- 25 April 2007 -

Filtration in the bulk chemicals industry

In the latest in a series of articles, Ken Sutherland looks at the technical requirements regarding filtration equipment in the bulk chemicals industry.

Within the totality of economic life, as defined, for example, in the Standard Industrial Classification, the chemicals industry incorporates three significant sectors of activity:

. bulk chemicals and petrochemicals manufacture,

. fine chemicals, pharmaceuticals and medicinals manufacture, and

. biotechnology.

It should be noted that there is a somewhat indistinct boundary between heavy chemicals production and mineral processing technologies. Thus the production of pure salt by the extraction of underground rock salt could be regarded as either - but in fact is classed as a mineral production process, as are all processes for the extraction of raw materials for the chemicals sector.

The bulk chemicals industry

The complete range of chemicals activities (including the makers of personal care and household consumable products), if taken together, is one of the largest of the end-users of filtration and separation equipment. The component producing bulk chemicals incorporates a wide range of industries, varying considerably in nature, including the manufacture of:

. industrial gases, acids, alkalis, fertilisers and other bulk inorganic chemicals;

. bulk organic chemicals and petrochemicals; and

. man-made fibres (from petrochemical sources).

The world's bulk and fine chemicals output in 2007 will be worth close to $2000 billion (including pharmaceutical intermediates, but excluding the sale of pharmaceutical products), with a division of output very much along GDP lines. Thus the largest industries are in the USA and Japan, with the whole of Europe roughly comparable in size with that of the USA. The German chemical industry is by far the largest within Europe.

In earlier years the industry was almost totally operated in the more highly developed regions of the world, but in the last twenty years or so, the chemicals industry has undergone a major structural change. At the start of this period, all large companies were quite well diversified over the whole range of chemical products. Slowly this has changed to a situation where many companies have now shifted to concentrate on specialty (fine) chemicals or life sciences. Bulk, or commodity, chemicals have largely been spun off or sold, quite often to investment groups, or moved to areas of the world where the feedstocks are more readily available or the labour is cheaper.

The key bulk chemicals are the inorganic acids (sulphuric, nitric and hydrochloric), phosphates, chlorine and caustic soda, plus fertilizers, and the organic intermediate materials for petrochemicals (olefins, methanol, and aromatics). Inorganic chemicals, on the whole, have been rather slow to grow over the past few years, while organics, especially petrochemicals, have been expanding more rapidly.

The bulk manufacturing component of the chemicals industry has been having a difficult time of late, with most of those companies left in the business, certainly in Western Europe, running with low profits, or at a loss. This is a major reason why most large companies have transferred significant parts of their manufacturing operations to areas where costs are lower - both of raw materials and of manpower (or sold them altogether). The component's markets are spread around the world, and are widespread in industrial terms too, such that place of manufacture is not a critical factor in the marketplace.

In a list of manufacturing companies classified by sales, there are about 35 bulk chemical makers with sales in excess of $1 billion, although this number is not easily derived, because of the need to split bulk from fine and pharmaceutical, and also of the chemicals operations of the energy companies - which would add another half dozen at least . The leading four, by some margin, are BASF, Bayer, Dow Chemical and Du Pont, all with sales of $20 billions or more.

Merger and acquisition activity has continued in the new millennium, but perhaps not at the scale of earlier years. Previous activities had been of two main kinds:

. combination of like companies to achieve the expected economies of scale (expected, but not always achieved); and

. disposing of bulk (or commodity) chemical production units, to concentrate on speciality chemicals, where the markets are more narrowly defined and profits are expected to be higher (again, expected but not always realised).

The second of these is very much the dominant reason currently, although the private equity companies have also been busy, buying attractive company components for investment purposes.

Process filtration

In all of these chemical production processes, the great majority of them carried out in the liquid phase, the process use of filtration (and, to a lesser extent, sedimentation) is widely found, as a solid recovery step, or in purifying ingredients, intermediates or final products, and in the recycling or treatment of waste streams.

The very wide range of filtration and separation equipment is of two broad types: the one being simple, almost certainly involved only in clarification of a gas or a liquid, and with a easily defined task, while the other is intended to deal with a possibly complex task, frequently involved in solids recovery, and probably having a very detailed performance specification.

Many of the first type of filter or separator are intended to fulfil a utility function, ancillary to the main process line, and providing a service to it. Utility applications are found throughout the whole of the manufacturing and service industries, and their characteristics are usually dictated by the nature of the application - steam or air or water supply, or hydraulic or pneumatic systems, for example. Such applications are frequently independent of the nature of the end-use sector in which they are found, and, on the whole, are of similar levels of importance throughout industry and commerce.

