RU2321607C1 - Composition of foamed cryogel and method of forming it - Google Patents

Abstract

FIELD: composition of foamed cryogel containing polyvinyl alcohol, sodium chloride, sodium nitrite, ammonium chloride, carbon black and water.

SUBSTANCE: foamed cryogel is formed by chemical foaming with the aid of nitrogen separating-out during oxidizing-reducing reaction between equimolar amount of sodium nitrite and ammonium chloride followed by freezing-defreezing cycle. Proposed foamed cryogel possesses improved thermo-physical and mechanical properties required for heat insulation of producing well mouth and avoidance of precipitation of paraffin deposits. Foaming of starting material is carried out chemically, thus forming finely-dispersed high-expansion foam; in the course of exothermic reaction, heat is released, thus enhancing homogenization of starting polymer solution; presence of sodium chloride hardens foamed cryogel and rises its melting point. Foamed cryogel thus obtained may be used in construction engineering and installation of equipment in oil and gas wells of North regions, as well as recultivation of soils in cryolite zones and technological processes of oil production and transportation.

EFFECT: improved thermo-physical and mechanical properties of product.

3 cl, 1 tbl, 9 ex

Description

The invention relates to the oil industry, in particular to the development of the optimal component composition and method for producing foamed cryogels - foamed materials that can be used in the construction and arrangement of oil and gas wells in the North, during land reclamation in the permafrost areas, in production and transportation processes oil.

The process of cryotropic gelation occurs at low temperatures in multicomponent compositions based on aqueous solutions of polyvinyl alcohol. After freezing aqueous solutions of polyvinyl alcohol (PVA) at a negative temperature and subsequent thawing at a positive temperature, elastic polymer bodies called cryogels are formed [V.I. Lozinsky. Cryogels based on natural and synthetic polymers: production, properties and applications. Advances in chemistry. T.71. No. 6. 2002].

A known method for producing pencryogel by freezing-thawing mechanically whipped aqueous solutions of PVA [V.I. Lozinsky, L.G. Damskaln. Journal of Applied Polymer Science, vol. 82, 1609-1619 (2001)]. The disadvantage of this method is the instability of coarse source foams and, as a consequence, poor reproducibility of the properties of the obtained pencryogels.

Known composition and method for producing cryogel (RF 2252945 C1, publ. 05.27.2005) based on polyvinyl alcohol. The inventive polymer composition having interconnected macropores of polyvinyl alcohol cryogel contains 3-25 wt.% Polyvinyl alcohol, 0.001-1 wt.% Ionogenic - cationic, anionic or amphoteric or nonionic surfactant and water (up to 100 wt.%). A disadvantage of the known solution is the poor reproducibility of the properties of the obtained cryogels and complex technology, including the removal of solvent from the system.

A known method of chemical foaming of a composition based on polyacrylamide using gas released as a result of a redox reaction. (RF 2087673 C1, publ. 08.20.1997). A viscoelastic foamed gel is formed with the help of nitrogen obtained as a result of the reaction between nitrite of an alkali or alkaline earth metal and ammonium chloride. The disadvantage of this method is the complex technology.

Closest to the proposed structure is the composition of the cryogel (US Pat. RF No. 2258141 C1, publ. 10.08.2005), which is used in mining and is intended to protect mine workings from underground water ducts, including, wt.% Polyvinyl alcohol - 5%, sodium chloride - 11% and water - 84%, the cryogel is foamed before injection into the wells. This foamed cryogel, injected into the wells, has a plastic viscosity, does not collapse during drilling and blasting operations and the possible deformation of the array during multiple temperature changes from positive to negative and vice versa. The disadvantage of this gel is the complexity of its formation and use, lack of stability and reproducibility.

Closest to the proposed method is the method according to (US Pat. RF No. 2258141 C1, publ. 08/10/2005). The disadvantage of this method is the complex technology (complex technological equipment), poor reproducibility of the properties of the obtained foamed cryogels, the need to drill additional wells.

The objective of the present invention is to develop a composition and method for producing pencryogel with thermophysical and mechanical properties necessary for thermal insulation of the mouth of producing wells and to prevent the precipitation of paraffin deposits in them.

