CN114835843A

CN114835843A - Method for continuously preparing stable and uniform high internal phase emulsion

Info

Publication number: CN114835843A
Application number: CN202111670762.9A
Authority: CN
Inventors: 顾子旭; 罗超; 苏卫卫; 杭渊; 刘旭
Original assignee: Suzhou Xingri Chemical Co ltd
Current assignee: Suzhou Xingri Chemical Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-08-02

Abstract

A process for continuously preparing stable homogeneous high internal phase emulsions is disclosed, the resulting high internal phase emulsions being generally polymerized to form an open cell foam which is capable of absorbing aqueous fluids. The invention improves the static mixing circulation unit which meets specific technical parameters and circulates part of the emulsion taken out of the static mixer. The method improves the stability and uniformity of the HIPE emulsion prepared by a continuous method.

Description

Method for continuously preparing stable and uniform high internal phase emulsion

Technical Field

The invention belongs to the emulsion preparation technology, and particularly relates to a method for continuously preparing stable and uniform high internal phase emulsion.

Background

The high internal phase emulsion refers to an emulsion in which the ratio (W/O ratio) of an aqueous phase as a dispersed phase (internal phase) to an oil phase as an external phase is 3/1 or more, and is hereinafter referred to as HIPE. The use of such HIPE polymerizations to make cellular polymers is well known. The porous polymer produced by HIPE polymerization can give a continuous open-cell foam having a fine pore diameter as compared with the porous polymer produced by using a blowing agent (hereinafter, also simply referred to as HIPE method).

It is well known that HIPE emulsions, particularly those having a high water phase as compared to oil, are unstable. Minor changes in the raw materials and temperature in the emulsion, particularly in the mixing conditions, can cause such emulsions to "break" or at least to some extent separate into their respective aqueous and oil phases, and thus, on a production scale, the continuous, stable production of polymerizable HIPE emulsions becomes more difficult. This occurs because the internal and external phases of the HIPE themselves have relatively low viscosities (e.g., 0.1 to 5.0 cps), but when an emulsion is formed, the viscosities become extremely high (e.g., 500 to 5000 cps). This viscosity difference results in a viscosity jump when the oil and water phases are mixed in the mixer, which is particularly acute when the water/oil ratio is greater than 15: 1. As a result, it was difficult to uniformly disperse the aqueous phase in the oil phase, and the HIPE obtained contained water droplets having a nonuniform size. This results in a HIPE that exhibits poor internal phase stability during subsequent polymerization, particularly at higher temperatures (e.g., 85 ℃), thereby resulting in a polymer foam with non-uniform cell sizes.

Furthermore, the flow rate of both the oil and water phases must be "extremely" stable from any minor fluctuations as the HIPE emulsion is formed in the mixer, as transient changes in flow rate can alter the instantaneous water/oil ratio, thereby causing the emulsion to "break". Such a requirement for the fluctuation control of the flow rate is difficult to realize in actual industrial production.

The prior art generally uses a dynamic mixer containing rotating elements to produce HIPEs. By its very nature, rotating elements such as blades, paddles, etc. do not have a consistent tangential velocity. For example, the difference in shear rates at which the axially flowing fluid experiences minimal shear at the axis and maximal shear at the radially outlet end makes it problematic to produce a uniform HIPE, and makes it difficult to scale up the dynamic mixer from laboratory or pilot plant scale to production scale. Therefore, it would be desirable to have an emulsion process for HIPE that: (1) continuously carrying out; (2) the water phase is highly and uniformly dispersed in the oil phase; (3) controllable process amplification.

Disclosure of Invention

The invention relates to an improved process for the preparation of high internal phase emulsions by a continuous process, using a static mixing and circulation unit to circulate a portion of the emulsion taken from the static mixer, which improves the stability of the final emulsion obtained by the continuous process and its uniform particle size distribution, and which, according to corresponding guidelines, is easy to scale up.

The invention adopts the following technical scheme:

a process for continuously preparing a stable homogeneous high internal phase emulsion comprising the steps of: providing a mixing cycle unit comprising a static mixer and a pump; continuously injecting the water phase and the oil phase into a mixing circulation unit at different positions, and mixing in a static mixer to obtain emulsion; then continuously injecting the emulsion into the static mixer through the pump to form circulation; a stable, uniform high internal phase emulsion is obtained downstream of the static mixer. Furthermore, the mixing circulation units are one group or a plurality of groups; when the mixed circulation units are in multiple groups, the mixed circulation units are connected in series; continuously injecting 55-99% of the emulsion into a static mixer through a pump to form circulation; the water phase and the oil phase are continuously injected into the mixing circulation unit at different positions, namely the water phase is directly injected into the static mixer, and the oil phase is injected into the static mixer through a pump. Preferably, when the mixing and circulating unit is a plurality of groups, 55 to 99 percent, preferably 60 to 95 percent of the emulsion downstream of the former static mixer is continuously injected into the static mixer again through the pump to form circulation, and the rest emulsion is injected into the next static mixer. When the mixing circulation unit is a plurality of groups, the water phase is divided into one group or a plurality of groups and input into the upstream of the static mixer, and the oil phase is divided into one group or a plurality of groups and input into the inlet of the pump.

