Method for purifying linear alkylbenzene

Abstract

The present invention relates to a simple and cost-effective method for purifying linear alkylbenzene (LAB) compounds. The method includes a purification / adsorption step including contacting the LAB compound with activated carbon to obtain a purified LAB compound and waste activated carbon, and a regeneration / reactivation / desorption step including contacting the waste activated carbon with benzene to obtain regenerated activated carbon. The method of the invention can be conveniently implemented in a continuous mode in an industrial plant having a system in which two or more reactors run in parallel, with at least one reactor being in an adsorption phase and at least another reactor being in a desorption phase. Treatment of LABs with activated carbon allows for removal or minimization of impurities that result in color and affect the quality of LABs as well as their end product linear alkylbenzene sulfonates (LAS).

Description

TECHNICAL FIELD

[0001] The present invention relates generally to a process for purifying linear alkylbenzenes (LAB), a class of compounds widely used as chemical intermediates to form linear alkylbenzene sulfonates (LAS), which are substances widely used in detergents and cleaning products, particularly as the main surfactant in household care detergent formulations, as well as for a variety of other applications, including agricultural herbicides, emulsion polymerization, wetting agents, cable oil, ink solvents, paints, etc. BACKGROUND

[0002] Linear alkylbenzenes (also referred to as LAB) are a family of organic compounds having the formula C6H5C n H 2n+1 where n is typically 8 to 16 when used as intermediates to produce surfactants for detergents and cleaning products. The C n H 2n+1 chain, i.e., the alkyl moiety, is unbranched.

[0003] Linear alkylbenzenes (LAB) are typically produced in the petrochemical industry, particularly for use in detergents, by a process involving dehydrogenation of linear paraffins to obtain linear mono-olefins and then alkylation of benzene with the mono-olefins at high temperature in the presence of a catalyst. The LAB can then be sulfonated to produce the corresponding linear alkylbenzene sulfonic acid (also referred to as LABSA or HLAS), which in turn is neutralized to provide the corresponding linear alkylbenzene sulfonate (also referred to as LAS as well as the abbreviation for its salts, particularly LASNa, which refers to sodium linear alkylbenzene sulfonate). LAS is the most versatile and most widely used surfactant in all types of detergent formulations, which are powdery, liquid, gelled, coalesced, striped or flaked.

[0004] Alkylation of benzene with olefins to produce LAB also means the production of byproducts such as heavy alkylbenzenes (HAB) as well as unreacted benzene, olefins and paraffins. HAB is used to refer to those chemicals that have a higher molecular weight than the mono-alkylated product, LAB. Heavy alkylate bottoms are composed primarily of di-alkylbenzenes. Other types of byproducts are not desired to form because they can reduce the quality of the alkylate produced, thereby reducing its grade. However, LAB can be conveniently separated from the heavy alkylate bottoms in a distillation column.

[0005] Typically, linear alkylbenzene is purified using several distillation steps. See, for example, Pujado, Linear Alkylbenzene (LAB) Manufacture, in Handbook of Petroleum Refining Processes, by Robert A. Meyers, 2nd Edition, pages 1.53 to 1.66, McGraw-Hill, New York (1996), especially pages 1.56 to 1.60. Typically, the alkylated 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 distilled to separate paraffins and unreacted olefins in a paraffin column. The overhead containing paraffins can be recycled to a paraffin dehydrogenation unit, while the bottoms stream passes to a heavy alkylate distillation system. The bottoms stream can be subjected to further steps, such as transalkylation, to increase the yield of linear alkylbenzene, if desired.

[0006] More challenging than removing HAB from the LAB product stream is the removal of impurities that have boiling points in the same range as LAB, but are present in typically small amounts, usually in the ppm / ppb concentration range, based on weight. These impurities, which are typically similar in molecular weight and boiling point to LAB, include secondary compounds produced in the LAB production process in secondary reactions, such as tetrahydronaphthalene, indane, naphthalene, phenylalkanes, anthracene, and other molecules typically having more than one aromatic ring (collectively referred to as polycyclic aromatic hydrocarbons or PAHs). Some of these compounds are present at concentrations below the detection limit of current technology, but even with these low concentrations, they can impart some color to the product or increase the absorption in the UV-A range of the electromagnetic spectrum, and if not properly removed prior to sulfonation, will significantly increase the color of the final product, alkylbenzene sulfonate.

[0007] Within the detergent field, one of the main parameters considered when analyzing the quality of LAS is its color. Although the parameter has no influence on its detergency properties, color has an appreciable economic relevance, especially when alkylbenzene sulfonates are used in liquid formulations. When producing liquid or gel detergents with high content of active material, the chromophores present in alkylbenzene sulfonates affect the color of the product, making it have a yellowish shade that masks the color of the coloring additives. This forces the expert to use larger amounts of coloring additives to obtain a certain color, and even in these cases, some color ranges, such as light blue, cannot be achieved.

[0008] Generally, the bromine index (BrI) is used to evaluate the quality of the alkylbenzene product. The bromine index is defined as the weight in mg of bromine that can react with 100 g of 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 groups of impurities in the LAB, the bromine index is a measure of the amount of non-aromatic double bonds in the linear alkyl chains. Although the bromine index is primarily related to the olefin content, there can be some correlation between the bromine index and the color of the alkylbenzene and sulfonated alkylbenzene made therefrom, e.g., as determined by Klett color index or by absorbance measurements. Linear alkylbenzenes used for detergent production generally need to have a bromine index of less than 10 mg / g.

