Title of Invention

"AN IMPROVED PROCESS FOR THE REMOVAL OF COLOUR AND SUGAR FROM BLACK LIQUOR

Abstract

An improved process for the removal of colour and sugar from black liquor The invention relates to an improved process for the removal of colour and sugar from black liquor A process to obtain significant reduction in colour and sugar of black liquor generated in pulp and paper industry using commercially available membrane, salt in single step operation was developed. By passing effectively diluted black liquor through selective membrane obtained permeate having 90% reduction in colour and retentate having 80% reduction in sugar. Whereas by the addition of ammonium sulphate the supernatant obtained with 95% colour reduction and precipitate with 90% sugar reduction. The passing of black liquor with salt through 100000 molecular weight cutoff membrane obtained permeate with 91% colour reduction. As the ammonium sulphate is used, the precipitate can be used as fertilizer. The retentate may be directly used for the lignin based byproduct.

Full Text

The present invention relates to an improved process for the removal of color and sugar from black liquor. More particularly it relates to the process to obtain significant reduction in colour and sugar of black liquor generated in pulp and paper industry using commercially available membrane, salt in single step operation. This finds application in effluent treatment of pulp and paper industry as well as in the production of lignin related byproducts such as lignosulphonates, lignin derivatives, fertilizer etc. Production of paper comprises different operations such as wood chipping, cooking of the chips (the kraft sulfite process) to extract cellulose and hemicellulose (and to discard the lignin components), and bleaching to produce white pulp and/or paper. The bleaching of pulp requires the treatment of strong oxidants such as chlorine or chlorine dioxide which react with the lignin to make it water soluble. These components when mixed with the residual sulfite liquor from the pulping operation produce a black, chemically undefined liquid known as 'black liquor'. Which contain lignin, sugars, aromatics, ethers and other organic compounds including chlorocarbons etc. In the past, the reason to remove colour from wastewater was entirely aesthetic. However, now it is necessary that the downstream wastewater should be treated for colour removal prior to discharge into public waterways. Secondly, colour difference is easy to measure and colour reduction is indicative of the decrease of BOD, COD, and other contaminants. The conventional effluent treatment can not remove the black colour. The colour removal from the effluent streams of pulp and paper industry continues to be a major problem. Another aspect, the presence of sugar significantly hampered the marketability of lignosulphonate produced as byproducts form black liquor. Therefore, there is a need to develop a process, which will remove colour as well as sugar from the black liquor. So far developed processes are based on multistep operations and no process is available which claimed the significant removal of colour and sugar form black liquor in single step operation. Different processes have been developed which proposed to remove colour from pulp and paper industry wastewater. The process of adsorption/absorption on activated charcoal, polymer was developed to remove colour ( Sarkar et al; U.S. Pat. No. 5,326,479: 1994). Another process includes contacting the wastewater with a cationic flocculent followed by adsorbing the residual colour with activated carbon and, after exhaustion, regenerating the carbon by pyrolysis (Zeff et al;U.S. Pat. No. 4,851,128: 1989). Other adsorption and absorption processes utilize macroreticular weak anion resin (Rock; U.S. Pat. No. 4,049,546: 1977); an activated resin (Pilon; U.S. Pat. No. 4,259,149: 1981); a macroporous resin (Newman et al; U.S. Pat. No. 4,895,662: 1990); and by absorption into barium sulfate during precipitation (Foster; U.S. Pat. No. 3,945,917: 1976). The process of chemical oxidation using either potassium permanganate, oxygen, ozone or hydrogen peroxide to remove colour are also available (Braasch et al; U.S. Pat. 5,529,697: 1996 and Weibel; U.S. Pat. 5,190,669:1993). Currently also similar methodologies are being followed for the removal of colour from black liquor such as use of metal ions for precipitation (Sundin and Nord., Pulp Pap. Res. J., 15(4), 306-312, 2000); use of flocculant (Swamy, et al., IPPTA, 12(2), 53-60 