In the invention, the rest part of the emulsion is injected into an outlet end static mixer, and stable uniform high internal phase emulsion is obtained at the downstream of the outlet end static mixer; or injecting the rest part of the emulsion and the water phase into an outlet end static mixer, and obtaining a stable uniform high internal phase emulsion at the downstream of the outlet end static mixer; or injecting the rest part of the emulsion and the initiator solution into an outlet end static mixer, and obtaining a stable uniform high internal phase emulsion at the downstream of the outlet end static mixer; or injecting the rest part of the emulsion, the water phase and the initiator solution into an outlet end static mixer, and obtaining a stable uniform high internal phase emulsion at the downstream of the outlet end static mixer; as a general sense, the emulsion may include other conventional additives in addition to the oil phase, the water phase, the initiator. The outlet static mixer comprises injecting the aqueous phase and/or aqueous initiator solution upstream of the outlet static mixer, subjecting the emulsion from the mixing and circulating unit to further mixing shear, and continuously outputting a stable high internal phase emulsion from the outlet static mixer, wherein the stable high internal phase emulsion formed can be polymerized to form a polymeric foam when an effective amount of polymerization initiator is included.

Preferably, the static mixer comprises one or more specifications of static mixing elements, and the elements are connected in series, and the static mixer is an existing device. In the static mixer, the material flow generates a shear rate of 500-10000S ^-1 Preferably 600 to 5000S ^-1 (ii) a Particularly preferably 700 to 3000S ^-1 (ii) a The pressure drop of at least one static mixer is more than 0.15MPa, the total pressure drop of the static mixer is more than 0.6MPa, the total pressure drop is more than 0.9MPa, and the total pressure drop is more than 1.2 MPa; during the continuous preparation of the stable homogeneous high internal phase emulsion, the flow rate fluctuation is less than 30%, more preferably less than 15%, and particularly preferably less than 5%; flow fluctuation refers to the change in flow rate of any one of the circulating pipe sections with a momentary deviation less than the average flow rate.

The invention discloses a stable and uniform high internal phase emulsion prepared by the method for continuously preparing the stable and uniform high internal phase emulsion, wherein the ratio of an aqueous phase to an oil phase is 10: 1-75: 1, and more preferably 20: 1-40: 1.

The method for continuously preparing the stable and uniform high internal phase emulsion comprises the following steps:

providing a liquid oil phase stream comprising an emulsifier;

providing a liquid aqueous phase stream comprising an electrolyte;

providing one or more groups of mixing circulation units consisting of static mixers and pumps, wherein the groups are connected in series;

injecting the water phase and the oil phase at different positions of the mixing and circulating unit;

after the water phase and the oil phase are mixed and emulsified through a static mixer, continuously outputting part of emulsion from the downstream of the static mixer by a pump and returning the part of emulsion to the upstream of the static mixer by the pump;

the remaining emulsion downstream of the static mixer is sent to the outlet static mixer.

In the present invention, the oil phase comprises oily monomers and emulsifiers, preferably, the oil phase comprises 85% to 95% by weight of oily monomers and 5% to 15% by weight of emulsifiers, wherein: the oily monomer is a polymerizable monomer; emulsifiers are surfactants that are soluble in the oil phase and can form a water-in-oil emulsion. The water phase is water solution of water soluble electrolyte, and is especially water solution containing water soluble electrolyte in 1-6 wt%.

The oil-based monomer is a polymerizable monomer (I) having 1 polymerizable unsaturated group in the molecule and/or a crosslinkable monomer (II) having at least 2 polymerizable unsaturated groups in the molecule, which can form a crosslinked structure by polymerization.

The polymerizable monomer (I) may be as follows:

it preferably contains at least a portion of (meth) acrylate, more preferably more than 40% by weight, preferably 50% to 85% by weight, for example 60% by weight of (meth) acrylate. Specifically, the polymerizable monomer (i) includes: styrene, ethylstyrene, α -methylstyrene, vinyltoluene, vinylethylbenzene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate. These monomers may be used alone or in combination of two or more.

The amount of the polymerizable monomer (I) is preferably 40 to 95 wt% based on the total weight of the oily monomers. When the amount is within this range, a porous polymer having a fine pore size can be obtained. Further preferably 50 to 90 wt%, particularly preferably 60 to 85 wt%. When the amount of the polymerizable monomer (I) used is less than 40% by weight, the resulting porous polymer becomes brittle or unsatisfactory in water absorption capacity. On the other hand, when the amount of the polymerizable monomer (I) exceeds 95% by weight, the strength, elastic recovery force and the like of the resulting porous polymer are insufficient, and sufficient water absorption capacity and water absorption rate cannot be secured.

The crosslinkable monomer (II) may be as follows:

there are no particular limitations as long as it has at least 2 polymerizable unsaturated groups in the molecule or can form a crosslinked structure by polymerization, and it can be dispersed or polymerized in a water-in-oil high internal phase emulsion as in the case of the polymerizable monomer (I). Specifically, examples of the crosslinkable monomer (II) include: divinylbenzene, trivinylbenzene, divinyltoluene, divinylxylene, p-ethylvinylbenzene, butadiene, isoprene, pentadiene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1, 3-butylene glycol di (meth) acrylate, 1, 4-butylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, octamethylene glycol di (meth) acrylate, decanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, isoprene oxide, and the like, Dipentaerythritol di (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate. These monomers may be used alone or in combination of two or more.

The amount of the crosslinkable monomer (II) is preferably 5 to 60 wt%, more preferably 10 to 50 wt%, and particularly preferably 15 to 40 wt% based on the total weight of the oily monomers. When the amount of the crosslinkable monomer (II) is less than 5% by weight, the resulting porous polymer is insufficient in strength, elastic recovery force, etc., or the amount of absorption per unit volume or unit weight is unsatisfactory, and sufficient water absorption amount and water absorption rate cannot be secured. On the other hand, when the amount of the crosslinkable monomer (1-2) exceeds 60% by weight, the porous polymer becomes brittle or the water absorption capacity is unsatisfactory.

