This study used steam treatment to evaluate the potential of this method to remove residual creosote content of sawdust from weathered, out-of-service poles. Steaming was successful in reducing the creosote content to a level of 1.31%, regardless of creosote content at the start of the steaming treatment. Poles with higher initial creosote contents required longer steaming durations. At any given initial preservative content, creosote removal from weathered poles was more difficult than from freshly treated poles. Moreover, creosote from samples taken near the inner core of the poles was also more difficult to remove than creosote in the outer portions of the poles. Steaming proved an efficient mechanism to remove creosote. Some other technology must be applied to remove creosote content below 1.31%

Hse, Chung Y.

Roliadi, Han

Shupe, Todd F.

English

Wood and Fiber Science (E-Journal)

REMOVAL OF CREOSOTE FROM WOOD PARTICLES AT DIFFERENTHORIZONTAL AND VERTICAL LOCATIONS OF DECOMMISSIONEDPOLES USING STEAM TREATMENT1Todd F. Shupe†Associate ProfessorLouisiana Forest Products Development CenterSchool of Renewable Natural ResourcesLouisiana State University Agricultural CenterBaton Rouge, LA 70803Chung Y. Hse†Principal Wood ScientistUSDA Forest ServiceSouthern Research StationPineville, LA 71360andHan RoliadiSenior Research ScientistForest Products Research CenterBogor, Indonesia(Received June 2005)ABSTRACTThis study used steam treatment to evaluate the potential of this method to remove residual creosotecontent of sawdust from weathered, out-of-service poles. Steaming was successful in reducing the creo-sote content to a level of 1.31%, regardless of creosote content at the start of the steaming treatment. Poleswith higher initial creosote contents required longer steaming durations. At any given initial preservativecontent, creosote removal from weathered poles was more difficult than from freshly treated poles.Moreover, creosote from samples taken near the inner core of the poles was also more difficult to removethan creosote in the outer portions of the poles. Steaming proved an efficient mechanism to removecreosote. Some other technology must be applied to remove creosote content below 1.31%.Keywords: Creosote, wood poles, sawdust, steam.INTRODUCTIONA major development in wood preservationhistory was the use of coal-tar creosote, whichwas patented in 1836 by Moll, in a pressureimpregnation process patented by John Bethellin 1838. Known as the Bethell, or full-cell, pro-cess, it was the first major use of pressure forwood treating and remains the basis of mostmodern wood treating operations (Hunt and Gar-ratt 1967; Freeman et al. 2003). Since the earlydays of its inception, creosote has grown in mar-ket share to be one of the most industrially im-portant wood preservatives.Creosote, a high boiling fraction of coal orpetroleum distillate, is widely used as a preser-vative for wood in utility structures, marine pil-ings, and other applications. Most of the volume1 This paper (No. 05-40-0289) is published with the ap-proval of the Director of the Louisiana Agricultural Experi-ment Station.† Member of SWST.Wood and Fiber Science, 38(2), 2006, pp. 345 – 350© 2006 by the Society of Wood Science and Technologyof material treated with creosote is for the rail-way industry. Approximately 78% of the vol-ume of creosote used is to treat crossties and anadditional 6% of the used creosote goes intoswitch and bridge ties (Micklewright 1998). In1997, for example, some 2.76 × 106 m3 (97.4 ×106 ft3) of wood was treated with 2.92 × 108 L(77.2 × 106 gals.) of creosote along with 1.78 ×107 L (4.7 × 106 gals.) of petroleum solvent,which represented approximately 13% of all in-dustrially preservative-treated wood (Mickle-wright 1998).Preservative-treated wood that goes into ser-vice almost always will be decommissioned andremoved from service for various reasons suchas mechanical damage, poor treatment or in-service maintenance, or obsolescence. It hasbeen estimated that approximately 2 × 106 m3(7.06 × 107 ft.3) of creosote-treated wood istaken out of service each year in the U.S. andthat total will grow to approximately 16 × 106m3 (5.65 × 108 ft.3) in 2020 (Cooper 1994). Fur-thermore, it has been estimated that a total vol-ume of 2.8 × 106 m3 (1.00 × 108 