Separation Technologies for the Industries of the Future (1998)

Separation processes are essential elements of the technological foundations of the seven IOF industries included in this report. For the chemical and petroleum refining industries, separation processes are used to separate and purify the products of reactions. For the aluminum, steel, and metal casting industries, separation processes are used, among other things, to purify molten metal and to sort scrap. For the glass industry, separation processes are essential to the recycling of preand postconsumer cullet, and for the forest products industry, separations are involved in nearly all process steps of pulping and papermaking. In addition to the importance of separation technologies in industrial processes, separation processes also present opportunities for waste reduction and more efficient use of energy and raw materials. New developments in separation technologies are, therefore, critical for the continued productivity and global competitiveness of these industries.

In its analysis of key separation process needs, the panel included the seven industries involved in the OIT research program at the time of the panel' s inception. These seven industries are the chemical, petroleum refining, aluminum, steel, metal casting, glass, and forest products industries. Although the panel identified a number of areas where separation issues affect more than one of these industries, the panel also concluded that they are highly diverse in terms of their separation needs and technologies and warrant individual treatment. In fact, the panel found that many important separation problems are industry-specific.

Although separation technologies are essential to all seven industries, there are few cross-cutting research opportunities. Because of the diversity of raw materials, product forms, and processing conditions in these industries, research opportunities are mostly industry-specific. The panel, therefore, does not believe that the OIT program would be significantly more efficient if a single cross-cutting research program in separation technology were established.

However, a relatively well developed separation technology in one industry might be transferable to another industry, and a few technology areas are relevant to some, if not all, of them. The panel, therefore, recommends that the technical program managers at OIT coordinate separation research among the IOF industries, and monitor and disseminate the results. The panel identified five opportunities for coordinated programs: improved separation processes for the chemical and petroleum refining industries; bulk sorting technologies for the materials processing industries (especially aluminum, steel, metal casting, glass, and polymer recycling); separation technologies for dilute gaseous and aqueous waste streams; drying and dewatering technologies; and lower cost oxygen production. These five areas are described further below.

The chemical and petroleum refining industries have a number of separation issues in common. In addition to general improvements in process efficiency, the panel identified two separation technology areas with the potential to meet some of the needs of both industries:

• separation methods that use multiple driving forces, including processes in which a naturally occurring driving force for a specific operation is enhanced by an intervention that changes the system thermodynamics or in which two or more separation techniques are coupled (combined membrane separations and distillation; affinity-based adsorbent separations; and electrically aided separations)
• separations associated with chemical reactions, in other words, methods that combine reaction and separation in one process step (reactive metal complex sorbents and chemically facilitated transport membranes; coupled chemical synthesis and separation processes; membrane reactors; and electrochemical methods of separation)

A number of the materials processing industries (aluminum, steel, metal casting, glass, and the polymer-recycling sector of the chemical industry) identified separation

needs that can be classified as materials handling and sorting issues, specifically, high-speed scrap separation. Examples include separation of wrought from cast aluminum alloys, separation of aluminum scrap from other metals, separation of copper and other contaminants from solid steel scrap, and separations of polymers for recycling.

Research and development in this area should focus on making processes more economical. Higher speed sorting technologies, such as air jet and conveyer belt technology systems, could be developed and implemented. This is an area where several industries could benefit from research and development of the same technology, including:

• on-line sensors for high-speed analysis of the composition of streams and the makeup of individual objects in these streams
• physical separation techniques, including gravity separations (e.g., air jet separations, flowing film separations), magnetic separations, and electrical separations (e.g., electrostatic separation and tribo-electrification)
• high-speed sorting technologies, including the fundamental mechanics of high-speed conveying, techniques to position individual scrap pieces in sequential arrays before analysis, and methods for physically diverting the analyzed pieces by material type

