического катализа и электрохимии
им. Д.В. Сокольского (ИОКЭ) Республика Казахстан 050010, Алматы, ул. Кунаева, 142
Новый цеолитсодержащий катализатор исследован в реакции взаимодействия между диоксидом углерода и реальным попутным нефтяным газом (ПНГ) в присутствии воды при варьировании температуры в интервале 300-900 oC и объемной скорости - 1000-6000 ч-1. Показано, что катализатор обладает высокой активностью в риформинге ПНГ. При 800 oC происходит полная конверсия фракции углеводородов C2+, степень конверсии метана достигает 92.2, а диоксида углерода - 93.4%. Основным продуктом реакции является синтез-газ (смесь оксида углерода и водорода) с отношением H2/CO=1.4 при 800 oC. Также образуются вода и следы кислородсодержащих продуктов (в основном уксусная кислота) при T < 600 oC. Катализатор работает практически с одинаковой активностью при увеличении объемной скорости в 4 раза. Достоинствами катализатора являются высокая активность, селективность, стабильность, способность работать в присутствии воды и устойчивость к коксообразованию.
Ключевые слова: углекислотная конверсия, попутные газы, катализатор, синтез-газ.
