Process for the production of 2-alkylalkanol

Abstract

A process for the production of a product 2-alkylalkanol stream the process comprises feeding a polished 2-alkylalkanol stream to a lights removal distillation column, wherein a lights stream is withd

Description

Field of the Invention The present invention relates to processes for the production of 2-alkylalkanol. In particular, but not exclusively, the present invention relates to processes for the production of 2-ethylhexanol and / or 2-propylheptanol. Background The general process for the production of oxo alcohols by hydroformylation, optionally aldolization, and hydrogenation is well-known. The feedstocks to the process are syngas and olefin. Those feedstocks can be obtained from any source. For example, olefin can be obtained from Fischer Tropsch reactions, methanol-to-olefin process, from a refinery, from sustainable sources, from propane dehydrogenation or from any other source of olefin. The syngas can, for example be obtained from reforming (of coal, natural gas, or any other suitable feedstock) or gasification. The syngas can also be obtained from sustainable feedstocks. An example is capturing carbon dioxide and producing hydrogen from electrolysis, or another source, before using the reverse water gas shift reaction to convert the carbon dioxide and hydrogen to syngas. Where there are contaminants present in the feedstocks these can be removed in a feedstock purification section. Hydroformylation is the reaction of carbon monoxide and hydrogen with olefin to form aldehyde. The aldehyde has one more carbon that the olefin. Hydroformylation is typically carried out using a homogeneous rhodium catalyst with an organophosphorus ligand, such as those listed in US4769498, US4885401, US5113022, US5202297, US5235113, US4668651, US4748261, US5254741, US5391801, US5059710, US3527809, US4283562, US4400548, US4482749, US4599206, US4716250, US4717775, US4731486, US4737588 or WO8001690. Typically, the hydroformylation reaction is carried out in two or more reactors. Aldehyde product and the rhodium catalyst are passed from the reactors to a catalyst recovery section which separates the aldehyde product from the rhodium catalyst and its solvent. The solvent may typically be the aldehyde, heavies formed in the reaction or any other suitable solvent. Examples of techniques to separate the rhodium catalyst, or to stabilise the rhodium catalyst can be found in US4774361, US5874640, US5892119, US6090987, US6294700, US6100432, US5114473, US4148830 and US4247486. The aldehyde will contain a mix of normal and iso aldehyde. The aldehyde may be hydrogenated to both normal and iso alcohol, or aldolized and hydrogenated to a mixture of branched alcohols, such as Cio alcohols in the form of a mixture of 2-propylheptanol isomers. For some products, such as 2-ethylhexanol, the aldehyde is typically sent to a lights removal distillation column to substantially separate the normal and iso aldehyde. Downstream of the lights removal distillation column, normal aldehyde, such as n-butyraldehyde, is typically then either hydrogenated to normal alcohol, such as n-butanol, or passed to an aldolization section. The iso-aldehyde may be used as a product or may, in some cases, such as when 2-propylheptanol is being produced, be passed with some or all of the normal aldehyde to an aldolization section. In aldolization the aldehyde reacts to form an acrolein (also known as an alkenal), which can then be hydrogenated to an alcohol. Examples include aldolization of n-butyraldehyde to form ethyl-propyl-acrolein (also known as 2-ethylhexenal), which is then hydrogenated to 2-ethylhexanol, or aldolization of valeraldehyde to propyl-butyl-acrolein (also known as 2-propylheptenal), which is then hydrogenated to 2-propylheptanol. The hydrogenation, whether of the normal- or iso-aldehyde coming from the lights removal distillation column, or of the acrolein from the aldolization, may be carried out in a reactor such as that disclosed in WO2012 / 110775 or WO2023 / 161612 . The product alcohols may be refined, typically in one or more distillation columns, to achieve desired purities. Examples of refining schemes are disclosed in WO2018 / 069714 and WO2019 / 197831 . This invention relates particularly to the production of 2-alkylalkanol, for example 2-ethylhexanol or 2-propylheptanol and preferably 2-ethylhexanol. In accordance with the above general process, the olefin and syngas are reacted via hydroformylation to produce normal- and iso-aldehyde. The normal- and iso-aldehyde are separated in a lights removal distillation column. The normal-aldehyde is aldolized to produce 2-alkylalkenal and the 2-alkylalkenal is hydrogenated to 2-alkylalkanol. The iso-aldehyde is typically either hydrogenated to iso-alkanol or sold as iso-aldehyde. In some processes, only some of the normal-aldehyde is used for 2-alkylalkanol production and some of the normal-aldehyde is hydrogenated to normal-alkanol. As a specific example, propene and syngas may be hydroformylated to form a mix of iso-butyraldehyde and normal-butyraldehyde. Following separation of the iso-butyraldehyde and normal-butyraldehyde