Pressure pretreatment for improving the acetylation of cellulose

Claim 2

A process for producing cellulose diacetate from a pulp comprising the steps of: a) pretreating and activating fluffed cellulose fibres (10 parts by wt.) in a pretreatment solution of glacial acetic acid (80-200 parts by wt.) and acetic anhydride (3.5-10 parts by wt.) at a pretreatment temperature of 15° C. to 40° C. and a pretreatment pressure of 2 to 150 psig for 15 to 90 minutes to form activated cellulose: b) mixing the activated cellulose containing acetic acid and anhydride further with an acetylation solution, the acetylation solution a mixture of glacial acetic acid (0-35 parts by wt.), acetic anhydride (14-30 parts by wt.) and sulphuric acid catalyst (0.3-1.0 parts by wt.), and acetylating the cellulose at an initial acetylation temperature of 10° C. to 28° C. and an end acetylation temperature of 35° C. to 60° C. to yield primary cellulose acetate; and c) partially neutralizing the sulphuric acid catalyst to a residual range of 0.1 to 5 parts by wt. and destroying the residual acetic anhydride by adding an aqueous solution of a neutralizing salt with dilute (50% to 70% by wt.) acetic acid to provide excess water (20 to 50 parts by wt.) in the reaction dope for hydrolysis to occur at a hydrolysis temperature of 50° C. to 100° C. and a hydrolysis pressure of 50 to 150 psig.

Claim 3

The process according to claim 1 in which the cellulose fibres may be softwood or hardwood or annual plant materials, high or low viscosity and high or low α-cellulose content, chemical pulp.

Claim 4

The process according to claim 1 in which the pulp is made by either a sulphite or a sulphate process.

Claim 5

The process according to claim 1 in which the α-cellulose content of the pulp is between 88% to 98%.

Claim 6

The process according to claim 1 in which the viscosity of the pulp is between 8 mPa.s to 30 mPa.s.

Claim 7

The process according to claim 1 in which the pretreatment time is 30 to 45 minutes.

Claim 8

The process according to claim 1 in which the pretreatment pressure is 70 psig to 100 psig.

Claim 9

The process according to claim 1 in which the pretreatment temperature is 18° C. to 40° C.

Claim 10

The process according to claim 1 in which a pretreatment pressuring gas is selected from nitrogen, helium, carbon dioxide and combinations thereof.

Claim 11

The process according to claim 1 in which the initial acetylation temperature is 16° C. to 24° C.

Claim 12

The process according to claim 10 in which the end acetylation temperature is 45° C. to 55° C.

Claim 13

The process according to claim 1 in which the hydrolysis reaction temperature is effected between 75° C. to 100° C.

Claim 14

The process according to claim 1 in which the hydrolysis pressure is maintained between 90 to 120 psig.

Claim 15

The process according to claim 1 in which the excess water for hydrolysis is controlled effectively between 20% and 30% water in the reaction mixture.

Claim 16

The process according to claim 1 in which the hydrolysis pressuring gas over the reaction mixture of hydrolysis is selected from nitrogen, helium and combinations thereof.

Claim 17

The process according to claim 1 in which the residual sulphuric acid is maintained between 3% and 4.5% based on the dry weight of cellulose pulp.

Claim 18

The process according to claim 1 where the neutralizing salt is magnesium acetate.

Claim 19

The process according to claim 1 in which the pretreatment solution consists of glacial acetic acid (160-180 parts by wt.) and acetic anhydride (9-10 parts by wt.).

Claim 20

The process according to claim 1 in which the activated cellulose and pretreatment solution directly mix with an acetylation solution of glacial acetic acid (30-35 parts by wt.), acetic anhydride (20 parts by wt.) and sulphuric acid (0.85 parts by wt.) at an initial acetylation temperature of 16° C. to 24° C.

Claim 21

A process for producing cellulose diacetate from a pulp comprising the steps of: a) pretreating and activating fluffed cellulose fibres (10 parts by wt.) in a pretreatment solution of glacial acetic acid (160-180 parts by wt.) and acetic anhydride (9-10 parts by wt.) at a pretreatment temperature of 18° C. to 40° C. and a pretreatment pressure of 70 to 100 psig for 30 to 45 minutes to form activated cellulose; b) mixing the activated cellulose containing acetic acid and an-hydride further with an acetylation solution, the acetylation solution a mixture of glacial acetic acid (0-35 parts by wt.), acetic anhydride (14-30 parts by wt.) and sulphuric acid catalyst (0.3-1.0 parts by wt.), and acetylating the cellulose at an initial acetylation temperature of 10° C. to 28° C. and an end acetylation temperature of 35° C. to 60° C. to yield primary cellulose acetate; and c) partially neutralizing the sulphuric acid catalyst to a residual range of 0.1% to 5.0% parts by wt. and destroying the residual acetic anhydride by adding an aqueous solution of a neutralizing salt (50% by wt.) with dilute (50% to 70% by wt.) acetic acid to provide excess water (20 to 50 parts by wt.) in the reaction dope for hydrolysis to occur at a hydrolysis temperature of 50° C. to 100° C. and a hydrolysis pressure of 50 to 150 psig.

Claim 22

A process for producing cellulose diacetate from a pulp comprising the steps of: a) pretreating and activating fluffed cellulose fibres (10 parts by wt.) in a pretreatment solution of glacial acetic acid (160-180 parts by wt.) and acetic anhydride (9-10 parts by wt.) at a pretreatment temperature of 18° C. to 40° C. and a pretreatment pressure of 70 to 100 psig for 30 to 45 minutes to form activated cellulose; b) mixing the activated cellulose containing acetic acid and an-hydride further with an acetylation solution, the acetylation solution a mixture of glacial acetic acid (0-35 parts by wt.), acetic anhydride (14-30 parts by wt.) and sulphuric acid catalyst (0.3-1.0 parts by wt.), and acetylating the cellulose at an initial acetylation temperature of 10° C. to 28° C. and an end acetylation temperature of 35° C. to 60° C. to yield primary cellulose acetate; and c) partially neutralizing the sulphuric acid catalyst to a residual range of 0.1% to 5.0% parts by wt. and destroying the residual acetic anhydride by adding an aqueous solution of a neutralizing salt (50% by wt.) with dilute (50% to 70% by wt.) acetic acid to provide excess water (20 to 50 parts by wt.) in the reaction dope for hydrolysis to occur at a hydrolysis temperature of 50° C. to 100° C. and a hydrolysis pressure of 50 to 150 psig.

Claim 23

A process for the pretreatment of cellulose fibres to form activated cellulose comprising mixing fluffed cellulose fibres in a pretreatment solution of glacial acetic acid and acetic anhydride at a pretreatment temperature of 15° C. to 40° C. and a pretreatment pressure of 2 to 150 psig.

Claim 24

A process for the pretreatment of cellulose fibres to form activated cellulose comprising mixing fluffed cellulose fibres in a pretreatment solution of glacial acetic acid and acetic anhydride at a pretreatment temperature of 15° C. to 40° C. and a pretreatment pressure of 2 to 150 psig.