EP3057938A1

EP3057938A1 - Method for ageing the reaction mixture in a sulfonation process

Info

Publication number: EP3057938A1
Application number: EP13779230.5A
Authority: EP
Inventors: Arkadiusz Chrusciel; Alfred Smyrek; Eugeniusz PRUS; Wolfgang Weber; Dirk HOLBACH; Thomas Müller-Kirschbaum
Original assignee: Henkel AG and Co KGaA; Henkel Polska Sp zoo
Current assignee: Henkel AG and Co KGaA; Henkel Polska Sp zoo
Priority date: 2013-10-18
Filing date: 2013-10-18
Publication date: 2016-08-24
Also published as: WO2015055251A1

Abstract

A method and a plant for ageing a liquid post-sulfonation reaction mixture comprising linear alkylbenzenesulfonic acid and unreacted linear alkylbenzene using a system of two or more stirred tank reactors which are operated in cycles in filling steps, during which there runs the first step of continuous ageing at nonsteady-state conditions, followed by ageing steps in batch process conditions.

Description

Method for ageing the reaction mixture in a sulfonation process Field of the invention

The present invention relates to the technology to carry out a continuous chemical process in a liquid reaction mixture, using continuous stirred tank reactors (CSTR). A modified, improved method to carry out a chemical process running in the kinetic area, specifically relatively slow chemical reactions of ageing a post-sulfonation mixture in a plant producing alkylbenzenesulfonic acid (LABSA) by sulfonating alkylbenzene using a sulfonating agent, particularly sulfur trioxide, is the subject of the invention. Furthermore, the invention relates to the plant for conducting the above-mentioned improved ageing method and to a method for the plant operation. Specifically, the invention relates to a modified, improved method to conduct the process of ageing a post- sulfonation mixture in an plant producing alkylbenzenesulfonic acid (LABSA), using a system of two or more stirred tank reactors, operated in a combined batch-and-continuous manner, comprising the reactor operation steps in a continuous unsteady state and steps of operation in batch process conditions as well as to a method to modify the ageing unit for handling the post-sulfonation mixture of an existing chemical facility, by means of a solution presented in the description of the invention.

In contrast to a conventional, state-of-the-art solution for the process of ageing a post-sulfonation mixture, in which a single ageing volume is used and the process is carried out in a continuous manner at steady-state conditions, the process conditions in the proposed solution are similar to a batch process or to a continuous process being carried out in a plug-flow tubular reactor, which enables elimination of dilution of the maturing reaction mixture with the incoming "fresh" stream of unreacted reaction mixture, which takes place in a continuous process, furthermore, the product has much better quality-determining parameters, such as the content of active matter (AM), unreacted substrate, and color.

Description of related art

Alkylbenzenesulfonic acid is an anionic surfactant and essential component of detergent formulations (mainly in its sodium salt form) for household and industrial use, a component of washing, dish-washing, and cleaning powders and liquids. LABSA is also used in other industries as a component of mixtures used for modifying the surface properties of aqueous solutions.

A well established state-of-the-art method to obtain alkylbenzenesulfonic acid in a commercial scale is based on the sulfonation of alkylbenzene after obtaining it usually by alkylation of benzene in the presence of a Friedel-Crafts catalyst. The sulfonating agents used are 20% oleum, sulfuric acid or sulfur trioxide or, less frequently, chlorosulfonic acid.

The most frequently used commercial method to obtain alkylbenzenesulfonic acid is by sulfonation with sulfur trioxide. The process of technology to manufacture LABSA by sulfonation with S0₃ comprises a number of steps, such as the obtaining of sulfur trioxide by sulfur combustion to obtain sulfur dioxide and its catalytic conversion as well as reacting sulfur trioxide with an organic raw material (alkylbenzene), digestion, hydrolysis of anhydrides and optional neutralisation.

Developments made in the technology to obtain LABSA in the recent couple of decades relate mainly to methods for carrying out the step of fast, exothermal sulfonation reaction, specifically to the aspect of its intense cooling, and the liquid-gas phase contact surface.

The method for conducting this step of synthesis using a cascade of tank reactors was described, for instance, in GB Pat. 664577, GB Pat. 988689, GB Pat. 1 121366, US Pat. 3198849,

US Pat. 3259645, US Pat. 3257175, US Pat. 3620684. The patents describe different CSTR solutions, specifically the issue of intense cooling of the reaction mixture by means of an internal cooling water coil, because of the requirement to maintain the reaction medium within a narrow range of relatively low temperatures. The step of ageing the post-sulfonation mixture tended to be solved by means of a commonly known, prior-art technique of using a retention volume prior to stabilization by hydrolysis. US Pat. 3243453 relates to a semibatch process of sulfonation. The method consisted in conducting a batch process of S0₃ absorption in a weighed amount of LAB to obtain the weight of LABSA resulting from the reaction stoichiometry.

A considerable progress in the intensification of cooling and improvement of the sulfonation reaction yield and final product quality was to use a film reactor, in which the sulfonation reaction runs between the gaseous substrate in the form of a mixture of S0₃ in inert gas (usually air) and a thin, organic substrate film flowing down the heat transfer surface. The solution is the subject of the inventions referred to in IT Pat. 1 124072, GB Pat. 2043067 describing multitube film reactors or US Pat. 5136088, US Pat. 20080306295 describing falling-film reactors, as well as their application in the sulfonation of selected organic raw materials, including LAB.