in a lights removal distillation column at least some of the normal-butyraldehyde is aldolized to 2-ethylhexenal, which is then hydrogenated to 2-ethylhexanol. The iso-butyraldehyde may be hydrogenated to iso-butanol or sold as isobutyraldehyde. Some of the normal-butyraldehyde may be hydrogenated to normal-butanol. The purity of 2-alkylalkanol streams may be defined by reference to acid colour. The skilled person will be familiar with acid colour, which may, for example, be specified in national specifications for 2-alkylalkanol products. Acid colour may, for example be measured by the tests set out in BS 4583 Standard "Methods of Test for Higher Alcohols for Industrial Use" 91st Edition, May 24, 2021. The test involves treating a sample with concentrated sulphuric acid under conditions specified in the Standard. Impurities in the sample form coloured compounds by reactions which are catalysed by the sulphuric acid. Once the sample has been reacted with the sulphuric acid, the colour is compared with that of a series of platinum cobalt standards of equal volume in matched 100 ml Nessler tubes. These colour standards are known as APHA standards and are defined by the US standard ASTM D1209. As an example, an APHA colour of less than 25 may be desirable for a 2-alkylalkanol product. Product refining may be carried out to improve the purity and meet the desired APHA colour. As described above, crude 2-alkylalkanol is produced via hydrogenation and then refined to produce the desired 2-alkylalkanol product. The refining of 2-alkylalkanol is typically carried out in one or more distillation columns, often also with a polishing hydrogenation reactor. The polishing hydrogenation reactor is located in the train of distillation columns and typically converts partially hydrogenated components, such as 2-alkylalkenol and 2-alkylalkanal, to the desired 2-alkylalkanol. The polishing hydrogenation reactor will also convert unreacted 2-alkylalkenal to the desired 2-alkylalkanol. An example refining scheme is disclosed in RU2312850C1 in which a complex series of 4 distillation columns is arranged between a first hydrogenation and a polishing hydrogenation. The 4 distillation columns are arranged such that no further distillation is required downstream of the polishing hydrogenation. A key feature of the arrangement of RU2312850 is that hydrogenation of 2-ethylhexenal to 2-ethylhexanol is carried out in the liquid phase at a pressure of 200-300atm, a temperature of 100-220°C on a nickel-containing catalyst with incomplete conversion of 2-ethylhexenal, and a mixture of the fraction of unreacted Cs aldehydes from the top of the second distillation column and 2-ethylhexanol are used as a recycle to the bulk hydrogenation step, in a mass ratio of Cs aldehydes:2-ethylhexanol equal to (0.03-0.5) :1, with a mass ratio of fresh raw materials: recycled materials of (0.3— 3):1. It is described as essential that separation in the second column, that releases the unreacted Cs aldehydes for the recycle is carried out at a top pressure of 50-200 mmHg, with a temperature difference between the 12th theoretical plate from the top and the top of the column in the range of 15-35°C, and the flow-rate of the recycle aldehyde fraction should be such that the potential withdrawal of 2-ethylhexanol in the distillate of the column is 1-5 wt%. A further example is WO2018 / 069714. In the refining scheme of WO2018 / 069714, following a bulk hydrogenation to produce a crude 2-alkylalkanol stream, heavies removal is carried out upstream of the polishing hydrogenation reactor and lights removal is carried out downstream of the polishing hydrogenation reactor. Such an arrangement can provide good results, for example because heavies are not broken down into acid colour forming products in the polishing hydrogenation reactor and the polished product is not exposed to the high temperatures of a heavies removal column, which can also result in acid colour forming products. However, it remains desirable to provide even better refining schemes. Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art. In particular, preferred embodiments of the present invention seek to provide improved refining schemes to further improve the cost and energy efficiency, and / or to provide improved product quality, of 2-alkylalkanol production. Summary of Invention According to a first aspect of the invention, there is provided a process for the production of a product 2-alkylalkanol stream, the process comprising feeding a polished 2-alkylalkanol stream to a lights removal distillation column, wherein a lights stream is withdrawn from at or near the top of the lights removal distillation column, and wherein a heavies containing stream is withdrawn from a first position at or near the bottom of the lights removal distillation column and wherein the product 2- alkylalkanol stream is withdrawn as a liquid side draw from a second position above the first position. The skilled person is familiar with the use of polishing hydrogenation reactors. Such reactors typically complete the final stages of a desired reactive conversion. As used herein, a polished 