[0009] Molecular sieve (zeolite) and clay treatments have been used to reduce the bromine index and color contaminants of various hydrocarbon products. Clay treaters and molecular sieves are used primarily as solid acid catalysts that effectively promote the reaction of olefin byproducts. Primarily, these solid beds reduce the bromine index of the LAB sample by removing olefin byproducts from the product mixture.

[0010] For example, the use of bauxite clay treatment and crystalline zeolites as effective adsorbents to remove color precursors from the detergent range of alkylbenzenes prior to sulfonation has been proposed in U.S. Patents Nos. 4,433,196 and 4,468,476.

[0011] U.S. Patent No. 4,795,550 discloses the use of aluminosilicate zeolites to remove trace amounts of olefins from aromatic and naphthenic feedstocks to reduce the bromine index of the feedstock from an initial value of 50 to 2000 to a final value of 0.1 to 50. Suitable feedstocks mentioned in the '550 patent include C 16 -C 20 Linear alkylbenzenes.

[0012] U.S. Patent No. 6,031,144 discloses a two-step process for reducing the residual olefin content of the alkylation reaction product of olefins, wherein in the first step at least a portion of the non-alkylated monocyclic aromatic hydrocarbons are removed; followed by a second step wherein the remaining reaction product is reacted in the presence of an acidic catalyst to produce a final alkylation reaction product having a reduced olefin content. The acidic catalyst can be a molecular sieve (e.g., natural or synthetic zeolite) or a clay. 16 Alkylation reaction product of olefins.

[0013] U.S. Patent No. 7,214,840 discloses a zeolite Y catalyst suitable for reducing the bromine index of linear alkylbenzene products, particularly in the presence of benzene and n-paraffin impurities conventionally present in the direct effluent of a LAB manufacturing plant.

[0014] However, the present inventors have found that treatment of LAB with the above-mentioned adsorbents (e.g. zeolite molecular sieves, clays) still results in undesired colouration of the resulting linear alkylbenzene sulfonate, indicating that the adsorbents are not useful for effectively removing all chromophore impurities that can be present in the LAB sample.

[0015] Therefore, there is still a need for a process for purifying LAB to remove or minimize certain impurities that cause colour and affect the quality of LAB and ultimately the quality of the alkylbenzene sulfonate (LAS). Furthermore, it is highly desirable that the adsorbent used for the purification of LAB can be suitably regenerated (reactivated) making it convenient for multiple re-use. SUMMARY

[0016] The present invention provides a simple and cost-effective process for removing colour impurities from LAB. In particular, the inventors have found that LAB can be conveniently purified from colour impurities by a specific adsorbent of activated carbon characterized by comprising at least 75 wt% of carbon and having a BET surface area of at least 500 m 2 / g. Surprisingly, the activated carbon treatment presented herein provides much better or complementary results compared to other materials commonly used as adsorbents in the prior art to purify LAB (e.g. molecular sieves (zeolites) or clays). Furthermore, the activated carbon once used to purify LAB can advantageously be regenerated with benzene for further use, which is one of the raw materials present in a LAB production plant, thus avoiding the need for additional substances. Moreover, it was found that the regeneration of activated carbon with benzene was the most efficient among the various fluids tested.

[0017] A first aspect of the present invention relates to a process for purifying a linear alkylbenzene (LAB) compound, the process comprising: a) contacting the LAB compound with activated carbon to obtain a purified LAB compound and exhausted activated carbon, wherein the activated carbon comprises at least 75 wt% of carbon and has a BET surface area of at least 500 m 2 / g; and b) contacting the exhausted activated carbon with benzene to obtain a regenerated activated carbon.

[0018] Step (a) in the process of the present invention is also referred to herein as the purification or adsorption stage. That is, it is the step or stage in which the impurities of the LAB are adsorbed on the surface of the activated carbon.

[0019] Step (b) in the process of the present invention is also referred to herein as a regeneration, reactivation or desorption stage. That is, it is the step or stage in which the impurities previously adsorbed on the activated carbon are released from the surface of the activated carbon so that the activated carbon can be used for further adsorption / desorption cycles.

[0020] For industrial purposes, the process of the present invention can conveniently be implemented in a continuous mode with a system of two or more reactors running in parallel, with at least one reactor in the adsorption stage and at least another reactor in the desorption stage.

[0021] These aspects and preferred embodiments thereof are additionally defined in the detailed description and claims hereinafter.

[0022] The treatment of linear alkylbenzenes described in the literature using molecular sieves (zeolites), clays or other adsorbents can be used in a complementary or synergistic manner together with the treatment by activated carbon proposed in the present invention. This particular embodiment can result in LAS detergents of superior quality.

[0023] In addition to combinations of mutually exclusive features, all features described in this specification (including the claims, the description and the drawings) can be combined in any combination. BRIEF DESCRIPTION OF DRAWINGS

[0024] For a better understanding of the present invention, its objects and advantages, reference should be made to the following drawings in conjunction with the ensuing description, in which the following is depicted: Figure 1 is a photograph showing a LAB sample treated with activated carbon (left) and an untreated LAB sample (right), both having been slightly sulfonated according to Example 1A. Treatment with activated carbon according to the present invention clearly leads to a reduction in color intensity compared to the untreated sample.

[0025] Figure 2 is a GCxGC / FID / ToF chromatogram of an untreated sample of LAB (top) and LAB treated with activated carbon (bottom). Treatment with activated carbon leads to the elimination of (alkyl)naphthalenes and a reduction in the concentration of tetrahydronaphthalenes and diphenylalkanes as explained in Example IB.

[0026] Figure 3 is a scheme of a three-reactor continuous system, with reactor 1 running in the adsorption stage and reactor 2 and reactor 3 running in the desorption stage.

