APPARATUS AND METHOD FOR HYDROLYSIS OF LIGNOCELLULOSIC MATERIALS

Abstract

The invention relates to a method for extraction of saccharides from a lignocellulose containing material and comprises the steps of mixing the lignocellulose containing material with an acidic water solution to create a slurry having a pH value in the interval of 0-4; controlling the water content of the slurry to obtain a specific dry solid content of more than 30%; and introducing the slurry into an apparatus and performing an acid hydrolysis of the slurry in the apparatus, wherein at least parts of the apparatus that come into contact with the slurry are made of a material that comprises iron in an amount of at least 50% by weight and nickel in an amount of at least 1.5% by weight. The invention relates also to an apparatus for performing said method.

Claims

1. A method for extraction of saccharides from a lignocellulose-containing material, comprising the steps of: mixing the lignocellulose-containing material with an acidic water solution to create a slurry having a pH value in the interval of 0-4; controlling the water content of the slurry to obtain a specific dry solid content of the slurry; and introducing the slurry into an apparatus and performing an acid hydrolysis of the slurry in the apparatus, wherein the specific dry solid content of the slurry is more than 30% and wherein at least parts of the apparatus that come into contact with the slurry are made of a material that comprises iron in an amount of at least 50% by weight and nickel in an amount of at least 1.5% by weight.

2. The method according to claim 1, wherein the step of controlling the water content of the slurry comprises dewatering of the slurry.

3. The method according to claim 1, wherein the step of controlling the water content of the slurry comprises measuring the dry solid content of the slurry.

4. An acid hydrolysis apparatus for extraction of saccharides from a lignocellulose-containing material, said apparatus being configured for acid hydrolysis of a slurry, which is a mixture of the lignocellulosic material and an acidic water solution and which has a pH value in the interval of 0-4 and a dry solid content of at least 30%, wherein at least parts of the apparatus that come into contact with the slurry comprise iron in an amount of at least 50% by weight and nickel in an amount of at least 1.5% by weight.

5. An acid hydrolysis apparatus according to claim 4, further comprising a detector for determining the water content of the slurry and a controller for controlling the water content of the slurry in response to a determined water content, the controller being arranged to control the water content of the slurry before acid hydrolysis takes place.

6. An acid hydrolysis apparatus according to claim 5, wherein the controller comprises a dewatering unit and a dilution unit.

Description

DETAILED DESCRIPTION

[0011] In the aforementioned European Patent No. 2132351, a number of experimental results are presented. In these experiments, ten different materials were tested, where five materials were different grades of stainless steels and five were nickel-based alloys. Samples of the materials were cut to specific dimensions and were carefully weighed. The samples were then placed in an autoclave, and a sulphuric acid solution considerably diluted with water in the form of a saccharide-containing hydrolysate was added. The saccharide-containing hydrolysate, which was collected from a pilot plant for extraction of saccharides from wood chips, had a pH value of 1.67. The temperature in the autoclave was set to 210 C. and the pressure to 35 bar, and the hydrolysate was circulated in the autoclave for 13 days, whereupon the samples were weighed; and from the loss of weight, the corrosion rates (expressed in millimeters per year) were calculated.

[0012] From these results, and also from further experiments on a sub-selection of the samples, it was concluded that the rate of corrosion was acceptable for all materials tested except one; and that the rate of corrosion was, in particular, surprisingly low also for the most inexpensive steel grade (EN 1.4301) in the study. The experiments conducted and presented were not designed to find an explanation for these surprisingly low rates of corrosion also for the simplest and thereby cheapest materials, but the speculation and theory brought forward in EP2132351 is that since the acidic water solution, which in this case was a sulphuric acid solution, not only consists of sulphuric acid and water but also of smaller and greater amounts of different chemical substances that have been released from the lignocellulose-containing material, it is very likely that one or more of said released substances work as protective agent (protector or inhibitor) for the stainless steel materials tested.

[0013] From an industrial applicability point of view such an explanation is highly unsatisfactory, because, for instance, it is often desired to use different types of lignocellulosic materials as raw materials in an industrial plant for extraction of saccharides, and since different types of lignocellulosic materials are likely to release different types and amounts of substances that may or may not work as protective agents for the stainless steel materials used in the hydrolysis equipment, it creates an uncertainty whether or not a specific steel grade in practice will be corrosive resistant during acid hydrolysis of a specific type of lignocellulosic material or a mixture of several types of lignocellulosic materials. Needless to say, although EP2132351 discloses that relatively cheap steel materials can be used, the design and set up of a production line is still associated with considerable costs, and an inherent uncertainty regarding the corrosion rates and thereby the useful lifetimes for the apparatuses used in such a production line is often, or even usually, not acceptable.

