A) Field of the Invention

This invention relates to wood pulping using chemical pulping media and more particularly relates to such media which result in superior wood pulps with a lower refining energy requirement.

B) History of the Prior Art

In the prior art, chemical pulping media were used to manufacture wood pulp. Such media have included both alkali and sulfur based media. The conventional pulping based on sulfur results in a good wood pulp but unfortunately the sulfur containing media (sulfite) contributes to both air and water pollution.

Attempts have been made to use low boiling alcohols as wood pulping media. In general, alcohols alone do not result in sufficiently effective pulping. An attempt has been made to use methanol in the presence of caustic soda. Unfortunately, methanol is too toxic to be used in such a process. BRIEF DESCRIPTION OF THE INVENTION

In accordance with the invention there is provided a method for manufacturing wood pulp which comprises pulping wood with a mixture of ethanol and sodium hydroxide. The invention also includes wood pulp manufactured in accordance with the method.

.- - S *HnE-~ET '

DETAILED DESCRIPTION OF THE INVENTION

It has been unexpectedly found that the combination of ethanol with sodium hydroxide delignifies wood to a much greater extent than either the ethanol or sodium hydroxide alone.

In accordance with the preferred embodiment of the invention, from about 10 to 25 weight percent of sodium hydroxide is used and from about 10 to about 60 volume percent of ethanol is used. The pulping time, in accordance with the preferred embodiment, is from about 1/2 to about 4 hours and the pulping temperature is from about 100 to about 200°C.

Essentially any wood can be pulped in accordance with the method of the invention to obtain a superior wood pulp than was obtained by commercially usuable prior arti chemical wood pulping methods.

The following examples serve to illustrate and not limit the present invention. Unless otherwise indicated, all parts and percentages are by weight. EXAMPLE _

Spruce chips are cooked in an electrically heated digester with mixtures of water and ethanol (1 :1 by volume), at a 5:1 liquor to wood ratio, 170°C for 2-1/2 hr. For comparison, cooks under the same conditions -were carried out with the addition of 20% NaOH (calculated on wood), and with alkali alone. Table 1 shows that ethanol plus NaOH (column 1) is more effective than either ingredient alone

TA3LE 1. Effect of Ethanol and NaOH in Pulping of Norway

Spruce.

TABLE _ Effect of Ethanol and NaOH in Pulping of Norway

Spruce. Cooking time 2-1/2 hr. Temp. 170°C. Pulp Properties at -300 ml CSF:

NaOH, % on wood 20 20 0

Ethanol, vol. % 50 0 50

Yield, % 47.4 52.5 77.6

Kappa No. • 44.3 93.1 157

Beating revs., PF1 5500 9500 8000

Density, g/cm^ 0.709 0.680 0.549

Burst index, KPam ² /g 8.20 6.68 2.60

Tensile index, Nm/g 109 87 44

Tear index, mNm^/g 9.0 10.9 8.7

Brightness, % 22.1 15.3 15.8

The increased selectivity with respect to lignin is evident from the lower yield, lower Kappa number, lower refining energy requirement, higher tensile index, and higher brightness of the pulp. EXAMPLE !_ _! .

In view of the greater delignif ication selectivity of the ethanol-NaOH process, the cooking time is soda pulping could be reduced substantially by addition of ethanol, without impairing the quality of the product. Table 2 illustrates this effect. It is evident that almost the same pulp yield can be obtained with ethanol-NaOH in 45 in. as with NaOH in 150 min. In addition, the former pulp has a lower Kappa number (75.5 vs 93.1). The strength properties of the two pulps are very similar.

- 5%EJt

OMPI IPO ^'

EXAMPLE 3

The ethanol-NaOH process is especially significant in the area of high-yield pulping, because it allows a greater preservation of carbohydrates than NaOH alone. So, e.g., an ethanol-NaOH pulp of 81.6% yield (obtained with 5% NaOH, 170°C, 45 min.) has a Kappa number of 157, while a soda pulp (obtained with 20% NaOH) of 66% yield has a very similar (147) Kappa number. This is because in soda pulping only limited delignification can occur, thus low Kappa number pulps are obtained.

O PI ^{' WIPO}

© TABLE 2. Effect of Cooking Time on Ethanol-NaOH Pulping of Norway Spruce,

CO 20% NaOll on Wood. Temp. 170°C. Pulp Properties at -300 ml CSF >

H U Kthanol, Vol. % 0 0 0 50 50 50

CL,

Time, min. 45 60 150 45 0 150

Yield, % 66.0 64.4 52.5 55.2 50.5 47.4

Kappa No. 1 7 131 93 75.5 59.9 44.3

Beating Revs. , PF1 17,000 16,000 9,500 13,000 10,000 5,500

Density, g/cn-H 0.619 0.658 0.680 0.671 0.694 0.709

Burst Index, KPam^/g 4.56 6.24 6.68 6.72 8.59 8.20

Tensile Index, Nm/g 67.7 77.8 87.0 89.4 108 104

Tear Index, mNm^/g 9.2 8.9 10.9 9.8 10.6 9.0

Brightness, "U 16.2 16.6 , 16.3 21.6 22.5 22.1

CO xn

CO

O