- Email: [email protected]
Pharmaceuticals and fine chemicals: Filtration and separation in the diverse fine chemical sectors
30
Feature Filtration+Separation November/December 2013
Pharmaceuticals and fine chemicals:
Filtration and separation in the diverse fine chemical sectors I
n this article Anthony Bennett investigates the use of filtration and separation technology in the fine chemical sectors, including the pharmaceutical and biotechnical chemical industries. He looks at the production of the chemicals themselves, the generation of process water for chemical dilution and the treatment of effluent from chemical synthesis processes.
Fine chemicals, especially the many chemicals produced in the pharmaceutical and biotechnical chemical sectors, are those synthesised in small-to-medium quantities but their definition is imprecise, use is wide ranging and processes employed incorporating filtration and separation technology tend to be patented and highly confidential. Here we will provide an outline of various example applications for filtration and separation technology with reference to three companies involved in the field: 3M Purification, Porvair Filtration Group and Synder Filtration. Filtration and separation technology is widely employed throughout the various chemical industries, with chemical manufacturing processes varying widely in nature and size. Numerous chemical products are synthesized and these can be categorised within the following two broad groups: Bulk Chemicals and Petrochemicals • bulk inorganic chemicals (such as gases, acids, alkalis and fertilizers) • bulk organic chemicals • man-made fibers Fine Chemicals • agrichemicals
• • • •
specialist chemicals high purity chemicals pharmaceutical ingredients chemicals and other products made by biochemical and biopharmaceutical means
The key bulk chemicals are the inorganic acids: sulfuric acid, nitric acid and hydrochloric acid. Also included are phosphates and fertilizers, chlorine, caustic soda and soda ash, and the organic intermediate materials for petrochemicals: olefins, methanol and aromatic compounds. As well as the petrochemicals themselves, other chemicals such as thermoplastic polymers are produced. Bulk chemicals are produced in massive quantities by standardised reactions for subsequent direct use. In contrast to bulk chemicals, fine chemicals are custom-produced in smaller bespoke quantities for highly specialised applications, often with a high degree of protection of intellectual property and associated confidentiality and secrecy. The methods of production need to be flexible and are often patented, and owing to the relatively small volumes required and the diversity of types, the definition of fine chemicals is wide ranging.
Production of fine chemicals is significantly more expensive per unit weight than for bulk chemicals, generates more effluent that can be difficult to treat, and requires a higher research investment per unit weight produced. Fine chemicals are, however, produced in industrial quantities unlike research grade chemicals, but batch production tends to be common as opposed to the continuous production techniques employed in bulk chemicals production. Fine chemicals can be defined as pure, single substances that are typically produced by chemical reactions for highly specialised applications. The fine chemicals produced can be categorised into active pharmaceutical ingredients and their intermediates, chemicals and other products made by biochemical and biopharmaceutical means, agrichemicals, specialty chemicals and high-purity chemicals for technical applications. Agrichemicals mainly include biocides, pesticides, herbicides and other specialised chemicals that are used in agriculture to inhibit or kill pests and weeds and improve crop yields. Specialist chemicals are a diverse category produced for a range of technical
Feature Filtration+Separation November/December 2013
applications, and are generally sold based on the performance characteristics achieved rather than price per unit weight. Types include: • inks, paints and other coatings • performance-enhancing additives • photographic chemicals • soap, detergents, toiletries and perfumes • explosives • glues • essential oils High purity chemicals include especially pure, high quality chemicals with low or undetectable levels of contaminants. Examples include specialist solvents for microelectronics. High purity chemicals are produced in batches and typically membrane technology is employed to filter out impurities on site prior to use. These chemicals are compositionally much less complex than agrichemicals or specialist chemicals but they are included in this summary because they must be significantly more pure than bulk chemicals from the perspective of dissolved and particulate contaminants.
Direct filtration and separation Figure 1: Nanofiltration System (Courtesy of Synder Filtration).
