METHOD FOR ACIDIFICATION OF TALL OIL FIELD OF TECHNOLOGY The present invention is related to the chemistry of the forest industry and particularly to the acidification of tall oil soap and to the fractionation technology connected to it. The invention concerns a method, where tall oil soap is contacted with high pressure carbon dioxide, and simultaneously, the formed brine containing aqueous-and tall oil phases are separated as defined in Claim 1. By this method the tall oil soap can be acidulated almost completely, and there is no need to add sulfuric acid. High quality tall oil can be produced by this method.

BACKGROUND OF THE INVENTION Tall oil is a by-product obtained from kraft pulping process, and it is composed mainly of resin-and fatty acids. The residual cooking liquor from the kraft pulping process known as black liquor, which contains most of the tall oil as soap, is pumped into the weak liquid skimmer. The crude tall oil soap is gradually rising onto the surface of the black liquor wherefrom it can be skimmed off for recovery in one or several stages. The solids content of black liquor can be increased by evaporation to increase the yield of crude tall oil soap to the highest possible.

Tall oil can be produced from crude tall oil soap by acidification, which traditionally utilizes sulfuric acid as a acidulation agent. After sulfuric acid treatment, the tall oil can be separated from the brine containing water phase in a settling tank after which tall oil can be fractionated by distillation into different products. Inks, adhesives, coatings and lubricants can be produced from tall oil among others.

Sulfur release of forest industry to environment is frequently discussed nowadays in public due to the increased environmental awareness. Acidulation of tall oil is a process, in which sulfur is added to the chemical recycle of the factory, and therefore sulfuric acid use for the acidulation increases the loading of sulfuric compounds in the mill and in the environment. There is a great need to find new alternative

solutions and techniques to reduce the amount of sulfur in the acidulation process of tall oil soap.

U. S. Patent No. 3,901, 869 discloses a process, in which crude tall oil soap is partly acidified by carbon dioxide. Tall oil soap is first acidified with carbon dioxide to a pH of 7-8. Atmospheric or higher pressure is applied in the process. The reaction mixture is allowed to settle whereupon the formed tall oil separates from the aqueous phase, and tall oil can be collected. In order to improve the conversion sulfuric acid is added to reach a pH of 3-4.

In WO 95/23838 (Metsa-Botnia Ab et al. ) a method is presented to separate water and tall oil soap in two stages. First pressurized carbon dioxide is applied, and after that pH is reduced close to neutral with sulfuric acid at ambient pressure. The neutralization phase is followed by a water separation phase U. S. Patent 4,495, 095 (Union Camp) discloses a process for acidification of tall oil soap, in which carbon dioxide at supercritical stage is used to first acidify tall oil soap and after this the formed acid fractions are extracted from the reaction mixture with carbon dioxide. According to the claims, the temperature can range from 31 to 400 °C, and pressure from 73 to 3400 bar. The drawback of the claimed process is the low solubility of the formed resin and fatty acids in supercritical carbon dioxide, due to which the amount of carbon dioxide necessary to accomplish the extraction operation is very large compared to the amount of soap.

The idea of using a water insoluble hydrocarbon additive in the acidification by <BR> <BR> carbon dioxide is presented in U. S. Patent 4,075, 188 (Westvaco Corp. ). In the patented method tall oil soap is mixed with carbon dioxide and a hydrocarbon solvent to adjust the pH to 7-8. Sulfuric acid is used to complete the acidification of the soap.

According to the U. S. Patent 5,286, 845 (Union Camp) the aqueous tall oil soap is allowed to contact pressurized carbon dioxide at pressures from 3 to 54 bar, after which the reaction mixture is allowed to settle at the same pressure to separate the tall oil phase and the brine containing aqueous phase from each other. The tall oil phase can be separated from the aqueous phase by simply letting the mixture to settle after which the tall oil phase can be separated. The reaction times presented in examples are 60 tol80 minutes and settling times range from 15 minutes to as long as 3 days. According to the example tests the sulfuric acid consumption could be reduced as much as 55 to 82% when pure carbon dioxide was applied. It is possible to use a hydrocarbon solvent as a additive solvent to increase the yield of tall oil compared to systems with pure carbon dioxide. In case of nafta as an additive solvent, a 94% reduction of the theoretical amount of sulfuric acid needed in acidification was measured. According to the text it is obvious for the person skilled in the art that the separation may be carried out using conventional means, such as gravity separation, centrifugation, coalescation etc.

