SE538215C2 - Biorefining of crude tall oil - Google Patents

Abstract

538 2 Summary The present invention provides an improved and efficient biorefining of crude tall oil (CTO) to valuable industries and fine chemicals. According to the present invention, there is provided an improved method for removing contaminants from a CTO.

Description

FIELD OF THE INVENTION The present invention relates to the biorefining of crude tall oil (CTO).

Technical background The term crude tall oil, in the following CTO, refers to a by-product flood obtained during pulp production of wood in the pulp cooking process. Tall oil (TO) comprises a fraction with acidic properties (functional group -COOH), typically about 75-80% by weight, and a neutral fraction, up to 25% by weight. The latter fraction is often referred to as the Non-Selectable Fraction. The non-selectable fraction includes a wide range of components such as carbohydrates, fatty alcohols, alcohols of plant sterols, aldehydes, etc. as choices as high molecular weight components such as ham & Iran internal reactions between components in the acidic and neutral fractions. The fraction comprising components with acid functionality can, on the other hand, in turn be divided into two large fractions, namely (i) the fatty acid fraction and (ii) the resin acid fraction, each containing a number of individual components.

From this description of the composition of tall oil, it is clear that CTO constitutes an attractive supply of renewable fine chemicals, which now attract a lot of attention due to strict environmental regulations and rising prices for fossil oils.

At present, CTO fractionation usually takes place by vacuum distillation. The targeting is quite straight forward, namely to divide the CTO into two fractions (i) acid fraction, which is up to 75% by weight, and a fraction of minor importance called (ii) tallbeck (tall oil pitch (TOP)). The acidic fraction is further treated in a sequence of fractionation towers operating at high temperatures and relatively high vacuum to obtain the river enriched in fatty acids and resin acids. TOP is normally returned to the pulp mills as an internal fuel or used as a biofuel in heat and power plants. It is important to minimize the TOP fraction produced in CTO refining processes and the present invention is directed to a CTO refining process with high yield of valuable chemicals and biofuels for vehicles.

A process for refining CTO to valuable biofuels is described in WO 2009/131510. WO 2009/131510 describes a method for converting crude tall oil to high quality diesel fuels comprising the steps (a) of removing non-oily contaminants present in crude tall oil and recovering valuable organic compounds present in the crude oil. tall oil, thereby forming a refined tall oil flood, (b) depositing the volatile fraction of the refined tall oil flood from step a), forming a flood free Than volatile material comprising organic components having boiling points, at atmospheric pressure, of 170 ° C or higher; (c) separating in a vacuum fractionation tower the oil stream free of volatiles from step b) into two process streams or phases, a first process stream or phase substantially comprising components having boiling points, at atmospheric pressure, in the range 170-400 ° C and a second process flow or phase substantially comprising components having boiling points, at atmospheric pressure, below 400 ° C, and (d) lowering the oxygen content of the river comprising components having boiling points in the range 170-400 ° C from step c) by decarboxylation and / or decarbonylation.

An object of the present invention is to provide an improved process for refining CTO. Another specific object of the present invention is to provide an improved pretreatment of CTO. There are also other objects of the present invention, which are presented below. Brief Description of the Drawings Figure 1 shows various steps during the treatment of CTO according to a first aspect of the invention, wherein crude tall oil is treated in a series of steps to substantially reduce the content of contaminants in the resulting flood.

Background of the Invention Tall oil resins (or resin acids) produced by vacuum distillation of CTO find use as an important component in adhesives, gums, inks, and emulsifiers, while tall oil fatty acids (TOFA) find inhalation in the production of whey and lubricants.