ft.3) of creosote-preserved wood is annually decommissioned(AWPI 1997).Historically, the most common treatment op-tions for this material were either incineration orlandfilling. Neither option is particularly eco-nomically viable nor without potential adverseenvironmental consequences. Thus, recyclingoptions, both removal of the toxic preservativesfrom the preservative-treated wood and recy-cling of the detoxified preserved wood, are ofgreat importance to those concerned with thelife-cycle management of treated wood.Previous research has examined the technicalfeasibility of recycling creosote-treated wood forparticleboard (Zhao and Gardner 2001a,b) andtimber production from reclaimed creosote-treated wood pilings (Shi et al. 2001). A studyby Roliadi et al. (2000a) found that decommis-sioned creosote-treated utility poles have ad-equate gluability and decay resistance for manyvalue-added applications.Although many value-added products can beproduced with recycled creosote-treated wood, itis acknowledged that residual creosote contentcan have an adverse effect on the marketabilityof these products. Removing creosote from de-commissioned creosote-treated wood productshas largely been done by two methods: (1) bio-remediation and (2) solvent extraction. Bothmethods can be effective to bring the creosotecontent to near zero percent; however, bioreme-diation can be time-consuming (Esslyn 1976),and solvent extraction is costly (Portier et al.1994). Catallo and Shupe (2003) used super-critical water to transform creosote-treatedwood. During treatment, the creosote-derivedhydrocarbon residues in the wood were nearlycompletely (>99%) recovered, and the wood it-self was transformed into a mixture of hydrocar-bons including substituted benzenes, phenolics,and light PAHs. The industrial application ofthis technology is highly dependent on the yetdetermined economics of the process.One method that has been used to removeresidual preservatives from wood is steam ex-plosion. Clausen and Smith (1998a,b) and Shiauet al. (2000) examined the potential of steamexplosion alone and following acid extractionand bacterial fermentation to remove metalsfrom chromated copper arsenate (CCA)-treatedwood. The results suggest that steam explosiondoes not increase the extractability of the metals.Steaming has been used to increase wood per-meability (Hickin 1971; Eaton and Hale 1993)and separate volatile compounds in wood extrac-tives (Browning 1967). However, the applica-tion of steam treatment to creosote-treated woodhas not been widely studied. The objective ofthis study is to determine the potential of usingsteam and hot water washing to remove creosotefrom sawdust produced from out-of-servicepoles. In this paper, this process will be referredto as steam treatment. The successful develop-ment of this technology will allow for de-commissioned creosote-treated wood to be usedfor numerous products in which residual creo-sote content is not only technically adverse tothe remanufacturing process but may also benot permissible according to current U.S. En-vironmental Protection Agency (EPA) regula-tions.WOOD AND FIBER SCIENCE, APRIL 2006, V. 38(2)346MATERIALS AND METHODSWeathered out-of-service southern yellowpine (SYP) poles of two service duration groups(5- and 25- years’ service duration) were se-lected. In addition, freshly treated poles of thesame species were used for comparative pur-poses. Five poles from each group were taken asreplicates. These poles were obtained from En-ergy Gulf States Utility Company and brought tothe LSU Agricultural Center’s Lee MemorialForest near Bogalusa, LA, for processing. Allthe poles were passed through a metal detectorto remove metal objects. After metal removal,the poles were cut into 2.4–3.0-m (8–10 ft.)long bolts. Three bolts (top, middle, and bottom)were selected from each pole. Each bolt wassawn into experimental specimens using a por-table Wood-Mizer band sawmill at horizontaldistances of 1.3, 3.8, 6.4, and 8.9 cm (0.5, 1.5,2.5, and 3.5 in.) from the bolt surface as mea-sured from the butt end of each bolt. Duringsawing, sawdust samples obtained from variousvertical and horizontal locations in the poleswere collected for creosote content determina-tion (Fig. 1). A plastic bag was fit around thesawdust outlet for each cut of the