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Autothermal Reforming Of Diesel To Hydrogen And Activity Evaluation Lin Lin, Ling-qiong Wu, Li-ran Sui, and Shao-heng He Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01431 • Publication Date (Web): 12 Jun 2018 Downloaded from http://pubs.acs.org on June 12, 2018
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Energy & Fuels 1
Autothermal Reforming Of Diesel To Hydrogen And Activity Evaluation Lin Lin*, Ling-qiong Wu, Li-ran Sui and Shao-heng He* Department of Translational Medicine Research Center, Shenyang Medical College, Shenyang 110034, P. R. China Supporting Information Placeholder autothermal reforming, thermal coupling between exothermic oxygen reforming and the endothermic water reforming must firstly be realized. In this respect, carbon analysis is easier to conduct when the carbon chain of the diesel oil has a long length. Furthermore, the catalyst used must also meet the requirements of high activity, and provide long life expectancy, good stability, be anti-carbon, and able to withstand repeated oxidation and reduction. [10-15]
ABSTRACT: Non-precious metal catalysts were prepared using the equal volume fractional impregnation method. The effect of catalyst bed inlet temperature and diesel liquid airspeed on the self-thermal reforming of diesel was investigated with respect to the LaCeCoCrFeNi/Al2O3 catalyst. Optimum operating conditions were determined as a catalyst bed inlet temperature of 700°C, diesel liquid airspeed 0.24 h-1, water and carbon ratio of 15, and oxygen-carbon ratio of 0.4.
In this paper, straight-run diesel is employed as a raw material to study a LaCeCoCrFeNi/Al2O3 catalyst that is created and used in the autothermal reforming of diesel hydrogen, with the aim of providing a foundation for further research on the autothermal reforming of diesel hydrogen process and associated catalyst system.[16-19]
1. INTRODUCTION The world is experiencing severe challenges with respect to the depletion of traditional energy sources, such as oil and coal, and the associated greenhouse effect and acid rain caused by emissions of CO2 and SO2 from combustion of these fossil fuels. The search for new clean energy sources and developing methods to enable the efficient and clean use of existing energy resources are currently major themes in achieving a sustainable society. [1-5]
2.EXPERIMENTAL SECTION 2.1 Diesel autothermal reforming hydrogen principle Diesel is complex and provides many reactions. It is understood that hydrocarbons contained in diesel oil can be cracked into methane under high temperature conditions, and related reactions, such as methane steam reforming, can then be employed in further processes. This paper provides the independent reactions involved in the diesel hydrogen complex reaction system.
[5-9]
Diesel is a secondary energy source . Diesel fuel is mainly directly combusted, but this method offers low thermal and energy efficiencies. In addition, toxic gases are released as pollutants after combustion, which are detrimental to the environment. However, by converting diesel fuel to hydrogen-rich fuel through reforming, the energy efficiency of fuel cells can be significantly enhanced and environmental pressures subsequently alleviated.
The autothermal reforming system of diesel containing carbon includes eight independent elements, C10H21, H2O, O2, C, CO, CO2, H2, and CH4, all of which involve three elements: C, H and O. In this respect, five independent reactions can occur. According to analysis of the composition of straight-run diesel, the simulation formula of diesel is C10H21. The following five independent reactions are thus used to describe the process of self-thermal reforming of diesel:
Steam reforming method is the most commonly used hydrogen reforming method because of its high hydrogen content. In this way, the fuel is mixed with water vapor and then put into the reformer. The main problems of this technology are the service life of adsorbent and catalyst and the complexity of system design. Compared with steam reforming, the structure of self-heating reforming is simple. It requires no large heat exchange device, and the manufacturing cost is low. Compared with partial reformer, the heat released by the oxidation reaction is directly absorbed by the steam reformer reaction which absorbs heat, so the efficiency of the system is also improved. However, it is difficult to control the ratio of oxygen, water vapor and fuel at the same time, and it is easy to produce carbon accumulation and damage the catalyst in the process of reforming.
R1: Diesel water reforming reaction 2C10H21 + 20H2O = 20CO + 41H2 △ H> 0 R2: diesel oxygen reforming reaction 2C10H21 + 10O2 = 20CO + 21H2 △ H 0
A variety of methods are used in reforming diesel to hydrogen, such as water reforming (SR), oxygen reforming (OX), partial oxidation reforming (POX) and autothermal reforming hydrogen (ATR). In this respect, diesel autothermal reforming hydrogen production is the most reasonable production method. To achieve
R4: CO conversion CO + H2O = CO2 + H2 △ H 0
(e) Temperature: catalyst bed inlet temperature (℃).