2000); use of 20% H2SO4 for precipitation (Zhang, Jian'an et al., CN 1272461 2000, Chinese Patent); use of coagulating agent (Faming et al; CN 1262234: 2000 Chinese Patent). Use of membranes is also reported in the treatment of black liquor however, their role in the removal of colour and sugar is not specified. The methodologies such as reverse osmosis, ultrafiltration, electrodialysis etc have been used to remove organic and inorganic material form black liquor and studies of their optimization are reported (Satyanarayana et al., Separation Purification Technology 20, 155-167, 2000)."Literature survey indicates one membrane based patent where ultracentrifugation, electrodialysis, acid precipitation used to remove lowmolecuiar weight aliphatic, aromatic compounds and lignin from black liquor ( Bowe; U.S. Pat. No. 725,720: 1985). Overall, the processes developed so far suffer the disadvantage of requiring large quantities of expensive chemicals, pH adjustment, use of corrosive materials, based on multistep operations etc. Although, many different processes have been proposed or experimented however, none has yet proven to provide an effective and practicable solution to the problem of colour and sugar removal form black liquor. The present invention overcomes the problems of the prior art by providing a process, which claims the significant reduction in colour and sugar of black liquor in a single step operation. There is no need to use expensive chemicals, no adjustment of pH, and no use of corrosive materials, easy handling and monitoring. The object of the present invention is to provide a process to obtain significant reduction in colour and sugar of black liquor generated in pulp and paper industry using commercially available membrane, salt in a single step operation. Accordingly the present invention provides an improved process for the removal of colour and sugar from black liquor which comprises, passing diluted black liquor through membrane at a pressure of 0.5 bar to obtain a permeate having 90% colour reduction and retentate having 80% sugar reduction, adding salt to form supernatant having 95% reduction in colour and precipitate having 90% reduction in sugar. In one of the embodiment of the present invention, the dilution of black liquor may be 10 to 50%, preferably 10%. In another embodiment of the present invention, the membrane may be any commercially available having molecular weight cutoff 5000 to 100000 preferably 5000, 10000. In another embodiment of the present invention, the salt may be any water structuring salt containing cations Rb +, K +, Na+, Cs+, Li+, Mg+, Ca2+, Ba2+,preferably NH4 + as ammonium sulphate. In still another embodiment of the present invention, the concentration of salt may be 5 to 40%, preferably 40%. In a feature of the present invention, the concentrated black liquor (spent sulphite liquor) was obtained from pulp and paper producing industry. The diluted black liquor was used as a starting material and termed as Teed'. The commercially available membranes with different molecular weight cutoff (MWCO) were used. The material passed through the membrane was termed as 'permeate' and retained by the membrane termed as 'retentate'. The reduction of colour was calculated by considering the optical density obtained for feed at 540 nm as 100%.The concentration of sugar was estimated using dinitrosalicylic acid reagent (Miller, Anal. Chem. 31, 420-428, 1959). The reduction of sugar was calculated by considering the concentration of sugar obtained for feed as 100%. In the experiments where salt was used, the reduction of colour and sugar was calculated considering the values obtained for feed contain same concentration of salt as 100%. In another feature, the feed was passed through the membrane using flatsheet module. The different samples were collected as feed, permeate, retentate and estimation of sugar, colour was carried out. In another feature, the different concentration of commercially available ammonium sulfate was added in the feed and the supernatant was collected by centrifugation. The samples such as feed, supernatant and precipitate were collected and the reduction of colour and sugar estimated. In another feature, the fixed concentration of commercially available ammonium sulfate was added in the feed and the supernatant was collected by centrifugation, filtration, and decantation. The samples such as feed, supernatant and precipitate were collected and the reduction of colour and sugar estimated. In still another feature, the fixed concentration