The commercial sulfonation facilities which are used at present and are based on the processes of technology licenced by e.g. DESMET BALLESTRA S.p.A., CHEMITHON, MAZZONI and other ones. The ageing process is effected by using a retention volume in the form of a typical, usually single continuous stirred tank reactor, operated at steady-state conditions. Information about that commonly used process of technology is provided in generally available descriptions and studies (e.g.: H. de Groot: Sulfonation Technology in the Detergent Industry. BALLESTRA S.p.A. Kluwer Academic Publisher, Dodrecht-Boston-London 1991 ).

Summary of the invention

Alkylbenzenesulfonic acid, which is commercially obtained in a process of technology comprising a naturally fast sulfonation reaction and a naturally slow ageing process, typically contains >90% of what is called active matter in the form of alkylbenzenesulfonic acid, approx. 0-3% of a matter other than the useful component, so-called free oils, and small amounts of water and sulfuric acid. The free oils fraction should contain <1 % sulfones, only traces of paraffins which contaminate the LAB raw material, and < 3% of linear alkylbenzene - the unreacted raw material. While the last mentioned component is a raw material which can be converted to obtain a useful component, both the sulfones and the paraffins are impossible to be converted to useful sulfonates, thus limiting process yield.

LAB conversion to LABSA may be improved by extending its time of residence in the ageing unit, which is generally known to those skilled in the art. Furthermore, those skilled in the art are aware of the fact that a maximum increase in conversion in the ageing process being conducted in a conventional state-of-the-art process of technology, i.e., in a CSTR reactor, is observed during the initial first hour. After that time, the increase in conversion is rather low; on the other hand, the process of ageing in conditions of high average residence times for the reaction mixture in CSTR's (large reactor tank volumes), has the disadvantage of side processes which occur leading to deep coloration of final product, as measured in the Klett color scale. In facilities based on sulfonation in film reactors and ageing with the use of ageing volume, a low-color product (Klett Colour < 25) is obtained for a relatively low content of active matter and higher content of unreacted LAB, which is known to those skilled in the art. Since the costs of raw materials are high, potential savings on the costs of manufacturing connected with potentially higher conversions are significant.

The reduced content of unreacted LAB, which is to be understood as a higher content of active matter due to the much longer time of residence in the ageing reactor tank, leads to much deeper coloration of product (Klett Colour » 25), thereby affecting its commercial attractiveness and limiting its applicability.

Surprisingly, it was found that the use of a solution for the ageing of alkylbenzenesulfonic acid according to the invention, i.e., the solution comprising two or more stirred tank reactors operated in a combined batch-and-continuous manner, and comprising the steps of reactor operation in a continuous unsteady state and steps of operation in batch process conditions has led to increased reaction yields, as measured by the value of active content and the content of free LAB, in addition to the obtaining of a final product having a low Klett color, definitely lower than the color of a product obtained during a comparable residence time in a typical ageing unit of which the design is known in the art and which comprises a single CSTR operating in continuous steady-state conditions. The above effect, obtained for the solution of the invention is a very important element of novelty and industrial usefulness of the subject of the invention.

Specifically, in the proposed solution, for relatively short (approx. 2 hrs) times of residence in the ageing unit, the obtained active matter content was 98.2% while the content of unreacted LAB was reduced to 0.0-0.1 %. Surprisingly, it was found that the color of the resulting product was rather low (<13) while conventional processes which are established in the art provide products with Klett colours of above 30 for comparable deep conversions of LAB; this disqualifies the products as raw materials for e.g. liquids, which require LABS with Klett colours of 25 or less. In the proposed improved solution for a post-sulfonation mixture ageing unit, two or more stirred tank reactors are used so that the tanks are operated in cycles in filling steps, during which there runs the first step of continuous ageing at nonsteady-state conditions, followed by ageing steps in batch process conditions. For the existing facility, modification consists in adding more tank reactors, in a particular case, one reactor. The gist of the invention is in the method to operate the reactor system, enabling the process conditions in the proposed solution to be similar to those of a batch process or to the operating conditions prevailing in a plug-flow tubular reactor, where the reaction mixture will not become diluted with more portions of "fresh" post-sulfonation mixture. The resulting improved reaction yield follows directly from the reactor's basic mass balance. According to the invention, the ageing process is carried out at unsteady-state conditions in its first step while feeding the reactor at a rate which is determined by the plant throughput, whereupon, after filling the first reactor and reaching a conversion which results from the time of filling the tank, the feeding process is discontinued and the second step of ageing is commenced in strictly batch process conditions without feeding the stream of unreacted post-sulfonation mixture. In the second step of ageing, the level of LAB decreases at a faster rate without being disturbed by more portions of the unreacted mixture; this results directly from the reactor's mass balance for this step of the process. In order to provide a continuous flow and maintain the plant throughput, the second tank reactor, in which there runs the ageing process at unsteady-state conditions, is filled during the second step. After filling the second reactor, the first reactor is emptied batchwise and the aged reaction mixture is sent to the hydrolysis reactor which is operated as a batch reactor in spite of being known in the art as a continuous reactor, and then is sent to a storage tank after being cooled down in a heat exchanger which is known in the art.