The key to diesel autothermal reforming of hydrogen is the use of appropriate catalysts to ensure that the product gas has a high H2 content, low CO content, and an adequate hydrogen yield. It is also necessary for the gas to be released through use of appropriate process conditions. In this respect, thermal reaction and endothermic reaction heat coupling is required to provide a rational use of energy. Furthermore the catalyst used should have a certain degree of anti-carbon ability, but also be able to appropriately increase the content of H2O to inhibit the occurrence of carbon precipitation reaction.
2.3 Catalyst system, preparation methods, and activity evaluation 2.3.1 Catalyst system The catalyst is LaCeCoCrFeNi/Al2O3 and the active ingredient is Ni. Ni-based catalysts are used frequently in the autothermal reforming of hydrocarbon diesel. They have considerable activity and selectivity with precious metals; however, their active components easily sinter and coke, and thus Ni is slowly lost. In addition, the dispersion degree of Ni is related to the amount of Ni added: if the content of Ni is too high, the dispersion and surface area of the catalyst will be reduced, and the anti-caking ability is also decreased.
2.2 Related parameters and experimental indicators definition The following parameters and experimental indicators used in this work are defined as follows:
2.3.2 Main additives and effects (a) Water carbon ratio: the number of moles of water vapor at the inlet of the reactor and the total number of carbon moles in diesel oil (mol/mol);
La is added to improve the activity and stability of the catalyst, and Ce is inside the Ni-based catalyst. The rare earth metal, Ce, enables the active component oxide to disperse more evenly and provides finer particles. Ce itself is inactive to the reaction, but the addition of Ce can increase the activity of the Ni-based catalyst in providing thermal stability of carbon [14-16]. Furthermore, Co, Cr, Fe are added to reduce the content of CO in the reaction gas.
(b) The ratio of oxygen to carbon: the oxygen molar number at the inlet of the reactor and the diesel carbon molar ratio (mol/ mol); (c) Diesel liquid airspeed: the unit time through the unit volume of catalyst diesel volume (V diesel/t.V catalyst);
2.3.3 Preparation of raw materials for catalyst and associated specifications
(d) Hydrogen yield: the number of moles (mol/mol) of hydrogen produced per mole of diesel oil. Table 1. Catalyst Preparation of raw materials Name Molecular Lanthanum nitrate Nickel nitrate Cobalt nitrate Ferric nitrate Cerium nitrate Chromium nitrate Aluminum oxide
Formula La（NO3）3·6H2O Ni（NO3）2·6H2O Co（NO3）2·6H2O Fe（NO3）3·9H2O Ce（NO3）3·6H2O Cr（NO3）3·9H2O Al2O3
2.3.4 Catalyst preparation method
Specifications Analytical pure (AR) Analytical pure (AR) Analytical pure (AR) Analytical pure (AR) Analytical pure (AR) Analytical pure (AR) Catalyst carrier
4. An appropriate amount of cerium nitrate was dissolved in deionized water solution, into the composite oxide (1) impregnated 0.5 h after drying, and then placed in a muffle furnace and calcined for 4 h to obtain a complex oxide (2);
In this paper, an equal volume fraction impregnation method was used to prepare the catalyst as follows:
5. A certain amount of nickel nitrate was dissolved in deionized water solution, into the composite oxide (2) impregnated 0.5 h after drying, and then placed in a muffle furnace calcined 7 h, to obtain a catalyst precursor LaCeCoCrFeNi / Al2O3.
1. The carrier Al2O3 was calcined at 600℃ for 6 h to obtain γAl2O3; 2. The carrier γ-Al2O3 was weighed. A certain amount of lanthanum nitrate was added to a deionized water solution and impregnated into γ-Al2O3 after drying for 30 min. The substance was then placed in a muffle furnace and calcined for 4 h to obtain an oxide;
2.3.5 Activity evaluation index Activity of the LaCeCoCrFeNi / Al2O3 catalyst was evaluated by its hydrogen yield and content.
3. Appropriate amounts of cobalt nitrate, chromium nitrate, and iron nitrate were dissolved in deionized water solution, into the calcined oxide, impregnated 0.5 h after drying, and then placed in a muffle furnace calcined 4 h to obtain a composite oxide (1);
2.3.6 Activity evaluation of device and process In this paper, an adiabatic tubular reactor with a preheating section was designed as a core, and the experimental procedure and associated processes are shown in Fig. 1.