We approached a number of filtration and separation companies for details on specific case studies describing the application of their technologies in the fine chemical sectors. Due to protection of intellectual property and secrecy surrounding the production of fine chemicals we were unable to obtain specific details of individual applications but we did discuss general business activities and applications with Kevin Donahue from Synder Filtration, Andy Bevis at the Porvair Filtration Group and Katherine Barnicoat at 3M Purification. Synder Filtration manufactures flat sheet and spiral wound cross flow membrane filtration products. The product range includes nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). “Synder products,” said Mr Donahue, “are used in the fine chemicals industry for purification and concentration of both low and high molecular weight compounds.” He went on to describe an example where a drug manufacturer uses NF to reduce the salt
content of a reaction mixture containing an intermediate chemical, which is used to make an API (a well-recognised acronym in the fine chemicals industry, it stands for Active Pharmaceutical Ingredient) with molecular weight of 349 Daltons, and also for preconcentrating the material prior to a drying process. The membrane filtration process begins with diafiltration, a unit operation that utilises NF, UF, or MF membranes to remove salts or other micro solutes from a solution. Small molecules are separated from a solution while retaining larger molecules in the retentate.
molecules larger than 150 Daltons in size. Mono-valent ionic species and any compounds less than 150 Daltons in size pass through the membrane along with water.
High purity water (see Table 1 for definition), in an amount equal to six times that of the reaction mixture, is added to the reaction mixture in a batch processing tank. The same volume of water added to the mixture is then removed from the batch by passing the API/water mixture through a cross flow NF system (see Figure 1).
Mr Donahue said: “NF is used because the process consumes less energy compared with thermal methods. Furthermore, the active compound degrades at higher temperatures. Use of NF allows the product to be concentrated without affecting integrity.”
The NF system operates at 20bar and 15°C, with the NF membranes retaining a high percentage of the multi-valent ions and all
“The fine chemicals market,” Porvair’s Mr Bevis explained, “is a highly diverse market sector and to which an equally diverse
When the salt concentration in the feed has been reduced to the required level, the NF process is continued, without further addition of water, in order to remove water and concentrate the API. The material remaining in the tank at the end of the batch is at 20%-40% total solids, which is then sent to a drying operation.
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Feature Filtration+Separation November/December 2013
Table 1: Process water for production/dilution of fine chemicals.
Purified Water Apyrogenic Water High Purity Water
Resistivity Megohm.cm at 25 °C 0.2 0.8 10
Maximum Micro Organisms CFU/ml 100 0.1 1
Maximum Total Dissolved Solids (TDS) mg/l 1 1 0.5
Pyrogens (Endotoxins) EU/ml not specified 0.25 not specified
In sodium chlorate and sodium chlorite synthesis an all polypropylene pre-filter, the Porvair Polyfil P03, at 3μm rating is used to control the turbidity of the chemical solutions as the turbidity cannot be permitted to exceed a set parameter. Both these chemicals are strong oxidising agents and disposal and use of the filters has to be optimised. “A lot of the material trapped on the filters is the product of corrosion and or polymer degradation of the process equipment due to the chemicals,” Mr Bevis said. “The chemicals have to be FDA approved because they are dosed into drinking water hence the material selection.”
Figure 2: Sanitary Filter Housings. Courtesy of Porvair Filtration Group.
selection of filtration solutions in filter cartridge and filter element form is required.” Porvair Filtration Group provides a range of filtration cartridges, elements and sanitary housings (see Figure 2) employed in the various examples below.
For the filtration of a highly viscous coating used in the manufacture of optical fibers, Porvair has developed a filter using a rigid netted layer to prevent pleat distortion, the Microfil HFHV, which operates at >5 bar differential pressure. The contaminant is a gel-like substance that can damage the coating process and prevent effective data transmission. Lithium-based electrolytes used for filling batteries in electric cars use a PTFE membrane filters with a filtration rating of 0.2μm, the Fluorofil F20, as preventing particulate contamination is crucial in the application.
Reactive Silica μg/l as SiO2 100 100 20
Total Organic Carbon (TOC) mg/l as C <0.5 0.05 – 0.07 not specified
3M offers a package of single-use systems for cell culture clarification applications for biopharmaceutical customers. Single-use Zeta Plus Encapsulated System depth filter clarification solutions are available in scalable capsule formats for research and development activities, process development, pilot/clinical production, and commercial large scale production. “Zeta Plus Encapsulated Systems are designed to make cell clarification by depth filtration fast, easy and clean,” Ms Barnicoat added. 3M offers three models of Zeta Plus Encapsulated System Holders (see Figure 3) - 16EZA, 16EZB and 16EZC as a convenient single-use depth filter system for cell culture clarification. Both the Single Round (Model 16EZB) and Multi-Round (Model 16EZC) can be pivoted between horizontal and vertical positions, allowing for convenient loading and unloading, minimal footprint during filtration, minimal fluid spills during unloading and full utilisation of the filter media. The pilot scale system, 16EZA, uses up to 3.2m squared of depth filter media and is not designed to pivot. Systems can be provided for large scale batch production of up to 5,000 liters per batch (see figure 4).
