Paper & pulp handbook

A cell name describes a production route

EPA’s supply-chain profile for sodium hydroxide sets out the manufacturing picture plainly. Sodium chloride is the primary raw material; the majority of caustic soda is produced by the chlor-alkali process, passing a direct current through a brine so that chloride is converted to chlorine at the anode while sodium ions and hydrogen collect at the cathode. The caustic is then separated from the solution by one of three methods: the diaphragm method, the membrane method, or the mercury cell method. EPA records the diaphragm method as the most common separation process used in North America.

Read that carefully and “membrane grade” resolves into what it actually is: the name of the separation step the caustic came out of. It is a production route, not a published specification, and the profile that describes the industry states no attribute limits at all. This matters for a mill because caustic is not a marginal purchase here—EPA puts pulp and paper manufacturing at 22 percent of North American sodium hydroxide consumption in 2015, against 3 percent for all water treatment applications combined. A designation that large a spend rests on should be written down as attributes, not as a word.

When a rule names a specification, it names an edition

21 CFR 184.1763 affirms sodium hydroxide as generally recognized as safe for direct use in food, and in doing so it does something a purchase order rarely does: it says which document the ingredient must satisfy. “The ingredient meets the specifications of the Food Chemicals Codex, 3d Ed. (1981), which is incorporated by reference.” One sentence, one document, one edition, pinned—and the edition it pins is from 1981. The Food Chemicals Codex is a purchased standard; it was not readable while this guide was written, so nothing here paraphrases its requirements or reproduces a limit from it.

The same section is also worth reading for its first paragraph, which records that sodium hydroxide “is prepared commercially by the electrolysis of sodium chloride solution and also by reacting calcium hydroxide with sodium carbonate.” Two routes, and they do not carry the same residual chemistry. If a route matters to a process—and in a mill it can—that is a question to put in writing, because a GRAS affirmation says nothing about it. Being affirmed as GRAS is not an approval of any particular supplier’s material, and nothing here states that an Alliance product is suitable, approved or recommended for a food-contact or any other application.

Where the mercury question actually lives

40 CFR part 63, subpart IIIII is the national emission standard for hazardous air pollutants for mercury cell chlor-alkali plants. It applies to each affected source at a plant site “where chlorine and caustic are produced in mercury cells,” and it reaches two affected sources: the production facility, meaning all cell rooms and ancillary operations, and the mercury recovery facility. An affected source is existing if construction commenced before July 3, 2002. The subpart is live: it was amended at 87 FR 27018 on May 6, 2022, with work-practice and electronic-reporting obligations dated November 7, 2022 and an emission limitation at § 63.8190(a)(2)(ii) applying on and after May 6, 2025.

That is where the mercury history sits in current federal law—as an air-emission and work-practice obligation on a producer, enforced through a title V permit. It is not an impurity limit on a delivered drum, and the continued existence of the subpart is not evidence about the provenance of any particular supply. If a mercury limit matters to a mill’s product or its own discharge, it has to appear on the purchase document the way any other requirement does: an attribute, a numeric limit, a named method, units and a reporting limit. A cell-technology word in a product name is not that.

Fifty percent is a band, and it does not stay put

The aggregated public record for sodium hydroxide describes the commercial article in commodity terms rather than specification terms: “Anhydrous (Rayon Grade) 99.0% minimum; Rayon Grade: 50% liquid; Regular Grade: 50% liquid, 47.7-51% purity.” Two observations follow. Rayon grade is another commercial designation sitting beside membrane grade with exactly the same problem—it names a market, not a document. And a nominal fifty percent is described there as a band roughly three points wide. A make-up calculation and an analytical control chart both depend on where in that band a delivery actually falls, which is a reason to ask whether a quoted figure is typical, a guaranteed limit, or a measured result for the lot.

The same record also explains why the number moves after delivery. Caustic solutions are hygroscopic and “when exposed to the air they absorb carbon dioxide, forming sodium carbonate,” and the stability entry is blunt about the consequence: containers “must be tightly closed to prevent conversion to sodium carbonate by carbon dioxide of air.” Carbonate is therefore an in-service impurity as well as a manufacturing one, and the vent arrangement on a storage tank belongs in the same conversation as the assay. Note the limits of this record too: it reports the melting point of the solid as 318 °C in one entry and 323 °C in another, from different agencies. Aggregated values describe the pure substance under someone else’s conditions; they are not measurements of a supplied lot, and this guide states no crystallisation temperature for any concentrated solution—that is a datum to request from the supplier for the exact product, with its basis and its method.

