Closed-loop sensor-controlled replenishment method for PFAS-free chrome bath surfactants

The closed-loop dosing method sits at the operational heart of the PFAS-free dielectric and process fluids portfolio. Its value proposition is not a new chemical — it is a new way to keep an existing PFAS-free surfactant system working reliably over the duration of a real production run. Hard chrome plating baths degrade continuously: surfactant molecules are oxidized by hexavalent chromium, consumed in foam collapse, and diluted by drag-in. Manual bath maintenance — the current industry norm — responds to degradation episodically, after mist suppression has already deteriorated. The result is intermittent OSHA-regulated chromic acid mist exceedances, unplanned downtime for bath corrections, and accelerated surfactant consumption. This method closes that loop by continuously reading process signals (surface tension, foam height, dissolved Cr(III), redox potential, or active surfactant concentration) and triggering a metering pump to replenish at precisely the dose computed from those readings. The system is bounded by a foam-height safety interlock that prevents over-dosing, a known failure mode of automated chemical addition. The timing argument is structural. Regulatory pressure on PFAS-containing mist suppressants — most notably perfluorooctane sulfonate (PFOS)-based products that have historically dominated hex-chrome plating — is converging with a wave of mandatory substitutions under EPA PFAS rules, EU REACH SVHC restrictions, and military-specification updates. PFAS-free replacements such as the fluorine-free surfactant compositions in the companion B1/B2 applications are chemically more susceptible to bath degradation than the PFOS benchmarks they replace, because they lack the extreme oxidative stability of the perfluorinated backbone. That susceptibility makes intelligent replenishment control not a luxury but a practical prerequisite for PFAS-free surfactants to match PFOS performance lifetimes. This method invention therefore functions as the enabling operational layer for the broader portfolio: it makes the chemistry work in production, not just in the laboratory flask. The filing sits within the same patent family as the B1/B2 bath compositions, sharing a priority date and extending the protected zone from composition into method-of-use. As a method claim, it is harder to design around through chemistry alone — a competitor could change the surfactant molecule yet still infringe if they adopt sensor-gated, signal-triggered replenishment tied to the claimed process parameters. That structural advantage in claim scope makes this a useful defensive and offensive complement to the composition filings.

This is a process-control invention, not a materials invention, so the technical substance lives in the logic of the control loop rather than in crystallography or electronic structure. The claimed method operates on a hexavalent chromium plating bath containing a PFAS-free surfactant system (as described in the companion B1/B2 compositions). The controller reads one or more of five distinct process signals: surface tension (measured inline by tensiometer), foam height (measured by optical or ultrasonic foam sensor), dissolved Cr(III) concentration (an indirect proxy for oxidative degradation of surfactant), redox potential (measured by a standard ORP electrode), and/or directly assayed active surfactant concentration via titration or spectroscopy. From the signal reading, a replenishment dose is computed — either by comparison against a set-point threshold, by integration of a deficit area below a target curve, or by a proportional-integral control law, depending on implementation — and dispatched to a metering pump on a continuous, periodic, or event-triggered basis. The key performance targets maintained by the control loop are demanding and operationally specific: surface tension held at or below 33 mN/m (the threshold at which mist suppression foam blanket integrity is reliably maintained over the chrome bath surface), foam collapse time held at or below 5 minutes after current is switched off (ensuring the foam does not persist as a process contamination risk), and active surfactant retention of 75% or more after 168 continuous bath hours. The 168-hour mark is significant — it corresponds to a standard work-week production cycle, meaning the system must sustain performance through a full operating week without a bath dump or major chemical correction. These are empirically grounded specifications tied to the chromic acid mist control requirements under OSHA 1910.1026 and analogous standards in the EU and UK. The foam-height safety interlock is an important technical design element. Excessive surfactant addition to a chrome bath produces a runaway foam condition that can carry chromic acid droplets out of the bath enclosure — the opposite of the desired mist-suppression effect. The claimed method includes explicit upper-bound foam-height limits as a dosing gate, so the metering pump is inhibited when foam exceeds a ceiling value. This bidirectional control logic (dose when surface tension rises above set-point; inhibit when foam exceeds ceiling) distinguishes the method from simple timed-addition systems and is the technical detail that most clearly separates it from prior-art manual dosing practices. From a systems-integration standpoint, the method is bath-agnostic with respect to the sensor hardware: the claims accommodate any commercially available inline tensiometer (bubble-pressure, Wilhelmy plate, or capillary-pressure type), any foam sensor capable of providing a height signal, and standard industrial ORP probes. This deliberate sensor-agnosticism is a drafting choice that broadens the claim footprint while avoiding dependence on any proprietary sensor hardware. The metering pump interface is similarly generic. The practical deployment architecture is a PLC or microcontroller reading analog sensor outputs, running the control logic, and driving a peristaltic or diaphragm metering pump — all standard components in industrial plating-line control cabinets.

