Hydrogen peroxide at 50% or 70% active content is metered into the post-refiner alkaline loop of thermomechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP) lines where residual transition metals such as Fe, Mn, and Cu from wood chips would otherwise preferentially decompose the peroxide and generate chromophoric hydroxyl radicals. Sodium silicate at 1.5–3.0 kg/t dry fibre and diethylenetriaminepentaacetic acid (DTPA) at 0.2–0.5 kg/t dry fibre are dosed ahead of the peroxide injection point to establish a stabilised bleach liquor of pH 10.5–11.0. The peroxide charge itself typically ranges from 10–30 kg/t dry fibre, depending on initial chip brightness and the target ISO brightness increase of 10–18 points measured in accordance with ISO 2470-1:2016. Retention is carried out in high-consistency towers at 25–35% stock consistency for 60–120 minutes at 60–80 °C; insufficient stabilisation in this window raises bleach consumption by more than 30% because catalase and metal ions decompose peroxide before the chromophoric quinone groups in lignin are oxidised. Medium-consistency pumps fitted with vacuum de-aeration are standard on continuous lines because peroxide decomposition releases oxygen and can cause gas binding in centrifugal pump volutes. After bleaching, residual peroxide in the pulper feed is quenched with catalase before paper machine approach flow to prevent interference with wet-end retention aids. Brightness values above 80% ISO are rarely achieved on mechanical furnishes without sacrificing bulk and opacity. The bleached furnish then transfers to paper machines for newsprint, lightweight coated grades, and folding boxboard, where ISO brightness and yellowness index are the release parameters.

What Governs Hydrogen Peroxide Decomposition in Pad–Steam Cotton Preparation?

Prepared and desized cotton fabric is impregnated with a pad liquor containing 20–40 mL/L of 50% hydrogen peroxide, 5–10 g/L sodium hydroxide, and 2–5 g/L sodium silicate or a polyacrylate-based organic stabiliser. The saturated pick-up is set at 80–100% on a two-roll padder with a nip pressure of 2–4 bar; lower pick-up values produce edge-drying and non-uniform whiteness after the steamer. The fabric then enters a U-box or roller-bed steam chamber at 100–102 °C for 15–20 minutes, during which the perhydroxyl anion concentration controls bleaching kinetics and the stabiliser suppresses catalytic decomposition caused by Fe, Cu, and Mn present in cotton and process water. Whiteness is assessed by AATCC 110-2015 or ISO 105-J02:2012, and the process is typically specified to deliver a CIE whiteness index above 140 without reducing the degree of polymerisation below 1800–2000 units. Tensile strength loss above 15% relative to grey fabric triggers a reduction in alkali addition rather than peroxide addition because the alkali swells cellulose and accelerates oxidative chain scission at fibre surfaces. In cold pad-batch operations, the same formulation is batched onto a roll at 20–25 °C for 16–24 hours, but the stabiliser system shifts toward magnesium sulfate at 1–2 g/L and organic chelates because sodium silicate deposits on padder rollers over long dwell times. Knitted cotton goods are preferably processed in rope form on overflow dyeing machines at 98 °C for 30–45 minutes with 2–4% owf hydrogen peroxide, and the exhaust liquor is then neutralised with catalase to remove residual oxidant before dyeing with reactive dyes. The stabiliser system is screened against ZDHC MRSL and EU REACH Annex XVII; nonylphenol ethoxylate stabilisers are excluded because they form endocrine-active degradation products. Finished fabric enters downstream optical brightening, dyeing, or printing.

When Methanol Serves as Solvent in Titanosilicate-Catalysed Epoxidation

Hydrogen peroxide at 30–50 wt% is fed with propylene and a methanol recycle stream into a fixed-bed or slurry epoxidation reactor containing titanium silicalite-1 (TS-1) catalyst. Methanol constitutes 50–90 wt% of the liquid phase and is not inert; it solvates the peroxide and permits simultaneous access of propylene and hydrogen peroxide to the isolated tetrahedral Ti(IV) sites that generate the peroxy intermediate. Reaction temperature is held at 40–60 °C and pressure at 2.0–4.0 MPa to maintain propylene in the liquid phase. Under these conditions, hydrogen peroxide conversion exceeds 95% and propylene oxide selectivity can exceed 95%; water is the main co-product, and trace oxygen from peroxide decomposition is removed in a vapour-liquid separator. Feed purity determines catalyst deactivation rate: carry-over of alkali, amines, or phosphate esters neutralises the Ti(IV) active sites, and organic acids accelerate TS-1 framework dissolution. The methanol recycle stream is therefore maintained below 0.1 mg/kg sodium and below 0.5 mg/kg total chloride, with continuous purge of the water formed by the reaction to avoid stripping titanium from the catalyst. The propylene-to-peroxide molar feed ratio is held between 1.05:1 and 1.50:1; higher propylene excess suppresses ring-opening to propylene glycol, but excessive propylene raises off-gas compression load. Propylene oxide product is purified in a multi-column distillation train, and the resulting oxide is used for polyether polyols, propylene glycol ethers, and polyurethane intermediates. Compliance is normally verified against REACH Annex XVII and ISO 9001:2015 process control, with methanol and propylene oxide inventories handled under the storage and pressure-equipment requirements of Seveso III Directive 2012/18/EU where applicable.

