Once a used PTFE filter has been cleaned and reclaimed, can it return to new-filter levels? Rather than answer with adjectives, it is better to look directly at the data. Below are side-by-side measurements of a new and a reclaimed 10 nm PTFE filter:
| Test item | Unit | Spec limit (10 nm item) | New filter | Reclaimed filter |
|---|---|---|---|---|
| Retention: 5 nm gold nanoparticles (GNP) | % | — | 99.4 | 99.3 |
| Organic contamination: non-volatile residue (NVR) | mg/device | 18 | 3.5 | 1.8 |
| Metal contamination: extractables of 23 metals | ng/device | 3,500 | 330.5 | 353.2 |
| Organic contamination: C12–C30 long-chain hydrocarbons | — | — | < 0.5 ppm | < 0.5 ppm |
Source: JIUNYUAN PTFE filter reclaim test data (the reclaim process was co-developed with the Industrial Technology Research Institute (ITRI); patent pending). Actual results vary with filter format, original process chemicals, and contamination level.
- Reading the four metrics one by one
- What does each of the nine cleaning steps do?
- Which filters can be reclaimed?
- Where are reclaimed filters most cost-effective?
- Reclaim service flow and report contents
- FAQ
Reading the four metrics one by one
Retention 99.4% → 99.3%: cleaning did not damage the membrane structure
The reclaim process uses SPM, aqua regia vapor, HF/HNO₃, and Gigasonic acoustic energy. The biggest concern is actually not incomplete cleaning but damaging the membrane during cleaning — if pores are stretched open or the membrane is locally damaged, retention drops.
In a 5 nm gold nanoparticle challenge, the new filter retained 99.4% and the reclaimed filter 99.3%. Converted to LRV, these are 2.22 and 2.15 respectively, and penetration goes from 0.6% to 0.7%. This difference indicates that the pore structure has remained essentially unchanged. After reclaim, an integrity tester is also used to confirm that the filter structure is intact. For how to read retention figures, see “Liquid Filter Efficiency: From Conventional to Nanometer Test Methods.”
NVR 3.5 → 1.8 mg/device: the reclaimed filter is actually cleaner than the new one
Non-volatile residue (NVR) is measured by evaporating the extract to dryness and weighing what remains. It represents how much non-volatile organic matter the filter releases. The spec limit is 18 mg/device. Each result as a share of that limit:
The reclaimed filter's NVR is only about half that of the new filter. New filters inherently carry small amounts of organic residue from manufacturing and packaging, which is one of the reasons new filters need flushing before going into service. In the reclaim flow, the IPA preclean and the 1% SPM oxidation step remove the organics adsorbed during use together with this residue. For how NVR is measured and what it means, see “Filter Organic Extractables: NVR vs TOC Test Methods Compared.”
23 metals 330.5 → 353.2 ng/device: slightly higher, still about one-tenth of the limit
The reclaimed filter is about 23 ng/device (about 7%) higher than the new filter, but both are only about one-tenth of the 3,500 ng/device spec limit for the 10 nm item. In addition, the shipping criterion for the metal cleanliness of reclaimed filters is Total metals < 2 µg/device (10-inch). For how metal extractables are measured, see “Filter Metal Extractables: How ICP-MS Evaluates Filter Cleanliness.”
C12–C30 long-chain hydrocarbons: both < 0.5 ppm
Long-chain hydrocarbons are analyzed by gas chromatography–mass spectrometry (GC-MS) and are often associated with oil, grease, and lubricant-type contamination. Both the new and the reclaimed filter are below 0.5 ppm.
What does each of the nine cleaning steps do?
Reclaim is not simply a matter of soaking the filter in strong acid. JIUNYUAN's Proposed BKM is divided into 4 modules and 9 steps, treating contaminants stage by stage according to type:
| Module | Step | Conditions | Purpose |
|---|---|---|---|
| 01 Conditioning and pre-wet | 1. UPW preclean | 1 L · one-pass · Gigasonic | Remove residual acid, pre-wash aqueous-phase contaminants |
| 2. IPA preclean | 1 L · 30 min · Gigasonic | Wet the hydrophobic membrane, pre-wash organic-phase contaminants | |
| 3. UPW exchange | 1 L · one-pass · Gigasonic | Replace IPA with water, return to aqueous phase | |
| 02 Organics removal | 4. 1% SPM clean | 1 L · 10 min · Gigasonic | Oxidize organics, crack higher-molecular-weight species |
| 5. UPW rinse | 1 L · one-pass · Gigasonic | Remove residual acid, return to aqueous phase | |
| 03 Metals removal | 6. 5% aqua regia vapor | 100 mL · vapor · 10 min | Remove metallic contaminants with heated aqua regia vapor |
| 7. UPW rinse | 1 L · one-pass · Gigasonic | Remove residual acid, return to aqueous phase | |
| 04 Silica removal and finish | 8. 1% HF + 1% HNO₃ | 1 L · 10 min · Gigasonic off | Remove silica-class contaminants |
| 9. UPW final rinse | 1 L · one-pass · Gigasonic | Remove residual acid, complete aqueous exchange |
Each UPW exchange is judged complete when pH and conductivity reach their endpoint. The concentrations and times in the table are the Proposed BKM; the actual recipe is adjusted to the filter format and contamination condition.