The panel identified the separation of components from dilute gaseous and aqueous streams as an opportunity for cross-cutting research in separations technology. All of the IOF industries identified one or both of these areas as important. Examples of separation needs regarding dilute gaseous streams include the removal of VOCs from various gases in the petroleum refining and steel industries; the removal of NO_x, SO_x, VOCs, and particulates from aluminum effluent streams; and the removal of CO₂ from O₂ combustion product exhaust streams. Examples of separation needs regarding dilute aqueous streams include: the separation of metal salts, inorganic compounds, and particulate matter from aqueous streams in the chemical industry; the removal of organics from wastewaters in the petroleum refining industry; and the removal of contaminants, such as inorganics and alkali-soluble elements, from pulping streams in the forest products industry. Potential areas for cross-cutting research include:

• methods for separating components from dilute gaseous streams, such as adsorption, high-selectivity membranes, inorganic membranes, and advanced-particle-capture technologies for the removal of submicron (< 2.5 micron) and micron-sized particles

• methods for separating components from dilute aqueous streams, such as reactive metal complex sorbents, reducing agents, air oxidation combined with absorption, membranes, steam and air stripping, electrically facilitated separations, destructive-oxidation techniques, electrodialysis, ion exchange, and crystallization

Another cross-cutting area for research is drying and dewatering technologies. Several industries, including the chemical, petroleum refining, metal casting, and forest products industries, have identified separation needs that could be met by improvements in drying and dewatering technologies. Examples include: the removal of solvents from polymers (devolatilization) in the chemical industry; the removal of entrained water from crude oil and the drying of natural gas in the petroleum refining industry; the drying of ceramic casting materials and reclamation sand in the metal casting industry; the drying of paper in the papermaking process of the forest products industry; and the drying of sludges from waste gas scrubbing and wastewater treatment.

The chemical, petroleum refining, aluminum, steel, and glass industries have stated that inexpensive, high-purity oxygen would be beneficial to them in combustion (oxy-fuel) and other processes. The attraction of oxy-fuel is lower NO_x emissions compared to air and significant energy savings from not having to heat the nitrogen in air. Although the cost of oxygen is relatively low compared to many other chemical products, it is currently high enough to be a significant barrier to the implementation of many new, energy-saving applications.

The panel identified five enabling technologies that, although they are not separation processes, would promote improvements in industrial separations. These are membrane materials, sorbent materials, on-line diagnostics and sensors, an improved understanding of thermodynamics, and particle characterization. The panel recommends that OIT focus its long-term, fundamental research on these areas.

No single material can have all of the desired characteristics for membrane separation technologies. Important properties for emerging membrane materials

include impact strength, flexibility, thermal stability, and transport properties. The development of materials for a specific application may be economical if the application is sufficiently widely used. In general, however, research should be focused on membrane materials that are useful for a variety of applications. Promising areas of research include the following:

• polymer membranes with improved selectivity and flux
• inorganic membranes, including thin, nanostructured membranes for gas separations (research should be focused on molecular template-directed synthesis of nanostructured zeolite or inorganic materials and an economical synthesis of carbon molecular sieve membranes with uniform and small pore sizes)
• polymer-inorganic hybrid materials for high-selectivity applications (research should be focused on tunable synthesis and the fabrication of low-cost membrane modules)

Sorbent materials could enable the development of several separation technologies. The newest class of sorbents can now be moved between sorbing and desorbing zones, much like the typical absorption/desorption cycle. A form of continuous processing has thus been commercialized. This process is currently being used to remove small concentrations of organic contaminants from gas vent streams.

On-line characterization of material streams in separation processes would benefit all of the IOF industries. Much of the technology to control key parameters, such as flow, temperature, pressure, or mass, are commercially available. Many feedback algorithms are well known, and ample computing power and memory are available to implement these on a real-time basis. In many cases, the limiting components are process sensors, especially accurate and selective chemical sensors that can maintain their performance in harsh or extreme manufacturing environments.