In front-end semiconductor wafer processing, hydrogen peroxide serves as the oxidising component in both Standard Clean 1 (SC-1) and Standard Clean 2 (SC-2) chemistries. The SC-1 bath, used for particle removal and organic oxidation, is prepared from 29% ammonium hydroxide, 30% hydrogen peroxide, and ultrapure water in a volume ratio of 1:1:5, although ratios down to 1:4:20 are used for low-etch-budget processes on sensitive SiGe or strained-silicon surfaces. Temperature is controlled at 75–80 °C, and megasonic transducers operate at 0.8–1.2 MHz to avoid cavitation damage to sub-10 nm gate oxides. The SC-2 bath, typically 37% hydrochloric acid, 30% hydrogen peroxide, and ultrapure water at 1:1:6 by volume, removes metal cations by forming soluble chloro complexes. Electronic-grade hydrogen peroxide used in these baths is specified under SEMI C30 and is subject to lot-by-lot trace metal and particle certification. The liquid must be transferred through fluoropolymer-lined distribution systems because even stainless steel extractables introduce Fe, Ni, and Cr above the 0.001–0.01 mg/kg threshold required for front-of-line cleaning. Table 1 summarises a typical control window for a sub-7 nm logic fabrication facility against a general industrial 50% peroxide grade.

Metal contamination from an improper peroxide grade manifests as surface roughening and minority-carrier lifetime degradation, and lot acceptance is normally tied to total organic carbon below 5 mg/L and anionic impurities below 0.1 mg/kg because organic residues decompose under subsequent plasma etch and create micromasking defects. Equipment for SC-1/SC-2 recirculation is fabricated from quartz or perfluoroalkoxy alkane (PFA) and is fitted with point-of-use filtration at 0.1 µm; bath replacement frequency is calculated from particle counts and peroxide half-life, which falls sharply above 80 °C due to thermal decomposition. Terminal use includes pre-gate oxide cleans, post-etch residue removal, and wafer reclaim processes.

COD Removal Windows in Fenton-Driven Industrial Effluent Polishing

Fenton oxidation is applied to non-biodegradable COD in chemical, pharmaceutical, and textile effluents where the initial COD concentration lies between 1,000 mg/L and 10,000 mg/L. Hydrogen peroxide is dosed at 0.5–5.0 g/L, and ferrous sulfate heptahydrate is added at a molar Fe²⁺:H₂O₂ ratio of 1:2 to 1:5; lower ratios leave unused peroxide in the effluent, while higher ratios generate excessive Fe³⁺ sludge and consume hydroxyl radicals through the radical-scavenging side reaction. The pH is maintained at 2.8–3.5 by sulfuric acid before the reaction tank because Fe²⁺ precipitates above pH 4 and hydroxyl radical formation is suppressed. Reaction time in a continuous stirred-tank reactor is 30–120 minutes, with ORP maintained between 400 mV and 600 mV versus Ag/AgCl to avoid overdosing. After oxidation, the pH is raised to 8–9 with lime or sodium hydroxide to precipitate Fe(OH)₃ and settle the resulting sludge. COD removal in this configuration typically reaches 60–85% as measured by ISO 6060:1989, but the exact endpoint depends on the proportion of recalcitrant organohalogen compounds and the H₂O₂:COD mass ratio. Table 2 gives process windows for three effluent classes.

For weak-acid dissociable (WAD) cyanide destruction in gold leach tailings, hydrogen peroxide is dosed into agitated thickener overflow streams at pH 9.5–10.5 following copper sulfate addition at 10–30 mg/L Cu²⁺. The stoichiometric mass requirement for oxidation of cyanide to cyanate is 1.31 kg H₂O₂ per kg CN⁻, but plant dosing typically exceeds this by 20–100% because sulfides, thiocyanate, and transition metals in tailings compete for the peroxide. Retention time in a baffled reactor is 15–60 minutes; residual WAD cyanide is measured by ISO 14403-1:2012 and is usually specified below 10 mg/L before discharge to a tailings storage facility. Lime slurry is used to hold pH within the alkaline band, because below pH 9.0 hydrogen cyanide volatilisation risk increases sharply. Hydrogen peroxide also finds use in uranium ore leaching as an oxidant in acid circuits, but the reaction with pyrite-bearing ores can generate excessive sulfate and heat, so the feed rate is trimmed against redox potential and pulp temperature. In silver and gold cyanidation, low-level peroxide dosing at 0.1–0.5 kg/t ore can supplement dissolved oxygen in oxygen-limited thickener pulps; published data for this specific configuration is limited, and site-specific jar leach tests are required before full-scale adoption. Terminal outputs are tailings compliant with local cyanide discharge limits and, in the uranium case, clarified uranyl sulfate pregnant leach solution.