Critical Toolbox for a Sustainable Industrial Chemistry

PI is more than just a series of novel reactors or equipments. It offers the full potential of redesigning industrial chemical process in line with sustainability concepts. PI presents a range ofexciting processing tools/opportunities for chemists. The smaller footprints ofprocesses offer new opportunities to insert them in a factory, as visually illustrated in Figure 1.2 (Chapter 1), allowing thus a significant reduction in terms of an eyesore for the general public. In some cases the plant may be mobile, thereby offering opportunity for distributed manufacturing of chemicals. This will reduce the quantities of chemicals currently being transported by road and rail, thereby improving safety. The improved energy efficiency foreseeable in intensified unit operations constitutes yet another highly attractive benefit of PI in a world where energy cost is dominant. Better use of energy also means a reduction of emissions of greenhouse gases and in general of pollutants. PI is thus a path for the future of chemical and process engineering demands, and a critical toolbox for sustainable industrial chemistry (Figure 3.3) [7, 8].

The core of PI refers to the development of more or less complex technologies that replace large, expensive, energy-intensive equipment or processes with ones that are smaller, less costly, more efficient plants, minimizing environmental impact, increasing safety and improving remote control and automation, or that combine multiple operations into a single apparatus or into fewer devices [7]. However, we prefer to consider PI as an holistic approach starting with an analysis of economic constraints followed by the selection or development of a production process. PI aims at drastic improvements in performance of a process, by rethinking the process as a whole. In particular it can lead to the manufacture of new products that could not be produced by conventional process technology. PI is thus strictly related to innovation and sustainability in the chemical industry, and together with catalysis is the enabling factor to proceed in this direction.

Although initially PI had a conservative reception from industries due to their unwillingness to take the risks with a new technology, subsequently many companies have started to understood the potential. Many companies, for example, ICI [9, 10], Sulzer [11], SmithKline Beecham [12], Eastman Chemical [13], Dow [14],

Planet

Profit People

Figure 3.3 PI provides radically innovative principles in process and equipment design that can benefit process and chain efficiency, capital and operating expenses, quality, wastes, process safety and more, and align perfectly with the "Triple-P" philosophy of sustainable industrial chemistry. Source: adapted from "EU Roadmapfor Process Intensification" (www.creative-energy.org).

Profit People

Figure 3.3 PI provides radically innovative principles in process and equipment design that can benefit process and chain efficiency, capital and operating expenses, quality, wastes, process safety and more, and align perfectly with the "Triple-P" philosophy of sustainable industrial chemistry. Source: adapted from "EU Roadmapfor Process Intensification" (www.creative-energy.org).

Degussa [15], and so on, have embraced the PI philosophy and adopted it in several of their recent processes with commercial success.

The "European Roadmap for Process Intensification" (www.creative-energy.org) promoted by the Dutch Ministry of Economic Affairs and prepared by a group of experts of Netherlands (from both academy and industry) in 2008, demonstrates how PI offers important opportunities to modernize the process industry (oil refinery, petrochemicals, bulk chemicals, specialty chemicals, pharmaceuticals and food). Substantial savings are possible over time (energy, CO2 emissions, waste production, etc.). It is estimated that process industry can achieve a 20% reduction in energy consumption by 2050 through PI implementation alone. However, the PI Roadmap is at the same time considered as the key part of the Business Plan for Innovation of the Chemical Industry. Four main areas of application of PI have been considered in the roadmap: (i) petrochemicals and bulk chemicals, (ii) specialty chemicals and pharmaceuticals, (iii) food ingredients and (iv) consumer food. By analyzing many process intensification technologies, the following potential benefits of PI have been identified:

• Petrochemicals, bulk chemicals:

higher overall energy efficiency - 5% (10-20 years), 20% (30-40 years).

• Specialty chemicals, pharmaceuticals:

overall cost reduction (and related energy savings due to higher raw material yield) - 20% (5-10 years), 50% (10-15 years).

• Food ingredients:

higher energy efficiency in water removal - 25% (5-10 years), 75% (10-15 years). Lower costs through intensified processes throughout the value chain - 30% (10 years), 60% (30-40 years).

higher energy efficiency in preservation processes - 10-15% (10 years), 30-40% (40 years). Through capacity increase - 60% (40 years). Through move from batch to continuous processes - 30% (40 years).

In particular, two main streams of PI applications have been identified: (i) PI innovations for reactors (e.g., microreactors, monolith reactors, spinning disc reactors, reactive separations) and (ii) PI technologies for more efficient energy transfer (e.g., ultrasound, pulse, plasma, microwave). Several PI technologies offer important potential, but require important fundamental/strategic research to reach proof-of-concept on the laboratory scale. These PI technologies are:

• monolith reactors,

• microreactors,

• membrane reactors,

• membrane absorption/stripping,

• membrane adsorption,

• reactive extraction,

• reactive extrusion,

• rotating packed beds,

• rotor-stator mixers,

• spinning disc reactors.

Several other novel PI technologies have already been implemented for a limited number of applications, but further applied research is necessary for a broader implementation. The skill of designing PI equipment on an industrial scale (materials, robustness, economics) is still lacking, but for some technologies industrialization is in progress:

• plate, plate-fin, plate-and-shell, flat tube-and-fin heat exchangers,

• static mixer reactors,

• membrane extraction,

• reactive absorption,

• reactive distillation,

• centrifugal extractors.