U. S. Patents 5,898, 065 and 5,891, 990 describe a method according to which aqueous tall oil soap can be neutralized partly with carbon dioxide, further to acidify the soap by adding sulfuric acid, separate brine containing aqueous phase from soap and cook the residual soap with sulfuric acid to get tall oil. In addition to carbon dioxide and sulfuric acid other acidulation agents can be applied, such as bisulphite, sulfur dioxide, hydrochloric acid, nitric acid or an organic acid. In the state of the art processes reaction and separation of phases occur after each other, not simultaneously. First there is the reaction, after which the reaction mixture is allowed to settle to separate tall oil phases and aqueous phases, and finally tall oil phase can be separated from the aqueous phase e. g. by decanting.

DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a process, where the reaction and the separation of the products occur simultaneously. By employing the foregoing process, higher conversion and shorter reaction time are obtained than by the state of

the art techniques. According to this invention no separate fractionating stage is needed and high quality tall oil is straight obtained.

In order to achieve this, the process according to the present invention is characterized by the fact, that tall oil soap or mixed soap originating from coniferous and soft wood is acidulated by pure pressurized carbon dioxide so close to the complete conversion that hydrocarbon additive solvent or sulfuric acid is not any more needed. The high conversion is achieved by using one single apparatus, in which both the reaction and the separation of tall oil phase occur simultaneously.

We have discovered that the acidification reaction proceeds almost to completion if aqueous tall oil soap is allowed to contact pressurized carbon dioxide in a continuously operated apparatus. In said process occurs the acidulation reaction of tall oil soap which produces an aqueous brine containing phase and a tall oil phase.

Simultaneously while the acidification reaction proceeds, the formed tall oil phase is separated from the aqueous brine containing phase. In order to be able to carry out both operations simultaneously, an apparatus based on centrifugal force is used, which operates simultaneously as a reactor and a separator.

In processes according to the state of the art, the reaction and the separation of phases follow each other in time. First occurs the reaction and after which the reaction mixture is allowed to settle to separate the tall oil phase and the aqueous phase from each other after which, the tall oil phase can be removed from the top of the mixture by e. g. decanting. In those state of the art methods and techniques processes, the benefits of, the process as defined in Claim 1 are not reached and the time required for the reaction and separation is longer than in this invented process. Further, the conversion is generally lower than in this invented process.

Thus, in accordance with the subject invention, several benefits are obtained.

Abandoning the use of sulfuric acid remarkably improves the sulfur balance in the factory, and reduces the health hazards related to sulfur release. In addition, the

formation of sulfur containing gases like mercaptanes, which are possibly forming during sulfur acidification are avoided, and thus no possible washing systems are needed.. Carbon dioxide is an environmentally benign solvent,. and thus the introduction of this process promotes establishment of"green image". A third advantage is that recycling of sodium in the factory strengthens. Carbon dioxide reacts in the acidification forming sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3), which breaks down to sodium carbonate, water, and carbon dioxide by heating. Sodium carbonate reacts with calcium oxide (CaO) producing sodium hydroxide (NaOH) according to the well known process. In the presently dominating process, sodium hydroxide is electrolytically fabricated from sodium chloride salt and chlorine is simultaneously produced. As the demand for chlorine and sodium hydroxide is not balanced nowadays, there is a world wide increasing interest in applying the above mentioned method of obtaining sodium hydroxide.

DETAILED DESCRIPTION When carbon dioxide reacts with tall oil soap following reaction occurs first 2 R-COONa + C02 + H20---) 2 R-COOH + Na2CO3 (1) The equilibrium of this reaction is influenced by several factors, such as the pressure of carbon dioxide, reaction temperature, and the amount of water in the mixture.

According to the present invention, the equilibrium in equation (1) is moved to the right by removing from the reaction mixture the formed fatty and resin acids simultaneously while the reaction proceeds in order to reach almost complete conversion of the reaction. In the reaction according to the present invention, the separation of the formed phases takes place in a continuously, by centrifugal force operating apparatus while the reaction proceeds. The apparatus can be e. g. a centrifuge or a decanter operated in accordance with centrifugal principles, or other such equipment, preferably a centrifuge.

In the subject invention, aqueous tall oil soap and carbon dioxide are fed into a continuously operating apparatus, which operates according to the centrifugal principles. As aqueous tall oil soap and carbon dioxide react an emulsion is formed, which contains aqueous sodium salts and crude tall oil which are formed in the reaction. Centrifugal force is used to separate crude tall oil from the aqueous phase while it is formed in the reaction.

