Palladium Membrane Technology for Hydrogen Production, Carbon Capture and Other Applications

Principles, Energy Production and Other Applications

A Doukelis, K Panopoulos, A Koumanakos, E Kakaras

• Publisher: Woodhead Publishing
• Year: 2014
• Print ISBN:
  9781782422341
• eBook ISBN:
  9781782422419
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria chimica e biochimica

Thanks to their outstanding hydrogen selectivity, palladium membranes have attracted extensive R&D interest. They are a potential breakthrough technology for hydrogen production and also have promising applications in the areas of thermochemical biorefining. This book summarises key research in palladium membrane technologies, with particular focus on the scale-up challenges. After an introductory chapter, Part one reviews the fabrication of palladium membranes. Part two then focuses on palladium membrane module and reactor design. The final part of the book reviews the operation of palladium membranes for synthesis gas/hydrogen production, carbon capture and other applications. - Review of manufacture and design issues for palladium membranes - Discussion of the applications of palladium membrane technology, including solar steam reforming, IGCC plants, NGCC plants, CHP plants and hydrogen production - Examples of the technology in operation

1

Introduction to palladium membrane technology

K. Atsonios¹; K.D. Panopoulos²; A. Doukelis³; A.K. Koumanakos³; E. Kakaras¹; T.A. Peters⁴; Y.C. van Delft^{5 1} National Technical University of Athens and Centre for Research and Technology Hellas, Thessaloniki, Greece
² Centre for Research and Technology Hellas, Thessaloniki, Greece
³ National Technical University of Athens, Athens, Greece
⁴ SINTEF Materials and Chemistry, Oslo, Norway
⁵ Energy Research Centre of the Netherlands, Biomass & Energy Efficiency, LE Petten, The Netherlands

1.1 Introduction

From the early 1950s, when the first palladium membranes were developed for pure hydrogen production, until the present, considerable effort has been made in this field. This is illustrated by the nearly 10 000 scientific articles in the Scopus database, and the number has increased at an exponential rate over the last two decades (Basile et al., 2011; Gallucci et al., 2013). This growing interest is strongly correlated with the rapid evolution of the hydrogen economy and its need for ultra-pure H₂ for applications such as fuel cell technology. Moreover, the necessity to reduce greenhouse gas (GHG) emissions by adopting the carbon capture and storage (CCS) concept has encouraged the investigation of pre-combustion capture schemes based on H₂/CO₂ separation employing Pd-based membranes.

The first scientific paper that reported on hydrogen permeation through palladium was by Graham in 1866 (Graham, 1866). Among materials, such as nickel, palladium and platinum, that are able to dissociate and dissolve H₂, palladium (Pd) dominates because of its more efficient permeability to hydrogen over a range of temperatures compared to the other materials (Brodowsky, 1968; Yun and Ted Oyama, 2011). Besides this, the H₂ stream produced has very high purity, owing to high selectivity. Another aspect is that the feed gas from which hydrogen is separated remains at the same pressure, unlike other purification technologies such as pressure swing adsorption (PSA). Moreover, Pd membranes can be applied in membrane reactors where H₂ is among the reactants (e.g. combustion, hydrogenation) or the products (e.g. water gas shift, reforming, dehydrogenation), preferably catalytic, offering special benefits to process intensification (Basile et al., 2011; Shu et al., 1991).

Palladium membranes are currently commercially applied in specific niche markets, such as the electronics industry, that require ultra-pure H₂. However, for large-scale application of the technology, issues with manufacturing cost and durability have to be solved. Therefore, the focus of research in recent decades has been on finding solutions to these challenges, which have to be demonstrated on a larger scale in order to make palladium membranes commercially practical in these markets.

The membranes used for H₂ permeation can also be classified based on the material from which they are composed:

• Metallic: Apart from Pd, H₂ permeation through dense metals has also been investigated with other metals such as Nb, Y and Ta, pure or alloyed (Scholes et al., 2010). The main reason that palladium attracts greater interest than other metals is its unique ability to maintain a high hydrogen permeation rate at relatively low temperatures, where the majority of the process occurs, while at the same time being relatively less expensive than the other noble metals such as Pt.

• Porous inorganic: The most common porous inorganic materials that have been studied for H₂ separation are silica (SiO₂) and carbon (C). Silica membranes have low cost, high permeability and are thermally and chemically stable, but low H₂ selectivity is achieved (Lu et al., 2007). The separation mechanism is based on Knudsen diffusion, while for high quality silica membranes the molecular sieving mechanism is used. Microporous membranes made from carbon are mainly used under non-oxidizing conditions to avoid carbon oxidation. In this case, the hydrogen separation mechanism relies on molecular sieving and surface diffusion. Other inorganic materials that have been examined for hydrogen separation are zeolites, alumina, and oxides (Scholes et al., 2010).

• Non-porous polymeric: The operational mechanism is solution–diffusion. Although good permeabilities have been observed, they generally suffer from poor H₂ selectivity against CO₂, making them unsuitable for CO₂ capture concepts (Scholes et al., 2010). Due to their general inability to operate at low temperatures, they are unsuitable for gas conditioning applications such as gasification processes. Additionally, they lose their selectivity at high water vapor due to swelling, so they are used for applications with low water vapor content in the feed gas. Polymeric membranes have industrial application for hydrogen separation in special low temperature processes (Gardner et al., 1977).

In Table 1.1 the main characteristics, advantages and disadvantages of membrane types are summarized comparatively. Palladium membranes offer higher H₂ fluxes and selectivity for a wide temperature range. The weaknesses they have are overcome by the following methodologies:

Table 1.1

Hydrogen permselective membrane types main characteristics

Membrane type	Dense metallic	Microporous ceramic	Porous carbon	Non-porous polymeric
Materials	Pd, Pd alloys	Silica, Alumina	Carbon	Polymers
Operating temperature range (°C)	300–700	200–600	500–900	<100
Mechanism	Solution–diffusion	Molecular sieving	Surface diffusion, molecular sieving	Solution–diffusion
H2 selectivity	>1000	5–140	4–20	Low
H2 flux (10^−3 mol/m^2s, Δp = 1 bar)	60–300	60–300	10–200	Low
Poisoning	H2S, HCl, CO	–	Organics, adsorbing vapors at C	HCl, CO, SOx
Stability	Phase transition	H2O	Embrittlement, oxidation	Compaction, swelling, water vapors
Cost	High	Low	Low	Low
Development status	Commercial up to 60 cm long	Non-commercial	Commercial at small scale	Commercial

• the phase change at low temperatures (<300°C) is overcome by alloying with other metals such as Cu, Ag, a...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• List of contributors
• Woodhead Publishing Series in Energy
• 1: Introduction to palladium membrane technology
• Part One: Membrane fabrication and reactor design
• Part Two: Application of palladium membrane technology in hydrogen production, carbon capture and other applications
• Index