Entropy production in the chemical reaction driven heat transformer

Abstract

A chemical heat transformer uses a chemically reacting system for the internal cycle. Chemical conversions in a chemical heat transformer produce entropy due to irreversibilities, which are taken into account in our derivation of a new, more realistic value for the thermal efficiency of this heat transformer. We studied the example of the endothermic dehydrogenation of 2-propanol, yielding acetone and hydrogen, versus the exothermic hydrogenation of acetone yielding 2-propanol. Different from other papers we allow the dehydrogenation temperature Tm to be higher than the boiling point Tb of the 2-propanol and we allow the isolation of 2-propanol from the mixture to be incomplete. The internal entropy production in the dehydrogenation and hydrogenation reactor is calculated as a function of the hydrogenation temperature Th with three different values of Th-Tm and several incomplete separation values. The thermal efficiency is much lower than Carnot's efficiency for low-temperature lifts because of the high irreversibilities that are already present for these temperatures and because of the low efficiency of the heat engine. A higher, but still low, efficiency is obtained for Tm>Tb and for the incomplete separation of 2-propanol from the mixture.

Iridium(0) Nanocluster, Acid-Assisted Catalysis of Neat Acetone Hydrogenation at Room Temperature: Exceptional Activity, Catalyst Lifetime, and Selectivity at Complete Conversion

“…Use of the polar, nanocluster-stabilizing solvent propylene carbonate did yield more stable, albeit less catalytically active, Ir(0) nanoclusters. The current Achilles heel of this system then, as with most soluble nanoclusters, is their limited catalytic lifetime and instability at raised temperatures. , The present system is not, for this reason, expected to have any impact on the acetone to 2-propanol heat pump problem, since temperatures in the 200 °C range are preferred there . However, the factors determining the stability of modern transition-metal nanoclusters are only just now becoming better understood, so that improvements in this area can be anticipated (and are beginning to appear , ).…”

“…The catalytic hydrogenation of acetone is an important reaction, one used to produce two industrial chemicals, 2-propanol and, at higher temperature (as a result of acetone condensation, dehydration, and subsequent hydrogenation), methyl isobutyl ketone ((CH 3 ) 2 CHCH 2 C(O)CH 3 ) . In addition, acetone hydrogenation to 2-propanol is of interest for use in chemical heat pumps or fuel cells, applications which require a higher selectivity to 2-propanol at high conversion than is presently available . The demand for 2-propanol is also increasing due to its transfer hydrogenation reactions, chemistry which exploits 2-propanol's relatively easy, selective reoxidation to acetone …”

Influence of reduction temperature on Pt–ZrO2 interfaces for the gas-phase hydrogenation of acetone to isopropanol

“…2,3 In particular, acetone hydrogenation plays an important role in renewable energy fields such as isopropanol (IPA)-acetone-hydrogen chemical heat pumps, H 2 storage schemes and direct IPA fuel cells (giving higher energy production and better stability than those of methanol or ethanol), which requires higher IPA selectivity and acetone conversion than presently available. 4,5 Conventionally, IPA is a valuable bulk commodity (massively produced by oil-derived propene hydration 6 ) extensively used in paint, medicine, and pesticide industries with growing demands, suffering from the deficiency of oil and intensive energy input. Moreover, the wide-spreading COVID-19 further stimulates IPA demand due to its disinfecting ability.…”