Quantification of lignin-carbohydrate complexes in hardwood pulps, Part 2: Effects of bleaching chemicals

High kappa number kraft and soda-anthraquinone (soda-AQ or SAQ) pulps from sugar maple (Acer saccharum) were investigated to see how the lignin-carbohydrate complexes (LCC) they contained affected lignin removal by oxygen, chlorine dioxide, and hydrogen peroxide. The chlorine dioxide and hydrogen peroxide doses were higher than normal because both pulps had unbleached kappa numbers in the range of 61-62. Only oxygen delignification was investigated with the SAQ pulp. The research focused on the strong lignin-carbohydrate (L-C) linkages only. The pulp carbohydrates were enzymatically degraded and solubilized, thus leaving an enzymatic lignin (EL) residue. The highest concentration of bound sugars (glucan, xylan, arabinan, and galactan) on any of the ELs was <2.1 wt%. Chlorine dioxide (D stage) was investigated at end pHs of 2.1, 2.9, and 4.0, followed by extraction with dilute sodium hydroxide. Lignin oligomers containing bound glucan and arabinan were unreactive and accumulated in the fibers. When oxygen was used to delignify kraft and SAQ pulps by ~50%, only ~10% of the lignin bound arabinan was solubilized. Galacto-lignin complexes were somewhat reactive to oxygen and hydrogen peroxide under alkaline conditions, but less reactive in the D stages. Consistent with literature data, xylo-lignin complexes were reactive toward oxygen and toward the other two oxidants. They do not appear to be major impediments in the bleaching process.

Study of an Evaporation System for Sodium Hydroxide Solution

The textile industry in Bangladesh uses a substantial quantity of caustic soda (sodium hydroxide) to clean and prepare fabrics for dyeing. In all textile mills dealing with finishing, particularly with the mercerizing of cotton and mixed cotton fabrics, dilute caustic soda solutions come out as effluent from mercerizing unit. Caustic soda is expensive and its disposal without neutralization is unacceptable. A considerable amount of caustic soda can be saved if the dilute solution leaving the mercerizing step can be collected, concentrated and recycled. The concentration of the dilute caustic soda solution can be carried out by means of evaporation. A single effect evaporation system to concentrate the dilute sodium hydroxide solution was constructed and operated. The operating results confirm the economic viability of such recovery scheme.Journal of Chemical Engineering Vol.ChE 24 2006 35-36

Microwave Assisted Enzymatic Hydrolysis of Corn Stalks for L-Lactic Acid Production

Glucose production from pretreated corn stalks by cellulose enzymatic hydrolysis with cellulase was investigated and compared with no pretreatment, as a reference. The corn stalks were pretreated with microwave, sulfuric acid hydrolysis and dilute sodium hydroxide solution hydrolysis respectively. The enzymatic hydrolysis experiments were carried out at 50°C, 50 g/l dry matter (DM) solid substrate concentration and 15 filter paper unit (IU)/g DM of a commercial cellulase. Fermentable sugar was able to be produced from all the pretreated corn stalks with an overall yield of 29-58% of the maximum theoretical yield, based on the glucan available in the solid and liquid substrate. The corn stalks pretreated with dilute acid had the best glucose yield as 58.09% followed by the corn stalks pretreated with acid and microwave with an overall yield of 57.02% with 15 IU/g DM of cellulase. Glucose was the main product with enzymatic hydrolysis yield ratio 38.89%in the dilute sulfuric acid pretreated corn stalks, while with enzymatic hydrolysis yield ratio 51.07%in the dilute sodium hydroxide solution and microwave pretreated corn stalks under enzymatic hydrolysis conditions. These advantages, along with their negative price, make these solids a valuable raw material for L-lactic acid production.