In a first aspect, the invention is thus directed to a method for ageing a liquid post-sulfonation reaction mixture comprising linear alkylbenzenesulfonic acid (LABSA) and unreacted linear alkylbenzene (LAB), said reaction mixture being obtained by a continuous chemical process of sulfonating linear alkylbenzene using a sulfonating agent, the method using a system of two or more stirred tank reactors and comprising the steps of:

(i) feeding a continuous stream of said reaction mixture into a closed first stirred tank reactor;

(ii) upon reaching a predetermined maximum reaction mixture level in the first stirred tank reactor discontinuing feeding the continuous stream of reaction mixture into the first stirred tank reactor and starting feeding the continuous stream of reaction mixture into a closed second stirred tank reactor;

(iii) ageing the reaction mixture in the first stirred tank reactor for a predetermined ageing time period to obtain an aged reaction mixture;

(iv) removing the aged reaction mixture from the first stirred tank reactor;

(v) upon reaching a predetermined maximum reaction mixture level in the second stirred tank reactor discontinuing feeding the continuous stream of reaction mixture into the second stirred tank reactor and starting feeding the continuous stream of reaction mixture into (a) the emptied closed first stirred tank reactor, or (b) a closed third stirred tank reactor;

(vi) ageing the reaction mixture in the second stirred tank reactor for a predetermined ageing time period to obtain an aged reaction mixture;

(vii) removing the aged reaction mixture from the second stirred tank reactor; and

(viii) repeating steps (ii) to (vii) if a system of two stirred tank reactors is used, or, if a system of three or more stirred tank reactors is used, repeating steps (v) to (vii) for the third and each subsequent stirred tank reactor before repeating steps (i) to (vii) for the first and second stirred tank reactor.

In various embodiments of this method a system of two stirred tank reactors is used and steps (iii) and (iv) are performed while feeding the continuous stream of reaction mixture into the second stirred tank reactor and prior to reaching the predetermined maximum reaction mixture level in the second stirred tank reactor.

In alternative embodiments, a system of three or more stirred tank reactors is used and steps (iii) and (iv) are performed while feeding the continuous stream of reaction mixture into the second, third or any subsequent stirred tank reactor and prior to reaching the predetermined maximum reaction mixture level in the second, third or any subsequent stirred tank reactor.

In the above described methods, the volume of the stirred tank reactors may be selected such that ageing and removing the reaction mixture from a given stirred tank is completed before the next cycle of feeding the continuous reaction mixture stream into said given tank reactor starts.

In specific embodiments of the invented methods, the method further comprises the step of (ix) feeding the aged reaction mixture into a hydrolysis reactor where it is combined with an amount of water necessary to stabilize the aged reaction mixture, preferably < 2 wt.-% water relating to the amount of the aged reaction mixture, wherein the hydrolysis reactor preferably has a volume equal to or larger than that of the largest stirred tank reactor used for ageing the reaction mixture; and optionally (x) feeding the stabilized aged reaction mixture, optionally after cooling, into a final product storage tank.

Each of the stirred tank reactors may comprise (a) at least one inlet, preferably having a valve and preferably being arranged at the top or the upper half of the stirred tank reactor; (b) at least one closable outlet, preferably having a valve and preferably being arranged at the bottom of the stirred tank reactor; (c) at least one level indicator allowing to determine the maximum reaction mixture level in said reactor; and/or (d) a cooling system to control the reaction mixture temperature in the reactor.

In various embodiments of the above methods, the step of feeding the reaction mixture into a tank reactor is performed in about 0,5 to about 2 h, preferably in about 1 h. The steps of feeding the reaction mixture into a tank reactor, ageing the reaction mixture in the tank reactor and removing the aged reaction mixture may be performed in about 1 ,5 to about 3 h, preferably in about 2 h. In another aspect, the present invention relates to a plant for the production of linear alkylbenzenesulfonic acid (LABSA) by a continuous chemical process of sulfonating linear alkylbenzene (LAB) using a sulfonating agent, the plant comprising a sulfonation unit and an ageing unit, characterized in that the ageing unit comprises two or more parallely operated ageing reactors and a single stabilization reactor, wherein the two or more ageing reactors are each connected to a common pipeline that alternately feeds a reaction mixture obtained in the sulfonation unit into said ageing reactors via an inlet stub pipe, and a common pipeline that feeds the aged reaction mixture into said stabilization reactor via an outlet stub pipe.

In this plant, the stabilization reactor (R4) may have a volume larger than or equal to the volume of the largest ageing reactor (R1 , R2, R3).

In various embodiments of the plant, each ageing reactor comprises: (a) a valve (V1.1 , V2.1 , V3.1 ) for opening and closing the inlet stub pipe; (b) a valve (V1.2, V2.2, V3.2) for opening and closing the outlet stub pipe; and/or (c) a level indicator (LICA1 , LICA2, LICA3) allowing to determine the maximum reaction mixture level in said ageing reactor; and/or a cooling system.

In various embodiments, the stabilization reactor (R4) is equipped with an inlet for the aged reaction mixture, an inlet for process water, an outlet for the product, and optionally a pump (P) for emptying the stabilization reactor. The outlet of the stabilization reactor may comprise a valve (V4.2) for opening and closing the outlet.

The sulfonation unit can be a cascade system of reactors or a film reactor or any other type known in the art.

The ageing reactors may be stirred tank reactors, for example those conventionally used in continuous processes, i.e. continuos stirred tank reactors (CSTRs).

The plant may further comprise a storage container connected to the stabilization reactor (R4) for storing the final product. Also a heat exchanger arranged between the stabilization reactor (R4) and the storage container may be present to cool the product fed from the stabilization reactor into the storage container/vessel.