Preferably, the oily monomer component comprises: 50-85 wt% of one or more selected from methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate; from 5% to 40% by weight of a monomer selected from the group consisting of ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1, 3-butylene glycol di (meth) acrylate, 1, 4-butylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, octamethylene glycol di (meth) acrylate, decanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol di (meth) acrylate, dipentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, triethylene glycol di (meth) acrylate, and mixtures thereof, One or more of dipentaerythritol tetra (meth) acrylate.

The emulsifier is not particularly limited as long as it is a high internal phase emulsion in which the oil phase and the aqueous phase form water-in-oil, and known nonionic emulsifiers, cationic emulsifiers, anionic emulsifiers, amphoteric emulsifiers, and the like can be used. Preferably, nonionic emulsifiers and cationic emulsifiers are used. The combination of both is particularly preferred, and the stability of the HIPE may be improved.

The nonionic emulsifiers may be as follows:

saturated and/or unsaturated fatty acid sorbitan esters, such as: sorbitan-monolaurate, sorbitan-monomyristate, sorbitan-monopalmitate, sorbitan-monooleate, sorbitan-monostearate, sorbitan-monoisostearate, sorbitan-trioleate, sorbitan-distearate, sorbitan-tristearate;

(Poly) Glycerol- (C) ₁₂ ~ C ₂₂ ) Saturated and/or unsaturated fatty acid esters, such as: glycerol-myristate, glycerol-stearate, glycerol-isostearate, glycerol-oleate; diglycerol-stearate, diglycerol-isostearate, diglycerol-oleate, diglycerol-tristearate; triglycerol-oleate, triglycerol-isostearate; tetraglycerol-monostearate, tetraglycerol-monooleate, tetraglycerol-tristearate, tetraglycerol-pentastearic acid, tetraglycerol-pentaoleate, tetraglycerol-monolaurate, tetraglycerol-monomyristate; hexaglycerol-monostearate, hexaglycerol-monooleate, hexaglycerol-tristearate, hexaglycerol-pentadecanoic acid, hexaglycerol-pentaoleate; decaglycerol-monolaurate, decaglycerol-monostearate, decaglycerol-monomyristate, decaglycerol-monoisostearate, decaglycerol-monooleate, decaglycerol-monolinoleic acid, decaglycerol-distearate, decaglycerol-diisostearate, decaglycerol-tristearate, decaglycerol-trioleate, decaglycerol-pentastearate;

the hydrocarbyl-substituted succinic polyol ester and/or the hydrocarbyl-substituted succinic polyamine ester and/or the hydrocarbyl-substituted succinic hydroxylamine ester.

The nonionic emulsifier has particularly preferably an HLB of 10 or less, particularly 2 to 6. 2 or more of these nonionic emulsifiers may be used in combination, and such combination sometimes improves the stability of the HIPE.

Cationic emulsifiers may be as follows:

comprising a long chain C ₁₂ -C ₂₂ Dialiphatic, short-chain C ₁ -C ₄ Dialiphatic quaternary ammonium salts, for example: ditalloyl dimethyl ammonium hydrochloride, bihydrogenated tallow dimethyl ammonium hydrochloride, ditridecyl dimethyl ammonium hydrochloride, ditalloyl dimethyl ammonium methyl sulfate, and bihydrogenated tallow dimethyl ammonium methyl sulfate;

comprising a long chain C ₁₂ -C ₂₂ Dialkanoyl (alkenoyl) -2-hydroxyethyl, short-chain C ₁ -C ₄ Dialiphatic quaternary ammonium salts, for example: ditalloyl-2-hydroxyethyl dimethyl ammonium hydrochloride;

comprising a long chain C ₁₂ -C ₂₂ Dialiphatic imidazolium quaternary ammonium salts, for example: methyl-1-tallowamidoethyl-2-tallowimidazolium methylsulfate, methyl-1-oleylamidoethyl-2-oleylimidazolium methylsulfate;

containing short chains C ₁ -C ₄ Dialiphatic, long-chain C ₁₂ -C ₂₂ Mono-aliphatic benzyl quaternary ammonium salts, for example: dimethyl stearyl benzyl ammonium hydrochloride, dimethyl tallow benzyl ammonium hydrochloride;

comprising a long chain C ₁₂ -C ₂₂ Dialkanoyl (alkenoyl) -2-aminoethyl, short-chain C ₁ -C ₄ Mono-aliphatic, short-chain C ₁ -C ₄ Monohydroxy aliphatic quaternary ammonium salts, for example: ditalloyl-2-aminoethylmethyl 2-hydroxypropyl ammonium methylsulfate, dioleoyl-2-aminoethylmethyl 2-hydroxyethyl ammonium methylsulfate;

2 or more of these cationic emulsifiers can be used in combination to further optimize the thermal stability of the emulsion.

The amount of the emulsifier is preferably 5 to 15 wt%, and more preferably 5 to 10wt%, based on the total weight of the oily monomer and the emulsifier. When the amount of the emulsifier used is less than 5% by weight, the dispersion stability of HIPE is deteriorated; on the other hand, when the emulsifier is used in an amount exceeding 15% by weight, the resulting porous polymer becomes too brittle and uneconomical.