• Which document defines the designation being requested, and which attributes does it limit?
• Is the stated assay typical, a guaranteed specification limit, or a measured lot result—and on which basis and at what temperature?
• Which impurities does this process actually control, each with a method, units and a reporting limit?
• What is the crystallisation temperature for the exact product as delivered, and what heating and venting does the receiving arrangement provide?

Ask for the grade, and for the certificate

Alliance publishes the grade a product carries in its structured product data, and that record—not the marketing copy, and not the handle—is what a purchase document should quote. Where a grade is not stated for a product, the correct action is to ask rather than to infer one. A nominal grade or concentration does not establish interchangeability between products or between suppliers, and being merchandised under a paper and pulp collection is merchandising: an industry listing is not an application approval.

Alliance sends a Certificate of Analysis when a customer asks, at no charge. Put the request in the purchase order and name what it must cover: the analytes, the methods, the units and the reporting limit for each. What grade designations do and do not certify in general is treated at length in this library’s laboratory and pharmaceutical research collection, under “What a grade designation certifies, and what it does not”; this guide does not repeat it. This is source-based editorial guidance and independent specialist review is pending.

Requirement → evidence → decision boundary

An editorial checklist for your review—not a table of product specifications.

“Alum” is not one substance

21 CFR 182.90 lists the substances migrating to food from paper and paperboard products that are generally recognized as safe for their intended use. The first entry reads: “Alum (double sulfate of aluminum and ammonium potassium, or sodium).” That is not aluminum sulfate. It is the ammonium, potassium or sodium double salt—a different compound, with a different formula and a different CAS number from the Al₂(SO₄)₃ that a mill orders as papermaker’s alum. The list goes on to name sodium aluminate, aluminum hydroxide, sodium hydrosulfite, sodium silicate and talc separately, each by its own name, because the rule is precise where the trade vocabulary is not.

This is the ordinary failure mode of the word. Write the CAS number and the hydrate on the purchase document, not the nickname, and check that the substance named in a specification is the substance being quoted against it. Note also what appearing on this list does and does not mean: § 182.90 addresses substances migrating into food from packaging. It is not an approval of any supplier’s material, and it is not a purity specification—as the next section shows, the rule that governs the list says so itself.

The percentage has a basis and the basis has a hydrate

The aggregated public record for aluminum sulfate carries “Papermaker’s Alum,” “Filter Alum” and “Pickle Alum” among its synonyms for CAS 10043-01-3, and records that the substance “is also obtained as an 18-hydrate Al₂(SO₄)₃·18H₂O,” for which it gives a molecular weight of 666.43 against 342.15 for the anhydrous salt. It then adds the sentence that ends most arguments about a number: the “article of commerce usually contains 5 to 10% less water than theory.” So a percentage can be expressed on an anhydrous basis, on a hydrated basis, or as an as-delivered solution strength, and those are three different figures describing the same drum.

Two more entries in the same record are worth carrying into a specification conversation, with their limits stated. “On long boiling of aqueous solution, insoluble basic salt precipitates”—basicity and insolubles are real, measurable attributes, not merchant folklore. And “one part of technical aluminum sulfate reduces the alkalinity as calcium carbonate by 0.55 parts,” a figure quoted with no temperature, no concentration and no method attached, which is exactly the sort of number that should be traced to its originating record before anyone designs against it. The same record also contains a consumption breakdown labelled 1981. A dated figure is not a current one.

Iron comes from the raw material, not from a polish

EPA’s supply-chain profile describes the manufacturing route: aluminum sulfate is produced by reacting aluminum hydroxide with sulfuric acid, and “the process may begin with ground bauxite in place of aluminum hydroxide.” Liquid alum, the more commonly sold form, is prepared by diluting that solution; evaporating and crystallising it gives the dry product. The aggregated chemical record completes the picture with the reason a low-iron product exists at all: the iron-free grade, quoted there at less than 0.005% ferric oxide maximum, is made “using pure alumina trihydrate in place of bauxite or clay.”

The consequence for a purchase is straightforward. Iron content is set upstream, by the feedstock, and a buyer asking for it has to ask for a limit with a method and units rather than for a word. The consensus commodity standard here is AWWA B403, Aluminum Sulfate—Liquid, Ground, or Lump, which EPA’s profile cites; it is sold by AWWA and was not read for this guide, so nothing here paraphrases its requirements. Where a specification invokes it, obtain the edition invoked and cite the clauses by number. Citing a standard by designation without having read it commits both parties to test methods and sampling frequencies nobody has looked at.

A reducing agent loses the thing you bought it for

The aggregated record for sodium bisulfite states the stability problem in one line: “on exposure to air it loses some sulfur dioxide and is gradually oxidized to sulfate.” It has no boiling point—it decomposes—and it is recorded as “corrosive to aluminum.” Its listed uses read like a mill inventory: bleaching groundwood, wood pulp digestion, and use as an antichlor in paper making. Each of those is a different job with a different endpoint.