In still another aspect, the invention also encompasses a method for operating the above plant according to the invention, comprising operating a system of two or more ageing reactors (R1 , R2, R3) in a combined continuous-and-batch manner, comprising the steps of operating the reactors in a continuous unsteady state and batch process conditions, by

(i) feeding a continuous stream of a reaction mixture from the sulfonation unit into a first ageing reactor (R1 );

(ii) discontinuing the feeding upon reaching a maximum reaction mixture level in said ageing reactor;

(iii) ageing the mixture in the filled ageing reactor for a predetermined ageing time period to obtain an aged reaction mixture; and

(iv) emptying the ageing reactor by feeding the aged reaction mixture into the stabilization reactor (R4); (v) adding process water to the stabilization reactor (R4) and incubating the

mixture for a predetermined time period to obtain the product; and

(vi) emptying the stabilization reactor (R4) by feeding the product into a storage container optionally including the step of cooling the product during feeding into the storage container by means of a heat exchanger (E);

(vii) repeating steps (ii)-(vi) for the second and each subsequent ageing reactor, wherein the step of feeding the second and each subsequent ageing reactor is commenced upon discontinuing the feeding into the respective preceding ageing reactor; and

(viii) repeating steps (i)-(vi).

In the above method feeding and emptying the ageing reactors may be controlled by means of automatic inlet valves (V1.1 , V2.1 , V3.1 ) and automatic outlet valves (V1.2, V2.2, V3.2) and level indicators (LICA1 , LICA2, LICA3). Similarly, emptying the stabilization reactor may be controlled by means of an automatic outlet valve (V4.2) and/or achieved by means of a pump (P).

Detailed description of the invention

Chemical reactions and the unit processes of sulfonation and ageing

The commercial synthesis of LABSA runs, generally, in two consecutive reactions, as reflected in the design of LABSA manufacturing plants and their separation into two unit processes:

Unit process 1 is the reaction between LAB and S0₃ in which p rosulfonic acid is generated:

The above reaction runs at a fast rate and, most usually, is conducted in a CSTR type sulfonator or in a CSTR cascade reactor system, or in a film reactor.

Unit process 2 is the so-called ageing step and is intended to increase the reaction yield. It is connected with the course of the reaction between the previously formed pyrosulfonic acid and any residual uncreacted LAB, according to Eguation (2)

Process (2) is several dozen times as slow as step (1 ), therefore, it is necessary to separate the reaction and use an additional unit for what is called "ageing" in the form of retention volume.

The kinetics of process (2) is affected by the course of an eguilibrium reaction in which sulfonic anhydride is formed: + H₂S0₄ (3) and its consequent conversion to LABS:

Any residual sulfonic anhydride, which remains unreacted after the process of ageing, is converted to LABS in the stabilization process:

In connection with considerable concentrations of pyrosulfonic acid being formed in the unit process (1 ) and with the completed average time of residence in the reaction unit with S0₃ (1 -2 min in the case of the film reactor), part of the pyrosulfonic acid is converted to LABSA as early as in the unit process 1 .

Since the ageing process (2) runs at a slow rate, some quantities of pyrosulfonic acid are not converted in the step of ageing. Any unreacted pyrosulfonic acid is hydrolyzed in the stabilization step according to the equation describing the reaction which is the source of sulfuric acid:

The sulfonation process is accompanied by undesirable side reactions one of which is the reaction, leading to the formation of sulfones which are impossible to be converted to LABS or eliminated by any steps:

The sulfones are a component of the free oils fraction and are present at a concentration of <1 %.

The ageing process kinetics, the conditional reaction rate constant

For engineering purposes, it has been assumed that the course of the ageing process is determined by reaction (2) while processes (3) and (4) are the links of a chain of consecutive reactions which constitute process (2) and any unreacted anhydride is neglected for the precision of these considerations which was assumed for technical purposes. Assuming that a half of the raw material is reacted in the step of fast sulfonation as described in Eguation (1 ), given an

approximately stoichiometric ratio of S0₃ to LAB (the molar ratio of S0₃:LAB = 1.01- 1 ,03: 1 ), the molar concentration of pyrosulfonic acid in the reaction mixture is approximately egual to that of LAB. Therefore, hypothetically, Eguation (8) can be used for describing the rate of reaction (3):

_ ^{d C}LAB _ _{! r r} _ _kci ^mo1 _m

'LAB ^{~ ~} ^PSA^LAB — ^LAB ' _T . °' at L - min or

^Γ LAB ^' 7 ^{~~ W}LAB ' ~ (9) at min

wherein

r_LAB - rate of conversion of LAB, mol/L min

r'LAB - rate of conversion of LAB, %/min

CPSA - molar concentration of pyrosulfonic acid (PSA) in the reaction mixture, mol/L

CLAB - molar concentration LAB in the reaction mixture, mol/L

k - reaction rate constant, (mo///.) ¹ m n^A

k' - conditional reaction rate constant (at a stable temperature), (%-min)^A

WLAB - mass fraction of LAB, %

The solution to Equation (9) leads to Equation (10) which enables determination of the reaction rate constant:

1 1

= k't + (10) w_LAB (t) w_LAB (0)

unless the assumption of the reaction order n=2 is incorrect.

Fig.1 shows the graph of LAB reverse mass fraction vs. time realationship in the process of batchwise ageing of the reaction mixture. The fit between the curve and the measurement points is good, indicating that the reaction order assumption in the measurement conditions is sufficiently correct.

The value of the conditional reaction rate constant was 0.19 (%-min)^'

Ageing reactor mass balance models for various cases of operation

Fig .2 shows a simplified diagram of the ageing process strirred tank reactor.

