Product Simplified reaction scheme Raw material Pulping

Processes

Bleaching

Processes

Acetate

Tow CellOH _ _CH3CO_2O H_ __

Cell_OCOOCH3_2_3

MHW,H, S, E, P AS (CCE),

PHK (CCE)

ECF,

CONV

Plastics P, CL PHK-CCE, SO ECF,

CONV

Nitrocellulose (NC)

High-N-NC (x = 3) CellOH _ HNO3

H_ __Cell_ONO2_x CL SO CONV

Low-N-NC (x = 2) CL, S SO, AS CONV,

ECF

Microcrystalline

Cellulose (MCC)

CellOH H_ __CellOHcryst MHW,H, S, E, P (AS), PHK ECF

Raw Material:

B (beech), E (eucalypt), S (spruce), H (hemlock), P (pine), MHW(mixed hardwood), CK (cotton linters)

*) sulfite cooking with pine and other resinous wood requires different pH profile → two-stage

Processes, or measures to remove the resins

Pulping Purification Processes:

AC (acid sulfite), PHK (prehydrolysis kraft), CCE (cold caustic extraction), SO (soda).

Products:

EO = ethylene oxide, PO = propylene oxide

MC (methylcellulose), MHPC (methylhydroxypropylcellulose), HEC (hydroxyethylcellulose).

Chemical Properties

Chemical Composition

Organic Compounds

Hemicelluloses (short-chain alkali-soluble carbohydrates)

One of the main objectives of dissolving pulp production is the removal of noncellulosic

Carbohydrates which constitute the major part of the short-chain material

in the polymer. The available purification processes – particularly the hot and cold

caustic extraction processes – contribute to a considerable increase in production

Costs, mainly due to high yield loss and high chemical charges (see Sections 8.3

And 8.4). Therefore, the extent of purification is adjusted to the demands on the

Particular further processing. However, even small amounts of alien polysaccharides

May influence the processability and properties of the final product.

During steeping, the first step of alkaline processing of dissolving pulps for

The viscose and etherification procedures, alkali-soluble hemicelluloses are

Removed to an extent depending on pulp quality, the process conditions and the

Dissolving Grade Pulp

Equilibrium concentration level in the recycled steeping liquor. In this definition,

The hemicelluloses consist of both alkali-soluble degraded cellulose and heteropolysaccharides

Such as degraded xylan or mannan. The accumulation of hemicelluloses

In the steeping lye inhibits cellulose degradation during ageing due to the

additional oxygen consumption through these degraded carbohydrates [13]. In

Addition, they react preferentially with carbon disulfide in the subsequent xanthation

Дата добавления: 2015-10-21