(182g) Enhanced Hydrogen Production with Integrated Carbon Sequestration Using Mg(OH)2 Sorbent

Hydrogen production is vital to our energy future, particularly as a raw material in synthetic fuel synthesis. Synthesis gas, generated from the gasification of carbonaceous material, typically has a CO:H2 ratio of approximately 2:1 while a ratio of 1:2 is desired for liquid fuel synthesis. In order to achieve the desired CO:H2 ratio, large catalytic reactors are often used to produce additional H2 via the industrial water-gas-shift (WGS) reaction. Some recent WGS system reaction designs integrate carbon capture technology. The removal of CO2 generated during WGS reaction, through CO2 capture (e.g., membrane or high temperature sorbent technologies), will shift the equilibrium towards the products; thus, enhancing the hydrogen yield. Ca-based sorbents seem to achieve the enhanced hydrogen production successfully, yet these materials are not a permanent carbon storage methods since they likely originate from naturally occurring carbonates like limestone. Thus, CO2 capture using Ca-based sorbents must regenerate the sorbent, adding the energy penalty and associated cost. In this study, we focus on another metal oxide sorbent, magnesium hydroxide (Mg(OH)2) because unlike Ca-based sorbent Mg(OH)2 does not require sorbent regeneration. Gas-solid carbonation of a Mg(OH)2 sorbent is thermodynamically favored within the temperature range associated with WGS reaction. Theoretically, when coupled with the WGS, the hydrogen conversion can sustain near 100% until the calcination temperature of MgCO3 is reached; thereby eliminating the need for the larger and inherently more costly, Low-Temperature Shift (LTS) reactor. Previous research into the carbonation of Mg(OH)2 showed that kinetics limit this reaction, and the exact reaction pathway is not well understood. Some have suggested that the dehydroxylation-carbonation process is very much path dependent. Thus, this study focuses on the synthesis of an engineered Mg(OH)2 sorbent with controlled mesoporous structures to provide maximum conversion during gas-solid reactions, while identifying the reaction rate and mechanisms of various reaction paths. The ultimate goal is to utilize abundant magnesium-silicate minerals like serpentine and olivine to synthesize a Mg(OH)2 sorbent that is both environmentally benign and highly reactive. This sorbent has the ability to fundamentally improve the industrial WGS reaction process while also sequestering CO2 that would otherwise have been vented to the atmosphere.