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PROCESS FOR PREPARING ALKYL HYDROXYALKYL CELLULOSE

IP.com Disclosure Number: IPCOM000032612D
Publication Date: 2004-Nov-09
Document File: 4 page(s) / 44K

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Abstract

Alkyl hydroxyalkyl celluloses with greater gel strength at a given viscosity or with a lower viscosity at a given gel strength can be produced in a process which comprises the steps of: (A) reacting a cellulose pulp with a first amount of aqueous alkali metal hydroxide, a first amount of an alkylating agent and a hydroxyalkylating agent at reaction conditions sufficient to alkylate the cellulose pulp to a first level of alkyl substitution which is about 20 percent or more of the desired level of alkyl substitution and to hydroxyalkylate the cellulose pulp; and (B) reacting the produced alkyl hydroxyalkyl cellulose of first level of alkyl substitution with a second amount of aqueous alkaline hydroxide and a second amount of an alkylating agent at reaction conditions sufficient to alkylate it to a second level of alkyl substitution which is about 40 percent or more of the desired level of alkyl substitution.

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PROCESS FOR PREPARING ALKYL HYDROXYALKYL CELLULOSE

Alkyl hydroxyalkyl celluloses, such as hydroxyethyl methyl cellulose (HEMC) and hydroxpropyl methyl cellulose (HPMC) are commercially available. The process described below allows the production of alkyl hydroxyalkyl celluloses with greater gel strength at a given viscosity or with a lower viscosity at a given gel strength.  They are particularly useful in food compositions and pharmaceutical capsules.

Alkyl hydroxyalkyl celluloses having viscosities of up to about 1,000,000 centipoise (cP), preferably of about 1 to about 600,000 cP, more preferably of about 1 to about 100,000 cP in a two percent aqueous solution at 20°C can be prepared according to the described process.  All viscosities of aqueous solutions are determined by Ubbelohde tube according to ASTM D1347-72 and D2363-79.

Preferred alkyl hydroxyalkyl celluloses that can be produced according to the process described below include, but are not limited to, hydroxyethyl methyl cellulose (“HEMC”), hydroxypropyl methyl cellulose (“HPMC”) and hydroxybutyl methyl cellulose (“HBMC”).  Preferred HPMC’s have a hydroxypropyl substitution of from about 1 to about 32 percent, more preferably from about 1 to about 14 percent, and most preferably from about 3 to about 12 percent; and a methoxyl substitution of from about 15 to about 40 percent, more preferably from about 18 to about 35 percent, and most preferably from about 19 to about 24 percent or from about 27 to about 30 percent.  The alkyl and hydroxyalkyl substitutions of the cellulose ethers are measured and calculated according to ASTM D3876. 

The process comprises the stages of: 

A)                reacting a cellulose pulp with a first amount of aqueous alkali metal hydroxide, a first amount of an alkylating agent and with a hydroxyalkylating agent at reaction conditions sufficient to alkylate the cellulose pulp to a first level of alkyl substitution which is 5 to 40% percent or more of the desired level of alkyl substitution and to hydroxyalkylate the cellulose pulp; and

B)                 reacting the produced alkyl hydroxyalkyl cellulose of first level of alkyl substitution with a second amount of aqueous alkaline hydroxide and a second amount of an alkylating agent at reaction conditions sufficient to alkylate it to a second level of alkyl substitution which is 60 to 95 percent of the desired level of alkyl substitution.

The cellulose utilized in stage A) is typically cellulose pulp obtained from wood or cotton.  The pulp is preferably fed in a powder or chip form in an alkalization and alkylation reactor.  If desired, the headspace of the reactor or reactors may be evacuated or purged with an inert gas such as nitrogen to control oxygen-catalyzed depolymerization of the alkyl hydroxyalkyl cellulose product.  Cellulose pulp is partially alkalized with an alkali metal hydroxide, such as aqueous sodium hydroxide, and partially alkylated with an alkylating agent in a first stage.  The pulp ma...