Crude pine oil, which is a residual flood Than kraft pulp boiling operation, however, contains a wide range of impurities. Typical CTO compounds include residual mineral acid, alkali salts and / or whey, alkaline earth metal salts and / or whey, transition metals, cellulosic fibers and large organic lignin compounds having molecular weights well over 1000 units. The presence of contaminants is most often caused by inefficient tall oil separation Than saline solution during the CTO processing at the kraft pulp factory. The small amount of saline that accompanies CTO contains most of the above-mentioned contaminants. The contaminants cause problems during CTO processing and have a detrimental effect on the yield of desired fractions, namely RTD, TOFA and tall oil resin acids (RA). Thus, different types of salt and / or whey, cellulosic fibers and lignin deposition on different heating surfaces can cause flow problems and / or limit heat transfer. Furthermore, the salts cause a stench in thin-film evaporator units (TFEs), which enables a chance for non-volatile components to be entrained in the gas phase. The remaining mineral acid (usually sulfuric acid), various salts and transition metals act as catalysts during CTO storage and processing. H2SO4 is a very effective catalyst for esterification reactions between free fatty acids (FFA) and various components of the neutral fraction that have a (-OH) functional group. The resulting esters are typically high molecular weight and thus end up in the less desirable TOP fraction. These high molecular weight esters are typically formed during CTO storage. During CTO processing, sulfuric acid esters attack double bonds within FFA, leading to high molecular weight polymerization products, which also end up in the TOP. Sulfuric acid is also an active catalyst for resin acid carboxylation which produces the corresponding hydrocarbons and thus significantly reduces the yield of tall oil resin acids. Depending on the process / equipment of the process, the obtained hydrocarbons are found either in RTD / TOFA or in the resin acid fraction, in which case the quality of the respective fraction decreases. Various types of salts and especially transition metals are also very active catalysts for activating double bond functionality and resin acid carboxylation.

During the years, efforts have been made to remove contaminants in the CTO before fractionation. The most successful approach to date seems to be so-called CTO depitching, where the incoming oil stream is passed through a TFE unit, where it is subjected to rapid heating and most of the FFA and resin acids are evaporated and further processed to obtain the individual TOFA and tall oil resin acid fractions. With this approach, most pollutants follow the TOP flow that is collected at the TFE bottom. Despite the short heat treatment, a significant portion of the CTO components are subjected to undesirable reactions promoted by the contaminants described previously. In addition, some of the contaminants are included in the produced fumes.

CTO pretreatment described in a first embodiment of the present invention contributes to the removal of typical CTO contaminants. The absence of CTO contaminants during the refining steps of the present invention leads to the preservation of the Onskvarda CTO components and thus higher yields for RTD / TOFA and RA products and also TOP of better quality. In addition, the RA fraction will be of higher quality when it comes to color and / or isomer distribution because color components are associated with harmful effects caused by the contaminants, while RA isomerization is avoided by the CTO contaminants in combination with the elevated temperatures required for fractionation.

In the following, we describe a process for improved tall oil refining and fractionation into valuable fractions obtained with higher yields and better quality compared to prior art.

Summary of the Invention As mentioned above, according to a first object of the present invention, an improved method for removing contaminants from a CTO is presented.

This object is achieved by a process for pretreating a crude tall oil (CO), said process comprising a first pretreatment step comprising a CTO wash and a separation of a first oil phase comprising refined CTO and an aqueous phase containing impurities, and a second steps comprising separating a second oil phase from the aqueous phase. It should be noted that the second stage comprises a separation of a second oil phase. The aqueous phase can be carried out in the same plant as the first stage, or in a unit or plant directly adjacent to the plant in which the first separation stage is carried out, but the second step can also be performed in another plant, as a separation step, or in a subsequent step comprising finishing, in which separation is part of the purpose. According to a specific embodiment, the second step comprising separating a second oil phase from the aqueous phase is carried out in a subsequent step in a separate unit which is not directly adjacent to a unit in which the first pretreatment step is performed.

As will be appreciated from the above, this aspect of the present invention relates to the effective removal of typical contaminants from crude tall oil, such as residual mineral acid, alkali metal, alkaline earth metal salts / whey, transition metals, fibers / promoters and lignin compounds for producing refined tall oil. Therefore, according to one embodiment of the process for pretreating a CTO of the present invention, the fibers, the salts, the remaining inorganic acid and / or the lignin constitute the impurities. The remaining inorganic acid is the acid used at pulp mills to convert tall oil monkey to tall oil, which is often sulfuric acid.

It may further be mentioned that other important aspects of the present invention are for example separation of a volatile fraction than the refined tall oil and fractionation of tall oil free from volatile substances into the river which comprises a) components boiling in the diesel range (RTD); b) high quality resin acids (RA); and (c) high molecular weight fraction (tall oil pitch, TOP) of the highest quality, particularly suitable as energy cold in a wide range of industrial applications.