Process water production Detergent based viscous cleaning solutions benefit from the use of absolute rated depth elements where the benefits of an enhanced pore oriented solids holding capacity is combined with an efficiency that is derived from a deep tortuous construction. These elements represent the “coarse” end of the market sector product offering and from Porvair are represented by the Klearfil product. Filtration of ether is provided in the electronics industry in wafer manufacture where nylon is preferred to polyethersulfone (PES) because of compatibility. Here the requirement is for a 0.2μm rating or finer because any particulate, especially metallic, is detrimental to the yields that can be achieved. Porvair manufactures a 0.03μm nylon filter for this requirement, the Hydrofil HT. Filtration of dimethyl sulfoxide (DMSO) and N-methyl pyrollidone (NMP) solvents, used for formulating pharmaceuticals predominately, requires the use of nylon, polypropylene and PTFE in place of PES for reasons of compatibility.
“A number of solvents that are used in the pharmaceutical sector, especially on the antibiotics front for liquid/liquid separation, are recycled through carbon and a PTFE membrane filter,” Mr Bevis added. At 1μm rating, Porvair’s Fluorofil F100 is used to filter the solvent removing the carbon fines that are generated. “At 3M,” Ms Barnicoat said, “our technology, products and innovation reflect what we do for our customer: advance, enhance and improve their products and processes to enable their success. 3M Purification’s dedicated technical services and laboratory personnel help solve customer’s most arduous separations problems. “Our engineers work to provide solutions that reduce the overall costs of ownership. Our researchers are constantly working on breakthroughs that make new separations platforms possible. Our products are used by researchers, process developers and manufacturing personnel for critical filtration, separation and process monitoring steps in the biopharmaceutical industry.”
Due to the wide definition and examples of fine chemicals highlighted above, process water types required for their production or dilution can vary considerably. Specifications for process water are typically defined in terms of resistivity, microorganism content, pyrogen (endotoxins) levels, reactive silica levels and total organic carbon (TOC) levels. In the production of fine chemicals we typically see that either Purified Water, Apyrogenic Water or High Purity Water is required as defined in Table 1. Purified water has a resistivity greater than 0.2 Megohm.cm (at 25°C) but is defined primarily as having a microorganisms content of less than 100CFU/ml as well as a total organic carbon (TOC) level of < 0.5mg/l as C. Apyrogenic water is purer than purified water at greater than 0.8Megohm.cm resistivity but a maximum level of 0.35EU/ml pyrogens (endotoxins) is the primary specification for this grade of water. High purity water has a resistivity of at least 10Megohm.cm.
Feature Filtration+Separation November/December 2013
Filtration and separation technology has a significant role in the production of the above grades of process water; depending on the feed water available, additional technologies may be incorporated as pre-treatment technologies. UF or MF technology can be effectively used as a pre-treatment for reverse osmosis (RO) or NF depending on the nature and variability of the feed supply to the water treatment system. UF and MF technology can also be used for final polishing of pure water and removal of bacterial endotoxins, bacteria and particles. Purified water can be produced using single pass RO systems followed by the use of ultraviolet (UV) emission technology to meet the requirement for low TOC levels. RO systems would be fitted with high rejection (HR) membranes to typically reject > 98% of the total dissolved solids (TDS) in the feed supply, thereby reducing the ionic loading onto downstream processes.
Figure 3: Zeta Plus Encapsulated Holders (Courtesy of 3M Purification).
Either electro deionisation (EDI), utilising membranes, or ion exchange technologies are required for producing high purity water; both technologies utilising specialist ion exchange resins. EDI is mainly used for deionization downstream of RO for polishing and removal of silica and other ions. When processing RO permeate, EDI systems typically achieve better than 99.5% rejection and they can produce water with up to 18Megohm.cm resistivity, the theoretical maximum resistivity of ‘ultra-pure water’ possible.