The mass balance for LAB in the ageing reactor is described by the mass balance basic stream eguation:

mLAB(0) + ^mLAB(r) ^{~ m}LAB(\) + ^mLAB(c) C ^ ) wherein:

m_LAB(0) - mass stream of LAB at the inlet to the reactor, kg-min^

m_LAB{r) - rate of LAB loss as the result of the chemical reaction, kg-min^ ™LAB(\ ' stream of LAB at the outlet from the reactor, kg-min^

m_LAB{c) - accumulation of LAB in the reactor, kg-min^

Assuming that the density of the reaction mixture in the ageing process is constant it can be shown that the above streams are linked by the following relationships:

r^hLAB₍₀) = ^rh - ^WLAB_{( 0}) 02) m LAB(r) (13)

m LAB l) m-w_LAB(t) (14) m - total reaction mixture mass stream, kgmiri

- concentration of LAB in the incoming stream to the reactor, %

- rate of changes of LAB mass in the reactor tank as a result of the chemical

reaction (2), kg-min^

m_v(t) - reaction mixture mass in the reactor tank at the time f, kg

( ^w_LAB(t)

- rate of increasing in LAB concentration in the reaction mixture as a result of the dt

chemical reaction (2), kg-min^

w_LAB(t) - concentration of LAB in the reaction mixture in the reactor tank, %

Material balances for three cases of the reactor's operation were considered in developing an optimum solution for an ageing unit according to the invention, including the batch process reactor, the continuous reactor, and the continuous reactor operated at unsteady-state conditions with accumulation of LAB.

1 ) batch process at unsteady-state conditions

The following conditions are satisfied for the operation of the ageing unit in purely batch process conditions:

mLAB(0) ^{~ m}LAB(\) 0 (16) and

wi_y (t) = const (17) therefore, given Equations 11 -15:

mLAB(r) ^{~ m}LAB(c) (18) and k'[w_LAB(t)] (19) dt

The solution to Equation (19), which corresponds to the basic kinetic Equation (9), provides the LAB concentration vs. time relationship which is similar to that for Equation (20): WLAB (0 = (20)

0.19t +

^WLAB(0)

2) continuous process at steady-state conditions

The continuous stirred tank reactor is operated at steady-state conditions for which the rate of accumulation of matter is equal to 0, from which the constant concentration of LAB results:

* ) ^{= 0} (²¹) w_LAB(t) = w_LAB = const (22) Assuming that the mass reacting in the reactor volume is constant, the mass balance for the continuous reactor is described by Equation (23):

mLAB(0) + ^mLAB(r) ^{= m}∑AB(l) (^3) hence

m^{■ W}LAB(O) - m_vk'w_L ² _AB = m^■ w_LAB (24) or

t^{■ k}'^wL²As - w_LAB + w_LAB(0) = 0 (25) where t is the average residence time, defined by the relationship: t=— ,min (26) m

The solution to Equation (25) provides the following relationship between LAB concentration and average residence time:

3) continuous process at unsteady-state conditions

Since the mass flow rate of the reaction mixture has a finite value, some attention was focused on a variant of the reactor's operation in the process of filling the tank with the reaction mixture, with the simultaneous course of the process, running at unsteady-state conditions.

For the particular case of the reactor's operation at unsteady-state conditions, in the absence of an outflow of the reaction mixture from the reactor, as defined by the condition (filling step):

m -LAB(Y) ^~ 0 (28) the reactor's mass balance equation takes the form:

m LAB(0) + m 'LAB(r) = m 'LAB(c) (29) and, given Equations 11 -15: , . dm_v (t) ,„(t)

™- _LAB(0) - m_v (t) . k'[w_LAB (t)]² = w_LAB (t)—p- + m_r (t) * ^K (30) at at

In connection with the relationship:

m_v (t) = m - t (31 ) Equation (30) takes the form of a Riccati type differential Equation (32):

^ W_LAB {t) ₂ W_LAB (t) W_LAB(0)

—— - ^~k \ w_LAB (t)\ — +— -—

at t t

A numerical approach was applied to solving Equation (32) for the purpose of the invention.

The course of variations of LAB concentration for different forms of mass balance for the ageing reactor and for the solution according to the invention

Fig.3. shows the curves of variations of LAB concentrations in time for the following cases: batch process (curve 1 ), prior-art continuous process (2) (dependence on average residence time), unsteady continuous process - filling stage (curve 3), unsteady batch process - ageing stage (curve 4).

The process of the invention describes a system of curves, comprising curve 3 - point A - curve 4. In the first step of the process of the invention, the process is conducted at continuous unsteady- state conditions without taking the reaction mixture from the tank while filling the stirred tank reactor after it was emptied. The content of LAB goes down in connection with its conversion, according to Eguation (32), which is shown graphically by curve obtained by solving Eguation (32) numerically. After reaching the maximum level in the reactor's tank (point A in the diagram - Fig. 3.) the inflow of the reaction mixture is stopped and the reaction mixture is aged while the concentration of LAB is reduced along curve described by the following eguation which is correct for a typical batch process: w LAB (33)

^WLAB(A)

wherein:

t_A - time at point A, min

WI_AB(A) - content of LAB at point t_A in the reaction mixture, %

The course of curve 3-A-4, i.e., the one showing variations in the LAB content according to the assumptions of the invention, indicates that the content w_LAB for e.g. f=120 min should be definitely lower than the LAB content achieved for the same residence time in a typical CSTR reactor system being operated in a prior-art ageing system, commonly used in known LAB sulfonation plants. Expectations based on the course of the model curves have been confirmed by experimental results, obtained in tests carried out in industrial facilities (see Example 2, 3.) As expected from the course of variations of LAB concentration in Fig. 3, the drop in LAB concentration after extending the time of residence of the reaction mixture being aged at continuous conditions or using a larger ageing reactor volume according to state-of-the-art solution by reducing the plant capacity thereby reducing the mass flow rate, appeared to be insignificant in comparison with the decrease in LAB concentration, achieved using the system of the invention (see: Example 4.). While the unreacted LAB content was stable at 0.58% after 120 min and remained at that level for as long as 240 min, the level of unreacted LAB in an example according to the invention was 0.0% after only 120 min. This means that the achieved active matter levels were significantly higher (98.2%), compared with those of LAB, achieved by means of the prior-art solution (97.6%).

