Assessment of cleaner process options: A case study from petroleum refining

Abstract

Assessment of process changes to reduce, recycle or avoid wastes requires attention to systems which are broader than the immediate process; that is, it is necessary to take a life cycle perspective. Definition of the system boundary for such an assessment can be problematic in itself. A real case study is presented to illustrate the problem of assessing clean technologies: possible modifications to an alkylation unit at a UK refinery. The process uses hydrogen fluoride as alkylation catalyst, and generates fluoridic wastes which are hazardous and require treatment both onand off-site. Possible changes to avoid, reduce or enable partial recycling of the waste are identified, representing different levels of change in the process and therefore requiring assessment with different system boundaries. The different system definitions lead to differences in the ways data must be compiled for quantitative environmental life cycle assessment, and in the range of stakeholders explicitly or implicitly involved in assessing and implementing the changes. The case study demonstrates some of the less familiar challenges introduced by the "pollution prevention" or "clean technology" paradigms of chemical processing.L'évaluation des modifications apportées dans les procédés dans le but de réduire, recycler ouéviter les gaspillages nécessite qu'on prête attention aux systèmes plutôt qu'aux procédés eux-mêmes, en ce sens qu'il faut travailler dans une perspective de cycle de vie. La définition de la limite de système pour une telleévaluation peutêtre problématique en soi. Uneétude de cas réelle est présentée pour illustrer le problème de l'évaluation de techniques propres; il s'agit de modifications possiblesà une unité d'alkylation dans une usine du Royaume-Uni. Le procédé emploie du fluorure d'hydrogène comme catalyseur d'alkylation et produit des déchets fluorés qui sont dangereux et qui nécessitent un traitement sur le site et en-dehors du site. Des changements possibles pouréviter ou réduire les déchets ou permettre leur recyclage sont identifiés; ils correspondentà différents niveaux de changements dans le procédé, et par conséquent, requièrent l'évaluation de différentes limites de systèmes. Les différentes définitions de système mènentà des différences dans la manière de compiler les données pour l'évaluation des cycles de vie environnementaux quantitatifs, et dans la manière de traiter les parties prenantes explicitement ou implicitement impliquées dans l'évaluation et la mise en oeuvre de ces changements. L'étude de cas illustre certains des défis les moins familiers introduits par les concepts prévention de la pollution ou technologie propre dans le génie des procédés.Keywords: clean technology, waste minimization, process selection, life cycle management, alkylation INTRODUCTIONThe Paradigm Shift in Chemical Processing O ver roughly the last two decades, there has been a shift in both thinking and practice away from the "clean-up" or "end-of-pipe" technology approach which had replaced the "dilute-and-disperse" approac...

Streamlined Life Cycle Approaches for Use at Oil Refineries and Other Large Industrial Facilities

“…The levels of decision in Figure 2 are closely associated with the levels of change to produce a particular product by a cleaner route as recognized by Allen 8 and discussed in this context by Weston et al. 9 These are as follows:…”

“…The routes by which fluorine is lost from the HF process are described in depth by Weston et al 9 Each route leads to its own form of fluoridic waste which include potassium fluoride (which goes to wastewater treatment), aluminum fluoride (used as a flux in external aluminum manufacturer), and sodium fluoride (treated at a waste facility). It is the latter that is the largest in volume, the costliest, and the most operationally intensive for the refinery to deal with.…”

Hydrogen fluoride capture by imidazolium acetate ionic liquid

“…Alkylation is a common process in oil refineries to produce high octane gasoline from isoparaffin olefins. 33 This process employs sulfuric and hydrofluoric acid as catalysts leaving traces of sulfur and fluorine as by-products. 34 Residual concentrations of hydrofluoric acid are enough to cause severe corrosion in pipe lines, storage tanks, containers, valves, etc.…”

“…These drastic problems motivate the search of efficient HF scavenger agents. 33,34 RTILs represent a promising option due to versatility of the exhibited inter-molecular interactions. RTILs can be considered a large and interesting group of solvents for adsorption and extraction of HF from alkylation gasoline.…”

Modelagem matemática de um reator industrial de alquilação de butenos utilizando HF como catalisador.

“…Na seção inferior da torre de regeneração há uma alimentação de iC4, cuja função é retificar o produto de fundo, de maneira a minimizar a perda de ácido pelo fundo da torre. O HF forma um azeótropo com a água, com aproximadamente 35% de ácido, portanto essa é uma grande fonte de perda de ácido da unidade (WESTON et al, 2008). Os hidrocarbonetos provenientes do decantador ácido são enviados para a seção de fracionamento, composta por um conjunto de torres de destilação com objetivo de fracionar essa corrente em HF (que foi arrastado do decantador), propano, iC4 (que foi alimentado em excesso ao riser), n-butano e alquilado.…”