DE10043644A1 - Production of biomethanol and bioethanol diesel comprises continuous re-esterification, removing glycerin after dosing the catalyst-alkanol mixture with removal of methanol in the biodiesel, and washing with phosphoric acid and water - Google Patents

Abstract

Biomethanol and bioethanol diesel are produced by continuous re-esterification in a multiple stage reactor cascade at Reynolds numbers of 1300-1500 and minimal dwell times; removing glycerin after dosing the catalyst-alkanol mixture with removal of methanol in the biodiesel in the last stage; and washing with phosphoric acid and water to give a final product containing 3 ppm potassium. Production of biomethanol and bioethanol diesel comprises continuous re-esterification in a multiple stage reactor cascade at Reynolds numbers of 1300-1500 and minimal dwell times; removing glycerin after dosing the catalyst-alkanol mixture with removal of methanol in the biodiesel in the last stage; and washing with phosphoric acid and water to give a final product containing 3 ppm potassium. The alkanol such as ethanol or methanol used in the re-esterification is pre-dried before the re-esterification e.g. using molecular sieves or by membrane separation to give a water content of less than 0.3%. The catalyst used is in the form of K- or Na-metholate and etholate after converting the starting compounds. The product volume can be adjusted in the region of 0.2 to more than t/d.

Description

The invention relates to a process for the continuous production of biomethanol and ethanol diesel in a multi-stage microreactor cascade of standardized Glass components for preferred use in agriculture.

It is known that biodiesel by transesterification of native glycid esters, in Europe dominant from rapeseed oil, with methanol using catalysts, mostly KOH or NaOH, is obtained (B. GUTSCHE: Technology of methyl ester production. Fat / Lipid 99 (1997) 418-27). Both batch processes come here. (transesterification from rapeseed oil to alternative diesel fuel, company publication VOGEL 1990), semi- Batch process (E. AHN et al .: A low-waste process for the production of biodiesel, September Sci. Techn. 30 (1995) 2021-33 and R. STERN u. G. HILLION: EP 0 356 317 (1988) Inst. Francais du Petrole) as well as continuous processes (J. CONNE- MAN: DP 42 09 779, US P 5 354878, EU 0 562 504 each 26.3.1992) for Commitment. A special, continuous process for biodiesel production too using used fats has been developed by L. U. T. (J. HAUPT: Biofuel and process for its production. DE 196 22 601 C1).

Especially about the transesterification of soybean oil with methanol and ethanol as well as about the Use of the transesterification products in combustion engines are reported by CLARC and Staff (S. J. CLARK et al .: Methyl- and Ethyl Soybean Esters as Renewable Fuels for Diesel Engines JAOCS 61 (1984) 1632-38).

A common feature of all the processes mentioned is that the transesterification is a 2-stage process either without pressure or up to max. 62 bar is operated and the transesterification stages a methanol separation and a washing process to reduce the Potassium content in the main product biodiesel or the glycerin phase with recovery are followed by potassium hydrogen phosphate.

It is also known that water and free fatty acids can significantly reduce the yield of the trans methylation reaction to form the so-called soap stick (B. FREEDMAN et al .: Varables Affecting the Yields of Fatty Esters from Transesterified Vegetable Oils. JAOCS 61 (1984) 1638 -43 and A. ZELLNER: Catalytic production of rapeseed oil methyl ester dissertation. Diusburg 1989). The

CH ₃ OH + KOH ⇄ CH ₃ OK + H ₂ O (Eq. 1)

CH ₃ C = OOR + KOH ⇄ CH ₃ OH + KO C = OR (Eq. 2)

HOC = OR + KOH ⇄ H ₂ O + KO C = OR (Eq. 3)

Water becomes, through the feed materials (raw glycid or methanol) other by the catalyst preparation according to Eq. 1 introduced into the process or Dia free fatty acids generated there get into the through the native oils Process or arise in the process when the temperature during the transesterification <60 ° C (M. MITTELBACH et al. Kinetics of Alkaline Catalyzed Methanolysis of Sunflower Oil. Fat. Sci. Technol. 92 (1990) 145-8) or by saponification according to (Eq. 2 or 3), as a slowly running, but in principle not out closing competitive reaction of the transesterification (principle of ester saponification).  