Two purchasing consequences follow, and only two. First, reducing capacity is a measurement with a date on it, in the same way a hypochlorite strength is, so a delivery record has to carry a fill date, a storage arrangement and an expected turnover rate against tank volume, not merely a grade. Second, a compatibility note like “corrosive to aluminum” belongs in the transfer-interface field of the purchase record, where the wetted materials are listed—not in an application recommendation. What this guide will not do is set a dose, a ratio or an endpoint. Residual control as a specification problem is treated in this library’s water and wastewater treatment collection, under “Dechlorination is two problems wearing one word,” and the decay of an oxidant strength under “A hypochlorite percentage is a measurement with a date on it.” Neither is repeated here, and neither supplies a dose either.

Purity with no number attached is not a specification

21 CFR 186.1 governs the list quoted at the top of this guide, and its wording on purity is the most useful sentence in it. Indirect food ingredients are GRAS “providing they comply with the purity specifications listed in this part or, in the absence of purity specifications, are of a purity suitable for their intended use in accordance with § 170.30(h)(1) of this chapter,” used “at a level no higher than reasonably required to achieve its intended technical effect in the food-contact article.” The rule also states outright that part 186 does “not authorize direct addition of any food ingredient to a food.”

Where a mill makes a food-contact grade, “suitable for its intended use” is a determination the mill and its own specialist make, and the only way to buy against it is to write the attributes down: each one with a limit, a method, units and a reporting limit. Alliance sends a Certificate of Analysis when a customer asks, at no charge; name in the purchase order which document is meant, because a typical or sample certificate describes what the product has generally looked like while a lot certificate reports results for the material being shipped. A sample COA is not a lot certificate. Nothing here states that a particular Alliance product is suitable, approved or recommended for any application, and independent specialist review of this collection is pending.

• Which compound is actually being quoted—CAS number, hydrate, and form as delivered?
• Is the stated percentage on an anhydrous basis, a hydrated basis, or as-delivered solution strength?
• Which attributes does your specification control—iron, insolubles, basicity, free acid—each with a limit, a method and units?
• For a reducing agent: what is the fill date, the storage arrangement, and the turnover rate against tank volume?

Requirement → evidence → decision boundary

An editorial checklist for your review—not a table of product specifications.

Which subcategory governs is a determination

40 CFR 430.00 applies to any pulp, paper or paperboard mill that discharges or may discharge process wastewater pollutants to waters of the United States, or that introduces or may introduce them into a publicly owned treatment works. It then divides that universe into twelve subcategories, A through L, keyed to the pulping route and to the product: Dissolving Kraft; Bleached Papergrade Kraft and Soda; Unbleached Kraft; Dissolving Sulfite; Papergrade Sulfite; Semi-Chemical; Mechanical Pulp; Non-Wood Chemical Pulp; Secondary Fiber Deink; Secondary Fiber Non-Deink; Fine and Lightweight Papers from Purchased Pulp; and Tissue, Filter, Non-Woven, and Paperboard from Purchased Pulp.

The subcategories are not interchangeable and they are not uniformly complete—subpart H reserves its new-source performance standards and both pretreatment standards, while subparts B and E carry an entire additional apparatus the others do not. Which one governs a given mill is a written determination somebody owns, and the limitations that follow are expressed as mass per unit of production. Subpart B’s best-practicable-technology limits for a bleached kraft mill producing market pulp, for example, are 15.45 kg of BOD₅ per 1,000 kg of product as a maximum for any one day and 8.05 as a 30-day average, with TSS at 30.4 and 16.4 on the same basis and pH held within 5.0 to 9.0 at all times. Those are limits on a mill’s output, not on anything in a drum.

What the category regulates

EPA’s summary page records the history in one paragraph: initial guidelines for the category in 1974 and 1977, amendments in 1982 and 1986, and a major 1998 amendment covering toxic pollutants—the “Cluster Rule,” which promulgated air standards for the industry under the Clean Air Act at the same time. The page was last updated March 24, 2026.

It also lists the regulated pollutants by class, and the shape of that list is the useful part. Conventional: biochemical oxygen demand, suspended solids, and pH. Priority: 2,4,6-trichlorophenol, 2,3,7,8-TCDD, pentachlorophenol and zinc. Nonconventional: adsorbable organic halides, chemical oxygen demand, chloroform, trichlorosyringol, and a series of trichloro- and tetrachloro- catechols, guaiacols and phenols. Almost every entry after the first three is a chlorinated organic. That is the category’s centre of gravity, and it is the reason the regulation cares so much about exactly where and with what a fiber line is bleached.