Surprisingly, it was found that the color indicator for the LABSA obtained according to the invention is much lower (Klett colour 15), compared with the color obtained by extending the residence time.

Description of the ageing plant and the method of its operation according to the invention

The ageing plant of the invention is shown in Fig. 4. In contrast to the prior-art ageing plant comprising a single ageing reactor operated in a continuous manner, the plant of the invention comprises a parallel system of 2 or more ageing reactors (R1, R2, R3) and a single stabilization reactor R4 with a working capacity egual to that of the largest of the reactors R1-R3 (or they may have same capacities). Even though reactor R4 is provided in prior-art solutions, the solution of the invention provides, at this point, for a reactor which is operated in batch process conditions.

Reactors R1-R3 are fed alternately with a reaction mixture from their common pipeline by means of automatic valves V 1.1., V 2.1., V 3.1. and are emptied alternately by means of automatic valves

V 1.2., V2.2., V3.2. Reactors R1-R3 are eguipped with level indicators LICA1, LICA2, LICA3, respectively. The stabilization reactor R4 according to prior-art solutions is fed with a reaction mixture from one of reactors R1-R3 and is emptied using valve V.4.2. and pump P. The reactor system's operation, i.e., filling and emptying through valves V 1.1. , V 2.1., V3.1., V 1.2., V2.2.,

V 3.2., V.4.2., pump P, is controlled automatically by means of a reaction mixture level indicator system LICA1, LICA2, LICA3 in reactors R1-R3 which are connected with a programable logic control unit. In contrast to a typical prior-art solution for ageing systems, where the ageing process is carried out in a continuous manner in continuous stirred tank reactors and the conversions achieved depend on the reactor volume, the solution of the invention provides for the use of two or more reactors being operated alternately so that the reaction mixture from the sulfonation unit, which is operated using a prior-art cascade system of reactors or a film reactor, is fed to the previously emptied tank reactor R1 through a stub pipe with valve V1.1 while valve V 1.2. is closed. While that reactor is filled at a rate which is determined by the flow rate indicated by the plant capacity, during the fill time of approx. 1-2 hr, there takes place the ageing process at unsteady- state conditions. The course of the ageing process at unsteady-state conditions is shown by the curve illustrating the LAB concentration vs. time relationship (Fig. 3. curve 3-point A.). Initially during the filling step, the LAB concentrations indicated by the solution to the balance eguation (29) are somewhat higher than the content for curve (2) because of the high ratio of the mass of the "fresh reaction mixture" with a rather high content of unreacted LAB to the mass of the ageing mixture in the tank. The amount of the post-reaction mixture in the tank will increase in time while the influence of the mixture volumes being introduced will be less pronounced, as the result of which the concentration curve will be approaching that for a continuous process.

After the maximum level in the tank, as controlled by level indicator LICA 1, is reached the stream being fed to that tank, i.e., the post-sulfonation mixture is switched to the other, previously emptied reactor R2, by closing valve V1.1. and opening valve V 2.1. The process taking place in the other reactor while it is being filled is similar to that previously described; after filling the first reactor, a batch process runs in it according to Equation (30) and curve 4 Fig.3. After the maximum level is reached in reactor R2, the maximum level signal from level indicator LICA2 closes valve V2.1 , whereupon reactor R3 starts to be filled if there are more than two reactors in the system. After the lapse of ageing time in reactor R1 , resulting from the quantity of reactors in the ageing system, the first filled reactor (R1 ) is emptied gravitationally at a high rate during approx. 1 min by opening valve V.1.2. so that the emptying time will not disturb the process continuity; the material is sent to the tank of reactor R4 which is fed with such an amount of process water as is indispensable to stabilize the aged reaction mixture and then, after the lapse of time which is indispensable for hydrolysis (<10 min), the material from reactor R4 is sent to the final product tank. The amount of water which is indispensable for stabilization is known from prior-art solutions and is <2% by weight.

As soon as reactor R1 is empty, valve V.1.2. is closed automatically and valve V.1.1. is opened to commence the cycle of filling reactor R1. Before the maximum permissible level in reactor R1 is reached, V.2.2. is opened to remove the aged reaction mixture from reactor R2, and valve V.2.2. is closed and, similarly, valve V.3.2 is opened etc.

The reactor filling and emptying cycles are carried out using a system of level indicators LICA1 , LICA2, LICA3 and automatic valves V1.2 - V3.3. which are connected to the PLC unit.

The ageing unit operation time diagram of the invention is shown in the form of the Gantt chart in Fig. 5.

The plant start up procedure is commenced by filling reactor R1 during 0 - 60 min. The ageing process in this step runs according to Equation (32) (Fig.3. curve 3). After filling reactor R1 , ageing of the mixture contained in it is commenced in batch process conditions, according to Equation (33) (Fig.3. curve 4) during 60-178 min; also during that time, i.e., during 60-120 min, the filling of reactor R2 is commenced.