Three design points
- Why treat organics first? The logic is similar to wafer wet cleaning: organics adhere to and coat surfaces, and only once they are removed can the later acids reach the metal and inorganic contamination underneath.
- Why rinse with UPW between every module? To keep the chemicals of one step from coming into direct contact with those of the next. The classic case is IPA and SPM: organic solvents react violently with strongly oxidizing SPM, so the IPA from step 2 must be fully replaced with water in step 3 before moving on to step 4.
- Why use IPA in step 2? PTFE is inherently hydrophobic, and water cannot enter the membrane pores. Low-surface-tension IPA first displaces the air in the pores; only then can the aqueous chemicals that follow reach the contaminants inside the pores. For the underlying principle, see “PTFE Filter Selection Guide: Hydrophilic vs Hydrophobic.”
Three in-house techniques
Which filters can be reclaimed?
| Criterion | Accepted scope | Notes |
|---|---|---|
| Filter media | PTFE membrane / PFA material | All wetted materials must withstand HF and strong oxidizing acids |
| Rating | 2 nm to 0.1 µm | — |
| Format | Disposable, cartridge | — |
| Contains stainless-steel parts | Accepted | Please tell us in advance; a split recipe will be used instead |
The rule for judging is simple: the reclaim flow uses SPM, aqua regia vapor, and HF/HNO₃, so every wetted component — membrane, hardware, end caps, and O-rings — must be able to withstand them. All-fluoropolymer filters with a PTFE membrane and PFA construction meet the criteria best. Membrane materials that do not tolerate strong acids, such as nylon, are not suitable. For filters that contain non-fluorinated materials such as PP or HDPE, please send samples first for a material and compatibility assessment.
When sending filters, please also provide: the original process chemicals, time in service, and nominal retention rating.
Where are reclaimed filters most cost-effective?
PTFE and PFA are extremely chemically stable. That is their strength, and it also means used filters are not easy to dispose of. The disposal of fluoropolymers has drawn growing regulatory attention in recent years. Extending the number of times each filter is used directly reduces the amount of waste.
Reclaim service flow and report contents
- Sample assessment: confirm whether the filter media and their chemical compatibility are suitable for this process.
- Quotation: confirmed based on filter quantity, material, and contamination level.
- Reclaim process: filters are processed through the four-module, nine-step flow, and the process parameters are recorded.
- Cleanliness and retention verification: ICP-MS/ICP-QQQ for metal extractables, GC-MS for C12–C30 long-chain organics, NVR and particle counting for cleanliness, a GNP 5 nm challenge to verify retention, and an integrity test to confirm the structure.
- Report delivery: a before-and-after verification report covering Total metals, NVR, particle count, and GNP 5 nm retention, with the process parameter record attached so the data are traceable.
Organic cleanliness (NVR) and retention are accepted against the specification of the filter's original model. Free trial bookings are currently available. For service details, see PTFE Filter Reclaim & Recycle Service.
FAQ
How many times can a filter be reclaimed?
There is no fixed number; it depends on the original process chemicals and the level of contamination. Every reclaim cycle is re-verified against the same set of metrics, with the specification of the filter's original model as the acceptance criterion, and comes with a before-and-after report.
Why test 5 nm gold nanoparticle retention? Isn't an integrity test alone enough?
An integrity test can catch obvious damage, but whether a 10 nm-class filter can still stop nanometer-scale particles after reclaim only shows up with nanometer-scale challenge particles. JIUNYUAN performs both.
Can a filter with a PTFE membrane and PP hardware be reclaimed?
It needs to be assessed first. The reclaim flow uses SPM, aqua regia vapor, and HF/HNO₃, and beyond the membrane, the hardware, end caps, and O-rings must all withstand them as well. Please provide the filter model and material information so that material and compatibility can be confirmed first.
Reclaimed filters show higher metals than new ones. Is there a risk?
In this data set, the reclaimed filter measured 353.2 ng/device and the new filter 330.5 ng/device; both are about one-tenth of the 3,500 ng/device spec limit. Every batch of reclaimed filters comes with a before-and-after report, so you can judge directly against the original model's specification whether they suit your process position.
Can a reclaimed filter go back into its original point-of-use filtration position?
In this data set, retention and organic cleanliness stay at new-filter level, and metals are slightly higher but still well within spec. Where the filter is actually installed, however, should be decided by the end user based on process risk. Common approaches are down-rating for continued service, repurposing as a pre-filter, or adding a filter in series, gradually building up experience in your own process.
Sources
- JIUNYUAN, “PTFE Filter Reclaim & Recycling”: reclaim test data for a 10 nm PTFE filter
- JIUNYUAN, “PTFE Filter Reclaim & Recycle Service” specifications (accepted scope, verification items, report contents)