Effluent treatment Another important application of filtration and separation technology in the fine chemicals sector is the treatment of effluent from processes where the chemicals are produced. Various specialist process contractors design and build filtration systems for effluent processing and subsequent treatment by wastewater treatment companies, discharge to local watercourses, or for re-use on site as an alternative supply of process water. The latter can realise the benefits of minimising raw water supply and costs and the associated and effluent discharge costs. Typically membrane bioreactor (MBR) systems are utilised for reduction of chemical oxygen demand (COD). Effective effluent treatment by MBR relies on the selection and design of the correct membrane and bioreactor for each specific application. A biomass concentration of more than four times the value of typical conventional activated sludge plant is usually reached in the MBR bioreactor. Indeed, some of the waste sludge is periodically removed from the bioreactor to maintain the desired concentration. In textiles, for example, large quantities of water are used in production and for rinsing out dye residues from machinery. For example, a bleach works requires 50m3 to 100m3 of
Figure 4: Large Scale Zeta Plus Encapsulated System (Courtesy of 3M Purification).
water per tonne of product, while a dye works uses between 20m3 and 50m3. This volume ends up as effluent, and most of the COD is organic in nature, highly suitable for treatment by MBR technology.
the development of innovative filtration and separation technology solutions in this sector.
Conclusions
3M Purification: www.3m.co.uk/purification
In this article we have given a flavour of the wide range of applications for filtration and separation technology in the fine chemicals sector with reference to various examples and through consideration of process water production and the treatment of effluent from chemical synthesis. Currently it is estimated that 25% of the filtration and separation equipment employed in the overall chemicals industry is utilised in the fine chemicals sector in a range of smaller scale applications. These niche, bespoke and specialist applications will continue to drive
•
Further information
Porvair Filtration Group: www.porvairfiltration.com Synder Filtration: www.synderfiltration.com Contact: Anthony Bennett E-mail: [email protected]
Anthony Bennett is a specialist technical author and process technologist at Clarity Authoring. www.clarityauthoring.com
33
Feature Filtration+Separation November/December 2013
Pharmaceuticals and fine chemicals:
Filtration and separation in the diverse fine chemical sectors I
n this article Anthony Bennett investigates the use of filtration and separation technology in the fine chemical sectors, including the pharmaceutical and biotechnical chemical industries. He looks at the production of the chemicals themselves, the generation of process water for chemical dilution and the treatment of effluent from chemical synthesis processes.
Fine chemicals, especially the many chemicals produced in the pharmaceutical and biotechnical chemical sectors, are those synthesised in small-to-medium quantities but their definition is imprecise, use is wide ranging and processes employed incorporating filtration and separation technology tend to be patented and highly confidential. Here we will provide an outline of various example applications for filtration and separation technology with reference to three companies involved in the field: 3M Purification, Porvair Filtration Group and Synder Filtration. Filtration and separation technology is widely employed throughout the various chemical industries, with chemical manufacturing processes varying widely in nature and size. Numerous chemical products are synthesized and these can be categorised within the following two broad groups: Bulk Chemicals and Petrochemicals • bulk inorganic chemicals (such as gases, acids, alkalis and fertilizers) • bulk organic chemicals • man-made fibers Fine Chemicals • agrichemicals
• • • •
specialist chemicals high purity chemicals pharmaceutical ingredients chemicals and other products made by biochemical and biopharmaceutical means
The key bulk chemicals are the inorganic acids: sulfuric acid, nitric acid and hydrochloric acid. Also included are phosphates and fertilizers, chlorine, caustic soda and soda ash, and the organic intermediate materials for petrochemicals: olefins, methanol and aromatic compounds. As well as the petrochemicals themselves, other chemicals such as thermoplastic polymers are produced. Bulk chemicals are produced in massive quantities by standardised reactions for subsequent direct use. In contrast to bulk chemicals, fine chemicals are custom-produced in smaller bespoke quantities for highly specialised applications, often with a high degree of protection of intellectual property and associated confidentiality and secrecy. The methods of production need to be flexible and are often patented, and owing to the relatively small volumes required and the diversity of types, the definition of fine chemicals is wide ranging.