[0027] Figure 4 is a graph showing the absorbance values of LAB purified with activated carbon and using benzene as desorbent after 9 adsorption / desorption cycles.

[0028] Figure 5is the adsorption kinetics corresponding to the purification of LAB with activated carbon for 4 cycles. In the first and third cycle benzene was used as desorbent, while in the second cycle nitrogen was used as desorbent. The Y-axis of the graph represents the absorbance (322 nm), while the X-axis represents the LAB volume (ml) / g AC (activated carbon).

[0029] Figure 6 is the adsorption kinetics corresponding to the purification of LAB with activated carbon for 7 cycles and using the same benzene as desorbent in each regeneration step. The Y-axis of the graph represents the absorbance (322 nm), while the X-axis represents the LAB volume (ml) / g AC (activated carbon). For this experiment, the amount of benzene was reused, indicating that the regeneration capacity of benzene is not affected by the reuse for at least 7 cycles.

[0030] Figure 7 is the adsorption kinetics corresponding to the purification of LAB with activated carbon and the regeneration of spent activated carbon with a paraffin (flushing phase) and then with benzene (desorption phase). The Y-axis of the graph represents the absorbance / absorbance of the untreated sample (measured at 322 nm), while the X-axis represents the LAB volume (ml) / g AC (activated carbon).

[0031] Figure 8 is the adsorption kinetics corresponding to the purification of LAB with activated carbon and the regeneration of spent activated carbon with benzene only. The Y-axis of the graph represents the absorbance / absorbance of the untreated sample (measured at 322 nm), while the X-axis represents the LAB volume (ml) / g AC (activated carbon). DETAILED DESCRIPTION

[0032] Unless otherwise defined, all technical and scientific terms and expressions used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0033] Linear alkylbenzene (LAB) is mainly used as a commodity to produce linear alkylbenzene sulfonic acid (LABSA) by sulfonation, which is neutralized to produce linear alkylbenzene sulfonic acid sodium (LASNa), which is the main anionic surfactant used in industry. It is desirable to have linear alkylbenzene sulfonate products (LAS) with low and stable color in production. Before sulfonation, aromatic and polycyclic aromatic compounds are included in the precursor stage (LAB) at very low concentrations as impurities. These impurities can be chromophore molecules themselves or can be converted into chromophore compounds that cause undesirable color. In particular, after sulfonation, these impurities cause even more extensive coloring of the resulting product. The present invention aims to reduce, minimize or avoid the presence of impurities in the LAB product, so that the final LAS product has high quality in terms of color.

[0034] As explained in the background section, the bromine index (BRI) or bromine number is a parameter used to estimate the amount of unsaturated aliphatic groups (olefins) in a hydrocarbon. The bromine index is a major criterion for the quality of LAB. The bromine index is expressed as the weight of bromine in mg that reacts with 100 g of sample and it can be measured by titrating the sample with a bromide-bromate solution as a titrant. During the titration, bromine is generated in situ by a redox reaction before the addition reaction with the unsaturated non-aromatic hydrocarbons. The bromine index is also related to the color, as LAB products with a high bromine index will produce highly colored sulfonates.

[0035] An alternative way to predict the color of a LAS or LABSA sample can be to measure the parent LAB sample in a spectrophotometer at a wavelength of 320 nm to 354 nm (e.g., 322 nm). Measuring the absorbance in this way allows to robustly predict the content of color-forming impurities in the LAB sample, as color-forming impurities (e.g., naphthalene, anthracene) significantly absorb electromagnetic radiation in this spectral region.

[0036] As shown by the examples provided herein, it has been found that the method of the present application reduces the absorbance of a LAB sample in the wavelength region of 320 nm to 354 nm (in particular at 322 nm), thereby demonstrating that color-forming impurities are removed or reduced from the LAB sample.

[0037] Clay or molecular sieve treatment of hydrocarbons is generally implemented in the petroleum and petrochemical industry in various processes to remove impurities from hydrocarbons. However, the inventors have found that treating LAB with clays, zeolites or other adsorbents disclosed in the prior art does not satisfactorily reduce color impurities (see Example 1C). Moreover, as can be understood from Example 2, although the clay treatment was determined to reduce the bromine index value, the LAB absorbance value was not consistently improved with the clay treatment. However, treating LAB with activated carbon always reduced the LAB absorbance value. This means that both clay treatment and treatment with activated carbon allow to improve the quality of LAB, but these treatments aim at removing different kinds of impurities.

[0038] The present application provides a method based on the removal of color-causing impurities from LAB using activated carbon as adsorbent. Moreover, once exhausted, activated carbon can be easily regenerated, i.e. reactivated, so that it can be reused for purifying LAB multiple times (cycles).

[0039] In particular, the method of the present application comprises: a) a purification / adsorption step comprising contacting a LAB compound with activated carbon, to obtain a purified LAB compound and a spent activated carbon; and b) a regeneration / reactivation / desorption step comprising contacting the spent activated carbon with benzene, to obtain a regenerated activated carbon.

[0040] The adsorption process consists of a solid of certain molecules that capture a fluid (liquid or gas) at its surface. In the present invention, the solid (called adsorbent) is activated carbon, the fluid is the LAB product, and the molecules that are captured (called adsorbate) include chromophore impurities and chromophore precursor impurities, which are compounds that directly impart color to the LAS product after the sulfonation and neutralization steps of the LAB. These impurities have molecular weights similar to that of the LAB, such that they also exhibit similar boiling points, and therefore distillation cannot be used to separate the LAB from the impurities. The present inventors have found that these impurities include tetrahydronaphthalene, indane, naphthalene, phenylalkanes, anthracene, and other aromatic and polycyclic aromatic hydrocarbons (PAHs).

