Manufacture of cellulose esters: recycle of caustic and/or acid from pre-treatment of pulp
A process for the manufacture of cellulose esters is described. The process includes the steps of: pre-treating pulp for the removal of impurities with either caustic or acid or both, esterifying the pre-treated pulp, and recycling the caustic or acid or both from the pre-treating step.
1 . In a process for the manufacture of cellulose esters wherein the process comprising the steps of pre-treating pulp for the removal of impurities with either caustic or acid or both and esterifying the pretreated pulp, the improvement comprising the steps of:
recycling the caustic or acid or both from a stream from the pre-treating step.
2 . The process of claim 1 wherein recycling caustic further comprising:
filtering the caustic stream from the pre-treating step; and
recovering caustic to form a filter concentrate.
3 . The process of claim 1 wherein recycling further comprises the steps of:
filtering impurities from the caustic stream from the pre-treating step, and
forming a filtrate for return to the pre-treating of pulp and a concentrate.
4 . The process of claim 3 wherein filtering comprises the step of:
nano-filtering impurities from the caustic stream.
5 . The process of claim 3 wherein filtering comprises the steps of:
pre-filtering particles having a predetermined size from the caustic stream,
nano-filtering impurities from the pre-filtered caustic stream, and
returning the filtrate from the nano-filtering to pre-treating the pulp.
6 . The process of claim 5 wherein the predetermined size being selected from the group consisting of a particle size of >5 microns.
7 . The process of claim 3 further comprising the step of:
precipitating impurities from the concentrate with a precipitating agent and forming precipitated impurities and a mixture of precipitating agent and caustic.
8 . The process of claim 7 wherein the precipitating agent being selected from the group consisting of alcohol, ketone, and mixtures thereof.
9 . The process of claim 8 wherein the alcohol being selected from the group consisting of alcohols containing 1 to 4 carbons.
10 . The process of claim 8 wherein the ketone being acetone.
11 . The process of claim 7 further comprising the step of:
separating precipitated impurities from the mixture of precipitating agent and caustic.
12 . The process of claim 7 further comprising the step of:
separating the precipitating agent from the mixture of precipitating agent and caustic and forming a precipitating agent stream and a caustic stream.
13 . The process of claim 12 wherein separating being distilling.
14 . The process of claim 12 further comprising the step of:.
removing impurities from the caustic stream prior to returning the caustic to the pre-treating of the pulp.
15 . The process of claim 14 wherein removing being selected from the group consisting of extracting and adsorbing.
16 . The process of claim 1 wherein recycling further comprising the steps of:
distilling the acid from the pre-treating step.
17 . The process of claim 1 wherein recycling further comprising the steps of:
filtering the acid from the pre-treating step and forming a filtrate stream and a concentrate stream;
separating acid from the filtrate stream; and
separating acid from the concentrate stream.
18 . The process of claim 1 wherein recycling further comprises the steps of:
filtering impurities from the acid stream from the pre-treating step, and
forming a filtrate and a concentrate.
19 . The process of claim 18 wherein filtering comprises the step of:
nano-filtering impurities from the acid stream.
20 . The process of claim 18 wherein filtering comprises the steps of:
pre-filtering particles having a predetermined size from the acid stream, and
nano-filtering impurities from the pre-filtered acid.
21 . The process of claim 20 wherein the predetermined size being selected from the group consisting of a particle size of >5 microns.
22 . The process of claim 18 wherein recycling further comprises extracting acid from the filtrate.
23 . The process of claim 22 wherein extracting further comprising contacting the acid stream with a solvent.
24 . The process of claim 23 wherein the solvent being selected from the group consisting of benzene, diethyl ether, diisobutyl ketone, ethyl acetate, methyl amyl ketone, methyl ethyl ketone, methyl t-butyl ether (MTBE), C-6 hydrocarbons, isopropyl acetate, isobutyl acetate, isopropyl ether, and mixtures thereof.
25 . The process of claim 23 further comprising separating acid from an acid/solvent stream.
26 . The process of claim 18 wherein recycling further comprises extracting acid from the concentrate.
27 . The process of claim 26 wherein extracting further comprising contacting the acid stream with a solvent.
28 . The process of claim 27 wherein the solvent being selected from the group consisting of hexane, pentane, heptane, and mixtures thereof.
29 . The process of claim 16 further comprising the step of removing any residual impurities.
30 . The process of claim 29 wherein said impurities being organic solvent extractives.