ARTICLE pubs.acs.org/est
Improving the Environmental Profile of Wood Panels via Co-Production of Ethanol and Acetic Acid J. Mason Earles,*,†,§ Anthony Halog,†,§ and Stephen Shaler†,‡,§ †
Forest Bioproducts Research Institute, University of Maine, 5737 Jennes Hall, Orono, Maine, United States Advanced Structures and Composites Center, University of Maine, 5793 AEWC Building, Orono, Maine, United States § School of Forest Resources, University of Maine, 5755 Nutting Hall, Orono, Maine, United States ‡
bS Supporting Information ABSTRACT: The oriented strand board (OSB) biorefinery is an emerging technology that could improve the building, transportation, and chemical sectors’ environmental profiles. By adding a hot water extraction stage to conventional OSB panel manufacturing, hemicellulose polysaccharides can be extracted from wood strands and converted to renewably sourced ethanol and acetic acid. Replacing fossil-based gasoline and acetic acid has the potential to reduce greenhouse gas (GHG) emissions, among other possible impacts. At the same time, hemicellulose extraction could improve the environmental profile of OSB panels by reducing the level of volatile organic compounds (VOCs) emitted during manufacturing. In this study, the life cycle significance of such GHG, VOC, and other emission reductions was investigated. A process model was developed based on a mix of laboratory and industrial-level mass and energy flow data. Using these data a life cycle assessment (LCA) model was built. Sensitive process parameters were identified and used to develop a target production scenario for the OSB biorefinery. The findings suggest that the OSB biorefinery’s deployment could substantially improve human and ecosystem health via reduction of select VOCs compared to conventionally produced OSB, gasoline, and acetic acid. Technological advancements are needed, however, to achieve desirable GHG reductions.
1. INTRODUCTION AND BACKGROUND Oriented strand board (OSB) is the most common structural wood composite panel used in the United States. In 1999, it held 50% of the market share,1 with North American production levels greater than 22 million m3.2 It has been proposed that the OSB manufacturing process can be modified to extract hemicellulose and other compounds from wood flakes prior to panel manufacturing.3,4 This extract has the potential to be converted into combustible alcohols (e.g., ethanol, butanol, methanol) and industrial chemicals (e.g., acetic acid, polylactic acid, and furfural), among other useful products. Whereas combustible alcohols would likely replace fossil-based transportation fuels such as gasoline, biobased industrial chemicals can be used to manufacture polymers and other products. Experimental results suggest that the addition of a hot water extraction process could remove about 10% of the OSB strand mass in the form of hemicelluloses and other dissolved compounds.3 Paredes4 estimates that around 409.3 million liters of ethanol could be produced annually from these hemicelluloses. Although this represents a relatively small percentage (less than 0.1%) of total U.S. gasoline consumption on an energy basis, OSB extracted hemicellulose could become one option within a diverse portfolio of feedstocks used to produce biobased transport fuel, among other chemicals. r 2011 American Chemical Society
The OSB biorefinery manufacturing process can be understood in three parts: shared, OSB, and ethanol/acetic acid pathways. Figure 1 illustrates these pathways. 1.1. Shared Pathway. Following harvest, logs are transported to an OSB mill in which they enter the debarking and flaking stage. Debarked logs are flaked by sets of rotating blades that cut strands of varying lengths, widths, and thicknesses. Bark is typically combusted to generate heat or sold as mulch.5 In conventional OSB manufacturing, OSB flakes next move to the drying and screening stage. The OSB biorefinery, however, adds an autohydrolysis, or hot water extraction, stage following debarking and flaking. Flakes and water are inserted into a vessel and heated to 140190 °C which leads to autohydrolysis at a pH near 3.3,6,7 Various combinations of temperature and time can be utilized to obtain the desired composition of dissolved solids. In addition to carbohydrates, acetic acid, hydroxymethylfurfural, furfural, and other chemical compounds are contained in the extract. This unit process results in two coproducts, wood flakes and hemicellulose extract, which are then converted into the final Received: June 26, 2011 Accepted: October 3, 2011 Revised: September 23, 2011 Published: October 03, 2011 9743
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Figure 1. OSB biorefinery process diagram.