[0041] Activated / active carbon or activated / active charcoal is defined as a carbonaceous material with a large internal surface area and a 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 various dissolved pollutants from water and process gas phase streams. The adsorption process in which activated carbon participates is due to a type of van der Waals force known as the London dispersion force, which occurs between covalent adsorbents and adsorbates that are also covalent. This adsorption is called physical adsorption. Physical adsorption does not cause modification of the chemical structure of the atoms and molecules that intervene in it. Therefore, it is reversible.

[0042] Activated carbon is typically made from a base material that generally includes a larger portion of raw material and a binder, which is used to provide strength by holding the particles of the base material together.

[0043] The activated carbon used in the method of the present invention comprises at least 75 wt% of carbon and has a BET surface area of at least 500 m 2 / g, preferably at least 700 m 2 / g, more preferably at least 900 m 2 / g.

[0044] In particular embodiments, the activated carbon has a carbon content of at least 76 wt%, at least 77 wt%, at least 78 wt%, at least 79 wt%, at least 80 wt%, at least 81 wt%, at least 82 wt%, at least 83 wt%, at least 84 wt%, at least 85 wt%, at least 86 wt%, at least 87 wt%, at least 88 wt%, at least 89 wt%, at least 90 wt%, at least 91 wt%, at least 92 wt%, at least 93 wt%, at least 94 wt%, at least 95 wt%, at least 96 wt%, at least 97 wt%, at least 98 wt%, at least 99 wt%, or 100 wt%.

[0045] In particular embodiments, the activated carbon comprises a binder, which typically includes silicon and / or aluminum, and more particularly, the activated carbon consists essentially of carbon and a binder. The binder material can be selected from the group consisting of coal tar, methyl cellulose, bentonite, clay, aluminum oxide, silicon dioxide, silicon dioxide / aluminum oxide, sugar, glycerol, ethylene glycol, and oil, or combinations thereof. In more particular embodiments, the activated carbon adsorbent has a content of the sum of Si) and Al of at most 25 wt%. In even more particular embodiments, the activated carbon adsorbent has a content of the sum of Si and Al of 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%.

[0046] According to particular embodiments, the activated carbon comprises at least 75 wt% to 80 wt% carbon and at most 25 wt% to 20 wt% Si+Al, such as at most 10 wt% Si+Al or at most 5 wt% Si+Al.

[0047] As known to the person skilled in the art, the content of carbon, silicon, and aluminum can be determined by X-ray fluorescence. In X-ray fluorescence techniques, the analyte is excited by X-ray radiation and the characteristic fluorescence of each element is recorded. Thus, the chemical composition of a sample can be determined using X-ray fluorescence spectroscopy.

[0048] In particular embodiments, the activated carbon has a surface area of at least 500 m 2 / g, at least 700 m 2 / g, at least 900 m 2 / g, at least 925 m 2 / g, at least 950 m 2 / g, at least 975 m 2 / g, at least 1000 m 2 / g, at least 1025 m 2 / g, at least 1050 m 2 / g, at least 1075 m 2 / g, or at least 1100 m 2 / g.

[0049] In another specific embodiment, the activated carbon has a BET surface area or specific surface area of 500 m 2 / g to 2000 m 2 / g, for example 500 m 2 / g to 1500 m 2 / g, 700 m 2 / g to 1500 m 2 / g, 900 m 2 / g to 1500 m 2 / g, 925 m 2 / g to 1500 m 2 / g, 950 m 2 / g to 1500 m 2 / g, 975 m 2 / g to 1500 m 2 / g, 1000 m 2 / g to 1500 m 2 / g, 1025 m 2 / g to 1500 m 2 / g, 1050 m 2 / g to 1500 m 2 / g, 1075 m 2 / g to 1500 m 2 / g, 1100 m 2 / g to 1500 m 2 / g, 500 m 2 / g to 1400 m 2 / g, 700 m 2 / g to 1400 m 2 / g, 900 m 2 / g to 1400 m 2 / g, 925 m 2 / g to 1400 m 2 / g, 950 m 2 / g to 1400 m 2 / g, 975 m2 / g to 1400 m 2 / g, 1000 m 2 / g to 1400 m 2 / g, 1025 m 2 / g to 1400 m 2 / g, 1050 m 2 / g to 1400 m 2 / g, 1075 m 2 / g to 1400 m 2 / g, 1100 m 2 / g to 1400 m 2 / g, 500 m 2 / g to 1300 m 2 / g, 700 m 2 / g to 1300 m 2 / g, 900 m 2 / g to 1300 m 2 / g, 925 m 2 / g to 1300 m 2 / g, 950 m 2 / g to 1300 m 2 / g, 975 m 2 / g to 1300 m 2 / g, 1000 m 2 / g to 1300 m 2 / g, 1025 m 2 / g to 1300 m 2 / g, 1050 m 2 / g to 1300 m 2 / g, 1075 m 2 / g to 1300 m 2 / g, 1100 m 2 / g to 1300 m 2 / g, 500 m 2 / g to 1200 m 2 / g, 700 m 2 / g to 1200 m 2 / g, 900 m 2 / g to 1200 m 2 / g, 925 m 2 / g to 1200 m 2 / g, 950 m 2 / g to 1200 m 2 / g, 975 m 2 / g to 1200 m 2 / g, 1000 m2 / g to 1200 m 2 / g, 1025 m 2 / g to 1200 m 2 / g, 1050 m 2 / g to 1200 m 2 / g, 1075 m 2 / g to 1200 m 2 / g, 1100 m 2 / g to 1200 m 2 / g. In more specific embodiments, the activated carbon has a BET surface area of 900 m 2 / g to 1400 m 2 / g or 900 m 2 / g to 1200 m 2 / g, preferably 925 m 2 / g to 1150 m 2 / g.

