Process for purifying linear alkylbenzenes

Abstract

The invention refers to a simple and cost-effective process for purifying a linear alkylbenzene (LAB) compound. Said process comprises a step of purification / adsorption which comprises contacting the LAB compound with activated carbon to obtain a purified LAB compound and exhausted activated carbon, and a step of regeneration / reactivation / desorption which comprises contacting said exhausted activated carbon with benzene to obtain regenerated activated carbon. The process of the invention may be conveniently implemented in continuous mode in an industrial plant with a system of two or more reactors operating in parallel, wherein at least one reactor is in adsorption stage and at least another reactor is in desorption stage. The treatment of LAB with activated carbon allows removing or minimizing impurities that are responsible for the color and that affect the quality of LAB as well as of its final product, the linear alkylbenzene sulfonate (LAS).

Description

[0001] PROCESS FOR PURIFYING LINEAR ALKYLBENZENES

[0002] FIELD OF THE INVENTION

[0003] The present invention refers in general to a process for purifying linear alkylbenzenes (LAB), a class of compounds extensively used as a chemical intermediate to form linear alkylbenzene sulfonates (LAS), which are substances widely employed in detergents and cleaning products, especially as the principal surfactants in home care detergent formulations, as well as in a variety of other applications including agricultural herbicides, emulsion polymerization, wetting agents, electric cable oil, ink solvents, paints, etc.

[0004] BACKGROUND OF THE INVENTION

[0005] Linear alkylbenzenes (also known as LAB) are a family of organic compounds with the formula CeHsCn^n+i, where n commonly lies in the range of 8 to 16 when used as intermediates in the production of surfactants for detergents and cleaning products. The CnH2n+i chain, i.e. , the alkyl moiety, is unbranched.

[0006] Linear alkylbenzenes (LAB) are often produced in the petrochemical industry, especially for applications in detergents, by a process which involves dehydrogenating linear paraffins to obtain linear mono-olefins and then carrying out the alkylation of benzene with said mono-olefins in the presence of a catalyst at elevated temperatures. Then, LAB may be sulfonated to produce the corresponding linear alkylbenzene sulfonic acid (also known as LABSA or HLAS), which is in turn neutralized to afford the corresponding linear alkylbenzene sulfonate (also known as LAS as well as by the acronym of its salts, significantly LASNa which refers to sodium linear alkylbenzene sulfonate). LAS is the most versatile and most widely used surfactant in all types of detergent formulations in powder, liquids, gels, agglomerates, bars or tablets.

[0007] The alkylation of benzene with olefins to produce LAB also implies the production of side products such as heavy alkyl benzene (HAB) along with unreacted benzene, olefins and paraffins. HAB is used to collectively designate those chemical species of higher molecular weight than the monoalkylated product, LAB. Heavy alkylate bottoms are made up mainly of dialkylbenzenes. The formation of other types of by-products is not desired because they can degrade the quality of the produced alkylate, thus reducing its quality. Nevertheless, LAB may be conveniently separated from heavy alkylate bottoms in distillation columns. Typically, linear alkylbenzene is purified using several distillation steps. For instance, see Pujado, Linear Alkylbenzene (LAB) Manufacture, in Handbook of Petroleum Refining Processes, by Robert A. Meyers, Second Edition, pp 1.53 to 1.66, McGraw-Hill, New York (1996), especially pages 1.56 to 1.60. In general, the alkylation reaction product is subjected to a first distillation in a benzene column to separate benzene as an overhead stream that can be recycled to the alkylation reaction. The bottoms stream from the benzene column is then subjected to a distillation to separate paraffins and unreacted olefin in a paraffins column. The paraffins-containing overhead is capable of being recycled to a paraffin dehydrogenation unit while the bottoms stream is passed to a heavy alkylate distillation system. In the heavy alkylate distillation column, heavies are separated from the lighter alkylbenzene, and a heavies-containing stream is withdrawn as a bottoms stream. If desired, the bottoms stream can be subjected to further steps for increasing the yield of linear alkylbenzene, such as transalkylation.

[0008] More challenging than removing HAB from the LAB product stream is removing impurities having a boiling point within the same range of LAB that are usually found in small amounts (typically in the ppm / ppb concentration range based on weight). These impurities of usually similar molecular weight and boiling point to LAB include minor compounds produced in secondary reactions during the production of LAB, such as tetralins, indanes, naphthalenes, phenylalkanes, anthracenes, and other molecules with usually more than one aromatic ring (collectively known as polycyclic aromatic hydrocarbons or PAHs). Some of these compounds are present in a concentration below the detection limits of current techniques, but even with these small concentrations, they may impart certain color to the product or increase absorption in the UV-A range of the electromagnetic spectrum and, if not removed properly before the sulfonation, will significantly increase the color in the final product alkylbenzene sulfonate.

[0009] One of the main parameters considered when analyzing the quality of LAS within the field of detergents is its color. Although said parameter has no influence on its detersive properties, color has an appreciable economic relevance especially when alkylbenzene sulfonates are used in liquid formulations. When a liquid or gel detergent with a high content of active material is produced, the chromophores present in the alkylbenzene sulfonate affect the color of the product, giving it a yellowish-brown hue that masks the color of the coloring additives. This forces the expert to use greater amounts of coloring additives to achieve a certain color, and even in these cases, some color ranges such as light blue cannot be achieved.

[0010] Often the bromine index (Brl) is used to evaluate the quality of an alkylbenzene product. The bromine index is defined as the weight of bromine in mg that can react with 100 g of the sample. Since bromine does not react with aromatic double bonds (due to resonance stabilization) and only reacts with non-aromatic double bonds in the alkyl group in impurities in the LAB, bromine index is a measure of the non-aromatic double bonds in the linear alkyl chain. Although the bromine index relates primarily to olefin content, a certain correlation may exist between the bromine index and the color of the alkylbenzene and of sulfonated alkylbenzenes made therefrom, e.g., as determined by the Klett color index or by absorbance measurement. Linear alkylbenzenes used in detergent production are typically required to have a bromine index of less than 10 mg / g.

[0011] Molecular sieves (zeolites) and clay treating have been used to reduce the bromine index and color contaminants of various hydrocarbon products. The clay treater and molecular sieves serve primarily as solid acid catalysts, effectively promoting reactions of the olefinic by-products. Mainly, these solid beds reduce the bromine index of a sample of LAB by removing olefinic by-products from the product mixture.