2-alkylalkanol stream is a stream that has undergone one or more, preferably at least two, stages of hydrogenation to convert 2-alkylalkenal to 2-alkylalkanol. The polished 2-alkylalkanol stream may thus in some embodiments be said to be a stream in which all the desired hydrogenation reaction steps have been carried out and which requires only non-reactive separations, such as distillations, to reach the desired product purity. In some embodiments the polished 2-alkylalkanol stream is a stream recovered from a polishing hydrogenation reactor. By withdrawing the product 2-alkylalkanol stream from a second position above the first position, the present invention allows the product 2-alkylalkanol stream to have a lower heavies concentration than would be the case if the product 2-alkylalkanol stream were withdrawn at or near the bottom of the distillation column in the conventional way. This may be particularly advantageous where the polished 2-alkylalkanol stream is obtained from a refining scheme comprising a bulk hydrogenation reactor and a polishing hydrogenation reactor, with heavies removal occurring between the bulk hydrogenation reactor and the polishing hydrogenation reactor. The applicant has identified that heavies with boiling point close to the 2-alkylalkanol product may not be completely removed in a heavies removal upstream of the polishing hydrogenation reactor and may then be hydrogenated to other impurities in the polishing hydrogenation reactor, which then affect the product purity. Additionally or alternatively, as the polishing catalyst in the polishing hydrogenation reactor approaches end-of-life conditions, including for example higher temperature, selectivity to heavies may increase and it may therefore be advantageous to remove some heavies downstream of the polishing hydrogenation reactor if that can be achieved at low cost and without high sump temperatures that lead to impurities affecting acid colour as described above in relation to the prior art. The present invention advantageously provides a method for such heavies removal, whilst also keeping the acid colour benefits of removing a majority of heavies upstream of the polishing hydrogenation reactor so as to advantageously avoid break-down of heavies to colour forming products in the polishing hydrogenation reactor. By taking the 2-alkylalkanol product as a liquid side draw from a lights removal distillation column downstream of the polishing hydrogenation reactor, no extra distillation columns are required and the capital cost of the distillation columns is not significantly increased, but the product quality is improved. The improved quality is advantageously also achieved at modest energy cost since only a small fraction of the 2-alkylalkanol must be vaporised, whereas including a full heavies removal column downstream of the polishing hydrogenation reactor would require nearly all of the 2-alkylalkanol to be vaporised. The process of the invention advantageously achieves a commercially useful reduction in heavies content in the product 2-alkylalkanol stream at a commercially acceptable cost. A particularly preferred aspect of the invention involves the following steps: (a) a bulk hydrogenation reactor in which 2-alkylalkenal is hydrogenated to 2-alkylalkanol, which is recovered in a crude 2-alkylalkanol stream; (b) a heavies removal distillation column, in which heavies are removed from the crude 2-alkylalkanol stream, wherein a heavies-removed crude 2-alkylalkenol stream is recovered from at or near the top of the heavies removal distillation column; (c) a polishing hydrogenation reactor in which one or more of 2-alyklalkenol, 2-alkylalkanal and 2-alkylalkenal in the heavies-removed crude 2-alkylalkanol stream are hydrogenated to 2-alkylalkanol, which is recovered, along with 2-alkylalkanol already present in the heavies-removed crude 2-alkylalkanol stream, in a polished 2-alkylalkanol stream; and (d) a lights removal distillation column, in which lights are removed from the polished 2-alkylalkanol stream, wherein a lights stream is withdrawn from at or near the top of the lights removal distillation column, and wherein a heavies containing stream is withdrawn from a first position at or near the bottom of the lights removal distillation column and wherein a product 2-alkylalkanol stream is withdrawn as a liquid side draw from a second position above the first position. Preferably the heavies removal distillation column is the only distillation column located between the bulk hydrogenation reactor and the polishing hydrogenation reactor. Preferably the lights removal distillation column is the only distillation column located downstream of the polishing hydrogenation reactor. It will be appreciated that extra distillation columns add to capital cost of construction and it is therefore advantageous to optimise the distillation column arrangement. In this context, upstream and downstream refer to the flow path of 2-alkylalkanol through the process to the product 2-alkylalkanol stream. An advantage of the invention is that it concentrates heavies in the lights removal distillation column into the heavies containing