The water-soluble electrolyte comprises one or more of water-soluble halide salt, nitrate and sulfate of alkali metal and alkaline earth metal; the water of the present invention may be treated HIPE production wastewater in addition to tap water, pure water, ion exchange water. The amount of water used varies depending on the use of the porous polymer. The HIPE foam of the present invention, the use of which is exemplified below:

a) feminine hygiene articles, for example: pads, pantiliners and tampons;

b) disposable diapers, incontinence articles, for example: pads, adult diapers;

c) household care articles, for example: wipes, pads, towels;

d) cosmetic care articles, for example: pads, wipes;

e) skin care articles, for example: an absorbent core for pore cleaning;

f) an oil absorbing material;

g) a sound insulating material;

h) a filter material;

the ratio (mass ratio) of the water phase/oil phase (W/O) of the HIPE is not particularly limited depending on the use, and is preferably 8/1 to 140/1, although not less than 3/1. For use in diapers, sanitary materials and the like, the W/O is preferably 10/1 to 75/1, more preferably 20/1 to 40/1.

The salt-type water-soluble electrolyte may be used as long as it is necessary to improve the stability of HIPE. Preferred electrolytes as the salts are monovalent inorganic salts, divalent inorganic salts, trivalent inorganic salts, such as: water-soluble alkali and alkaline earth metal halides, nitrates, sulfates. Examples include: sodium chloride, calcium chloride, sodium sulfate and magnesium sulfate. Calcium chloride is most preferred in the preparation process of the present invention. The electrolyte is typically used in the aqueous phase of the HIPE at a concentration of about 0.1 to 10 weight percent of the aqueous phase. More preferably, the concentration of the electrolyte is 1-6 wt% of the aqueous phase.

In order to complete the HIPE polymerization in a very short time, it is preferable to use a polymerization initiator. Any one or more of water-soluble, oil-soluble may be used. Such initiator components are typically added to the aqueous phase of the HIPE and may be any conventional water-soluble free radical initiator. Such as: azo compounds such as 2, 2' -azobis (2-amidinopropane) dihydrochloride; persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; peroxides such as potassium peracetic acid, sodium peracetic acid, potassium percarbonate, sodium percarbonate, etc. The amount of the polymerization initiator to be used is preferably in the range of 0.5 to 15 wt%, more preferably 1 to 10wt%, based on 1 part by weight of the total amount of the oily monomers. When the amount of the polymerization initiator used is less than 0.5 wt%, the amount of the unreacted polymerizable monomer component increases, and therefore the amount of the monomer remaining in the resulting porous polymer increases. On the other hand, in the case where the amount of the polymerization initiator used exceeds 15% by weight, the control of polymerization becomes difficult, and the mechanical properties in the resulting porous polymer are deteriorated, which is also not preferable. Further, a redox polymerization initiator system in which the polymerization initiator is combined with a reducing agent may also be used. Among the reducing agents, examples of the water-soluble reducing agent include sodium bisulfite, potassium bisulfite, sodium thiosulfate, potassium thiosulfate, L-ascorbic acid, erythorbic acid, and ferrous salts. Examples of the oil-soluble reducing agent include dimethylaniline. These reducing agents of the redox polymerization initiator system may be used alone, or 2 or more of them may be used in combination. In the redox polymerization initiator system, the initiator (oxidizing agent)/reducing agent (mass ratio) is preferably 1/0.01 to 1/5.

Further, as a means for initiating polymerization of a trace amount of monomer to reduce monomer residues: an oil-soluble photoinitiator or a water-soluble photoinitiator may be added to the oil phase or the water phase. The photoinitiator can react rapidly and effectively with the light source to generate free radicals, cations and other substances capable of initiating polymerization, thereby initiating polymerization of the monomers, and the content of the photoinitiator can be about 0.1-10%, preferably 0.2-3% by weight of the oily monomers. If the polymerization is carried out in an oxygen-containing environment, there should be sufficient photoinitiator to initiate the polymerization and overcome the oxygen inhibition. The photoinitiators useful in the present invention can absorb ultraviolet light at wavelengths of about 200nm (nanometers) to about 800nm, preferably 200nm to about 450 nm. If the photoinitiator is in the oil phase, a suitable type of oil-soluble photoinitiator comprises benzyl ketal, α -hydroxyalkyl phenones, α -aminoalkyl phenones, and acylphosphine oxides. If the photoinitiator present in the aqueous phase may be at least partially water soluble, suitable types of water soluble photoinitiators include benzophenones, benzils, and thioxanthones.

The initiator (including redox initiator system) may be present only when the HIPE is polymerized, and with respect to the addition method, (I) the HIPE may be previously added to the oil phase and/or the aqueous phase to form the HIPE, (II) the initiator may be added simultaneously with the HIPE formation, and (III) the initiator may be added after the HIPE formation. Preference is given to (II), in particular in the examples. In the case of redox polymerization initiator systems, the initiator (oxidizing agent) and the reducing agent may be added separately.

The emulsion of the present invention may further comprise other various additives, which may be suitably used as long as the manufacturing conditions can be improved or the HIPE characteristics or the properties of the porous polymer can be optimized. For example: to adjust the pH, acids and/or bases and/or buffers may be added; to improve the absorption properties, water-soluble monomers may be added, such as: acrylic acid, vinyl acetate; other functional additives, such as: active carbon, inorganic powder, organic powder, metal powder, deodorant, antibacterial agent, antifungal agent, perfume, various polymers, and emulsifier.