Production of fine chemicals is significantly more expensive per unit weight than for bulk chemicals, generates more effluent that can be difficult to treat, and requires a higher research investment per unit weight produced. Fine chemicals are, however, produced in industrial quantities unlike research grade chemicals, but batch production tends to be common as opposed to the continuous production techniques employed in bulk chemicals production. Fine chemicals can be defined as pure, single substances that are typically produced by chemical reactions for highly specialised applications. The fine chemicals produced can be categorised into active pharmaceutical ingredients and their intermediates, chemicals and other products made by biochemical and biopharmaceutical means, agrichemicals, specialty chemicals and high-purity chemicals for technical applications. Agrichemicals mainly include biocides, pesticides, herbicides and other specialised chemicals that are used in agriculture to inhibit or kill pests and weeds and improve crop yields. Specialist chemicals are a diverse category produced for a range of technical
Feature Filtration+Separation November/December 2013
applications, and are generally sold based on the performance characteristics achieved rather than price per unit weight. Types include: • inks, paints and other coatings • performance-enhancing additives • photographic chemicals • soap, detergents, toiletries and perfumes • explosives • glues • essential oils High purity chemicals include especially pure, high quality chemicals with low or undetectable levels of contaminants. Examples include specialist solvents for microelectronics. High purity chemicals are produced in batches and typically membrane technology is employed to filter out impurities on site prior to use. These chemicals are compositionally much less complex than agrichemicals or specialist chemicals but they are included in this summary because they must be significantly more pure than bulk chemicals from the perspective of dissolved and particulate contaminants.
Direct filtration and separation Figure 1: Nanofiltration System (Courtesy of Synder Filtration).
We approached a number of filtration and separation companies for details on specific case studies describing the application of their technologies in the fine chemical sectors. Due to protection of intellectual property and secrecy surrounding the production of fine chemicals we were unable to obtain specific details of individual applications but we did discuss general business activities and applications with Kevin Donahue from Synder Filtration, Andy Bevis at the Porvair Filtration Group and Katherine Barnicoat at 3M Purification. Synder Filtration manufactures flat sheet and spiral wound cross flow membrane filtration products. The product range includes nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). “Synder products,” said Mr Donahue, “are used in the fine chemicals industry for purification and concentration of both low and high molecular weight compounds.” He went on to describe an example where a drug manufacturer uses NF to reduce the salt
content of a reaction mixture containing an intermediate chemical, which is used to make an API (a well-recognised acronym in the fine chemicals industry, it stands for Active Pharmaceutical Ingredient) with molecular weight of 349 Daltons, and also for preconcentrating the material prior to a drying process. The membrane filtration process begins with diafiltration, a unit operation that utilises NF, UF, or MF membranes to remove salts or other micro solutes from a solution. Small molecules are separated from a solution while retaining larger molecules in the retentate.
molecules larger than 150 Daltons in size. Mono-valent ionic species and any compounds less than 150 Daltons in size pass through the membrane along with water.
High purity water (see Table 1 for definition), in an amount equal to six times that of the reaction mixture, is added to the reaction mixture in a batch processing tank. The same volume of water added to the mixture is then removed from the batch by passing the API/water mixture through a cross flow NF system (see Figure 1).
Mr Donahue said: “NF is used because the process consumes less energy compared with thermal methods. Furthermore, the active compound degrades at higher temperatures. Use of NF allows the product to be concentrated without affecting integrity.”
The NF system operates at 20bar and 15°C, with the NF membranes retaining a high percentage of the multi-valent ions and all
“The fine chemicals market,” Porvair’s Mr Bevis explained, “is a highly diverse market sector and to which an equally diverse
When the salt concentration in the feed has been reduced to the required level, the NF process is continued, without further addition of water, in order to remove water and concentrate the API. The material remaining in the tank at the end of the batch is at 20%-40% total solids, which is then sent to a drying operation.
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Feature Filtration+Separation November/December 2013
Table 1: Process water for production/dilution of fine chemicals.
