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In the upcoming decades, cement production growth is expected to exceed the increase in availability of clinker substitutes. Increased clinker replacement rates in cement and use of alternatives fuels were pointed out as the main alternatives for reducing emissions of the national cement industry, whilst increasing cement production in 2050. Consequential life cycle assessment (CLCA) offers a framework to capture environmental consequences from demand alterations. Modelling the cement production and markets involved is however challenging, given conceptual (only unconstrained markets are considered) and practical modelling limitations (e.g. model granularity compatible with CLCA interests). This paper refers to an ongoing work and adopts a two-stage approach to discuss the effects of the change on the average cement production process in Brazil. We first performed a CLCA without formal affected market identification to estimate the potential environmental impacts of the technology change proposed in the Brazilian Cement Technology Roadmap. Secondly, we used a Computable General Equilibrium (CGE) Model of the Brazilian economy to (more) realistically foresee short-term effects induced by such change. The CGE model comprises 102 economic activities, including cement production and its production chain. Our results indicate that (i) increasing the proportion of calcined clay and limestone filler as clinker partial substitutes and (ii) excluding charcoal from the fuel mix composition at the kiln would impact all economic sectors. Our preliminary findings suggest that the increased efficiency in cement production would create some rebound effect that would not invalidate the emission benefits from displacing energy and virgin materials. Additional impact categories and consequences in other economic sectors should be further investigated.

ABSTRACT:The aim of this work was to assess the impact of hemicellulose extraction in eucalyptus wood, through alkaline leaching (NaOH) of wood chips, on the subsequent kraft process (with varying sulphidity) and the quality of the pulp. The chips were initially saturated with water and treated with a NaOH solution in a liquor to wood ratio of 6:1 m 3 /t. The reaction times (3, 8, 14 and 16 hours), temperatures (70, 84 and 90°C) and NaOH concentrations (60, 80, 90, 120 and 156g/L) were assessed in atmospheric conditions. In the pressurized treatments (300 kPa), the reaction times, temperature and NaOH concentrations assessed were, respectively: 30, 60 and 120 minutes, 100°C and 100, 150 and 200g/L. The optimal alkaline leaching condition was determined taking into account the hemicellulose concentrations remaining in the chips and the gravimetrical yield. Chips not subjected to alkaline treatment (control) and leached with NaOH in optimum conditions were kraft cooked until kappa number 17 -18. The results indicate that alkaline leaching of chips is not efficient in extracting hemicelluloses in the wood studied. The highest extraction of 4-Omethyl-glucuronoxylan acetate reached 42% in very severe conditions (100°C, 60 minutes, 200g/L of NaOH and 300 kPa pressure). The pulp yield of the leached chips was approximately 7% lower than that of the non-leached chips (control).

ABSTRACT:The search for a better use of wood in the pulp industry has fuelled interest in a more rational use of its components, particularly xylans. The impact of xylans removal and of xylans redeposition on pulp properties for tissue and P&W paper grades are discussed in this paper. Kraft pulp (15.6% xylans) treatment with 10-70 g . L -1 NaOH resulted in pulps of 14.5-5.9% xylans. The treatments decreased pulp lignin and HexA contents and caused significant positive impact on subsequent oxygen delignification and ECF bleaching. Xylan removal decreased pulp beatability, water retention value and tensile index but increased drainability, water absorption capacity, capillarity Klemm and bulk. Overall, xylan depleted pulps showed almost ideal properties for tissue paper grade pulps. In a second step of the research, xylans extracted from unbleached (BXL) and bleached eucalyptus pulps (WXL) by cold caustic extraction (CCE) were added to a commercial brown pulp in the oxygen delignification (O-stage) and further bleached. Xylans deposition occurred at variable degree (up to 7% on pulp weight) depending upon the O-stage reaction pH. Pulp bleachability was not impaired by WXL xylan deposition but slightly negatively affected by BXL xylans. Pulp beatability was improved by xylan deposition. The deposited xylans were quite stable across bleaching and beating, with the WXL xylans being more stable than the BXL ones. At low energy consumption, the deposited xylans improved pulp physical and mechanical properties. Xylans extraction by CCE with subsequent deposition onto pulp in the O-stage proved attractive for manufacturing high xylan P&W paper grades. EFEITOS DA XILANA NA PRODUÇÃO DE CELULOSE DE EUCALIPTORESUMO: A busca por uma melhor utilização da madeira na indústria de celulose tem alimentado o interesse em uma utilização mais racional dos seus componentes, em particular as xilanas. O impacto da remoção das xilanas e de sua redeposição nas propriedades da polpa solúvel e tipos de papel de imprimir e escrever (P&W), são discutidos neste trabalho.

The present work focused on characterizing the chemical and structural properties of isolated lignin from six hardwoods and their kraft pulps in an attempt to better understand the relationship between lignin’s chemical properties and resultant oxygen delignification performance. Several hardwood samples were cooked under the same conditions with varying alkali charges to obtain unbleached pulps with kappa numbers between 19 and 20. These pulps were then subjected to an oxygen delignification stage. Both processes were evaluated for pulp quality, residual lignin, and O-stage delignification efficiency. The oxygen delignification stage was carried out under fixed conditions and evaluated with regards to kappa number, which was corrected for hexenuronic acid (HexA) contributions.Results revealed that different hardwood species exhibited differing oxygen delignification efficiencies. A high correlation was found between the O-stage delignification efficiency and the content of phenolic groups in the unbleached lignin, which confirmed that free phenolic groups are the reactive site for molecular oxygen attack. When different hardwood species were compared, the HexA contents were not found to affect O-stage delignification efficiencies.