WO2023175530A1

WO2023175530A1 - Process for obtaining oxyalkylates in a loop reactor

Info

Publication number: WO2023175530A1
Application number: PCT/IB2023/052517
Authority: WO
Inventors: Jerzy WACEK; Miroslaw PLOCIENIAK
Original assignee: PCC Rokita SA
Current assignee: PCC Rokita SA
Priority date: 2022-03-17
Filing date: 2023-03-15
Publication date: 2023-09-21
Anticipated expiration: 2024-09-17
Also published as: PL440663A1; RO138586A2; HUP2200442A1

Abstract

The invention relates to a process for obtaining oxyalkylates by the addition reaction of at least one alkylene oxide to a starter being a chemical substance containing at least one active hydrogen atom in the presence of an alkaline catalyst carried out in a loop reactor. In the process according to the invention the circulation ratio K_c [h^-1] expressed as the ratio of the volume flow rate of the reactor circulating liquid V̇ [m³/h] to the volume of liquid in the reactor Vc [m³] defined by equation (1): K_c= V̇ / Vc (1) is at least 10 h^-1.

Description

PROCESS FOR OBTAINING OXYALKYLATES IN A LOOP REACTOR

Field of the Invention

The invention relates to a process for obtaining oxyalkylates by the addition reaction of at least one alkylene oxide to a starter being a chemical substance containing at least one active hydrogen atom in the presence of an alkaline catalyst, carried out in a loop reactor. The oxyalkylates obtained by this process are used, among others, in the manufacture of low-foam and anti-foam products intended for industrial cleaning, paper production or food processing.

Prior Art

Processes for obtaining oxyalkylates by the addition reaction of alkylene oxides to a starter (also referred to as an initiator), being a chemical substance containing at least one active hydrogen atom in the presence of an alkaline catalyst, are known in the art.

Typically, the process for obtaining oxyalkylates by the anionic polymerisation of alkylene oxides with an initiator containing active hydrogen atoms is carried out in a semibatch reactor into which an alkylene oxide or a mixture of such oxides is dosed at a defined rate after the addition of an initiator premixed with a catalyst such as KOH, while maintaining the required temperature and pressure. The dosing rate of alkylene oxide is determined by the amount of heat absorbed by the polymerisation reaction and the mass transfer rate of the reactants (Martino Di Serio, Riccardo Tesser, Elio Santacesaria "Comparison of Different Reactor Types Used in the Manufacture of Ethoxylated, Propoxylated Products" Ind. Eng. Chem. Res. 2005, 44, 9482-9489).

Conventional stirred reactors are characterised by a limited heat transfer surface area and a relatively low-efficiency mixing of reactants. When the oxide polymerisation reaction takes place in the liquid phase, it is important to have good contact between the monomer in the gas phase and the liquid because this determines its rapid conversion. Such conditions are ensured by the loop reactor, which, with the use of a pump, allows the reaction liquid to circulate through an external heat exchanger with a much higher cooling capacity than the stirred reactor. The loop reactor may have various additional mixing systems to contribute to the intensity of gas-liquid mixing, such as static mixers, mechanical mixers, jet mixers, diffusers. In the publication by G. Mugaishudeen and K. Saravanan "Influence of the sparger in a down flow jet loop reactor on the neutralization of alkaline solution by carbon dioxide absorption" (Bulgarian Chemical Communications, Volume 52, Issue 4 (pp. 435-439) 2020), the effect of the circulation rate of the alkaline solution on the change in its pH during the absorption of carbon dioxide (CO2) introduced into the reactor is presented. The study showed that, at a constant rate of gaseous CO2 supply, neutralisation of the alkaline solution (pH decrease) occurred faster as the rate of solution circulation increased. The additional placement of a gas sparger to intensify the mass transfere rate also resulted in shorter neutralisation times given the increasing circulation rate. The study showed that the mixing system (sparger) reduced the neutralisation time compared to the loop without any sparger for the same circulation rate.

US 8,461,285 discloses a method for obtaining polyether polyols by defining a range of input power per unit volume of reactor from 0.001 to 1 kW/m³ as the basic criterion for obtaining high-quality polyols.

For a loop reactor with a circulating pump, the input power is calculated according to the formula: P = Ap * rh where

Ap - pressure drop between the pump outlet and the reactor inlet [Pa], m - flow rate [m³/s].

Although the state-of-the-art processes described above have been successful in obtaining high-quality oxyalkylates, the need to provide even more efficient, and at the same time cheaper, manufacturing processes remains valid and real.

Summary of the Invention

In the course of the research work, the inventors found that, for a given dosing rate of alkylene oxide, a higher circulation ratio results in a lower pressure in the reactor during the reaction and a shorter time of the polymerisation reaction compared to the process carried out at a lower circulation ratio.

