Methanol reformer

A methanol reformer is a chemical technology device that is used in fuel cell technology to generate pure hydrogen from a methanol - water mixture with the release of carbon dioxide . The chemical reaction is based on steam reforming .

${\displaystyle \mathrm {CH_{3}OH_{(g)}+H_{2}O_{(g)}\;\longrightarrow \;CO_{2}+3\ H_{2}\qquad } \Delta H_{R\ 298}^{0}=49{,}2\ \mathrm {kJ/mol} }$

Methanol is reacted with water vapor on a heterogeneous catalyst with the addition of thermal energy to hydrogen and carbon dioxide.

technology

A methanol-water mixture with a molar water- methanol ratio of 1.3-1.5 is compressed to up to 20 bar , evaporated and superheated to 250-280  ° C. The generated hydrogen is by means of a hydrogen permeable membrane made of a palladium - silver - alloy separated (PdAg).

There are two basic methods for technical implementation.

• The catalyst is located in a heated tubular reactor . At the reactor inlet , the water vapor methanol vapor mixture is supplied. The hydrogen is then separated off in a downstream apparatus. The reformate flows over the PdAg membrane and a large part of the hydrogen passes through the membrane.
• The other variant is an integrated membrane reactor. Here the wall of the reaction zone consists of a ceramic tube coated with PdAg and the hydrogen is separated off directly from the reaction zone.

In both variants, the retentate , which contains a significantly depleted hydrogen content, is burned in a catalytic burner with air . The heat energy released is used for heating purposes.

Advantages and disadvantages

Methanol reformers are being considered as a component of a hydrogen drive for cars so that they do not have to carry hydrogen in pressurized gas tanks. In this way, acceptance problems in the population could be countered, where hydrogen is often viewed as too dangerous. The advantage of methanol in this context is that it is liquid and has a higher volumetric energy density than hydrogen. However, like gasoline, methanol is poisonous and highly flammable. The problem is the expensive and failure-prone palladium alloy, which has only moderate thermal shock resistance. Daimler-Chrysler presented the prototype of such a vehicle in 2000 with the NECAR 5 .

literature

• Emonts, B. et al .: Compact methanol reformer test for fuel-cell powered light-duty vehicles , J. Power Sources 71 (1998) 288-293
• Wiese, W. et al .: Methanol steam reforming in a fuel cell drive system , J. Power Sources 84 (1999) 187-193
• Peters, R. et al .: Investigation of a methanol concept considering the particular impact of dynamics and long-term stability for use in a fuel-cell-powered passenger car , J. Power Sources 86 (1999) 507-514

Web links

• Micro-applications: micro-reformers make hydrogen from methanol ( Memento from December 12, 2007 in the Internet Archive )
• Environment and traffic - fuels and operating materials methanol ( Memento from November 12, 2005 in the Internet Archive )