[0012] For instance, in U.S. Pat. Nos. 4,433,196 and 4,468,476, the use of bauxite clay treatment and crystalline zeolites has been proposed as effective adsorbents to remove color precursors from detergent range alkyl benzene prior to sulfonation.

[0013] U.S. Pat. No. 4,795,550 discloses the use of aluminosilicate zeolites to remove trace olefins from aromatic and naphthenic feedstocks to reduce the bromine index of the feedstocks from initial values of 50 to 2000 to final values of 0.1 to 50. Among the feedstocks mentioned as suitable in the '550 patent are Cieto C20 linear alkylbenzenes.

[0014] U.S. Pat. No. 6,031 ,144 discloses a two-step process for reducing the residual olefin content of an alkylation reaction product of a single-ring aromatic hydrocarbon with an at least C16 olefin in which at least a portion of a non-alkylated single-ring aromatic hydrocarbon is removed in a first step; followed by a second step in which the remaining reaction product is reacted in the presence of an acidic catalyst to produce a final alkylation reaction product having reduced olefin content. The acidic catalyst can be a molecular sieve (such as a natural or synthetic zeolite) or clay.

[0015] U.S. Pat. No. 7,214,840 discloses a zeolite Y catalyst suitable for reducing the bromine index of linear alkylbenzene products, especially in the presence of the benzene and n- paraffin impurities conventionally present in the direct effluent of a LAB manufacturing plant.

[0016] However, the present inventors have seen that the treatment of LAB with the above- mentioned adsorbents (e.g., zeolite molecular sieves, clays) still results in undesirable coloration in the resulting linear alkylbenzene sulfonate, indicating that said adsorbents are not useful for removing all the chromophore impurities that can occur in a sample of LAB efficiently.

[0017] Therefore, there is still a need for a process for purifying LAB to remove or minimize certain impurities that are responsible for the color and that affect the quality of LAB as well as of the final alkylbenzene sulfonate (LAS). Moreover, it would be highly desirable that the adsorbent used for purification of LAB can be appropriately regenerated (reactivated) making it ready for multiple reuses.

[0018] BRIEF DESCRIPTION OF THE INVENTION

[0019] The present invention provides a simple and cost-effective process for the removal of color impurities from LAB. In particular, the inventors have found that LAB may be conveniently purified from color impurities by a specific adsorbent of activated carbon, which is characterized by comprising at least 75 wt % of carbon and having a BET surface area of at least 500 m2 / g. Surprisingly, the activated carbon treatment as proposed herein provided much better or complementary results compared to other materials commonly used as adsorbents to purify LAB in the state of the art such as molecular sieves (zeolites), or clays. Further, the activated carbon once used for purifying LAB can be advantageously regenerated for further use with benzene, which is one of the raw materials present in LAB production plants, thus avoiding the need of additional substances. Moreover, the regeneration of activated carbon with benzene was found to be the most effective among various fluids tested. A first aspect of the invention refers to a process for purifying a linear alkylbenzene (LAB) compound, said process comprising: a) contacting the LAB compound with activated carbon to obtain a purified LAB compound and an exhausted activated carbon, wherein said activated carbon comprises at least 75 wt % of carbon and has a BET surface area of at least 500 m2 / g; and b) contacting said exhausted activated carbon with benzene to obtain regenerated activated carbon.

[0020] Step (a) in the process of the invention is also referred herein as purification or adsorption stage. That is, it is the step or stage where the impurities of LAB are adsorbed on the surface of activated carbon.

[0021] Step (b) in the process of the invention is also referred herein as regeneration, reactivation or desorption stage. That is, it is the step or stage wherein the previously adsorbed impurities on activated carbon are released from its surface so that the activated carbon may be used in further adsorption / desorption cycles.

[0022] For industrial purposes, the process of the invention may be conveniently implemented in continuous mode with a system of two or more reactors operating in parallel, wherein at least one reactor is in adsorption stage and at least another reactor is in desorption stage.

[0023] These aspects and preferred embodiments thereof are additionally also defined hereinafter in the detailed description and in the claims.

[0024] The treatment of linear alkylbenzene described in the literature employing molecular sieves (zeolites), clays, or other adsorbents may be employed in a complementary or synergistic manner with the treatment by activated carbon proposed in the present invention. This special embodiment may lead to a superior quality of LAS detergent.

[0025] All the features described in this specification (including the claims, description and drawings) can be combined in any combination thereof, with the exception of combinations of such mutually exclusive features. BRIEF DESCRIPTION OF THE FIGURES

[0026] To better understand the invention, its objects and advantages, the following figures are attached to the specification in which the following is depicted:

[0027] Figure 1 is a photograph showing a sample of LAB treated with activated carbon (left) and an untreated sample of LAB (right), both of them having been subjected to a mild sulfonation according to example 1A. The treatment with activated carbon according to the present invention clearly resulted in a decrease of color intensity compared with the untreated sample.

[0028] Figure 2 are the GCxGC / FID / ToF chromatograms of an untreated sample of LAB (top) and LAB treated with activated carbon (bottom). As explained in example 1 B, the treatment with activated carbon resulted in an elimination of (alkyl) naphthalenes and a reduction of the concentration of tetralins and diphenylalkanes.

[0029] Figure 3 is a scheme of the three-reactor continuous system in which reactor 1 operates in adsorption stage and reactors 2 and 3 operate in desorption stage.

[0030] Figure 4 is a graph showing the absorbance value of a LAB purified with activated carbon and using benzene as desorbent after 9 adsorption / desorption cycles.

[0031] Figure 5 is the adsorption kinetics corresponding to 4 cycles of purification of LAB with activated carbon. Benzene was used as desorbent in the first and third cycle whereas nitrogen was used as desorbent in the second cycle. The Y-axis of the graph represents absorbance (322 nm) whereas the X-axis represents LAB volume (ml) / g AC (activated carbon).

[0032] Figure 6 is the adsorption kinetics corresponding to 7 cycles of purification of LAB with activated carbon and using the same benzene as desorbent in each regeneration step. The Y-axis of the graph represents absorbance (322 nm) whereas the X-axis represents LAB volume (ml) / g AC (activated carbon). For the experiment the amount of benzene was re-used, showing that the regenerative capacity of benzene is not affected by the re-use for at least 7 cycles. Figure 7 is the adsorption kinetics corresponding to purification of LAB with activated carbon and regeneration of the exhausted activated carbon with paraffin (flushing stage) followed by benzene (desorption stage). The Y-axis of the graph represents absorbance I absorbance of untreated sample (measured at 322 nm) whereas the X-axis represents LAB volume (ml) / g AC (activated carbon).