The continuous process of the present invention for preparing HIPE comprises: providing one or more groups of mixing circulation units consisting of static mixers and pumps, wherein the groups are connected in series; continuously injecting the water phase and the oil phase into the circulating unit at different point positions of the mixed circulating unit; after the water phase and the oil phase are mixed and emulsified through a static mixer, continuously taking out part of emulsion from the downstream of the static mixer by a pump and pumping the part of emulsion back to the upstream of the static mixer; the circulation unit may be plural, and the remaining emulsion downstream of the static mixer of the last circulation unit is sent to the outlet-end static mixer, and then an emulsion, i.e., a stable uniform high internal phase emulsion, is obtained downstream thereof.

The prior art generally uses a dynamic mixer containing rotating elements to produce HIPEs. By its very nature, rotating elements such as blades, paddles, etc. do not have a consistent tangential velocity. For example, the difference in shear rates at which the axially flowing fluid experiences minimal shear at the axis and maximal shear at the radially outlet end makes it problematic to produce a uniform HIPE, and makes it difficult to scale up the dynamic mixer from laboratory or pilot plant scale to production scale.

In contrast, the present invention uses a static mixer, a delivery unit (pump) to force the liquid through a tube provided with static mixing elements. The liquid following the main flow axis is divided into sub-streams and stretched, sheared, agitated, mixed with each other, and the relative velocities of the fluid and the mixing elements can be relatively constant over the cross-section of the flow, so that an in-line mixer using static mixing elements can be dimensioned predictably according to production needs. A "static mixer" is an assembly of one or more segments, a "segment" is a combination of "elements" inserted into a flow channel, an "element" is a portion of a segment that divides the fluid flowing through the conduit into at least two streams, and an "element" can be of the same type and of the same size or of different types and sizes. The shear agitation applied to any element of the static mixer is generally at a rate of about 500 to 10000S in this case, provided that it is sufficient to form at least part of the liquid as a water-in-oil emulsion ^-1 More preferably 500- ^-1 Particularly preferably 500 to 3000S ^-1 。

Taking a Model GX mixer as an example, the shear rate can be calculated by the following formula:

γ=5×10 ⁷ ×D ^-3.207 ×Q

wherein: γ: shear rate, S ^-1 (ii) a D: static mixer diameter, mm; q: flow rate (flow velocity) m of material ³ /h。

Suitable static mixing elements, such as: (I) a Model GXR mixer, a Model GX mixer, a Model SMB mixer, available from StaMixCo Ltd.; (II) OHR MIXER MIXER, available from OHR Laboratory Corporation. As is conventional, the static mixer used to prepare the HIPE should be adjusted according to the element size, element orientation or duct cross-section or all of these parameters in accordance with the objectives of the present invention to provide varying velocities and shear forces along the mixer axis.

The pumps used for the recycle streams should not generate high shear forces, and the preferred pumps are volumetric pumps, such as: lobe pump, plunger pump, diaphragm pump, gear pump, sliding vane pump, screw pump, etc. Further preferred are lobe pumps and screw pumps based on factors such as output pressure, shear, pulsation, etc. As with any Positive Displacement (PD) pump, pump efficiency is greatly affected by slippage, which is the backflow of liquid from the high pressure (discharge) side through the rotor to the low pressure (suction) side of the pump. Excessive slip can result in reduced pump efficiency and limit the maximum output pressure of the pump. The degree of slip is controlled on the one hand by the viscosity characteristics of the stream; on the other hand, by the type of rotor and the machining accuracy.

The present invention indicates that stable "slippage" is critical to the stable continuous acquisition of HIPE: when the mixing ratio of the water phase and the oil phase fluctuates or the mixing is not uniform, the viscosity of the material flow is dynamically changed, which causes the 'slippage' quantity in the pump cavity to also dynamically change, thereby further causing the dynamic change of the pump efficiency, which is represented by the dynamic fluctuation of the flow, the dynamic fluctuation of the pipeline pressure and the dynamic fluctuation of the shearing rate at the static mixer, and further aggravating the dynamic fluctuation of the viscosity. Thus "slippage" will destroy the stability and uniformity of the HIPE by means of iterative enhancement.

In general, "slip" can be reasonably controlled by the type of rotor and machining accuracy, but there is currently no suitable theory or experience for guiding the selection of equipment parameters for HIPE systems. The invention firstly provides that the instantaneous deviation of the flow speed of any circulating pipe section is less than 50 percent of the average flow speed, further preferably less than 30 percent, and particularly preferably less than 10 percent; taking a cam pump as an example, the rotor in the cavity has various forms, such as: three-bladed rotors, six-bladed rotors, two-bladed curved wing rotors, helical rotors, although each blade has advantages and tradeoffs in pump efficiency, solids handling, maintenance and fluid pulsation, the prior art gives no guidance as to the process characteristics of HIPE, and the present invention reduces the clearances between the rotors and the pump body, and between the rotors to minimize slippage, preferably less than 0.2mm, more preferably less than 0.1mm, and even more preferably less than 0.05 mm. They provide an effective dynamic seal as they rotate within the pumping chamber.

The viscosity of the HIPE is significantly affected by the shear rate in the pump chamber, and changes in viscosity are often accompanied by an increase in material "slip", which in turn results in large fluctuations in the actual output flow rate of the pump, which is highly detrimental to the stable formation of a uniform HIPE. Such as: fluctuations in flow rate will alter the water-to-oil ratio of the HIPE, which often results in the formation of HIPE surfaces with varying degrees of "water droplets" that are highly undesirable for subsequent polymerizations, especially high temperature polymerizations, as evidenced by increased pore size, broadened distribution, and non-uniform mechanical properties of the porous polymer. Higher shear rates will cause the internal phase to fuse, appearing as a break, and such fusion is often irreversible.