OSB and chemical products along two distinct pathways. As a result of extraction, wood flake mass is reduced proportionally to the amount of solids removed. 1.2. OSB Pathway. The manufacturing processes along the OSB pathway after hot water extraction are the same as conventional manufacturing. Mass and energy flows, however, are altered. Wood flakes are dried following hot water extraction. In conventional OSB manufacturing, the drying process is energy intensive, often demanding up to 80% of the heat requirement in a mill.8 The primary heat source for drying is from wood fuel generated as a byproduct of OSB manufacturing.5 In an OSB biorefinery, the pressurized conditions during hot water extraction significantly increase strand moisture content to near full saturation conditions.3 Consequently, additional energy will likely be required for drying; although significant amounts of moisture may be flashed off as strands leave the extraction unit at high temperature.3 Because the drying stage is a major consumer of wood heat input, it contributes significantly to airborne volatile organic compound (VOC), particulate matter (PM), and greenhouse gas (GHG) emissions. To meet U.S. regulatory standards, the VOCs and PM released from drying must be reduced using emission control equipment such as a regenerative thermal oxidizer (RTO) and wet electrostatic precipitator (WESP). As VOCs are primarily produced via hemicellulose decomposition,9 and past research has shown significant VOC reduction from hot water extraction in the pressing process,3 it is expected that reductions will occur in the drying process as well. The presence of fewer VOCs consequently increases CO2 emissions from natural gas combustion (see Supporting Information, Section 1.2.4). The screening process follows drying. It aims to screen out fine wood materials from the dried flakes that are too small for
OSB mat formation. These screening fines are burned to generate heat. The blending process combines strands with resin binders and a small amount of wax. Then, these strands are oriented in the mat formation process before pressing. During the pressing stage the OSB mat is pressed under high heat and pressure, creating a rigid, dense structural panel. The press is also a significant consumer of heat and emitter of VOCs. Importantly, hot water extraction is shown to reduce select VOCs between 15% and 75% during the pressing stage of OSB production.3 As with the drying process, VOC reduction offers an opportunity to reduce energy consumption and related CO2 emissions. The final stage of OSB manufacturing is finishing, in which panels are cooled, cut to size, grade stamped, stacked in bundles, and packaged for shipping.5 Scrap material in the form of sawdust, sander dust, and reject boards is used for heat generation. Regarding the final panel, prior research suggests that following moderate hot water extraction mechanical properties of panels manufactured from extracted material are improved or not significantly different compared to conventional panels.3 The resultant panels also exhibit significantly improved resistance to moisture.3 To maintain the same number of panels per unit wood input, it would be necessary to reduce panel density in proportion to the weight reduction associated with extraction. It is expected that such a density reduction would reduce transportation costs and environmental impacts related to transportation from the manufacturing facility to the construction site. 1.3. Ethanol and Acetic Acid Pathway. Following hot water extraction, the extract must meet a desirable concentration of hemicellulose. If the concentration is too low, evaporation, 9744
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Environmental Science & Technology recirculation, or ultrafiltration can be used. Each of these techniques has unique technoeconomic strengths and weaknesses.10 Once the desired hemicellulose concentration is achieved, the extract enters the acid hydrolysis stage in which sulfuric acid (H2SO4) is added. Following hot water extraction (or autohydrolysis) the pH of the extracted liquid is about 34 due to the presence of acetic acid released from acetylated polysaccharides.7,11 For acid hydrolysis a pH of approximately 1 is desirable.10 Thus, the corresponding amount of sulfuric acid is added to lower the pH from approximately 3 to 1. It is assumed that all of the lignin in the extract is precipitated due to the low pH. Because it is desirable to minimize the production of gypsum during the liming stage, and as gypsum production is a function of sulfuric acid input, low sulfuric acid consumption is also preferable. One way to reduce overall sulfuric acid consumption is through an acid recovery process, such as membrane separation. Acid recovery using membrane separation can achieve at least 80% recovery and often higher.12 In the sensitivity section, we examine a scenario in which an acid recovery is performed following acid hydrolysis. The