[0050] As known to the person skilled in the art, the surface can be determined by gas adsorption on the inner and outer surface of a material at different pressures according to the BET (Brunauer-Emmett-Teller) theory. The surface is then calculated according to the Brunauer-Emmett-Teller theory. Nitrogen in the form of a gas or liquid can be used as the gas for adsorption.

[0051] According to specific embodiments, the activated carbon comprises at least 75 wt% to 80 wt% of carbon and has a BET surface area of at least 500 m 2 / g, at least 700 m 2 / g, at least 900 m 2 / g, for example 900 m 2 / g to 1400 m 2 / g. Furthermore, the content of the sum of Si and Al in the activated carbon adsorbent is typically at most 25 wt% to 20 wt%, for example at most 10 wt% or at most 5 wt%.

[0052] The activated carbon used in the process of the present application can be in any form, including but not limited to powder and compacted forms. For industrial purposes, compacted forms, such as pellets, granules and tablets, are preferred as they are easier to handle and guarantee a reduction in the loss of material in each cycle. Thus, in specific embodiments, the activated carbon is in the form of granules, pellets or tablets.

[0053] In certain embodiments, the ratio between the volume of LAB and the mass of activated carbon is between 1 : 1 (mL / g) and 50: 1 (mL / g), for example between 2: 1 (mL / g) and 40: 1 (mL / g), preferably between 3: 1 (mL / g) and 30: 1 (mL / g). This means that the activated carbon can purify several times its mass in volume of LAB (for example, 40 times, when the ratio is 40: 1 (mL / g)), while still obtaining a good quality product after purification.

[0054] In the second step of the method of the present application, the activated carbon adsorbent is reactivated with benzene. It has been found that by passing liquid benzene through the spent activated carbon, the impurities of the spent activated carbon can be conveniently removed from the spent activated carbon.

[0055] Several methods of reactivating activated carbon have been disclosed in the prior art, including for example heat treatment, acid or base treatment and treatment with solvents or gases (for example steam, nitrogen). It is important to note that depending on the reactivating agent medium used, the operating capacity of the adsorbent after reactivation can be less than the operating capacity of the fresh adsorbent. This is because not all of the active sites are freed again after the desorption cycle. Advantageously, the present application shows that benzene can fully reactivate activated carbon during many cycles (see Example 3 and Example 5). However, as can be understood from Example 4 and Example 6, other fluids such as nitrogen or alkanes are not able to properly reactivate activated carbon. In Examples 3 to 6, benzene is in liquid state.

[0056] The method of the present application can be carried out at any scale, from small scale using laboratory equipment to industrial scale in a chemical plant using large purification units.

[0057] In a preferred embodiment, the method of the present application is carried out 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 spent activated carbon; and b) passing a stream of benzene through the spent activated carbon to obtain reactivated activated carbon.

[0058] The method of the present application can be applied to any stream containing LAB within an industrial plant (industrial environment).

[0059] Likewise, the process can be carried out in various configurations, including batch process configurations and continuous process configurations. Preferably, it is carried out in a unit of a system with two or more reactors in parallel, wherein at least one reactor is configured to perform step a) (purification / adsorption phase) and at least another reactor is configured to perform step b) (regeneration / reactivation / desorption phase). 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). A particular embodiment of this configuration is Figure 3 the configuration shown in Figure 1.

[0060] For industrial plants with a system of two or more reactors in parallel for continuous mode, it is preferred that all reactors operate at the same temperature, or at least 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, for example 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 about 0°C.

[0061] 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 at 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 at 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 at a temperature of about 100°C.

[0062] 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.

[0063] In certain embodiments, step a), step b) or both are carried out at a temperature of 25 °C to 250 °C, for example 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 for both steps, running at a temperature close to 100 °C, for example 50 °C to 150 °C or 75 °C to 125 °C (for example about 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C or 125 °C) allows to reduce the energy consumption and at the same time to achieve full desorption of the impurities in the activated carbon in step b) and adsorption in step a) without degradation of the LAB. In preferred embodiments, both step a) and step b) are carried out at a temperature of about 100 °C.

[0064] In certain embodiments, step a), step b) or both are carried out at a pressure of 0 to 30 bar, for example 5 to 25 bar or 10 to 20 bar. Preferably, step a) is carried out at a pressure of 10 to 30 bar, for example 15 to 25 bar, and / or step b) is carried out at a pressure of 0 to 20 bar, for example 5 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.

[0065] 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.

[0066] In certain embodiments, the liquid hourly space velocity (LHSV) (defined as the ratio of the hourly volume flow of LAB to the volume of activated carbon) in step a), step b) or both is 0.1 h -1 to 10 h -1 , preferably 0.2 h -1 to 8 h -1 , more preferably 0.4 h -1 to 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 -1 and the liquid hourly space velocity (LHSV) in step b) is about 10 h -1 .

[0067] In certain embodiments, step a) is carried out for 1 hour to 24 hours, and step b) is carried out for 1 hour to 24 hours. In a more particular embodiment, step a) is carried out for 1 hour to 5 hours, and step b) is carried out for 1 hour to 10 hours. In an even more particular embodiment, step a) is carried out for about 2 hours, and step b) is carried out for about 4 hours.

