Author

Kefyalew Dido

Date of Award

5-2014

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Adriaan R.P. van Heiningen

Second Committee Member

Joseph M. Genco

Third Committee Member

Barbara J. W. Cole

Abstract

Research into the production of sustainable and renewable products is presently receiving strong interest due to the increase in fossil fuel consumption and its effect on global warming. Dissolving pulp is an example of such a renewable product which is produced from wood grown on non-agricultural land. Dissolving pulp fibers are used for textiles and compete with cotton-based clothing. However cotton production is less sustainable because it requires prime agricultural land, 15 to 35 times more water, and significant quantities of fossil fuel-based fertilizers. As a result it is forecasted that man-made cellulosic fiber production (dissolving pulp, regenerated cellulose, and derivatives of cellulose) will increase almost five-fold from 2010 to 2030.

The pre-hydrolysis Kraft process is used for the production of dissolving pulp. The prehydrolysate is not recovered industrially because of precipitation of "sticky lignin" during handling and further processing of the prehydrolysate. Recent research in our laboratory has shown that the "sticky lignin" precipitates are not formed when formic acid (FA) is present at relatively low concentrations of 5-10 g/L during the pre-hydrolysis stage. Therefore in the present study FA prehydrolysis was investigated on Northeastern hardwood chips prior to kraft cooking to produce dissolving pulp. Wood chips were processed through four stages: 5-10 g/L FA extraction, distilled water washing, white liquor impregnation and kraft cooking. It was confirmed that the addition of FA during pre-hydrolysis at 160 °C for 100 minutes eliminated the dark resin-like sticky-lignin precipitate seen without FA addition. After subsequent water washing for 70 min at 160 °C, the extracted chips were impregnated with white liquor for 60 min at 115 °C followed by kraft cooking for 60 min at 160 °C using different effective alkali (EA) charges. For comparison the chips were also subjected to regular kraft cooking for 2 hours at 160 °C using different EA charges. The final pulp products were analyzed for yield, kappa number, intrinsic viscosity, and percentages of hemicellulose and cellulose present in the pulps. The composition of the FA extracts, wash filtrates and black liquors are also measured.

The desired properties of a dissolving pulp (i.e. kappa no of about 10, hemicellulose content of 3% and intrinsic viscosity of about 900 mL/g) were obtained after pre-hydrolysis at 160°C with 10g/L formic acid (FA) for 100 minutes followed by washing and subsequently Kraft pulping at 14% EA at 160°C for 60 minutes. The dilute FA prehydrolysate does not lead to formation of dark sticky lignin precipitates, and the combined drained pre-hydro lysate and wash water contains 7.7% sugars, 2.2% lignin and 2.6% acetyl groups/acetic acid (all on original wood basis) which could be used for as a feed stock for renewable products.

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