Pore Structure Determination of Pyrolysis Products from Cosmetic and Medical Waste: Principles, Meth

Pore structure determination of pyrolysis products from cosmetic and medical waste provides critical quantitative data on specific surface area, pore volume, and pore size distribution, which directly govern the adsorption performance and material value of waste-derived carbonaceous chars. Accredited third-party laboratories perform this characterization using low-temperature gas adsorption (BET, BJH, DFT) and mercury intrusion porosimetry in accordance with ISO 9277, ISO 15901, ASTM D3663, and related national standards. This article presents a comprehensive overview of sample types, measurable parameters, analytical methodologies, and industrial applications of pore structure testing for cosmetic and medical waste pyrolysis products.

Technical Overview

Cosmetic and medical waste streams, including expired cosmetics, contaminated personal care products, used protective masks, and non-hazardous medical plastics, are increasingly treated through pyrolysis as a sustainable alternative to landfilling or incineration. During thermal decomposition in an oxygen-free or oxygen-limited environment at temperatures typically ranging from 400 °C to 900 °C, the organic fraction of these wastes is converted into three product phases: pyrolysis oil, syngas, and a carbonaceous solid residue known as pyrolysis char or semi-coke. The char frequently develops an intricate internal pore network consisting of residual micropores, newly formed mesopores, and interparticle macropores.

The pore structure of these pyrolysis products determines their suitability for high-value applications such as adsorbents, activated carbon precursors, catalyst supports, and electrode materials. Quantitative characterization of the pore system is therefore essential for both process optimization and product qualification. According to the IUPAC classification, pores are categorized as micropores (width below 2 nm), mesopores (width between 2 nm and 50 nm), and macropores (width above 50 nm), and each pore class is assessed using dedicated analytical techniques and calculation models.

Modern pore structure determination combines physical gas adsorption analysis with mercury intrusion porosimetry, following internationally recognized standards including ISO 9277, the ISO 15901 series, ASTM D3663, ASTM D4284, and corresponding national standards such as GB/T 19587 and the GB/T 21650 series. Together, these methods deliver a complete pore size profile spanning from sub-nanometer ultramicropores to millimeter-scale interparticle voids.

Testing Samples

Pyrolysis Char from Expired and Recalled Cosmetic Products

Solid carbon residues recovered from the pyrolysis of expired creams, lotions, powders, emulsions, and recalled cosmetic formulations. These samples typically contain high carbon content with embedded inorganic pigments and may exhibit heterogeneous pore development depending on feedstock composition.

Carbon Residues from Medical and Cosmetic Packaging Waste

Chars derived from mixed plastic packaging, pump dispensers, dropper bottles, and contaminated containers from both cosmetic and medical sources. The pore structure of these residues is strongly influenced by polymer type, ash content, and pyrolysis severity.

Activated Carbon Derived from Cosmetic and Medical Waste

Physically activated (steam or CO2) or chemically activated (KOH, ZnCl2, H3PO4) carbons produced from waste-derived chars. These samples require extended degassing protocols and are tested to verify activation efficiency through enhanced surface area and micropore volume.

Semi-Coke and Thermal Treatment Residues

Intermediate solid products from staged pyrolysis, gasification residues, and fly char captured from exhaust systems in waste treatment facilities. These materials are characterized to evaluate residual porosity, burn-off degree, and potential for downstream valorization.

Testing Items

Comprehensive pore structure characterization of cosmetic and medical waste pyrolysis products typically encompasses the following measurable parameters:

• BET multi-point specific surface area (m2/g) per ISO 9277 and GB/T 19587
• Single-point surface area and Langmuir surface area
• t-plot micropore area and external surface area
• Total pore volume measured at a relative pressure of approximately 0.99
• Micropore volume determined by t-plot, Horvath-Kawazoe (HK), or Saito-Foley (SF) models
• BJH adsorption and desorption pore size distributions for mesopores
• DFT or NLDFT pore size distributions covering micro- and mesopore ranges
• Average pore diameter calculated as 4V/A
• Most probable pore size and pore size distribution curves
• Mercury intrusion pore distribution for macropores and porosity percentage
• Apparent density, bulk density, and interparticle void fraction
• Adsorption-desorption isotherm typing and hysteresis loop classification per IUPAC

Testing Methods

Low-Temperature Nitrogen Adsorption Analysis

Samples are first degassed under vacuum or flowing gas at a temperature between 105 °C and 300 °C to remove physically adsorbed moisture and volatile contaminants without altering the pore structure. Nitrogen adsorption-desorption isotherms are then measured at 77 K (liquid nitrogen temperature) across the full relative pressure range. The BET specific surface area is calculated from the linear region of the isotherm between relative pressures of 0.05 and 0.30, following ISO 9277, GB/T 19587, and ASTM D3663. This method reliably covers pore widths from approximately 0.35 nm to 500 nm.