hydrolyzed extract, or hydrolyzate, enters the lignin filtration stage in which lignin is removed, presumably at a rate of 100%.10 During the acid hydrolysis step, a considerable amount of acetic acid will be generated and can be sold as a coproduct. Additionally, acetic acid must be removed as it inhibits the fermentation of C5 and C6 sugars to ethanol.13 The liquidliquid extraction process removes acetic acid, and some furfural, using a suitable solvent.14,15 Consistent with Mao,10 it is assumed that ethyl acetate is used as the solvent for liquidliquid extraction which is recovered at a rate of 100%. Once the acetic acid is removed from the extract, the remaining solution enters the liming process in which the pH is raised from approximately 1 to about 6 by adding lime (calcium oxide, CaO). The liming process aims to (1) raise the pH of the extract, (2) precipitate sulfate ions as gypsum (CaSO4 3 H2O), and (3) detoxify the hydrolyzate.9 The gypsum is then removed by filtration and typically disposed to a landfill.16 The hydrolyzate now enters the fermentation process. Assuming the sugar concentration is suitable, and inhibitors like furfural and hydroxyl methyl furfural are removed, micro-organisms such as E-coli B (KO11)17,18 or Z. mobiliz19 are used to convert five and six carbon sugars into ethanol and CO2. Consistent with Mao,10 this study assumes that fermentation takes place under anaerobic conditions with approximately 90% conversion efficiency of hexose and pentose sugars to ethanol (see Supporting Information). Because anerobic fermentation of glucoronic acid forms acetic acid, the acetic acid is sent to the liquidliquid extraction process. The final output is a very dilute ethanol which is sent to ethanol distillation, where it is rectified and dehydrated to 99% concentration.10 1.4. Expected Environmental Benefits of the OSB Biorefinery. The OSB biorefinery has the potential to improve the environmental profile of OSB panels, ethanol, and acetic acid compared to conventional production systems. The primary environmental benefit of replacing fossil-based gasoline and acetic acid with hemicellulosic ethanol and acetic acid is the possibility of GHG emission reduction. More specifically, a GHG reduction can occur during the combustion of biobased ethanol compared to gasoline. Upon combustion biobased ethanol releases biogenic CO2 which is not typically considered as a contributor to global warming since it was originally sequestered during plant growth.20 Thus, assuming that GHG emissions
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Table 1. Functional Unit for OSB Biorefinery and Conventional Production System OSB biorefinery
a
quantity
conventional system
quantity
ethanol
1000 kg
gasoline
613 kg
acetic acid OSB panels
368 kg 55.3 MSFa
acetic acid OSB panels
368 kg 55.3 MSFa
MSF = 1000 square feet (3/800 panel thickness).
released in other parts of ethanol’s lifecycle are not substantially higher than gasoline, a reduction can occur. Acetic acid, on the other hand, is typically produced in the U.S. via the reaction of CO with natural gas-derived methanol.21 In both cases, switching from a fossil feedstock to renewable feedstock decreases depletion of fossil resources. The hemicellulose extraction process could also improve the environmental profile of OSB panels. First, hemicellulose extraction is shown to reduce select VOCs between 15% and 75% in the pressing stage of OSB production.3 More specifically, Paredes4 found that methanol was reduced by about 26%, acetaldehyde by 74%, and formaldehyde by 15% (at varying degrees of significance). Although no direct evidence exists to suggest that such reductions will occur in the drying process as well, the fact that VOCs are primarily produced by the decomposition of hemicellulose, much of which is removed during hot water extraction, implies this will be the case. Because select VOCs are damaging to human and ecosystem health, and the OSB manufacturing process is major emitter of VOCs,22 their removal could represent a substantial environmental improvement. Second, due to improved mechanical properties and flake density reduction from hemicellulose extraction, a mass reduction of about 9.25% per panel could be achieved, which increases resource use efficiency and reduces overall transportation requirements per panel.3 Whereas the OSB biorefinery holds many potential environmental benefits, their relative significance from a life cycle perspective is not obvious. This study aims to characterize these impacts with respect to all stages of the supply chain—including raw material extraction, manufacturing, use, and all intermediary transportation. A number of uncertain process parameters are included via sensitivity analysis. Finally, a target OSB biorefinery process is presented that minimizes key environmental impacts. Due to potential GHG and VOC reductions associated with the OSB biorefinery, emphasis is placed on climate change and toxicity-related impacts.