stream and removes them from the product. Advantageously, the heavies containing stream is recycled upstream in the process, preferably to the heavies removal distillation column or upstream of the heavies removal distillation column. Heavies can then be removed from the process in the heavies removal distillation column and any 2-alkylalkanol slipped into the heavies containing stream can be recovered. This may advantageously mean that the lights removal distillation column can be operated more efficiently because more 2-alkylalkanol slip into the heavies containing stream can be tolerated than if the heavies containing stream was being sent directly to waste. It may also advantageously avoid high temperatures in the bottom of the lights removal distillation column, thus reducing the possibility for formation of compounds that can affect acid colour and avoiding the need for higher grade heat sources. Compared to adding a heavies removal column downstream of the polishing hydrogenation reactor, it may be a significant advantage of the invention that removing heavies using a process according to the invention may advantageously require only a small increase in temperature at the bottom of the lights removal distillation column because a high proportion of 2- alkylalkanol can be slipped in the heavies containing stream without overall loss of 2-alkylalkanol to the process. While the heavies containing stream is preferably recycled upstream in the process, preferably to the heavies removal distillation column or upstream of the heavies removal distillation column, in some embodiments a separate further heavies removal column may be provided to recover a recovered 2-alkylalkanol stream from the heavies containing stream. The recovered 2-alkylalkanol stream is preferably an overhead stream from the further heavies removal column. Such recovered 2-alkylalkanol stream may be combined with the 2-alkylalkanol product stream or recycled upstream in the process, preferably to the heavies removal distillation column or upstream of the heavies removal distillation column. Because the heavies containing stream is a small stream, such a column may advantageously operated efficiently and without excessive energy requirements and may permit more efficient purging of heavies from the process. Preferably the flowrate of the heavies containing stream is not more than 10%, preferably not more than 7% and more preferably not more than 5% of the flowrate of the product 2-alkylalkanol stream. In that way the concentration of the heavies in the product 2-alkylalkanol stream may advantageously be significantly reduced, but the size, and hence cost, of the equipment needed to treat the heavies containing stream, or the increase in size, and hence cost, of the upstream equipment to which the heavies containing stream is recycled, is small. In some embodiments the 2-alkylalkenal is produced by aldolization of an aldehyde, typically a normal aldehyde. In some embodiments the aldehyde is produced by hydroformylation of an olefin with syngas. While the process may be applicable to the production of various 2-alkylalkanols, particularly important 2-alkylalkanols are Cg-Cio 2-alkylalkanols. Thus, the aldehyde is preferably butyraldehyde or valeraldehyde or mixture of butyraldehyde and valeraldehyde. The skilled person will understand which Cg-Cio 2-alkylalkenals are produced from the aldolization, including cross-aldolization, of butyraldehyde and valeraldehyde, typically normal-butyraldehyde and a mixture of normal- and iso-valeraldehyde, and which Cg-Cio 2-alkylalkanols are produced from the subsequent hydrogenation of those Cg-Cio 2-alkylalkenals. Thus, the olefin is preferably a Ca to C4 olefin, the aldehyde is preferably a C4 to C5 aldehyde, the 2-alkylalkenal is preferably a Cs to C10 2-alkylalkenal, and the 2-alkylalkanol is preferably a Cs to C10 2-alkylalkanol. In a most preferred aspect, the olefin is propene, the aldehyde is butyraldehyde, the 2-alkylalkenal is 2-ethylhexenal, and the 2-alkylalkanol is 2-ethylhexanol. In some embodiments, the lights removal distillation column may be a falling film reboiler. A falling film reboiler may advantageously reduce the residence time in the reboiler, and thus reduce for example the formation of new heavies. For example, the product 2-alkylalkanol stream may preferably be taken as a liquid draw from the 2nd theoretical stage of the lights removal distillation column, which may advantageously further reduce the heavies content of the product 2-alkylalkanol stream by reducing the effect of heavies in the reboiler vapour due to the heavies concentration in the reboiler. Such an arrangement may benefit from an extra stage in the lights removal distillation column compared to a column in which the product 2-alkylalkanol stream is taken from the tray 1 liquid. In the process of the invention the product 2-alkylalkanol stream is withdrawn as a liquid side draw. By taking a liquid side draw, the invention advantageously takes advantage of the dilution effect of the reflux in the lights removal distillation column to achieve commercially useful reduction in heavies without significant