Specific Embodiments of the Invention According to the present invention, the CTO flood is pretreated to remove contaminants before fractionation. In one embodiment of the CTO pretreatment process, the CTO is brought into contact with water in a CTO washing step, the amount of water used being less than about 5% by weight (based on incoming CTO). The wash water may contain additives. According to the present invention, the contact between CTO and wash water can be performed with the aid of a dynamic stirrer. It should be noted, however, that any equipment which is capable of effecting intimate contact between the CTO and the aqueous phase is suitable in accordance with the present invention. The means for achieving efficient agitation is important due to the low amount of wash water. The wash water focuses on the removal of some CTO contaminants (inorganic salts and residual acid (H2SO4)), while water additives focus on the removal of other contaminants such as transition metals and various whey. Furthermore, the additive incorporates metal ions in order to increase their preference for the aqueous phase. Substantial agitation as such, such as a static stirrer, does not provide the necessary contact according to the present pretreatment procedure. Therefore, according to a specific embodiment, CTO washing is performed by a stirring procedure which provides intimate contact between the CTO and the aqueous phase.

One parameter that facilitates intimate contact between wash water and CTO is temperature. Thus, according to a specific embodiment of the present invention, contact is made at temperatures above 90 ° C and preferably at about 95 ° C.

According to the invention, various additives can be added in the washing step and thereby facilitate the removal of CTO contaminants. One function of such additives may be to bind all metal ions within the CTO. 538 2 The bonding is usually done by complex formation between ore metal ion and the additive (in compound complex terminology often referred to as ligand). Ligands may comprise alits from the ionic type to the molecular type and consequently varying vagins for complex formation. According to the invention, the complex thus formed is water-soluble. There are several ligands that can be used as additives according to the invention. According to a specific embodiment, at least one chelating agent is added in the first pretreatment step. The term "chelating agent" herein specifies how a complex is formed. Oxalic acid is a preferred chelating agent. Citric acid and ethylenediaminetetraacetic acid (EDTA) are also preferred chelating agents because they are commonly used in other applications as well, and because they also cover a wide range of metal ions, i.e. are not specific for a particular ion.

A possible example of how to use additives in the process of the present invention is described below. Preheated CTO is combined with additional solution. The additive solution should be relatively concentrated, such as e.g. 30% additive, as less water allows for 6kad efficiency of the distribution of the additive throughout the CTO and thus better contact with metal contaminants. The dose of additives is often in about ten times the excess in relation to the total amount of metal impurities. CTO and additives are stirred intimately with the aid of, for example, a dynamic stirrer and the mixture thus obtained is transferred to a reactor (simple tank without stirring) where the reactor size allows a minimum residence time of 15 minutes. The residence time is needed to ensure the completion of the reaction between additives and metal contaminants. After completion of the reaction, the mixture is combined with the remaining amount of water (up to 5% in total) which is passed through a stirrer (not necessarily of the dynamic type) and centrifuged. Thus, once additives and metal contaminants have been contacted and reacted, the water-soluble metal contaminants can be extracted with additional water.

As will be appreciated from the foregoing, the oil phase obtained according to the pretreatment procedure is intended to be further processed. According to a specific embodiment of the present invention, the recovered second oil phase is introduced into the first oil phase comprising refined CTO. The total yield for further processing thus increases. Another option is to recycle the second oil phase back to the layer of (unrefined) CTO. The goal for recovery and / or recycling of the second oil phase in the first refined oil phase is to achieve a high CTO yield for the pretreatment step. The CTO yield for this 6 538 2 pretreatment step (matt as in / refined CTO out) is higher than 96 (:) / 0, preferably more than 98 w / o.

The separation of the phases in said first and second pretreatment steps can be performed with different process equipment according to the present invention. According to a specific embodiment, the separation of phases is performed in the first pretreatment step in a separator unit where the separation is driven by centrifugal force. Other types of separation equipment can also be used alone or in combination, such as a combination of filtration and decantation. In the latter case, filtration is advantageously preceded by decantation because lignin, fibers and other non-oily contaminants can prevent aqueous phase separation. A process unit where separation is driven by centrifugal force is, on the other hand, preferred process equipment because it effectively separates the aqueous phase and solid contaminants Than tall oil (TO) in a very short time in a single compact equipment. According to a further specific embodiment of the present invention, separation of phases in the second step is performed by decantation. For the river intended in this step, the oil-water proportions are smoother and the flow rate for this river is much lower, which opens up the possibility of using decanting efficiently. It is advantageous to maintain the high temperature used during the first washing step because the temperature assists the separation in the second separation step.