[0033] Figure 8 is the adsorption kinetics corresponding to purification of LAB with activated carbon and regeneration of the exhausted activated carbon only with benzene. The Y- axis of the graph represents absorbance I absorbance of untreated sample (measured at 322 nm) whereas the X-axis represents LAB volume (ml) / g AC (activated carbon).

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] Unless defined otherwise, all technical and scientific terms and expressions used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs.

[0036] Linear alkylbenzene (LAB) is mainly used as a commodity to produce linear alkyl benzene sulfonic acid (LABSA) through sulfonation, which is neutralized to produce linear alkylbenzene sodium sulfonate (LASNa), the main anionic surfactant used in the industry. It is desirable to have a linear alkylbenzene sulfonate product (LAS) that has a low and stable color in production. Aromatic and polycyclic aromatic compounds are contained as impurities in very low concentrations in the precursor stage (LAB), before sulfonation. These impurities may be chromophore molecules themselves or can transform into chromophore compounds that give rise to undesirable color. Especially, after the sulfonation, these impurities lead to an even more extensive coloration of the resulting product. This invention aims at reducing, minimizing or avoiding the presence of impurities in the LAB product so that the final LAS product features a high quality in terms of color.

[0037] As explained in the background section, bromine index (Brl), or bromine number, is a parameter used to estimate the amount of unsaturated aliphatic groups (olefins) in a hydrocarbon. Bromine index is one main criteria of LAB quality. Bromine index is expressed as weight of bromine in mg reacted with 100 g of a sample and it can be measured by titration of a sample with a bromide-bromate solution as titrant. During the titration, bromine is produced in situ by a redox reaction before undergoing an addition reaction with unsaturated, non-aromatic hydrocarbons. Bromine index also relates to the color, since a LAB product with a high bromine index will create a highly colored sulfonate.

[0038] An alternative way to predict the color of a sample of LAS or LABSA can be the measurement of the parent LAB sample at a wavelength of 320-354 nm (e.g., 322 nm) in a spectrophotometer. By this way measuring the absorbance allows a robust prediction of the content of color forming impurities in the sample of LAB, as color forming impurities (e.g., naphthalenes, anthracenes) significantly absorb electromagnetic radiation in that spectral region.

[0039] As shown in the examples provided herein, the process of the invention has been found to reduce the absorbance of a sample of LAB in the wavelength area of between 320- 354 nm, specifically at 322 nm, thus confirming the removal or reduction of color forming impurities from said sample of LAB.

[0040] The clay or molecular sieve treatment of hydrocarbons is commonly practiced in a wide variety of processes in the petroleum and petrochemical industries to remove impurities from hydrocarbons. However, the present inventors have found that the treatment of LAB with clays, zeolites or other adsorbents disclosed in the state of the art does not allow reducing color impurities satisfactorily (see example 1C). Further, as can be appreciated from example 2, while it is certain that the clay treatment reduces the bromine index value, the LAB absorbance value is not consistently improved with the clay treatment. However, the treatment of LAB with activated carbon always decreases the LAB absorbance value. This means that both clay treatment and treatment with activated carbon allow improving the quality of LAB, but these treatments are intended for removing different kinds of impurities.

[0041] The present invention provides a process for removing color causing impurities from LAB based on the use of activated carbon as adsorbent. Further, the activated carbon, once exhausted, may be easily regenerated, that is reactivated, so that it can be used again for purifying LAB multiple times (cycles).

[0042] Specifically, the process of the invention comprises: a) a step of purification / adsorption which comprises contacting the LAB compound with activated carbon to obtain a purified LAB compound and exhausted activated carbon; and b) a step of regeneration / reactivation / desorption which comprises contacting said exhausted activated carbon with benzene to obtain regenerated activated carbon.

[0043] The adsorption process consists of a solid that traps a certain molecule of a fluid (liquid or gas) in its surface. In the present invention, the solid (called adsorbent) is activated carbon, the fluid is a LAB product and the trapped molecules (called adsorbate) include chromophore impurities and chromophore precursor impurities, that are compounds that impart color directly as well as to the LAS product after the sulfonation and neutralizations steps of LAB. These impurities have a molecular weight like that of LAB, so that they also exhibit similar boiling points and therefore distillation cannot be used to separate the LAB from said impurities. The inventors have found that these impurities include tetralins, indanes, naphthalenes, phenylalkanes, anthracenes, and other aromatic and polycyclic aromatic hydrocarbons (PAHs).

[0044] Activated carbon (sometimes also referred to as active carbon or activated / active charcoal) is defined as a carbonaceous material with a large internal surface area and highly developed porous structure resulting from the processing of raw materials under high temperature reactions. Activated carbon is an inert solid adsorbent material commonly used to remove diverse, dissolved contaminants from water and process gasphase streams. The adsorption process in which activated carbon participates is due to one of the types of Van der Waals forces, called London dispersion forces, which occur between a covalent adsorbent and an adsorbate, also covalent. This kind of adsorption is called physical adsorption. Physical adsorption does not cause a modification in the chemical structure of the atoms and the molecules that intervene in it. Therefore, it is reversible.

[0045] Activated carbons are normally made from base materials which generally comprise the larger portion of the raw material and binders which are used to give strength by holding together the particles of base material. The activated carbon used in the process of the invention comprises at least 75 wt % of carbon and has a BET surface area of at least 500 m2 / g, preferably at least 700 m2 / g, more preferably at least 900 m2 / g.

[0046] In a particular embodiment, the carbon content of the activated carbon is at least 76 wt %, at least 77 wt %, at least 78 wt %, at least 79 wt %, at least 80 wt %, at least 81 wt

[0047] %, at least 82 wt %, at least 83 wt %, at least 84 wt %, at least 85 wt %, at least 86 wt

[0048] %, at least 87 wt %, at least 88 wt %, at least 89 wt %, at least 90 wt %, at least 91 wt

[0049] %, at least 92 wt %, at least 93 wt %, at least 94 wt %, at least 95 wt %, at least 96 wt

[0050] %, at least 97 wt %, at least 98 wt %, at least 99 wt % or 100 wt %.