The pressure of carbon dioxide has an effect on the reaction conversion. Generally, increase of reaction pressure increases reaction conversion. At least a pressure of 10 bar is needed in order for the reaction to proceed considerably. On the other hand, there is an economical limit in applying pressures of several hundreds of bars due to the increased investment costs. In the present invention, the necessary carbon dioxide pressure is about 10-200 bar, preferably 50-100 bar.

In principle it is possible to affect on the reaction conversion also by changing the temperature. Decrease in temperature adds solubility of carbon dioxide to aqueous tall oil soap solution which means higher conversion.. On the other hand, high temperature lowers the viscosity of the mixture, which improves separation of the phases and reduces the solubility of sodium bicarbonate. As centrifugal force is utilized in phase saparation in the process according to the subject invention it is possible to apply higher temperature than what is generally reasonable in processes where separation of tall oil and water phases is obtained by letting the reaction mixture to settle. The reaction temperature is typically 50-130 °C, preferably 70-90 °C, even though other temperatures can be applied as well.

Water can be added to tall oil soap before it is allowed to contact carbon dioxide. It is generally known that the water/tall oil soap ratio is preferably 0.5-2, even though other water/tall oil soap ratios can be applied.

Carbon dioxide is environmentally benign, non-flammable, chemically stable, non- toxic, relatively inexpensive and non-corrosive. Even though there is a potential

danger of suffocation, carbon dioxide is considered to be a very safe chemical to employees. Carbon dioxide is a good acidification agent due to environmental reasons.

Pressurized carbon dioxide can be fluid or supercritical. The word supercritical refers to the physical state of a substance. Carbon dioxide is at supercritical state, when simultaneously temperature is over 31 °C and pressure is over 73.8 bar. A supercritical fluid exhibits both fluid and gaseous properties, such as fluid density and gaseous viscosity. Further, the value of diffusion coefficient is between gaseous and fluid properties.

In the following the present invention is further described by examples. Examples 1 and 2 describe a method, in which a batch type of reactor is used. Example 3 describes a method in accordance with the present invention, where the reaction proceeds continuously. Centrifuge is the reactor vessel. According to the results, a better conversion is obtained by the method according to the invention.

It is obvious to a person skilled in the art that the different embodiments of the invention are not only limited to the presented examples but they can vary within the scope of the hereinafter mentioned claims.

EXAMPLES 1. Acidification of tall oil soap in carbon dioxide in a batch system.

1502 g of tall oil soap and 1575 g of water were weighed into a batch type reaction or which volume was 5 litres. The reactor was sealed and the reaction mixture was heated to 75 °C. The reactor was pressurized to 100 bar by pumping into it 2200 g of carbon dioxide after which the reaction mixture was mixed for 2 hours with a speed rotation of 750 rpm. The mixer was turned off and it was allowed to settle for about 4 hours. Samples were taken both from the oil phase and from the water phase. The acid number of the collected tall oil was 131, and the soap number was 28. The yield of tall oil was 79% of the theoretical maximum yield.

2. Acidification of tall oil soap with carbon dioxide in a batch system.

Further experiments were carried out by varying the parameter values presented below. The results are seen in Table 1. No. Reaction Settling Water Pressure Temperature Acid number Yield time time content (bar) (°C) (mg KOH/g) (%) (min) (min) (wt%) 100 240 50 100 53 113 64 2 100 200 50 180 136 133 80 3 60 200 40 20 75 94 42 4 20 15 50 178 132 72 23 Table 1. Acidification of tall oil soap with carbon dioxide 3. Acidification of tall oil soap with carbon dioxide in a centrifuge functioning as a reactor 400 kg/h of tall oil soap, which contained 60 wt-% water, was fed together with carbon dioxide (200 kg/h) into a continuously operated centrifuge. The centrifuge was designed to operate under high pressure by equipping it with a pressure resistant sheath. The diameter of the vertically placed centrifuge was 50 cm and it was equipped with 40 blades.. Both the aqueous tall oil soap and carbon dioxide were fed through the central axis of the centrifuge into 80 bar pressure, and the temperature was 77 °C. It was observed that by a speed rotation of 4000 rpm and at a temperature of 77 °C the phases separated from each other so that samples could be taken from the foaming tall oil phase and aqueous phase. The acid number of the tall oil was 153, soap number was 7, and density was 0.957. The mother liquid contained 1. 1 wt % tall oil. It's density was 1.092, and pH 8.82. The yield of tall oil was 93% of the theoretical maximum yield.