[0068] In a particular embodiment, the purification of LAB is carried out in a continuous system consisting of three reactors running in parallel (as shown in Figure 3 ). Reactor 1 is running in the adsorption phase (about 2 hours), while reactor 2 and reactor 3 are running in the desorption phase. In the three reactors, the temperature is about 100 °C, the flow rate is about 20 L / min (LHSV 5 h -1 ) and the flow direction is upward flow. Alternatively, the purification is carried out in a purification unit comprising two reactors, wherein the reactor in the adsorption phase is running at a LHSV of about 5 h -1 and the reactor in the desorption phase is running at a LHSV of about 10 h -1at a LHSV of 1 to 10.

[0069] In certain embodiments, the process for purifying linear alkylbenzene compounds (LAB) of the present application further comprises contacting the (unpurified) LAB compounds of step a) or the purified LAB compounds obtained in step a) with a further adsorbent different from activated carbon. This treatment with a further adsorbent can be performed before, simultaneously or after the treatment with activated carbon of step a). The further adsorbent is preferably selected from molecular sieves (zeolites) and clays or a combination thereof. As explained previously, the treatment with activated carbon mainly leads to the reduction of aromatic and polycyclic aromatic hydrocarbons (PAHs), whereas the treatment with other solid adsorbents such as clays (clay treatment) mainly leads to the reduction of non-aromatic unsaturated compounds, and thus both treatments can be used complementarily or synergistically for the purification of LAB (see Example 2).

[0070] In some embodiments, the process further comprises sulfonating the purified LAB to obtain the corresponding linear alkylbenzene sulfonic acid (LABSA).

[0071] In some embodiments, the process further comprises neutralizing the LABSA to obtain the corresponding linear alkylbenzene sulfonate (LAS).

[0072] In some embodiments, the LAB to be purified is obtained by a process comprising the alkylation of benzene with a mono-olefin.

[0073] As used herein, the term "about" or "approximately," as applied to one or more of the values of a parameter, refers to a value that is similar to a stated reference value. In certain embodiments, the term "about" or "approximately" means a value that can be within ±20%, preferably ±10%, and more preferably ±5% of a stated reference value. When "about" or "approximately" precedes a numerical range, it applies to both the upper range endpoint and the lower range endpoint.

[0074] Indeed, those skilled in the art realize that values associated with measurements are subject to measurement error that limits their accuracy. When terms such as "about" or "approximately" are applied to a particular value (e.g., "about 200 °C" or "approximately 200 °C") or range (e.g., "about x to about y"), the value or range can be interpreted as being as accurate as the method used to measure it. Unless explicitly stated otherwise, the general conventions of the scientific and technical literature can be applied, whereby the last digit of a value preferably indicates the precision of the measurement. Thus, unless other error tolerances are given, the maximum tolerance is preferably determined by applying the rounding convention to the last decimal place. For example, a value of 3.5 preferably has an error tolerance of 3.45 to 3.54, and a range of 2% to 10% preferably covers a range of 1.5% to 10.4%. Those skilled in the art understand the stated variations of particular values and that the variations are within the context of the present invention. Furthermore, to provide a more concise description, some of the quantitative expressions given herein are not prefaced by the term "about." It should be understood that every quantity given herein is intended to indicate both actual given values and also approximations based on reasonable inferences from the ordinary skill in the art, including equivalents and approximations of the given values resulting from experimental and / or measurement conditions, whether or not the term "about" is explicitly used.

[0075] Concentrations, amounts, and other numerical data can 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 construed as having

[0076] The following examples illustrate the present invention and are not to be construed as limiting the scope thereof.

[0077] Example

[0078] Example 1 - Purification of LAB on laboratory scale

[0079] Example 1A - Proof of concept test for purification of LAB with activated carbon

[0080] 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 characteristics: carbon 87.3 wt%, BET surface area 1390 m 2 / g.

[0081] 50 g of LAB product was mixed with 14 g of activated carbon for 20 min. Then, the mixture was filtered under vacuum pressure through a simple Buchner funnel to separate the purified LAB (liquid) from the activated carbon (solid).

[0082] The effectiveness of the purification procedure in removing colour impurities was measured by absorbance. Specifically, a sample of LAB purified with activated carbon as described above and a sample of LAB that was not purified (raw) were taken and then the absorbance of both samples was measured at 322 nm (characteristic wavelength for monitoring the quality of LAB). The absorbance of the sample purified with activated carbon was measured as 0.8, while the absorbance of the untreated sample was measured as 1.6.

[0083] Figure 1 is a photograph showing a sample of LAB treated with activated carbon (left) and a sample of LAB that was not treated (right), both of which had previously been treated with a slight sulfonation with sulfuric acid. Treating the sample of LAB with activated carbon visually caused a reduction in the colour intensity of the sample of LAB after sulfonation.

[0084] Example 1B - Identification of impurities in LAB product

[0085] A number of secondary compounds have been identified in the LAB product by using a sophisticated two-dimensional gas chromatography system (GCxGC) with two detectors in parallel, FID (flame ionization detector, for quantification) and ToF (time of flight, for measurement). The analysis was based on an in-house two-dimensional chromatography method developed specifically for LAB samples (in-house reference CI-M8, GCxGC configuration A with a non-polar column in the first dimension and a semi-polar column in the second dimension).

[0086] Figure 2 is a GCxGC / FID / ToF chromatogram of a sample of LAB that was not treated (top) and a sample of LAB treated with activated carbon (bottom). The activated carbon used in this example had the following characteristics: carbon 87.3 wt%, BET surface area 1390 m 2 / g. As shown in Figure 2 the products that were mainly removed in the treatment with activated carbon were: alkyl naphthalenes, tetrahydronaphthalenes and diphenylalkanes. Specifically, the reduction of alkyl naphthalenes was particularly complete. There were even lower concentrations of other compounds with higher aromaticity, although it was not possible to quantify them, they were also completely removed or greatly removed: phenyltetrahydronaphthalenes, fluorenes and terphenyls, etc.

