Moving from discovery to real applications for your catalyst

Abstract

We discuss the importance of operating conditions and feed gas composition in evaluating any catalyst. Test conditions are often simplified in early catalyst evaluations, but ultimately catalysts need to be evaluated close to the anticipated process conditions if one wants to make generalizations about performance with regard to an anticipated product in the marketplace; the sooner the better. This will allow others to focus on the crucial steps that one has to take to apply a new discovery to a new or existing product. We examine several different test parameters that can significantly impact a number of different reactions. One focus is on testing catalysts early during the discovery/optimization stage under conditions which anticipate major operational hurdles down the road to eventual development and onto commercialization. In particular we discuss the importance of realistic feed-gas compositions, extreme operating conditions, understanding duty cycles, in test protocols, carbon formation, catalyst attrition, wet process feeds, transient exposure to contaminants in the feed, the need to understand the impact of pressure, and catalyst morphology. These catalyst features are applied to a variety of reactions including FCC, water gas shift, steam methane reforming, auto exhaust cleanup, ozone removal in aircraft, and refinery hydrogen production. A few extended examples are also provided using prior references that describe the conversion of lab discoveries to established commercial processes.

Introduction

Successfully commercializing catalysts is an important goal of catalyst companies. It requires a multi-disciplined team composed of personnel from R&D, marketing and sales, manufacturing and technical service. One of the most important technical factors for success in the catalyst business is having a complete understanding of the expected performance goals, life and the probable conditions the catalyst may experience during its’ life. This is referred to as the “duty cycle.”

Catalyst companies must develop testing protocols to consider variable feedstock compositions, flow rates, temperature and pressure variations, start up and shut down procedures, and of course pressure drop, life and costs among the most notable. Naturally this requires close communication with the customer, the data of which is often protected by secrecy agreements. An awareness of the expected operating conditions needs to be factored into the test protocol to qualify the catalyst.

Some processes are operated in a coking regime and therefore catalyst regeneration must be integrated into the process. Fluid bed catalytic cracking of crude oil fractions to gasoline and olefins incorporates a regenerator to remove coke from the zeolite based catalyst. The heat of combustion is integrated into the feed preheat. The catalytic dehydrogenation of propane to propylene, using an oxide of chromium (i.e. chromia) or a precious metal catalyst, generates appreciable amounts of coke which requires regeneration. In the Houdry Process for dehydrogenation of alkanes, multiple catalyst beds cycle through various process gases during which the accumulated coke is burnt off the catalyst in a separate regeneration stage (which provides the heat for the endothermic dehydrogenation), followed by evacuation, and repeating the dehydrogenation step [1]. The test protocol for both these commercial processes, therefore, must include a number of regeneration conditions as an important factor in the design and qualification of a suitable catalyst. Besides carbon formation, preventing catalyst attrition in slurry or fluidized processes is another catalyst design feature. Thus, an important factor in qualifying an acceptable catalyst for processes where the catalyst is continuously moving is its mechanical strength. Examples of such important requirements are presented throughout this article.

In this manuscript, while discussing the importance of evaluating catalysts under conditions close to actual processing conditions, we will also point out several gaps/needs in specific catalyst testing technology and methodology which are driven by the varying process conditions. Within the industry, such gaps/needs might not be pursued due to staffing, equipment and limited demands on time, while in the academic community such skills and focused characterization techniques are looking for new problems to solve. In industry fundamental research is needed, but pointed closer to the commercial target conditions. A few examples are also given of processes as they moved from discovery to commercial and the challenges that were addressed, often around the duty cycle. The authors will share some of their experiences that, following discovery, are typically factored into research and development of new commercial catalytic materials. Examples will be given for ozone abatement catalysts, water gas shift, FCC, deNO_x, catalytic reforming of hydrocarbons for H₂ generation for low temperature fuel cells and for refinery hydrogen, syngas generation and the challenges in replacing precious metals with base metal oxides in gasoline three-way automobile exhaust catalysts.

Duty cycle conditions are predictable while upsets are not and must be addressed after extensive field or in process life testing. Some examples of such transients follow. Lack of adequate temperature control, due to a failed upstream heat exchanger, will generate abnormally high inlet temperatures that will likely cause extensive catalyst/support sintering. Leaking from the failed heat exchanger will introduce oils to the feed causing selective or non-selective poisoning requiring regeneration to return the catalyst to acceptable performance. Deposition of corrosion products or sublimation of catalyst components, from upstream process equipment, will shorten catalyst life by masking reactant access to catalytic sites within the porous network of the support and may also increase pressure drop. Such is the case for many stationary pollution abatement applications. Unexpected deactivation modes are addressed in the duty cycle and are revealed by extensive field testing. Catalyst characterization, coupled with performance data is essential in determining the deactivation mode responsible for loss of life. These occurrences lead to new regeneration inventions and recommendations to the plant manager for changes in the process such as adding upstream filters or sorbents. In summary, a catalyst may work perfectly well at the optimum set conditions but upsets (due to variations in process feed conditions, delivery, weather, etc.) must be considered as possibilities before moving to a development stage or when qualifying it for commercial use. This involves looking at the expected feed conditions, temperature, pressure, etc. Anticipating these possibilities can give one commercial supplier a major operating advantage over another. Experience and a close working relationship with the customers is critical for predetermining the most probable issues to be addressed during both the development stage as well as the during implementation of any process.