[0051] In a particular embodiment, the activated carbon comprises a binder, which typically comprises silicon and / or aluminium, and more particularly, the activated carbon substantially consists of carbon and a binder. Binder materials can be selected from the group of coal tar, methyl cellulose, bentonite, clay, alumina, silica, silica / alumina, sugars, glycerine, glycol and oils or combinations thereof. In a more particular embodiment, the content of the sum of silicon (Si) and aluminium (Al) in the adsorbent of activated carbon is at most 25 wt %. In an even more particular embodiment, the content of the sum of Si and Al in the adsorbent of activated carbon is at most 24 wt %, at most 23 wt %, at most 22 wt %, at most 21 wt %, at most 20 wt %, at most 19 wt %, at most 18 wt %, at most 17 wt %, at most 16 wt %, at most 15 wt %, at most 14 wt %, at most 13 wt %, at most 12 wt %, at most 11 wt %, at most 10 wt %, at most 9 wt %, at most 8 wt %, at most 7 wt %, at most 6 wt %, at most 5 wt %, at most 4 wt %, at most 3 wt %, at most 2 wt %, at most 1 wt %, or 0 wt %.

[0052] According to a particular embodiment, the activated carbon comprises at least 75-80 wt % carbon and at most 25-20 wt % Si + Al, e.g., at most 10 wt % Si + Al or at most 5 wt % Si + Al.

[0053] As the skilled person is aware, the content of carbon, silicon and aluminium may be determined by x-ray fluorescence. In the x-ray fluorescence technique, the analyte is excited by x-ray radiation and the characteristic fluorescence of every element recorded. An x-ray fluorescence spectrum can thus be used to determine the chemical composition of a sample. In a particular embodiment, the activated carbon has a BET surface area of at least 500 m2 / g, at least 700 m2 / g, at least 900 m2 / g, at least 925 m2 / g, at least 950 m2 / g, at least 975 m2 / g, at least 1000 m2 / g, at least 1025 m2 / g, at least 1050 m2 / g, at least 1075 m2 / g or at least 1100 m2 / g,

[0054] In another particular embodiment, the activated carbon has a BET surface area or specific surface area between 500 m2 / g and 2000 m2 / g, e.g. between 500 m2 / g and 1500 m2 / g, between 700 m2 / g and 1500 m2 / g, between 900 m2 / g and 1500 m2 / g, between 925 m2 / g and 1500 m2 / g, between 950 m2 / g and 1500 m2 / g, between 975 m2 / g and 1500 m2 / g, between 1000 m2 / g and 1500 m2 / g, between 1025 m2 / g and 1500 m2 / g, between 1050 m2 / g and 1500 m2 / g, between 1075 m2 / g and 1500 m2 / g, between 1100 m2 / g and 1500 m2 / g, between 500 m2 / g and 1400 m2 / g, between 700 m2 / g and 1400 m2 / g, between 900 m2 / g and 1400 m2 / g, between 925 m2 / g and 1400 m2 / g, between 950 m2 / g and 1400 m2 / g, between 975 m2 / g and 1400 m2 / g, between 1000 m2 / g and 1400 m2 / g, between 1025 m2 / g and 1400 m2 / g, between 1050 m2 / g and 1400 m2 / g, between 1075 m2 / g and 1400 m2 / g, between 1100 m2 / g and 1400 m2 / g, between 500 m2 / g and 1300 m2 / g, between 700 m2 / g and 1300 m2 / g, between 900 m2 / g and 1300 m2 / g, between 925 m2 / g and 1300 m2 / g, between 950 m2 / g and 1300 m2 / g, between 975 m2 / g and 1300 m2 / g, between 1000 m2 / g and 1300 m2 / g, between 1025 m2 / g and 1300 m2 / g, between 1050 m2 / g and 1300 m2 / g, between 1075 m2 / g and 1300 m2 / g, between 1100 m2 / g and 1300 m2 / g, between 500 m2 / g and 1200 m2 / g, between 700 m2 / g and 1200 m2 / g, between 900 m2 / g and 1200 m2 / g, between 925 m2 / g and 1200 m2 / g, between 950 m2 / g and 1200 m2 / g, between 975 m2 / g and 1200 m2 / g, between 1000 m2 / g and 1200 m2 / g, between 1025 m2 / g and 1200 m2 / g, between 1050 m2 / g and 1200 m2 / g, between 1075 m2 / g and 1200 m2 / g, between 1100 m2 / g and 1200 m2 / g. In a more particular embodiment, the activated carbon has a BET surface area between 900 m2 / g and 1400 m2 / g or between 900 m2 / g and 1200 m2 / g, preferably between 925 m2 / g and 1150 m2 / g.

[0055] As the skilled person is aware, the surface, according to the BET (Brunauer-Emmett- Teller) theory may be determined by absorption of a gas on the internal and external surface of the material under different pressures. The surface is then calculated according to the Brunauer-Emmett-Teller theory. As a gas for absorption, nitrogen in gaseous or liquid form can be used. According to a particular embodiment, the activated carbon comprises at least 75-80 wt % carbon and has a BET surface area of at least 500 m2 / g, at least 700 m2 / g, at least 900 m2 / g, e.g., between 900 m2 / g and 1400 m2 / g. Further, the content of the sum of Si and Al in the adsorbent of activated carbon is normally at most 25-20 wt %, e.g., at most 10 wt % or at most 5 wt %.

[0056] The activated carbon used in the process of the invention may be in any form including, but not limited to, powder and compacted form. For industrial purposes, compacted forms such as pellets, granules and flakes are preferred since they are easier to handle and guarantee a very reduced loss of material upon each cycle. Thus, in particular embodiments, the activated carbon is in a granular, pellet or flake form.

[0057] In certain embodiments, the ratio between LAB volume and activated carbon mass is from 1 :1 (mL / g) to 50:1 (mL / g), e.g. from 2:1 (mL / g) to 40:1 (mL / g), preferably from 3:1 (mL / g) to 30:1 (mL / g). This means that the active carbon can purify several times the volume in LAB related to its mass (for example 40-times when the ratio is 40:1 (mL / g)) while still obtaining a good quality product after the purification.