The addressable market for this method is the population of plating-line operators and plating-line equipment and chemistry vendors who need to switch away from PFOS-based mist suppressants under regulatory compulsion and who will then face the operational problem of maintaining PFAS-free surfactant performance over multi-day production runs. The estimated addressable market is in the range of $0.2 billion to $0.5 billion. This is an estimate, not a measured figure, and reflects the subset of the global hard chrome plating market most immediately affected by PFAS surfactant substitution mandates — primarily aerospace and defense subcontractors, automotive OEM suppliers, and industrial tooling manufacturers in North America, the EU, and the UK, where regulatory timelines are most advanced. The commercial logic for this method invention is primarily a licensing play layered on top of the companion bath composition patents. A plating-chemistry supplier who licenses the B1/B2 surfactant compositions would have a strong incentive to also license or co-develop the closed-loop dosing system, because it directly addresses the customer objection that PFAS-free surfactants require more frequent manual attention than PFOS benchmarks. Bundled chemistry-plus-control solutions command meaningfully higher margins than chemistry alone in industrial process markets — analogous to how ion-exchange resin suppliers bundle regeneration control systems, or how metalworking fluid vendors bundle fluid-life monitoring instruments. The method patent therefore expands the monetizable surface of the portfolio beyond chemistry royalties into process-equipment and system-integration licensing. Plating-line OEMs and bath-control system vendors represent a second distinct customer class: they would implement the control logic in their equipment and need a license to do so cleanly. This creates a dual-channel licensing opportunity — chemistry suppliers on one side, equipment vendors on the other — which is commercially attractive because the two channels rarely compete with each other.

extends consistent surfactant performance over long bath operation

process-signal-gated replenishment tied to surface tension / foam / redox / active surfactant

The most natural acquirers or licensees fall into two categories. The first is specialty plating-chemistry suppliers who are actively building PFAS-free surfactant product lines — companies such as MacDermid Enthone, Atotech (now MKS Instruments), and Coventya, all of whom sell into hard chrome plating markets and all of whom face the same customer demand for drop-in PFAS-free solutions that maintain PFOS-equivalent bath life. For these buyers, the method patent bundles cleanly with the B1/B2 composition portfolio, giving them a more defensible and differentiated product offering than chemistry alone. The second category is plating-line control system OEMs and bath-monitoring instrument vendors who want to offer closed-loop surfactant management as a hardware-software system, and who need a clean IP position to do so without risk of infringement by a future patent assertion. This filing provides that position directly. Defense and aerospace supply-chain integrators are a secondary buyer class, given that hard chrome plating of landing gear, actuators, and hydraulic components is heavily regulated under MIL-SPEC standards that are themselves being updated to exclude PFAS-containing process chemicals. A Tier 1 aerospace supplier or a defense contractor managing a captive plating facility might value the method as part of a broader technology acquisition aimed at PFAS compliance across their manufacturing operations.

The central risk is the open experimental validation gate. The 168-hour continuous closed-loop controlled-bath run has not yet been completed as reported in the current context, meaning the key performance claims — surface tension at or below 33 mN/m, foam-collapse at or below 5 minutes, active retention at or above 75% over a full production week — are design targets rather than demonstrated results. A buyer performing technical due diligence will rightly ask for that data, and its absence reduces negotiating leverage. The de-risking path is straightforward: run the controlled validation experiment with inline tensiometer and foam sensor instrumentation, log the output, and generate a reportable dataset. This is a practical experiment, not a difficult one, and the cost is modest relative to the IP value being claimed. A secondary risk is claim scope under examination. Method-of-use claims in process-control contexts can attract prior-art rejections that narrow the claim to a specific sensor type or specific dosing logic, reducing the breadth of coverage. Prosecution strategy should anticipate this by maintaining fallback dependent claims that explicitly enumerate the foam-ceiling interlock and the multi-signal input combination as distinguishing limitations — both of which appear to be genuinely novel based on the current FTO reading. A third risk, common to all PFAS-free chemistry plays, is that the regulatory substitution timeline slips or that PFAS exemptions for industrial uses are extended, reducing the urgency of adoption. This is a market-timing risk rather than a technical risk and is partially offset by the fact that the EU and UK timelines are advancing independently of U.S. EPA pace.