of commercially available ammonium sulfate was added in the feed and the supernatant was collected by filtration of feed throughlOOOOO MWCO membrane. The samples such as permeate was collected and the reduction of colour estimated. The process of the present invention is described by following examples, which are illustrative only and should not be construed to limit the scope of the present invention in any manner. Example 1: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The feed was passed through the different membranes using flat sheet module operated at 0.5 bar pressure. The samples such as feed, permeate was collected to estimate the colour. Highest colour and sugar reduction obtained from 5000 MWCO membrane (Table 1). Tablet: (Table Remove) Example 2: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The feed was passed through the 10000 MWCO membranes using flat sheet module operated at 0.5 bar pressure. The samples such as feed, permeate and retentate was collected. The permeate showed 92% reduction in colour. Example 3: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The different concentration of ammonium sulphate added to the feed. The precipitate and supernatant was collected by centrifugation and the reduction of colour and sugar estimated (Table 2). Table 2: (Table Remove)Example 4: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The ammonium sulphate was added as to make its concentration 40% in teed. The precipitate and supernatant was collected by centrifugation and the reduction of colour and sugar estimated. The supernatant showed 95% reduction in colour and precipitate showed 90% reduction in sugar. Example 5: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The ammonium sulphate was added as to make its concentration 40% in feed. The precipitate and supernatant was collected by filtration using filter paper and the reduction of colour and sugar estimated. The supernatant showed 95% reduction in colour and precipitate showed 87% reduction in sugar. Example 6: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The ammonium sulphate was added as to make its concentration 40% in feed and allow standing for one hour to settle the precipitate. The supernatant was collected with the help of pipette and the reduction of colour estimated. The supernatant showed 95% reduction in colour. Example 7: The concentrated black liquor was diluted with water as to make the 10% solution and used as feed. The ammonium sulphate was added as to make its concentration 40% in feed. Then the feed was passed through the 100000 MWCO membranes using flat sheet module operated at 0.5 bar pressure. The sample such as permeate was collected to estimate the colour. The permeate showed 91% reduction in colour. We claim: 1. An improved process for the removal of colour and sugar from black liquor which comprises, passing diluted black liquor through membrane at a pressure of 0.5 bar to obtain a permeate having 90% colour reduction and retentate having 80% sugar reduction, adding salt to form supernatant having 95% reduction in colour and precipitate having 90% reduction in sugar. 2. A process as claimed in claim 1, wherein the dilution of black liquor is 10 to 50%, preferably 10%. 3. A process as claimed in claim 1 to 2, wherein the membrane is any commercially available having molecular weight cutoff 5000 to 100000, preferably 5000 or 10000. 4. A process as claimed in claim 1 to 3, wherein the salt is any water structuring salt containing cations Rb +, K +, Na+ , Cs+ , Li+ , Mg+ , Ca2+, Ba2+, preferably NH4 + as ammonium sulphate. 5. A process as claimed in claim 1 to 4, wherein the concentration of salt is 5 to 40%, preferably 40%. 6. An improved process for the removal of colour and sugar from black liquor described herein before with reference to examples.

Documents:

218-DEL-2003-Abstract-(10-12-2008).pdf

218-del-2003-abstract.pdf

218-DEL-2003-Claims-(10-12-2008).pdf

218-DEL-2003-Claims-(12-01-2009).pdf

218-del-2003-claims.pdf

218-DEL-2003-Correspondence-Others-(10-12-2008).pdf

218-DEL-2003-Correspondence-Others-(12-01-2009).pdf

218-del-2003-correspondence-others.pdf

218-del-2003-correspondence-po.pdf

218-DEL-2003-Description (Complete)-(10-12-2008).pdf

218-DEL-2003-Description (Complete)-(12-01-2009).pdf

218-del-2003-description (complete).pdf

218-DEL-2003-Form-1-(12-01-2009).pdf

218-del-2003-form-1.pdf

218-DEL-2003-Form-18-(10-12-2008).pdf

218-del-2003-form-18.pdf

218-del-2003-form-2.pdf

218-DEL-2003-Form-3-(10-12-2008).pdf

218-del-2003-form-3.pdf