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Energy & Fuels 3
Figure 1. Autothermal reforming of diesel to hydrogen flow chart: 1. diesel tanks, 2. oil pumps, 3. hydrogen generator, 4. diesel vaporization chamber, 5. static mixer, 6. water vaporization chamber, 7. water tanks, 8. water pump, 9. preheating, 10. catalyst bed, 11. condenser, 12. cold hydrazine, 13. gas chromatograph, 14. wet gas flowmeter In this system, a certain proportion of diesel oil and water are respectively measured by a parallel flow pump and delivered to the diesel vaporization chamber and the water vaporization chamber. The entrained nitrogen enters the vaporization chamber and the oxygen enters the diesel vaporization chamber. The vaporized diesel oil, oxygen, water, and nitrogen enter the static mixer together for mixing and are then preheated into the catalyst bed with the catalyst for reaction. The product gas enters the water cooler, and the cold hydrazine condenses and separates the unreacted diesel oil and excess water, either after metering, venting or entering the gas chromatograph for on-line analysis, completing the hydrogen production based on product gas dry gas flow, composition and diesel analysis Rate calculation.
an important factor to evaluate the performance of catalyst.The activity of different catalysts changed with the time of reaction.
The hydrogen reaction of diesel self - heat reforming is carried out in self - produced reactor.Catalyst bed layer containing 10 ml of catalyst, temperature under N2 protection to the reaction temperature, the raw material of diesel fuel and water evaporation by advection pump into the vaporizing chamber, respectively, and then mixed with oxygen into the reactor, gas product online by chromatographic analysis.The activity of catalyst was evaluated by hydrogen yield and hydrogen content.Stability experiment is
Figure 2 Reactor diagram.
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Energy & Fuels 4 In figure 2，the diameter of the reactor was 12mm, and the preheating segment was 2:1 with the length ratio of adiabatic segment. The internal loading size of the adiabatic segment was 20%-40, PtLaCe/Al2O3 catalyst, and the ceramic ring at the bottom.Figure 1.2. A type of reactor, reaction from the gasification chamber materials (superheated steam, diesel fuel and oxygen) first came to the preheating section of the reactor, preheated to A specified temperature after entering the diesel hydrogen response of catalyst bed.The catalyst bed layer is equipped with an adiabatic insulation layer to prevent heat loss.
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2.3.7 Catalyst characterization method
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1. Specific surface area test
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In this paper, a SSA-4300 pore and surface area analyzer was used to determine the specific surface area of the catalyst.
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2. SEM characterization:
Figure 3. Effect of catalyst bed inlet temperature on H2 content
In this paper, the Japanese JSM-6360LV high and low vacuum scanning electron microscope was used to determine catalyst morphology.
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2.4 Analysis and testing methods
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hydrogen yield(mol/mol)
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Analyzes of the composition of the diesel and product gas were conducted using SP-3420 GC with the test conditions shown in Table 2. Table 2. Gas chromatography test conditions Stationary phase
detection method
16 14 12 10 8 6
Diesel Product
SE-54
FID
GDX-502
TCD
5A Molecular sieve
Double valve double column
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catalyst bed inlet temperature(℃)
Figure 4. Effect of catalyst bed inlet temperature on H2 yield The figure shows that the hydrogen yield and the hydrogen content, which represent the activity of the catalyst, both increase with an increase in the catalyst bed inlet temperature. The hydrogen content and hydrogen yield were lowest with a temperature of 550°C, while from 550°C to 600°C there was a clear increase in the hydrogen content and yield, which gradually stabilized after 600°C. The hydrogen yield and hydrogen content reached a maximum of 14.86 (mol / mol) and 47.12%, respectively, at a bed inlet temperature of 700°C. From these experimental results, it is evident that a high temperature is favorable for the reaction; however, this also causes a higher energy loss and is economically unreasonable. Moreover, various alkanes in diesel oil are unstable under high temperature, and the material is extremely vulnerable to damage.[21-26]
3. RESULTS AND DISCUSSION 3.1 Process conditions for LaCeCoCrFeNi / Al2O3 catalyst activity 3.1.1 Catalyst bed inlet temperature Figures 3 and 4 show the effect of catalyst bed inlet temperature on H2 content and yield with the following conditions: oxygen–carbon ratio of 0.4, liquid-hourly space velocity of diesel of 0.16 h-1, water-carbon ratio of 20, and change in inlet temperature of the catalyst bed.
3.1.2 Water carbon ratio Figure 5 shows the effect of H2O/C feed ratios on H2 yield, and Fig. 6 shows the effect of H2O/C feed ratios on H2 content for liquid nitrogen with the following conditions: a liquid hourly 4
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5 space velocity of 0.16 h-1, a catalyst bed inlet temperature of 650°C, and an oxygen-carbon ratio of 0.4.