The object of the invention is therefore a process for obtaining oxyalkylates by the addition reaction of at least one alkylene oxide to a starter being a chemical substance containing at least one active hydrogen atom in the presence of an alkaline catalyst carried out in a loop reactor. The process according to the invention is characterised in that the circulation ratio K_c [h ¹] expressed as the ratio of the volume flow rate of the reactor circulating liquid V [m³/h] to the volume of liquid in the reactor Vc [m³] defined by equation (1):

K_c = V/ Vc (1) is at least 10 h ^-1, and preferably at least 20 h ¹.

Preferably, in the process of the invention, the alkaline catalyst is an alkali metal hydroxide or an alkoxide thereof, and in particular is selected from NaOH, KOH and CsOH or sodium, potassium and caesium alkoxides. Preferably, the alkaline catalyst is used in such an amount that the concentration of alkali metal ions in the product obtained in the process according to the invention is between 500 and 5000 ppm, preferably between 1000 and 3000 ppm.

Preferably, in the process according to the invention, the starter is selected from glycerol, trimethylolpropane (TMP), triethanolamine, propylene glycol, dipropylene glycol, ethylene glycol, diethylene glycol, n-butanol, o-toluylenediamine, sorbitol, saccharose, pentaerythritol, 2,2-bis(4-hydroxyphenyl)propane, methanol, allyl alcohol, methallyl alcohol, C6-C24 fatty alcohols, an alkylphenol preferably selected from nonylphenol and dodecylphenol, and an amine preferably selected from diethanolamine, triethanolamine and ethylenediamine.

Preferably, in the process according to the invention, the alkylene oxide is selected from ethylene oxide, propylene oxide, butylene oxide and mixtures thereof.

Preferably, in the process according to the invention, the circulation ratio in the loop reactor in the semicontinuous process decreases over the course of the reaction due to the increase in the volume of liquid Vein the reactor during the dosing of at least one alkylene oxide, expressed by equation (2):

Vc = (m_s + rhtt)/p (2) where m_s - initiator mass [kg] rht - oxide mass flow [kg/h] t - oxide dosing time [h] p - reaction liquid density [kg/m³]. Preferably, the process according to the invention uses a loop reactor having at least two loops and the volumetric flow of the reactor circulating liquid V is the sum of the flows of the operating loops Vj_: according to equation (3):

V= E Vi: (3) where i is an integer of at least 1.

Brief Description of the Drawing

The invention in an embodiment is illustrated in the drawing, wherein: Fig. 1 shows pressure profiles in the reactor during the dosing of ethylene oxide and digestion for the processes in Examples 1 and 2 discussed below.

Detailed Description of the Invention

The process for obtaining oxyalkylates according to the invention in a loop reactor having an external loop for the reaction liquid with a circulation pump and a heat exchanger consists in reacting a starter/initiator containing active hydrogen atoms with alkylene oxides in the presence of an alkaline catalyst. The circulation ratio Kc [h ¹] expressed by equation (1) above is at least 10 h ¹ and preferably at least 20 h ¹.

In a preferred embodiment of the process according to the invention, the reaction of the polyaddition of alkylene oxides to the starter is preceded by the formation of an alkoxide in the reaction of the starter with an alkaline catalyst from the group of alkali metal hydroxides such as NaOH, KOH, CsOH, used in such an amount that the concentration of alkali metal ions in the crude product (polyether polyol) is 500 to 5000 ppm, preferably 1000 to 3000 ppm.

In the reaction of the starter with an alkaline catalyst, (here KOH) occurring according to equation:

R-OH + KOH - ► R-OK + H₂O, water is formed as a by-product and must be removed from the reaction medium. The reaction which forms alkoxides takes place at an elevated temperature (100 - 130°C) and under maximally reduced pressure, allowing the removal of the water formed in the reaction to a content of less than 0.1 wt%, preferably less than 0.05 wt%. After dehydration, the starter-catalyst mixture is sent to the loop reactor, where it is heated to the required reaction temperature by activating the loop with a circulating pump through a heat exchanger. After heating to a reaction temperature determined according to the type of oxyalkylate, ranging from 70 to 180°C, and adding nitrogen in order to ensure control of the oxide concentration in the gas phase in the reactor, a required amount of alkylene oxide or a mixture of such oxides, selected from the group comprising ethylene oxide, propylene oxide and butylene oxide, is introduced at a predetermined dosing rate. The effective circulation ratio of the reaction liquid ensures that the heat of the reaction is removed and preferable mass transfer coefficients are achieved. For a semi-batch loop reactor, there is an increase in the volume of liquid Vc in the reactor during the dosing of at least one alkylene oxide, expressed by equation (2) given above.

