Three Novel Wax Removal Methods for Wax Containing Old Corrugated Containers: Carbon Dioxide Extraction, Kraft Pulping and Agglomeration Richard A. Venditti, John F. Kadla, Richard D. Gilbert, Hasan Jameel, Hou-min Chang North Carolina State University Department of Wood and Paper Science

Background Waxboard products are a $3 billion a year business Currently wax containers are separated from OCC and landfilled Problems associated with wax products in recycling Wax deposits on paper machine Lower paper physical properties

Important Characteristics of Waxes: Main Component is paraffin wax Based on hydrocarbons and as such are hydrophobic. Are soluble in organic solvents. Are not strong/tough materials. Have low viscosity. Melt at temperatures around 125 F. Often have higher molecular weight modifiers Serve to strengthen the wax film. Increase melting point. Decrease solubility in organic solvents.

Strategy of the Research: Wax and fibers are significantly different in their properties and these differences can be exploited for separation purposes (1) Dispersion/emulsification tendency in a water based phase: Can this be exploited to wash the wax away in kraft cooking liquors? (2) Hydrophobicity: Can this be exploited to agglomerate and screen the wax in the water phase? (3) Solubility: Can this be exploited to extract the wax by supercritical CO2?

Can Wax-OCC be Processed in a Kraft Digester Hypothesis: The high temperatures and presence of fatty acids in a kraft digester will stabilize wax in the liquor. Approach: use a pilot plant digester to compare the pulping performance and resulting pulps from Control: 100% Hardwood Chips Trial: 90% Hardwood Chips and 10% Wax-OCC

Kraft Pulping of Hardwood Chips and Waxed OCC Blends 100% HW or 90% HW 10% WOCC M&K Digester AA % = 18 T= 335 F S% = 25 H-factor= 800 L/W=4 Rinsed with 40 liters of 180 F Water Disintegrated Screened 0.014 inch slots Screened Pulp for Testing

Kraft Pulping HW-WOCC Blends Pulping Results: 100% HW 90/10 HW/WOCC Screening Accepts (%) 46 47 Kappa Number 16.2 14.8 Viscosity 30.4 26.2 Hexane Extractives 1.4 0.5 in Accepts(%) Black Liquor Solids (g/l) 177 183

Kraft Pulping HW-WOCC Blends Paper Properties : 100% HW 90/10 HW/WOCC CS Freeness (ml) 650 635 Density (g/cm3) 0.63 0.70 Breaking Length (Km) 5.4 6.0 STFI (klbf ft/lb) 9.1 9.9 Slide Angle (degrees) 20.5 22.5

Summary of Processing Wax-OCC in a Kraft Digester Comparison of 10% level of Wax-OCC in HW chips to a 100% HW chips control The resulting pulp extractives % were similar The paper properties were similar No operating difficulties were experienced in the pulper, disintegrator or screen

Can Wax-OCC be Agglomerated in a Re-pulper and Screened? Approach: use lab-scale pulper to evaluate pulping conditions on the agglomeration and dispersion of the wax in the pulper. Investigate: Time Temperature Consistency pH Agglomerating Agents

Agglomeration Process Curtain Coated Waxboard (16.5% Wax, m.p. = 64 C) Tap Water Pulmac Screen (0.006 inch slots) Collection Screen (150 mesh) Accepts Filtrate Rejects (Fisher Filter Paper - P8)

Material Balance around Pulmac Screen and Collection Basket Feed Accepts Fiber Wax Fiber Wax Rejects Filtrate Fiber Wax Fiber and fines Wax Losses (filtrate) = Feed - Rejects - Accepts

Effect of Pulping Temperature on Wax Distribution 5% K, 30 min.

