The present Kraft pulping system is more than one hundred years old.

When the Kraft pulping system was first put into use there was no polymer industry of any significance. However, today in the United States alone the polymer industry produces over 70 billion pounds of various polymer products with the majority derived from petrochemical feedstock. Worldwide production is over 270 billion pounds annually. This demand for polymers creates a market for polymers from lignin which is part of this process. In the current kraft pulping process the lignin is burned as a fuel and its only value is its BTU value. This is an inefficient use of the lignin.

Current technology has demonstrated that lignin can be used in the foundry industry, urethane foam industry and also the plastics industry.

Lignin has more value when it is used in lignin based products in the polymer industry as compared to lignin used as a fuel. Once the lignin is removed from the black liquor it is possible to easily separate the sugars that are present and convert them into ethanol that can be added to gasoline. Obviously, the use of ethanol as a fuel supplement to gasoline was not popular or even known at the time of the Kraft pulping process.

Natural gas is readily available as a fuel and is environmentally clean.

Natural gas boilers can provide the necessary steam requirements for a pulp mill at a fraction of the cost of a recovery boiler. Recovery boilers which burn lignin are difficult to control and maintain in compliance with environmental laws. Natural gas boilers are environmentally friendly and clean.

At the present time in the kraft pulping process, the kraft soda pulping process and the semi-chemical pulping process it is necessary to have the black liquor concentrated and burned in a recovery furnace in order to have

the sodium compounds converted into sodium carbonate. Then the sodium carbonate is reacted with calcium hydroxide to produce sodium hydroxide which is the desired pulping chemical. However the capital costs for such processing steps as oxidation of the black liquor, using a multiple effect evaporator and then further evaporation of the black liquor with a direct contact evaporator are very expensive. The most expensive piece of equipment is the recovery furnace and also the most dangerous to operate.

Additionally, recovery furnaces fired by black liquor are not environmentally clean to operate. This novel process produces valuable byproducts from the black liquor and enables alternate, cheaper fuels such as natural gas, to be used in the process without a recovery boiler. Boilers fired by natural gas and other fuels are used in the process to produce the required steam.

Another major advantage of this invention is that by removing the lignin from the black liquor it now becomes possible and economical to produce a variety of other products such as sodium acetate, sodium sulfate, wood sugars, acetic acid, and lignin.

It is this equipment (recovery furnace) that contributes to the high cost of operating a pulping mill and significantly affects the profitability of a pulp mill. It is the major advantage of this present invention that allows all of this equipment to be eliminated from a pulp mill.

By acidifying the black liquor with an acid, it is possible to precipitate the lignin and produce a sodium salt which has a commercial value in the marketplace. Organic acids and inorganic acids may be used. As an example one such acid is acetic acid whereby sodium acetate is produced or phosphoric acid could be used which produces a sodium phosphate salt. By producing sodium salts which are more valuable than sodium carbonate, it is more economical and more profitable than using the present recovery furnace to produce sodium carbonate by using the present recovery furnace and its auxiliary equipment. Also, sodium salts do not have to be more valuable than

sodium carbonates to make this process economical.

Fig. 1 is a schematic representation of a pulping process without a recovery furnace.

Fig. 2 is a schematic of a known pulping process with a recovery furnace.

As an example, addition of acetic acid to the black liquor until the lignin is insoluble, will render the lignin insoluble and will be filtered from the liquor by various means. A filter press, vacuum filter belt or ordinary filters are some of those means.

As an additional example, 10% solution of sulfuric acid may be added to the black liquor until the lignin is insoluble enabling the lignin to be filtered from the liquor by various means. Most of the lignin is insoluble at pH of approximately 2-3. After the lignin is removed, the solution is concentrated by evaporation or other means forming crystals of sodium sulfate. Then the sodium sulfate crystals are filtered from the solution thereby producing a sugar solution which can be used to produce alcohols or other products. A filter press, vacuum filter belt or ordinary filter may be used to filter the sodium sulfate crystals.

Optionally, carbon dioxide and sulphur dioxide may be added to the black liquor. These gases become acids when added to the black liquor as they react with water.

Those skilled in the art will recognize that many changes may be made to the invention heretofore described without departing from the spirit and the scope of the appended claims. Commercially valuable sodium salts are also produced by the addition of the acid to the black liquor. This process enables the pulping process to occur without a recovery furnace.