The internal and external phases of the HIPE themselves have relatively low viscosities (e.g., 0.1 to 5.0 cps), but when an emulsion is formed, the viscosities become extremely high (e.g., 500 to 5000 cps). This viscosity difference results in a viscosity jump when the oil and water phases are mixed in the mixer, which is particularly acute when the water/oil ratio is greater than 15: 1. The result is less aqueous phase uniformly dispersed in the oil phase and the HIPE obtained contains water droplets of non-uniform size. This results in a HIPE that exhibits poor internal phase stability during subsequent polymerization, particularly at higher temperatures (e.g., 85 ℃), thereby resulting in a polymer foam with non-uniform cell sizes.

The invention divides the inner phase and the outer phase into one or more groups to be input to different positions of the circulating pipeline for the first time, and can effectively solve the problem of viscosity mutation. By improving the way, the inner phase and the outer phase are respectively mixed with the formed emulsion, so that the direct mixing of the inner phase and the outer phase is effectively avoided, the viscosity in a circulating pipeline is stable, and the stability can be further improved along with the increase of the circulating amount. In the known technology, in order to avoid that the pressure fluctuation in the circulating pipeline influences the fluctuation of the internal and external input flow, stream conveying is often carried out by adopting a plunger pump and the like, the pump of the type has inherent pulse, and the research shows that the extremely weak pulse can also substantially influence the viscosity and the pressure in the circulating pipeline. When the material flow injection mode of the invention is adopted, the influence of the instantaneous change of the input flow of the inner phase and the outer phase on the viscosity and the pressure in the circulating pipeline can be eliminated, and the stability and the uniformity of the HIPE are further improved. In practice, the oil phase flow may be stopped for a period of time, provided that the circulation rate is sufficient to reflux enough of the emulsified oil phase so that the ratio of the total oil phase (un-emulsified/emulsified) to the added water phase at that circulation rate does not exceed a stable amount of emulsifier. The preferable scheme is that the oil phase (external phase) is divided into one or more groups to be input to the inlet of the pump; the aqueous (internal) phase is fed into the static mixer upstream in one or more stages.

Oil and water phase streams are fed to the static mixer and circulation zone. The components are mixed using conventional techniques and the oil phase is prepared by any suitable method. The mixing of the components is carried out in any suitable order of addition of the components, either continuously or batchwise. The oil phase thus prepared is typically formed and stored in a supply tank and then pumped as a liquid stream at any desired flow rate. In the same way, an aqueous stream can be prepared and stored. The method is a conventional technology, and the realization of the technical effect of the invention is not influenced. As an example, the flow rate of the stream is set at a lower ratio of aqueous phase to oil phase, while the aqueous phase stream is injected upstream of the static mixer, the oil phase stream is injected into the inlet of the circulation pump, which can be turned on once the circulation line is full of liquid, and an emulsion will form in the static mixer. Once the flow rate and pressure in the circulating pipeline tend to be stable, the proportion of the water phase and the oil phase can be gradually increased to a target value, and meanwhile, parameters such as the shearing rate, the pressure drop and the like at the static mixer can be optimized by changing the frequency of the circulating pump and adjusting the circulating flow.

The volume of emulsified components present in the recycle stream is important relative to the total volume of oil and water phase components present in the static mixer. For example, the volume of the recycle stream can affect the degree of stability of the emulsion present in the static mixer, particularly when the input rate of the oil phase stream to the static mixer is reduced or stopped as described above. Conversely, the larger the volume of the recycle stream, the less reaction to changes in flow rate or HIPE composition in a continuous process. For a HIPE production system intended for a longer time to be used only to prepare one particular type, a larger volume of recycle stream is used, i.e., the volume of recycle stream is 2 to 10 times the total volume of the oil and water phases present in the static mixer; for systems requiring faster reaction to changes in flow rate or HIPE composition, it is preferred to use a smaller circulation volume, i.e., a volume of the circulation stream corresponding to 0.3 to 3 times the total volume of the oil and water phases present in the static mixer.

The conditions within the static mixer during emulsion formation also affect the properties of the HIPE prepared by this process. One aspect that may have an effect on the properties of the HIPE produced is the temperature of the emulsion components within the static mixer. The emulsified material in the static mixer should be maintained at 25 to 95 deg.C, more preferably 55 to 90 deg.C, and particularly preferably 65 to 85 deg.C during HIPE formation. When the temperature is less than 25 ℃, the time required for curing may be prolonged, while when the temperature exceeds 95 ℃, the uniformity of the HIPE formed may be deteriorated.

In the process of the present invention, the emulsion components are continuously withdrawn from the circulation unit downstream of the static mixer, merged with the aqueous phase and/or aqueous initiator solution (which may also include other additives), and injected into the outlet end upstream of the static mixer for further mixing and shearing, and the stable high internal phase emulsion is continuously withdrawn from the outlet end static mixer and fed to the polymerization apparatus. The polymerization step of the HIPE is not particularly limited, and polymerization is usually heated by a static polymerization method under conditions that do not destroy the structure in the HIPE. In this case, either batch polymerization in which such HIPE is polymerized in batches or continuous polymerization in which casting polymerization is carried out while continuously feeding into a heating zone, for example, is possible, but a polymerization method in which both the polymerization effect is more effectively exerted and the productivity is improved is preferable to the batch polymerization. That is, a continuous polymerization method in which a sheet-like or film-like HIPE is continuously cast, heated, and polymerized on, for example, a running belt can be cited. Among these, heating means and control means suitable for the polymerization method may be provided, and for example, heating means capable of heating and maintaining the polymerization temperature by using an active heat ray such as microwave or near infrared ray such as radiation energy or a heat medium such as hot water or hot air may be used.