This results in an increased consumption of catalyst due to undesirable Soap formation and an increased loss of biodiesel through formation of the Soap stick, a mixture of soap and biodiesel. This soap stick will either subsequently separated, acidic again with glycerol and sulfuric acid reesterified and returned to the process (M. MITTELBACH: procedure for Manufacture of fatty acid alkyl esters. WO 95/02661 26.1.95.) Or its formation in Large-scale plants in the chemical industry through acidic pre-esterification of the free Fatty acids suppressed (L. JEROMIN et al .: Process for the pre-esterification of free Fatty acids in raw fats and / or oils. DP 3 501 761 (1986)).

The disadvantage of these two process steps is that they are economical only in large chemical plant are applicable, in which methyl ester as Synthesis precursors are produced, but not in regionally operated small ones Biodiesel plants with <10 kt / a production volume can be used. Sympathy with the soap formation and the associated dispersing effect of the soap stick is the phase separation between biodiesel and Glycerol water phase complicates both the saponification of the methyl ester accelerated as well as the space-time yield decreased.

To improve the phase separations, different methods are therefore presented in the literature:

• - the use of demulsifiers (C. AUSCHRA: dispersing cooligomers and copolymers. DE 44 23 358 A1 4.7.94)
• - the use of coal separators, such as wire or plastic mesh, Packings or glass fibers (J. FALKOWSKY et al .: Process for the production lower alkyl ester. DE 197 21 474 C1 23.5.1997)
• - or washing with glycerin (M. GROSS et al. WO 94/170 27 19.1.1994).

It is also known that in one of ASSMANN et al. patented process (G. ASSMANN et al .: Continuous process for the preparation of lower alkyl esters. DE 39 32 514 A1 29.9.89) Microreactors in combination with tubular reactors for the Transesterification can be used.

The invention has for its object to provide an easy to use continuous process for the production of biodiesel in stationary or small mobile systems for regional supply, preferably in rural areas To create space. As an additional requirement, there is also the task of Process with a much higher space-time yield compared to known state of the art to operate and with the same device configuration accruing by-products of the glycerol phase create value for the market work up.

The object is achieved in that the method from a Cascade consists of at least 3 microreactors. After each of the first three Microreactor stages rapidly separate the glycerin phase in decanters or separators; in a 4th stage, wash with dilute phosphoric acid. becomes In the present process, it is virtually depressurized and at a very low temperature worked at approx. 60 ° C. On a post-reaction phase in so-called Tube reactors are also dispensed with, as far as such a technical solution is concerned actually contradicts the thermodynamics of the equilibrium reaction. Much more shorter residence times in the separators are deliberately enforced by the fact that a reduction in the water content in the starting compounds, especially the . used Alcohols and the catalysts through careful predrying of these starting components is made. The water content of the Educt mixture must be well below 1%.  

For pre-drying it can generally be stated that before the Umes Removed water in the starting compounds is not present in the product processing. z. B. must be separated for glycerol production; ultimately for the Holistic processing of the oil used is hardly an additional effort arises.

It is essential for the transesterification reaction that with the lowering of the Water in the reaction mixture as a reduction in soap formation subsequent reaction of methyl or ethyl ester formation goes hand in hand. in the In the special case of transesterification with (bio) ethanol, it comes with very much well-dried alcohol component for reaction.

If the transesterification is to be carried out as a continuous process and without intermediate residence times in run additional tube reactors, a lower percentage of soap bars causes a faster phase separation of the resulting products by a sympath ongoing reduction of the emulsifier effect between biodiesel phase and Glycerol phase. This leads to an increase in space-time Yield. This effect is supported in that at temperatures < 60 ° C the competition reaction of the saponification according to Eq. 2 largely suppressed will therefore also result in less soap or soap stock through this driving style can.