Purified Water Apyrogenic Water High Purity Water
Resistivity Megohm.cm at 25 °C 0.2 0.8 10
Maximum Micro Organisms CFU/ml 100 0.1 1
Maximum Total Dissolved Solids (TDS) mg/l 1 1 0.5
Pyrogens (Endotoxins) EU/ml not specified 0.25 not specified
In sodium chlorate and sodium chlorite synthesis an all polypropylene pre-filter, the Porvair Polyfil P03, at 3μm rating is used to control the turbidity of the chemical solutions as the turbidity cannot be permitted to exceed a set parameter. Both these chemicals are strong oxidising agents and disposal and use of the filters has to be optimised. “A lot of the material trapped on the filters is the product of corrosion and or polymer degradation of the process equipment due to the chemicals,” Mr Bevis said. “The chemicals have to be FDA approved because they are dosed into drinking water hence the material selection.”
Figure 2: Sanitary Filter Housings. Courtesy of Porvair Filtration Group.
selection of filtration solutions in filter cartridge and filter element form is required.” Porvair Filtration Group provides a range of filtration cartridges, elements and sanitary housings (see Figure 2) employed in the various examples below.
For the filtration of a highly viscous coating used in the manufacture of optical fibers, Porvair has developed a filter using a rigid netted layer to prevent pleat distortion, the Microfil HFHV, which operates at >5 bar differential pressure. The contaminant is a gel-like substance that can damage the coating process and prevent effective data transmission. Lithium-based electrolytes used for filling batteries in electric cars use a PTFE membrane filters with a filtration rating of 0.2μm, the Fluorofil F20, as preventing particulate contamination is crucial in the application.
Reactive Silica μg/l as SiO2 100 100 20
Total Organic Carbon (TOC) mg/l as C <0.5 0.05 – 0.07 not specified
3M offers a package of single-use systems for cell culture clarification applications for biopharmaceutical customers. Single-use Zeta Plus Encapsulated System depth filter clarification solutions are available in scalable capsule formats for research and development activities, process development, pilot/clinical production, and commercial large scale production. “Zeta Plus Encapsulated Systems are designed to make cell clarification by depth filtration fast, easy and clean,” Ms Barnicoat added. 3M offers three models of Zeta Plus Encapsulated System Holders (see Figure 3) - 16EZA, 16EZB and 16EZC as a convenient single-use depth filter system for cell culture clarification. Both the Single Round (Model 16EZB) and Multi-Round (Model 16EZC) can be pivoted between horizontal and vertical positions, allowing for convenient loading and unloading, minimal footprint during filtration, minimal fluid spills during unloading and full utilisation of the filter media. The pilot scale system, 16EZA, uses up to 3.2m squared of depth filter media and is not designed to pivot. Systems can be provided for large scale batch production of up to 5,000 liters per batch (see figure 4).
Process water production Detergent based viscous cleaning solutions benefit from the use of absolute rated depth elements where the benefits of an enhanced pore oriented solids holding capacity is combined with an efficiency that is derived from a deep tortuous construction. These elements represent the “coarse” end of the market sector product offering and from Porvair are represented by the Klearfil product. Filtration of ether is provided in the electronics industry in wafer manufacture where nylon is preferred to polyethersulfone (PES) because of compatibility. Here the requirement is for a 0.2μm rating or finer because any particulate, especially metallic, is detrimental to the yields that can be achieved. Porvair manufactures a 0.03μm nylon filter for this requirement, the Hydrofil HT. Filtration of dimethyl sulfoxide (DMSO) and N-methyl pyrollidone (NMP) solvents, used for formulating pharmaceuticals predominately, requires the use of nylon, polypropylene and PTFE in place of PES for reasons of compatibility.
“A number of solvents that are used in the pharmaceutical sector, especially on the antibiotics front for liquid/liquid separation, are recycled through carbon and a PTFE membrane filter,” Mr Bevis added. At 1μm rating, Porvair’s Fluorofil F100 is used to filter the solvent removing the carbon fines that are generated. “At 3M,” Ms Barnicoat said, “our technology, products and innovation reflect what we do for our customer: advance, enhance and improve their products and processes to enable their success. 3M Purification’s dedicated technical services and laboratory personnel help solve customer’s most arduous separations problems. “Our engineers work to provide solutions that reduce the overall costs of ownership. Our researchers are constantly working on breakthroughs that make new separations platforms possible. Our products are used by researchers, process developers and manufacturing personnel for critical filtration, separation and process monitoring steps in the biopharmaceutical industry.”