increase in column duty. In the present invention the heavies containing stream has a greater concentration of heavies than the product 2-alkylalkanol stream. This is preferably achieved by withdrawing the product 2-alkylalkanol stream from a second position such that the product 2-alkylalkanol stream does not comprise reboiler liquid and withdrawing the heavies containing stream from a first position such that the heavies containing stream comprises reboiler liquid. This may be advantageous because a large amount of liquid may be vaporised in the reboiler and it may thus be possible to get a step increase in heavies concentration in the reboiler liquid. Preferably the product 2-alkylalkanol stream is withdrawn from liquid in the first three theoretical stages above the reboiler of the lights removal distillation column. The lights removal distillation column is preferably a packed column and the product 2-alkylalkanol stream is preferably withdrawn from liquid in the first three theoretical stages of the packing above the reboiler. If the lights removal distillation column is a trayed column, the product 2-alkylalkanol stream is withdrawn from the tray 1, 2 or 3 liquid of the lights removal distillation column. In some embodiments, the heavies containing stream is preferably withdrawn from the bottoms liquid of the lights removal distillation column. It will be understood that the bottoms liquid comprises reboiler liquid and liquid descending the lights removal distillation column, for example descending from tray 1 or the first theoretical stage of packing above the reboiler. In some embodiments, the heavies containing stream is preferably withdrawn from the reboiler liquid of the lights removal distillation column. It will be appreciated that features described in relation to one aspect of the invention may be equally applicable in another aspect of the invention. Some features may not be applicable to, and may be excluded from, particular aspects of the invention. Description of the Drawings Embodiments of the present invention will now be described, by way of example, and not in any limitative sense, with reference to the accompanying drawings, of which: Figure 1 is a block diagram of a process for the production of a product 2-alkylalkanol stream according to the present invention; Figure 2 is a block diagram of a process for the production of a product 2-alkylalkanol stream according to the present invention; Figure 3 is a view of the bottom of a lights removal distillation column for use in the present invention; and Figure 4 is a view of the bottom of a lights removal distillation column for use in the present invention. Detailed Description In figure 1 a polished 2-alkylalkanol stream 10 is fed to a lights removal distillation column 11. At or near the top of the lights removal distillation column 11 a lights stream 12 is withdrawn. Toward the bottom of the lights removal distillation column 11 a product 2-alkylalkanol stream 15 is withdrawn as a side draw at a first position. A heavies containing stream 17 is withdrawn from at or near the bottom of the lights removal distillation column 11. The lights removal distillation column 11 comprises a reboiler 20. A bottoms stream 19 from the lights removal distillation column is passed to the reboiler 20 where it is heated and returned as a reboiler stream 21 to the lights removal distillation column 11. In Figure 2, where like numbered items are as in Figure 1 and not described again, a stream comprising 2-alkylalkenal 2 is fed to a bulk hydrogenation reactor 4. From the bulk hydrogenation reactor 4, a crude 2-alkylalkanol stream 5 is recovered, which is fed to a heavies removal distillation column 6. In heavies removal distillation column 6, heavies are removed from the crude 2-alkylalkanol stream 5 and a heavies-removed crude 2-alkylalkenol stream 7 is recovered from at or near the top of the heavies removal distillation column 6. The removed heavies are removed in a heavies bottom stream 3 from at or near the bottom of the heavies removal distillation column 6. The heavies-removed crude 2-alkylalkanol stream 7 is fed to a polishing hydrogenation reactor 8 in which one or more of 2-alyklalkenol, 2-alkylalkanal and 2-alkylalkenal in the heavies-removed crude 2-alkylalkanol stream 7 are hydrogenated to 2-alkylalkanol. The 2-alkylalkanol is recovered, along with 2-alkylalkanol already present in the heavies-removed crude 2-alkylalkanol stream 7, in polished 2-alkylalkanol stream 10, which is fed to the lights removal distillation column 11 as described above in relation to Figure 1. The heavies containing stream 17 from the lights removal distillation column 11 is recycled to the heavies removal distillation column 6. In Figure 3, the bottom of a lights removal distillation column 100, suitable for use in any of the processes described in relation to Figures 1 and 2 above, contains a packed column with a series of theoretical stages 101, 102, 103, 104, 105. The first theoretical stage 101 is located at the bottom of the series, above the reboiler, and the theoretical stages are counted upwards, so the second theoretical stage 102 is above