Veikko J. Pohjola

Stationary and transient kinetics of the high temperature water-gas shift reaction

The high temperature water-gas shift reaction over an industrial Fe3O4Cr2O3 catalyst was investigated by stationary and transient experiments in isothermal conditions and at elevated pressures. A new modular computer controlled catalyst evaluation unit which can be operated either as a plug flow tubular reactor (PFTR) or a gradientless reactor was used. The plug flow mode was used to produce kinetic data for power-law kinetic models and the gradientless reactor to generate kinetic data for classical kinetic models. Separate chemisorption of CO, CO2, and H2 were done at 293, 373, 473 and 623 or 673 K to study the importance of these components as surface intermediates in the shift reaction. In PFTR the kinetic experiments were performed at 3–5 bar and 573–633 K in two separate series during the slow decay of the catalyst activity. The age of the catalyst in these experimental series was 200–280 and 725–763 h, respectively. The transient experiments were performed in the gradientless reactor at 573–623 K and 5 bar the age of the catalyst being 200–870 h. According to the stationary studies, the reaction rate is strongly dependent on the CO concentration, weakly dependent on the H2O concentration and practically independent on the CO2 and H2 concentrations. The reaction orders with respect to CO and H2O were around 1 and 0.5. In transient experiments CO2 was always liberated faster than H2 when the catalyst pretreatment was done without water. During the pretreatment of the catalyst with H2ON2, small amounts of H2 were formed. The H2O pretreatment retarded the CO2 response. Based on these results a reaction mechanism was proposed which consisted of CO adsorption and oxidation steps as well as of H2O adsorption, decomposition and H2 formation steps. The rate determining steps were the CO oxidation and H2 formation steps. Non-dissociative (CO, CO2) and dissociative (H2) adsorption were described with Langmuir isotherms.

Re-defining waste, the concept of ownership and the role of waste management

In an attempt to construct a new agenda for waste management, this paper explores the complex relationship between definitions of waste and their subsequent impact on its ownership and management. A range of internationally accepted definitions for waste are analysed and it is concluded that they are inadequate in scope in an attempt to describe waste. The philosophical ramifications inherent in such definitions mean that they are not capable of constructing a system that by its very nature results in a sustainable waste management system. This paper explores the concept of waste and a new waste taxonomy is proposed, based on the reason for waste creation, this has profound implications for ownership which in itself often dictates which waste management options are preferentially adopted by a given community. The role of legislation in producing monitoring systems for the transfer of ownership as well as abandonment of ownership is analysed. The new agenda for waste management focuses upon the development of more appropriate, sustainable definitions so that what is now commonly perceived as being waste will in fact be increasingly seen as resource-rich, ‘non-waste’. To avoid obstacles to resource conservation due to materials being considered waste, a definition for non-waste is introduced. Finally, a new definition for waste management is proposed, one that has profound implications for the introduction of a more sustainable waste practice.

Investigation of CO oxidation and NO reduction on three-way monolith catalysts with transient response techniques

The kinetics of CO oxidation and NO reduction reactions over alumina and alumina-ceria supported Pt, Rh and bimetallic Pt/Rh catalysts coated on metallic monoliths were investigated using the step response technique at atmospheric pressure and at temperatures 30–350°C. The feed step change experiments from an inert flow to a flow of a reagent (O2, CO, NO and H2) showed that the ceria promoted catalysts had higher adsorption capacities, higher reaction rates and promoting effects by preventing the inhibitory effects of reactants, than the alumina supported noble metal catalysts. The effect of ceria was explained with adsorbate spillover from the noble metal sites to ceria. The step change experiments CO/O2 and O2/CO also revealed the enhancing effect of ceria. The step change experiments NO/H2 and H2/NO gave nitrogen as a main reduction product and N2O as a by-product. Preadsorption of NO on the catalyst surface decreased the catalyst activity in the reduction of NO with H2. The CO oxidation transients were modeled with a mechanism which consistent of CO and O2 adsorption and a surface reaction step. The NO reduction experiments with H2 revealed the role of N2O as a surface intermediate in the formation of N2. The formation of NN bonding was assumed to take place prior to, partly prior to or totally following to the NO bond breakage. High NO coverage favors N2O formation. Pt was shown to be more efficient than Rh for NO reduction by H2.