The composition for producing pencryogel contains polyvinyl alcohol, sodium chloride, sodium nitrite, ammonium chloride, soot and water in the following ratios of components, wt.%:

Polyvinyl alcohol 5-10 Sodium chloride 7-11 Sodium nitrite 7-14 Ammonium chloride 6-12 Soot 3-7 Water rest

The formation method involves foaming an aqueous solution of polyvinyl alcohol with the addition of sodium chloride, sodium nitrite, ammonium chloride and carbon black chemically using nitrogen released as a result of the redox reaction between equimolar amounts of sodium nitrite and ammonium chloride, then the composition is frozen and thawed.

The chemical method for the formation of pencryogel, with improved heat-insulating properties, is that in the initial aqueous solution of polyvinyl alcohol, the concentration of which varies in the range from 5 to 10%, a redox reaction is carried out to obtain foam:

NaNO ₂ + NH ₄ Cl → NaCl + 2Н ₂ О + N ₂ ↑, ΔН = - 309 kJ / mol.

To carry out foaming, two equal volumes of a solution of polyvinyl alcohol in water of the same concentration are prepared. Equimolar amounts of sodium nitrite and ammonium chloride are added to each of the solutions with stirring. Sodium nitrite NaNO ₂ is added to one solution with stirring, and an equimolar sodium nitrite is dissolved in the other, the amount of ammonium chloride NH ₄ Cl. Then these solutions are drained and thoroughly mixed. As a result of the redox reaction, nitrogen is released, which foams the polymer system.

The chemical method for generating foam has several advantages over the mechanical one. First, a stable finely dispersed foam of high multiplicity is formed, which cannot be obtained in a highly viscous solution by mechanical means. Secondly, during storage of the polymer solution at room temperature, macromolecules are associated and the solution is stratified due to sedimentation of associates having a slightly higher density than the solvent. This negatively affects the strength properties of the obtained pencryogels. In the course of the exothermic reaction, heat is released, which contributes to the homogenization of the initial polymer solution. Thirdly, in addition to nitrogen, sodium chloride is also the reaction product, the presence of which strengthens the pencryogel and increases the melting point of the material.

The standard method for producing two-component homogeneous cryogels without a gas phase (foam multiplicity is 1) is described in examples 1-2. The physical properties of the resulting cryogels depend on the concentration of the polymer and the conditions of the freeze-thaw cycle.

To improve the heat-insulating properties of cryogels (to reduce the coefficient of thermal conductivity), it is necessary to introduce the gas phase into the homogeneous two-component PVA solution and obtain the foam cryogel from the resulting foam after a freeze-thaw cycle. Example 3 describes a mechanical method for producing foams. In accordance with the invention, in examples 4-9, the gas phase was introduced by conducting a redox reaction in a polymer solution, one of the products of which was nitrogen. From the obtained foam after a cycle of freezing and thawing, penocryogel was obtained.

Example 1-2. Aqueous solutions of PVA, the mass polymer content of which is 5 and 10%, is poured into a cylindrical cuvette and placed for 20 hours in a refrigerating chamber at a temperature (-20 ° C). After freezing, an ice hard sample is taken out of the cylinder and thawed at room temperature (+ 20 ° C) for 4 hours. After thawing, the sample passes from crystalline to elastic (rubber-like) state. The characteristics of the obtained two-component homogeneous cryogel (elastic modulus G, melting point Tm and thermal conductivity coefficients λ) are shown in table 1.

Example 3. Sparging air through a porous filter, foaming a liquid multicomponent composition, which includes PVA - 5%; NaCl - 10%; soot - 3% and water - 82%. Then, to obtain a pencryogel from a foam containing equal volumes of liquid and gas phase (multiplicity 2), a freeze-thaw cycle is carried out. The results of the measurements of the physical characteristics of the obtained pencryogels are shown in Table 1. The obtained pencryogels have significantly lower thermal conductivity coefficients compared to continuous two-component cryogels.