Due to the wide definition and examples of fine chemicals highlighted above, process water types required for their production or dilution can vary considerably. Specifications for process water are typically defined in terms of resistivity, microorganism content, pyrogen (endotoxins) levels, reactive silica levels and total organic carbon (TOC) levels. In the production of fine chemicals we typically see that either Purified Water, Apyrogenic Water or High Purity Water is required as defined in Table 1. Purified water has a resistivity greater than 0.2 Megohm.cm (at 25°C) but is defined primarily as having a microorganisms content of less than 100CFU/ml as well as a total organic carbon (TOC) level of < 0.5mg/l as C. Apyrogenic water is purer than purified water at greater than 0.8Megohm.cm resistivity but a maximum level of 0.35EU/ml pyrogens (endotoxins) is the primary specification for this grade of water. High purity water has a resistivity of at least 10Megohm.cm.
Feature Filtration+Separation November/December 2013
Filtration and separation technology has a significant role in the production of the above grades of process water; depending on the feed water available, additional technologies may be incorporated as pre-treatment technologies. UF or MF technology can be effectively used as a pre-treatment for reverse osmosis (RO) or NF depending on the nature and variability of the feed supply to the water treatment system. UF and MF technology can also be used for final polishing of pure water and removal of bacterial endotoxins, bacteria and particles. Purified water can be produced using single pass RO systems followed by the use of ultraviolet (UV) emission technology to meet the requirement for low TOC levels. RO systems would be fitted with high rejection (HR) membranes to typically reject > 98% of the total dissolved solids (TDS) in the feed supply, thereby reducing the ionic loading onto downstream processes.
Figure 3: Zeta Plus Encapsulated Holders (Courtesy of 3M Purification).
Either electro deionisation (EDI), utilising membranes, or ion exchange technologies are required for producing high purity water; both technologies utilising specialist ion exchange resins. EDI is mainly used for deionization downstream of RO for polishing and removal of silica and other ions. When processing RO permeate, EDI systems typically achieve better than 99.5% rejection and they can produce water with up to 18Megohm.cm resistivity, the theoretical maximum resistivity of ‘ultra-pure water’ possible.
Effluent treatment Another important application of filtration and separation technology in the fine chemicals sector is the treatment of effluent from processes where the chemicals are produced. Various specialist process contractors design and build filtration systems for effluent processing and subsequent treatment by wastewater treatment companies, discharge to local watercourses, or for re-use on site as an alternative supply of process water. The latter can realise the benefits of minimising raw water supply and costs and the associated and effluent discharge costs. Typically membrane bioreactor (MBR) systems are utilised for reduction of chemical oxygen demand (COD). Effective effluent treatment by MBR relies on the selection and design of the correct membrane and bioreactor for each specific application. A biomass concentration of more than four times the value of typical conventional activated sludge plant is usually reached in the MBR bioreactor. Indeed, some of the waste sludge is periodically removed from the bioreactor to maintain the desired concentration. In textiles, for example, large quantities of water are used in production and for rinsing out dye residues from machinery. For example, a bleach works requires 50m3 to 100m3 of
Figure 4: Large Scale Zeta Plus Encapsulated System (Courtesy of 3M Purification).
water per tonne of product, while a dye works uses between 20m3 and 50m3. This volume ends up as effluent, and most of the COD is organic in nature, highly suitable for treatment by MBR technology.
the development of innovative filtration and separation technology solutions in this sector.
Conclusions
3M Purification: www.3m.co.uk/purification
In this article we have given a flavour of the wide range of applications for filtration and separation technology in the fine chemicals sector with reference to various examples and through consideration of process water production and the treatment of effluent from chemical synthesis. Currently it is estimated that 25% of the filtration and separation equipment employed in the overall chemicals industry is utilised in the fine chemicals sector in a range of smaller scale applications. These niche, bespoke and specialist applications will continue to drive
•
Further information
Porvair Filtration Group: www.porvairfiltration.com Synder Filtration: www.synderfiltration.com Contact: Anthony Bennett E-mail: [email protected]
Anthony Bennett is a specialist technical author and process technologist at Clarity Authoring. www.clarityauthoring.com
33