bolts to collectthe sawdust. The sawdust was thoroughlymixed, and the bags were coded according tohorizontal and vertical position within the pole.The sawmill was thoroughly cleaned with an airhose between each cut to avoid cross contami-nation.Creosote content (C) (% of dry, extractedwood) was determined using toluene extractionin accordance with AWPA (1984) Standard A6-83, as follows:C  [(W1 − W2 − W3)/W2] × 100 [1]where W1 is weight of wood samples beforeextraction, W2 is weight of oven-dry extractedsample, and W3 is weight of water in sample.Creosote content (C) (pcf) was also deter-mined as follows:C  [A/100 × 32] [2]where A is the creosote content (% of dry, ex-tracted wood) and 32 is the assumed density(pcf) of the wood.FIG. 1. Sawing pattern of the experimental poles.Shupe et al.—REMOVAL OF CREOSOTE FROM WOOD PARTICLES 347Sawdust samples weighing 5 grams, with pre-determined creosote contents using toluene ex-traction in accordance with AWPA StandardA6-83 (AWPA 1984), were placed in a frittedglass crucible and then steam-treated in a retortat atmospheric pressure of 100°C (212°F) for upto 3 h. At intervals of 15 min, the samples wereremoved from the retort and washed with boilingwater to facilitate the removal of as much creo-sote as possible. The remaining creosote con-tents in the samples were determined again.Steam treatment was terminated when the re-sidual creosote content became stable and valuesat this point were considered as the final creo-sote content. Criteria used to evaluate the effec-tiveness of steam treatment were final creosotecontent and steaming duration.RESULTS AND DISCUSSIONFigure 2 shows the effect of steaming durationon creosote content. The freshly treated, 5 yearsof service, and 25 years of service poles con-tained initial creosote contents, creosote contentprior to steam treatment, of 34.18, 9.12, and2.84%, respectively. It is interesting to note thatregardless of the initial creosote content, steam-ing was successful in reducing the final creosotecontent to approximately 1.2–1.5% (Fig. 2).The high degree of success of the steam treat-ment can be largely attributed to the basic phys-ics of the steam-treatment. The heat from thesteam would have resulted in the volatilizationof some of the lower molecular weight volatileorganic compounds in the creosote and loweredthe creosote’s viscosity. Consequently, themovement of creosote, which is not chemicallybound or fixed in the wood, would have beengreatly enhanced by the steam treatment. How-ever, the capability of the steam treatment waslimited in its ability to remove creosote. Thesteam treatment was unable to reduce the finalcreosote content to less than approximately1.5%, which is less than the final creosote con-tent attainable through solvent extraction or bio-remediation (Portier et al. 1994) due to the factthat creosote is oil-soluble and therefore immis-cible in a polar substance such as steam. It islikely that the remaining creosote after steamtreatment will contain a greater fraction of high-boiling compounds, which are difficult to evapo-rate by steam (Andrew 1952; Wells and Bor-denca 1955).The analysis of variance (ANOVA) (Table 1)shows that the final creosote contents are notsignificantly different among all the variablestested; hence, the final content values can beaveraged or pooled, which yields a value of1.31%. The approximate steaming duration forvarious initial contents could be determined, byinterpolating it to the overall mean of 1.31%,which was regarded as the effective final creo-sote content. As a result, when the experimentaldata of initial creosote content were plottedagainst steaming duration (Fig. 3), the plot re-veals, as expected, that higher initial content re-quired longer steaming duration.FIG. 2. Effect of steaming duration on creosote contentof freshly treated, 5 years of service, and 25 years of servicecreosote-treated utility poles.TABLE 1. Analysis of variance of final creosote content andsteaming duration.Source of variationFinal creosote content Steaming durationDF F-values DF F-valuesService duration (S) 2 2.13 2 14.98*Error (a) — 12Vertical location (V) 2 2.08 2 2.47Horizontal location (H) 1 2.55 1 9.22**Interaction:S*V 4 1.98 4 1.78S*H 2 1.77 2 3.67*V*H 2 1.13 2 1.34S*V*H 4 0.97 4 0.91Initial creosote content — 1 