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Research Papers

# Tin as a Possible Candidate for Solar Thermochemical Redox Process for Hydrogen Production

[+] Author and Article Information
Irina Vishnevetsky1

Solar Research Facilities Unit, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israelirina.vishnevetsky@.weizmann.ac.il

Michael Epstein

Solar Research Facilities Unit, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel

1

Corresponding author.

J. Sol. Energy Eng 131(2), 021007 (Apr 02, 2009) (8 pages) doi:10.1115/1.3090825 History: Received July 30, 2007; Revised June 05, 2008; Published April 02, 2009

## Abstract

The feasibility to produce hydrogen in the $Sn–H2O/SnO2–C$ thermochemical water splitting redox process depends mainly on the efficiency of the tin hydrolysis step, which has not been studied adequately so far, while the cassererite carboreduction is implemented by industry for tin production. The present work deals with the hydrolysis of different kinds of tin powders at different experimental conditions at moderate temperature range $180–620°C$. In spite of the fact that the rate of hydrogen production is lower compared with other metals, e.g., zinc, at the same reactor temperature, high conversion level was obtained in a controllable reaction. Consequently, tin can be a relevant candidate for solar hydrogen production considering the advantage of significant lower temperatures required for the solar carboreduction of its oxide.

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## Figures

Figure 1

Equilibrium constant versus temperature for Sn, In, and Ga redox reactions

Figure 2

Equilibrium constants versus temperature for hydrolysis of tin and tin monoxide

Figure 3

Sample holder (a) before and (b)after test

Figure 4

Structures of different tin powders observed in TEM after sonication: (a) nano-, (b) 10 μm, and (c) 44 μm powders

Figure 5

The main parameters of tin powder (10 g) hydrolysis versus time from heating beginning: (1) temperature in the middle of reactor below sample holder, (2) temperature in reaction zone, (3) steam temperature at the exit of boiler, (4) pressure in reactor, (5) hydrogen flow rate from Eq. 4, (6) hydrogen flow rate from Eq. 5, and (7) mass water flow rate×10 from pump

Figure 6

Comparison of temperature in reaction zone (2, 4, 6) and hydrogen flow rate (1, 3, 5) as a function of reactor temperature for 1.8 g of boron (3, 4), 10 g zinc (1, 2) and 10 g tin (5, 6) hydrolysis; mass water flow rate 0.25 g/min for boron and 0.55 g/min for tin and zinc

Figure 7

Hydrogen flow rate calculated by Eq. 5 for (1) 10 μm, (2) nano-, and (3) 44 μm powders (all results are reduced to 10 g powder, ṀH2O=0.55 g/min)

Figure 8

Hydrogen flow (Eq. 4) developing versus time since a steam flow started (a) and temperature (b) at different steam flow starting temperatures: (1) 180°C, (2) 360°C, (3) 500°C, and (4) 580°C (M0∼9.5 g, ṀH2O=0.55 g/min) during heating period up to 620°C

Figure 9

Conversion versus time period after the steam flow starts at different temperatures

Figure 10

Hydrogen flow (Eq. 4) output rate (a) and conversion (b) versus time since a steam flow started (steady state temperature condition: (1) 350°C, (2) 420°C, (3) 525°C, and (4) 600°C); M0∼9.5 g, ṀH2O=0.55 g/min

Figure 11

Mass fractions of tin, tin monoxide, and tin dioxide in powder after three 3 h tests at different constant temperatures (a) and portion of monoxide in tin oxides versus reactor temperature after tests completion (b)

Figure 12

Hydrogen flow output (Eq. 4) versus time since a steam flow started (a) versus temperature in reaction zone (b) at the same temperature condition (c) for tests with tin (1, 3) and tin monoxide (2), M0=9.5 g, ṀH2O=0.55 g/min

Figure 13

Relative hydrogen output versus steam partial pressure

Figure 14

Conversion versus time since the steam flow starts at 360°C (M0∼9.5 g, (●)ṀH2O=0.55 g/min, and (◼) ṀH2O=1.65 g/min)

Figure 15

Structures of 10 μm powders after tests that were done at different temperatures: (a) 420°C, (b) 600°C, and (c) 360–620°C

Figure 16

Hydrogen flow rate as a function of the temperature in the (a) reaction zone and(b) Arrhenius plot (M0∼9.5 g, PH2O0≈0.93 bar)

Figure 17

Deviation of exponential behavior of the reaction rate at different conversion levels

Figure 18

Examples of calculated rate-decreasing factor f(χ,T) for (a) different isothermal conditions and(b) different preheating history

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