On the other hand, the reduction in the formation of soaps allows a reduction in the Catalyst insert (Table 1 and embodiment a). So be in your own Process on 1 kg of untreated crude oil only requires 1.35-2.7 g of catalyst (Table 1, last row). In contrast, the best competitive process demands Use of neutral glycides 2.5 g / kg of catalyst. Because the acid number of rapeseed oil on average not significantly <2, must be for the real technical process However, a further 2 g / kg of oil is added (Table 1, 4. Row).

The reduced consumption of your own process is plausible. The after the Reverse reaction according to Eq. 1 KOH formed can dissociate in an aqueous medium (Eq. 4). The resulting OH ions are known to form with the Methyl ester is an equilibrium from which the carboxylate anion and the methanol in an irreversible subsequent reaction. Molar amounts of KOH used up, d. that is, lost through soap formation.  

Table 1

Overview of the catalyst consumption

This is associated with a relatively low potassium content in the biodiesel produced by about 3 ppm.

In contrast to all of the above-mentioned procedures, this is done in-house no separate feed of catalyst and alcohol component. Much more become KOH or NaOH with the respective alkanol, i.e. methanol or ethanol mixed, dried over molecular sieves or by membrane process and this Mix with the natural linseed, soybean, sunflower or dragon head oil and in particular rapeseed oil reacted in the microreactor. It is enough Reynolds numbers of approximately 1300 ≦ Re ≦ 1500 for dispersing the oil-alkanol Catalyst mixture completely.

embodiments a) Preparation of the alkanolates

KOH and methanol (ethanol) are in a ratio of 10-20 g / l alkanol with each other mixed (with NaOH as catalyst 28 g / l) and over a molecular sieve of type 3A or 4A dried until the water content is significantly below 1%.

b) transesterification

The addition of the catalyst-alkanol mixture to the oil is controlled according to Fig. 1 by metering pumps so that a total of <3 moles of alkanol / alkanolate solution are reacted per mole of oil. The oil and alcohol phases are mixed in stages in a microreactor cascade consisting of a microreactor and a separator as shown in Fig. 1. Biodiesel phase and glycerol phase are separated from each other in each stage. After the third microreactor stage, a degree of conversion of approximately 98% is achieved.

Quality of the methyl ester (standard values according to DIN 51 606)

c) working up the glycerol water phase

The combined batches of several glycerol phases are until the pH 2 with 85% phosphoric acid in the 4th reactor stage with each other mixed and the resulting 3 phases after demethanolization separated from each other. The lower phase, the potassium dihydrogen phosphate with Water and the. Excess phosphoric acid, is with the aqueous phase the washing stage from the biodiesel stage and serves as liquid fertilizer. The upper phase consists of the mixture of free fatty acids and biodiesel middle phase consists predominantly of glycerin. The composition of the 3rd Phases: approx. 22% fatty acid mixture / biodiesel, approx. 54% glycerin / water and 23% potassium hydrogen phosphate / water / residual glycerin.

From the middle phase, approx. 75% can be of the total glycerol content can be obtained as high-purity glycerol.

Claims (1)

Process for the continuous production of biomethanol and bioethanol diesel in small plants, characterized in that
the transesterification process is carried out continuously in a multi-stage microreactor cascade at Reynolds numbers around 1300 ≦ Re ≦ 1500 and minimum residence time, each cascade stage consisting of a microreactor and a separator, but does not require any equipment parts for subsequent reaction;
Intermediate separation of the glycerol takes place in 3 stages each after metering in the catalyst-alkanol mixture, in the last stage the biodiesel is demethanolized and washed with phosphoric acid and water so that the end product has potassium contents of approx. 3 ppm;
the alkanols used for the transesterification, such as ethanol or methanol before the transesterification, for. B. before using molecular sieves or a membrane separation process so that their water content is <0.3%;
the catalysts used in the form of the K or Na metholates or etholates are dried in the same way after the reaction of the starting compounds;
the inevitable occurrence of the by-product soap bar is minimal and thus also its negative dispersing effect on the biodiesel phase / glycerol phase to be separated;
that the production volume can be variably adjusted in the range from 0.2 t / d to <2.5 t / d solely by preselecting the reactor runtime, but not by the reactor volume;