The bleach plant has a boundary written in the rule

40 CFR 430.01(c) defines the bleach plant as all process equipment used for bleaching “beginning with the first application of bleaching agents (e.g., chlorine, chlorine dioxide, ozone, sodium or calcium hypochlorite, or peroxide), each subsequent extraction stage, and each subsequent stage where bleaching agents are applied to the pulp,” and it excludes oxygen delignification carried out before bleaching agents are applied. 430.01(f) then defines elemental chlorine-free as any process bleaching “in the absence of elemental chlorine and hypochlorite that uses exclusively chlorine dioxide as the only chlorine-containing bleaching agent.” Hypochlorite is named on both sides of that line, in the list of bleaching agents and in the exclusion.

The regulation also anticipates a mill changing its bleaching chemistry. 430.01(j)(2) lists changes that do not by themselves make an existing mill a new source, and paragraph (iv) reads: “Bleach plant modifications including changes in methods or amounts of chemical applications, new chemical applications, installation of new bleaching towers to facilitate replacement of sodium or calcium hypochlorite, and installation of new pulp washing systems.” What follows from a change is monitoring, not permission. 430.02(a) sets minimum frequencies for subpart B and E discharges keyed to the bleaching route: for a fiber line that is not exclusively totally chlorine-free, AOX daily, chloroform weekly, and the chlorinated phenolics monthly. For a line that is, the same table specifies no monitoring frequency for AOX and records that the regulation specifies no limit for the individual chlorinated phenolics—those lines are instead given their own AOX limitation of less than the minimum level at § 430.24(a)(2). Which route a line uses is disclosed by the discharger in its permit application under 40 CFR 122.21(g)(3) and certified under 40 CFR 122.22. None of this is something a chemical supplier can determine, and nothing in this library states that any product is suitable, approved or recommended for a bleaching stage, nor supplies an application rate.

The rule names an internal owner

40 CFR 430.03 requires best management practices for spent pulping liquor, soap and turpentine at direct and indirect discharging mills with pulp production in subparts B and E. Its primary objective is to prevent leaks and spills; its secondary objective is to contain, collect and recover them at the immediate process area. The obligations are concrete: return spilled or diverted material to the process to the maximum extent practicable, run a programme to identify and repair leaking equipment with regular visual inspections and a means of tracking repairs over time, and operate the continuous automatic monitoring the mill determines is necessary—high-level alarms on storage tanks, conductivity or pH monitors in process areas and sewers.

Two definitions in that section are worth a purchasing team’s attention. An action level is “a daily pollutant loading that when exceeded triggers investigative or corrective action,” and mills set it themselves by statistical analysis of six months of their own daily measurements—the rule offers the 75th and 90th percentiles of running seven-day averages as an example, not a requirement. And the BMP plan is reviewed by a “senior technical manager,” defined as the chief engineer, the manager of pulping and chemical recovery operations, or another responsible person designated by the mill manager who has knowledge of and responsibility for those operations. The regulation names an internal owner because there is no external one. A purchase record should name the same person.

What this brief did not read

The analytical apparatus behind the category is partly in the regulation and partly outside it. Methods 1650 for AOX and 1653 for the chlorinated phenolics are printed in Appendix A to part 430, and 40 CFR 430.01(i) fixes their minimum levels—20 µg/L for AOX, 2.5 or 5.0 µg/L for the individual phenolics, and 10 pg/L for 2,3,7,8-TCDD by Method 1613. Part 136 governs approved test procedures for the analysis of pollutants more generally. All of these were promulgated for discharge reporting. An approved discharge method is not an acceptance test for a delivered drum, and a minimum level is not a purity limit.

TAPPI standards and ASTM test methods are the documents a mill specification is most likely to invoke for the material itself, and both are sold by their publishers. Neither was readable while this brief was written, so neither is paraphrased here and no limit is reproduced from either. Where a specification cites one, obtain the edition invoked and cite the clauses by number. This brief performed no original testing, evaluates no study, and makes no waste, permit or exposure determination—those belong to the mill, its environmental professional and its permitting authority. Independent specialist review of this collection is pending.

• Which subpart of 40 CFR part 430 governs this mill, and who made and recorded that determination?
• Is the fiber line certified as non-TCF, ECF or TCF, and what monitoring frequency follows from that certification?
• Does the material enter inside or outside the bleach plant boundary as § 430.01(c) draws it?
• Who is the senior technical manager for the BMP plan, and who is the named permit holder reporting against the limits?

Requirement → evidence → decision boundary

An editorial checklist for your review—not a table of product specifications.