[0058] In the second step of the process of the present invention, the adsorbent of activated carbon is regenerated with benzene. It has been found that the impurities of the exhausted activated carbon can be conveniently displaced from the exhausted activated carbon by passing liquid benzene through the exhausted activated carbon.

[0059] Several methods of regeneration of activated carbon have been disclosed in the prior art, including for instance thermal treatment, acid or alkaline treatment, and treatment with solvents or gases (e.g. steam, nitrogen). It is important to note that the working capacity of adsorbents after being regenerated may be less than that of fresh adsorbents depending on the regenerant media used. This is because not all active places become vacant again after the desorption cycle. Advantageously, the present invention shows that benzene can regenerate activated carbon completely during numerous cycles (see examples 3 and 5). However, other fluids such as nitrogen or paraffins do not allow regenerating the activated carbon appropriately, as can be appreciated from examples 4 and 6. In examples 3-6, benzene was in liquid state. The process of the invention may be carried out at any scale, from small set-ups using laboratory equipment to industrial scale in chemical plants using large purification units.

[0060] In preferred embodiments, the process of the invention takes place by the following steps: a) passing a stream of LAB compound through a bed of activated carbon to obtain a stream of purified LAB compound and exhausted activated carbon; and b) passing a stream of benzene through said exhausted activated carbon to obtain regenerated activated carbon.

[0061] The process of the invention may be applied to any stream containing LAB within an industrial plant (industrial environment).

[0062] Likewise, the process may be carried out in a variety of configurations, including batch process and continuous process configurations. Preferably, it is carried out in continuous mode in a unit with a system of two or more reactors in parallel, wherein at least one reactor is configured to perform step a) (purification / adsorption stage) and at least another reactor is configured to perform step b) (regeneration / reactivation / desorption stage). In a particular embodiment, the system has one reactor configured to perform step a) and one reactor configured to perform step b). In another particular embodiment, the system has one reactor configured to perform step a) and two reactors configured to perform step b). One particular embodiment of this configuration is that shown in figure 3.

[0063] For an industrial plant with a system of two or more reactors in parallel for continuous mode, it is preferably that all the reactors operate at the same temperature or at least that the temperature difference is as small as possible. In certain embodiments, the temperature difference between step a) and step b) is less than or equal to 200 °C, e.g., less than or equal to 100 °C, 50 °C or 25 °C, preferably less than or equal to 10 °C, more preferably less than or equal to 5 °C, and even more preferably is about 0 °C.

[0064] In certain embodiments, step a), step b) or both are carried out at a temperature of at least 25 °C, at least 30 °C, at least 35 °C, at least 40 °C, at least 45 °C, at least 50 °C, at least 55 °C, at least 60 °C, at least 65 °C, at least 70 °C, at least 75 °C, at least 80 °C, at least 85 °C, at least 90 °C, at least 95 °C, at least 100 °C, at least 105 °C, at least 110 °C, at least 115 °C, at least 120 °C, at least 125 °C, at least 130 °C, at least 135 °C, at least 140 °C, at least 145 °C, at least 150 °C, at least 155 °C, at least 160 °C, at least 165 °C, at least 170 °C, at least 175 °C, at least 180 °C, at least 185 °C, at least 190 °C, at least 195 °C, at least 200 °C, at least 205 °C, at least 210 °C, at least 215 °C, at least 220 °C, at least 225 °C, at least 230 °C, at least 235 °C, at least 240 °C, at least 245 °C or a temperature of 250 °C. Preferably, step a), step b) or both are carried out at a temperature of at least 50 °C, at least 55 °C, at least 60 °C, at least 65 °C, at least 70 °C, at least 75 °C, at least 80 °C, at least 85 °C, at least 90 °C, at least 95 °C, or a temperature of about 100 °C. More preferably, step a), step b) or both are carried out at a temperature of at least 75 °C, at least 80 °C, at least 85 °C, at least 90 °C, at least 95 °C, or a temperature of about 100 °C.

[0065] In certain embodiments, step a), step b) or both are carried out at a temperature of 25 °C or at a temperature of at most 30 °C, at most 35 °C, at most 40 °C, at most 45 °C, at most 50 °C, at most 55 °C, at most 60 °C, at most 65 °C, at most 70 °C, at most 75 °C, at most 80 °C, at most 85 °C, at most 90 °C, at most 95 °C, at most 100 °C, at most 105 °C, at most 110 °C, at most 115 °C, at most 120 °C, at most 125 °C, at most 130 °C, at most 135 °C, at most 140 °C, at most 145 °C, at most 150 °C, at most 155 °C, at most 160 °C, at most 165 °C, at most 170 °C, at most 175 °C, at most 180 °C, at most 185 °C, at most 190 °C, at most 195 °C, at most 200 °C, at most 205 °C, at most 210 °C, at most 215 °C, at most 220 °C, at most 225 °C, at most 230 °C, at most 235 °C, at most 240 °C, at most 245 °C or at most 250 °C. Preferably, step a), step b) or both are carried out at a temperature of about 100 °C or at a temperature of at most 105 °C, at most 110 °C, at most 115 °C, at most 120 °C, at most 125 °C, at most 130 °C, at most 135 °C, at most 140 °C, at most 145 °C, or at most 150 °C. More preferably, step a), step b) or both are carried out at a temperature of about 100 °C or at a temperature of at most 105 °C, at most 110 °C, at most 115 °C, at most 120 °C, or at most 125 °C.

[0066] In certain embodiments, step a), step b) or both are carried out at a temperature ranging 25 °C to 250 °C, e.g., 25 °C to 225 °C, 25 °C to 200 °C, 25 °C to 175 °C, 25 °C to 150 °C, preferably 40 °C to 200 °C, more preferably 50 °C to 150 °C, or 75 °C to 125 °C, most preferably about 100 °C. It has been found that operating at a temperature close to 100 °C such as of 50 °C to 150 °C or of 75 °C to 125 °C (e.g. about 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C or 125 °C) for both steps allows a reduction in energy consumption and at the same time complete desorption of the impurities in the activated carbon in step b) and adsorption without LAB degradation in step a) is achieved. In a preferred embodiment, step a) and step b) are both carried out at a temperature of about 100 °C.