Example 4. In an aqueous solution of PVA, the polymer content of which is 10%, a redox reaction is carried out by adding equimolar volumes of the oxidizing agent NaNO ₂ and the reducing agent NH ₄ Cl. As a result of the reaction, gas is released and foam is formed (multiplicity 5), which is subjected to a freeze-thaw cycle as in Example 1. The results of measurements of the physical characteristics of the obtained pencryogels are shown in Table 1. The obtained pencryogels have significantly lower thermal conductivity coefficients compared to single-phase two-component cryogels (examples 1 and 2).

Example 5-6. According to the procedure described in example 3, from a 5% PVA solution, 5 and 10 foam cryogels are prepared and examined. The results are shown in table 1. A decrease in the foam multiplicity slightly increases the elastic modulus and does not affect the thermal conductivity and the melting temperature of the foam cryogel.

Example 7. In a two-component system consisting of PVA - 5% and water - 95%, carbon black 5% is introduced. In this solution, a redox reaction is carried out, and a foam is obtained. After a freeze-thaw cycle of the prepared composition, penocryogel is formed (table 1). The addition of soot to the composition increases the elastic modulus of the pencryogel, does not affect the coefficient of thermal conductivity, but lowers the melting point of the pencryogel.

Example 8. Prepare a composition that contains PVA - 5%, NaCl - 4% and water - 91%. Equimolar volumes of an oxidizing agent and a reducing agent (1.25 mol / L) are added, and a foam is formed. As mentioned earlier, the reaction product, in addition to nitrogen, is also sodium chloride, therefore, the total salt concentration in the system reaches its maximum value (11%), above which polymer precipitation occurs. A freeze-thaw cycle is carried out. The results of measurements of the physical characteristics of the obtained pencryogels are shown in Table 1. The obtained pencryogel practically does not differ in elastic and heat-insulating properties from the previous samples (examples 4-6), but its melting temperature rises markedly.

Example 9. In a multicomponent system consisting of PVA - 5%, NaNO ₂ - 7%, NH ₄ Cl - 6%, NaCl - 4% and water - 73%, an additional 5% carbon black was added and foamed by chemical reaction to multiplicity foam, equal to 5. After a cycle of freezing-thawing get penokriogel with a higher elastic modulus than the sample in example 8.

Thus, the proposed composition and method for generating foams during a chemical reaction allows to obtain stable high-multiplicity foamcryogels with improved thermophysical properties.

Table 1. No. Structure Concentration,% Foam ratio λ, W / Km G, kPa Mp, ° C one PVA
H ₂ O 5
95 one 0.35 four 73 2 PVA
H ₂ O 10
90 one 0.33 thirty 73 3 PVA
NaCl
soot
H ₂ O 5
10
3
82 2 0.26 6 110 four PVA
NaNO ₂
NH ₄ Cl
H ₂ O 10
7
6
77 5 0.13 7 85 5 PVA
NaNO ₂
NH ₄ Cl
H ₂ O 5
7
6
82 10 0.12 1,5 85 6 PVA
NaNO ₂
NH ₄ Cl
H ₂ O 5
7
6
82 5 0.14 2.0 85 7 PVA
NaNO ₂
NH ₄ Cl
soot
H ₂ O 5
7
6
5
77 5 0.14 5 80 8 PVA
NaNO ₂
NH ₄ Cl
NaCl
H ₂ O 5
7
6
four
78 5 0.14 2,5 110 9 PVA
NaNO ₂
NH ₄ Cl
soot
NaCl
H ₂ O 5
7
6
5
four
73 5 0.14 7 110

Claims (2)

1. The composition for producing pencryogel containing polyvinyl alcohol, sodium chloride and water, characterized in that the composition further comprises sodium nitrite, ammonium chloride and soot in the following ratios of components, wt.%: Polyvinyl alcohol 5-10 Sodium chloride 7-11 Sodium nitrite 7-14 Ammonium chloride 6-12 Soot 3-7 Water rest 2. A method of forming a pencryogel by foaming an aqueous solution of polyvinyl alcohol, characterized in that the foaming of an aqueous solution of polyvinyl alcohol with the addition of sodium chloride, sodium nitrite, ammonium chloride and soot is carried out chemically using nitrogen released as a result of the redox reaction between equimolar amounts sodium nitrite and ammonium chloride, then carry out a freeze-thaw cycle of the composition.