Many also of the first type, but all of the second type are used for a process function, intrinsic to the manufacturing process, without which the plant would not work. These process applications are found widely throughout the bulk chemicals sector, usually very specific to its industrial processes, with important variations imposed by operating temperatures and pressures, by the corrosiveness of the liquid or abrasiveness of the solids in the system, and by the individual process needs, such as cake dryness or filtrate clarity.

This apparently useful division is obviously complicated by the need to decide which of the two types of filter is being considered, and it is all too true that what is a service application in one industry may be a vital process application in another.

However, another two-fold division of the filtration and separation market, that between gas and liquid filtration, can be related to the process/utility classification. With the important exception of engine air intake filters, almost all gas filtration applications can be regarded as service operations, although drawing such a sharp boundary line may not be all that obvious in some cases (for example in air conditioning systems). By contrast, however, a large proportion of liquid filtration applications are for process use, with performance characteristics dictated by downstream needs.

Filtration equipment market

Filters of all types are used in the process operations of the bulk chemicals sector, many of them large units. The utility applications are, relatively speaking, much less important, although steam and power are very often generated locally by the leading companies in this industry.

An important feature of this sector is that its range of applications is so wide that it employs every type of filtration, sedimentation and centrifugation equipment, in both process and utility applications. It is the largest user of membrane separations, again of every kind. Whilst most other industrial sectors deal with fluids that are relatively bland as far as separation processes go - moderate operating temperatures and pressures, with low viscosities and non-corrosive - this is most definitely not the case in the bulk chemicals sector. Here, filtration and separation equipment frequently have to be designed to withstand high temperatures, high pressures, and, especially, highly corrosive liquids and toxic materials. The trends in these factors are for increased severity, rather than less.

Of particular interest within this sector is the production of man-made fibres, which now represent a major component of the materials used as filter media. It is the case that a filter medium made from finer fibres than another is a more efficient filter, so the trend in the supply of filter media has been to the provision of ever-finer fibres. This, in turn, creates a demand for good filtration in the fibre production process, to keep the extrusion nozzles free of blockages. Only a very small proportion (less than 1%) of this fibre production is used for filter media - but all of it uses filters in its production.

The bulk chemical sector, like most others, is keenly aware of the benefits of finer levels of filtration, but the main developments will involve the use of membranes (and the associated cross-flow process) for liquids processing, and the need for higher temperature filters in the processing of both liquids and gases.

The bulk chemicals sector is a large one in investment terms, sitting at sixth position among the 19 classes counted as manufacturing industry (although bulk and fine chemicals taken together would be the largest such classification). It is expected to constitute just under 10% of the total global market for filtration and related separation equipment, reaching just over $3.7 billions in 2007. In overall chemical terms, the bulk component is the larger, but will have much the smaller growth rate: 4.8% per annum, compared with 7.3% for the fine chemical and pharmaceuticals component.

Equipment characteristics

A major feature of the bulk chemicals sector is its operation with large continuous plants. A corresponding feature of its filters, or at least its process filters, is that they are likely to be large, and wherever possible to have reliability of continuity as a key operating characteristic. Batch filters are still used in considerable quantity, but they will tend to be installed in batteries, side by side, so that each can be taken off line in turn.

As many processes will have corrosive fluids, then the equipment will need to be made from stainless or more exotic steels, or from ceramic materials. A high proportion of the filters made from special materials are to be found in the chemicals sector.

Many of the processes operating in the bulk chemical industries handle quite toxic materials and need very clean working conditions. This creates a need for careful containment of the process materials and therefore for very good vent air filters to prevent the escape of toxic materials into the external environment, either as solid particulate or as gaseous impurities, for which combination filters may be necessary.

As with almost all of the process industries, the key development required in separation equipment needed here is the ability to achieve very fine degrees of filtration in both liquid and gas processing or containment, and to do this with the minimum of energy consumption.

Equipment range

As has already been stated, this end-use sector has such a wide range of applications that it employs every type of filtration, sedimentation and centrifugation equipment, in both process and utility applications. Some types of process filter exist only for their use in bulk chemical manufacture. Thus, considering just the fertiliser industry, one finds:

. special screens used in grading superphosphates, and compound fertilisers;

. the tilting pan filter, developed for and mainly used in the manufacture of phosphoric acid, for the removal of gypsum; and

. filters used in especially aggressive conditions for the recovery of catalysts during the manufacture of ammonia and nitric acid.

As well as being a major user of membrane filters for process water intake and intermediate and final product purification, this sector also uses a high proportion of the whole range of filtration centrifuges, in crystal recovery and separation of polymer granules. Particle size classification is another important use of continuous centrifuges, both by filtration and sedimentation.

Contact:
Ken Sutherland
E-mail: ken.suth@ntlworld.com