[0067] In certain embodiments, step a), step b) or both are carried out at a pressure ranging 0 bar to 30 bar, e.g. 5 bar to 25 bar or 10 bar to 20 bar. Preferably, step a) is carried out at a pressure ranging 10 bar to 30 bar, e.g. 15 bar to 25 bar, and / or step b) is carried out at a pressure ranging 0 bar to 20 bar, e.g. 5 bar to 15 bar. More preferably step a) is carried out at a pressure of about 20 bar and / or step b) is carried out at a pressure of about 10 bar.

[0068] In certain embodiments, step a) is carried out at a temperature of about 100 °C and a pressure of about 20 bar and step b) is carried out at a temperature of about 100 °C and a pressure of about 10 bar.

[0069] In certain embodiments, the liquid hourly space velocity (LHSV) in step a), step b) or both, defined as the ratio of LAB volume flow per hour to activated carbon volume, is comprised between 0.1 IT1and 10 h’1, preferably between 0.2 h-1and 8 h’1, more preferably between 0.4 and 5 h’1. In a particular embodiment, the liquid hourly space velocity (LHSV) in step a) and step b) is about 5 h’1. In an alternative embodiment, the liquid hourly space velocity (LHSV) in step a) is about 5 h-1and the liquid hourly space velocity (LHSV) in step b) is about 10 h’1.

[0070] In certain embodiments, step a) is carried out for 1-24 h and step b) is carried out for 1- 24 h. In a more particular embodiment, step a) is carried out for 1-5 h and step b) is carried out for 1-10 h. In an even more particular embodiment, step a) is carried out for about 2 h and step b) is carried out for about 4 h.

[0071] In a particular embodiment, the purification of LAB is carried out in a continuous system made of three reactors operating in parallel (as shown in Figure 3). Reactor 1 operates in adsorption stage (for about 2 h) whereas reactors 2 and 3 operate in desorption stage. In the three reactors the temperature is about 100 °C, the flow rate is about 20 L / min (LHSV 5 IT1) and the flow direction is upflow. Alternatively, the purification is carried out in a purification unit comprising two reactors, in which the reactor in adsorption stage is operated at a LHSV of about 5 h-1and the reactor in desorption stage at a LHSV of about 10 hr1.

[0072] In certain embodiments, the process for purifying a linear alkylbenzene compound (LAB) of the present invention further comprises contacting the (unpurified) LAB compound of step a) or the purified LAB compound obtained in step a) with an additional adsorbent different from activated carbon. This treatment with an additional adsorbent can be carried out either before, simultaneously with or after the treatment with activated carbon of step a). The additional adsorbent is preferably selected from molecular sieves (zeolites) and clays or a combination thereof. As previously explained, the treatment with activated carbon primarily allows reducing aromatic and polycyclic aromatic hydrocarbons (PAHs) while the treatment with other solid adsorbents such as clays (clay treatment) primarily allows reducing non-aromatic unsaturated compounds and therefore both treatments can be employed complementarily or synergistically to purify LAB (see example 2).

[0073] In some embodiments, the process further comprises sulfonating the purified LAB to obtain the corresponding linear alkylbenzene sulfonate acid (LABSA).

[0074] In some embodiments, the process further comprises neutralizing the LABSA to obtain the corresponding linear alkylbenzene sulfonate (LAS).

[0075] In some embodiments, the LAB to be purified is obtained by a process which comprises alkylating benzene with mono-olefins.

[0076] As used herein, the term "approximately" or "about" as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term "approximately" or "about" refers to a value that can vary up to ± 20 %, preferably within ± 10 %, and more preferably within ± 5 % of the stated reference value. When “approximately" or "about" is used before a numerical range, it applies to the upper and lower range end-points.

[0077] Indeed, the skilled person knows that numerical values relating to measurements are subject to measurement errors which place limits on their accuracy. Where terms such as "about" or "approximately" are applied to a particular value (e.g., "about 200 °C" or "approximately 200 °C") or to a range (e.g., "about x to approximately y"), the value or range may be interpreted as being as accurate as the method used to measure it. Unless explicitly stated otherwise, the general convention in the scientific and technical literature may be applied so that the last digit of numerical values preferably indicates the precision of measurement. Thus, unless other error margins are given, the maximum margin is preferably ascertained by applying the rounding-off convention to the last decimal place. For instance, a value of 3.5 preferably has an error margin of 3.45 to 3.54 and a range of 2% to 10% preferably covers a range of 1 .5% to 10.4%. Said variations of a specified value are understood by the skilled person and are within the context of the present invention. Further, to provide a more concise description, some of the quantitative expressions given herein are not qualified with the term “about”. It is understood that, whether the term “about” is used explicitly or not, every quantity given herein is meant to refer to the actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including equivalents and approximations due to the experimental and / or measurement conditions for such given value.

[0078] Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of "about 1 % to about 5 %" should be interpreted to include not only the explicitly recited values of about 1 % to about 5 %, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3 and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting only one numerical value. It should also be understood that ranges formed by combination of any of the end points of different disclosed ranges and / or particular values therein are included in the present disclosure.

[0079] The following examples illustrate the invention and must not be considered as limiting the scope thereof.

[0080] Examples Example 1 - Purification of LAB at laboratory scale

[0081] Example 1 A - Proof-of-concept test for purifying LAB with activated carbon

[0082] The purification of LAB by adsorption on activated carbon (AC) was initially tested at laboratory scale as a proof-of-concept. The activated carbon used in this example had the following features: Carbon 87.3 wt %, BET surface area 1390 m2 / g.

[0083] 50 g of LAB product were mixed with 14 g of activated carbon for 20 min. Then, the mixture was filtered through simple Buchner funnel under vacuum pressure in order to separate the purified LAB (liquid) from the activated carbon (solid).

[0084] The efficacy of the purification procedure in removing color impurities was measured by absorbance. Specifically, a sample of LAB purified with activated carbon as above described and a sample of unpurified (original) LAB were taken and then the absorbance of both samples was measured at 322 nm (characteristic wavelength for monitoring LAB quality). The absorbance of the sample purified with activated carbon was measured to be 0.8 whereas the absorbance of the untreated sample was measured to be 1 .6.

[0085] Figure 1 is a photograph showing the sample of LAB treated with activated carbon (left) and the untreated sample of LAB (right), both of them having previously been subjected to a mild sulfonation treatment with sulfuric acid. The treatment of the LAB sample with activated carbon visually resulted in a decrease of color intensity after the LAB sample was sulfonated.