the first theoretical stage 101, the third theoretical stage 103 is above the second theoretical stage 102 and so on. The lights removal distillation column 100 includes a reboiler 142. Liquid bottoms stream 141 is withdrawn from the lights removal distillation column 100 and passed to the reboiler 142. Steam 144 is also fed to the reboiler 142, which condenses heating the liquid bottoms stream 141. The condensed steam leaves as condensed stream 145 and the heated liquid bottoms stream 141 leaves as reboiler stream 143, which is fed back to the lights removal distillation column 100. The product 2-alkylalkanol stream can be withdrawn from a number of positions 121, 122, 123 in the lights removal distillation column 100. The heavies containing stream can be withdrawn from position 131, which is a bottoms stream that comprises reboiler liquid from the reboiler stream 143 and liquid descending from the first theoretical stage 101. Position 121 is liquid from the first theoretical stage 101, position 122 is liquid from the second theoretical stage 102 and position 123 is liquid from the third theoretical stage 103. The concentration of heavies in a stream withdrawn from position 131 will be higher than in a stream withdrawn from position 5 121, position 122, or position 123 because the reboiler 142 effects a step increase in the heavies concentration in reboiler stream 143. Thus, in an example of the invention, the product 2-alkylalkanol stream is withdrawn from position 123 and the heavies containing stream is withdrawn from 10 position 131. An example according to the invention (Example 1) and a comparative example (Comparative Example 2), in which the 2-alkylalkanol product is withdrawn from the bottom of the lights removal distillation column at position 131 and there 15 is no heavies removal stream, are simulated. The skilled person will appreciate that simulation is a well-established method of assessing flowsheet options. The results are as follows : Example 1 Comparative example 2 Polished 2-alkylalkanol stream 10 flowrate kg / h 12639 12045 Product 2-alkylalkanol stream 15 flowrate (example 1) kg / h 11888 - Product 2-alkylalkanol stream flowrate from kg / h - 11888 position 131 (comparative example) Heavies containing stream 17 flowrate (example 1) kg / h 595 - Reflux flowrate kg / h 8686 8909 Reboiler duty MW 2.495 2.495 Composition of heavies in polished 2-alkylalkanol stream 10 wt% 0.218 0.218 Composition of heavies in product 2-alkylalkanol stream wt% 0.076 0.221 Compositions in the above table are wt% relative to the total flowrate in the stream. It can be seen that, in the process of the invention, the composition of heavies in the product 2-alkylalkanol stream is 0.076 wt% compared to 0.218 wt% in 5 the product 2-alkylalkanol stream withdrawn at position 131 in the comparative example. This significantly reduced heavies content is achieved without increasing the reboiler duty and with only a relatively small heavies containing stream 17 being recycled to the heavies removal column 6. 10 In Figure 4, the bottom of a lights removal distillation column 100' , similar to lights removal distillation column 100 and also suitable for use in any of the processes described in relation to Figures 1, 2 or 3 above, includes a reboiler 142 that operates as described for Figure 3 with like numbered items being the same and not described again here. In Figure 4 only the first theoretical stage 101 and the corresponding position 121 from which a liquid normal-aldehyde stream may be withdrawn are shown. However, the skilled person will appreciate that the other theoretical stage and corresponding positions would also be present up the packed column. In Figure 4 a weir 150 is provided onto which the liquid 51 from the reboiler stream 143 is fed. The vapour 52 from the reboiler stream 143 passes up through the first theoretical stage 101. Some of the liquid 51 from the reboiler stream is withdrawn at position 131' as a heavies containing stream, while some flows 53 over the weir and back into the bottoms liquid. The concentration of heavies in the heavies containing stream at position 131' will be higher than that in a 2-alkylalkanol stream withdrawn at position 121, or indeed withdrawn from the bottoms liquid of the lights removal distillation column 100'. Thus, in an example embodiment, a product 2-alkylalkanol stream may be withdrawn at position 121 and a heavies containing stream, having a higher heavies concentration, may be withdrawn at position 131'. The heavies containing stream comprises reboiler liquid 51 from reboiler stream 143, while the product 2-alkylalkanol stream does not. The embodiment thus takes advantage of the step increase in heavies concentration in the reboiler stream 143 due to the large amount of vaporisation in the reboiler 142 . It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, while the lights removal distillation column has been described in relation to theoretical stages in a packed column, various column configurations and packing types are possible and the skilled person will understand how 5 references to theoretical stages would be applied in such columns .