2. METHODOLOGY This study compares three OSB biorefinery coproducts with a conventional manufacturing system as shown in Table 1. Detailed mass and energy flow data for the shared, OSB, and ethanol/acetic acid pathways can be found in the Supporting Information. Several steps were taken to evaluate the environmental impacts of the OSB biorefinery. First, since no existing process model was identified, a baseline mass and energy flow model of an OSB biorefinery was developed based on best available data. The process model integrated and modified data from existing studies on conventional OSB manufacturing,5 hot water extraction of hemicellulose,3 and hemicellulosic ethanol production,10 among other sources. To develop a life cycle inventory (LCI), Kline5 collected process-specific data via survey from four OSB 9745
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Table 2. LCIA Comparison of Overall OSB Biorefinery and Conventional Production Systems code GWP
impact category global warming
equivalence factor (kg)
conventional system
baseline OSB biorefinery
% difference
CO2-Eq
1.89 104
2.16 104
14.6%
1.30 104
19.5%
HTP
human toxicity
1,4-DCB-Eq
1.62 10
FEP
freshwater eutrophication
P-Eq
9.89 101
1.08
FETP
freshwater ecotoxicity
1,4-DCB-Eq
5.35 101
4.82 101
MEP
marine eutrophication
N-Eq
1.77 102
1.77 102
0.1%
4
9.2% 9.8%
METP
marine ecotoxicity
1,4-DCB-Eq
5.85 10
5.24 101
10.5%
ODP
ozone depletion
CFC-11-Eq
3.87 106
1.40 105
261.9%
2
2.2% 0.3%
1
PMFP POFP
particulate matter formation photochemical oxidant formation
PM10-Eq NMVOC
3.43 10 1.42 103
3.51 102 1.41 103
TAP
terrestrial acidification
SO2-Eq
8.81 102
9.13 102
TETP
terrestrial ecotoxicity
1,4-DCB-Eq
1.66
1.22
manufacturing plants in the southeastern United States. Kline5 was modified to include a hot water extraction process. Extraction conditions (i.e., time, temperature, liquid-to-wood ratio, and wood species) and dissolved solid composition were taken from laboratory scale results found by Paredes.4 The ethanol and acetic acid production pathway was based on a modified version of Mao.10 Modifications were made regarding extract composition (e.g., carbohydrates, acids, and lignin), acid hydrolysis conversion efficiency, and fermentation efficiency to account for the difference between hardwood modeled by Mao10 and the softwood species (i.e., southern yellow pine) assumed to be used in this study. Because an operational OSB biorefinery does not currently exist, many of the assumptions made in the model above are uncertain. Thus, the model was parameterized to facilitate identification of sensitive processes with respect to the system’s environmental impacts. The mass and energy flow model was created such that thirteen parameters could be varied (listed in Supporting Information). Of these thirteen parameters, seven were identified as critical and tested for sensitivity in the following section. Next, mass and energy flows for each scenario were brought into OpenLCA software23 to estimate the related life cycle environmental impacts using the ReCiPe 2008 impact method.24 Life cycle inventory (LCI) data originated from a variety of sources. Timber harvesting and production was based on LCI data collected by the Consortium for Research on Renewable Industrial Materials (CORRIM) on forest management and harvesting.25 LCI data associated with natural gas combustion in the OSB biorefinery originated from the U.S. LCI database3 which was based on the GREET model.26 Ethanol transportation, distribution, and combustion in a vehicle also originated from Wu et al.26 More detailed system boundary diagrams are provided in the Supporting Information. Generally, most background data in this study originated from the U.S. LCI database.27 All energy related processes, such as electricity generation, natural gas production, and transport processes, were taken from the U.S. LCI database. Quicklime production is also available via the U.S. LCI database. Sulfuric acid production was taken from a report compiled by the Swiss Centre for Life Cycle Inventories entitled Ecoinvent Report No. 8, Chemicals (2007). Thus, sulfuric acid may not represent U.S. production technology. Data for potassium fertilizer production was acquired from an LCA report on U.S. pork production by Schenck.29 Finally, landfilling is modeled using one of two processes available through the European ELCD core database.30 More specifically, either a municipal solid waste or inert solid waste landfilling process was used since no better U.S. data are
3.6% 26.3%
publicly available. Such a limitation affects this study’s ability to comment on the life cycle impacts of gypsum disposal with any certainty (see Supporting Information). LCI data for the conventional production system of gasoline, acetic acid, and OSB panels was taken almost exclusively from the U.S. LCI database; with the exception of gasoline transportation, distribution, and combustion which originated from the GREET model.26 For this study the ReCiPe 2008 Hierarchist impact assessment method was utilized.24 The impact categories included are contained within Table 2.