[0014] The present invention therefore presents an improved and more reliable method for the extraction of saccharides from a lignocellulosic material (or a mixture of several types of lignocellulosic materials) by performing hydrolysis of the lignocellulosic material in an apparatus by mixing or contacting the lignocellulosic material with an acidic water solution to create a slurry having a pH value in the interval of 0-4, which method specifically takes into account not only the characteristics of the material (or materials) in the apparatus (or least in parts or in surfaces thereof) but also the characteristics of the lignocellulosic material, i.e. the characteristics that in practice create the preconditions for the corrosion resistance of the material(s) of which at least components or parts of said apparatus are made. The invention also relates to an apparatus for extraction of saccharides from a lignocellulosic material by performing hydrolysis of the lignocellulosic material in this apparatus, wherein both the properties of the material(s) in said apparatus and the properties of the lignocellulosic material(s) are specified, to make the apparatus or at least parts thereof corrosion resistant during said hydrolysis, or to provide the apparatus with a predetermined and acceptable rate of corrosion during said hydrolysis.

[0015] The apparatus for extraction of saccharides from a lignocellulosic material preferably comprises a a detector for determining the water content of the slurry and a controller for controlling the water content of the slurry in response to a determined water content, the controller being arranged to control the water content of the slurry before acid hydrolysis takes place. Thus, the detector and controller can be arranged upstream from a vessel where acid hydrolysis takes place so that a slurry entering the apparatus passes the detector first and a water content is determined before the slurry passes to the controller. The controller comprises a dewatering unit that decreases the water content of the slurry and a dilution unit where dilution fluid is supplied and a thorough mixing of the slurry and dilution fluid is performed. Depending on the determination of the water content of the slurry, the slurry is subjected to dewatering or dilution by the controller to achieve a desired water content.

[0016] After the water content of the slurry has been controlled in this way, the slurry passes into the vessel where acid hydrolysis takes place.

[0017] Below results from two experiments are presented, the purposes of which were to find and isolate the characteristics of a lignocellulosic material that effectively make an apparatus for performing hydrolysis of the lignocellulosic material in an acidic water solution corrosion resistant during said hydrolysis and, at the same time, to find the characteristics of the steel materials that are necessary for successful use in such an apparatus, and to expand the set of materials that can be used for successful use in such an apparatus.

EXAMPLE 1

[0018] Three different slurries, being mixtures of sawdust and sulphuric acid, were produced with 15% dry substance (ds), 30% ds, and 50% ds. The slurry sample (of a specific percentage of dry substance) was placed in a steel reactor vessel, which in turn was heated by a copper vessel, which stood insulated in an autoclave furnace, and corrosion probes were placed in the slurry sample. The corrosion probes, also referred to as electrodes, were made from five different alloys: 316L (EN 1.4404), SAF 2205 (EN 1.4462), SAF 2507 (EN 1.4401), 904L (EN 1.4539) and the Ni-based super-alloy 625 (EN 2.4856), the chemical compositions of which can be found in Table 1 below.

[0019] The corrosion measurements, which were performed at 200 C., utilized so-called LPR (Linear Polarisation Resistance) monitoring, which involves measurement of the polarisation resistance of a corroding electrode using a small amplitude (25 mV) sinusoidal polarisation of the electrode. The results, which are taken from graphs obtained during the study, are summarized in Table 2 below.

TABLE-US-00001 TABLE 1 Chemical compositions [in weight-%] for the alloys used in Example 1 and Example 2. Alloy Fe Cr Ni Mo Mn Si P S N C 316L Bal 17 12 2.5 2 0.75 0.045 0.03 0.1 0.03 SAF 2205 Bal 22 5 3.2 <2 <1 <0.03 <0.015 0.018 0.03 SAF 2507 Bal 25 7 4 1.2 0.8 0.035 0.015 0.3 0.03 904 L Bal 21 25.5 4.5 2 1 0.45 0.035 Cu: 1.5 Alloy 625 <5 21.5 Bal 9 0.5 0.5 0.015 0.015 Nb: 0.1 Al: 0.4 Ta: 4 Co: 1 LDX 2101 Bal 21.5 1.5 0.3 5 0.22 0.03