Figures 7 and Figure 8 show the hydrogen production rate and hydrogen content as a function of the oxygen-carbon ratio for the following conditions: a diesel liquid space velocity of 0.16 h-1, catalyst bed inlet temperature of 650°C, and a water-carbon ratio of 20, respectively.
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hydrogen yield(mol/mol)
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Oxygen carbon ratio( mol/mol)
Figure 5. Effect of H2O/C feed ratios on H2 yield
Figure 7. Effect of O2/C feed ratios on H2 content 52
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hydrogen yield(%)
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Figure 6. Effect of H2O/C feedratios on H2content Figure 8. Effect of O2/C feedratios on H2 yield
The figure shows that the hydrogen content and the hydrogen yield firstly decrease then increase with an increase in the watercarbon ratio, which may be attributed to the initial reaction occurring. No carbon reaction occurred during the reaction process. As the reaction progressed, the smaller ratio of water to carbon caused deactivation of the catalyst due to carbon precipitation, while the larger ratio of water to carbon eliminated carbon deposition and facilitated the reaction. In theory, it is beneficial to improve the water-carbon ratio in a water reforming reaction, but it is also necessary to prevent the occurrence of carbon precipitation reaction to a certain extent and thus inhibit carbon precipitation.[27-31]
As shown by the figure, the hydrogen content and the hydrogen yield firstly increase then decrease with an increase in the oxygen-carbon ratio. The hydrogen content and hydrogen yield reached 47.12% and 12.34 (mol/mol) respectively at an oxygen to carbon ratio of 0.4. According to mechanistic analyzes, the oxygen-carbon ratio is a very important factor for use in realizing self-thermal reforming of diesel. Oxygen reforming emits heat to provide the heat required for water reforming and the subsequent autothermal reaction. In addition, increasing the ratio of oxygen to carbon can release a large amount of heat during combustion, and thus improve both the temperature of the reaction system and hydrogen yield; however, if too much oxygen is used it will react with hydrogen and result in a decreased hydrogen yield.[32-37]
3.1.3 Oxygen to carbon ratio 5
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Energy & Fuels 6 3.1.4. Diesel liquid airspeed
As previously mentioned, each of the components added provides a different effect. Figures 11 and 12 show the effect of related components in the relationship between the hydrogen yield and the CO content over time for auto-thermal reforming of diesel on Ni / Al2O3, CoNi / Al2O3, CoCrNi / Al2O3 and CoCrFeNi / Al2O3 catalysts.
Figures 9 and Figure 10 show the relationship between the hydrogen production rate and hydrogen content and the liquid hourly space velocity of diesel fuel, respectively, when the following conditions were employed: ratio of oxygen to carbon of 0.4, entrance temperature of catalyst bed of 650°C, and ratio of water to carbon of 20.
Ni/Al O 2 3
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hydrogen yield(mol/mol)
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Carbon-containing raw materials have a certain effect on the hydrogen production, and CO can poison the electrodes in the PEMFC of PEMFC. Research is currently focused on developing methods for reducing the CO content in the reaction gas. Figure 10 shows that the CO content of the catalyst with the addition of transition elements such as Co, Cr and Fe is significantly lower than that without the addition of additives; this proves the effect of the transition group elements and also proves that the catalyst prepared herein has the advantages of reducing the reaction Advantage of CO content in gas.[44-47] It can be clearly seen in Figure 12 with respect to Ni / Al2O3, that catalysts with rare earth elements of La and Ce as auxiliaries provide a marked increase in the hydrogen yield, which thus proves that the addition of La and Ce can effectively improve the activity and stability of the catalyst Sex. Table 3 shows the specific surface area of different catalysts before use and the hydrogen yield and hydrogen content produced during reforming hydrogen. The data calculated by isothermal curve of each catalyst in the multilayer adsorption quantity under different nitrogen partial pressure, the X axis for P/P0, P/V(P0-P) for the Y axis, linear fitting by BET equation do figure, get straight slope and intercept of Vm obtained values calculated for each catalyst surface. It can be seen from the specific surface area test results of the catalyst that when the carrier is Al2O3, the smaller the component of the catalyst, the larger the specific surface area. It can be seen from the data in the table that the activity of LaCeCoCrFeNi/Al2O3 catalyst is significantly better than that of other catalysts, which also indicates that the specific surface area of catalyst is not the only indicator to evaluate the activity of catalyst.