3. RESULTS AND DISCUSSION The following section presents the results for the baseline OSB biorefinery impacts, tests for sensitive process parameters, and proposes a target process to minimize key environmental impacts. As shown in Table 2, compared to the conventional system the OSB biorefinery offers improvements with respect to toxicityrelated impact categories, such as HTP, FETP, METP, and TETP. The largest potential reductions occur in the FETP and HTP category at 26.3% and 19.5%, respectively. Decreased acrolein emissions from hot water extraction primarily drive such reductions in both cases. Barium from crude oil production and natural gas extraction undergoes the second largest reduction in the HTP category. Other VOCs, such as formaldehyde, acetaldehyde, and methanol have a less noticeable effect on FETP and HTP. Some categories, most notably GWP and FEP, increase compared to the conventional production system. Increased CO2 from electricity and heat consumption almost exclusively explains the higher GWP impact of the OSB biorefinery baseline compared to the conventional production system. Detailed process and flow contributions for each impact category can be found in the Supporting Information. Whereas toxicity-related impact categories experience significant reduction, GWP impacts should be lowered in order for ethanol produced at an OSB biorefinery to qualify as a renewable fuel under U.S. biofuel policy as outlined in the Renewable Fuel Standard 2 (RFS2).31 Based on the results for the baseline scenario, seven process parameters were identified as potentially important in achieving this goal (see Table 3 and Figure 2). Three parameters pertain to the hot water extraction process. First, higher levels of heat recovery reduce energy consumption in the extraction process. Heat recovery was assumed to occur at 50% in the baseline scenario. For the alternative scenario an 9746
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Environmental Science & Technology Table 3. Parameters Tested for Sensitivity Analysis
Figure 2. Sensitivity analysis of LCIA categories with respect to select process parameters.
arbitrary value of 80% was selected as a reasonable upper bound. Ultimately, actual heat recovery efficiency will be decided by process design and cost considerations. Second, depending on carbohydrate concentration levels following extraction an evaporation process could be required to concentrate these carbohydrates to desirable levels for the fermentation process. Evaporation of water is a highly energy intensive process. Whereas the baseline scenario assumes that no evaporation will be needed (due to the use of extract recirculation), the alternative scenario examined the case where it is required. Third, higher liquid to wood ratios result in greater energy consumption for achieving the desired cook time and temperature. Consistent with Paredes,4 a liquid to wood ratio of 4 to 1 was tested in the baseline scenario. For the alternative scenario, this ratio was lowered to 2 to 1. Prior research compared liquid-to-wood ratios of 4 to 1 and 8 to 1, finding that both liquid-to-wood ratios (at time and temperature conditions similar to this study) had a minor effect on extract yields during autohydrolysis.32 Based on these findings, we assume a negligible loss in extract yield will occur at lower liquid-to-wood ratios given the presumed time and temperature extraction conditions. The baseline scenario assumes that recirculation will be used to concentrate the solids to a level of 8.5%. Presumably doing this would have a negligible effect on overall mass and energy flows. The fourth parameter describes the percent mass reduction permissible per panel. Whereas Paredes4 finds that manufacturing lower density panels that maintain/improve mechanical properties is possible, actual density will be determined by the manufacturer based on their own technical specifications. In the base scenario, it was assumed that each panel can weigh 4.62% less than conventional panels. In this alternative scenario, the permissible value was raised to 9.25%. Doing this increases the