However, there are already examples of (semi)-commercially available equipment:

• Sulzer SMR static mixer, which has mixing elements made of heat-transfer tubes, and Sulzer's open-crossflow structure catalysts, so-called Katapaks; Sulzer (www. sulzer.com) is a Swiss company active in the field of machinery and equipments;

• HIGEE (high gravity rotating contactor with a compact design, Figure 3.2); Protensive, Newcastle upon Tyne, UK, and GasTran Systems, Cleveland, Ohio, provide this technology, which also is known as the rotating packed bed;

• HIGRAVITECs rotating packed beds (Higravitec Center of the Beijing University of Chemical Technology); a 50 and a 300tonh~1 Higrav machine for oil field flooding water deaeration at Shengli Oilfield, Sandong, China have been installed [6];

• BHRs improved mixing equipment, HEX reactors (integrated reactor-heat exchangers), FlexReactor (flexible and re-configurable); (www.bhrgroup.co.uk);

• high-pressure homogenizers for emulsifications;

• the spinning disc reactor (SDR); (www.protensive.co.uk);

• supersonic gas/liquid reactor.

Various ultrasonic transducers and reactors are now commercially available. The cited roadmap identified 46 key PI technologies, even if some of them still not available commercially, and reported also their potential for saving energy and CO2 emissions, and for improving cost competiveness. Table 3.1 lists these key PI technologies and their potential, but the roadmap advises that, sometimes, the identified potential reflects in part personal opinions or expectations.

For the successful industrial implementation of PI technologies, the following enabling technologies need to be developed:

• Process analytical technology:

(in situ) measurement and analysis methods for better understanding of kinetic and thermodynamic characteristics of chemical processes at the molecular level.

• Numerical process modeling:

faster, more robust, often nonlinear numerical modeling of chemical reactions;

• Process control systems.

to cope with the incorporation of (often continuous) PI modules in (often batch) processes.

A critical element for success is to link PI to chain optimization, but this often requires a socio/economic paradigm shift, and calls for optimization studies along the value chain as well as the development of longer-term transition paths. For example, milk separation into water, proteins and fats can be conducted on-site (i.e., at the farm) with low energy-consuming micro-separators. Product transportation to, and handling at, the factory can be limited to the relevant components, proteins and fat, saving energy and reducing CO2 emissions by avoiding the unnecessary transportation of water and its removal at the factory.

The cited roadmap also reports some examples that demonstrate the role of PI towards achieving sustainability in industrial chemical processes:

• Petrochemicals, bulk chemicals:

a common traditional technology is absorption-stripping; in the application to HClO synthesis, the use of HIGEE rotating packed beds allows (i) a reduction in equipment size by a factor about 40, (ii) an increase in product yield of about

Table 3.1 General overview of the PI key technologies. Source: adapted from " EU Roadmapfor Process Intensification" (www.creative-energy.org).

PI technology Class Potential for

Energy saving Eco impact C02 Cost effectiveness

Advanced plate-type heat exchangers

Structured devices

Non-reactive

M

M

H

Advanced shell and tube type heat exchangers

M

M

M

Static mixers

M

M

M

Heterog. catalyzed solid foam reactors

Reactive

L

L

L

Monolithic reactors

M

M

M

Millisecond (gauze) reactors

L

L

M

Structured reactors

M

M

M

Micro-channel reactors

L

L

L

Membrane reactors (nonselective)

L

L

L

Static mixer reactors for cont. reactions

H

H

M

Adsorptive distillation

Hybrid

Non-reactive

M

M

L

Extractive distillation

M

L

L

Heat-integrated distillation

H

H

H

Membrane crystallization technology

M

M

M

Membrane distillation technology

M

M

M

Distillation-pervaporization

M

M

M

HEX reactors

Reactive

L

L

H

Simulated moving bed reactors

L

L

L

Rotating annular chromatograp. reactors

L

L

H

Gas-solid-solid trickle flow reactors

L

L

H

Reactive extraction columns, HT and H S

M

M

L

Reactive absorption

H

H

L

Reactive distillation

H

H

H

Membrane-assisted reactive distillation

Centrifugal liquid-liquid contractors Energy transfer

Rotating packed beds

Rotor stator devices

Hydrodynamic cavitation reactors

Impinging streams reactor

Pulsed compression reactor

Sonochemical reactors (ultrasound and low frequency sonics)

Ultrasound enhanced crystallization

Ultrasound reactors for enhanced disintegrat./phase dispersion/mass transfer

Supersonic gas-liquid reactors

Electric field-enhanced extraction

Induction and ohmic heating

Microwave heating/microwave drying

Microwave reactors for non-catal. and homog. catalyzed liquid phase process

Microwave reactors for heterogeneously catalyzed chemical processes

Microwave reactors for polymerization reactors and polymer processing

Photochemical

Plasma (GlidArc) reactors Dynamic

Oscillatory

Reverse flow reactor operation Pulse combustion drying

Supercritical separations Other

Rotating H M M

MM H

Impulse ML M

ML M

ML M

ML M

MM M

Electro-magnetic H L L

ML H

ML M

15%, (iii) a reduction to half the stripping gas and (iv) a reduction of one-third waste water.

• Specialty chemicals, pharmaceuticals:

by substituting a stirred tank reactor with microreactor the equipment size can be reduced to one-third and selectivity increased by 20%.

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