LaCeCoCrFeNi/Al O 2 3
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Figure 11. Effect of different catalysts and reaction time on CO content
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Figure 9. Effect of LHSV on H2 yield
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hydrogen content(%)
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-1
diesel fuel airspeed(h )
Figure 10. Effect of LHSV on H2 content It can be seen from the figure that the hydrogen content and the hydrogen yield increase monotonically with an increase in the liquid airspeed. The analysis shows that with a small diesel flow, an increase in the liquid air velocity of diesel fuel can make the flow rate of diesel vaporization chamber more uniform, stable, and conducive to the hydrogen production process.[38-43] 3.1.5 Additives used in catalytic activity
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7 Figure 12. Effect of different catalysts and reaction time on H2 yield LaCeNi/Al O 2 3
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According to test results determining the specific surface areas of catalysts, if the carrier is Al2O3 then the smaller the component contained in the catalyst the larger the specific surface area. It can be seen from the data in the table that the activity of LaCeCoCrFeNi/Al2O3 catalyst is obviously better than that of several other catalysts, which also shows that the specific surface area of the catalyst is not the only index that should be used to evaluate the activity of a catalyst. Figures 13 and 14 show SEM images of LaCeCoCrFeNi/Al2O3 and LaCoCrFeNi/Al2O3, respectively, prior to use at a magnification of x5000.[48-52]
L aN i/Al O 2 3 N i/Al O 2 3
hydrogen yield( mol/mol)
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Table 3. Surface areas and parameters of catalysts prior to use Catalyst
Specific surface area (m2/g)
Hydrogen yield (mol/mol)
LaCeCoCrFeNi/Al2O3
88.90
17
0.2865
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LaCeCoFeNi/Al2O3
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LaCoFeNi/Al2O3
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LaFeNi/Al2O3
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10
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LaNi/Al2O3
146.7
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4.98
Ni/Al2O3
155.8
8
0.3785
4.65
Total pore volume (m3/g)
(n
Aperture m )
Figure 13. LaCeCoCrFeNi/ Al2O3 SEM diagram prior to use From these images, the particle distribution of the surface component of the LaCeCoCrFeNi/Al2O3 sample is seen to be relatively uniform and smooth with a loose and porous structure. Analysis shows that the addition of Ce effectively improves the dispersibility of the active components and causes the catalyst surface to have a more uniform distribution.
Figure 14. LaCoCrFeNi/ Al2O3 SEM diagram prior to use
4. CONCLUSIONS 7
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8 As the precious metal catalyst, its characteristic is with high activity and selectivity, but the precious metal catalyst reaction temperature is higher, mostly in 600-800 ℃, and costly. And LaCeCoCrFeN I/Al2O3 based on Ni active component and add a variety of rare earth elements of non-noble metal catalysts, the precious metals Ni base has quite the activity and selectivity of catalyst and precious metals, but it is the active component of sintering, easy to coking, Ni will be slow to drain. Therefore, the addition of appropriate rare earth element additives can effectively inhibit the decarbonization of active components and improve the stability of catalysts. Therefore, we choose non - precious metal catalyst and get the following conclusions：
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1. The equal volume of sub-impregnation method was used in the diesel self-heating hydrogen production of non-precious metal catalyst preparation. (2) LaCeCoCrFeNi/Al2O3 is a non-precious metal catalyst that can be used in the autothermal reforming of diesel and provides a hydrogen yield of 17 mol/mol and a hydrogen content of 54%; thereby evidencing good catalytic activity.[53-55] (3) The LaCeCoCrFeNi/Al2O3 catalyst prepared in this paper is used for autothermal reforming hydrogen from diesel. Suitable operating conditions were determined as follows: reaction temperature 700℃, liquid hourly space velocity of 0.24 h-1, watercarbon ratio of 15, and oxygen–carbon ratio of 0.4. ⑷ The addition of transition elements, such as Co, Cr, and Fe, can effectively reduce the CO content in the reaction gas. The addition of Ce makes the catalyst surface distribution more uniform and further increases the activity of the catalyst.
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Corresponding Author
[email protected] Notes The authors declare no competing financial interests.
ACKNOWLEDGMENT This work was supported financially by the Science and Technology Program of Shenyang (No. 18-013-99).
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This paper investigated the influences of catalyst bed inlet temperature and diesel fuel space velocity on the autothermal reforming of diesel to hydrogen, and suitable conditions for the catalyst bed inlet were found to be: temperature of 700 ℃, diesel fuel space velocity of 0.24 h-1, molar ratio of water to carbon of 15, and a molar ratio of oxygen to carbon of 0.4.
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