Niels J. Schenk

The Nonlinear Relationship between Paper Recycling and Primary Pulp Requirements

Waste paper is suitable for recycling back into paper or for incineration for energy recovery. If waste paper is used for recycling, secondary pulp replaces virgin pulp. Fiber recycling is limited, however, because of physical constraints—particularly the breakage of fiber in the recycling process—and a permanent input of virgin fiber to the system is required. Therefore one can expect that the relationship between recycling rates and resource requirements is represented by a curved line rather than a straight one. In this article, we present a mathematical model which confirms that the relationship between recycling rates and primary pulp requirements can be described as nonlinear. Furthermore, we show that this nonlinear relationship leads to an optimal recycling rate with regard to energy consumption: 93% for paper produced from chemical pulp, and 81% for paper produced from mechanical pulp. Sensitivity testing additionally reveals that at low recycling rates increasing waste paper recycling is energy efficient, but it becomes less efficient at higher recycling rates. Close to the optimum recycling rates (within 10%), increasing or decreasing the rate affects the total energy requirement less than 0.3%.

Biobased chemicals in a carbon-restricted world

In the quest for a more sustainable society, researchers, policy makers, and businesses are looking for options to reduce the use of fossil resources. Replacing these with renewable resources is a way to both ensure long-term material and energy security and reduce CO2 emissions. 1 Biomass based products are relevant in this context, but it is important to select the routes that are most beneficial in the context of an integrated energy and materials system. In such an integrated system biomass should be used primarily to produce “drop-in” chemicals for the petrochemicals industry like ethylene, propylene, methanol and benzene, toluene and xylene (BTX). To study the sustainability of biobased BTX a complex life cycle analysis was conducted looking at several products from woody biomass. In this paper we argue that production of biobased BTX yields good economic and environmental benefits for the following reasons:

Synthesis of Bio-aromatics from Black Liquors Using Catalytic Pyrolysis

Bio-aromatics (benzene, toluene, xylenes, BTX) were prepared by the catalytic pyrolysis of six different black liquors using both in situ and ex situ approaches. A wide range of catalysts was screened and conditions were optimized in microscale reactors. Up to 7 wt % of BTX, based on the organic fraction of the black liquors, was obtained for both the in situ and ex situ pyrolysis (T = 500–600 °C) using a Ga-modified H-ZSM-5 catalyst. The in situ catalytic pyrolysis of black liquors from hardwood paper mills afforded slightly higher yields of aromatics/BTX than softwood black liquors, a trend that could be confirmed by the results obtained in the ex situ catalytic pyrolysis. An almost full deoxygenation of the lignin and carbohydrate fraction was achieved and both organic fractions were converted to a broad range of (substituted) aromatics. The zeolite catalyst used was remarkably stable and even after 100 experiments in batch mode with intermittent oxidative catalyst regeneration, the yields and selectivity toward BTX remained similar. The ex situ pyrolysis of black liquor has potential for large-scale implementation in a paper mill without disturbing the paper production process.