Drawings

FIG. 1 is a schematic process flow diagram for carrying out the method of the present invention; a first circulation pipeline is formed by the static mixer A, the pump A and a matched pipeline thereof. Water phase a and oil phase a are pumped (not shown) from a tank (not shown) into the first circulation line, water phase a being fed upstream from the static mixer a through the T-tee and oil phase a being fed from the inlet of the pump a through the T-tee. Once the circulation line is full, the circulation pump A is started, the emulsion is formed in the static mixer A, a part of the emulsion downstream of the static mixer A enters the inlet of the pump A to participate in the recirculation, and the other part of the emulsion enters a second circulation line (which is optional according to the process requirements) formed by the static mixer B, the pump B and the matching line thereof, and the inlet is positioned upstream of the static mixer B. The aqueous phase B (optional) is fed upstream from the static mixer B through a T-tee and the oil phase B (optional) is fed at the inlet of the pump B through a T-tee. Once the circulation line is full, pump B is turned on and the emulsion is further shear mixed in static mixer B, with a portion of the emulsion downstream of static mixer B entering the inlet of pump B and participating in recirculation and another portion of the emulsion entering the outlet upstream of the static mixer. The aqueous phase C and/or initiator (optional) are fed upstream from the outlet static mixer through a T-junction, subjected to further mixing shear, and the stable high internal phase emulsion is continuously withdrawn from the outlet static mixer and fed to the polymerization apparatus.

The elements not shown in the figure are conventional devices, and the dosage of the oil phase A and the oil phase B and the dosage of the water phase A, the water phase B and the water phase C are designed according to the proportion of the required product.

Detailed Description

The invention relates to the existing products of raw materials, all devices are commercially available products, and the invention is mainly creative in proposing circulating mixing and preparation parameters, and the specific operation method and the test method are the prior art.

There are a number of techniques for determining the average cell size of a foam. These techniques include mercury porosimetry, which is well known in the art. However, the most commonly used technique for determining the cell size of a foam is simple photogrammetry of foam samples. For the purposes of the present invention, the average cell size of the foam produced by polymerizing such a HIPE can be used to quantify the amount of shear agitation applied to the emulsified material in the static mixer. In particular, after adjusting the oil phase and aqueous phase flow rates to the desired aqueous phase/oil phase ratio, the emulsified material in the static mixer is subjected to shear agitation sufficient to ultimately form a HIPE capable of producing a foam having an average cell size of 5 to 100 μm during subsequent polymerization. More preferably, such agitation should result in an average cell size of the subsequently formed foam of 10-90 μm.

Example 1: preparation of HIPE and preparation of foams from HIPE

To prepare the HIPE, the water, oil and initiator phases included the components shown in Table 1 below.

TABLE 1 raw materials

The HIPE emulsification equipment was started according to the process flow shown in FIG. 1. The first circulation line is formed by a static mixer a (static mixer type Model GX, element combination 9.3 x 48: diameter 9.3mm, number 48) and a pump a (Herold WK-Pumps, three-blade screw rotor, rotor gap 0.04 mm) and its supporting lines (lines including temperature, pressure, flow rate measurement points). The aqueous phase was continuously pumped through a tubular heat exchanger at a flow rate of 81g/min, the temperature of the aqueous phase was controlled at 80 ℃ and delivered to the inlet upstream of the static mixer a. When the flow of the aqueous phase out of the outlet static mixer is observed (the outlet is higher than any one unit in the emulsifying device so that the pump does not run dry), pump A is started at a theoretical rate of 500 ml/min. The oil phase was pumped to the inlet of circulation pump A at a flow rate of 3.2 g/min. The emulsion now forms in static mixer a, a portion of the emulsion downstream of static mixer a enters the inlet of pump a for recirculation, another portion of the emulsion merges with the initiation phase (3.13 g/min) into the upstream inlet of the outlet static mixer (Model GX, 9.3 x 36+4.0 x 36: 36 elements with a diameter of 9.3mm in series with 36 elements with a diameter of 4.0 mm), undergoes further mixing shear, and a stable high internal phase emulsion is continuously output from the outlet static mixer, at a water to oil ratio of 26: 1.

The high internal phase emulsion is removed, deposited on a conveyor belt and continuously passed into a steam oven (temperature 98 ℃) to complete the polymerization.

Examples 2 to 9 and comparative examples 1 to 7:

the raw materials of the examples and comparative examples were identical, except that the variables were adjusted as shown in tables 2 and 3, the injection point of the oil phase A and the injection point of the water phase A in comparative example 1 were at the same position (upstream of the static mixer), and a two-blade rotor pump (rotor gap of 0.25 mm) was used in comparative examples 6 and 7, and the remainder was the same as in example 1.

