Materials LCA for PLLA
Materials LCA for PLLA based on sugar cane Purac, manufacturer of lactides and lactic acid from Gorinchem, The Netherlands recently announced the construction of a 75,000 t/a lactide plant in Thailand. Since the end of 2007 Purac is already running a plant for the production of lactic acid in Thailand with an annual capacity of 100,000 tonnes. The market development for lactide monomers is supported by sustainability studies. This article summarizes the results of a Life Cycle Assessment (LCA) recently carried out for L(+)-lactide and Poly- L(+)-Lactic Acid (PLLA) made from sugar cane in Thailand. This article provides the most important conclusions of the study. The full LCA will be available for download from www.bioplasticsmagazine.com/201002 as soon as it has been accepted for publication. Method LCA is a commonly used tool to assess environmental performance and is currently recognized as best practice to holistically identify the ecological burden and impact of a production system and the ecological consequences of changes. LCA was chosen as the instrument for investigating the interactions between Purac’s production activities and the environment, and the possible consequences of these value chains replacing traditional alternatives. The aims of the LCA are: • Characterize the environmental profile of the existing production of lactic acid in Thailand; Fig. 1: Schematic of the production chain from agriculture to PLA. PLA to customers T Lactide PLA Diesel fuel Fertilizer Herbicides Sugar cane cultivation Land preparation and planting Fertilizing and weeding Harvesting Sugar cane Filter cake Emission Fuel Electricity Aux. chemicals Lactide production (Purac) Granulation Lactide purification Lactide synthesis Fuel Electricity Aux. chemicals T Byproducts Emissions PLA production Granulation PLA finishing PLA synthesis Emissions Transport T Sugar cane processing Sugar milling Sugar refining Sugar Biogase Rice husk Wood waste Steam and electricity congeneration Fuel Electricity Nutirents Aux. chemicals Surplus electricity to grid Molasses Emissions Lactic acid production (Purac) Lactic acid Purification Lactic acid recovery Fermentation Byproducts Solid waste Emissions T 24 bioplastics MAGAZINE [02/10] Vol. 5
Materials PLLA Kg CO 2 eq./ton 500 Kg CO 2 eq./ton 0 500 1,000 1,500 2,000 2,500 PP granulate 1,900 PE-LD granulate 2,200 PE-HD granulate 1,800 -1833 Sugar Sugar feedstock production (sugarcane) Auxiliary chemicals Transportation Power Steam Total PLLA at gate PLLA 500 Fig. 2: CO 2 emission build-up in the PLLA production chain Fig. 3: CO 2 emission involved with the production of PLLA and other polymers • Identify the environmental consequences related to the planned production of L-lactide, D-lactide and PLLA from sugar cane in Thailand; • Generate eco-profile modules for use in LCA’s of customer applications; • Highlight the critical aspects and hot spots and find optimization potentials; • Set up a mathematical LCA tool that can be used in process development. The LCA reported here is a cradle-to-customer gate analysis, including the sugar cane agricultural system, industrial activities related to auxiliary chemicals, distribution, processing of sugar cane into sugar and final production of lactide and PLA (fig. 1). The analysis was based on data for Purac’s lactic acid plant in Thailand, current designs of large scale lactide and PLA plants and public data on the sugar cane agriculture in Thailand. These data were combined with emission data from public databases and recalculated to environmental impacts in a life cycle impact assessment (LCIA), covering the following environmental impact categories: primary renewable and non-renewable energy, nonrenewable abiotic resource usage, farm land use, global warming, acidification, photochemical ozone creation and nutrient enrichment. The environmental profile of biopolymer PLA was compared on an equal weight basis with the profiles of fossil based polymers which can be used as alternative raw materials in several PLA applications. Similar studies have been carried out by NatureWorks for PLA derived from corn starch. These studies of 2003 and 2007 indicate the beneficial CO 2 profile for PLA compared to fossil based plastics, and also reflect the continuous process improvements in present day industry to arrive at attractive bioplastics made from renewable resources. Global Warming Potential Fig. 2 shows a so called ‘waterfall-plot‘ of the global warming potential by means of balancing the CO 2 emissions of PLLA production. The plot shows the additive parts in greenhouse gas emissions in making L-lactide. The starting point, by convention, is the amount of CO 2 fixated in the lactide itself, -1833 kg CO 2 /ton lactide. The calculation does not start at the fixation of CO 2 into the sugarcane, but calculates the amount of CO 2 , that would be released when the PLLA would be converted to CO 2 and uses this number as the CO 2 captured in PLLA. From fig. 2 it becomes clear that with Purac‘s current production technology, L-lactide and PLLA from cane sugar still have a net positive emission of greenhouse gases. For L-lactide this is 348 kg/ton and for PLLA this is 500 kg/ton. The net CO 2 emission of 500 kg CO 2 /ton PLLA is also considering the electricity production of the sugar mills, notably the electricity generated from the boiler operated on bagasse. The figure of 40 kWh/ton used for this calculation has been derived from published data on Thai sugar mills. Data on the electricity production as high as 95 kWh/ton cane for Thai mills have been reported, while the average is in the order of 30-50 kWh/ton. This implicates that there is great potential through optimization and investment of sugar mills to decrease the CO 2 emissions to net values even lower that 500 kg CO 2 /ton bioplastics MAGAZINE [02/10] Vol. 5 25