BJH and DFT Pore Size Distribution Analysis

Mesopore distributions are derived from the desorption or adsorption branch of the nitrogen isotherm using the Barrett-Joyner-Halenda (BJH) method, which applies the Kelvin equation and a corrected multilayer film thickness model in accordance with ISO 15901-2. For heterogeneous carbonaceous materials with mixed micro- and mesopores, non-local density functional theory (NLDFT) provides a more physically rigorous description using a slit-pore carbon model, resolving the full distribution from 0.4 nm upward.

Carbon Dioxide Adsorption for Ultramicropores

For pyrolysis chars with narrow ultramicroporosity that nitrogen at 77 K cannot fully probe due to diffusion limitations, CO2 adsorption at 273 K is employed. Combined with grand canonical Monte Carlo (GCMC) or DFT fitting, this technique accurately quantifies pores between 0.35 nm and 1 nm, which dominate the adsorption capacity of highly carbonized medical and cosmetic waste chars.

Mercury Intrusion Porosimetry

Macropore structure, bulk porosity, and pore size distributions from approximately 3.6 nm to 360 µm are measured by mercury intrusion following ISO 15901-1, ASTM D4284, and GB/T 21650.1. Non-wetting mercury is forced into the sample under progressively increasing pressure, and the Washburn equation converts intrusion pressure to pore throat diameter. This method is particularly valuable for granular chars, pellets, and monolithic residues where interparticle and macro-scale porosity control performance.

Applications

Pore structure data for cosmetic and medical waste pyrolysis products directly support research, development, and industrial decision-making across multiple sectors:

• Development of waste-derived adsorbents for the removal of dyes, heavy metals, pharmaceuticals, and personal care product residues from wastewater
• Production and quality control of activated carbon for air purification, VOC capture, and odor control applications
• Screening of char candidates as catalyst supports and catalyst carrier materials in chemical processing
• Evaluation of pyrolysis chars as electrode materials for supercapacitors and battery components
• Assessment of biochar suitability for soil amendment and carbon sequestration
• Optimization of pyrolysis process parameters such as temperature, heating rate, residence time, and activation conditions based on pore development trends
• Regulatory compliance documentation and valorization certification for waste-to-material conversion projects

FAQ

What sample quantity is required for pore structure testing?

For gas adsorption analysis, approximately 0.1 g to 5 g of sample is typically sufficient, depending on the expected surface area. High-surface-area activated carbons require less material, while low-porosity semi-cokes may require larger quantities. Mercury intrusion porosimetry generally requires 0.5 g to 3 g of granular or powdered material.

What pore size range can be measured?

Nitrogen adsorption covers pore widths from approximately 0.35 nm to 500 nm, CO2 adsorption resolves ultramicropores down to 0.35 nm, and mercury intrusion porosimetry extends from roughly 3.6 nm up to 360 µm. Combining these techniques yields a complete pore structure profile across all IUPAC pore classes.

Why is sample degassing critical before measurement?

Pyrolysis chars from cosmetic and medical waste retain moisture, residual oils, and volatile organic compounds that block pore entrances and cause significant underestimation of surface area and pore volume. Controlled degassing removes these contaminants while preserving the intrinsic pore architecture, ensuring accurate and reproducible results.

Which standard should be selected for reporting surface area?

BET specific surface area should be reported according to ISO 9277 or GB/T 19587, while catalyst- and carbon-related materials may additionally reference ASTM D3663. Mesopore and macropore distributions follow the ISO 15901 series and GB/T 21650 series, and test reports should clearly state the calculation model, degassing conditions, and measurement temperature.

What is the typical testing turnaround time?

Standard pore structure analysis, including degassing, isotherm measurement, and data reduction, is generally completed within 3 to 7 working days. Samples requiring extended degassing protocols, multiple gas probes, or combined mercury intrusion analysis may require additional time, which the testing laboratory will confirm upon sample receipt.