Effect of Pulping Consistency on Wax Distribution 70 C, 30 min

Summary of Pulping and Agglomeration Wax detachment is promoted by low consistency and temperatures greater than the mp of wax (less than 1% remaining on fiber) Agglomeration is promoted by low consistency Dispersion is promoted by high consistency Simple lab air flotation removed 80% of the wax from the wash filtrates The addition of “agglomerating” chemicals did not enhance agglomeration (octadecanol, non-ionic surfactant, polyethylene, polystyrene)

Can wax be extracted from Wax-OCC by supercritical CO2? Proposed Process: Wax is removed from dry Wax-OCC in a high pressure extraction vessel. The dewaxed OCC is then pulped and recycled. The wax is sold as a valuable by-product. Approach: Extraction of pre-consumer wax-OCC with CO2 in a lab-scale high pressure extraction vessel has been conducted and evaluated.

Advantages and Attributes of Supercritical CO2 Region g s l P T PC = 72.2 atm; TC = 31oC PC TC Solvating characteristics similar to many organic solvents Tunable solvating properties Gas-like viscosity Gas-like diffusivity Inexpensive Non-toxic Environmentally benign 1. Pc is the lowest pressure at which an increase in temperature no longer results in an increase in the vapor phase. 2. Tc is the lowest temperature at which increasing the pressure no longer results in an increase in the liquid phase. 3. In the region above Tc and Pc the two phases coalesce; and, there exists neither gas phase nor liquid phase but a supercritical fluid with properties of both liquids and gases.

SC-CO2 Extraction Process 500 mL Extractor Heater Pump Cyclone Separator CO2 Source Chiller Wax Waxed OCC

Extractions of Saturated and Curtain-Coated Corrugated Containers 300 Atm, 100 °C, 1 hour, ~50g CO2 / min Residual Wax as % Board Weight after CO2 Extraction (determined by Soxhlet-hexane) Wax Extraction Efficiency with CO2 Saturated Containers Curtain-Coated 2.0% 0.5% 70% 99% *Total and residual wax content determined by Soxhlet extraction with hexane for 24 hours. Extractions of Saturated and Curtain-Coated Corrugated Containers 1. Comparison of 3 mL and 500 mL extractions. 2. Sample weight for 500 mL chosen on wt/vol ratio of 3 mL. 3. Wt loss of 3 and 500 are essentially the same. Correspond to > 99 % removal with 500 mL. 4. Achieved > 99% removal with 38 g CO2 (500mL) compared to 200 g (3 mL). 5. Due to large difference in Flow-rate of two reactors, the time of 60 minutes was arbitrarily chosen and used as reference time for 500 mL vessel. 6. Don’t forget to mention Soxhlet results 7. If it comes up, differences in extractable wax is due to the following: a) differences in amount of wax on a given section of board b) difficult to oven dry waxed samples due to the loss of melted wax. c) differences in the amount of water before and after SC-CO2 (with and without wax). Dewaxed board retains more than 4 times the amount of water as waxed board, and absorbs it extremely fast.

Bar / ºC Effect of Time-Temperature-Pressure on the Extraction Efficiency of Saturated Containers

Waxed Untreated Soxhlet Extracted SC-CO2 Extracted Unwaxed SEM of Soxhlet and SC-CO2 Extracted OCC Images are 250 microns wide at 500X magnification

Effects of SC-CO2 Extraction on the Papermaking Properties of Recycled OCC

Summary of CO2 Wax Extraction Wax removal efficiencies can be greater than 99%. Extractive levels in the fibers can be reduced to less than 1%. Paper properties of the SC-CO2 extracted material are slightly lower than a control (unwaxed, recycled board) and are attributed to a small amount of residual wax. The SC-CO2 extracted wax may be recovered as a recyclable wax product. The cost of capital for implementation is prohibitive under the current price structure.

Acknowledgements The careful work of Li Wang, Qing-min Chen and Thad Stauffer is greatly appreciated. We would like to thank SCA, Ecosynthetix, Weyerhaueser, Nippon Paper and Shell for supporting the agglomeration research. We would like to thank the AF&PA Containerboard Technical Group for supporting the CO2 extraction research. We would like to thank Pulmac and Apogee for their generous donations of equipment to NCSU.