[0086] Example 1 B - Identification of impurities in LAB product

[0087] A number of minor compounds have been identified in the LAB product by using a complex two-dimensional gas chromatography system (GCxGC) with two detectors in parallel, an FID (flame ionization detector, for quantification) and a ToF (time of flight, for measurement). The analyses are based on internal bi-dimensional chromatography methods, developed specifically for LAB samples (internal reference CI-M8, GCxGC configuration A with a nonpolar column in the first dimension, and a semipolar column in the second dimension). Figure 2 are the GCxGC / FID / ToF chromatograms of an untreated sample of LAB (top) and LAB treated with activated carbon (bottom). The activated carbon used in this example had the following features: Carbon 87.3 wt %, BET surface area 1390 m2 / g. As shown in Figure 2, the products mostly removed in the treatment with activated carbon are: alkyl naphthalenes, tetralins and diphenylalkanes. Specifically, the reduction of alkyl naphthalenes was specifically total. There are other compounds with even lower concentrations that, although it was not possible to quantify them, were also removed completely or to a great extent: phenyl tetralins, fluorenes and terphenyls among others, with greater aromaticity.

[0088] Example 1C - Comparison of activated carbon with other adsorbents

[0089] This example compares the efficacy of 9 different activated carbons to purify LAB to that of other 3 common adsorbents of different nature.

[0090] These solids were tested by the following procedure: 50 g of low-quality LAB (Absorbance at 322 nm = 1.64) and 14 g of each solid were placed in a bottle under orbital shaking for 2 hours. Subsequently, the solids were separated by filtration to recover the LAB sample, in which the quality was measured by determining the absorbance at 322 nm.

[0091] The following table shows the activated carbons and other purifying solids tested and the absorbance of light at 322 nm:

[0092] These results prove that all the activated carbons tested improved the LAB quality considerably. However, the other adsorbents were unsuitable for purifying LAB or the level of quality improvement was quite low (in terms of content of color impurities, i.e. those measurable by absorbance at 322 nm such as aromatics and polycyclic aromatics).

[0093] Example 2 - Treatment with Activated Carbon vs Clay Treatment in pilot plant

[0094] Two LAB products of different qualities were treated with activated carbon M5 from example 1C and clay (clay treater) (Si+AI: 48.7 wt %, BET surface area 201 m2 / g) in pilot plant to assess the different behavior of both solids.

[0095] The following table shows the results obtained from the tests carried out for a LAB having initially an absorbance at 322 nm of 0.620 and a bromine index <0.5 (intermediate quality):

[0096] In this case, the treatment with activated carbon resulted in an improvement in the absorbance value, indicating that the activated carbon adsorbs aromatic and polycyclic aromatic chromophore compounds. However, the treatment with clay did not improve the absorbance value, which reflects that it is not suitable for adsorbing such kind of compounds. Rather, the clay could eliminate non-aromatic unsaturated compounds (that, once sulfonated, give color) and this would be reflected by a decrease in the bromine index (however, in this experiment the initial bromine index was already low).

[0097] The following table shows the results obtained from the tests carried out for a LAB having initially an absorbance at 322 nm of 0.885 and a bromine index of 10 (below intermediate quality).

[0098] With this sample, the treatment with activated carbon did not improve the bromine index value but the absorbance decreased drastically, indicating that non-aromatic unsaturated compounds were not adsorbed but aromatic and polycyclic aromatic ones were. This effect was not seen with the clay, which, although allowed decreasing the bromine index value (that is, eliminated unsaturated compounds), was not capable of improving the absorbance value, probably due to the low capability of adsorbing aromatics and polycyclic aromatics from LAB.

[0099] As a summary, both solids improve the color quality of the LAB but they do so by different routes: while the clay removes the non-aromatic unsaturated compounds that mainly give color after sulfonation, the activated carbon removes the aromatics and polycyclic aromatics that give color both directly and after sulfonation and that, in view of the results seen in the second sample, have more importance on the effect of the absorbance value than the unsaturated ones.

[0100] Example 3 - Life Cycle of Activated Carbon

[0101] The regeneration capacity of the activated carbon adsorbent M5 from example 1C was tested in consecutive cycles using a LAB with an initial absorbance of 0.620 at 322 nm. Complete regeneration of activated carbon may be obtained for at least 9 cycles. The capacity of activated carbon to adsorb color-causing impurities is not affected even after 9 cycles of purification, as can be seen in Figure 4 which shows the absorbance of a LAB purified with activated carbon and using benzene as desorbent for all cycles. This shows that the same adsorbent can be applied for various cycles indicating that the adsorbent according to the invention is versatile and can be fully exploited in an economic way.

[0102] Example 4 - Comparative of benzene vs N2 as desorbent

[0103] This experiment was designed to compare the desorption capacity of benzene vs nitrogen in a continuous setup using a bed of activated carbon M5 from example 1C. Four samples were collected from a feed of untreated LAB. The samples of untreated LAB showed an absorbance of 0.620 at 322 nm before treatment. For the experiment, a sample of untreated LAB was used for each cycle. In the first cycle, the first sample of untreated LAB was purified with activated carbon according to the present invention to obtain a LAB having an absorbance at 322 nm of 0.343 before switch to the regeneration step and the exhausted activated carbon was regenerated with benzene at 100 °C during 8 h.

[0104] In the second cycle, the second sample of untreated LAB was purified with the activated carbon regenerated from the first cycle to obtain a LAB having an absorbance at 322 nm of 0.383 before switch to the regeneration step and the exhausted activated carbon was regenerated with nitrogen at 200 °C during 24 h.

[0105] In the third cycle, the third sample of untreated LAB was purified with the activated carbon regenerated from the second cycle to obtain a LAB having an absorbance at 322 nm of 0.604 before switch to the regeneration step and the exhausted activated carbon was regenerated with benzene at 100 °C during 8 h.

[0106] In the fourth cycle, the fourth sample of untreated LAB was purified with the activated carbon regenerated from the third cycle to obtain a LAB having an ABS at 322 nm of 0.334 at the end of the cycle.

[0107] After desorption with N2 even at strong conditions (at 200°C for 24h), activated carbon was not able to recover its original capacity. However, when benzene was subsequently used at milder conditions (at 100°C for 8 h), its initial capacity was recovered.

[0108] Figure 5 shows the adsorption over time corresponding of these 4 cycles of purification of LAB with activated carbon (CA) and desorption with benzene (Bz) and nitrogen (N2).