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amount of panels that can be produced given the same input of logs. As a result, the functional unit for the OSB biorefinery and conventional systems change from 55.30 MSF panels to 57.85 MSF panels per 1000 kg of ethanol produced. Essentially, this represents an efficiency gain spread across all stages of the OSB biorefinery lifecycle. The fifth parameter tests the presence of sulfuric acid recovery which is 80% effective. As mentioned earlier, membrane separation technology has achieved acid recovery efficiencies of 80% for sulfuric acid, while continuous ion exchange has reached 97% with 2% sugar loss.12 This alternative scenario assumes that 80% acid recovery occurs with negligible heat input requirements. This can be compared to the baseline scenario which assumes that 0% acid recovery occurs as was modeled in Mao.10 The sixth parameter investigates the model’s assumption that only 10% additional heat is needed to dry flakes following hot water extraction compared to conventional OSB manufacturing process (without hot water extraction). In this alternative scenario, the value of 10% was arbitrarily raised to 20% to test for parameter sensitivity. Finally, based on recent trends in the literature ultrafiltration is tested as an alternative concentration process following hot water extraction.3336 Ultrafiltration is used as a low-energy separation technology when isolating a substance at a low concentration. Although membrane fouling is generally a major concern with ultrafiltration, past studies have observed almost no fouling when hydrophilic membranes were used to separate hemicelluloses from pulp mill water.37,38 Moreover, a recent study found that hemicelluloses could be concentrated nearly 15 times, from 0.7 to 1015 g/L, with only a 10% loss factor using ultrafiltration.36 Recall that the baseline OSB biorefinery performed well on toxicity measures, but poorly on GWP. The results above suggest that the greatest GWP reduction potential exists with respect to parameters 1 and 3. By increasing heat recovery from 50% to 80%, system-wide kg CO2eq. emissions can be lowered by 8.6%. Similarly, reducing the liquid to wood ratio from 4:1 to 2:1 results in a 9.4% reduction in kg CO2eq. emissions. Doing either of these options alone, however, does not reduce system-wide emissions below the conventional level—as the baseline scenario has over 14% greater kg CO2eq. emissions compared to conventional production. The third largest reduction in GWP can be made by adding a sulfuric acid recovery process, leading to 5.4% less system-wide emissions compared to the baseline scenario. The fifth largest GWP improvement is associated with increasing the permissible mass reduction per panel from 4.62% to 9.25%. This results in a 3.5% decrease in system-wide kg CO2eq. emissions. A large increase in GWP (at 13.7%) results from adding an evaporation process after hot water extraction. Ultrafiltration offers a less energy- and GWP-intensive form of separation than evaporation, only resulting in about a 2.5% increase in GWP. Raising the drying heat requirement from 10% to 20% results in a rather modest GWP increase of 3.5%. Other impact categories exhibited some sensitivity to the parameters tested. Generally, the effects were relatively small with the exception of ODP in relation to parameter 5. While the percent change was relatively large, the absolute release of kg CFC-11 eq. was very small. Thus, this impact category is not discussed in further detail. It is important to consider the interaction among these different parameters which can have aggregate effects. This is especially relevant for those parameters which pertain to the hot water extraction process. A liquid to wood ratio of 2 to 1 9747
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Figure 3. Percent change in each LCIA category for target and baseline scenarios with respect to conventional production system.