Fundamentals of safety conscious process design

An approach to safety conscious chemical process design is described and illustrated. It is taken for granted that the way the process is represented has a profound influence upon the way process design is done. Thus safety conscious process design can result only from a proper incorporation of safety into the process model. From this starting point a general purpose modeling language (the PSSP language) is introduced. The language is capable of unified object oriented representation of reality and of knowledge integration on that basis. Using the language chemical process is represented as an object having the generic list of four attributes: Purpose, Structure, State, and Performance. Safety is made an explicit property of process via Purpose, and environment is included as one of the structural parts of process via Structure. Finally Process object is associated with Design and Management activity objects to make up a mutually communicating set of the three objects called design cycle representing safety conscious process design.

Development and verification of a simulation model for a non-isothermal water-gas shift reactor

Abstract A fixed-bed test reactor suitable for studying non-isothermal reaction kinetics was developed. The reactor allows axial and radial temperature measurem The water-gas shift reaction over a commercial iron-based catalyst was chosen as the subject of a case study. A non-isothermal reactor operating at tem with feed compositions corresponding to industrial conditions was used. A method of sequential regression analysis was applied to determine the kinetic conversion profiles of the bed. The experimental data could be fitted by a power-law type of reaction rate expression. The rate equation combined with successfully used to predict the fixed-bed behaviour within large temperature, concentration and space velocity intervals.

Methodology of process design

Abstract Methodology of process design is presented as a procedural model of how process design is done. Design project, represented as an object, acts as an adaptive controller of design process by updating its own attributes. Performance driven strategy of process design is introduced and implies description of process related concepts at various levels of abstraction. Object taxonomy of declarative process knowledge is built upon a linguistic definition of process concept.

An approach to the formal theory of waste management

A solid foundation for a formal theory of waste management is offered in terms of consistent building blocks: language, conceptual schemes, models, and sentence systems. The language used to formulate the theory is the PSSP language, which is a formal modeling language having certain unique features stemming from the ontology behind the language. Via conceptual schemes, which are explications of domain concepts translated to the PSSP language, the language is enriched to cover domain terms and to become the theory-language of waste management. The models have functionality, which makes it possible to simulate waste management. The functionality is implemented as mutual communication of objects representing reality, i.e. activities and things acted on. The models are transparent dynamic object hierarchies capable of providing a holistic view of waste management, providing consistent explanation of all waste related concepts and offering a formal methodology of waste management. The plausibility test requires more sentence systems, i.e. propositions with empirical reference to waste management, to be included.

Phenomenon driven process design methodology: Focus on reactive distillation

Abstract The phenomena oriented process design approach was introduced in a previous paper [1]. In the present paper the approach is formalized into what is called ‘Phenomenon driven process design methodology’. The features of the methodology are demonstrated by applying the methodology to the design of MTBE production process. The example aims at illustrating how creativity can be included in process design in a systematic way.

A robust method for predicting state profiles in a reactive distillation

Abstract A rigorous method for solving the modified MESH equations for reactive distillation is elaborated. The equations were formulated as a problem-dependent homotopy in such a way that the homotopy path to a solution is continuous in the prescribed domain of distillation problems and rarely has turning points. This allowed us to develop a fast homotopy continuation solving method. The solution is found without any need for manual iteration, and no initial guess needs to be given by the user. The method has been tested extensively for highly non-ideal distillation. In this paper, similar success with reactive distillation will be reported and several examples of MTBE reactive distillation will be given. The robustness of the method makes it a valuable tool in the early design considerations of multicomponent ordinary and reactive distillation.

Using holistic product models to describe industrial production

Abstract The paper introduces a novel approach to taking a holistic view of industrial products and building formal product models capable of integrating data in a wider perspective than what is implemented in the ISO-10303 and ISO-14040,…, 14043 product models. The approach is unique in the sense that it is built upon a unifying ontology according to which any real thing can be represented as an object with four prefixed attributes: Purpose, Structure, State, and Performance. The approach is illustrated by building a holistic model for a fibrous product of a pulping process. The model, which is an object hierarchy, is displayed by using graphical notation. The model demonstrates, in particular, how a product in a process industry can be formally associated with material resources, their conservation and recycling.