Environmentally improved process for preparing recycled lignocellulosic materials for bleaching

摘要

Waste lignocellulosic material, for example brown kraft grocery bag and corrugated paperboard, is treated in a multi-step process to produce a recycle brownstock pulp having a sufficiently low kappa number that it may be bleached according to conventional means such that its final optical and strength properties are comparable to that of virgin pulps bleached according to similar means; biological enzymes are used in conjunction with medium consistency pulping to separate fibers and loosen contaminants, such as wax and adhesives; low temperature soaking of waste lignocellulosic material in an alkaline peroxide liquid using long reaction times is used to minimize energy consumption, degrade contaminants, and to selectively remove lignin; loosened contaminants and poorly bonding lignocellulose debris are removed by screening and cleaning methods; high consistency peroxygen cooking is used to substantially delignify the pulp and to destroy contaminants in an energy efficient manner; liquid streams are treated and internally recycled to reuse chemicals and to eliminate environmental liquid discharge; organic solids are recovered and incinerated as fuel to provide heat energy to the process; spent sodium salts are recovered as sodium hydroxide and reused in the process as a delignification agent; the recycled pulp can be employed in the manufacture of brown paper and paperboard products, or can be bleached to provide a pulp for white paper or paperboard products.