TABLE 2 summary of the process parameter adjustments for the examples and comparative examples

TABLE 3 summary of the process parameter adjustments of the examples and comparative examples

The effects of the examples 1 to 9 and comparative examples 1 to 7 are shown in Table 4:

TABLE 4 effects of examples 1 to 9 and comparative examples 1 to 7

The technical effect can be seen that the example has uniform pore size distribution and no large pore size defect (the pores are all smaller than 120 μm), while the comparative example has pore size defect, specifically:

comparative examples 1 to 3 show that when the percent circulation is greater than 55%, the flow rate fluctuation is less than 30%, and the shear rate is greater than 1000S ^-1 When the pressure drop of the static mixer is more than 0.15MPa and the total pressure drop of the static mixer is more than 0.6MPa, the stable and uniform HIPE emulsion and the foam obtained by HIPE polymerization can be obtained by combining different forms of static mixing elements;

comparative examples 3 to 5 show that process scale-up can be easily achieved by using a static mixer;

compared with examples 6-7, the two-stage circulation process is adopted, so that the stable and uniform HIPE with high water-oil ratio can be obtained, and the process amplification is easy to realize;

compared with the comparative example 1, the water phase and the oil phase are added at different positions of the circulating pipeline, so that the stability of the circulating flow can be obviously improved, and stable and uniform emulsion and foam with uniform pore diameter can be obtained;

comparing example 4 with comparative example 2, the decrease in circulation flow rate of comparative example 2 resulted in the deterioration of the uniformity of the emulsion and the foam;

comparing example 4 with comparative example 3, the shear rate reduction of comparative example 3 results in poor emulsion stability;

comparing example 4 with comparative example 4, the shear rate of comparative example 4 is too high resulting in poor emulsion stability;

comparing example 4 with comparative example 5, the static mixing elements of comparative example 5 are small in number, and the pressure drop and the shearing time are insufficient to cause deterioration of the emulsion stability;

comparing example 4 with comparative examples 6 and 7, comparative examples 6 and 7 adopt a two-blade rotor pump, the rotor clearance is large, and the flow pulse and the internal reflux of the pump are increased, so that the stability of the emulsion is deteriorated;

in the prior art, the foam obtained by emulsifying and polymerizing the oil phase and the water phase which are considered to be good in dynamic mixing or static mixing plus dynamic mixing has the phenomenon of large pore diameter (larger than 200 mu m), and particularly, when the flow rate of example 5 is adopted, the prior art can not produce uniform emulsion and cannot be applied.

Claims

1. A process for continuously preparing a stable homogeneous high internal phase emulsion comprising the steps of: providing a mixing cycle unit comprising a static mixer and a pump; continuously injecting the water phase and the oil phase into a mixing circulation unit at different positions, and mixing in a static mixer to obtain an emulsion; then continuously injecting the emulsion into the static mixer through the pump to form circulation; a stable, uniform high internal phase emulsion is obtained downstream of the static mixer.

2. The continuous process for preparing stable homogeneous high internal phase emulsions according to claim 1 wherein the mixing cycle units are in one or more groups; when the mixed circulation units are in multiple groups, the mixed circulation units are connected in series; continuously injecting 55-99% of the emulsion into a static mixer through a pump to form circulation; the water phase and the oil phase are continuously injected into the mixing circulation unit at different positions, preferably, the water phase is directly injected into a static mixer, and the oil phase is injected into the static mixer through a pump.

3. The process for continuously preparing a stable homogeneous high internal phase emulsion according to claim 2 wherein the remainder of the emulsion is fed into an outlet static mixer to obtain a stable homogeneous high internal phase emulsion downstream of the outlet static mixer; or injecting the rest part of the emulsion and the water phase into an outlet end static mixer, and obtaining a stable uniform high internal phase emulsion at the downstream of the outlet end static mixer; or injecting the rest part of the emulsion and the initiator solution into an outlet end static mixer, and obtaining stable and uniform high internal phase emulsion at the downstream of the outlet end static mixer; or the rest part of the emulsion, the water phase and the initiator solution are injected into the outlet end static mixer, and a stable and uniform high internal phase emulsion is obtained at the downstream of the outlet end static mixer.

4. The continuous process for preparing a stable homogeneous high internal phase emulsion according to claim 2,characterized in that in the static mixer, the shear rate generated by the material flow is 500-10000S ^-1 Preferably 600 to 5000S ^-1 (ii) a The pressure drop of at least one static mixer is more than 0.15MPa, and the total pressure drop of the static mixer is more than 0.6 MPa; the flow rate fluctuation during the continuous preparation of the stable, uniform, high internal phase emulsion is less than 30%.

5. The method for continuously preparing a stable homogeneous high internal phase emulsion according to claim 2, wherein when the mixing circulation unit is a plurality of groups, 55% to 99% of the emulsion downstream of the previous static mixer is continuously re-injected into the static mixer through the pump to form circulation, and the rest of the emulsion is injected into the next static mixer.

6. The method for continuously preparing a stable homogeneous high internal phase emulsion according to claim 1 wherein the oil phase comprises oily monomers, emulsifiers; the water phase is water solution of water-soluble electrolyte.

7. A stable homogeneous high internal phase emulsion prepared according to the method of claim 1 for the continuous preparation of a stable homogeneous high internal phase emulsion.

8. The stable homogeneous high internal phase emulsion of claim 7, wherein the aqueous phase is from 10:1 to 75:1 as compared to the oil phase.

9. Use of a mixing and recirculation unit for the continuous preparation of a stable, homogeneous, high internal phase emulsion according to claim 1 wherein the mixing and recirculation unit comprises a static mixer and a pump.

10. Use of the stable homogeneous high internal phase emulsion of claim 7 in the preparation of a foamed material.