A WOOD DELIGNIFICATION CHEMICAL PROCESS USING AMMONIUM MAGNESIUM BISULPHITE AS THE ACTIVE REAGENT

Abstract: The present innovation consists of the use of a reagent solution (FINAL COOKING ACID) where ammonium magnesium bisulphite is the active chemical. This new process is particularly useful to those industrial plants where the cellulose pulp is obtained by the magnesium acid process. The present innovation consists of the introduction of ammonium ions in the cooking acid used in such plants (initial cooking acid). The final cooking acid is obtained by the reaction of the initial cooking acid with ammonium hydroxide. Experimental results show the superiority of the present innovation over the magnesium acid bisulphite pulping process which is expressed by: production of cellulosic fibres with higher mechanico-physical index values; decrease in the percentage of uncooked material; increase in wood yield and less environmental impact.

Description: DESCRIPTION A WOOD DELIGNIFICATION CHEMICAL PROCESS USING AMMONIUM MAGNESIUM BISULPHITE AS THE ACTIVE REAGENT Several sulphite wood delignification process with industrial application have been known for a number of years. The distinction between them is based on the active chemical present in the reagent solution (cooking acid). The compounds used as active chemicals are all monocationic bisulphites, mainly of calcium, magnesium, sodium or ammonium. The pulping process with calcium bisulphite is an exception, when dolomite is used to prepare the acid. In the last 30 years the bisulphite cellulosic pulps have been losing competivness to KRAFT pulps, which are obtained by a chemical process in an alkaline medium. The major disadvantage of bisulphite pulps is the weaker mechano- physical characteristics of their cellulosic fibres when compared with those obtained by the KRAFT process. The present innovation refers to a chemical process for wood delignification and consists of the use of a reagent solution where ammonium and magnesium bisulphites are together the active chemicals. The combination of both ammonium and magnesium cations as bisulphite is the novelty of this application This new pulping process is particularly useful to those industrial plants where cellulose pulp is obtained by the magnesium acid bisulphite process. The specific cooking acid of magnesium acid bisulphite pulping process is, physically, a gas-liquid system. The liquid phase is a magnesium bisulphite and sulphur dioxide aqueous solution in equilibrium with the S0 2 gas phase. The system is kept at temperature and pressure values of about 50°C and 2 Kg cm "2 , respectively. This particular cooking acid will be referred further on this document as the INICIAL COOKING ACID. The basis of the present innovation is the inclusion of the ammonium ion in the initial cooking acid, as described by the following equation: INITIAL COOKING ACID: Mg(HS0 3 ) (aq) + SO 2 (g) + Ammonium hydroxide addition: NH 4 OH(aq) II Reaction product: NH 4 (HSO 3 )(ag) The cooking acid obtained by this reaction will be referred to in this document as the FINAL COOKING ACID. FINAL COOKING ACID composition: Mg(HSO 3 ) 2 + NH 4 (HSO 3 ) + [SO 2 =/(pH)] The amount of S0 2 stoichiometrically in excess is a function of pH. The addition of ammonium hydroxide must drive the initial pH value of inicial cooking acid (1.5) to a final value between 2 and 4, depending on the needs of the process. This operation could be performed in a tank with the initial cooking acid under pressure (accumulator) or in the reactor (digester). In the FINAL COOKING ACID the percentage of total S0 2 , free plus combined forms, must be kept within 4% to 7% , depending on the requirements of the process. The pulping process operated at a higher pH value, such as that attained after ammonium hydroxide addition, decreases the wood degradation process, enables the production of cellulosic fibres with higher mechanico-physical index values, and decreases the specific consumption of wood. On the other hand, the presence of ammonium ions accelerate the reaction process decreasing both wood chip impregnation time and percentage of uncooked material. This latter effect improves the wood yield of the process. The experimental results obtained with hard wood, namely eucalyptus, show the superiority of the present innovation over the magnesium acid bisulphite pulping process, which is expressed by: a - Production of cellulosic fibres with a higher mechanico-physical index values. b - Decreased percentage of uncooked material. c - Increased wood yield. d - Less environmental impact.

Claims: CLAIMS 1 Chemical process for wood delignification characterized by the use ammonium magnesium bisulphite as active reagent. 2 Preparation process for the ammonium magnesium bisulphite reagent referred to in claim 1 , characterized by having as reaction reagents the initial cooking acid and ammonium hydroxide, according to the equation: INITIAL COOKING ACID: Mg(HSO 3 ) 2 (aςr) + SO 2 (g) + AMMONIUM HYDROXIDE ADDITION: NH 4 OH(aq) II REACTION PRODUCT: NH 4 (HSO 3 )(ag) FINAL COOKING ACID COMPOSITION: Mg(HSO 3 ) 2 +NH 4 (HSO 3 )+[SO 2 =/(pH)] 3 Chemical process for wood delignification, according to claims 1 and 2, characterized by a pH value between 2 and 4 at which the process must be run by the controlled addition of NH 4 0H to the initial cooking acid. 4 Chemical process for wood delignification, according to claim 3, which being applied to eucalyptus and taking the magnesium acid bisulphite pulping process as a reference standard, is characterized by a pulp production having cellulosic fibres with higher mechanico-physical index values. 5 Chemical process for wood delignification, according to claim 3, which being applied to eucalyptus and taking the magnesium acid bisulphite pulping process as reference standard, is characterized by a decrease in the percentage of uncooked material and an increase in the wood yield. Chemical process for wood delignification, according to claim 3, which taking the magnesium acid bisulphite pulping process as reference standard is characterized by the significant improvement of the environmental impact resulting from the lower amount of sulphur dioxide released to the air when the cook is discharged.

Inventors: ALMEIDA OLIVEIRA BAPTISTA JOAO, ALMEIDA OLIVEIRA BAPTISTA, JOAO, MANUEL
Applicants: ALMEIDA OLIVEIRA BAPTISTA JOAO, ALMEIDA OLIVEIRA BAPTISTA, JOAO, MANUEL
Application year: 1998
Main classification: D21C3
IPC codes: D21C3