[0087] Example 1C - Comparison of activated carbon with other adsorbents

[0088] This example compares the efficacy of nine different activated carbons in purifying LAB with the efficacy of three other common adsorbents with different properties.

[0089] These solids were tested using 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 track shaking for 2 hours. Subsequently, the solids were separated by filtration to recover the LAB sample, wherein the quality was measured by measuring the absorbance at 322 nm.

[0090] The table below shows the absorbance of the tested activated carbon and other purified solids at 322 nm:

[0091] These results demonstrate that activated carbon significantly improved LAB quality for all tested samples. However, other adsorbents were unsuitable for purifying LAB or showed only minimal improvement in quality (in terms of the content of color impurities, i.e., those measurable by absorbance at 322 nm, such as aromatic and polycyclic aromatic compounds).

[0092] Example 2 - Treatment with activated carbon vs. treatment with clay in pilot plant

[0093] In the pilot plant, activated carbon M5 from Example 1C and clay (clay treatment agent) (Si+Al: 48.7wt%, BET surface area 201 m²) were used. 2 / g) Two LAB products of different qualities were treated to evaluate the different performances of the two solids.

[0094] The table below shows the results obtained from tests performed on LAB (medium quality) with an initial absorbance of 0.620 at 322 nm and a bromine index of <0.5:

[0095] In this case, treatment with activated carbon resulted in an improvement in absorbance values, indicating that activated carbon adsorbs aromatic and polycyclic aromatic chromophore compounds. However, treatment with clay did not improve absorbance values, reflecting its unsuitability for adsorbing such compounds. Conversely, clay can eliminate non-aromatic unsaturated compounds (which produce color upon sulfonation), and this will be reflected by a decrease in the bromine index (however, in this experiment, the initial bromine index was already low).

[0096] The table below shows the results obtained from tests performed on LAB (below medium quality) that initially had an absorbance of 0.885 at 322 nm and a bromine index of 10.

[0097]

[0098] Using this sample, treatment with activated carbon did not improve the bromine index value, but the absorbance was greatly reduced, indicating that non-aromatic unsaturated compounds were not adsorbed, but aromatic and polycyclic aromatic compounds were adsorbed. This effect was not seen in the clay, which, although allowed to reduce the bromine index value (i.e. eliminate unsaturated compounds), did not improve the absorbance value, possibly due to the low capacity of the clay to adsorb aromatic and polycyclic aromatic compounds from the LAB.

[0099] In summary, both solids improved the color quality of the LAB, but they did so by different routes: the clay eliminated non-aromatic unsaturated compounds, which mainly produce color after sulfonation, while the activated carbon eliminated aromatic and polycyclic aromatic compounds, which directly produce color and produce color after sulfonation, and considering the results seen in the second sample, the influence of aromatic and polycyclic aromatic compounds on the absorbance value is of greater importance than that of unsaturated compounds.

[0100] Example 3 - Life cycle of activated carbon

[0101] The ability of the activated carbon adsorbent M5 from Example 1C to regenerate was tested in a continuous cycle using LAB with an initial absorbance of 0.620 at 322 nm. Full regeneration of the activated carbon was obtained in at least 9 cycles. The ability of the activated carbon adsorption to cause impurities of color was not affected even after 9 purification cycles, as can be seen in Table 2, which shows the absorbance of the LAB purified with activated carbon in all cycles and using benzene as desorbent. Figure 4 Figure 4 shows the absorbance of the LAB purified with activated carbon in all cycles and using benzene as desorbent. This shows that the same adsorbent can be applied to different cycles, indicating that the adsorbent according to the invention is versatile and can be fully exploited in an economic way.

[0102] Example 4 - Comparison of benzene as desorbent with N2

[0103] This experiment was designed to compare the desorption capacity of benzene with nitrogen in a continuous device using a bed of activated carbon M5 from Example 1C. Four samples were collected from the feed of untreated LAB. The untreated LAB sample showed an absorbance of 0.620 at 322 nm before treatment. For this experiment, the untreated LAB sample was used for each cycle.

[0104] In the first cycle, before switching to the regeneration step, the first sample of untreated LAB was purified with activated carbon according to the invention to obtain LAB with an absorbance of 0.343 at 322 nm, and the spent activated carbon was regenerated with benzene at 100°C during 8 hours. ​

[0105] In the second cycle, before switching to the regeneration step, a second sample of untreated LAB was purified with activated carbon regenerated from the first cycle to obtain LAB with an absorbance at 322 nm of 0.383, and the spent activated carbon was regenerated with nitrogen at 200°C during 24 hours.

[0106] In the third cycle, before switching to the regeneration step, a third sample of untreated LAB was purified with activated carbon regenerated from the second cycle to obtain LAB with an absorbance at 322 nm of 0.604, and the spent activated carbon was regenerated with benzene at 100°C during 8 hours.

[0107] In the fourth cycle, a fourth sample of untreated LAB was purified with activated carbon regenerated from the third cycle to obtain LAB with an ABS at 322 nm of 0.334 at the end of the cycle.

[0108] After desorption with N2, the activated carbon was not able to recover its original capacity even under strong conditions (24 h at 200°C). However, it recovered the initial capacity when benzene was used subsequently under milder conditions (8 hours at 100°C).