After the lapse of approx. 178 min the material in reactor R1 is emptied to reactor R4. The mixture in reactor R4 is stabilized by introducing water in accordance with prior-art solutions, mixed for 5 min and is then removed through heat exchanger E during approx. 53 min. The operating cycle for reactor R1 is repeated for each consecutive reactor, due to which a single batch leaves reactor R4 during every hour of the system's operation while the plant capacity is maintained. Owing to the solution of the invention, after the lapse of the ageing time indicated by the number of reactors, several times as low, near-zero values of LAB concentration are obtained by increasing conversions, higher than those known from prior-art solutions for same residence times. This is an effect of making the course of the process similar to that running in batch process conditions or in continuous conditions in a plug-flow tubular reactor. Surprisingly, it was found that running the ageing process in a system of the invention gives products having Klett colours several times as low as in other, prior-art solutions for same residence times.

The above effect is explained as the result of running the reaction at a relatively short time which prevents the occurrence of any side-processes leading to the formation of colored compounds; regrettably, the latter is observed in prior-art solutions where the residence time in the ageing unit is several times as long. The above effect is considerable progress and evidence of the particular usefulness of the invention in technological solutions.

Examples

Example 1.

Analysis of free oils fraction in alkylbenzenesulfonic acid

Equipment

Agilent Technologies 7890A Gas Chromatograph equipped with mass detector Agilent

Technologies 7000 GC / Triple Quad, non-polar capillary column Phenomenex ZB-5HT; 15m x 0.32 mm x 0.10 m, and mass spectra library: NIST MS SEARCH 2.0. PerkinElmer Autosystem XL Gas Chromatograph, equipped with the flame ionization detector, chromatographic column Phenomenex Zebron-5HT; 15m x 0.32mm x 0.10 microns and autosampler. Scaltec SBA 31 analytical scale, precision of weighing ± 0.0001 g. Brand Transferpette type multidimensional automatic pipette, with measured volumes ranging from 100μΙ to 1000μΙ; with PLASTIBRAND tips of capacity 1000μΙ. Glassware, including Brand volumetric flasks 10mL capacity.

Analysis

20mL of a mixture of ethanol, water and 0.1 % phenolphthalein solution in ethanol at a volume ratio of the components of: 2: 1 :0.05 respectively, was added to 1.2 g of the sample. After complete dissolution of the sample 50% aqueous solution of potassium hydroxide was added dropwise to the mixture until pink color of the mixture became permanent. Then, 3mL of potassium chloride was added and mixed thoroughly. Next, 1 mL of the internal standard solution (octacosane) in 1 -heptane at a concentration of 0.008g/mL and 3mL of pure 1-heptane was added to the mixture. After shaking of the mixture the phases were separated and the organic phase (the upper one) was analyzed by GC. Two to three independent determinations were done for each sample. The internal standard solution was prepared by weighing 0.08g octacosane to the 10mL volumetric flask and filling it up to the mark with 1-heptane.

A typical chromatogram of the free oils fraction is shown in Fig. 6. Example 2.

Kinetics of ageing process.

Determination of apparent reaction rate constant.

Sulfonation of linear alkylbenzene (LAB) was carried out in the sulfonation unit of the

alkylbenzenesulfonic acid synthesis plant at SULPHUREX DESMET BALLESTRA S.p.A. using a multitube film reactor.

Linear alkyl benzene was reacted with sulfur trioxide in a multitube film reactor from BALLESTRA. A sample of the reaction mixture from the film reactor was collected to a 1000 mL laboratory reactor tank which was thermostatted and subjected to the ageing process during approx.120 min while stirring intensely.

Samples were collected from the reactor after running the reaction for 10, 20, 60 and 120 min. A reaction mixture sample was also collected right from the stream leaving the film reactor. The samples were hydrolyzed by adding water and then were analyzed for its content of unreacted LAB. A decrease in the content of LAB in time was shown in Fig.1.

Example 3.

The effect of average residence time for the reaction mixture in the continuous reactor on LABSA parameter values.

Sulfonation of alkylbenzene was carried out as described in Example 1.

The reactor mixture from the film reactor was sent to one of two ageing reactors, equipped with a sampling pipe. The process was carried out in a continuous manner at steady-state conditions at a temperature of 50°C, adjusting suitable plant throughputs and volumes of the ageing reactors so as to reach average residence times for the reaction mixture in the reactor tanks in the range

60-240 min. As soon as the process was stabilized, the reaction mixture samples were collected for determination of material characteristics of LABS. Analytical results are shown in Table 1.

Table 1. Values of qualitative characteristics of LABS depending on average residence time

Example 4.

The ageing process of the invention

Sulfonation of alkylbenzene was carried out as described in Example 1. The reaction mixture from the film reactor was sent to the empty ageing reactor which was equipped with a sampling pipe located at the level of the stirring blades.100 mL samples of the reaction mixture were collected at 10 min intervals and stabilized by adding water. After 60 min, when the material in the ageing reactor was at the level of the overflow pipe, the material from the mixer was transferred by means of a high-capacity pump to a tank equipped with a stirring device and water jacket (the tank was a non-standard component of the plant). The second step of ageing was conducted in that tank in batch process conditions for the next 60 min. 100 mL samples were collected at 10 min intervals and were stabilized by adding water. The collected samples were analyzed. Analytical results for the content of unreacted LAB and active matter are shown in the diagram in Fig. 6.