TABLE-US-00002 TABLE 2 Corrosion rates [mm/year] in five different alloys at 200 C. for three different percentages of dry content (ds). Alloy ds 316L SAF 2205 SAF 2507 904 L A625 15% 28 17 27 10 8 30% 5.5 5 1.2 Not done 0.02 50% 0.06 Not done Not done Not done Not done

EXAMPLE 2

[0020] To verify the measurements done in Example 1, and to also investigate whether an even simpler steel grade can be used, the experiment above was repeated with LDX 2101 (EN 1.4162, see Table 1) and with SAF 2205 as reference sample. Three slurries, being mixtures of sawdust and diluted sulphuric acid, were prepared with three different dry solid contents: 15% ds, 30% ds and 50% ds. The temperature was ramped up to 200 C., where it was maintained. The test results are presented in Table 3 below.

TABLE-US-00003 TABLE 3 Corrosion rates [mm/year] for two different alloys at 200 C. for three different percentages of dry content (ds). Alloy ds LDX 2101 SAF 2205 15% 13.8 12.9 30% 3.9 2.2 50% 0.04 Not done

[0021] From Table 2 and Table 3 it is evident that the corrosion rates exhibit a clear dependence on the dry solid contents of the slurries, although a higher-quality steel grade generally corrodes less, as is expected. It can further be concluded that there is no linear dependence between the corrosion rate and the dry solid content of the slurry prepared, but instead it can be seen that for the highest dry solid content (i.e. a dry solid content of 50%) there is essentially no corrosion taking place even in the simplest steel grades, e.g. in LDX 2101 and 316L. (Generally, a steel grade having a corrosion rate below 0.1 mm/year is classified as corrosion resistant.) Further, also for a dry solid content of 30% in the slurry, the corrosion rates amount to a few millimeters per year also for the simplest steel grades, LDX 2101 and 316L, whichalthough presumably being too high for some applicationsmakes such relatively inexpensive steel grades interesting and useful as materials in apparatuses in, for example, pilot and test plants, which nevertheless are expected to have a relatively short useful life time, especially if the dry solid contents of the slurries introduced into these apparatuses actually are (at least somewhat) higher than 30%. However, cheap metals having corrosion rates in the order of a few millimeters per year can be useful also in full scale plants, especially if regular maintenance and replacement of spent parts can be accepted. It can further be noted that all of the tested steel grades have an iron content of more than fifty percent. The simplest steel grade in the tests was LDX 2101, which is characterized by a nickel content of about 1.5 percent by weight, which therefore is considered to be the lowest useful nickel content for a material in an apparatus for acid hydrolysis of a slurry comprising a lignocellulosic material and an acidic water solution and having a pH value in the interval of 0-4 and a dry content of at least 30%.

[0022] The present invention is based on the novel and surprising finding that the corrosion rate of a specific steel material, when used in an apparatus for acid hydrolysis of a lignocellulosic material (or a mixture of different types of lignocellulosic materials), is dependent on the water content of a slurry, being a mixture of the lignocellulosic material and an acidic water solution, introduced into the apparatus, wherein an acceptable corrosion rate during the acid hydrolysis is obtained when the slurry has a pH value in the interval of 0-4 and a specific dry solid content of more than 30%, and the specific steel material comprises iron in an amount of at least 50% by weight and nickel in an amount of at least 1.5% by weight. In preferred embodiments of the invention, the nickel content can be in the interval of 1.5% to 10% by weight, while the dry solid content of the slurry is in the interval of over 30% to 50%, or even over 30% to 55%, although even higher dry solid contents are possible and within the scope of the invention. The acidic water solution can be a mineral acid, such as a sulphuric acid, a hydrochloric acid, a nitric acid, or a mixture thereof, diluted with water to a pH value in the interval of 0-4, such that also the slurry, which is a mixture of the acidic water solution and the lignocellulosic material, has a pH value in the interval of 0-4. The acidic water solution can, however, also be an organic acid, such as a weak organic acid, e.g. a formic acid or an acetic acid, which, if necessary, is diluted to a pH value in the interval of 0-4.

[0023] Finally, without being bound by theory, it is here submitted that when the lignocellulosic material that is used as raw material for the hydrolysis exhibits a high dry solid content, such that a slurry being a mixture of the lignocellulosic material in question and an acidic water solution also has a high dry solid content (i.e. over 30%) then essentially all of the acidic water solution is absorbed by the lignocellulosic material, such that there is no (or very little) free water and no free (or relatively few) hydrogen ions that can create the excessive corrosion which previously was expected in this field.

[0024] Although the present invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below.