[0109] Therefore, benzene, which is a starting material in the manufacture of LAB, can be used as a desorbent for the regeneration of the activated carbon material. Thus, no new material has to be introduced into the process for the manufacture of LAB since existing streams containing benzene can be used to carry out the regeneration of the activated carbon bed.

[0110] Example 5 - Quality of benzene as desorbent This experiment was designed to study the quality of benzene as desorbent after several cycles in a continuous setup using a bed of activated carbon M5 from example 1C. Figure 6 shows the adsorption kinetics corresponding to 7 cycles of purification of LAB with activated carbon (CA) and using the same benzene as desorbent. The sample of untreated LAB showed an absorbance of 0.620 at 322 nm before treatment.

[0111] By using the same benzene (i.e., without any treatment to remove impurities in the benzene) for several desorption cycles, it was observed that its capacity to regenerate the bed of activated carbon to 100% remained complete, allowing to obtain a high-quality LAB.

[0112] The adsorption curve maintained its behavior at each cycle.

[0113] The desorption curve gradually increased in absorbance value due to the saturation of the benzene in chromophore compounds. This slight saturation does not significantly affect its regeneration capacity and in turn the LAB quality. In any case, if desired, benzene could be purged (e.g., by distillation).

[0114] Example 6 - Comparative of benzene vs paraffin as desorbent for activated carbon regeneration

[0115] This experiment was designed to compare the desorption capacity of benzene vs paraffin (mixture of C10-C13 n-paraffins) using a bed of activated carbon M5 from example 1C.

[0116] As illustrated in Figure 7, paraffin was incapable of adequately desorbing all contaminants retained on the solid during the adsorption stage but just a “flushing” of the activated carbon was obtained (see flushing cycle / stage in Figure 7). However, the subsequent treatment of the flushed activated carbon with benzene allowed continuing the desorption of contaminants, leading to an excellent regeneration of the activated carbon (see desorption cycle / stage in Figure 7). The capacity of the bed was quantified as the area under the curve: the flushing stage yielded a value of 6.3, while desorption with benzene resulted in a value of 25.5. In terms of percentages, flushing with paraffin eliminated 19.8% of the total contaminant area, with benzene accounting for the remaining 80.2%. When the same regeneration test was performed exclusively with benzene, the area under the curve was calculated to be 31 .8 (see Figure 8). This is equivalent to the sum of the areas from the flushing and desorption stages in Figure 7.

[0117] This observation substantiates that benzene alone can desorb a substantially higher amount of the adsorbed compounds with an absorption at wavelength of 322 nm. In contrast, other fluids such as paraffins can only regenerate less than 20% of the bed capacity compared to the benzene desorbent.

[0118] Conclusions

[0119] It has been demonstrated that the treatment of alkylbenzene with activated carbon significantly improves the color and, therefore, the quality of the alkylbenzene sulfonate. This property is critical for the final use of said product in formulations of detergents and household cleaning products.

[0120] Experimental tests have been carried out with other solid adsorbents (including for instance clays and zeolites) but the results obtained were clearly worse than with activated carbon.

[0121] The purification by adsorption with activated carbon can be applied as a complimentary method to treatment of LAB streams with clay or Zeolites. The improvement of the quality was observed to be more consistent. Furthermore, the activated carbon can be regenerated multiple times with benzene which allows for an efficient use of the activated carbon adsorbent.

[0122] Further, families of compounds that cause color, PAH-type aromatics have been identified. It has been demonstrated that the treatment with activated carbon implies a reduction or even total elimination of these chromophore compounds that, although present in very low concentrations, have a great impact on the coloration of the final surfactant.

[0123] The implications for this method are important as an LAB product with enhanced and reliable quality can be obtained from an industrial process, thus reducing the amount of material produced with an insufficient quality. Therefore, the described invention represents an improvement of the purification technology of linear alkyl benzene.

Claims

CLAIMS1. A process for purifying a linear alkylbenzene compound (LAB), said process comprising: a) contacting the LAB compound with activated carbon to obtain a purified LAB compound and exhausted activated carbon, wherein said activated carbon comprises at least 75 wt % of carbon and has a BET surface area of at least 500 m2 / g; and b) contacting said exhausted activated carbon with benzene to obtain regenerated activated carbon.

2. The process according to claim 1 , said process taking place by the following steps: a) passing a stream of the LAB compound through a bed of the activated carbon to obtain a stream of purified LAB compound and exhausted activated carbon; and b) passing a stream of benzene through said exhausted activated carbon to obtain regenerated activated carbon.

3. The process according to claim 1 or 2, wherein the process takes place in continuous by using a system of two or more reactors operating in parallel, wherein at least one reactor is configured to carry out step a) and at least other one reactor is configured to carry out step b).

4. The process according to any one of claims 1 to 3, wherein the temperature difference between step a) and step b) is less than or equal to 200 °C.

5. The process according to any one of claims 1 to 4, wherein step a), step b) or both are carried out at a temperature ranging 25 °C to 250 °C, preferably 40 °C to 200 °C, more preferably 50 °C to 150 °C.

6. The process according to any one of claims 1 to 5, wherein step a), step b) or both are carried out at a pressure ranging 0 bar to 30 bar, preferably 5 bar to 25 bar, more preferably 10 bar to 20 bar.

7. The process according any one of claims 1 to 6, wherein the LHSV in step a), step b) or both is comprised between 0.1 h-1and 10 h’1, preferably between 0.2 h-1and 8 h’1, more preferably between 0.4 and 5 h’1.

8. The process according any one of claims 1 to 7, wherein step a) is carried out for 1- 24 h and step b) is carried out for 1-24 h.

9. The process according to any one of claims 1 to 8, said process further comprising sulfonating the purified LAB to obtain the corresponding linear alkylbenzene sulfonic acid (LABSA).

10. The process according to claim 9, said process further comprising neutralizing the LABSA to obtain the corresponding linear alkylbenzene sulfonate (LAS).11 . The process according to any one of claims 1 to 10, wherein the LAB to be purified is obtained by a process which comprises alkylating benzene with mono-olefins.

12. The process according to any one of claims 1 to 11 that reduces the absorbance of a sample of LAB in the wavelength area of between 320-354 nm.

13. The process according to any one of claims 1 to 12, wherein the activated carbon is in compacted form, preferably in a granular, pellet or flake form.

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