1. Introduction
Cartridge filters are designed for use within a wide range of applications and will come into contact with many chemicals that are either being filtered in their own right or are used to supplement the overall process. As well as using a cartridge filter to purify a fluid, its ability to be cleaned whilst in situ within its housing (cleaned in place – CIP) is a desirable option for many users. The purpose of this document is to detail how domnick hunter determines filter chemical compatibility as a guideline to users. These data are used as the basis for recommendations on filter use. However, it should be noted that in addition to these basic data, domnick hunter has a dedicated technical support group who can advise on specific applications and conduct additional compatibility trials where base line information is not available or insufficiently detailed.
2. Chemical Compatibility Analysis
Determination of filter chemical compatibility can be divided into three functional procedures.
i) Determination of Component Compatibility
This provides data based on physical changes to components following defined exposure to the test chemical. Compatibility judgements are then based on variance from the non-exposed component.
ii) Filter Cartridge Compatibility
This provides data following exposure of the complete filter cartridge to the test chemical. Compatibility judgements following exposure can then be based on functional and physical parameters such as cartridge dimensions, flow rates, burst strength, bubble point and where applicable integrity tests correlated to bacterial challenges such as diffusional flow and water intrusion tests.
iii) User Validation
In some cases it may be necessary to conduct specific compatibility tests to ensure compatibility under very defined conditions (e.g. unusual exposure times, temperatures and pressures). These tests may be conducted either at the user facility or in the domnick hunter laboratory facility. Details of these functional procedures are detailed as follows.
i) Component Chemical Compatibility
Representative samples of cartridge filter components are evaluated against set key parameters as a benchmark prior to exposure to the test chemical. The components are then placed in contact with the test chemical and are removed after specified periods to enable the key parameters to be re-checked. Visual appraisal is also conducted during and after the contact period. Table 1 details the test parameters and limits. Standard test conditions are based on 72 hours contact at designated test temperature (typically 20°C (68°F)). These conditions may be changed to reflect user specific requirements. Intermediate inspection of the components may be carried out to provide data for shorter contact times, particularly if limited compatibility has already been determined. Based on the results, the components are given designations of compatible, not compatible or limited compatibility. In the latter case it may be necessary to undertake additional tests to determine if limited compatibility is acceptable in the target application. domnick hunter Technical Support Group should be contacted for further advice.
Table 1 - Filter component test parameters and limits
Notes: Percentage values given are defined change in measured parameter for limited compatibility. Unless otherwise shown, percentage change refers to both increase and decrease in the measured parameter. Extent of change outside these ranges imply that the component is compatible (lesser change) or not compatible (greater change) under the test conditions.
ii) Filter Cartridge Chemical Compatibility
Standard production samples of the required filter cartridge type are selected. The samples are subjected to a series of functional and physical tests as detailed in Table 2. In any cases where the component compatibility tests suggested potential disruption to the filter media, cartridge flow characteristics are also assessed. The samples are then immersed in the test chemical. Duration and temperature are chosen according to specific requirements, or a standard contact period of 72 hours at 20°C (68°F) is used. The samples are removed, rinsed and re-assessed against the same key parameters as detailed in Table 2. Where determination of flow characteristics was initially carried out, this is repeated. Visual appraisal is conducted during and after the contact period. The filter cartridge is deemed compatible if all test parameters remain within the specifications defined in Table 2, and where applicable meet integrity test limits.
Table 2 - Filter cartridge test parameters and limits
Notes: (1) Tests carried out in water for hydrophilic products and 60:40 v/v IPA/water for hydrophobic products. (2) Visual bubble-point technique carried out for media filter cartridges. (3) Full aerosol retention required for sterilising grade gas filters. Percentage penetration measured for others. Percentage values given are defined change in measured parameter for limited compatibility. Unless otherwise shown, percentage change refers to both increase and decrease in the measured parameter. Extent of change outside these ranges imply that the component is compatible (lesser change) or not compatible (greater change) under the test conditions.
iii) Process Simulation and User Validation
To take into account erosive effects of the process, controlled trial under simulated or actual process conditions may be carried out. The protocol for these tests is agreed with the end user and will usually incorporate the need for the filtered product to meet specification as well as the filter itself maintaining integrity for the required duration. Please contact domnick hunter Technical Support Group for more information.
3. Chemical clean in place (CIP)
Cleaning in place (CIP) minimises operator resource requirements, avoids the need to compromise the filtration installation and substantially reduces system downtime. CIP may be achieved by using steam (steam in place – SIP), hot water or chemicals and, by proper choice of cleaning agents for chemical CIP, the procedure can be enhanced to provide a degree of regeneration (i.e. unblocking) of the filter. The process of chemical CIP can generally be separated into two major functional groups: i) Major cleaning and sanitising of process pipelines and plant to remove long term build-up of deposits from pipe walls and valve seats. Acidic descalers and caustic detergents are often used, and these procedures should be treated separately from filter CIP (see point ii) to avoid premature blockage of the filters from deposition of debris on the filter media. It is therefore recommended that filters are either removed from the system prior to this type of cleaning activity or by-passed. ii) Routine filter CIP programs, developed to minimise dirt and bacterial build up in and around filter installations. domnick hunter filters are designed to have wide ranging compatibility with commonly used CIP chemicals and procedures. The Technical Services Group can advise on the general procedures for CIP and will work to align these to users’ standard operating procedures wherever possible.
4. Technical Support Group activities
domnick hunter have a trained team of scientists and engineers available to answer questions regarding the technical capabilities of our products, to assist in the selection and design of appropriate filtration systems and to provide user training programs. The following services can be delivered both on site and in-house;
- filterability testing to optimise filter system design
- advice on the development of integrity testing, steam sterilisation and clean in place procedures
- development of validation procedures
- troubleshooting
- facility audits to ensure continued optimisation of filter use
- operator training including filtration theory, filter system design and management, validation, etc.
For more information on any of the above support services please contact your local domnick hunter representative. email: tsg@domnickhunter.com