22.31**** and * denote significant at alpha  0.01 and 0.05 levels, respectively.WOOD AND FIBER SCIENCE, APRIL 2006, V. 38(2)348The effects of the horizontal and vertical sam-pling locations and different service durationswere also analyzed by the ANOVA. Longersteaming durations were required for samplesfrom poles of older service ages and from samplestaken from inner portions of poles as comparedto samples from freshly treated poles and outerportions (Fig. 4). The longer steam periodsneeded for the older poles again inferred that theresidual creosote in 5- and 25-year weatheredpoles had greater high-boiling fractions, due tomore evaporation of low-boiling compounds, ascompared to the freshly treated poles.It is noted that the reason that the creosote ismore difficult to remove in the inner portions ofthe poles could also be due to the greater occur-rence of aspirated pits in the cell walls in thisportion of the pole. Pit aspiration was found tobe less common on the outer surfaces of thepoles due to the presence of sapwood. Moreover,the steam in the pre-treatment prior to the intro-duction of creosote in the treating process tendsto relieve pit aspiration on the pole surface (Ro-liadi 1997).This work is part of a larger on-going projectthat is examining the technical feasibility of re-cycling decommissioned preservative-treatedwood into value-added products. Although pre-vious research (Roliadi 1997; Roliadi et al.2000a) has examined the gluability of creosote-treated lumber, this work clearly has not. Addi-tional research is needed to examine the feasi-bility of using steam treatment on large-size,creosote-treated wood and assess the subsequentgluability properties.CONCLUSIONSThe objective of this study was to determinethe potential of using steam to remove creosotefrom out-of-service poles. This research hasshown that the initial creosote content in saw-dust samples from poles greatly determined thenecessary steaming duration to remove as muchcreosote as possible. Regardless of initial creo-sote content, steaming reduced the creosote to1.31%. Beyond this level, steaming caused nosignificant reduction in creosote content.At a given initial creosote content, removal ofcreosote by steam was more difficult for poleswith longer service duration and for materialsfrom the inner pole regions. Steaming, however,does appear to be an efficient and relatively in-expensive method of reducing the creosote con-tent in weathered poles. Additional treatment us-ing a different technology will be necessary toremove all of the residual creosote from decom-missioned or discarded creosote-treated wood.REFERENCESAmerican Wood Preservers Institute (AWPI). 1997. Tech-nical profile creosote-preserved wood as an alternate fuel.Fairfax, VA.American Wood-Preservers’ Association (AWPA). 1984.Standard methods for the determination of oil-type pre-servative in wood. AWPA A6–83. Stevensville, MD.ANDREW, J. W. 1952. Volatility of some of the compoundsFIG. 3. Relationship between initial creosote contentand steaming duration to reach 1.31% final creosote con-tent, which is the mean value of final creosote content for allage classes of poles.FIG. 4. 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SMITH, AND B. AVELLAR. 2000. Effects ofsteam explosion processing and organic acids on CCAremoval from treated wood waste. Wood Sci. Tech. 34:377–388.WELLS, J. H., AND C. BORDENCA. 1955. A study of creosotetreatment of seasonal and green southern pine poles.Proc. Am. Wood Preserv. Assoc. 51:59–65.ZHAO, J. H., AND D. J. GARDNER. 2001a. Recycling creosote-treated wood in particleboard. Pages 425–427 in WoodAdhesives 2000. Proc. No. 7252. Forest Prod. Soc.,Madison, WI.———, AND ———. 2001b. Volatile organic compoundsfrom hot-pressing of particles containing creosote-treatedwood. Pages 428–430 in Wood adhesives 2000. Proc.No. 7252. Forest Prod. Soc., Madison, WI. 428–430.WOOD AND FIBER SCIENCE, APRIL 2006, V. 38(2)350

Removal of Creosote from Wood Particles at Different Horizontal and Vertical Locations of Decommissioned Poles Using Steam Treatment

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Removal of Creosote from Wood Particles at Different Horizontal and Vertical Locations of Decommissioned Poles Using Steam Treatment

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