After removal of contaminants according to the principles described above, said refined CTO is further treated by removal of volatile substances from the refined CTO river. According to a specific embodiment of the present invention, said refined CTO obtained from the pretreatment is introduced into a process system which provides separation of volatile components with boiling points below 170 ° C to give a "tall oil flood depleted on volatile substances". The process system used to remove volatile substances from the refined CTO flood may include unit combinations such as a flash vessel - TFE (thin film evaporator) or a stripper type tower (packed column equipped with large surface area packing). A TFE is the most preferred process system for removing volatile substances from a flood of refined CTO according to the invention.

It is understood that there are a number of volatile associations that are eliminated in this step. Volatile compounds include water, various gases dissolved in water (if water is present), terpenes and various sulfur-containing compounds such as methyl sulfide and methyl mercaptan. Detailed Description of the Drawings Figure 1 shows various steps during the processing of CTO according to the present invention.

In the first stage, referred to as "CTO washing", the crude tall oil is treated in a series of agitation, reaction and separation steps, where the content of contaminants in the resulting river (referred to as "Refined CTO") is substantially reduced or significantly reduced. down to the limit of analysis methods used for quantification. To achieve the removal of contaminants, the CTO is contacted with a relatively small amount of water (up to 5% by weight (10 on the CTO base) which contains at least one additive component by intensive stirring at elevated temperatures (just below the boiling point of the water). The use of water is controlled by the excellent solubility that CTO contaminants have in water, such as residual mineral acid and various inorganic salts. It should be emphasized that the water used should meet certain quality requirements (pH 6.5 to 7.2; hardness <0 dH, Ca + Mg + Na <1 mg / kg), where a typical example is steam condensate. are typically chelating agents that have a high affinity for metal cations and especially transition metal cations.Sadan additives form very stable and water-soluble complexes with these metal cations. With affinity for a wide range of metal cations, it is preferred to keep the process simple where typical examples are, but are not limited to, oxalic acid, citric acid, ethylenediaminetetraacetic acid (EDTA), etc. The separation unit facilitates phase separation. Particularly advantageous units are those which use centrifugal force for phase separation. Typical such separation units, together with the liquid phase separation, combine the separation and discharge of any solids (such as fibers, non-oily components and lignin). In view of the limited amount of water added, clarifier-type separators are of particular interest in the present invention. Salunda thanks the use of a combination of agitation, reaction and separation to the full diversity of CTO contaminants and in fact their significant reduction or practical removal.

The aqueous phase is advantageously subjected to a second separation step where the second oil phase is separated from the aqueous phase and other solid contaminants. The second oil phase thus recovered can be combined with the refined CTO flood (possibility shown by the dashed arrow in Figure 1). Another alternative is to determine the quality of the second oil phase thus extracted and, if not satisfactorily, return it to the CTO for a second passage through the pre-treatment sequence (possibility shown by the dashed arrow in Figure 1). 9

Claims (12)

538 2 Patent claims A process for pretreating a crude tall oil (CTO) for removing contaminants, characterized in that the process comprises a first pretreatment step comprising a CTO wash and a separation of a first oil phase comprising refined CTOs and an aqueous phase containing contaminants, and a second step comprising separating a second oil phase than the aqueous phase. The method of claim 1, wherein said CTO is contacted with water in an amount of less than 5% by weight for the CTO water. The method of claim 1 or 2, wherein at least one additive is added in the first pretreatment step to bind metal ions in the CTO to produce water-soluble metal complexes. A process according to any one of the preceding claims, wherein at least one chelating agent is added in the first pretreatment step. The method of claim 4, wherein that chelating agent is oxalic acid. A method according to any one of claims 1-5, wherein the recovered second oil phase is fed into the first oil phase comprising refined CTO. A method according to any one of claims 1-5, wherein the recovered second oil phase is fed into said CTO. A method according to any one of claims 1 to 6, wherein the separation of the first pretreatment step is performed in a separator unit where the separation is driven by centrifugal force. A method according to any one of claims 1-8, wherein the separation of the second step is performed by decantation. A method according to any one of claims 1-9, wherein said refined CTO is introduced into a process system providing separation of volatile components with boiling points below 170 ° C present in the CTO to provide a tall oil stream depleted on volatile substances. A process according to claim 10, wherein the tall oil stream depleted of volatile substances is fed into a vacuum distillation system to obtain individual valuable fractions of fatty and resin acids. A method according to any one of the preceding claims, wherein the second step comprises a separation of a second oil phase from the aqueous phase 10 is carried out in a subsequent step in a separate unit which is not directly adjacent to a unit in which the first pretreatment step is carried out . 11 Vatter Tsat CIO CTO-