CN1141441C

CN1141441C - Alkali recovery from paper making black liquor by wet method

Info

Publication number: CN1141441C
Application number: CNB001006452A
Authority: CN
Inventors: 孙连超; 许玮
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-01-26
Filing date: 2000-01-26
Publication date: 2004-03-10
Anticipated expiration: 2020-01-26
Also published as: CN1259600A

Abstract

The present invention discloses an alkali recovering method for black liquor by a wet method, which comprises the steps that sulfur dioxide is used as an acidifying agent, the alkaline papermaking pulping black liquor is acidified to separate lignin, sugar containing liquor carries out anaerobic fermentation to generate marsh gas or is hydrolyzed into furfural, and lime powder is precipitated and separated to obtain calcium sulfite and an alkali solution which are recycled for pulp preparation. The recovery of resources, such as lignin, etc., is realized, and the alkali recovery of the papermaking black liquor is realized by the chemical reaction of the wet method.

Description

Warm alkali recovery from black liquor of paper making

The present invention relates to resource recovery of papermaking black liquor, and is especially alkali recovering process.

The existing 1-3 ten thousand ton/year scale paper making and pulp making factories in China are hundreds, and the traditional combustion method alkali recovery is difficult to stably operate for the small-scale pulp factories and cannot be adopted. Therefore, it is very significant to find a small-scale alkali recovery method for black liquor in paper making, which is suitable for the national conditions of China and has small investment.

The applicant's Chinese patent No. CN89106694.2 discloses a method for treating alkaline pulping black liquor by a sulfur dioxide acidification method to recover lignin; the present applicant's chinese patent No. ZL93118743.5 discloses a method for converting acidic filtrate into calcium sulfite and sugar-containing lye using calcium hydroxide, but the full utilization of lye is limited because the recovery of soda ash alone has not been achieved.

The invention aims to provide a novel alkali recovery method for alkaline pulping black liquor, which is called wet alkali recovery, and is used for recovering lignin, converting saccharides into methane through anaerobic fermentation or preparing furfural through acid hydrolysis, and obtaining sodium hydroxide solution after calcium sulfite is separated out through calcium oxide.

The invention not only recycles the lignin and the glucide in the papermaking pulping black liquor, but also better recycles the caustic soda which is an important raw material for pulping, thereby making up the defect that the traditional alkali recycling technology by a combustion method is difficult to be applied to the papermaking pulping factory with the scale of 1-3 ten thousand tons/year, and opening a way for the clean production of the ten thousand tons of papermaking pulping factory in China.

The method of the invention is realized by the following steps: the black liquor is acidified by sulfur dioxide, and lignin is precipitated under heating and heat preservation, and the detailed content can be referred to the patent application No. CN 89106694.2. Anaerobic fermentation to convert saccharide into marsh gas or acid hydrolysis into furfural, causticizing with lime powder to produce calcium sulfite precipitate, and causticizing the filtrate into sodium hydroxide solution. Calcium sulfite feverDecomposed into CaO and SO₂。

The main reactions in the above process are as follows:

1. acid precipitation lignin Wherein L is lignin

2.

Causticizing reaction of CaO powder

The preferred embodiments of the present invention are:

1. sulfur dioxide gas is generated in an easily available and cheap form such as burning sulfur, roasting sulfur-containing ore, preparing sulfuric acid tail gas, high-sulfur boiler flue gas and the like;

2. directly introducing sulfur dioxide gas into the black liquor, wherein the pH is less than 4, and separating out lignin for separation;

3. adjusting pH of the filtrate to 6.5-8.5, adding into a fermentation tank containing anaerobic bacteria, controlling temperature to 25-35 deg.C, and converting saccharide into biogas; wherein, the anaerobic bacteria is the common anaerobic for conventional anaerobic fermentation, such as activated sludge, and the like, as long as the anaerobic bacteria can be generated; in addition, it is known to those skilled in the art that the conditions may be appropriately adjusted according to the anaerobic bacteria used.

In the other scheme, steam is added to hydrolyze and distill under the condition of 3-5% diluted acid, and xylan is converted into furfural; it is to be noted that furfural is obtained by acid hydrolysis, which is a technique well known to those skilled in the art, and the pH, temperature, etc. of the acid hydrolysis may be appropriately changed as needed.

4. Adding lime powder, heating, and CaSO₃Precipitating;

in a pyrolysis furnace at 900 ℃ and 1100 DEG C₃Pyrolysis into CaO and SO₂

5. Filtering out CaSO₃The filtrate is caustic soda solution, i.e. obtained by boiling soda by wet reactionTo recover;

6. the filtrate can be completely reused as pulping and cooking liquor, and if the water quantity is more than the cooking requirement, the filtrate can be properly evaporated and concentrated to be matched with pulping.

Compared with the prior art such as combustion method alkali recovery, the method has the advantages and positive effects that:

1. the lignin in the black liquor can be recycled into high-value products instead of being burnt at low price, so that the economic benefit is increased, and the investment is reduced;

2. converting xylan and the like in the black liquor into methane to be used as combustible gas or hydrolyzing the methane into furfural;

3. sodium ions in the black liquor do not need to be burnt into Na₂CO₃Then the causticized caustic soda solution is dissolved and directly converted into NaOH solution in the solution,the equipment is greatly simplified, and the investment is reduced; the conversion process is carried out in aqueous solution

The alkali recovery by the wet method is realized, the process is simple, the investment is low, and the pulping scale is suitable, so that a large number of ten-thousand-ton papermaking pulping plants can obtain the suitable pollution control technology and survive.

Compared with the ZL93118743.5 patent method, the method has the positive effects that:

1. converting the saccharides in the black liquor into methane or hydrolyzing the saccharides into furfural;

2. the alkali liquor without the saccharides can be completely reused for cooking pulping, thereby realizing wet alkali recovery,

enterprises gain great economic benefits and are more popular.

Claims

1. A process for converting the black liquid of paper-making pulping into lignin and alkali solution features use of sulfur dioxide acidifying method to separate lignin, hydrolysis to remove saccharide from black liquid, use of lime powder to deposit and separate calcium sulfite and obtain alkali solution for pulping, and wet chemical reaction to recover alkali from black liquid of paper-making.