Tab.2. Comparison of LABSA parameters obtained with using of typical and invented method of ageing

ageing method active matter free LAB Klett colour

wt. % wt. % typical 96.8 1.28 15 invention 98.2 0.04 18

Claims

1. Method for ageing a liquid post-sulfonation reaction mixture comprising linear

alkylbenzenesulfonic acid (LABSA) and unreacted linear alkylbenzene (LAB), said reaction mixture being obtained by a continuous chemical process of sulfonating linear alkylbenzene using a sulfonating agent, the method using a system of two or more stirred tank reactors and comprising the steps of:

(iv) removing the aged reaction mixture from the first stirred tank reactor;

2. The method according to claim 1 , wherein a system of two stirred tank reactors is used and steps (iii) and (iv) are performed while feeding the continuous stream of reaction mixture into the second stirred tank reactor and prior to reaching the predetermined maximum reaction mixture level in the second stirred tank reactor.

3. The method according to claim 1 , wherein a system of three or more stirred tank

reactors is used and steps (iii) and (iv) are performed while feeding the continuous stream of reaction mixture into the second, third or any subsequent stirred tank reactor and prior to reaching the predetermined maximum reaction mixture level in the second, third or any subsequent stirred tank reactor.

4. The method according to any one of claims 1 to 3, wherein the volume of the stirred tank reactors is selected such that ageing and removing the reaction mixture from a given stirred tank is completed before the next cycle of feeding the continuous reaction mixture stream into said given tank reactor starts.

5. The method according to any one of claims 1 to 4, wherein the method further

comprises the step of (ix) feeding the aged reaction mixture into a hydrolysis reactor where it is combined with an amount of water necessary to stabilize the aged reaction mixture, preferably < 2 wt.-%, wherein the hydrolysis reactor preferably has a volume equal to or larger than that of the largest stirred tank reactor used for ageing the reaction mixture; and optionally (x) feeding the stabilized aged reaction mixture, optionally after cooling, into a final product storage tank.

6. The method according to any one of claims 1 to 5, wherein each of the stirred tank reactors comprises

(a) at least one inlet, preferably having a valve and preferably being

arranged at the top or the upper half of the stirred tank reactor;

(b) at least one closable outlet, preferably having a valve and preferably being arranged at the bottom of the stirred tank reactor;

(c) at least one level indicator allowing to determine the maximum reaction mixture level in said reactor; and/or

(d) a cooling system to control the reaction mixture temperature in the

reactor.

7. The method according to any one of claims 1 to 6, wherein the step of feeding the reaction mixture into a tank reactor is performed in about 0,5 to about 2 h, preferably in about 1 h.

8. The method according to any one of claims 1 to 7, wherein the step of feeding the reaction mixture into a tank reactor, ageing the reaction mixture in the tank reactor and removing the aged reaction mixture are performed in about 1 ,5 to about 3 h, preferably in about 2 h.

9. Plant for the production of linear alkylbenzenesulfonic acid (LABSA) by a continuous chemical process of sulfonating linear alkylbenzene (LAB) using a sulfonating agent, the plant comprising a sulfonation unit and an ageing unit, characterized in that the ageing unit comprises two or more parallely operated ageing reactors (R1 , R2, R3) and a single stabilization reactor (R4), wherein the two or more ageing reactors are each connected to a common pipeline that alternately feeds a reaction mixture obtained in the sulfonation unit into said ageing reactors via an inlet stub pipe, and a common pipeline that feeds the aged reaction mixture into said stabilization reactor via an outlet stub pipe.

10. The plant according to claim 9, wherein the stabilization reactor (R4) has a volume larger than or equal to the volume of the largest ageing reactor (R1 , R2, R3).

1 1. The plant according to claim 9 or 10, wherein each ageing reactor comprises:

(a) a valve (V1 .1 , V2.1 , V3.1 ) for opening and closing the inlet stub pipe;

(b) a valve (V1 .2, V2.2, V3.2) for opening and closing the outlet stub pipe; and/or

(c) a level indicator (LICA1 , LICA2, LICA3) allowing to determine the

maximum reaction mixture level in said ageing reactor.

12. The plant according to any one of claims 9 to 1 1 , wherein the stabilization reactor (R4) is equipped with an inlet for the aged reaction mixture, an inlet for process water, an outlet for the product, and optionally a pump (P) for emptying the stabilization reactor.

13. The plant according to claim 12, wherein the outlet comprises a valve (V4.2) for

opening and closing the outlet.

14. The plant according to any one of claims 9 to 13, wherein the sulfonation unit is a cascade system of reactors or a film reactor.

15. The plant according to any one of claims 9 to 14, wherein the ageing reactors are stirred tank reactors that may optionally comprise a cooling system.

16. The plant according to any one of claims 9 to 15, further comprising a storage

container connected to the stabilization reactor (R4).

17. The plant according to claim 16, further comprising a heat exchanger (E) arranged between the stabilization reactor (R4) and the storage container.

18. Method for operating the plant according to any one of claims 9 to 16, comprising operating a system of two or more ageing reactors (R1 , R2, R3) in a combined continuous-and-batch manner, comprising the steps of operating the reactors in a continuous unsteady state and batch process conditions, by

(iv) emptying the ageing reactor by feeding the aged reaction mixture into the stabilization reactor (R4);

(v) adding process water to the stabilization reactor (R4) and incubating the

mixture for a predetermined time period to obtain the product; and

(viii) repeating steps (i)-(vi).

19. The method according to claim 17, wherein feeding and emptying the ageing reactors is controlled by means of automatic inlet valves (V1.1 , V2.1 , V3.1 ) and automatic outlet valves (V1.2, V2.2, V3.2) and level indicators (LICA1 , LICA2, LICA3).

20. The method according to claim 17 or 18, wherein emptying the stabilization reactor is controlled by means of an automatic outlet valve (V4.2) and/or achieved by means of a pump (P).