Catalyst Preparation

The catalyst was prepared by the impregnation method using hexa-hydrated nickel nitrate (PA-ECIBRA) and tri-hydrated cupper II nitrate (PA-ECIBRA), as precursors of the “active elements”, and distilled water for aqueous solution preparation. Pellets of y – alumina (OXITENO, 200 m2.g_1, 0.04 m3.g”, and pellets of 1 cm length) were used to support the metals.

The impregnated support (6% Cu and 6% Ni, w/w) was dried in air at 100°C during 12 h and calcinated at 500°C during 3 h.

The catalyst was not reduced before testing and the data with respect to catalyst performance was acquired after 2 h of ethanol processing. A stoichiometric mixture of ethanol and water (1:3) was chosen as the first approximation for process evaluation.

1.1. Catalyst and System Performance in Ethanol Steam-Reforming

Efficiency for hydrogen production can be defined as the product between the selectivity for its substance, at a specific thermal condition, and the fuel conversion (activity of the catalyst for processing the fuel).

This maximum value occurred at approximately 600°C, and was better analyzed. The catalyst behavior is illustrated in Fig. 3.

image227

Fig. 3. NiCu / у – A1203 performance on steam-reforming of ethanol.

The distribution of products coming from the steam-reforming of ethanol was obtained by analyzing the collected samples by gas chromatography. For high concentration syn-gas, the analysis was carried out with a TCD (Thermal Conductivity Detector), a 3.6 m Porapak N column (80-100 mesh) followed by another 0.90 m molecular sieve 5A column (60-80 mesh). Argon was the carrier gas.

The tests were carried out with the reactor operating under temperature fluctuations not superior to 4°C. The mixture was supplied at 40 ml. h’1 and the fuel conversion was always superior to 93%, for temperatures between 590 and 640°C. The H2 originated from this mixture flow would provide 57 W (electrical) if used in a PEM fuel cell with an electrical efficiency of 50%.

The optimal temperature for H2 production was 613°C which corresponds to 5.38 mol of H2 yielded per mol of ethanol processed. This means a H2 production efficiency of approximately 89.7%.

A preliminary analysis of the results of ethanol steam-reforming product distribution at 613°C leads to the occurrence of ethanol decomposition followed by methane steam-reforming and the promotion of a single exchange reaction between CO and water. This mechanism can be represented as follows:

C2H5OH -» CH4 + CO + H2 CH4 + H20 -> 3H2 + CO CO + h2o -> H2 + co2

Подпись:Подпись: (5) (6) At 598°C, very close to optimum, the promotion of methane steam-reforming is highly unfavorable what implies in the decrease of H2 concentration. This situation could be also characterized by a small CO methanation:

2CO + 2H2 -> CH4 + C02 (7)

image228

The syn-gas was conducted to the purification step. The result after 16 minutes of operation is presented in Fig. 4.

Fig. 4. Performance of purification without water gas shift reaction.

The purification system is composed of two columns. The first contains silica-gel (Synth, spheres of 1-4 mm, PA) as the dehydrating agent for chemical water removal, and activated carbon (Synth, dispersed particles of 1-2 mm) for CH4 and C02 removal, preferentially.

The second column is mainly dedicated to CO removal and is composed of 5A zeolites (Baylith-Bayer, spheres of 1-4 mm). The quantity of each element on the columns is not equal, but proportional to the importance of each contaminant.

Accordingly to the data illustrated in Fig. 4, the H2 purity was approximately 99.98% with a maximum 25 pmoLmol"1 CO concentration which was measured up to 16 minutes.

The results show large potential for practical applications, even without a water gas shift reactor (WGSR) for CO depletion.

The CO shift reactor is being developed based on Cu-ZnO / у – A1203 dispersed ceramic catalyst. This catalyst will be obtained from nitrate species and must contain 7% w/w of each active metallic element. At least 85% of activity in water gas shift reaction is expected, with no depletion of H2 concentration in the syn-gas. This characteristic would provide, at least, an increase of 85% in the СО-purification life-time. The new system, showed in Fig. 2, collapses the purification unit for one single column. It could be duplicated to perform a “push-pull” operation in practical systems.

2. Conclusions

The present work reports the development and initial results of an ethanol steam­reforming processor and the ancillary systems to produce pure hydrogen for PEM fuel cell applications. The initial results were obtained for NiCu / y-Al203 steam-reforming catalyst. The best selectivity for hydrogen was around 68% at 613°C and catalyst activity was always superior to 93%, which resulted in 5.38 mol of H2 per mol of ethanol processed. The catalyst longevity analysis was not reported yet.

The hydrogen purity was about 99.98%, for an interval of 16 minutes of operation with carbon monoxide concentration remaining below 25 pmol. mol"1. The purification was carried out by physical and chemical adsorption processes by means of molecular sieves.

The results achieved in this work will be used to develop an autothermal ethanol reforming system, initially designed to provide 5 kW when coupled to a PEM fuel cell.

The advantages and opportunities of using bio-ethanol from sugar-cane for electricity generation in select applications were also discussed.

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