During the reaction, the circulation ratio Kc decreases, from the highest value at the beginning of the synthesis to the lowest value at the end of the dosage of alkylene oxide/mixture of such oxides after the required molecular mass of the product, i.e. polyether polyol, has been achieved. An improvement, i.e. an increase in the circulation ratio, can be achieved by means of loop pumps with a power reserve, which allows the capacity of the loop pump to be increased as the volume of the reaction liquid increases, from the nominal capacity to the maximum capacity. Alternatively, an increase in the circulation ratio can be achieved by means of a second, parallel circulation loop, activated during the polymerisation reaction at a predetermined volume of reaction liquid.

It was found that, for a given dosing rate of alkylene oxide, a higher circulation ratio results in a lower pressure in the reactor during the reaction and a shorter time of the polymerisation reaction compared to the process carried out at a lower circulation ratio. Optimally, it is preferable for product quality and system efficiency to maintain a circulation ratio of not less than 10 [h ¹] and preferably not less than 20 [h ¹].

Examples

Example 1

40 kg of propoxylated glycerine with a molecular mass of 560 Da and 3.3 kg of 50% KOH aqueous solution were introduced into a preparator, the preparator was purged with nitrogen, the contents were heated to 110°C for 3 hours with continuous stirring and then, after activation of sparging with nitrogen and connection to a vacuum system, the water was distilled to a content of 0.04 wt%. The starter-catalyst mixture prepared in this way was introduced into a nitrogenated loop reactor equipped with a stirrer and an external loop system consisting of a loop pump and a heat exchanger. After the stirrer and the loop pump with the capacity 12060 l/h have started, nitrogen was added until a pressure of 1 bar was reached and 480 kg of propylene oxide was added into the reactor at a temperature of 112°C, maintaining a constant flow rate of propylene oxide of 40 kg/h.

After pressure stabilisation, degassing and re-nitriding, 80 kg of ethylene oxide was added at a temperature of 130°C while maintaining a constant flow rate of ethylene oxide of 40 kg/h. After digestion and removal of volatile components by degassing, the crude polyether polyol was sent for purification.

Example 2

The process from Example 1 was repeated with the same amounts of reaction substrates, the same parameters of temperature and dosing rate, but with the capacity of the loop pump reduced to 1842 l/h.

The comparative results obtained are compiled in the table:

Fig. 1 shows a graph illustrating pressure profiles during the dosing of ethylene oxide and the digestion period in the second phase of Example 1 and Example 2. In Example 1, the dosing time for ethylene oxide was 7620 seconds (2h 7 min), and in Example 2, it was 7230 seconds (2h 0 min).

Claims

Claims A process for obtaining oxyalkylates by the addition reaction of at least one alkylene oxide to a starter being a chemical substance containing at least one active hydrogen atom in the presence of an alkaline catalyst, carried out in a loop reactor, characterised in that the circulation ratio K_c [h ¹] expressed as the ratio of the volume flow rate of the reactor circulating liquid V [m³/h] to the volume of liquid in the reactor Vc [m³] defined by equation (1):

K_c = V/ Vc (1) is at least 10 h ¹. The process according to claim 1, characterised in that the circulation ratio K_c is at least 20 h ¹. The process according to claim 1 or 2, characterised in that the alkaline catalyst is an alkali metal hydroxide or an alkoxide thereof, and preferably is selected from NaOH, KOH and CsOH or sodium, potassium and cesium alkoxides. The process according to one of claims 1 to 3, characterised in that the starter is selected from glycerol, trimethylolpropane (TMP), triethanolamine, propylene glycol, dipropylene glycol, ethylene glycol, diethylene glycol, n-butanol, o-toluenediamine, sorbitol, saccharose, pentaerythritol, 2,2-bis(4-hydroxyphenyl)propane, methanol, allyl alcohol, methallyl alcohol, C6-C24 fatty alcohols, an alkylphenol preferably selected from nonylphenol and dodecylphenol, and an amine preferably selected from diethanolamine, triethanolamine and ethylenediamine. The process according to one of claims 1 to 5, characterised in that the alkylene oxide is selected from ethylene oxide, propylene oxide, butylene oxide and mixtures thereof. The process according to one of claims 1 to 6, characterised in that the circulation ratio in the loop reactor in the semicontinuous process decreases over the course of the reaction due to the increase in the volume of liquid Vein the reactor during the dosing of at least one alkylene oxide, expressed by equation (2):

Vc = (m_s + rh_tt)/p (2) where m_s - initiator mass [kg] rht - oxide mass flow [kg/h] t - oxide dosing time [h] p - reaction liquid density [kg/m³]. The process according to one of claims 1 to 7, characterised in that a loop reactor having at least two loops is used and the volumetric flow of the reactor circulating liquid V is the sum of the flows of the operating loops Vj_: according to equation (3):

V= E Vi: (3) where i is an integer of at least 1.