occurring with 80% heat recovery will have an even more dramatic effect, for instance, than either of the parameters varied individually. The compounded effect of changing parameters simultaneously was considered next by formulating a best environmental case (see Table 3). Essentially, the best case scenario assumes that process improvements are made to the baseline scenario with respect to extraction heat recovery, extraction liquid to wood ratio, percent panel mass reduction permissible, and sulfuric acid recovery. In making these changes, this analysis aimed to examine potential reductions and set a target for the OSB biorefinery process development that minimizes environmental impacts. Figure 3 shows the percent change for each LCIA category compared to the conventional production system. The baseline system is also shown to demonstrate the reduction potential of achieving the parameter values set for the best case scenario. The graph above shows that a substantial reduction in kg CO2eq. is possible for the best case scenario. In fact, an absolute reduction of about 2367 kg CO2eq. can be achieved at the system-wide level. Compared to the emissions for 613 kg gasoline (the energy equivalent of 1000 kg ethanol) at 2157 kg CO2eq., this represents a major reduction, exceeding the requirement of 60% lifecycle GHG emission reductions set by the RFS2. Additionally, significant reductions can be achieved across toxicity-related categories due to (1) the reduction of acrolein during OSB manufacturing by adding hot water extraction and (2) the reduction in barium due to decreased demand for crude oil refining to produce gasoline (see Supporting Information for details). It is also worth noting that the best case scenario reduces LCIA impacts across every category measured with the exceptions of FEP and ODP. FEP is likely to increase compared to conventional production so long as fertilizer is used for the production of biomass. In the case where natural regeneration is utilized for timber production, this would probably not be the case. In summary, this study examined the potential of the OSB biorefinery to improve the environmental profile of OSB panels, ethanol, and acetic acid compared to conventional production systems. The general finding was that toxicity-related impacts can be substantially reduced in the baseline OSB biorefinery system compared to conventionally produced OSB panels, gasoline, and acetic acid. Specifically, the impact categories of HTP and TETP could be reduced by about 20% and 25%, respectively, by switching from conventional products to those produced at an OSB biorefinery. Other toxicity-based categories, or FETP and METP, experienced less dramatic reductions due to lowered
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crude oil refining (for gasoline production) compared to the conventional system. Furthermore, after identifying and adjusting certain process parameters it is possible to achieve even greater impact reductions. Thus, one can conclude that the VOC reductions from hot water extraction appear to have the desired effect of significantly reducing lifecycle impacts related to VOC emissions. A second important finding deals with the lifecycle GHG impacts of the OSB biorefinery. As formulated in the baseline scenario, the OSB biorefinery system adds substantial GHG burdens compared to conventionally produced gasoline. However, through sensitivity analysis key process parameters are identified that could potentially reduce this burden, leading to an overall GHG reduction. Under the target scenario, this study shows that substantial reductions in GHGs compared to the conventional system is possible. Achieving such reductions, concurrent to large toxicity-related reductions from hot water extraction, should be a priority for future OSB biorefinery research.
’ ASSOCIATED CONTENT
bS
Supporting Information. Additional details on the process model mass and energy flows, system boundaries, and lifecycle impact assessment results. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]; phone: +1 314-479-6570; fax: +1 207-581-2875.
’ ACKNOWLEDGMENT We are grateful to Dr. Peter van Walsum, Dr. Adriaan van Heiningen, and Dr. Jonathan Rubin at the University of Maine for their valuable feedback. ’ REFERENCES (1) Bowyer, J. L.; Shmulsky, R.; Haygreen, J. G. Forest Products and Wood Science: An Introduction, 4th ed.; Iowa State University Press: Ames, IA, 2003. (2) Adair, C. Regional Production and Market Outlook: Structural Panels and Engineered Wood Products 20042009; APA E170; APAThe Engineered Wood Association: Tacoma, WA, 2004. (3) Paredes, J.; Shaler, S.; Edgar, R.; Cole, B. Selected volatile organic compound emissions and performance of oriented strandboard from extracted southern pine. Wood Fiber Sci. 201042 (4). (4) Paredes, J.; Jara, R.; Shaler, S.; van Heiningen, A. Influence of hot water extraction on the physical and mechanical behavior of OSB. For. Prod. J. 200858. (5) Kline, E. Gate-to-gate life cycle inventory of oriented strandboard production. Wood Fiber Sci. 2005, 37, CORRIM Special Issue. (6) Yoon, S. H.; Macewan, K.; van Heiningen, A. Hot water preextraction from loblolly pine (Pinus taeda) in an integrated forest products biorefinery. TAPPI 2008June. (7) Tunc, M.; van Heiningen, A. R. P. Hemicellulose extraction of mixed southern hardwood with water at 150°C: Effect of time. Ind. Eng. Chem. Res. 2008, 47 (18), 7031–7037, DOI: 10.1021/ie8007105. (8) Lees, A. Future OSB plants will require latest environmental technologies. Panel World 1993May. 9748
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