Chemistry: natural resins or derivatives; peptides or proteins; – Natural resins or derivatives – Recovery of tall oil or derivatives from papermaking waste,...
Reexamination Certificate
1999-10-21
2001-01-09
Acquah, Samuel A. (Department: 1711)
Chemistry: natural resins or derivatives; peptides or proteins;
Natural resins or derivatives
Recovery of tall oil or derivatives from papermaking waste,...
C530S205000, C530S208000, C530S230000, C526S062000
Reexamination Certificate
active
06172183
ABSTRACT:
The present invention relates to a process and apparatus for the cleaning of crude tall oil soap. According to the invention, the crude soap is cleaned prior to a final separation of crude soap and black liquor. After separation of the cleaned crude soap from the black liquor, the soap may be treated in a conventional manner to free the tall oil.
Tall oil is composed mainly of resin acids and fatty acids. Tall oil is recovered from black liquor which is formed primarily in the kraft pulping process. In the pulping process the digesting liquors are removed from the fibers and washed with water. Black liquor is removed at the early stages of the washing, Most of the tall oil is removed as soap with the black liquor and it gradually rises to the surface of the black liquor in the form of crude tall oil soaps. In order to improve the recovery of the crude soap, the liquor may be subjected to evaporation to increase its solids content. The crude soap is skimmed in one or several stages from the main portion of the black liquor. The skimmed crude soap is traditionally acidified with sulfuric acid, separated from the aqueous phase and fractionated to provide desired end products.
The acidification of tall oil soap with sulfuric acid brings additional sulfur into the pulp mill and increases the loading of sulfurous compounds in the mill. Impurities contained in the soap add to the amount of acid needed for proper acidification. Since environmental considerations are making it increasingly unacceptable to discharge sulfurous pollutants into the environment and since tall oil acidification is one of the processes of the pulp mill which include addition of sulfuric compounds, there is a great need in the art for a process providing a reduction of the amount of sulfuric acid required in the treatment of the crude soap and in the production of tall oil.
U.S. Pat. No. 3,901,869 discloses a process for acidifying skimmed crude tall oil soap, wherein a part of the traditional sulfuric acid is replaced by carbon dioxide. The soap is mixed with water, acidified to a pH of about 7 to 8 with carbon dioxide at atmospheric pressure or higher pressures. The reaction mixture is then removed and allowed to settle at ambient pressure, whereafter the soap layer is separated from the sodium bicarbonate brine layer. The soap fraction is then further acidified in the conventional way with sulfuric acid to pH 3 to 4 to provide crude tall oil.
According to WO 95/23837 (Oy Mets{umlaut over (a)}-Botnia Ab et al.) the prior art problem caused by poor separation of water from the soap is solved by neutralizing skimmed crude soap in two stages, first with pressurized carbon dioxide and then with sulfuric acid at ambient pressure to provide a pH close to neutral. The neutralization stage is followed by a water separation stage and a traditional “cook” with sulfuric acid.
U.S. Pat. No. 4,495,095 (Union Camp) describes a process for the acidulation and extraction of skimmed crude tall oil soaps with fluid carbon dioxide in a supercritical state. U.S. Pat. No. 5,286,845 (Union Camp) describes a process for acidulation of skimmed soap with pressurized carbon dioxide. The reaction is allowed to proceed for a few hours with vigorous mixing. The resulting crude tall oil and sodium bicarbonate brine are then allowed to separate, also under pressure. Proper settling of the layers may take up to three days.
Uloth, C. V. et al. in Pulp and Paper Canada 85:5 (1984), p 69-71, report that the separation rate of acidulated tall oil soap in a tall oil recovery system may be accelerated by adding phase separation aids such as lignosulphonates or spent sulfite liquor to the tall oil phase separation stage.
The prior art processes have concentrated on improving the treatment of the crude soap after its final separation from the black liquor, i.e. at a point where no more black liquor will be recovered as black liquor. The prior art processes have especially been directed at decreasing the amount of sulfuric acid needed to acidify the separated crude soap and to improve the separation of the aqueous phase from the acidified soap or tall oil phase. However, none of the above mentioned prior art processes have aimed at improving the separation of the crude soap from black liquor at the stage when the soap is still in contact with the black liquor.
An object of the present invention is to provide an improvement in the production of tall oil.
Another object of the invention is to reduce the amount of sulfurous compounds required in the production of tall oil.
A specific object of the invention is to improve the separation of crude tall oil soap from black liquor in the recovery of tall oil soap.
An object of the invention is also to provide an apparatus for cleaning crude tall oil soap in a tall oil recovery system. The present invention is based on the discovery that crude tall oil soap which is still in contact with significant amounts of black liquor may be cleaned with carbon dioxide. This cleaning process is performed at an earlier stage in the tall oil recovery system than the prior art processes. The soap is cleaned prior to the final separation of black liquor and soap, said final separation being defined as the stage at which the last portions of black liquor are removed from the soap as black liquor. The process according to the invention cleans the crude soap from impurities which otherwise would go with the soap fraction. Hence the cleaning reduces the amount of acid needed to acidify the soap. It also facilitates the separation of soap from black liquor and speeds up the separation process.
The characteristics of the present invention are defined in the appended claims.
Thus, the present invention relates to a process for the cleaning of crude tall oil soap prior to a final separation of said crude soap and black liquor, comprising cleaning crude tall oil soap floating on top of a layer of black liquor or a mixture of crude tall oil soap and black liquor with carbon dioxide, and subsequently discharging the black liquor separately from the soap.
The carbon dioxide cleaning according to the invention is performed prior to, i.e. upstream of any actual neutralization or acidulation of the tall oil soap. The cleaning causes a greater portion of non-tall oil components, i.e. soap impurities to separate from the soap fraction and to move into the black liquor fraction. Said components, will be removed with the black liquor in the subsequent black liquor discharging step.
The carbon dioxide for the cleaning step according to the present invention is preferably in the form of CO
2
gas at atmospheric pressure or a higher pressure. According to a preferred embodiment of the present invention, carbon dioxide is provided by feeding a fluid capable of liberating carbon dioxide into said soap or black liquor or said mixture thereof. Such a carbon dioxide liberating fluid may comprise bicarbonate brine or a mixture of bicarbonate brine and soap containing dissolved carbon dioxide.
An embodiment of the invention comprises feeding an aqueous mixture containing an excess of carbon dioxide in a mixture of bicarbonate and tall oil soap into the crude soap layer for liberating carbon dioxide in said soap layer. A suitable source of bicarbonate is sodium bicarbonate brine recirculated from a downstream step of the process. Such a step may comprise a reaction of carbon dioxide with separated cleaned soap.
Said reaction may be a conventional carbon dioxide neutralization or acidulation step subsequent to, i.e. downstream of the cleaning step. In a preferred embodiment of the invention a portion of the cleaned soap, which has been separated from the black liquor, is brought into contact with carbon dioxide and is thereafter recirculated to said cleaning stage as said carbon dioxide liberating fluid. Said fluid preferably contains an excess of carbon dioxide gas which will be liberated into the soap which is to be cleaned. Water and/or a phase separation aid may be added to the reaction mixture.
The present invention also relates to an apparatus su
Acquah Samuel A.
AGA Aktiebolag
Browdy and Neimark
LandOfFree
Process and apparatus for the cleaning of crude tall oil soap does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and apparatus for the cleaning of crude tall oil soap, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and apparatus for the cleaning of crude tall oil soap will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2508548