Molecular weight reduction of polysaccharides by electron beams

• US 20040072699A1
• Filed: 06/24/2003
• Published: 04/15/2004
• Est. Priority Date: 06/25/2002
• Status: Active Grant

• Current Assignee: Specialty Operations France
• Original Assignee: Rhodia Incorporated
• Inventors: Priou, Christian, Liu, Leo Zhaoqing
• Granted Patent: US 7,259,192 B2
• Time in Patent Office: Days
• US Class Current: 507/200
• CPC Class Codes: C08B 37/00 Preparation of polysaccharides not provided for in groups C08B1/00 - C08B35/00; Derivatives thereof cellulose D21; microbiological processes C12P
• CPC Class Codes: C08B 37/0033 Xanthan, i.e. D-glucose, D-mannose and D-glucuronic acid units, saubstituted with acetate and pyruvate, with a main chain of (beta-1,4)-D-glucose units; Derivatives thereof
• CPC Class Codes: C08B 37/0087 Glucomannans or galactomannans; Tara or tara gum, i.e. D-mannose and D-galactose units, e.g. from Cesalpinia spinosa; Tamarind gum, i.e. D-galactose, D-glucose and D-xylose units, e.g. from Tamarindus indica; Gum Arabic, i.e. L-arabinose, L-rhamnose, D-galactose and D-glucuronic acid units, e.g. from Acacia Senegal or Acacia Seyal; Derivatives thereof
• CPC Class Codes: C08B 37/0096 Guar, guar gum, guar flour, guaran, i.e. (beta-1,4) linked D-mannose units in the main chain branched with D-galactose units in (alpha-1,6), e.g. from Cyamopsis Tetragonolobus; Derivatives thereof
• CPC Class Codes: C09K 8/68 containing organic compounds
• CPC Class Codes: C09K 8/90 of natural origin, e.g. polysaccharides, cellulose

Abstract

A method of depolymerizing galactomannan-type polysaccharide polymers and xanthan, preferably galactomannans, to a pre-selected lower molecular weight by irradiation with high energy electron beams. The preferred galactomannans for treatment according to this method are guar gum, guar splits and hydroxypropyl guar. In a preferred embodiment the guar gum is depolymerized preferably to a molecular weight of about 150,000 Daltons to about 200,000 Daltons. The depolymerized guar has a polydispersity of less than about 3.0 and is useful in oil well fracturing to enhance oil production.

Claims

1. A method of depolymerizing polysaccharides selected from the group consisting of galactomannans, modified galactomannans and xanthan to a pre-selected molecular weight comprising the step of subjecting the polysaccharides to radiation consisting essentially of electron beams.

2. The method of claim 1, wherein the galactomannans are depolymerized to a molecular weight of less than about 700,000 Daltons.

3. The method of claim 1, wherein the galactomannans are depolymerized to a molecular weight of less than about 500,000 Daltons.

4. The method of claim 1, wherein the galactomannans are depolymerized to a molecular weight of less than about 300,000 Daltons.

5. The method of claim 3, wherein the galactomannans are depolymerized to a molecular weight of between about 100,000 Daltons and about 250,000 Daltons.

6. The method of claim 1, wherein the galactomannans are present in a material selected from the group consisting of guar gum, guar splits, hydroxypropyl guar, cationic guar, locust bean guar, tara guar, carboxymethyl guar, carboxymethyl hydroxypropyl guar, cationic hydroxypropyl guar, hydroxyl alkyl guar and carboxyalkyl guar.

7. A galactomannan produced according to the method of claim 1.

8. The galactomannan of claim 5, wherein the galactomannan is selected from the group consisting of guar gum, guar splits, hydroxypropyl guar, cationic guar, locust bean guar, tara gum, carboxymethyl guar, carboxymethylhydroxypropyl guar, cationic hydroxpropyl guar, hydroxyalkyl guar and carboxyalkyl guar.

9. An oil well fracturing agent, said agent comprising:

a) an additive; and

b) a galactomannan which is crosslinkable with said additive and has a molecular weight of between about 100,000 Daltons and about 250,000 Daltons.

10. The fracturing agent of claim 9, wherein the galactomannan also as a polydispersity of below about 3.0 and is at least 90% hydrated within three (3) minutes.

11. The fracturing agent of claim 9, wherein the crosslinking additive is selected from the group consisting of borate, titanate or zirconate organometallic crosslinking agents.

12. The fracturing agent of claim 9, wherein the agent further comprises a proppant.

13. An oil well fracturing agent, said agent comprising:

a) a proppant; and

b) a galactomannan which has a molecular weight of between about 100,000 Daltons and about 250,000 Daltons.

14. The oil well fracturing agent of claim 13, wherein the galactomannan also has a polydispersity of below about 3.0 and is at least 90% hydrated within three (3) minutes.

15. An oil well fracturing agent, said agent comprising:

a) a proppant;

b) a crosslinking additive; and

c) a galactomannan which is crosslinkable with said additive and has a molecular weight of between about 100,000 Daltons and 250,000 Daltons and a polydispersity of below about 3.0.

16. An oil well fracturing agent, said agent comprising:

a) a proppant;

b) a crosslinking additive; and

c) a galactomannan which has a molecular weight of between about 100,000 Daltons and about 250,000 Daltons and in which at least 90% changes to a hydrated product within three (3) minutes.