Utilising renewable resources economically: new challenges and chances for process development

Abstract

In recent years a considerable increase in interest in the development of processes based upon renewable resources has occurred. One reason for this development is the call for more sustainable and environmentally benign production processes and products.

Increased utilisation of renewable resources, however, poses new challenges to chemical and process industries. These challenges arise from increased competition for renewable but still finite resources, the de-centralised production of the renewable resources and the complexity of the raw materials. These new challenges require new approaches to process development, as production systems become more complex and interlinked, logistical considerations become increasingly important and new technological solutions must be adapted to local and regional settings. As the structure of complex production systems must be newly developed and optimised, process synthesis will play an increasingly important role in process development.

Introduction

Over the last 50 years chemical engineering became focussed on fossil oil and more recently on natural gas as its main raw material resources. Oil and natural gas replaced coal that acted as the primary source for chemical products during much of the 19th century up to the middle of the 20th century.

As a matter of fact, the raw material source shapes the structure of the industry that utilises it. With coal as a base of synthesis, the bulk production of chemicals centred around the big coal fields or along rivers that provided convenient arteries for the transportation of coal. Almost all synthesis processes started with the products from coal gasification, mainly via the Fischer–Tropsch synthesis. This required chemical engineering to start from fairly small molecules and then build synthesis of more complex molecules on this small set of intermediaries.

The switch to oil in turn diversified both the raw material base and the choice of sites for chemical plants. As an ever expanding net of pipelines efficiently distributed crude oil throughout industrialised countries, refineries sprung up in locations that were closer to demand, especially demand of fuel. One of the advantages of fossil oil over coal is the much increased set of intermediary materials that can subsequently be used for chemical products. Refineries now act not only as major distribution hubs but also as a “switchboard” for materials by separating the multitude of divers materials contained in crude oil into a rich set of intermediaries for further treatment. Bulk products, like polymers (polyethylene, polypropylene), are produced close to these refineries. Other intermediaries, however, may be easily transported as they are predominantly liquid and distributed to chemical plants that are more free now to follow economical incentives like closeness to demand, good infrastructure and, increasingly, cheap labour.

The switch to crude oil as the primary raw material source considerably invigorated chemical engineering. The diverse set of intermediaries that can be extracted with reasonable effort from crude oil allowed for a much richer roster of processes and products. Additionally, synthesis of complex materials could be started from more complex intermediaries. This reduced synthesis costs and added a boost of the chemical sector in the second half of the 20th century.

Crude oil, however, is a finite resource. Although there is no immediate danger that this resource will be completely depleted within the next few years (strategic reserves are estimated to be anywhere between 30 and 80 years), development of supply and demand of crude oil as well as the rate of discovery of new exploitable reserves indicate problems for this resource and all sectors based on it over the next one or two decades.

Fig. 1, from Schindler and Zittel [1], graphically depicts these problematic developments. As can be seen from this figure, actual crude oil production deviated from technically possible production around the time of the first oil shock in the early 1970s and has consistently lagged behind ever since. Following the path of technically feasible production, we would have already experienced the production maximum around 1990. As real oil production lagged behind the technically possible production, this production maximum must now be expected at a point around 2010. It must be stated again that this does not mean crude oil will be depleted by that time. However, prices for this resource will consistently increase as the increase in demand can no longer be offset by increasing production. A typical forewarning preceding such a situation are price fluctuations, since prices become increasingly vulnerable to anticipated influences on production capacities, a situation we already faced over the last years.

Fig. 1 also shows the mean of yearly new discoveries of exploitable crude oil reserves. It can be clearly seen from this figure, that there is a consistent decrease in the amount of new discoveries, adding to the overall picture of a finite resource at the height of its exploitation rate.

In the energy sector we have experienced a significant switch from oil-based fuels towards natural gas as a fuel, especially in industry. This change has been driven by prices on the one hand but on the other hand also by environmental considerations, as natural gas has a significantly lower impact on global warming than oil or coal. However, the supply and demand pattern of natural gas follows that of crude oil with a delay of some 20 years. This means that a switch to natural gas as a resource for the chemical industry is an interim solution at best, buying time but not solving the underlying problem. Besides natural gas would require considerable restructuring of the sector, as pathways of its utilisation from the point of view of chemical engineering is closer to the utilisation of coal than that of oil. A switch back to coal seems to be impossible from the environmental point of view, as a much larger impact on global warming must be expected in this case.

Taken together the analysis of the current situation of raw material supply to the chemical sector implies a profound change of the material base of chemical industry within the next one or two decades. A leading contender to take the position of crude oil as the primary source of raw materials for chemical industries is biomass. This paper explores the implications of a switch to this “new” raw material base and the necessary changes in structure as well as technology that will be entailed by a wider use of renewable resources in the chemical sector.