[0109] Figure 5 Adsorption over time corresponding to these 4 cycles of purification of LAB with activated carbon (CA) and desorption with benzene (Bz) and nitrogen (N2) is shown.

[0110] Therefore, benzene, which is a starting material in the manufacture of LAB, can be used as a desorbent for the regeneration of activated carbon material. Thus, it is not necessary to introduce new material into the manufacturing process of LAB, since the regeneration of the activated carbon bed can be carried out using the existing flow containing benzene.

[0111] Example 5 - Quality of benzene as desorbent

[0112] This experiment was designed to study the quality of benzene as desorbent after several cycles in a continuous device using a bed of activated carbon M5 from Example 1C. Figure 6 Adsorption kinetics corresponding to 7 cycles of purification of LAB with activated carbon (CA) and using the same benzene as desorbent are shown. The sample of untreated LAB showed an absorbance at 322 nm of 0.620 before treatment.

[0113] By using the same benzene in several desorption cycles (i.e. without carrying out any treatment to remove impurities in the benzene), it was observed that its ability to regenerate the activated carbon bed to 100% remained completely, allowing high quality LAB to be obtained.

[0114] The adsorption curve maintained its morphology in each cycle.

[0115] Due to the saturation of the benzene in the chromophore compound, the desorption curve increases gradually in absorbance values. This slight saturation does not significantly affect its regeneration ability and turns to affect the LAB quality. In any case, if needed, the benzene can be purified (e.g. by distillation).

[0116] Example 6 - Comparison of benzene as desorbent for activated carbon regeneration with paraffins

[0117] This experiment was designed to compare the desorption ability of benzene with that of a paraffin (C 10 -C 13 mixture of n-paraffins) using a bed of activated carbon M5 from Example 1C.

[0118] As Figure 7 shown, during the adsorption phase, the paraffin did not desorb enough of the contaminants retained on the solid, but only reached the "flushing" of the activated carbon (see flushing cycle / phase in Figure 7 ). However, the subsequent treatment of the flushed activated carbon with benzene allowed the continuation of the desorption of the contaminants, resulting in an excellent regeneration of the activated carbon (see desorption cycle / phase in Figure 7 ). The capacity of the bed was quantified as the area under the curve: the flushing phase produced a value of 6.3, while the desorption with benzene produced a value of 25.5. In terms of percentage, the flushing with paraffin eliminated 19.8% of the total contaminants area, and benzene was responsible for the remaining 80.2%.

[0119] When the same regeneration test was performed with benzene only, the area under the curve was calculated as 31.8 (see Figure 8 ). This corresponds to the sum of the areas from the flushing and desorption phases in Figure 7 .

[0120] This observation confirms that benzene alone can desorb a substantially higher amount of adsorbed compounds with absorption at a 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.

[0121] Conclusion

[0122] It has been demonstrated that the treatment of alkylbenzenes with activated carbon significantly improves the color of the alkylbenzenesulfonates and thus the quality of the alkylbenzenesulfonates. This property is important for the end use of the product in the formulation of detergents and household cleaning products.

[0123] Experimental tests have been performed with other solid adsorbents, including for example clays and zeolites, but the results obtained were significantly worse than with activated carbon.

[0124] The purification by adsorption with activated carbon can be applied as a complementary method to the treatment of the LAB stream with clays or zeolites. An improvement in quality is observed more consistently. In addition, activated carbon can be regenerated with benzene several times, which allows the efficient use of the activated carbon adsorbent.

[0125] In addition, a family of compounds responsible for the color, aromatic compounds of the PAH type, has been identified. It has been demonstrated that the treatment with activated carbon implies a reduction or even complete elimination of these chromophore compounds, which, although present in very low concentrations, have a great influence on the coloring of the final surfactant.

[0126] The impact of this method is important since it is possible to obtain a LAB product with enhanced and reliable quality from the industrial process, reducing the amount of material produced with insufficient quality. Thus, the invention represents an improvement in the linear alkylbenzene purification technology.

Claims

1. A method for purifying linear alkylbenzene compounds (LAB), the method comprising: a) Contact the LAB compound with activated carbon to obtain purified LAB compound and spent activated carbon, wherein the activated carbon contains at least 75 wt% carbon and has a density of at least 500 μm. 2 / g of BET surface area; as well as b) Contact the waste activated carbon with benzene to obtain regenerated activated carbon.

2. The method according to claim 1, wherein the method is performed by the following steps: a) Passing the LAB compound stream through the bed of activated carbon to obtain a purified LAB compound stream and spent activated carbon; and b) Passing benzene through the waste activated carbon to obtain regenerated activated carbon.

3. The method according to claim 1 or 2, wherein the method is carried out continuously using a system with two or more reactors operating in parallel, wherein at least one reactor is configured to perform step a), and at least another reactor is configured to perform step b).

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

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

7. The method according to any one of claims 1 to 6, wherein the LHSV in step a), step b), or both is 0.1 h. -1 Up to 10 h -1 Preferably 0.2 h -1 up to 8 h -1 More preferably 0.4 h -1 up to 5 hours -1 .

8. The method according to any one of claims 1 to 7, wherein step a) is performed for 1 hour to 24 hours, and step b) is performed for 1 hour to 24 hours.

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

10. The method of claim 9, further comprising neutralizing the LABSA to obtain the corresponding linear alkylbenzene sulfonate (LAS).

11. The method according to any one of claims 1 to 10, wherein the LAB to be purified is obtained by a method comprising alkylating benzene with a monoolefin.

12. The method according to any one of claims 1 to 11, which reduces the absorbance of the LAB sample in the wavelength region of 320 nm to 354 nm.

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

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