Specific opportunities for improving on-line sensor technology are listed below:

• sensors to determine compositions on-line at various points within a distillation column so it can operate as close as possible to minimum reflux
• sensors that can detect inorganic compounds, such as dissolved metals and transition metals, in aqueous systems
• sensors that can characterize the amount, size, and shape of particles

• sensors that can characterize the composition of streams and the makeup of individual objects in these streams for sorting

Four factors that must be considered in the development of new sensors for manufacturing are: the potential for fouling, interference from minor contaminants, ease of maintenance and replacement, and cost.

The ability to separate a mixture efficiently is closely linked to the best possible use of the driving forces available for the separation. In most separations, the thermodynamic description of equilibrium between two phases is an indispensable tool for characterizing driving forces. Research in phase equilibrium is hardly new, and the volume of information available to researchers is extensive. Nevertheless, several areas of phase equilibrium relevant to separation processes have been sparsely researched. Opportunities for fundamental research in phase equilibrium include the following:

• mixtures in which one or more components of importance are at very low concentrations (e.g., parts per billion)
• systems in which reaction accompanies the attainment of equilibrium (e.g., the absorption of H2_S into amine and other basic solutions)
• ''extreme-condition'' equilibrium (e.g., temperatures well above 100°C or well below 0°C and pressures in the supercritical-fluid range)

To supply the critical thermodynamic information for many separations in these areas, advanced analytical-chemistry technology must be combined with phaseequilibrium equipment, followed by the derivation of correlations that accurately describe and generalize the experimental data.

Particles are ubiquitous in industrial processes. The properties of particles that are important to characterize depend on the process and the nature of the particles. Particle characterization has many significant process applications. Characterization methods must, therefore, be robust and have appropriately rapid response times for the system. For some applications, such as the monitoring of particulates in stack gases, the characterization device must either withstand a harsh environment or function via remote sensing.

Based on the opportunities identified by the panel for each industry and the maturity of separations technologies, the panel has identified some general criteria

for OIT to select research and development projects. The panel determined that the following selection criteria should be used:

• Time Scale. Projects should focus on high-impact technologies that have been demonstrated in the laboratory and will be ready for commercial application in five to seven years.

Although the industry vision statements focus on goals for 2020, moving as quickly as possible toward new, practical, and economically viable technologies is imperative because of the long commercialization times for the large-scale processes used by the IOF industries. Five to ten years may easily pass between laboratory demonstration of a concept and its subsequent first commercialization. Widespread commercialization can take several more years. Also, revolutionary technologies naturally take longer to commercialize because of higher risk of failure. Technologies that take longer than five to seven years to develop will have an insignificant effect on energy consumption and raw-materials utilization by 2020.

A portfolio designed to meet the five to seven year time frame will limit the projects OIT should consider funding. First of all, fundamentally oriented, diffuse projects will not be likely to have commercial applications by 2020, except in cases where the experimental data obtained can have a significant impact on the large existing capital-equipment base of the IOF industries. Second, each project should include process design and economics components, including the economics of the current technologies against which the proposed technology will be evaluated and reasonable economic targets. Every project in the portfolio should be evaluated annually to ensure that the work is progressing satisfactorily toward these targets.

• Cross-cutting Criteria. OIT should only support cross-cutting research in separation technologies that are either (1) embryonic technologies that could lead to major advances in several industries or (2) improvements in mature, high-use technologies where incremental improvements could have a substantial effect.

In some instances, a separation technology is well developed in one industry but not well known in another where it might be profitably used. In these cases, cross-industry conferences and other exchanges of information should be fostered and facilitated by OIT. Because of certain technological similarities among the IOF industries, significant technology transfers between industries may be possible. OIT should encourage this aspect of research.

• Impact on Existing Processes and Equipment. Proposed projects should be evaluated for the potential economic impact of a new separation method

• and for the potential effect of that new method on existing processes and equipment. OIT should consider funding the development of fundamental data when knowledge of such data can produce substantial improvements in existing separation processes.
• • New Technologies. Projects for the development of new separation technologies should be multidisciplinary and should be potentially scaleable to production volume, both in technical and economic terms.