Claims

1. A process for the production of a product 2-alkylalkanol stream, the process comprising feeding a polished 2-alkylalkanol stream to a lights removal distillation column, wherein a lights stream is withdrawn from at or near the top of the lights removal distillation column, and wherein a heavies containing stream is withdrawn from a first position at or near the bottom of the lights removal distillation column and wherein the product 2-alkylalkanol stream is withdrawn as a liquid side draw from a second position above the first position.

2. A process according to claim 1, wherein the product 2-alkylalkanol stream withdrawn from the second position does not comprise reboiler liquid and the heavies containing stream withdrawn from the first position comprises reboiler liquid.

3. A process according to claim 1 or claim 2 wherein the polished 2-alkylalkanol stream is a stream recovered from a polishing hydrogenation reactor.

4. A process according to any of claims 1 to 3, wherein the process comprises a bulk hydrogenation reactor and a polishing hydrogenation reactor, with heavies removal occurring between the bulk hydrogenation reactor and the polishing hydrogenation reactor.

5. A process according to any preceding claim, wherein the process comprises the following steps:a. a bulk hydrogenation reactor in which 2-alkylalkenal is hydrogenated to 2-alkylalkanol, which is recovered in a crude 2-alkylalkanol stream;b. a heavies removal distillation column, in which heavies are removed from the crude 2-alkylalkanol stream, wherein a heavies-removed crude 2-alkylalkenol stream is recovered from at or near the top of the heavies removal distillation column;c. a polishing hydrogenation reactor in which one or more of 2-alyklalkenol, 2-alkylalkanal and 2-alkylalkenal in the heavies-removed crude 2-alkylalkanol stream are hydrogenated to 2-alkylalkanol, which is recovered, along with 2-alkylalkanol already present in the heavies-removed crude 2-alkylalkanol stream, in the polished 2-alkylalkanol stream; andd. the lights removal distillation column, in which lights are removed from the polished 2-alkylalkanol stream, wherein the lights stream is withdrawn from at or near the top of the lights removal distillation column, and wherein the heavies containing stream is withdrawn from a first position at or near the bottom of the lights removal distillation column and wherein the product 2-alkylalkanol stream is withdrawn as a liquid side draw from a second position above the first position.

6. A process according to claim 5, wherein the heavies removal distillation column is the only distillation column located between the bulk hydrogenation reactor and the polishing hydrogenation reactor.

7. A process according to claim 5 or 6, wherein the heavies containing stream is recycled to the heavies removal distillation column or upstream of the heavies removal distillation column.

8. A process according to any of claims 3 or 5 to 7, wherein the lights removal distillation column is the only distillation column located downstream of the polishing hydrogenation reactor.

9. A process according to any of claims 1 to 7, wherein the heavies containing stream is sent to a further heavies removal column to recover a recovered 2-alkylalkanol stream from the heavies containing stream.

10. A process according to claim 9, wherein the recovered 2-alkylalkanol stream is combined with the 2-alkylalkanol product stream.

11. A process according to claim 9, wherein the recovered 2-alkylalkanol stream is recycled to the heavies removal distillation column or upstream of the heavies removal distillation column.

12. A process according to any preceding claim, wherein the flowrate of the heavies containing stream is not more than 20%, preferably not more than 10%, more preferably not more than 7% and yet more preferably not more than 5% of the flowrate of the product 2-alkylalkanol stream.

13. A process according to any preceding claim, wherein the 2-alkylalkanol is a Cs to Cio 2-alkylalkanol.

14. A process according to claim 13, wherein the 2-alkylalkanol is 2-ethylhexanol.5 15. A process according to claim 13, wherein the 2-alkylalkanol is 2-propylheptanol.

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